STUDY AND ANALYSIS OF MICROWAVE SYSTEMS AND RADAR APPLICATIONS

[Type the company name]STUDY AND ANALYSIS OF MICROWAVE SYSTEMS AND RADAR APPLICATIONS[Type the document subtitle]

Shivendra Singh[Pick the date]

ACKNOWLEDGEMENT

Apart from the efforts from me, the successful completion of any project depends largely on encouragement and guidelines from many others. I take this opportunity to express my gratitude to the people who have been instrumental in the successful and timely completion of this project.I would like to show my greatest appreciation to Mr. B. S. Matheru (Scientist F) for allowing me to pursue my training in his department.I would like to express my sincere gratitude to Mrs. Kirti Bansal (Scientist C) without whose guidance and encouragement this project would not have been materialized. The training was extremely productive and fruitful and was an endowing experience in both technical and practical aspect.

CERTIFICATE

This is to certify that SHIVENDRA SINGH, student of 3rd year in Electrical and Electronics Department of Krishna Institute of Engineering and Technology has successfully undergone training in the Microwave Division, Solid State Physics Laboratory, DRDO, Delhi from 9/7/2013 to 2/8/2013 on the topic titled:STUDY AND ANALYSIS OF MICROWAVE SYSTEMSAND RADAR APPLICATIONS

The project is an original work of the candidate completed successfully on time. The candidate had a good code of conduct and sincerity towards his tasks during the course of training.I wish him success in all his future endeavors.

Dated: Mr. B. S. Matheru Scientist F SSPL, DRDO Mrs. Kirti Bansal Scientist C SSPL, DRDO

DISCLAIMER

This project/training work entitled STUDY AND ANALYSIS OF MICROWAVE SYSTEMS AND RADAR APPLICATIONS submitted to the Department of Electrical and Electronics Engineering, Krishna Institute of Engineering and Technology, is a result of work carried out by me under the guidance of Mr. B.S. Matheru (Scientist F) and Mrs. Kirti Bansal (Scientist E), SSPL, DRDO. None of the information about DRDO or SSPL included in the report is classified and is obtained from their websites.

CONTENTS

INTRODUCTION TO DRDO6

INTRODUCTION TO SSPL7

INTRODUCTION TO MICROWAVES9

RADAR13

PHASED ARRAY RADAR18

PHASE SHIFTERS21

BIBLIOGRAPHY28

D.R.D.O.

The Defense Research and Development Organization (DRDO) works under the Ministry of Defense, Government of India. DRDO is an agency of the Republic of India, responsible for the development of technology for use by the military, headquartered in New Delhi, India. It was formed in 1958 by the merger of the Technical Development Establishment and the Directorate of Technical Development and Production with the Defense Science Organization.DRDO has a network of 52 laboratories which are engaged in developing defense technologies covering various fields, like aeronautics, armaments, electronic and computer sciences, human resource development, life sciences, materials, missiles, combat vehicles development and naval research and development. The organization includes more than 5,000 scientists and about 25,000 other scientific, technical and supporting personnel.

S.S.P.L.Solid State Physics Laboratory (SSPL), one of the establishments under the Defense R&D Organization (DRDO), Ministry of Defense, was established in 1962 with the broad objective of developing an R&D base in the field of Solid State Materials, Devices and Sub-systems. The Laboratory has a vision to be the centre of excellence in the development of Solid State Materials, Devices and has a Mission to develop and characterize high purity materials and solid state devices and to enhance infrastructure, technology for meeting the futuristic challenges.The major activities at SSPL include development of semi-conductor materials, solid state devices, electronic components/sub-systems and investigation of solid state materials/devices. Over the years, the Laboratory has developed core competence in the following areas:- Design & Development of GaAs based Microwave devices and circuits IR devices Ferrite components SAW devices & sensors MEMs components Materials Development & Characterization Products

Space quality silicon solar cells. Solar Cells Poly crystalline Garnets & Microwave Substrates Dual Mode Phase Shifter Remotely Activated Acoustic Warning system(RAAWS) Intruder Alarm System MMIC Strain Gauges MEMS

INTRODUCTION TO MICROWAVES

The field of radio frequency (RF) and microwave engineering generally covers the behavior of alternating current signals with frequencies in the range of 100 MHz (1 MHz = 106 Hz) to 1000 GHz (1 GHz = 109 Hz). RF frequencies range from very high frequency (VHF) (30300 MHz) to ultra high frequency (UHF) (3003000 MHz), while the term microwave is typically used for frequencies between 3 and 300 GHz, with a corresponding electrical wavelength between = c/ f = 10 cm and = 1 mm, respectively. On the surface, the definition of a microwave would appear to be simple because, in electronics, the prefix "micro" normally means a millionth part of a unit. Micro also means small, which is a relative term, and it is used in that sense in this module. Microwave is a term loosely applied to identify electromagnetic waves above 1000 megahertz in frequency because of the short physical wavelengths of these frequencies. Short wavelength energy offers distinct advantages in many applications. For instance, excellent directivity can be obtained using relatively small antennas and low-power transmitters. These features are ideal for use in both military and civilian radar and communication applications. Small antennas and other small components are made possible by microwave frequency applications. Microwave frequency usage is especially important in the design of radars because it makes possible the detection of smaller targets.

The above figure shows the electromagnetic spectrum.

The above figure shows the frequency and wavelengths of various bands in the radio frequency region.

APPLICATIONS OF MICROWAVE ENGINEERING

1. Antenna gain is proportional to the electrical size of the antenna. At higher frequencies, more antenna gain can be obtained for a given physical antenna size, and this has important consequences when implementing microwave systems.2. More bandwidth (directly related to data rate) can be realized at higher frequencies. A 1% bandwidth at 600 MHz is 6 MHz, which (with binary phase shift keying modulation) can provide a data rate of about 6 Mbps (megabits per second), while at 60 GHz a 1% bandwidth is 600 MHz, allowing a 600 Mbps data rate.3. Microwave signals travel by line of sight and are not bent by the ionosphere as are lower frequency signals. Satellite and terrestrial communication links with very high capacities are therefore possible, with frequency reuse at minimally distant locations.4. The effective reflection area (radar cross section) of a radar target is usually proportional to the targets electrical size. This fact, coupled with the frequency characteristics of antenna gain, generally makes microwave frequencies preferred for radar systems.5. Various molecular, atomic, and nuclear resonances occur at microwave frequencies, creating a variety of unique applications in the areas of basic science, remote sensing, medical diagnostics and treatment, and heating methods.The majority of todays applications of RF and microwave technology are to wireless networking and communications systems, wireless security systems, radar systems, environmental remote sensing, and medical systems.

RADARSRadar, or radio detection and ranging, is the oldest application of microwave technology, dating back to World War II. In its basic operation, a transmitter sends out a signal, which is partly reflected by a distant target, and then detected by a sensitive receiver. If a narrow beam antenna is used, the targets direction can be accurately given by the angular position of the antenna. The distance to the target is determined by the time required for a pulsed signal to travel to the target and back, and the radial velocity of the target is related to the Doppler shift of the return signal. Below are listed some of the typical applications of radar systems.Civilian applications1. Airport surveillance2. Marine navigation3. Weather radar4. Altimetry5. Aircraft landing6. Security alarms7. Speed measurement (police radar)8. Geographic mappingMilitary applications1. Air and marine navigation2. Detection and tracking of aircraft, missiles, and spacecraft3. Missile guidance4. Fire control for missiles and artillery5. Weapon fuses6. ReconnaissanceScientific applications1. Astronomy2. Mapping and imaging3. Precision distance measurement4. Remote sensing of the environmentEarly radar work in the United States and Britain began in the 1930s using very high frequency (VHF) sources. A major breakthrough occurred in the early 1940s with the British invention of the magnetron tube as a reliable source of high-power microwaves.Higher frequencies allowed the use of reasonably sized antennas with high gain, allowing mechanical tracking of targets with good angular resolution. Radar was quickly developed in Great Britain and the United States, and played an important role in World War II.

Principle:A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivityespecially by most metals, by seawater and by wet lands. Some of these make the use of radar altimeters possible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either toward or away from the transmitter, there is a slight equivalent change in the frequency of the radio waves, caused by the Doppler Effect.Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, they can be strengthened by electronic amplifiers. More sophisticated methods of signal processing are also used in order to recover useful radar signals.The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long rangesranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are avoided in designing radars, except when their detection is intended.Radar relies on its own transmissions rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat). This process of directing artificial radio waves towards objects is called illumination, although radio waves are invisible to the human eye or optical cameras.

Radar Equation:

The power Pr returning to the receiving antenna is given by the equation:

where Pt = transmitter power Gt = gain of the transmitting antenna Ar = effective aperture (area) of the receiving antenna = radar cross section, or scattering coefficient, of the target F = pattern propagation factor Rt = distance from the transmitter to the target Rr = distance from the target to the receiver.In the common case where the transmitter and the receiver are at the same location, Rt = Rr and the term Rt Rr can be replaced by R4, where R is the range. This yields:

This shows that the received power declines as the fourth power of the range, which means that the received power from distant targets is relatively very small.Additional filtering and pulse integration modifies the radar equation slightly for pulse-Doppler radar performance, which can be used to increase detection range and reduce transmit power.The equation above with F = 1 is a simplification for transmission in a vacuum without interference. The propagation factor accounts for the effects of multipath and shadowing and depends on the details of the environment. In a real-world situation, path loss effects should also be considered.

Radar Range Measurement:

PHASED ARRAY RADARS

In antenna theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array is a group of multiple active antennas coupled to a common source or load to produce a directive radiation pattern. Usually, the spatial relationship of the individual antennas also contributes to the directivity of the antenna array. Use of the term "active antennas" is intended to describe elements whose energy output is modified due to the presence of a source of energy in the element (other than the mere signal energy which passes through the circuit) or an element in which the energy output from a source of energy is controlled by the signal input.A phased array antenna is composed of lots of radiating elements each with a phase shifter. Beams are formed by shifting the phase of the signal emitted from each radiating element, to provide constructive/destructive interference so as to steer the beams in the desired direction.The main beam always points in the direction of the increasing phase shift. Well, if the signal to be radiated is delivered through an electronic phase shifter giving a continuous phase shift then the beam direction will be electronically adjustable. However, this cannot be extended unlimitedly. The highest value, which can be achieved for the Field of View (FOV) of a planar phased array antenna is 120 (60left and 60right). With the sine theorem the necessary phase moving can be calculated.

Conventional radar tracks targets by physically turning its main beam 360 degrees and then measuring how reflective itemsblipshave moved since previous sweeps.But phased-array radars work differently; they steer the main beam by manipulating the pattern emanating from an array of hundreds or thousands of radiating elements, nearly instantaneously moving the location of the overlapping waves instead of an actual dish.

Thus, each element emits a radio wave with crests and troughs that are slightly out of sync with the crests and troughs of the radio waves emitted by its neighbors. For example, a wave being radiated from element A may start at a crest, while the wave emanating from element B begins life as a trough.The effect is that the beam swings from the center to the right or left (see diagram, opposite). With the new elements added, the beam can be pointed up or down as well. The direction of the beam can be changed in 20 microseconds or less.The main advantage to this approach is that the radar can keep a constant eye on a targetit can shoot and watch for radio reflections thousands of times per second instead of going blind until the next rotation sweeps the main beam past the target again.Since the main beam can be pointed almost instantaneously, it can jump from object to object as they come into range.Phased-array radars are not without disadvantages. Most are functional through a cone of just 120 degrees, because the width of the main beam diminishes the farther it gets from broadside. As an example, think of how narrow your wide-screen television looks when youre in an adjacent room.For this reason, at least four radars are needed to cover a hemisphere. To compensate for the narrow field of view, the SBXs main array rotates and tilts; its one of the few phased arrays to do that.Although the initial cost is 100,000 times more expensive than conventional radar with the same beam width, a phased-array device may be cheaper long-term because the system will still function as needed even if many of its smallest components fail.

PHASE SHIFTERS

Phase shifters are used to change the transmission phase angle (phase of S21) of a network. Ideal phase shifters provide low insertion loss, and equal amplitude (or loss) in all phase states. While the loss of a phase shifter is often overcome using an amplifier stage, the less loss, the less power that is needed to overcome it. Most phase shifters are reciprocal networks, meaning that they work effectively on signals passing in either direction. Phase shifters can be controlled electrically, magnetically or mechanically. Most of the phase shifters described on this web site is passive reciprocal networks; we will concentrate mainly on those that are electrically-controlled.While the applications of microwave phase shifters are numerous, perhaps the most important application is within a phased array antenna system (a.k.a. electrically steerable array, or ESA), in which the phase of a large number of radiating elements are controlled to force the electro-magnetic wave to add up at a particular angle to the array. For this very purpose, phase shifters are often embedded in TR modules. The total phase variation of a phase shifter need only be 360 degrees to control an ESA of moderate bandwidth. Networks that stretch phase more than 360 degrees are often called time delay bits or true time delays (part of a TDU), and are constructed similar to the switched line phase shifters that are described below.Analog versus digital phase shiftersPhase shifters can be analog or digital. Analog phase shifters provide a continuously variable phase, perhaps controlled by a voltage. Electrically controlled analog phase shifters can be realized with varactor diodes that change capacitance with voltage, or nonlinear dielectrics such as barium strontium titanate, or Ferro-electric materials such as yttrium iron garnet. A mechanically-controlled analog phase shifter is really just a mechanically lengthened transmission line, often called a trombone line. Analog phase shifters are a mere side-show and will not be covered here in depth at this time. If you are interested in more information on any of these analog phase shifter topics, let us know and we will try to accommodate you.Most phase shifters are of the digital variety, as they are more immune to noise on their voltage control lines. Digital phase shifters provide a discrete set of phase states that are controlled by two-state "phase bits." The highest order bit is 180 degrees, the next highest is 90 degrees, then 45 degrees, etc., as 360 degrees is divided into smaller and smaller binary steps. A three bit phase shifter would have a 45 degree least significant bit (LSB), while a six bit phase shifter would have a 5.6 degree least significant bit. Technically the latter case would have a 5.625 degree LSB, but in the microwave world it is best to ignore precision that you cannot obtain. If you can't comprehend this point, you might want to consider a different career such as accounting.The convention followed for phase shifters is that the shortest phase length is the reference or "off" state, and the longest path or phase length is the "on" state. Thus a 90 degree phase shifter actually provides minus ninety degrees of phase shift in its "on" state.Types of phase shiftersSwitched line (delay line) phase shiftersSwitched filter phase shiftersHigh-pass/low-pass phase shifters Loaded-line phase shiftersFerroelectric phase shiftersReflection phase shifters180 degree hybrid phase shiftersQuadrature hybrid phase shiftersVaractor phase shiftersSchiffman phase shiftersMEMS phase shifters

FERRITES:A FERRITE is a device that is composed of material that causes it to have useful magnetic properties and, at the same time, high resistance to current flow. The primary material used in the construction of ferrites is normally a compound of iron oxide with impurities of other oxides added. The compound of iron oxide retains the properties of the ferromagnetic atoms, and the impurities of the other oxides increase the resistance to current flow. This combination of properties is not found in conventional magnetic materials. Iron, for example, has good magnetic properties but a relatively low resistance to current flow. The low resistance causes eddy currents and significant power losses at high frequencies. Ferrites, on the other hand, have sufficient resistance to be classified as semiconductors. The compounds used in the composition of ferrites can be compared to the more familiar compounds used in transistors. As in the construction of transistors, a wide range of magnetic and electrical properties can be produced by the proper choice of atoms in the right proportions.

Ferrites have long been used at conventional frequencies in computers, television, and magnetic recording systems. The use of ferrites at microwave frequencies is a relatively new development and has had considerable influence on the design of microwave systems. In the past, the microwave equipment was made to conform to the frequency of the system and the design possibilities were limited. The unique properties of ferrites provide a variable reactance by which microwave energy can be manipulated to conform to the microwave system. At present, ferrites are used as LOAD ISOLATORS, PHASE SHIFTERS, VARIABLE ATTENUATORS, MODULATORS, and SWITCHES in microwave systems.

The magnetic property of any material is a result of electron movement within the atoms of the material. Electrons have two basic types of motion. The most familiar is the ORBITAL movement of the electron about the nucleus of the atom. Less familiar, but even more important, is the movement of the electron about its own axis, called ELECTRON SPIN. You will recall that magnetic fields are generated by current flow. Since current is the movement of electrons, the movement of the electrons within an atom create magnetic fields. The magnetic fields caused by the movement of the electrons about the nucleus have little effect on the magnetic properties of a material. The magnetic fields caused by electron spin combine to give material magnetic properties. In most materials the spin axes of the electrons are so randomly arranged that the magnetic fields largely cancel out and the material displays no significant magnetic properties. The electron spin axes within some materials, such as iron and nickel, can be caused to align by applying an external magnetic field. The alignment of the electrons within a material causes the magnetic fields to add, and the material then has magnetic properties.

In the absence of an external force, the axis of any spinning object tends to remain pointed in one direction. Spinning electrons behave the same way. Therefore, once the electrons are aligned, they tend to remain aligned even when the external field is removed. Electron alignment in a ferrite is caused by the orbital motion of the electrons about the nucleus and the force that holds the atom together. When a static magnetic field is applied, the electrons try to align their spin axes with the new force. The attempt of the electrons to balance between the interaction of the new force and the binding force causes the electrons to wobble on their axes. The wobble of the electrons has a natural resonant WOBBLE FREQUENCY that varies with the strength of the applied field. Ferrite action is based on this behavior of the electrons under the influence of an external field and the resulting wobble frequency.FERRITE PHASE SHIFTER:When microwave energy is passed through a piece of ferrite in a magnetic field, another effect occurs. If the frequency of the microwave energy is much greater than the electron wobble frequency, the plane of polarization of the wave front is rotated. This is known as the FARADAY ROTATION EFFECT and is illustrated in figure 1-76. A ferrite rod is placed along the axis of the waveguide, and a magnetic field is set up along the axis by a coil. As a wave front enters the section containing the ferrite, it sets up a limited motion in the electrons. The magnetic fields of the wave front and the wobbling electrons interact, and the polarization of the wave front is rotated. The amount of rotation depends upon the length of the ferrite rod. The direction of rotation depends upon the direction of the external magnetic field and can be reversed by reversing the field. The direction of rotation will remain constant, no matter what direction the energy in the waveguide travels, as long as the external field is not changed.

Ferroelectric materials have the potential to overcome all the limitations of MEMS, ferrite and MMIC phase shifters. Several groups have investigated the possibility of implementing phase shifter circuits using barium strontium titanate (BST), which has an electric field tunable dielectric constant. In these circuits the ferroelectric material (BST) either forms the entire microwave substrate on which the conductors are deposited (thick film/bulk crystal) or a fraction of the substrate with thin BST film sandwiched between the substrate and the conductors, as seen in Figure 4. These circuits rely on the principle that because part or all of the microwave fields pass through the ferroelectric layer, the phase velocity of waves propagating on these structures can be altered by changing the permittivity of the ferroelectric layer. However, this approach has several limitations: The amount of capacitive loading due to the ferroelectric film cannot be easily varied to optimize phase performance; Conductor losses are high in this structure due to the high dielectric constant of the ferroelectric film on which the transmission lines are fabricated; The tunability of the film is not efficiently utilized; and The control voltages required for this approach tend to be very high (more than 100 Volts).

BIBLIOGRAPHY

The content of this project has been gathered from various sources which are as follows:1. Microwave engineering,4th edition by David M. Pozar 2. Module 11: Microwave Principles, Navy Electricity and Electronics Training Series3. Hollmann, Martin, "Radar Family Tree" 4. Penley, Bill, and Jonathan Penley, "Early Radar History5. Phased Array Antennas, 2nd Ed., by R. C. Hansen, John Wiley and Sons, 1998 6. "Ferroelectric Phase Shifters". Microwaves 101.