Antenna (radio)From Wikipedia, the free encyclopedia  (Redirected from Radio antenna)

For other uses, see Antenna.

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An antenna (or aerial) is an electrical device which converts electric power into radio waves, and vice versa.[1] It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter supplies an electric current oscillating at radio frequency (i.e. a high frequency alternating current (AC)) to the antenna's terminals, and the antenna radiates the energy from the current aselectromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce a tiny voltage at its terminals, that is applied to a receiver to be amplified.

Antennas are essential components of all equipment that uses radio. They are used in systems such as radio broadcasting,broadcast television, two-way radio, communications receivers, radar, cell phones, and satellite communications, as well as other devices such as garage door

openers, wireless microphones, Bluetooth-enabled devices, wireless computer networks, baby monitors, and RFID tags on merchandise.

Typically an antenna consists of an arrangement of metallic conductors (elements), electrically connected (often through atransmission line) to the receiver or transmitter. An oscillating current of electrons forced through the antenna by a transmitter will create an oscillating magnetic field around the antenna elements, while the charge of the electrons also creates an oscillating electric field along the elements. These time-varying fields radiate away from the antenna into space as a moving transverse electromagnetic field wave. Conversely, during reception, the oscillating electric and magnetic fields of an incoming radio wave exert force on the electrons in the antenna elements, causing them to move back and forth, creating oscillating currents in the antenna.

Antennas can be designed to transmit and receive radio waves in all horizontal directions equally (omnidirectional antennas), or preferentially in a particular direction (directional or high gain antennas). In the latter case, an antenna may also include additional elements or surfaces with no electrical connection to the transmitter or receiver, such as parasitic elements, parabolic reflectors or horns, which serve to direct the radio waves into a beam or other desired radiation pattern.

The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of electromagnetic waves predicted by the theory ofJames Clerk Maxwell. Hertz placed dipole antennas at the focal point of parabolic reflectors for both transmitting and receiving. He published his work in Annalen der Physik und Chemie (vol. 36, 1889).

Contents  [hide] 

1 Terminology 2 Overview 3 Reciprocity 4 Characteristics

o 4.1 Resonant antennas 4.1.1 Current and voltage distribution 4.1.2 Bandwidth

o 4.2 Gaino 4.3 Effective area or apertureo 4.4 Radiation patterno 4.5 Field regionso 4.6 Impedanceo 4.7 Efficiencyo 4.8 Polarizationo 4.9 Impedance matching

5 Basic antenna modelso 5.1 Examples of antenna models

6 Antenna design criteria 7 Effect of ground 8 Mutual impedance and interaction between antennas 9 Antenna gallery

o 9.1 Antennas and antenna arrayso 9.2 Antennas and supporting structureso 9.3 Diagrams as part of a system

10 See also

11 Notes 12 References

o 12.1 General referenceso 12.2 "Practical antenna" referenceso 12.3 Theory and simulationso 12.4 Patents and USPTO

13 Further reading

Terminology[edit]

Electronic symbol for an antenna

The words antenna (plural: antennas[2] in US English, although both "antennas" and "antennae" are used in International English[3]) and aerial are used interchangeably. Occasionally a rigid metallic structure is called an "antenna" while the wire form is called an "aerial". However, note the important international technical journal, the IEEE Transactions on Antennas and Propagation.[4] In the United Kingdom and other areas where British English is used, the term aerial is sometimes used although 'antenna' has been universal in professional use for many years.

The origin of the word antenna relative to wireless apparatus is attributed to Italian radio pioneer Guglielmo Marconi. In the summer of 1895, Marconi began testing his wireless system outdoors on his father's estate near Bologna and soon began to experiment with long wire "aerials". Marconi discovered that by arranging these "aerials" vertically and placing them in the ground (earthing them) that the range of his wireless system was significantly increased. [5] Soon he was able to transmit signals over a hill, a distance of approximately 2.4 kilometres (1.5 mi).[6] In Italian a tent pole is known as l'antenna centrale, and the pole with the wire was simply called l'antenna. Until then wireless radiating transmitting and receiving elements were known simply as aerials or terminals.

Because of his prominence, Marconi's use of the word antenna (Italian for pole) spread among wireless researchers, and later to the general public.[7][8][9]

In common usage, the word antenna may refer broadly to an entire assembly including support structure, enclosure (if any), etc. in addition to the actual functional components. Especially at microwave frequencies, a receiving antenna may include not only the actual electrical antenna but an integrated preamplifier or mixer.

Overview[edit]

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Antennas of the Atacama Large Millimeter submillimeter Array.[10]

Antennas are required by any radio receiver or transmitter to couple its electrical connection to the electromagnetic field. Radio waves areelectromagnetic waves which carry signals through the air (or through space) at the speed of light with almost no transmission loss. Radio transmitters and receivers are used to convey signals (information) in systems including broadcast (audio) radio, television, mobile telephones, Wi-Fi (WLAN) data networks, trunk lines and point-to-point communications links (telephone, data networks), satellite links, many remote controlled devices such as garage door openers, and wireless remote sensors, among many others. Radio waves are also used directly for measurements in technologies including radar, GPS, and radio astronomy. In each and every case, the transmitters and receivers involved require antennas, although these are sometimes hidden (such as the antenna inside an AM radio or inside a laptop computer equipped with Wi-Fi).

Whip antenna on car, common example of an omnidirectional antenna

According to their applications and technology available, antennas generally fall in one of two categories:

1. Omnidirectional  or only weakly directional antennas which receive or radiate more or less in all directions. These are employed when the relative position of the other station is unknown or arbitrary. They are also used at lower frequencies where a directional antenna would be too large, or simply to cut costs in applications where a directional antenna isn't required.

2. Directional  or beam antennas which are intended to preferentially radiate or receive in a particular direction or directional pattern.

In common usage "omnidirectional" usually refers to all horizontal directions, typically with reduced performance in the direction of the sky or the ground (a truly isotropic radiator is not even possible). A "directional" antenna usually is intended to maximize its coupling to the electromagnetic field in the direction of the other station, or sometimes to cover a particular sector such as a 120° horizontal fan pattern in the case of a panel antenna at a cell site.

One example of omnidirectional antennas is the very common vertical antenna or whip antenna consisting of a metal rod (often, but not always, a quarter of a wavelength long). A dipole antenna is similar but consists of two such conductors extending in opposite directions, with a total length that is often, but not always, a half of a wavelength long. Dipoles are typically oriented horizontally in which case they are weakly directional: signals are reasonably well radiated toward or

received from all directions with the exception of the direction along the conductor itself; this region is called the antenna blind cone or null.

Half-wave dipole antenna

Both the vertical and dipole antennas are simple in construction and relatively inexpensive. The dipole antenna, which is the basis for most antenna designs, is a balanced component, with equal but opposite voltages and currents applied at its two terminals through a balanced transmission line (or to a coaxial transmission line through a so-called balun). The vertical antenna, on the other hand, is a monopole antenna. It is typically connected to the inner conductor of a coaxial transmission line (or a matching network); the shield of the transmission line is connected to ground. In this way, the ground (or any large conductive surface) plays the role of the second conductor of a dipole, thereby forming a complete circuit. Since monopole antennas rely on a conductive ground, a so-called grounding structure may be employed to provide a better ground contact to the earth or which itself acts as a ground plane to perform that function regardless of (or in absence of) an actual contact with the earth.

Diagram of the electric fields (blue) and magnetic fields (red) radiated by adipole antenna (black rods) during

transmission.

Antennas more complex than the dipole or vertical designs are usually intended to increase the directivity and consequently the gain of the antenna. This can be accomplished in many different ways leading to a plethora of antenna designs. The vast majority of designs are fed with a balanced line (unlike a monopole antenna) and are based on the dipole antenna with additional components (or elements) which increase its directionality. Antenna "gain" in this instance describes the concentration of radiated power into a particular solid angle of space, as opposed to the spherically uniform radiation of the ideal radiator. The increased power in the desired direction is at the expense of that in the undesired directions. Power is conserved, and there is no net power increase over that delivered from the power source (the transmitter.)

For instance, a phased array consists of two or more simple antennas which are connected together through an electrical network. This often involves a number of parallel dipole antennas with a certain spacing. Depending on the relative phase introduced by the network, the same combination of dipole antennas can operate as a "broadside array" (directional normal to a line connecting the elements) or as an "end-fire array" (directional along the line connecting the elements). Antenna arrays may employ any basic (omnidirectional or weakly directional) antenna type, such as dipole, loop or slot antennas. These elements are often identical.

Rooftop televisionYagi-Uda antennas like these six are widely used at VHF and UHFfrequencies.

However a log-periodic dipole array consists of a number of dipole elements of different lengths in order to obtain a somewhat directional antenna having an extremely wide bandwidth: these are frequently used for television reception in fringe areas. The dipole antennas composing it are all considered "active elements" since they are all electrically connected together (and to the transmission line). On the other hand, a superficially similar dipole array, the Yagi-Uda Antenna (or simply "Yagi"), has only one dipole element with an electrical connection; the other so-called parasitic elements interact with the electromagnetic field in order to realize a fairly directional antenna but one which is limited to a rather narrow bandwidth. The Yagi antenna has similar looking parasitic dipole elements but which act differently due to their somewhat different lengths. There may be a number of so-called "directors" in front of the active element in the direction of propagation, and usually a single (but possibly more) "reflector" on the opposite side of the active element.

Greater directionality can be obtained using beam-forming techniques such as a parabolic reflector or a horn. Since high directivity in an antenna depends on it being large compared to the wavelength, narrow beams of this type are more easily achieved at UHF and microwave frequencies.

At low frequencies (such as AM broadcast), arrays of vertical towers are used to achieve directionality [11] and they will occupy large areas of land. For reception, a long Beverage antenna can have significant directivity. For non directional portable use, a short vertical antenna or small loop antenna works well, with the main design challenge being that of impedance matching. With a vertical antenna a loading coil at the base of the antenna may be employed to cancel the reactive component of impedance; small loop antennas are tuned with parallel capacitors for this purpose.

An antenna lead-in is the transmission line (or feed line) which connects the antenna to a transmitter or receiver. The antenna feed may refer to all components connecting the antenna to the transmitter or receiver, such as an impedance matching network in addition to the transmission line. In a so-called aperture antenna, such as a horn or parabolic dish, the "feed" may also refer to a basic antenna inside the entire system (normally at the focus of the parabolic dish or at the throat of a horn) which could be considered the one active element in that antenna system. A microwave antenna may also be fed directly from a waveguide in lieu of a (conductive) transmission line.

Cell phone base station antennas

An antenna counterpoise or ground plane is a structure of conductive material which improves or substitutes for the ground. It may be connected to or insulated from the natural ground. In a monopole antenna, this aids in the function of the natural ground, particularly where variations (or limitations) of the characteristics of the natural ground interfere with its proper function. Such a structure is normally connected to the return connection of an unbalanced transmission line such as the shield of a coaxial cable.

An electromagnetic wave refractor in some aperture antennas is a component which due to its shape and position functions to selectively delay or advance portions of the electromagnetic wavefront passing through it. The refractor alters the spatial characteristics of the wave on one side relative to the other side. It can, for instance, bring the wave to a focus or alter the wave front in other ways, generally in order to maximize the directivity of the antenna system. This is the radio equivalent of an optical lens.

An antenna coupling network is a passive network (generally a combination of inductive and capacitive circuit elements) used for impedance matching in between the antenna and the transmitter or receiver. This may be used to improve the standing wave ratio in order to minimize losses in the transmission line and to present the transmitter or receiver with a standard resistive impedance that it expects to see for optimum operation.

Reciprocity[edit]

It is a fundamental property of antennas that the electrical characteristics of an antenna described in the next section, such as gain, radiation pattern, impedance, bandwidth,resonant frequency and polarization, are the same whether the antenna is transmitting or receiving.[12][13] For example, the "receiving pattern" (sensitivity as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator. This is a consequence of thereciprocity theorem of electromagnetics.[13] Therefore in discussions of antenna properties no distinction is usually made between receiving and transmitting terminology, and the antenna can be viewed as either transmitting or receiving, whichever is more convenient.

A necessary condition for the aforementioned reciprocity property is that the materials in the antenna and transmission medium are linear and reciprocal. Reciprocal (or bilateral) means that the material has the same response to an electric current or magnetic field in one direction, as it has to the field or current in the opposite direction. Most materials used in antennas meet these conditions, but some microwave antennas use high-tech components such as isolators and circulators, made of nonreciprocal materials such asferrite.[12][13] These can be used to give the antenna a different behavior on receiving than it has on transmitting,[12] which can be useful in applications like radar.

Characteristics[edit]

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See also: Antenna measurement § Antenna parameters

Antennas are characterized by a number of performance measures which a user would be concerned with in selecting or designing an antenna for a particular application. Chief among these relate to the directional characteristics (as depicted in the antenna's radiation pattern) and the resulting gain. Even in omnidirectional (or weakly directional) antennas, the gain can often be increased by concentrating more of its power in the horizontal directions, sacrificing power radiated toward the sky and ground. The antenna'spower gain (or simply "gain") also takes into account the antenna's efficiency, and is often the primary figure of merit.

Resonant antennas are expected to be used around a particular resonant frequency; an antenna must therefore be built or ordered to match the frequency range of the intended application. A particular antenna design will present a particular feedpoint impedance. While this may affect the choice of an antenna, an antenna's impedance can also be adapted to the desired impedance level of a system using a matching network while maintaining the other characteristics (except for a possible loss of efficiency).

Although these parameters can be measured in principle, such measurements are difficult and require very specialized equipment. Beyond tuning a transmitting antenna using an SWR meter, the typical user will depend on theoretical predictions based on the antenna design or on claims of a vendor.

An antenna transmits and receives radio waves with a particular polarization which can be reoriented by tilting the axis of the antenna in many (but not all) cases. The physical size of an antenna is often a practical issue, particularly at lower frequencies (longer wavelengths). Highly directional antennas need to be significantly larger than the wavelength. Resonant antennas usually use a linear conductor (or element), or pair of such elements, each of which is about a quarter of the wavelength in length (an odd multiple of quarter wavelengths will also be resonant). Antennas that are required to be small compared to the wavelength sacrifice efficiency and cannot be very directional. Fortunately at higher frequencies (UHF, microwaves) trading off performance to obtain a smaller physical size is usually not required.

Resonant antennas[edit]While there are broadband designs for antennas, the vast majority of antennas are based on the half-wave dipole which has a particular resonant frequency. At its resonant frequency, the wavelength (figured by dividing the speed of light by the resonant frequency) is slightly over twice the length of the half-wave dipole (thus the name). The quarter-wave vertical antenna consists of one arm of a half-wave dipole, with the other arm replaced by a connection to ground or an equivalent ground plane (or counterpoise). A Yagi-Uda array consists of a number of resonant dipole elements, only one of which is directly connected to the transmission line. The quarter-wave elements of a dipole or vertical monopole imitate a series-resonant electrical element due to the standing wave present along the conductor. At the resonant frequency, the standing wave has a current peak and voltage node (minimum) at the feed-point, thus presenting a lower impedance than at other frequencies. What's more, the large current and small voltage are in phase at that point, resulting in a purely resistive impedance, whereas away from the design frequency the feed-point impedance both rises and becomes reactive. Contrary to an ideal (lossless) series-resonant circuit, a finite resistance remains (corresponding to the relatively small voltage at the feed-point) due to the antenna's radiation resistance (as well as any actual electrical losses).

A common misconception is that the ability of a resonant antenna to transmit (or receive) fails at frequencies far from the resonant frequency. The reason a dipole antenna needs to be used at the resonant frequency has to do with the impedance match between the antenna and the transmitter or receiver (and its transmission line). For instance, a dipole using a fairly thin conductor [14] will have a purely resistive feedpoint impedance of about 63 ohms at its design frequency. Feeding that antenna with a current of 1 ampere will require 63 volts of RF, and the antenna will radiate 63 watts (ignoring losses) of radio frequency power. If that antenna is driven with 1 ampere at a frequency 20% higher, it will still radiate as efficiently but in order to do that about 200 volts would be required due to the change in the antenna's impedance which is now largely reactive (voltage out of phase with the current). A typical transmitter would not find that impedance acceptable and would deliver much less than 63 watts to it; the transmission line would be operating at a high (poor) standing wave ratio. But using an appropriate matching network, that large reactive impedance could be converted to a resistive impedance satisfying the transmitter and accepting the available power of the transmitter.

This principle is used to construct vertical antennas substantially shorter than the 1/4 wavelength at which the antenna is resonant. By adding an inductance in series with the vertical antenna (a so-called loading coil) the capacitive reactance of this antenna can be cancelled leaving a pure resistance which can then be matched to the transmission line. Sometimes the resulting resonant frequency of such a system (antenna plus matching network) is described using the construct of "electrical length" and the use of a shorter antenna at a lower frequency than its resonant frequency is termed "electrical lengthening". For example, at 30 MHz (wavelength = 10 meters) a true resonant monopole would be almost 2.5 meters (1/4 wavelength) long, and using an antenna only 1.5 meters tall would require the addition of a loading coil. Then it may be said that the coil has "lengthened" the antenna to achieve an "electrical length" of 2.5 meters, that is, 1/4 wavelength at 30 MHz where the combined system now resonates. However, the resulting resistive impedance achieved will be quite a bit lower than the impedance of a resonant monopole, likely requiring further impedance matching. In addition to a lower radiation resistance, the reactance becomes higher as the antenna size is reduced, and the resonant circuit formed by the antenna and the tuning coil has a Q factor that rises and eventually causes the bandwidth of the antenna to be inadequate for the signal being transmitted. This is the major factor that sets the size of antennas at 1 MHz and lower frequencies.

Current and voltage distribution[edit]The antenna conductors have the lowest feed-point impedance at the resonant frequency where they are just under 1/4 wavelength long; two such conductors in line fed differentially thus realizes the familiar "half-wave dipole". When fed with an RF current at the resonant frequency, the quarter wave element contains a standing wave with the voltage and current largely (but not exactly) in phase quadrature, as would be obtained using a quarter wave stub of transmission line. The current reaches a minimum at the end of the element (where it has nowhere to go!) and is maximum at the feed-point. The voltage, on the other hand, is the greatest at the end of the conductor and reaches a minimum (but not zero) at the feedpoint. Making the conductor shorter or longer than 1/4 wavelength means that the voltage pattern reaches its minimum somewhere beyond the feed-point, so that the feed-point has a higher voltage and thus sees a higher impedance, as we have noted. Since that voltage pattern is almost in phase quadrature with the current, the impedance seen at the feed-point is not only much higher but mainly reactive.

It can be seen that if such an element is resonant at f0 to produce such a standing wave pattern, then feeding that element with 3f0 (whose wavelength is 1/3 that of f0) will lead to a standing wave pattern in which the voltage is likewise a minimum at the feed-point (and the current at a maximum there). Thus, an antenna element is also resonant when its length is 3/4 of a wavelength (3/2 wavelength for a complete dipole). This is true for all odd multiples of 1/4 wavelength, where the feed-point impedance is purely resistive, though larger than the resistive impedance of the 1/4 wave element. Although such an antenna is resonant and works perfectly well at the higher frequency, the antenna radiation pattern is also altered compared to the half-wave dipole.

The use of a monopole or dipole at odd multiples of the fundamental resonant frequency, however, does not extend to even multiples (thus a 1/2 wavelength monopole or 1 wavelength dipole). Now the voltage standing wave is at its peak at the feed-point, while that of the current (which must be zero at the end of the conductor) is at a minimum (but not exactly zero). The antenna is anti-resonant at this frequency. Although the reactance at the feedpoint can be cancelled using such an element length, the feed-point impedance is very high, and is highly dependent on the diameter of the conductor (which makes only a small difference at the actual resonant frequency). Such an antenna does not match the much lower characteristic impedance of available transmission lines, and is generally not used. However some equipment where transmission lines are not involved which desire a high driving point impedance may take advantage of this anti-resonance.

Bandwidth[edit]Main article: Antenna bandwidth

Although a resonant antenna has a purely resistive feed-point impedance at a particular frequency, many (if not most) applications require using an antenna over a range of frequencies. An antenna's bandwidth specifies the range of frequencies over which its performance does not suffer due to a poor impedance match. Also in the case of a Yagi-Uda array, the use of the antenna very far away from its design frequency reduces the antenna's directivity, thus reducing the usable bandwidth regardless of impedance matching.

Except for the latter concern, the resonant frequency of a resonant antenna can always be altered by adjusting a suitable matching network. To do this efficiently one would require remotely adjusting a matching network at the site of the antenna, since simply adjusting a matching network at the transmitter (or receiver) would leave the transmission line with a poor standing wave ratio.

Instead, it is often desired to have an antenna whose impedance does not vary so greatly over a certain bandwidth. It turns out that the amount of reactance seen at the terminals of a resonant antenna when the frequency is shifted, say, by 5%, depends very much on the diameter of the conductor used. A long thin wire used as a half-wave dipole (or quarter wave monopole) will have a reactance significantly greater than the resistive impedance it has at resonance, leading to a poor match and generally unacceptable performance. Making the element using a tube of a diameter perhaps 1/50 of its length, however, results in a reactance at this altered frequency which is not so great, and a much less serious mismatch which will only modestly damage the antenna's net performance. Thus rather thick tubes are typically used for the solid elements of such antennas, including Yagi-Uda arrays.

Rather than just using a thick tube, there are similar techniques used to the same effect such as replacing thin wire elements with cages to simulate a thicker element. This widens the bandwidth of the resonance. On the other hand, amateur radio antennas need to operate over several bands which are widely separated from each other. This can often be accomplished simply by connecting resonant elements for the different bands in parallel. Most of the transmitter's power will flow into the resonant element while the others present a high (reactive) impedance and draw little current from the same voltage. A popular solution uses so-called traps consisting of parallel resonant circuits which are strategically placed in breaks along each antenna element. When used at one particular frequency band the trap presents a very high impedance (parallel resonance) effectively truncating the element at that length, making it a proper resonant antenna. At a lower frequency the trap allows the full length of the element to be employed, albeit with a shifted resonant frequency due to the inclusion of the trap's net reactance at that lower frequency.

The bandwidth characteristics of a resonant antenna element can be characterized according to its Q, just as one uses to characterize the sharpness of an L-C resonant circuit. However it is often assumed that there is an advantage in an antenna having a high Q. After all, Q is short for "quality factor" and a low Q typically signifies excessive loss (due to unwanted resistance) in a resonant L-C circuit. However this understanding does not apply to resonant antennas where the resistance involved is the radiation resistance, a desired quantity which removes energy from the resonant

element in order to radiate it (the purpose of an antenna, after all!). The Q is a measure of the ratio of reactance to resistance, so with a fixed radiation resistance (an element's radiation resistance is almost independent of its diameter) a greater reactance off-resonance corresponds to the poorer bandwidth of a very thin conductor. The Q of such a narrowband antenna can be as high as 15. On the other hand a thick element presents less reactance at an off-resonant frequency, and consequently a Q as low as 5. These two antennas will perform equivalently at the resonant frequency, but the second antenna will perform over a bandwidth 3 times as wide as the "hi-Q" antenna consisting of a thin conductor.

Gain[edit]Main article: Antenna gain

Gain is a parameter which measures the degree of directivity of the antenna's radiation pattern. A high-gain antenna will preferentially radiate in a particular direction. Specifically, the antenna gain, or power gain of an antenna is defined as the ratio of the intensity (power per unit surface) radiated by the antenna in the direction of its maximum output, at an arbitrary distance, divided by the intensity radiated at the same distance by a hypothetical isotropic antenna.

The gain of an antenna is a passive phenomenon - power is not added by the antenna, but simply redistributed to provide more radiated power in a certain direction than would be transmitted by an isotropic antenna. An antenna designer must take into account the application for the antenna when determining the gain. High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully in a particular direction. Low-gain antennas have shorter range, but the orientation of the antenna is relatively inconsequential. For example, a dish antenna on a spacecraft is a high-gain device that must be pointed at the planet to be effective, whereas a typical Wi-Fiantenna in a laptop computer is low-gain, and as long as the base station is within range, the antenna can be in any orientation in space. It makes sense to improve horizontal range at the expense of reception above or below the antenna.[15]

In practice, the half-wave dipole is taken as a reference instead of the isotropic radiator. The gain is then given in dBd (decibels over dipole):

NOTE: 0 dBd = 2.15 dBi. It is vital in expressing gain values that the reference point be included. Failure to do so can lead to confusion and error.

Effective area or aperture[edit]Main article: Antenna effective area

The effective area or effective aperture of a receiving antenna expresses the portion of the power of a passing electromagnetic wave which it delivers to its terminals, expressed in terms of an equivalent area. For instance, if a radio wave passing a given location has a flux of 1 pW / m2 (10−12 watts per square meter) and an antenna has an effective area of 12 m2, then the antenna would deliver 12 pW of RF power to the receiver (30 microvolts rms at 75 ohms). Since the receiving antenna is not equally sensitive to signals received from all directions, the effective area is a function of the direction to the source.

Due to reciprocity (discussed above) the gain of an antenna used for transmitting must be proportional to its effective area when used for receiving. Consider an antenna with noloss, that is, one whose electrical efficiency is 100%. It can be shown that its effective area averaged over all directions must be equal to λ2/4π, the wavelength squared divided by 4π. Gain is defined such that the average gain over all directions for an antenna with 100% electrical efficiency is equal to 1. Therefore the effective area Aeff in terms of the gain G in a given direction is given by:

For an antenna with an efficiency of less than 100%, both the effective area and gain are reduced by that same amount. Therefore the above relationship between gain and effective area still holds. These are thus two different ways of expressing the same quantity. Aeff is especially convenient when computing the power that would be received by an antenna of a specified gain, as illustrated by the above example.

Radiation pattern[edit]Main article: Radiation pattern

Polar plots of the horizontal cross sections of a (virtual) Yagi-Uda-antenna. Outline connects points with

3db field power compared to an ISO emitter.

The radiation pattern of an antenna is a plot of the relative field strength of the radio waves emitted by the antenna at different angles. It is typically represented by a three-dimensional graph, or polar plots of the horizontal and vertical cross sections. The pattern of an idealisotropic antenna, which radiates equally in all directions, would look like a sphere. Many nondirectional antennas, such as monopoles anddipoles, emit equal power in all horizontal directions, with the power dropping off at higher and lower angles; this is called anomnidirectional pattern and when plotted looks like a torus or donut.

The radiation of many antennas shows a pattern of maxima or "lobes" at various angles, separated by "nulls", angles where the radiation falls to zero. This is because the radio waves emitted by different parts of the antenna typically interfere, causing maxima at angles where the radio waves arrive at distant points in phase, and zero radiation at other angles where the radio waves arrive out of phase. In adirectional antenna designed to project radio waves in a particular direction, the lobe in that direction is designed larger than the others and is called the "main lobe". The other lobes usually represent unwanted radiation and are called "sidelobes". The axis through the main lobe is called the "principal axis" or "boresight axis".

Field regions[edit]Main article: Near and far field

The space surrounding an antenna can be divided into three concentric regions: the reactive near-field, the radiating near-field (Fresnell region) and the far-field (Fraunhofer) regions. These regions are useful to identify the field structure in each, although there are no precise boundaries.

In the far-field region, we are far enough from the antenna to neglect its size and shape. We can assume that the electromagnetic wave is purely a radiating plane wave (electric and

magnetic fields are in phase and perpendicular to each other and to the direction of propagation). This simplifies the mathematical analysis of the radiated field.

Impedance[edit]As an electro-magnetic wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance (E/H, V/I, etc.). At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source,[16] forming a standing wave in the feed line. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment. Minimizing impedance differences at each interface (impedance matching) will reduce SWR and maximize power transfer through each part of the antenna system.

Complex impedance of an antenna is related to the electrical length of the antenna at the wavelength in use. The impedance of an antenna can be matched to the feed line and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer. More commonly, the impedance is adjusted at the load (see below) with anantenna tuner, a balun, a matching transformer, matching networks composed of inductors and capacitors, or matching sections such as the gamma match.

Efficiency[edit]Main article: Antenna efficiency

Efficiency of a transmitting antenna is the ratio of power actually radiated (in all directions) to the power absorbed by the antenna terminals. The power supplied to the antenna terminals which is not radiated is converted into heat. This is usually through loss resistance in the antenna's conductors, but can also be due to dielectric or magnetic core losses in antennas (or antenna systems) using such components. Such loss effectively robs power from the transmitter, requiring a stronger transmitter in order to transmit a signal of a given strength.

For instance, if a transmitter delivers 100 W into an antenna having an efficiency of 80%, then the antenna will radiate 80 W as radio waves and produce 20 W of heat. In order to radiate 100 W of power, one would need to use a transmitter capable of supplying 125 W to the antenna. Note that antenna efficiency is a separate issue from impedance matching, which may also reduce the amount of power radiated using a given transmitter. If an SWR meter reads 150 W of incident power and 50 W of reflected power, that means that 100 W have actually been absorbed by the antenna (ignoring transmission line losses). How much of that power has actually been radiated cannot be directly determined through electrical measurements at (or before) the antenna terminals, but would require (for instance) careful measurement of field strength. Fortunately the loss resistance of antenna conductors such as aluminum rods can be calculated and the efficiency of an antenna using such materials predicted.

However loss resistance will generally affect the feedpoint impedance, adding to its resistive (real) component. That resistance will consist of the sum of the radiation resistanceRr and the loss resistance Rloss. If an rms current I is delivered to the terminals of an antenna, then a power of I2Rr will be radiated and a power of I2Rloss will be lost as heat. Therefore the efficiency of an antenna is equal to Rr / (Rr + Rloss). Of course only the total resistance Rr + Rloss can be directly measured.

According to reciprocity, the efficiency of an antenna used as a receiving antenna is identical to the efficiency as defined above. The power that an antenna will deliver to a receiver (with a proper impedance match) is reduced by the same amount. In some receiving applications, the very inefficient antennas may have little impact on performance.

At low frequencies, for example, atmospheric or man-made noise can mask antenna inefficiency. For example, CCIR Rep. 258-3 indicates man-made noise in a residential setting at 40 MHz is about 28 dB above the thermal noise floor. Consequently, an antenna with a 20 dB loss (due to inefficiency) would have little impact on system noise performance. The loss within the antenna will affect the intended signal and the noise/interference identically, leading to no reduction in signal to noise ratio (SNR).

This is fortunate, since antennas at lower frequencies which are not rather large (a good fraction of a wavelength in size) are inevitably inefficient (due to the small radiation resistance Rr of small antennas). Most AM broadcast radios (except for car radios) take advantage of this principle by including a small loop antenna for reception which has an extremely poor efficiency. Using such an inefficient antenna at this low frequency (530–1650 kHz) thus has little effect on the receiver's net performance, but simply requires greater amplification by the receiver's electronics. Contrast this tiny component to the massive and very tall towers used at AM broadcast stations for transmitting at the very same frequency, where every percentage point of reduced antenna efficiency entails a substantial cost.

The definition of antenna gain or power gain already includes the effect of the antenna's efficiency. Therefore if one is trying to radiate a signal toward a receiver using a transmitter of a given power, one need only compare the gain of various antennas rather than considering the efficiency as well. This is likewise true for a receiving antenna at very high (especially microwave) frequencies, where the point is to receive a signal which is strong compared to the receiver's noise temperature. However in the case of a directional antenna used for receiving signals with the intention of rejecting interference from different directions, one is no longer concerned with the antenna efficiency, as discussed above. In this case, rather than quoting the antenna gain, one would be more concerned with the directive gain which does not include the effect of antenna (in)efficiency. The directive gain of an antenna can be computed from the published gain divided by the antenna's efficiency.

Polarization[edit]See also: Polarization (waves) § Antennas

The polarization of an antenna refers to the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation; note that this designation is totally distinct from the antenna's directionality. Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally. As a transverse wave, the magnetic field of a radio wave is at right angles to that of the electric field, but by convention, talk of an antenna's "polarization" is understood to refer to the direction of the electric field.

Reflections generally affect polarization. For radio waves, one important reflector is the ionosphere which can change the wave's polarization. Thus for signals received following reflection by the ionosphere (a skywave), a consistent polarization cannot be expected. For line-of-sight communications or ground wave propagation, horizontally or vertically polarized transmissions generally remain in about the same polarization state at the receiving location. Matching the receiving antenna's polarization to that of the transmitter can make a very substantial difference in received signal strength.

Polarization is predictable from an antenna's geometry, although in some cases it is not at all obvious (such as for the quad antenna). An antenna's linear polarization is generally along the direction (as viewed from the receiving location) of the antenna's currents when such a direction can be defined. For instance, a vertical whip antenna or Wi-Fi antenna vertically oriented will transmit and receive in the vertical polarization. Antennas with horizontal elements, such as most rooftop TV antennas, are horizontally polarized

(broadcast TV usually uses horizontal polarization). Even when the antenna system has a vertical orientation, such as an array of horizontal dipole antennas, the polarization is in the horizontal direction corresponding to the current flow. The polarization of a commercial antenna is an essential specification.

Polarization is the sum of the E-plane orientations over time projected onto an imaginary plane perpendicular to the direction of motion of the radio wave. In the most general case, polarization is elliptical, meaning that the polarization of the radio waves varies over time. Two special cases are linear polarization (the ellipse collapses into a line) as we have discussed above, and circular polarization (in which the two axes of the ellipse are equal). In linear polarization the electric field of the radio wave oscillates back and forth along one direction; this can be affected by the mounting of the antenna but usually the desired direction is either horizontal or vertical polarization. In circular polarization, the electric field (and magnetic field) of the radio wave rotates at the radio frequency circularly around the axis of propagation. Circular or elliptically polarized radio waves aredesignated as right-handed or left-handed using the "thumb in the direction of the propagation" rule. Note that for circular polarization, optical researchers use the opposite right hand rule from the one used by radio engineers.

It is best for the receiving antenna to match the polarization of the transmitted wave for optimum reception. Intermediate matchings will lose some signal strength, but not as much as a complete mismatch. A circularly polarized antenna can be used to equally well match vertical or horizontal linear polarizations. Transmission from a circularly polarized antenna received by a linearly polarized antenna (or vice versa) entails a 3dB reduction in signal-to-noise ratio as the received power has thereby been cut in half.

Impedance matching[edit]Main article: Impedance matching

Maximum power transfer requires matching the impedance of an antenna system (as seen looking into the transmission line) to the complex conjugate of the impedance of the receiver or transmitter. In the case of a transmitter, however, the desired matching impedance might not correspond to the dynamic output impedance of the transmitter as analyzed as a source impedance but rather the design value (typically 50 ohms) required for efficient and safe operation of the transmitting circuitry. The intended impedance is normally resistive but a transmitter (and some receivers) may have additional adjustments to cancel a certain amount of reactance in order to "tweak" the match. When a transmission line is used in between the antenna and the transmitter (or receiver) one generally would like an antenna system whose impedance is resistive and near thecharacteristic impedance of that transmission line in order to minimize the standing wave ratio (SWR) and the increase in transmission line losses it entails, in addition to supplying a good match at the transmitter or receiver itself.

Antenna tuning generally refers to cancellation of any reactance seen at the antenna terminals, leaving only a resistive impedance which might or might not be exactly the desired impedance (that of the transmission line). Although an antenna may be designed to have a purely resistive feedpoint impedance (such as a dipole 97% of a half wavelength long) this might not be exactly true at the frequency that it is eventually used at. In some cases the physical length of the antenna can be "trimmed" to obtain a pure resistance. On the other hand, the addition of a series inductance or parallel capacitance can be used to cancel a residual capacitative or inductive reactance, respectively.

In some cases this is done in a more extreme manner, not simply to cancel a small amount of residual reactance, but to resonate an antenna whose resonance frequency is quite different from the intended frequency of operation. For instance, a "whip antenna" can be made significantly shorter than 1/4 wavelength long, for practical reasons, and then

resonated using a so-called loading coil. This physically large inductor at the base of the antenna has an inductive reactance which is the opposite of the capacitative reactance that such a vertical antenna has at the desired operating frequency. The result is a pure resistance seen at feedpoint of the loading coil; unfortunately that resistance is somewhat lower than would be desired to match commercial coax.[citation needed]

So an additional problem beyond canceling the unwanted reactance is of matching the remaining resistive impedance to the characteristic impedance of the transmission line. In principle this can always be done with a transformer, however the turns ratio of a transformer is not adjustable. A general matching network with at least two adjustments can be made to correct both components of impedance. Matching networks using discrete inductors and capacitors will have losses associated with those components, and will have power restrictions when used for transmitting. Avoiding these difficulties, commercial antennas are generally designed with fixed matching elements or feeding strategies to get an approximate match to standard coax, such as 50 or 75 Ohms. Antennas based on the dipole (rather than vertical antennas) should include a balun in between the transmission line and antenna element, which may be integrated into any such matching network.

Another extreme case of impedance matching occurs when using a small loop antenna (usually, but not always, for receiving) at a relatively low frequency where it appears almost as a pure inductor. Resonating such an inductor with a capacitor at the frequency of operation not only cancels the reactance but greatly magnifies the very small radiation resistance of such a loop.[citation needed] This is implemented in most AM broadcast receivers, with a small ferrite loop antenna resonated by a capacitor which is varied along with the receiver tuning in order to maintain resonance over the AM broadcast band

Basic antenna models[edit]

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A "Turnstile" type transmitting antenna (two dipole antennas aligned at right angles) for a VHF low band

television broadcasting station.

There are many variations of antennas. Below are a few basic models. More can be found in Category:Radio frequency antenna types.

The isotropic radiator is a purely theoretical antenna that radiates equally in all directions. It is considered to be a point in space with no dimensions and no mass. This antenna cannot physically exist, but is useful as a theoretical model for comparison with all other antennas. Most antennas' gains are measured with reference to an isotropic radiator, and are rated in dBi (decibels with respect to an isotropic radiator).

The dipole antenna is simply two wires pointed in opposite directions arranged either horizontally or vertically, with one end of each wire connected to the radio and the other end hanging free in space. Since this is the simplest practical antenna, it is also used as a reference modelfor other antennas; gain with respect to a dipole is labeled as dBd. Generally, the dipole is considered to be omnidirectional in the plane perpendicular to the axis of the antenna, but it has deep nulls in the directions of the axis. Variations of the dipole include the folded dipole, the half wave antenna, the ground plane antenna, the whip, and the J-pole.

The Yagi-Uda antenna is a directional variation of the dipole with parasitic elements added which are functionality similar to adding a reflector and lenses (directors) to focus a filament light bulb.

The random wire antenna is simply a very long (at least one quarter wavelength[citation needed]) wire with one end connected to the radio and the other in free space, arranged in any way most convenient for the space available. Folding will reduce effectiveness and make theoretical analysis extremely difficult. (The added length helps more than the folding typically hurts.) Typically, a random wire antenna will also require an antenna tuner, as it might have a random impedance that varies non-linearly with frequency.

The horn antenna is used where high gain is needed, the wavelength is short (microwave) and space is not an issue. Horns can be narrow band or wide band, depending on their shape. A horn can be built for any frequency, but horns for lower frequencies are typically impractical. Horns are also frequently used as reference antennas.

The parabolic antenna consists of an active element at the focus of a parabolic reflector to reflect the waves into a plane wave. Like the horn it is used for high gain, microwave applications, such as satellite dishes.

The patch antenna consists mainly of a square conductor mounted over a groundplane. Another example of a planar antenna is the tapered slot antenna (TSA), as theVivaldi-antenna.

Examples of antenna models[edit]

Dipole antenna ("Rabbit ears") for television reception

 

Folded dipole antenna

 

A Yagi-Uda beam antenna

 

Rooftop TV antenna. It is actually three Yagi antennas. The longest elements are for the low band, while the medium and short elements are for the high and UHF band.

 

A random wire antenna

 

Pyramidal microwave horn antenna

 

Large parabolic antennafor communicating with spacecraft

 

A patch antenna and a cutaway view

Antenna design criteria[edit]

"Rabbit ears" set-top antenna

Almost any arrangement of conductors with radio frequency currents driven by a voltage applied across two points will radiate as an antenna. However to be practical an antenna will be designed to meet certain specifications among the characteristics listed above. One extremely important characteristic is the driving point impedance, as this impedance is usually very large (and highly reactive) for an arbitrarily designed antenna, or even for a well designed antenna used at a frequency well outside of its design range. For non-directional antennas, forcing the impedance to a usable value (often that of the transmission line to be used to connect to it) and an impedance with a relatively small amount of reactance, is the main design task. For instance, the design of dipole

antennas (which many other antennas are based on) dictates a total length just under half the wavelength (thus each arm being one quarter wavelength). This provides a purely resistive feedpoint impedance (at the design frequency) of a bit under 72Ω (depending on the diameter of the conductors). Likewise, a dipole antenna which is an odd multiple of half wavelengths long will supply a reasonable (but different) feedpoint impedance which is purely resistive. Such an antenna used at the frequency where its driving point impedance is purely resistive is called a resonant antenna, even though the "resonance" involved usually is characterized by a rather low Q. In fact a small Q factor is generally sought, since a larger Q implies a smaller bandwidth over which the antenna will provide a good impedance match to the transmission line or matching network. In the case of a dipole antenna, increasing the diameter of the two conductors, increases the usable bandwidth of the antenna.

Having thus eliminated reactance from the feedpoint impedance, what remains is a pure resistance, which is the sum of two parts. The main part (usually) is the radiation resistance due to the conversion of electrical energy into a transmitted wave. Of course this is what the antenna was meant to do. But there can be an additional contribution to the feedpoint impedance due to the ohmic resistance of the conductors, which is a source of inefficiency. This inefficiency can be reduced by using larger conductors, for instance, but that will have other effects as well.

The third important design criterion for many antennas is the antenna's directionality (expressed by its radiation pattern and gain). This is often not a design goal however. An antenna much smaller than a wavelength in all its dimensions cannot have much directionality, so at lower frequencies a directional antenna generally becomes impractically large. Antennas for use in portable or mobile equipment cannot be conveniently pointed in the direction of the other station, so directionality is undesired in these applications. The vertical "whip" antenna, for instance, is completely omnidirectional in the horizontal plane, and widely used in such applications.

However for fixed stations communicating with other fixed stations, directionality allows for a significant antenna gain (factor by which power is concentrated in one direction), improving the received signal level by that factor. Thus a beam antenna with a 13dB gain compared to an omnidirectional antenna, will allow use of a transmitter of only 1/20th of the power. A rural location might require a Yagi rooftop antenna with such a gain for TV reception, whereas increasing the TV station's power by a factor of 20 would be out of the question. At higher and higher frequencies, the feasibility of higher gain (more directional) antennas increases, with high gain microwave antennas typically employing parabolic reflectors or horns.

The gain of such a directional antenna will also have a certain operating bandwidth, in addition to the bandwidth associated with the feedpoint impedance. Thus the Yagi TV antenna will only maintain its high gain over a few TV channels. For use over an entire frequency band, a wideband design such as the log periodic antenna may be chosen. Although superficially similar in appearance to a high gain Yagi, the log-periodic dipole array often used for TV can cover the entire UHF TV band, for

instance. In return for being wideband, however, the antenna gain is much less than that of a comparable Yagi. Practical antenna designs always involve such trade-offs in order to best meet the performance requirements imposed by a particular application.

Effect of ground[edit]

Main article: Multipath propagation

It has been suggested that this section be merged into Multipath propagation. (Discuss) Proposed since November 2014.

Ground reflections is one of the common types of multipath. [17] [18] [19] The radiation pattern and even the driving point impedance of an antenna can be influenced by the dielectric constant and especially conductivity of nearby objects. For a terrestrial antenna, the ground is usually one such object of importance. The antenna's height above the ground, as well as the electrical properties (permittivity and conductivity) of the ground, can then be important. Also, in the particular case of a monopole antenna, the ground (or an artificial ground plane) serves as the return connection for the antenna current thus having an additional effect, particularly on the impedance seen by the feed line.

When an electromagnetic wave strikes a plane surface such as the ground, part of the wave is transmitted into the ground and part of it is reflected, according to the Fresnel coefficients. If the ground is a very good conductor then almost all of the wave is reflected (180° out of phase), whereas a ground modeled as a (lossy) dielectric can absorb a large amount of the wave's power. The power remaining in the reflected wave, and the phase shift upon reflection, strongly depend on the wave's angle of incidence andpolarization. The dielectric constant and conductivity (or simply the complex dielectric constant) is dependent on the soil type and is a function of frequency.

For very low frequencies to high frequencies (<30 MHz), the ground behaves as a lossy dielectric, [20] Thus the ground is characterized both by a conductivity [21] and permittivity(dielectric constant) which can be measured for a given soil (but is influenced by fluctuating moisture levels) or can be estimated from certain maps. At lower frequencies the ground acts mainly as a good conductor, which AM middle wave broadcast (.5 - 1.6 MHz) antennas depend on.

At frequencies between 3 and 30 MHz, a large portion of the energy from a horizontally polarized antenna reflects off the ground, with almost total reflection at the grazing angles important for ground wave propagation. That reflected wave, with its phase reversed, can either cancel or reinforce the direct wave, depending on the antenna height in wavelengths and elevation angle (for a sky wave).

On the other hand, vertically polarized radiation is not well reflected by the ground except at grazing incidence or over very highly conducting surfaces such as sea water. [22]However the grazing angle

reflection important for ground wave propagation, using vertical polarization, is in phase with the direct wave, providing a boost of up to 6 db, as is detailed below.

The wave reflected by earth can be considered as emitted by the image antenna.

At VHF and above (>30MHz) the ground becomes a poorer reflector. However it remains a good reflector especially for horizontal polarization and grazing angles of incidence. That is important as these higher frequencies usually depend on horizontal line-of-sight propagation (except for satelite communications), the ground then behaving almost as a mirror.

The net quality of a ground reflection depends on the topography of the surface. When the irregularities of the surface are much smaller than the wavelength, we are in the regime of specular reflection, and the receiver sees both the real antenna and an image of the antenna under the ground due to reflection. But if the ground has irregularities not small compared to the wavelength, reflections will not be coherent but shifted by random phases. With shorter wavelengths (higher frequencies), this is generally the case.

Whenever both the receiving or transmitting antenna are placed at significant heights above the ground (relative to the wavelength), waves specularly reflected by the ground will travel a longer distance than direct waves, inducing a phase shift which can sometimes be significant. When a sky wave is launched by such an antenna, that phase shift is always significant unless the antenna is very close to the ground (compared to the wavelength).

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The phase of reflection of electromagnetic waves depends on the polarization of the incident wave. Given the larger refractive index of the ground (typically n=2) compared to air (n=1), the phase of horizontally polarized radiation is reversed upon reflection (a phase shift of   radians or 180°). On the other hand, the vertical component of the wave's electric field is reflected at grazing angles of incidence approximately in phase. These phase shifts apply as well to a ground modelled as a good electrical conductor.

The currents in an antenna appear as an image in opposite phase when reflected at grazing angles. This causes a

phase reversal for waves emitted by a horizontally polarized antenna (left) but not a vertically polarized antenna

(center).

This means that a receiving antenna "sees" an image of the antenna but with reversed currents. That current is in the same absolute direction as the actual antenna if the antenna is vertically oriented (and thus vertically polarized) but opposite the actual antenna if the antenna current is horizontal.

The actual antenna which is transmitting the original wave then also may receive a strong signal from its own image from the ground. This will induce an additional current in the antenna element, changing the current at the feedpoint for a given feedpoint voltage. Thus the antenna's impedance, given by the ratio of feedpoint voltage to current, is altered due to the antenna's proximity to the ground. This can be quite a significant effect when the antenna is within a wavelength or two of the ground. But as the antenna height is increased, the reduced power of the reflected wave (due to the inverse square law) allows the antenna to approach its asymptotic feedpoint impedance given by theory. At lower heights, the effect on the antenna's impedance is very sensitive to the exact distance from the ground, as this affects the phase of the reflected wave relative to the currents in the antenna. Changing the antenna's height by a quarter wavelength, then changes the phase of the reflection by 180°, with a completely different effect on the antenna's impedance.

The ground reflection has an important effect on the net far field radiation pattern in the vertical plane, that is, as a function of elevation angle, which is thus different between a vertically and horizontally polarized antenna. Consider an antenna at a height h above the ground, transmitting a wave considered at the elevation angle θ. For a vertically polarized transmission the magnitude of the electric field of the electromagnetic wave produced by the direct ray plus the reflected ray is:

Thus the power received can be as high as 4 times that due to the direct wave alone (such as when θ=0), following the square of the cosine. The sign inversion for the reflection of horizontally polarized emission instead results in:

where:

 is the electrical field that would be received by the direct wave if there were no ground.

θ is the elevation angle of the wave being considered.

 is the wavelength.

 is the height of the antenna (half the distance between the antenna and its image).

Radiation patterns of antennas and their images reflected by the ground. At left the polarization is

vertical and there is always a maximum for  . If the polarization is horizontal as at right, there is

always a zero for  .

For horizontal propagation between transmitting and receiving antennas situated near the ground reasonably far from each other, the distances traveled by tne direct and reflected rays are nearly the same. There is almost no relative phase shift. If the emission is polarized vertically, the two fields (direct and reflected) add and there is maximum of received signal. If the signal is polarized horizontally, the two signals subtract and the received signal is largely cancelled. The vertical plane radiation patterns are shown in the image at right. With vertical polarization there is always a maximum for θ=0, horizontal propagation (left pattern). For horizontal polarization, there is cancellation at that angle. Note that the above formulae and these plots assume the ground as a perfect conductor. These plots of the radiation pattern correspond to a distance between the antenna and its image of 2.5λ. As the antenna height is increased, the number of lobes increases as well.

The difference in the above factors for the case of θ=0 is the reason that most broadcasting (transmissions intended for the public) uses vertical polarization. For receivers near the ground, horizontally polarized transmissions suffer cancellation. For best reception the receiving antennas for these signals are likewise vertically polarized. In some applications where the receiving antenna must work in any position, as in mobile phones, the base stationantennas use mixed polarization, such as linear polarization at an angle (with both vertical and horizontal components) or circular polarization.

On the other hand, classical (analog) television transmissions are usually horizontally polarized, because in urban areas buildings can reflect the electromagnetic waves and create ghost images due to multipath propagation. Using horizontal polarization, ghosting is reduced because the amount of reflection of electromagnetic waves in the ppolarization

(horizontal polarization off the side of a building) is generally less than s (vertical, in this case) polarization. Vertically polarized analog television has nevertheless been used in some rural areas. In digital terrestrial television such reflections are less problematic, due to robustness of binary transmissions and error correction.

Mutual impedance and interaction between antennas[edit]

Current circulating in one antenna generally induces a voltage across the feedpoint of nearby antennas or antenna elements. The mathematics presented below are useful in analyzing the electrical behaviour of antenna arrays, where the properties of the individual array elements (such as half wave dipoles) are already known. If those elements were widely separated and driven in a certain amplitude and phase, then each would act independently as that element is known to. However because of the mutual interaction between their electric and magnetic fields due to proximity, the currents in each element are not simply a function of the applied voltage (according to its driving point impedance), but depend on the currents in the other nearby elements. Note that this now is a near field phenomenon which could not be properly accounted for using the Friis transmission equation for instance.

The elements' feedpoint currents and voltages can be related to each other using the concept of mutual impedance   between every pair of antennas just as the mutual impedance   describes the voltage induced in one inductor by a current through a nearby coil coupled to it through a mutual inductance M. The mutual impedance  between two antennas is defined[23] as:

where   is the current flowing in antenna i and   is the voltage induced at the open-circuited feedpoint of antenna j due to   when all other currents ik are zero. The mutual impendances can be viewed as the elements of a symmetric square impedance

matrix Z. Note that the diagonal elements,  , are simply the driving point impedances of each element.

Using this definition, the voltages present at the feedpoints of a set of coupled antennas can be expressed as the multiplication of the impedance matrix times the vector of currents. Written out as discrete equations, that means:

where:

 is the voltage at the terminals of antenna 

 is the current flowing between the terminals of antenna 

 is the driving point impedance of antenna 

 is the mutual impedance between antennas   and  .

Mutual impedance between parallel   dipoles not staggered. Curves Re and Im are the resistive

and reactive parts of the impedance.

As is the case for mutual inductances,

This is a consequence of Lorentz reciprocity. For an antenna element   not connected to anything (open circuited) one can write  . But for an element   which is short circuited, a current is generated across that short but no voltage is allowed, so the corresponding  . This is the case, for instance, with the so-called parasitic elements of aYagi-Uda antenna where the solid rod can be viewed as a dipole antenna shorted across its feedpoint.

Parasitic elements are unpowered elements that absorb and reradiate RF energy according to the induced current calculated using such a system of equations.

With a particular geometry, it is possible for the mutual impedance between nearby antennas to be zero. This is the case, for instance, between the crossed dipoles used in theturnstile antenna.

Antenna gallery[edit]

Antennas and antenna arrays[edit]

A multi-band rotary directional antenna for amateur radio use.

 

A terrestrial microwave radio antenna array.

 

Wire dipole antennausing open-wire ladder line feedline for amateur radio use.

 

Low cost LF time signalreceiver, antenna (left) and receiver

 

Rotatable log-periodic array for VHF and UHF.

 

Shortwave antennas inDelano, California.

 

AM loop antenna

Antennas and supporting structures[edit]

A building rooftop supporting numerous dish and sectored mobile

telecommunications antennas (Doncaster,Victoria, Australia).

 

A water tower inPalmerston, Northern Territory with radio broadcasting and

communications antennas.

 

A three-sector telephone site in Mexico City.

 

Telephone site concealed as a palm tree.

Mobile phoneFrom Wikipedia, the free encyclopedia

  (Redirected from Cell phone)

"Cell Phone" redirects here. For the film, see Cell Phone (film).

"Handphone" redirects here. For the film, see Handphone (film).

An evolution of mobile phones

A mobile phone (also known as a cellular phone, cell phone, hand phone, or simply a phone) is a phone that can make and receivetelephone calls over a radio link while moving around a wide geographic area. It does so by connecting to a cellular network provided by amobile phone operator, allowing access to the public telephone network. By contrast, a cordless telephone is used only within the short range of a single, private base station.

In addition to telephony, modern mobile phones also support a wide variety of other services such as text messaging, MMS, email, Internet access, short-range wireless communications (infrared, Bluetooth), business applications, gaming, and photography. Mobile phones that offer these and more general computing capabilities are referred to as smartphones.

The first hand-held cell phone was demonstrated by John F. Mitchell [1] [2]  and Dr. Martin Cooper of Motorola in 1973, using a handset weighing around 4.4 pounds (2 kg).[3] In 1983, the DynaTAC 8000x was the first to be commercially available. From 1983 to 2014, worldwide mobile phone subscriptions grew from zero to over 7 billion, penetrating 100% of the global population and reaching the bottom of the economic pyramid.[4] In 2014, the top cell phone manufacturers were Samsung, Nokia, Apple, and LG.[5]

Contents  [hide] 

1   History 2   Features

o 2.1   Text messaging o 2.2   SIM card o 2.3   Multi-card hybrid phones o 2.4   Kosher phones

3   Mobile phone operators 4   Manufacturers 5   Use of mobile phones

o 5.1   In general o 5.2   Smartphones o 5.3   For distributing content o 5.4   While driving o 5.5   Mobile banking and payments o 5.6   Tracking and privacy o 5.7   Thefts

6   Health effects 7   Future evolution 8   Environmental impact 9   Conflict minerals 10   See also 11   References 12   Further reading 13   External links

HistoryMain article: History of mobile phones

File:A-Netz-Funktelefon 4967.jpg

Martin Cooper of Motorola made the first publicized handheld mobile phone call on a prototype DynaTAC model on

April 4, 1973. This is a reenactment in 2007.

The Motorola DynaTAC 8000X from 1984 (First hand-held cellular mobile phone which was commercially available)

A hand-held mobile radiotelephone is an old dream of radio engineering. One of the earliest descriptions can be found in the 1948 science fiction novel Space Cadet by Robert Heinlein. The protagonist, who has just traveled to Colorado from his home in Iowa, receives a call from his father on a telephone in his pocket. Before leaving for earth orbit, he decides to ship the telephone home "since it was limited by its short range to the neighborhood of an earth-side [i.e. terrestrial] relay office." Ten years later, an essay by Arthur C. Clarke envisioned a "personal transceiver, so small and compact that every man carries one." Clarke wrote: "the time will come when we will be able to call a person anywhere on Earth merely by dialing a number." Such a device would also, in Clarke's vision, include means for global positioning so that "no one need ever again be lost." Later, in Profiles of the Future, he predicted the advent of such a device taking place in the mid-1980s. [6]

Early predecessors of cellular phones included analog radio communications from ships and trains. The race to create truly portable telephone devices began after World War II, with developments taking place in many countries. The advances in mobile telephony have been traced in successive generations from the early "0G" (zeroth generation) services like the Bell System's Mobile Telephone Service and its successor, Improved Mobile Telephone Service. These "0G" systems were not cellular, supported few simultaneous calls, and were very expensive.

The first handheld mobile cell phone was demonstrated by Motorola in 1973. The first commercial automated cellular network was launched in Japan by NTT in 1979. In 1981, this was followed by the simultaneous launch of the Nordic Mobile Telephone (NMT) system in Denmark, Finland, Norway and Sweden.[7] Several other countries then followed in the early to mid-1980s. These first generatiion ("1G") systems could support far more simultaneous calls, but still used analog technology.

In 1991, the second generation (2G) digital cellular technology was launched in Finland by Radiolinja on the GSM standard, which sparked competition in the sector, as the new operators challenged the incumbent 1G network operators.

Ten years later, in 2001, the third generation (3G) was launched in Japan by NTT DoCoMo on the WCDMA standard.[8] This was followed by 3.5G, 3G+ or turbo 3G enhancements based on the high-speed packet access (HSPA) family, allowing UMTS networks to have higher data transfer speeds and capacity.

By 2009, it had become clear that, at some point, 3G networks would be overwhelmed by the growth of bandwidth-intensive applications like streaming media.[9] Consequently, the industry began looking to data-optimized 4th-generation technologies, with the promise of speed improvements up to 10-fold over existing 3G technologies. The first two commercially available technologies billed as 4G were the WiMAX standard (offered in the U.S. by Sprint) and the LTE standard, first offered in Scandinavia by TeliaSonera.

FeaturesMain article: Mobile phone features

See also: Smartphone

All mobile phones have a number of features in common, but manufacturers also try to differentiate their own products by implementing additional functions to make them more attractive to consumers. This has led to great innovation in mobile phone development over the past 20 years.

The common components found on all phones are:

A battery, providing the power source for the phone functions. An input mechanism to allow the user to interact with the phone. The most common input

mechanism is a keypad, but touch screens are also found in most smartphones. A screen which echoes the user's typing, displays text messages, contacts and more. Basic mobile phone services to allow users to make calls and send text messages. All GSM phones use a SIM card to allow an account to be swapped among devices.

Some CDMA devices also have a similar card called a R-UIM. Individual GSM, WCDMA, iDEN and some satellite phone devices are uniquely identified by

an International Mobile Equipment Identity (IMEI) number.

Low-end mobile phones are often referred to as feature phones, and offer basic telephony. Handsets with more advanced computing ability through the use of native software applications became known as smartphones.

Several phone series have been introduced to address a given market segment, such as the RIM BlackBerry focusing on enterprise/corporate customer email needs; the Sony-Ericsson 'Walkman' series of music/phones and 'Cybershot' series of camera/phones; the Nokia Nseries of multimedia phones, the Palm Pre the HTC Dream and the AppleiPhone.

Text messagingMain article: SMS

The most commonly used data application on mobile phones is SMS text messaging. The first SMS text message was sent from a computer to a mobile phone in 1992 in the UK, while the first person-to-person SMS from phone to phone was sent in Finland in 1993.

The first mobile news service, delivered via SMS, was launched in Finland in 2000, and subsequently many organizations provided "on-demand" and "instant" news services by SMS.

SIM cardMain articles: Subscriber Identity Module and Removable User Identity Module

Typical mobile phone SIM card

GSM feature phones require a small microchip called a Subscriber Identity Module or SIM card, to function. The SIM card is approximately the size of a small postage stamp and is usually placed underneath the battery in the rear of the unit. The SIM securely stores the service-subscriber key (IMSI) and the Ki used to identify and authenticate the user of the mobile phone. The SIM card allows users to change phones by simply removing the SIM card from one mobile phone and inserting it into another mobile phone or broadband telephony device, provided that this is not prevented by a SIM lock.

The first SIM card was made in 1991 by Munich smart card maker Giesecke & Devrient for the Finnish wireless network operatorRadiolinja.[citation needed]

Multi-card hybrid phonesA hybrid mobile phone can hold up to four SIM cards. SIM and RUIM cards may be mixed together to allow both GSM and CDMAnetworks to be accessed.[10][11]

From 2010 onwards they became popular in India and Indonesia and other emerging markets,[12] attributed to the desire to obtain the lowest on-net calling rate. In Q3 2011, Nokia shipped 18 million of its low cost dual SIM phone range in an attempt to make up lost ground in the higher end smartphone market.[13]

Kosher phonesThere are Jewish orthodox religious restrictions which, by some interpretations, standard mobile telephones do not meet. To solve this issue, some rabbinical organizations have recommended that phones with text messaging capability not be used by children.[14] These restricted phones are known as kosher phones and have rabbinical approval for use in Israel and elsewhere by observant Orthodox Jews. Although these phones are intended to prevent immodesty, some vendors report good sales to adults who prefer the simplicity of the devices. Some phones are even approved for use by essential workers (such as health, security and public services) on the sabbath, even though use of any electrical device is generally prohibited.[15]

Mobile phone operators

Global mobile phone subscribers per country from 1980 to 2009. The growth in users has been exponential since

they were first made available.

Main article: Mobile phone operator

The world's largest individual mobile operator by subscribers is China Mobile with over 500 million mobile phone subscribers.[16] Over 50 mobile operators have over 10 million subscribers each, and over 150 mobile operators had at least one million subscribers by the end of 2009. [17] In 2014, there were more than seven billion mobile phone subscribers worldwide, a number that is expected to keep growing.

ManufacturersSee also: List of best-selling mobile phones and List of mobile phone makers by country

Quantity Market Shares by Gartner(New Sales)

BRAND Percent

Samsung 2012   22.0%

Samsung 2013   24.6%

Nokia 2012   19.1%

Nokia 2013   13.9%

Apple 2012   7.5%

Apple 2013   8.3%

LG Electronics 2012

  3.3%

LG Electronics 2013

  3.8%

ZTE 2012   3.9%

ZTE 2013   3.3%

Others 2012   34.9%

Others 2013   34.0%

Note: Others-1 consist of Sony Ericsson, Motorola, ZTE, HTC and Huawei.(2009-2010)

Prior to 2010, Nokia was the market leader. However, since then competition emerged in the Asia Pacific region with brands such as Micromax, Nexian, and i-Mobile and chipped away at Nokia's market share. Android powered smartphones also gained momentum across the region at the expense of Nokia. In India, their market share also dropped significantly to around 31 percent from 56 percent in the same period. Their share was displaced by Chinese and Indian vendors of low-end mobile phones.[18]

In Q1 2012, based on Strategy Analytics, Samsung surpassed Nokia, selling 93.5 million units and 82.7 million units, respectively. Standard & Poor's has also downgraded Nokia to 'junk' status at BB+/B with negative outlook due to high loss and still declined with growth of Lumia smartphones was not sufficient to offset a rapid decline in revenue from Symbian-based smartphones over the next few quarters.[19]

Top Five Worldwide Total Mobile Phone Vendors, 2013

Rank Manufacturer Gartner [20] IDC [21]

1 Samsung 24.6% 24.5%

2 Nokia 13.9% 13.8%

3 Apple Inc. 8.3% 8.4%

4 LG 3.8% 3.8%

5 ZTE 3.3% -

5 Huawei - 3.0%

Others 34.0% 46.4%

Note: Vendor shipments are branded shipments and exclude OEM sales for all vendors

Other manufacturers outside the top five include TCL Communication, Lenovo, Sony Mobile Communications, Motorola. Smaller current and past players include Karbonn Mobile, Audiovox (now UTStarcom), BenQ-Siemens, BlackBerry, Casio, CECT, Coolpad, Fujitsu, HTC, Just5, Kyocera, Lumigon, Micromax Mobile, Mitsubishi Electric, Modu,NEC, Neonode, Openmoko, Panasonic, Palm, Pantech Wireless Inc., Philips, Qualcomm Inc., Sagem, Sanyo, Sharp, Sierra Wireless, SK Teletech, Soutec, Trium, Toshiba, and Vidalco.

Use of mobile phonesIn general

Mobile phone subscribers per 100 inhabitants.2014 figure is estimated.

Mobile phones are used for a variety of purposes, including keeping in touch with family members, conducting business, and having access to a telephone in the event of an emergency. Some people carry more than one cell phone for different purposes, such as for business and personal use. Multiple SIM cards may also be used to take advantage of the benefits of different calling plans—a particular plan might provide cheaper local calls, long-distance calls, international calls, or roaming. The mobile phone has also been used in a variety of diverse contexts in society, for example:

A study by Motorola found that one in ten cell phone subscribers have a second phone that often is kept secret from other family members. These phones may be used to engage in activities including extramarital affairs or clandestine business dealings. [22]

Some organizations assist victims of domestic violence by providing mobile phones for use in emergencies. They are often refurbished phones.[23]

The advent of widespread text messaging has resulted in the cell phone novel; the first literary genre to emerge from the cellular age via text messaging to a website that collects the novels as a whole.[24]

Mobile telephony  also facilitates activism and public journalism being explored by Reuters and Yahoo! [25]  and small independent news companies such as Jasmine News inSri Lanka.

The United Nations reported that mobile phones have spread faster than any other technology and can improve the livelihood of the poorest people in developing countries by providing access to information in places where landlines or the Internet are not available, especially in the least developed countries. Use of mobile phones also spawns a wealth of micro-enterprises, by providing work, such as selling airtime on the streets and repairing or refurbishing handsets. [26]

In Mali and other African countries, people used to travel from village to village to let friends and relatives know about weddings, births and other events, which are now avoided within mobile phone coverage areas, which is usually greater than land line penetration.

The TV industry has recently started using mobile phones to drive live TV viewing through mobile apps, advertising, social tv, and mobile TV.[27] 86% of Americans use their mobile phone while watching TV.

In parts of the world, mobile phone sharing is common. It is prevalent in urban India, as families and groups of friends often share one or more mobiles among their members. There are obvious economic benefits, but often familial customs and traditional gender roles play a part. [28] It is common for a village to have access to only one mobile phone, perhaps owned by a teacher or missionary, but available to all members of the village for necessary calls. [29]

Smartphones

Active mobile broadband subscriptions per 100 inhabitants, from ITU

Smartphones have a number of distinguishing features but the ITU measures those with internet connection which it callsActive Mobile-Broadband subscriptions (which includes tablets etc.) In the developed world these have now overtaken the usage of earlier mobile systems but in the developing world account for only 20%.

For distributing contentIn 1998, one of the first examples of distributing and selling media content through the mobile phone was the sale ofringtones by Radiolinja in Finland. Soon afterwards, other media content appeared such as news, video games, jokes, horoscopes, TV content and advertising. Most early content for

mobile tended to be copies of legacy media, such as the banner advertisement or the TV news highlight video clip. Recently, unique content for mobile has been emerging, from the ringing tones and ringback tones in music to "mobisodes", video content that has been produced exclusively for mobile phones.

In 2006, the total value of mobile-phone-paid media content exceeded Internet-paid media content and was worth 31 billion dollars.[30] The value of music on phones was worth 9.3 billion dollars in 2007 and gaming was worth over 5 billion dollars in 2007.[31]

While drivingMain article: Mobile phones and driving safety

A sign along Bellaire Boulevard in Southside Place, Texas (Greater Houston) states that using mobile phones while

driving is prohibited from 7:30 AM to 9:30 AM and from 2:00 PM to 4:15 PM

Mobile phone use while driving is common but controversial. Being distracted while operating a motor vehicle has been shown to increase the risk of accidents. Because of this, many jurisdictions prohibit the use of mobile phones while driving. Egypt, Israel, Japan, Portugal and Singapore ban both handheld and hands-free use of a mobile phone; others —including the UK, France, and many U.S. states—ban handheld phone use only, allowing hands-free use.

Due to the increasing complexity of mobile phones, they are often more like mobile computers in their available uses. This has introduced additional difficulties for law enforcement officials in distinguishing one usage from another as drivers use their devices. This is more apparent in those countries which ban both handheld and hands-free usage, rather than those who have banned handheld use only, as officials cannot easily tell which function of the mobile phone is being used simply by looking at the driver. This can lead to drivers being stopped for using their device illegally on a phone call when, in fact, they were using the device for a legal purpose such as the phone's incorporated controls for car stereo orsatnav.

A recently published study has reviewed the incidence of mobile phone use while cycling and its effects on behaviour and safety.[32]

Mobile banking and payments

Mobile payment system

Main articles: Mobile banking and Mobile payment

See also: Branchless banking and Contactless payment

In many countries, mobile phones are used to provide mobile banking services, which may include the ability to transfer cash payments by secure SMS text message. Kenya's M-PESA mobile banking service, for example, allows customers of the mobile phone operator Safaricom to hold cash balances which are recorded on their SIM cards. Cash may be deposited or withdrawn from M-PESA accounts at Safaricom retail outlets located throughout the country, and may be transferred electronically from person to person as well as used to pay bills to companies.

Branchless banking has also been successful in South Africa and the Philippines. A pilot project in Bali was launched in 2011 by theInternational Finance Corporation and an Indonesian bank Bank Mandiri.[33]

Another application of mobile banking technology is Zidisha, a US-based nonprofit micro-lending platform that allows residents of developing countries to raise small business loans from Web users worldwide. Zidisha uses mobile banking for loan disbursements and repayments, transferring funds from lenders in the United States to the borrowers in rural Africa using the Internet and mobile phones.[34]

Mobile payments were first trialled in Finland in 1998 when two Coca-Cola vending machines in Espoo were enabled to work with SMS payments. Eventually, the idea spread and in 1999 the Philippines launched the country's first commercial mobile payments systems on the mobile operators Globe and Smart.

Some mobile phone can make mobile payments via direct mobile billing schemes or through contactless payments if the phone and point of sale support near field communication (NFC).[35] This requires the co-operation of manufacturers, network operators and retail merchants to enable contactless payments through NFC-equipped mobile phones. [36][37][38]

Tracking and privacySee also: Cellphone surveillance and Mobile phone tracking

Mobile phones are also commonly used to collect location data. While the phone is turned on, the geographical location of a mobile phone can be determined easily (whether it is being used or not), using a technique known as multilateration to calculate the differences in time for a signal to travel from the cell phone to each of several cell towers near the owner of the phone.[39][40]

The movements of a mobile phone user can be tracked by their service provider and, if desired, by law enforcement agencies and their government. Both the SIM card and the handset can be tracked.[39]

China has proposed using this technology to track commuting patterns of Beijing city residents. [41] In the UK and US, law enforcement and intelligence services use mobiles to perform surveillance. They

possess technology to activate the microphones in cell phones remotely in order to listen to conversations that take place near the phone.[42][43]

TheftsAccording to the Federal Communications Commission, one out of three robberies involved the theft of a cellular phone. Police data in San Francisco showed that one-half of all robberies in 2012 were thefts of cellular phones. An online petition on Change.org called Secure our Smartphones urged smartphone manufacturers to install kill switches in their devices to make them unusable in case of theft. The petition is part of a joint effort by New York Attorney General Eric Schneiderman and San Francisco District Attorney George Gascon and was directed to the CEOs of the major smartphone manufacturers and telecommunication carriers.[44]

On Monday, 10 June 2013, Apple announced it would install a kill switch on its next iPhone operating system, due to debut in October 2013.[45]

Health effectsMain article: Mobile phone radiation and health

Further information: Mobile phones on aircraft

The effect mobile phone radiation has on human health is the subject of recent interest and study, as a result of the enormous increase in mobile phone usage throughout the world. Mobile phones use electromagnetic radiation in the microwave range, which some believe may be harmful to human health. A large body of research exists, bothepidemiological and experimental, in non-human animals and in humans, of which the majority shows no definite causative relationship between exposure to mobile phones and harmful biological effects in humans. This is often paraphrased simply as the balance of evidence showing no harm to humans from mobile phones, although a significant number of individual studies do suggest such a relationship, or are inconclusive. Other digital wireless systems, such as data communication networks, produce similar radiation.

On 31 May 2011, the World Health Organization stated that mobile phone use may possibly represent a long-term health risk,[46][47] classifying mobile phone radiation as "possibly carcinogenic to humans" after a team of scientists reviewed studies on cell phone safety.[48] Mobile phones are in category 2B, which ranks it alongside coffee and other possibly carcinogenic substances.[49][50]

At least some recent studies have found an association between cell phone use and certain kinds of brain and salivary gland tumors. Lennart Hardell and other authors of a 2009 meta-analysis of 11 studies from peer-reviewed journals concluded that cell phone usage for at least ten years "approximately doubles the risk of being diagnosed with a brain tumor on the same ('ipsilateral') side of the head as that preferred for cell phone use."[51]

One study of past cell phone use cited in the report showed a "40% increased risk for gliomas (brain cancer) in the highest category of heavy users (reported average: 30 minutes per day over a 10‐year period)."[52] This is a reversal from their prior position that cancer was unlikely to be caused by cellular phones or their base stations and that reviews had found no convincing evidence for other health effects.[47][53] Certain countries, including France, have warned against the use of cell phones especially by minors due to health risk uncertainties.[54] However, a study published 24 March 2012 in the British Medical Journal questioned these estimates, because the increase in brain cancers has not paralleled the increase in mobile phone use.[55]

Communications satelliteFrom Wikipedia, the free encyclopedia

  (Redirected from Satellite communications)

An Advanced Extremely High Frequency communications satellite relays secure communications for the United

States and other allied countries.

A communications satellite or comsat is an artificial satellite sent to space for the purpose of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, Molniya orbits, elliptical orbits and low (polar and non-polar) Earth orbits.

For fixed (point-to-point) services, communications satellites provide a microwave radio relay technology complementary to that ofcommunication cables. They are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals, and for TV and radio broadcasting.

Contents  [hide] 

1   History o 1.1   Geostationary orbits o 1.2   Low-Earth-orbiting satellites o 1.3   Molniya satellites o 1.4   Medium Earth Orbit (MEO) o 1.5   Polar Orbit

2   Structure 3   Frequency Allocation for satellite systems 4   Applications

o 4.1   Telephone o 4.2   Television o 4.3   Digital cinema o 4.4   Radio o 4.5   Internet access o 4.6   Military

5   See also 6   References 7   External links

History[edit]

The Merriam-Webster dictionary defines a satellite as a celestial body orbiting another of larger size or a manufactured object or vehicle intended to orbit the earth, the moon, or another celestial body. [1]

Today's satellite communications can trace their origins all the way back to the Moon. A project named Communication Moon Relay was a telecommunication project carried out by the United States Navy. Its objective was to develop a secure and reliable method of wireless communication by using the Moon as a natural communications satellite.

The first artificial satellite used solely to further advances in global communications was a balloon named Echo 1.[2] Echo 1 was the world's first artificial communications satellite capable of relaying signals to other points on Earth. It soared 1,000 miles (1,609 km) above the planet after its Aug. 12, 1960 launch, yet relied on humanity's oldest flight technology — ballooning. Launched by NASA, Echo 1 was a giant metallic balloon 100 feet (30 meters) across. The world's first inflatable satellite — or "satelloon", as they were informally known — helped lay the foundation of today's satellite communications. The idea behind a communications satellite is simple: Send data up into space and beam it back down to another spot on the globe. Echo 1 accomplished this by essentially serving as an enormous mirror, 10 stories tall, that could be used to reflect communications signals.

The first American satellite to relay communications was Project SCORE in 1958, which used a tape recorder to store and forward voice messages. It was used to send a Christmas greeting to the world from U.S. President Dwight D. Eisenhower.[3] NASA launched the Echo satellite in 1960; the 100-foot (30 m) aluminised PET film balloon served as a passive reflector for radio communications. Courier 1B, built by Philco, also launched in 1960, was the world's first active repeater satellite.

The first communications satellite was Sputnik 1. Put into orbit by the Soviet Union on October 4, 1957, it was equipped with an onboard radio-transmitter that worked on two frequencies: 20.005 and 40.002 MHz. Sputnik 1 was launched as a step in the exploration of space and rocket development. While incredibly important it was not placed in orbit for the purpose of sending data from one point on earth to another. And it was the first artificial satellite in the steps leading to today's satellite communications.

Telstar was the second active, direct relay communications satellite. Belonging to AT&T as part of a multi-national agreement between AT&T, Bell Telephone Laboratories, NASA, the British General Post Office, and the French National PTT (Post Office) to develop satellite communications, it was launched by NASA from Cape Canaveral on July 10, 1962, the first privately sponsored space launch. Relay 1 was launched on December 13, 1962, and became the first satellite to broadcast across the Pacific on November 22, 1963.[4]

An immediate antecedent of the geostationary satellites was Hughes' Syncom 2, launched on July 26, 1963. Syncom 2 revolved around the earth once per day at constant speed, but because it still had north-south motion, special equipment was needed to track it.

Geostationary orbits[edit]Main article: Geostationary orbit

Geostationary orbit

To an observer on the earth, a satellite in a geostationary orbit appears motionless, in a fixed position in the sky. This is because it revolves around the earth at the earth's own angular velocity (360 degrees every 24 hours, in an equatorial orbit).

A geostationary orbit is useful for communications because ground antennas can be aimed at the satellite without their having to track the satellite's motion. This is relatively inexpensive. In applications that require a large number of ground antennas, such as DirectTVdistribution, the savings in ground equipment can more than outweigh the cost and complexity of placing a satellite into orbit.

The concept of the geostationary communications satellite was first proposed by Arthur C. Clarke, building on work by Konstantin Tsiolkovsky and on the 1929 work by Herman Potočnik (writing as Herman Noordung) Das Problem der Befahrung des Weltraums — der Raketen-motor. In October 1945 Clarke published an article titled "Extra-terrestrial Relays" in the British magazine Wireless World.[5] The article described the fundamentals behind the deployment of artificial satellites in geostationary orbits for the purpose of relaying radio signals. Thus, Arthur C. Clarke is often quoted as being the inventor of the communications satellite.[citation needed]

The first geostationary satellite was Syncom 3, launched on August 19, 1964, and used for communication across the Pacific starting with television coverage of the 1964 Summer Olympics. Shortly after Syncom 3, Intelsat I, aka Early Bird, was launched on April 6, 1965 and placed in orbit at 28° west longitude. It was the first geostationary satellite for telecommunications over the Atlantic Ocean.

On November 9, 1972, Canada's first geostationary satellite serving the continent, Anik A1, was launched by Telesat Canada, with the United States following suit with the launch of Westar 1 by Western Union on April 13, 1974.

On May 30, 1974, the first geostationary communications satellite in the world to be three-axis stabilized was launched: the experimental satellite ATS-6 built for NASA

After the launches of the Telstar through Westar 1 satellites, RCA Americom (later GE Americom, now SES[disambiguation needed]) launched Satcom 1 in 1975. It was Satcom 1 that was instrumental in helping early cable TV channels such as WTBS (now TBS Superstation), HBO, CBN (now ABC Family) and The Weather Channel become successful, because these channels distributed their programming to all of the local cable TV headends using the satellite. Additionally, it was the first satellite used by broadcast television networks in the United States, like ABC, NBC, and CBS, to distribute programming to their local affiliate stations. Satcom 1 was widely used because it had twice the communications capacity of the competing Westar 1 in America (24 transponders as

opposed to the 12 of Westar 1), resulting in lower transponder-usage costs. Satellites in later decades tended to have even higher transponder numbers.

By 2000, Hughes Space and Communications (now Boeing Satellite Development Center) had built nearly 40 percent of the more than one hundred satellites in service worldwide. Other major satellite manufacturers include Space Systems/Loral, Orbital Sciences Corporation with the STAR Bus series, Indian Space Research Organization,Lockheed Martin (owns the former RCA Astro Electronics/GE Astro Space business), Northrop Grumman, Alcatel Space, now Thales Alenia Space, with the Spacebus series, andAstrium.

Low-Earth-orbiting satellites[edit]Main article: Low Earth orbit

Low Earth orbit in Cyan

A low Earth orbit (LEO) typically is a circular orbit about 200 kilometres (120 mi) above the earth's surface and, correspondingly, a period (time to revolve around the earth) of about 90 minutes. Because of their low altitude, these satellites are only visible from within a radius of roughly 1000 kilometers from the sub-satellite point. In addition, satellites in low earth orbit change their position relative to the ground position quickly. So even for local applications, a large number of satellites are needed if the mission requires uninterrupted connectivity.

Low-Earth-orbiting satellites are less expensive to launch into orbit than geostationary satellites and, due to proximity to the ground, do not require as high signal strength (Recall that signal strength falls off as the square of the distance from the source, so the effect is dramatic). Thus there is a trade off between the number of satellites and their cost. In addition, there are important differences in the onboard and ground equipment needed to support the two types of missions.

A group of satellites working in concert is known as a satellite constellation. Two such constellations, intended to provide satellite phoneservices, primarily to remote areas, are the Iridium and Globalstar systems. The Iridium system has 66 satellites.

It is also possible to offer discontinuous coverage using a low-Earth-orbit satellite capable of storing data received while passing over one part of Earth and transmitting it later while passing over another part. This will be the case with the CASCADE system of Canada'sCASSIOPE communications satellite. Another system using this store and forward method is Orbcomm.

Molniya satellites[edit]Main article: Molniya orbit

Geostationary satellites must operate above the equator and therefore appear lower on the horizon as the receiver gets the farther from the equator. This will cause problems for extreme northerly latitudes, affecting connectivity and causing multipath (interference caused by signals reflecting off the ground and into the ground antenna). For areas close to the North (and South) Pole, a geostationary satellite may appear below the horizon. Therefore Molniya orbit satellite have been launched, mainly in Russia, to alleviate this problem. The first satellite of the Molniya series was launched on April 23, 1965 and was used for experimental transmission of TV signal from a Moscow uplink station todownlink stations located in Siberia and the Russian Far East, in Norilsk, Khabarovsk, Magadan and Vladivostok. In November 1967 Soviet engineers created a unique system of national TV network of satellite television, called Orbita, that was based on Molniya satellites.

Molniya orbits can be an appealing alternative in such cases. The Molniya orbit is highly inclined, guaranteeing good elevation over selected positions during the northern portion of the orbit. (Elevation is the extent of the satellite's position above the horizon. Thus, a satellite at the horizon has zero elevation and a satellite directly overhead has elevation of 90 degrees.)

The Molniya orbit is designed so that the satellite spends the great majority of its time over the far northern latitudes, during which its ground footprint moves only slightly. Its period is one half day, so that the satellite is available for operation over the targeted region for six to nine hours every second revolution. In this way a constellation of three Molniya satellites (plus in-orbit spares) can provide uninterrupted coverage.

Medium Earth Orbit (MEO)[edit]A MEO satellite is in orbit somewhere between 8,000 km and 18,000 km above the earth’s surface. MEO satellites are similar to LEO satellites in functionality. MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours. MEO satellites have a larger coverage area than LEO satellites.A MEO satellite’s longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network.One disadvantage is that a MEO satellite’s distance gives it a longer time delay and weaker signal than a LEO satellite, though not as bad as a GEO satellite.

A medium earth orbit satellite (MEO) is a satellite that orbits the earth in between Low Earth Orbit Satellites (LEO), which orbit the earth at a distance from the earth of about 200-930 miles (321.87-1496.69 km) and those satellites which orbit the earth at geostationary orbit, about 22,300 miles (35,888.71 km) above earth. Each type of satellite can provide a different type of coverage for communications and wireless devices. Like LEOs, these satellites don’t maintain a stationary distance from the earth. This is in contrast to the geostationary orbit, where satellites are always approximately 22,300 miles from the earth.

Any satellite that orbits the earth between about 1000-22,000 miles (1609.34- 35,405.57 km) above earth is an MEO. Typically the orbit of a medium earth orbit satellite is about 10,000 miles (16,093.44 km) above earth. In various patterns, these satellites make the trip around earth in anywhere from 2-12 hours, which provides better coverage to wider areas than that provided by LEOs. In 1962, the first communications satellite, Telstar, was launched. It was a medium earth orbit satellite designed to help facilitate high-speed telephone signals, but scientists soon learned what some of the problematic aspects were of a single MEO in space. It only provided transatlantic telephone signals for 20 minutes of each approximately 2.5 hours orbit. It was apparent that multiple MEOs needed to be used in order to provide continuous coverage.

Polar Orbit[edit]In the United States, the National Polar-orbiting Operational Environmental Satellite System (NPOESS) was established in 1994 to consolidate the polar satellite operations of NASA (National Aeronautics and Space Administration) NOAA (National Oceanic and Atmospheric Administration) NPOESS manages a number of Location Company METSAT stands for meteorological satellite

EUMETSAT stands for the European organization for the exploration of the METSAT program. METOP stands for meteorological operations. These orbits are sun synchronous, meaning that they cross the equator at the same local time each day. For example, the satellites in the NPOESS (civilian) orbit will cross the equator, going from south to north, at times 1:30 P.M., 5:30 P.M., and 9:30 P.M.

Structure[edit]

Communications Satellites are usually composed of the following subsystems:

Communication Payload, normally composed of transponders, antenna, and switching systems Engines used to bring the satellite to its desired orbit Station Keeping Tracking and stabilization subsystem used to keep the satellite in the right orbit,

with its antennas pointed in the right direction, and its power system pointed towards the sun Power subsystem, used to power the Satellite systems, normally composed of solar cells, and

batteries that maintain power during solar eclipse Command and Control subsystem, which maintains communications with ground control

stations. The ground control earth stations monitor the satellite performance and control its functionality during various phases of its life-cycle.

The bandwidth available from a satellite depends upon the number of transponders provided by the satellite. Each service (TV, Voice, Internet, radio) requires a different amount of bandwidth for transmission. This is typically known as link budgeting and a network simulator can be used to arrive at the exact value.

Frequency Allocation for satellite systems[edit]

Allocating frequencies to satellite services is a complicated process which requires international coordination and planning. This is carried out under the auspices of theInternational Telecommunication Union (ITU). To facilitate frequency planning, the world is divided into three regions: Region 1: Europe, Africa, what was formerly the Soviet Union, and Mongolia Region 2: North and South America and Greenland Region 3: Asia (excluding region 1 areas), Australia, and the southwest Pacific

Within these regions, frequency bands are allocated to various satellite services, although a given service may be allocated different frequency bands in different regions. Some of the services provided by satellites are:

Fixed satellite service (FSS) Broadcasting satellite service (BSS) Mobile satellite services Navigational satellite services Meteorological satellite services

Applications[edit]

Telephone[edit]

An Iridium satellite

The first and historically most important application for communication satellites was in intercontinental long distance telephony. The fixed Public Switched Telephone Network relays telephone calls from land line telephones to an earth station, where they are then transmitted to a geostationary satellite. The downlink follows an analogous path. Improvements in submarine communications cables, through the use of fiber-optics, caused some decline in the use of satellites for fixed telephony in the late 20th century.

Satellite communications are still used in many applications today. Remote islands such as Ascension Island, Saint Helena, Diego Garcia, andEaster Island, where no submarine cables are in service need satellite telephones. There are also regions of some continents and countries where landline telecommunications are rare to nonexistent, for example large regions of South America, Africa, Canada, China, Russia, andAustralia. Satellite communications also provide connection to the edges of Antarctica and Greenland. Other land use for satellite phones are rigs at sea, a back up for hospitals, military, and recreation. Ships at sea often use satellite phones, and planes.[6]

Satellite phones can be accomplished in many different ways. On larger scale often there will be local telephone system in the isolated area with a link to a telephone system in a main land area. There are services that will patch a radio signal to a telephone system in this example most any type of satellite can be used. Satellite phones connect directly to a constellation of either geostationary or low-earth-orbit satellites. Calls are then forwarded to a satellite teleport connected to the Public Switched Telephone Network .

Television[edit]Main article: Satellite television

As television became the main market, its demand for simultaneous delivery of relatively few signals of large bandwidth to many receivers being a more precise match for the capabilities of geosynchronous comsats. Two satellite types are used for North American television and radio: Direct broadcast satellite (DBS), and Fixed Service Satellite (FSS).

The definitions of FSS and DBS satellites outside of North America, especially in Europe, are a bit more ambiguous. Most satellites used for direct-to-home television in Europe have the same high power output as DBS-class satellites in North America, but use the same linear polarization as FSS-class satellites. Examples of these are the Astra, Eutelsat, and Hotbird spacecraft in orbit over the European continent. Because of this, the terms FSS and DBS are more so used throughout the North American continent, and are uncommon in Europe.

Fixed Service Satellites use the C band, and the lower portions of the Ku bands. They are normally used for broadcast feeds to and from television networks and local affiliate stations (such as program feeds for network and syndicated programming, live shots, and backhauls), as well as being used for distance learning by schools and universities,business television (BTV), Videoconferencing, and general commercial telecommunications. FSS satellites are also used to distribute national cable channels to cable television headends.

Free-to-air satellite TV channels are also usually distributed on FSS satellites in the Ku band. The Intelsat Americas 5, Galaxy 10R and AMC 3 satellites over North Americaprovide a quite large amount of FTA channels on their Ku band transponders.

The American Dish Network DBS service has also recently utilized FSS technology as well for their programming packages requiring their SuperDish antenna, due to Dish Network needing more capacity to carry local television stations per the FCC's "must-carry" regulations, and for more bandwidth to carry HDTV channels.

A direct broadcast satellite is a communications satellite that transmits to small DBS satellite dishes (usually 18 to 24 inches or 45 to 60 cm in diameter). Direct broadcast satellites generally operate in the upper portion of the microwave Ku  band . DBS technology is used for DTH-oriented (Direct-To-Home) satellite TV services, such as DirecTV and DISH Network in the United States, Bell TV and Shaw Direct in Canada, Freesat and Sky in the UK, Ireland, and New Zealand and DSTV in South Africa.

Operating at lower frequency and lower power than DBS, FSS satellites require a much larger dish for reception (3 to 8 feet (1 to 2.5m) in diameter for Ku band, and 12 feet (3.6m) or larger for C band). They use linear polarization for each of the transponders' RF input and output (as opposed to circular polarization used by DBS satellites), but this is a minor technical difference that users do not notice. FSS satellite technology was also originally used for DTH satellite TV from the late 1970s to the early 1990s in the United States in the form of TVRO (TeleVision Receive Only) receivers and dishes. It was also used in its Ku band form for the now-defunct Primestar satellite TV service.

Some satellites have been launched that have transponders in the Ka  band , such as DirecTV's SPACEWAY-1 satellite, and Anik F2. NASA and ISRO [7] [8]  have also launched experimental satellites carrying Ka band beacons recently.[9]

Some manufacturers have also introduced special antennas for mobile reception of DBS television. Using Global Positioning System (GPS) technology as a reference, these antennas automatically re-aim to the satellite no matter where or how the vehicle (on which the antenna is mounted) is situated. These mobile satellite antennas are popular with some recreational vehicle owners. Such mobile DBS antennas are also used by JetBlue Airways for DirecTV (supplied by LiveTV, a subsidiary of JetBlue), which passengers can view on-board on LCD screens mounted in the seats.

Digital cinema[edit]Main article: Digital cinema

Realization and demonstration, on October 29, 2001, of the first digital cinema transmission by satellite in Europe [10] [11] [12]  of a feature film by Bernard Pauchon[13] and Philippe Binant.[14]

Radio[edit]Main article: Satellite radio

Satellite radio offers audio services in some countries, notably the United States. Mobile services allow listeners to roam a continent, listening to the same audio programming anywhere.

A satellite radio or subscription radio (SR) is a digital radio signal that is broadcast by a communications satellite, which covers a much wider geographical range than terrestrial radio signals.

Satellite radio offers a meaningful alternative to ground-based radio services in some countries, notably the United States. Mobile services, such as SiriusXM, and Worldspace, allow listeners to roam across an entire continent, listening to the same audio programming anywhere they go. Other services, such as Music Choice or Muzak's satellite-delivered content, require a fixed-location receiver and a dish antenna. In all cases, the antenna must have a clear view to the satellites. In

areas where tall buildings, bridges, or even parking garages obscure the signal, repeaters can be placed to make the signal available to listeners.

Initially available for broadcast to stationary TV receivers, by 2004 popular mobile direct broadcast applications made their appearance with the arrival of two satellite radio systems in the United States: Sirius and XM Satellite Radio Holdings. Later they merged to become the conglomerate SiriusXM.

Radio services are usually provided by commercial ventures and are subscription-based. The various services are proprietary signals, requiring specialized hardware for decoding and playback. Providers usually carry a variety of news, weather, sports, and music channels, with the music channels generally being commercial-free.

In areas with a relatively high population density, it is easier and less expensive to reach the bulk of the population with terrestrial broadcasts. Thus in the UK and some other countries, the contemporary evolution of radio services is focused on Digital Audio Broadcasting (DAB) services or HD Radio, rather than satellite radio.

Amateur radio operators have access to the amateur radio satellites that have been designed specifically to carry amateur radio traffic. Most such satellites operate as spaceborne repeaters, and are generally accessed by amateurs equipped with UHF or VHF radio equipment and highly directional antennas such as Yagis or dish antennas. Due to launch costs, most current amateur satellites are launched into fairly low Earth orbits, and are designed to deal with only a limited number of brief contacts at any given time. Some satellites also provide data-forwarding services using the X.25 or similar protocols.

Internet access[edit]Main article: Satellite Internet access

After the 1990s, satellite communication technology has been used as a means to connect to the Internet via broadband data connections. This can be very useful for users who are located in remote areas, and cannot access a broadband connection, or require high availability of services.

Military[edit]Communications satellites are used for military communications applications, such as Global Command and Control Systems. Examples of military systems that use communication satellites are the MILSTAR, the DSCS, and the FLTSATCOM of the United States, NATO satellites, United Kingdom satellites (for instance Skynet), and satellites of the former Soviet Union. India has launched its first Military Communication satellite GSAT-7, its transponders operate in UHF, F, C and Ku  band  bands.[15] Typically military satellites operate in the UHF, SHF (also known as X-band) or EHF (also known as Ka  band ) frequency bands.

Further information: X Band Satellite Communication

BreadboardFrom Wikipedia, the free encyclopedia

This article is about electronics. For other uses, see Breadboard (disambiguation).

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (August 2012)

Solderless breadboard with 400 connection points

A breadboard (or protoboard) is a construction base for prototyping of electronics. Originally it was literally a bread board, a polished piece of wood used for slicing bread. In the 1970s the solderless breadboard (AKA plugboard, a terminal array board) became available and nowadays the term "breadboard" is commonly used to refer to these. "Breadboard" is also a synonym for "prototype".

Because the solderless breadboard does not require soldering, it is reusable. This makes it easy to use for creating temporary prototypes and experimenting with circuit design. For this reason, solderless breadboards are also extremely popular with students and in technological education. Older breadboard types did not have this property. A stripboard (veroboard) and similar prototyping printed circuit boards, which are used to build semi-permanent soldered prototypes or one-offs, cannot easily be reused. A variety of electronic systems may be prototyped by using breadboards, from small analog and digital circuits to complete central processing units (CPUs).

Contents  [hide] 

1   Evolution o 1.1   Alternatives

2   Solderless breadboard o 2.1   Typical specifications o 2.2   Bus and terminal strips

2.2.1   Diagram o 2.3   Jump wires o 2.4   Inside a breadboard: construction o 2.5   Advanced solderless breadboards o 2.6   High frequencies and dead bugs o 2.7   Limitations

3   Gallery 4   See also 5   References 6   External links

Evolution[edit]

This 1920s TRF radio manufactured by Signal was constructed on a wooden breadboard.

In the early days of radio, amateurs nailed bare copper wires or terminal strips to a wooden board (often literally a board to slice bread on) and soldered electronic components to them.[1] Sometimes a paper schematic diagram was first glued to the board as a guide to placing terminals, then components and wires were installed over their symbols on the schematic. Using thumbtacks or small nails as mounting posts was also common.

Breadboards have evolved over time, with the term now being used for all kinds of prototype electronic devices. For example, US Patent 3,145,483,[2] filed in 1961 and granted in 1964, describes a wooden plate breadboard with mounted springs and other facilities. US Patent 3,496,419, [3] filed in 1967 and granted in 1970, refers to a particular printed circuit board layout as a Printed Circuit Breadboard. Both examples refer to and describe other types of breadboards as prior art.

The breadboard most commonly used today is usually made of white plastic and is a pluggable (solderless) breadboard. It was designed by Ronald J. Portugal of EI Instruments Inc. in 1971.[4]

Alternatives[edit]

Wire wrap backplane

Alternative methods to create prototypes are point-to-point construction (reminiscent of the original wooden breadboards), wire wrap,wiring pencil, and boards like the stripboard. Complicated systems, such as modern computers comprising millions of transistors, diodes, and resistors, do not lend themselves to prototyping using breadboards, as their complex designs can be difficult to lay out and debug on a breadboard.

Modern circuit designs are generally developed using a schematic capture and simulation system, and tested in software simulationbefore the first prototype circuits are built on a printed circuit board. Integrated circuit designs are a more extreme version of the same process: since producing prototype silicon is costly, extensive software simulations are performed before fabricating the first prototypes. However, prototyping techniques are still used for some applications such as RF circuits, or where software models of components are inexact or incomplete.

Solderless breadboard[edit]

Typical specifications[edit]A modern solderless breadboard consists of a perforated block of plastic with numerous tin plated phosphor bronze or nickel silver alloy spring clips under the perforations. The clips are often called tie points or contact points. The number of tie points is often given in the specification of the breadboard.

The spacing between the clips (lead pitch) is typically 0.1 in (2.54 mm). Integrated circuits (ICs) in dual in-line packages (DIPs) can be inserted to straddle the centerline of the block. Interconnecting wires and the leads of discrete components (such as capacitors, resistors, and inductors) can be inserted into the remaining free holes to complete the circuit. Where ICs are not used, discrete components and connecting wires may use any of the holes. Typically the spring clips are rated for 1 ampere at 5 volts and 0.333 amperes at 15 volts (5 watts).

Bus and terminal strips[edit]

The hole pattern for a typical etched prototyping PCB (printed circuit board) is similar to the node pattern of the

solderless breadboards shown above.

Solderless breadboards are available from several different manufacturers, but most share a similar layout. The layout of a typical solderless breadboard is made up from two types of areas, called strips. Strips consist of interconnected electrical terminals.

Terminal stripsThe main areas, to hold most of the electronic components.In the middle of a terminal strip of a breadboard, one typically finds a notch running in parallel to the long side. The notch is to mark the centerline of the terminal strip and provides limited airflow (cooling) to DIP ICs straddling the centerline[citation needed]. The clips on the right and left of the notch are each connected in a radial way; typically five clips (i.e., beneath five holes) in a row on each side of the notch are electrically connected. The five clip columns on the left of the notch are often marked as A, B, C, D, and E, while the ones on the right are marked F, G, H, I and J. When a "skinny" dual in-line pin package (DIP) integrated circuit (such as a typical DIP-14 or DIP-16, which have a 0.3-inch (7.6 mm) separation between the pin rows) is plugged into a breadboard, the pins of one side of the chip are supposed to go into column E while the pins of the other side go into column F on the other side of the notch.Bus stripsTo provide power to the electronic components.A bus strip usually contains two columns: one for ground and one for a supply voltage. However, some breadboards only provide a single-column power distributions bus strip on

each long side. Typically the column intended for a supply voltage is marked in red, while the column for ground is marked in blue or black. Some manufacturers connect all terminals in a column. Others just connect groups of, for example, 25 consecutive terminals in a column. The latter design provides a circuit designer with some more control over crosstalk (inductively coupled noise) on the power supply bus. Often the groups in a bus strip are indicated by gaps in the color marking.Bus strips typically run down one or both sides of a terminal strip or between terminal strips. On large breadboards additional bus strips can often be found on the top and bottom of terminal strips.

Some manufacturers provide separate bus and terminal strips. Others just provide breadboard blocks which contain both in one block. Often breadboard strips or blocks of one brand can be clipped together to make a larger breadboard.

In a more robust variant, one or more breadboard strips are mounted on a sheet of metal. Typically, that backing sheet also holds a number of binding posts. These posts provide a clean way to connect an external power supply. This type of breadboard may be slightly easier to handle. Several images in this article show such solderless breadboards.

Diagram[edit]A "full size" terminal breadboard strip typically consists of around 56 to 65 rows of connectors, each row containing the above-mentioned two sets of connected clips (A to E and F to J). Together with bus strips on each side this makes up a typical 784 to 910 tie point solderless breadboard. "Small size" strips typically come with around 30 rows. Miniature solderless breadboards as small as 17 rows (no bus strips, 170 tie points) can be found, but these are only suitable for small and simple designs.

Jump wires[edit]

Stranded 22AWG jump wires with solid tips

Jump wires (also called jumper wires) for solderless breadboarding can be obtained in ready-to-use jump wire sets or can be manually manufactured. The latter can become tedious work for larger circuits. Ready-to-use jump wires come in different qualities, some even with tiny plugs attached to the wire ends. Jump wire material for ready-made or homemade wires should usually be 22 AWG (0.33 mm2) solid copper, tin-plated wire - assuming no tiny plugs are to be attached to the wire ends. The wire ends should be stripped 3⁄16 to 5⁄16 in (4.8 to 7.9 mm). Shorter stripped wires might result in bad contact with the board's spring clips (insulation being caught in the springs). Longer stripped wires

increase the likelihood of short-circuits on the board. Needle-nose pliers and tweezers are helpful when inserting or removing wires, particularly on crowded boards.

Differently colored wires and color-coding discipline are often adhered to for consistency. However, the number of available colors is typically far fewer than the number of signal types or paths. Typically, a few wire colors are reserved for the supply voltages and ground (e.g., red, blue, black), some are reserved for main signals, and the rest are simply used where convenient. Some ready-to-use jump wire sets use the color to indicate the length of the wires, but these sets do not allow a meaningful color-coding schema.

Inside a breadboard: construction[edit]The following images show the inside of a bus strip.

Inside breadboard 1

 

Inside breadboard 2

 

Inside breadboard 3

 

Inside breadboard 4

 

Inside breadboard 5

 

Inside breadboard 6

Advanced solderless breadboards[edit]Some manufacturers provide high-end versions of solderless breadboards. These are typically high-quality breadboard modules mounted on a flat casing. The casing contains additional equipment for breadboarding, such as a power supply, one or more signal generators, serial interfaces, LED or LCD display modules, and logic probes.[5]

Solderless breadboard modules can also be found mounted on devices like microcontroller evaluation boards. They provide an easy way to add additional periphery circuits to the evaluation board.

High frequencies and dead bugs[edit]For high-frequency development, a metal breadboard affords a desirable solderable ground plane, often an unetched piece of printed circuit board; integrated circuits are sometimes stuck upside down to the breadboard and soldered to directly, a technique sometimes called "dead bug" construction because of its appearance. Examples of dead bug with ground plane construction are illustrated in a Linear Technologies application note. [6] For other uses of this technique see dead bugs.

Limitations[edit]

An example of a complex circuit built on a breadboard. The circuit is an Intel 8088 single

board computer.

Due to relatively large stray capacitance compared to a properly laid out PCB (approx 2pF between adjacent contact columns[7] ), highinductance of some connections and a relatively high and not very reproducible contact resistance, solderless breadboards are limited to operation at relatively low frequencies, usually less than 10 MHz, depending on the nature of the circuit. The relatively high contact resistance can already be a problem for some DC and very low frequency circuits. Solderless breadboards are further limited by their voltage and current ratings.

Solderless breadboards usually cannot accommodate surface-mount technology devices (SMD) or components with grid spacing other than 0.1 in (2.54 mm). Further, they cannot accommodate components with multiple rows of connectors if these connectors don't match the dual in-line layout—it is impossible to provide the correct electrical connectivity. Sometimes small PCB adapters called "breakout adapters" can be used to fit the component to the board. Such adapters carry one or more components and have 0.1 in (2.54 mm) spaced male connector pins in a single in-line or dual in-line layout, for insertion into a solderless breadboard. Larger components are usually plugged into a socket on the adapter, while smaller components (e.g., SMD resistors) are usually soldered directly onto the adapter. The adapter is then plugged into the breadboard via the 0.1 in (2.54 mm) connectors. However, the need to solder the components onto the adapter negates some of the advantage of using a solderless breadboard.

Very complex circuits can become unmanageable on a solderless breadboard due to the large amount of wiring required. The very convenience of easy plugging and unplugging of connections also makes it too easy to accidentally disturb a connection, and the system becomes unreliable. It is possible to prototype systems with thousands of connecting points, but great care must be taken in careful assembly, and such a system becomes unreliable as contact resistance develops over time. At some point, very complex systems must be implemented in a more reliable interconnection technology, to have a likelihood of working over a usable time period.

Gallery[edit]

A solderless breadboard with a completed circuit.

 

A binary counter wired up on a large solderless breadboard.

 

Logical 4-bit adder with output bits linked to LEDs on a typical breadboard.

 

Close-up of a solderless breadboard. An IC straddling the centerline is probed with anoscilloscope probe. The solderless breadboard is mounted on a blue painted metal plate base. Red and black binding posts are also present on the base; the black one is partly obscured by the oscilloscope probe.

 

Example breadboard drawing. Two bus strips and one terminal strip in one block. 25 consecutive terminals in a bus strip connected (indicated by gaps in the red and blue lines). Fourbinding posts depicted at the top.

See also[edit]

Electronics portal

Brassboard Expansion spring Fahnestock clip Iterative design Perfboard Stripboard Veroboard Wire wrap