LAB MANUAL EC-604 A&WP

ANTENNA AND WAVE PROPAGATION

(EC-604)

THEORY

Basic antenna concept

This section is a concise review of some important theory aspects concerned by the operation of this

trainer. This discussion does mean to be exhaustive but just serve as a guide to help student to relate what

he has learned in his theory course to the hardware he is facing.

Transmission lines are used to convey energy from a source (generator) to the load. The generator are sine

wave voltage sources. The sine wave voltage applied to the line input determines a sine wave current in it.

The ensemble of the sine wave voltage and sine wave current is generally called a wave.

The wave propagates along the line.

The concept of a wave traveling from the source through the line is in harmony with the idea of energy

flowing from the generator to the load.

We now suppose that our transmission line , instead of being infinitely long, is cut and shorted at a certain

length.

LAB MANUAL AND WORKBOOK 40


(EC-604)The short circuit is a nopower load (ohm's law), therefor the energy inside the short circuit must go some

ware.

The only way the energy may go from the short circuit is to come back along the or be reflected. To do this

the short must evidently be capable to generate a voltage equalling in modulus and opposed in phase with

the incident wave.

This concept allows us to draw the pattern of the reflected wave given the pattern of the incident one. It

simply is the incident pattern reverted.

We can extend our narrative , non mathematical reasoning on the line to the cases where the line open

instead of shorten and then terminated with the generic load.

Equalizing the characteristic impedance of the line . The characteristic impedance is a parameter

depending on the physical nature and construction characteristics of the line.

when a line is terminated on a matched load there is no reflected wave,therefore the energy transfer from

the line to the load ( which are in our cases antennas ), is maximized.

Radiation mechanism and evolution of dipole:

Consider the opencircuited transmission line of fig 2.it is seen that the forward and reverse travelling

waves combine to form a standing wave pattern on the line, with a voltage anti node at the open – circuited

point, but not all the forward energy is reflected by the open circuit.

As shown, a

small portion

of

electromagnetic energy escapes from the system and its thus radiated. This occurs because the line of

focus, travelling towards the open circuit, are required to undergo a complete phase reversal when they



(EC-604)posses the equivalent of mechanical inertia, and thus some do escape, it must be added that the proportion,

of the wave escaping the system to those remaining is very small, for two reasons.

First, if we consider the surrounding space as the load for the transmission line, we see that a mis match

exist, and thus very little power is dissipated in this “load”. Second, since the two wires are close together,

it is apparent that the radiation from one tip will just about cancel that from other. This is because they are

of opposite polarities and at a distance apart that is tiny compared to a wavelength. Conversely, this is also

the reason why lowfrequency parallelwire transmission lines do not radiate.

The cure for this problem seems to be an”enlargement “ of the open circuit i.e. Spreading of two wires, as

in fig. 3. there is now less likelihood of cancellation of radiation from the two wire tip. By the same token,

the radiating transmission line is now batter coupled to the surrounding space. This is another way of

saying that more power will be”dissipated” in the surrounding space i.e. Radiated. Moreover, because of

the spreading out, waves traveling along the line find it more difficult to undergo the phase reversal at the

end. Thus everything points to an increase in radiation.

The radiation efficiency of this system is improved even more when the two wires are bent so as to be in

the same line, as in fig.3. The electric (and also the magnetic ) field is now fully coupled to the surrounding

space, instead of being confined between the two wires, and the maximum possible amount of radiation



(EC-604)result. This type of radiation is called a dipole. When the total length of the two wires is a half wavelength,

the antenna is called a half wave dipole. It has the form indicated in figure.3 and now even great radiation

occurs. The reason for this increase is the half wave dipole may be regarded as having the same basic

properties ( for the point of view of impedance particularly) as a similar length of transmission line.

Accordingly, we have the antenna behaving as a piece of quarterwave transmission line bent out and open

circuited at the far end. This results in the high impedance at the far and of the antenna reflected as a low

impedance at the end connected to the main transmission line. This in turn, means that a large current will

flow at the main transmission line. This intern, means that a large current will flow at the input to the half

wave dipole, and efficient radiation will take place.

Standing wave ratio:

The standing wave ratio (SWR) is defined as the ratio between maximum and minimum values of

voltage( and current )alo0ng the time.

Fig 4 shows the SWR pattern along a line with a mismatched load and helps understanding the definition

of SWR.

The SWR is an index of the mismatch existing between the load and the line feeding it. The SWR equals 1

in the perfectly matched case, impossible to reach in practice, and tends to reach very high values (infinity)

for lines shorted or open. In practice SWR values in range 1.4 to 2 are to be considered a good matching

condition in an antenna system, while rather larger values are acceptable with our trainer. This is because

unlike large power system where the design aim is maximum power transfer, in a trainer, in a trainer

system the aim is in handiest operability and simple construction.

The directional coupler:



(EC-604)To sense the direction of power travel, as well as the amount of power, is sensing device must have diodes

as circuit elements.

The directional coupler of figure 5 consist of two line trunks placed along with a main transmission line

carried energy from generator to antenna.

The power traveling from input to output of the device will cause induced voltages in the upper and lower

loops. In the lower one the voltage will build across the sensing devices thanks to the forward conducting

diode, while this will not happened in the upper loop.

As for the power traveling from load to generator, the situation is reverted the upper loop will sense, the

lower one will not.

There fore the device of figure 5 allows separate metering of direct and reverse power.

The practical procedure to use the directional coupler to measure the SWR is the following.

Turn on the transmitter.

place the switch of SWR meter on FORWORD and note the reading, you can also adjust the level for full

scale deflection (50 in the case of our trainer. Adjust RF level if needed).

Switch the meter to REVERSE. Note the reading. Calculate the SWR by the formula.



(EC-604)

Antenna Matching:

Let's consider a shortcircuited transmission line having length ¼ of the wavelength of the signal

impressed by the generator.

At the shorted end there will be a null voltage a maximum current while at the other end(generator side),

there will be opposite situation of maximum voltage and zero current. The line there fore appears to the

generator as an infinity impedance , since no current is drawn.

Let's now consider another line,half wavelength long, shorted at the opposed to that of the generator.

The junction point of the generator to the line will be zero voltage maximum current point. The

impedance of the line, as “seen” from the generator, shall be a short circuit(zero impudence).

In all the intermediate cases of a line having length between ¼ and ½ wavelength, the generator shall see

impedance between 0 and infinity.

Going on furtherly with the same reasoning we find out that for shorted line ¼ wave lengthlong to zero

length, the impedance goes again from infinity zero.



(EC-604)Since our line is loss less, the impedance must be purely reactive and if we consider the pattern of the

current together to that of the voltage, we soon find out that in the ½ to ¼ wave length interval the

impedance goes from 0 to infinity and is capacitive, while in the ¼ wavelength to zero length interval

impedance goes from infinity to zero and is inductive.

All this leads us to think of a very handy way to match the impedance seen from the generator by placing

in parallel to the mismatched load a trunk of shorted line of a proper length . See fig 6 these devices are

gener4ally called MATCHING STUBS.

An adjustable length matching stub can be adjusted to have a reactive impedance equal in modulus and

opposed sign of a mismatched load, in order to cancel its reactive components and make it appear to the

line as purely resistive.

Types of antenna:

antenna can be broadly classified by the directions in which radiate or receive electromagnetic radiation.

They can be isotropic, omni directional or directional.

An isotropic antenna is a hypothetical antenna that radiates uniformly in all directions so that the electric

field at any point on a sphere (with the antenna at its center) has the same magnitude. Such radiation



(EC-604)cannot be realized in practice since in order to radiate uniformly in all directions an isotropic antenna

would have to be a point source. The nearest equivalent to an isotropic antenna is a hertzian dipole.

The hertzian dipole is the name given to a dipole which is very small compared to its wavelength that is

about onehundredths of the wavelength at its operating frequency; even in this case its pattern is not truly

isotropic.

An omni directional antenna radiates uniformly in one place. Examples of omni directional antennas are

Monopoles,Dipole etc. The radiation of a vertical dipole is uniform in the horizontal plane and a figure of 8

in the vertical plane.

Important characteristics of Antenna:

An antenna is chosen for a particular application according to its main physical and electrical

characteristics. Further , an antenna must perform in a desired manner for the particular application. An

antenna can be characterized by the following factors , not all are applicable to all types of antennas. Most

of the characteristics mentioned below can be studied using this trainer.

1. Radiation resistance.

2. Radiation pattern.

3. Beam width.

4. Bandwidth.

5. Gain of main lobe.

6. Position and magnitude of side lobes.

7. Front to back ratio.

8. Aperture.

9. The polarization of the electric field.

There are two principles planes in which the antenna characteristics are measured. these are the horizontal

and vertical planes for land based antennas. Some characteristics such as beamwidth and side lobes are the

same in both planes for symmetrical antennas such as helical and reflectors. other characteristics such as



(EC-604)gain on bore sight. (i.e where the azimuth and the elevation planes intersect ) can only have a single

value .In general , for unsymmetrical antennas the characteristics are different in the two principles.

Radiation Resistance:

We can consider an antenna as a load that terminates the transmission line that feeds it. In the ideal case

this load will have an impedance which is purely resistive that is, the load will not have any reactive

component such as an inductance or capacitance. In practice the impedance of an antenna is made up of a

self impedance and a mutual impedance .The self impedance is the impedance that would be measured at

the terminals of the antenna when it is in free space, given no other antennas or reflecting objects in the

vicinity. The mutual impedance accounts for the coupling between the driven element and the other

parasitic passive elements.

When the antenna has the same impedance as the transmission lines that feeds it , the antenna is said to be

matched on the line. When this occurs , maximum power is transfered from the transmission line to the

antenna . In general ,the impedance of the antennas not the same as that of the transmission line. When the

transmission line has the purely resistive impedance and the antenna has an impedance that contains a

different resistive values as well as reactive part , the optimum transfer of power can be achieved via the

use of the tuning circuits consist of an LC circuits in which the capacitance of the capacitor is altered in

order to provide the maximum transfer of power.

In this trainer antenna match tuning capacitor does this.

Radiation Pattern:

The antenna is a reciprocal device, means it radiates or receives electromagnetic energy in the same way.

Thus, although the radiation pattern is identified with an antenna that is transmitting power,the same

properties would apply to the antenna even it was receiving power. Any difference between the received

and radiated powers can be attributed to the difference between the feed networks and the equipment

associated with the receiver and transmitter. The antenna radiates the greatest amount of power along its

boresight and also receives power most efficiently in this direction.

The radiation pattern of an antenna is peculiar to the type of antenna and its electrical characteristics as

well as its physics dimensions. It is measured at a constant distance in the far field. The radiation pattern



(EC-604)of an antenna is usually plotted in terms of relative power. The power at boresight , that is at the position of

maximum radiated power, is usually plotted at 0 degrees; thus the power in all other positions appears as a

negative value. In other words, the radiated power is normalised to the power at bore sight. The main

reason for using dB instead of linear power is that the power at the nulls is often of the order of 10,000

times less than the power on the boresight , which means that the scales would have to be very large in

order to cover the whole range of power values.

For the convenience of the students to plot the polar graph the readings are plotted after converting them

into dB. A conversion chart is provided in this manual. Also the boresight reading is taken as maximum in

dB and other readings are plotted in lower values in dB.

The radiation pattern is usually measured in the two principal planes,namely , the azimuth and the

elevation planes. The radiated / received dB is plotted against the angle that is made with the boresight

direction. If the antenna is not expect its radiation pattern in these planes to be unsymmetrical. The

radiation pattern can be plotted using the Polar or the Rectangular / Cartesian Coordinates.

Polar Plots:

In a Polar Plot the angles are plotted from the boresight and the levels (dBuV/ dBuA) are plotted along the

radius. The angles may be selected at any convenient interval. However 5 degrees or 100 degrees may be

chosen. Choosing of 1 deg. is also possible in the trainer but this does not serve any special purpose

because the readings will not change much and will consume more time. The polar plot gives a pictorial

representation of the radiation pattern of the antenna and is easier to visualise than the rectangular plots.

The students will easily understand the polar plot drawn by them.

The beam width and gain of main lobe:

The beam width of an antenna is commonly defined in two ways . The most well known definition is the 3

db or half power beam width but the 10 db beam width is also used specially for antennas with narrow

beams. The 3 db or half power beam width of an antenna is taken as the width in degrees at the point on

either side of the main beam where the radiated level is 3 db lower than the maximum lobe value. The 10

db value is taken as the width in degrees on either side of the main beam where the radiated level is 10 db

lower than the maximum lobe value.



(EC-604)The IEEE definition of gain of an antenna relates to the power radiated by the antenna to that radiated by

an isotropic antenna ( that radiates equally in all direction ) and is quoted.

as a linear ratio or an db refereed to an isotropic ( dbi , i:for isotropic)when we say that the gain of an

antenna is for instance , 20 dbi( 100 in linear terms) we mean that an isotropic antenna would have to

radiate 100 times more power to give the same intensity in the same distance as that particular directional

antenna.

The radiation pattern of an antenna shows the power on the bore sight as 0 db and the power in other

directions as negative vales. The gain in all directions is plotted relative to the gain on boresight. in order

to find the absolute gain in any direction the gain on bore sight must be known. If this gain is expressed in

decibels, then this value can simply be added to the gain at any point to give the absolute gain. the absolute

gain on bore sight is measured by comparison with a standard gain antenna, which functions as a reference

antenna whose gain is calculated or measured with a high degree of accuracy.

The position

and

magnitude of side lobes:

The side levels is usually quoted as the level below the bore sight gain. Strictly all peaks on either side of

the main lobe are side lobes. However, in practice only the “ near in “ lobes, those which are adjacent on

either side of the bore sight maxima are referred to as side lobes. Their amplitude and angle are easily

measured using the polar plot. For an antenna that is symmetrical about its main axis, the radiation pattern

is in general also symmetrical. Thus the level of the side lobes on opposite sides of the main beam would



(EC-604)be the same. The average value is taken where the two side lobes are different. The absolute level of side

lobes can only be calculated if the absolute bore sight gain is known.

Bandwidth:

The bandwidth of an antenna is a measure of its ability to radiate or receive different frequencies. It refers

to the frequency range over which operation is satisfactory and is generally taken between the half power

point in the direction of maximum radiation. The bandwidth is the range of frequencies that the antenna

can receive (or radiate) with a power efficiency of 50% (0.5) or more or a voltage efficiency of 70.7% (that

is 3DB point). The operating frequency range is specified by quoting the upper and lower frequencies,

but the bandwidth is often quoted as a relative value. Bandwidth is commonly expressed in one of the two

ways; 1) AS percentage or, 2) As a fraction or multiple of an octave (An octave is a band of frequencies

between one frequency and the frequency that is double or half the first frequency; for instance, we have

an octave between 400 MHz and 800 MHz ) When it is expressed as a percentage bandwidth, its center

frequency should be quoted and the percentage expressed in octaves, Its lower and upper frequency

should be also quoted.

The front to back ratio:

The front to back ratio is a measure of the ability of a directional antenna to concentrate the beam in the

required forward direction. In liner terms, it is defined as the ratio of the maximum power in the main bean

(boresight) to that in the back lobe. It is usually expressed in decibels, as the difference between the level

on boresight and at 180 Degrees off boresight. If this difference is say 35 dB then the frontto back ratio of

the antenna is 35dB; in linear terms it would mean that the level of the back lobe is 3,162 times less than

the level of the of the bore sight.

Aperture / Capture area

in simple words aperture or capture area of antenna is effective receiving area of the antenna and may be

calculated from the power received and its comparison with the power density of the signal being received

If, S= power density of the wave in watts/ sq meter.

A= capture area of the antenna.

P= total power absorbed by the antenna.



(EC-604)then P= S.A Watts or A=P/S.

The aperture size can be defined in two ways; either in terms of actual physical size in meters or in terms

of wavelength. for instance. if we say that an antenna has an aperture of two wavelengths,then its actual

size depends on its operating frequency. at a frequency of 1 GHZ, the physical aperture would be 60 cms.

it is more meaningful to refer an antenna size in terms of its operating wavelength when the antenna is

narrow band or single frequency because its beamwidth and gain are directly related to the aperture in

terms of its wave length. in this case we have to calculate its wavelength to find its physical dimensions.

However,in the case of broadband antennas, its physical size is more appropriate because there are a range

of operating frequencies. the aperture of an antenna governs the size of its beam width. In general, the

larger the aperture, the narrower the beam width, the higher is the gain at a given frequency.

The polarization of electric field:

Polarization is used almost exclusively to describe the shape and orientation of the locus of the extremity

of the electric field vector as it varies with time at a fixed point in space. This locus could be a straight line,

an ellipse or a circle.

In the case of linear polarization, the electric field varies sinusoidally in one plane.

When this plane is vertical it is called vertical polarization. When this plane horizontal, it is called

horizontal polarization. The electric field can also be polarized in any other angle between 0 to 90 degree

to the horizontal. In general the only other commonly used angle is 45 degrees, which is known as the slant

polarization.

The polarization of a receiving antenna must match that of the incident radiation in order to detect the

maximum field. If the angles are not the same, only that components that is parallel to the plane of incident

polarisation will be detected. If we have a vertically polarised, the magnitude of its component in the

vertical plane will be reduced by a factor of cosine 45 degrees.

ARRANGEMENT

Arranging the trainer and performing functional checks:



(EC-604)1. Keep the main unit on the table and connect power cord. the mains voltage and switch on the

unit.The indicator lamp should glow.Switch off the main unit.

2. Assemble the coaxial antenna must and fix it on the goniometer scale of the main unit.

3. Assemble detector assembly and mount detector unit on the mast.

4. Keep main unit and detector assembly at a distance of 1.5 m.

5. Install folded dipole antenna on the transmitting mast and allign the direction and the height of both

transmitting and receiving antennas.

6. Switch ON the main unit & check for deflection in the meter of directional coupler. Adjust RF

level and FS adjust (if required). The toggle switch can be in either FWD or REV position.

7. Check for deflection in detector meter. Adjust Level of detector meter for #/4 deflection in the

meter.

8. Rotate transmitting antenna between 0360o and observe the deflection on the detector assembly.

The variation indicates that the transmitter & the receiver are working and radiation pattern is

formed.

9. The unit is ready for further experiments.

Important Note:

The adjustment of the following may be very rarely necessary to optimise the maximum radiations from

different antennas. They are.

1. Z (output impedance of generator).

2. Antenna match.

However this can be done by removing the screws and adjust them gently with the aligner/screwdriver

More details are given in the test and calibration procedure in the operating manual.



(EC-604)



(EC-604)

EXPERIMENT1

AIM:

To find the radiation pattern, beam width and gain of half wave length simple Dipole antenna.

APPARATUS REQUIRED:

Experimental set and simple half wave length Dipole antenna.

THEORY:

A simple dipole is the simplest form of antenna having 2 poles each of length ( /2). The nominalλ

impedance of this antenna is 73 ohms. The actual value departs from this due to construction constraints,

such on nonzero diameter rods, presence of BNC connector body and the antenna mast. The effect of all

these are partially corrected by an “Y match” arrangement connection. The radiation pattern of simple

dipole ( /2) is uniform in forward and reverse direction. The polarization is horizontal.λ

PROCEDURE:

1. Arrange the set up.

2. Mount the simple dipole ( /2)λ on the transmitting mast.

3. Bring the detector assembly near to main unit and adjust the height of both transmitting and

receiving antenna same.

4. Keep detector assembly away from main unit approximately 1.5m and align both of them Ensure

that there are no reflector sort things in the vicinity of the experiment such as steel structure, pipes,

cables etc.

5. Keep the RF level and FS adjust to minimum and directional coupler switch to FWD.

6. Keep detector level control in the centre approximately.

7. Increase RF level gradually and see that there is deflection in detector meter.

8. Adjust RF level and detector level so that the deflection in detector meter is approximately 30 35

µA.



(EC-604)9. Align arrow mark on the disk with zero of goniometer scale.

10. Start taking reading at the interval of 5 or 10 degrees and note the deflection on the deflection

assembly.

11. Convert the µA reading of detector assembly into dBs with the help of conversion chart.

12. Plot the polar graph in degrees of rotation of antenna against level in the detector in dBs.

13. Calculate the beam width. front to back ratio and the gain of the antenna with the help of this graph.

CALCULATIONS:

BEAMWIDTH:

1. look for main lobe Draw bore sight maximum line AA' mark3dB from maximum on the bore sight

line point B Draw an arc of radius AB.

2. This arc will intersect main lobe at C and D.

3. Measure the angle CAD. This angle is 3dB beam width.

FRONT TO BACK RATIO:

1. look for main lobe Draw bore sight maximum line AA'.

2. look for main lobe.

3. Front to back ratio=AA'/1 dB .

4. If there is lobe, then measure it (AE), where E is the maximum of back lobe.

5. Then, front to back ratio= AA'/AE dB.

GAIN OF THE ANTENNA:

1. G=(Maximum radiation intensity) /(Maximum radiation intensity form a reference antenna i.e.

isotropic antenna with same power input).



(EC-604)2. We presume here that maximum radiation intensity of isotropic antenna is 1 DB and is 100%

efficient. under this assumption.

3. G=AA'/1 dB.

RESULT:

PRECAUTIONS:

1. Ensure the there are no reflector sort things in the vicinity of the experiment such.

2. As steel structure, pipes, cables etc.

3. Don't place your hand between transmitting antenna and receiving antenna.

4. Antenna should be property mounted on the transmitting mast.

5. Conversion of µA to dB µA should be correct.

6. Distance between main unit and the detector unit should not exceed 1.5 meters.



(EC-604)

VIVA VOCE

Ques1: Define antenna ?

Ans: An antenna (or aerial) is an electrical device which couples radio waves in free space to an

electrical current used by a radio receiver or transmitter. In reception, the antenna intercepts

some of the power of an electromagnetic wave in order to produce a tiny voltage that the radio

receiver can amplify.

Ques2: Define gain of the antenna ?

Ans: Gain is a parameter which measures the degree of directivity of the antenna's radiation pattern.

G=(Maximum radiation intensity) /(Maximum radiation intensity form a reference antenna i.e.


Ques3: What is radiation pattern.

Ans: 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.

Ques4: Define polarization of antenna ?

Ans: The polarization of an antenna is the orientation of the electric field (Eplane) 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.

Ques5: What is radiation resistance for a half wave dipole ?

Ans: Radiation resistance for a half wave dipole is 73 ohm.



(EC-604)

EXPERIMENT–2

AIM:

To find the radiation pattern, beam width and gain of half wave length folded Dipole antenna.

APPARATUS REQUIRED:

Experimental set and folded Dipole antenna.

THEORY:

Compared to a simple dipole, this antenna has substantially higher radiation resistance approximately 300

ohms for the presence of folded arm. The actual impedance is derived from rod diameter and distance from

centre shape of the end bends, the presence of BNC connector and balun etc, The typical radiation pattern

in horizontal plane for this antenna is same as that was for simple dipole. The polarization is horizontal.

ROCEDURE:


2. Mount folded dipole antenna ( /2) λ on the transmitting mast.





cables etc.





(EC-604)7. Increase RF level gradually and see that there is deflection in detector meter.


µA.

9. Align arrow mark on the disk with zero of goniometer scale.


assembly.




CALCULATIONS:

BEAMWIDTH:








3. Front to back ratio=AA'/1 dB.






(EC-604)1. G=(Maximum radiation intensity) /(Maximum radiation intensity form a reference antenna i.e.


2. We presume here that maximum radiation intensity of isotropic antenna is 1 DB and is 100%


3. G=AA'/1 dB.

RESULT:

PRECAUTIONS:

1. Ensure the there are no reflector sort things in the vicinity of the experiment such.

2. as steel structure, pipes, cables etc.







(EC-604)



(EC-604)



(EC-604)

VIVA VOCE

Ques1: What is the impedance a the feed point of a folded dipole antenna.

Ans: 300 ohm.

Ques2:Define aperture of antenna ?

Ans: The effective aperture of an antenna Ae is the area presented to the radiated or received signal. It

is a key parameter, which governs the performance of the antenna. The aperture efficiency de

pends on the distribution of the illumination across the aperture. If this is linear then Ka= 1. This

high efficiency is offset by the relatively high level of side lobes obtained with linear illumina

tion. Therefore, antennas with more practical levels of side lobes have an antenna aperture effi

ciency less than one (Ae< A).

Ques3: Define directivity ?

Ans: In electromagnetics, directivity is a figure of merit for an antenna. It measures the power density

the antenna radiates in the direction of its strongest emission, versus the power density radiated

by an ideal isotropic radiator (which emits uniformly in all directions) radiating the same total

power.

Ques4: What isotropic antenna ?

Ans: An isotropic antenna is a hypothetical antenna radiating the same intensity of radio waves in all

directions. It has a directivity of 0 dBi (dB relative to, isotropic).

Ques5: Define front to back ratio ?

Ans: The fronttoback ratio of an antenna is the proportion of energy radiated in the principal

direction of radiation to the energy radiated in the opposite direction. A high fronttoback ratio

is desirable because this means that a minimum amount of energy is radiated in the undesired

direction.



(EC-604)

EXPERIMENT–3

AIM :

To find the radiation pattern, beam width and polarization of log periodic antenna.

APPARATUS REQUIRED:

Experimental set and log periodic antenna .

THEORY:

The main feature of this antenna is frequency independence for both radiation resistance and pattern. The

radiation pattern may be unidirectional or bidirectional. Bandwidth of 10:1 is easily achievable. The array

consists of number of dipoles of different lengths and spacing and fed form a two wire line which is

transposed between each adjacent pair of dipoles. The array is fed from narrow end and the maximum

radiation is in this direction. If a graph is plotted input impedance v/s frequency,a repetitive variation will

be noticed.If plotted against log of frequency instead of frequency, then variation is periodic consisting of

identical cycles. It is this behavior of antenna, which has given the name. This is a horizontally polarized

antenna.

PROCEDURE:


2. Mount the log periodic antenna on the transmitting mast.





cables etc.







µA.



assembly.




14. For polarization test, turn the detector box at 90 degree by fixing the screw at the back of detector

box. Note the readings again.

Since, we have changed the plane of receiving antenna to vertical keeping transmitting antenna still in the

horizontal plane that detector antenna receives practically no signal. Rotate the transmitting antenna from 0

to 360 degree gradually and take the readings.

CALCULATIONS:

BEAMWIDTH:




3. Measure the angle CAD. This angle is 3dB beamwidth.



(EC-604)FRONT TO BACK RATIO:

1. look for main lobe Draw bore sight maximum line AA' .










3. G=AA'/1 dB.

RESULT:

PRECAUTIONS:

1. Ensure the there are no reflector sort things in the vicinity of the experiment such as steel structure,

pipes, cables etc.







(EC-604)



(EC-604)

VIVA VOICE

Ques1: What is log periodic antenna ?

Ans: A logperiodic antenna (LP, also known as a logperiodic array) is a broadband, multielement,

unidirectional, narrowbeam antenna that has impedance and radiation characteristics that are

regularly repetitive as a logarithmic function of the excitation frequency.

Ques2: Explain reciprocity theorem for antenna ?

Ans: If an emf is applied to the terminals of an antenna no. 1 and the current measured at terminals

of another antenna no.2, then an equal both in amplitude and phase will be obtained at the

terminals of antenna no. 1if the same emf is applied to terminals of antenna no. 2.

E12=E21 PROVIDED I1=I2

Ques3: What is effective height of antenna ?

Ans: Effective height= 2/ physical height.π

Ques4: What is the range of HF ?

Ans: 3 to 30 MHZ.

Ques5: What are the region in log periodic dipole array ?

Ans: 1. Inactive transmission line region ( L< /2).λ

2. Active region (L= /2).λ

3. Inactive reflective region(L> /2).λ



(EC-604)

EXPERIMENT–4

AIM:

To find the radiation pattern and beam width of cut parabolic antenna.

APPARATUS REQUIRED:

Experimental set and cut parabolic antenna .

THEORY:

The most widely used antenna for microwaves is the paraboloid reflector antenna, which consists of a

primary antenna such as a dipole situated at the focal point of a paraboloid reflector. The directivity of the

paraboloid reflector is a function of the primary antenna directivity and the ratio of focal length of reflector

diameter, F/D. This ratio is known as aperture number.

PROCEDURE:


2. Mount the cut paraboloid reflector antenna without reflector on the transmitting mast.



4. Keep detector assembly away from main unit approximately 1m away from the transmitter.

5. Note the reading in the detector rotating the transmitting mast on the goniometer scale. At suitable

intervals (30 degrees).

6. Now connect the cut paraboloid on the PCB with the help of screw.

7. Observe the change in detector readings.

8. Note the new readings in the detector by rotating the transmitter mast on the goniometer scale 0

360 deg. at the same interval.



(EC-604)9. The New readings show the effect of paraboloid reflector.

CALCULATIONS:

BEAMWIDTH:




3. Measure the angle CAD. This angle is 3dB beamwidth.

GAIN OF THE ANTEN:





3. G=AA'/1 dB.

RESULT:

PRECAUTIONS:


pipes, cables etc.





(EC-604)4. Conversion of µA to dB µA should be correct.




(EC-604)

VIVA VOICE

Ques1: Define beam width of antenna ?

Ans: Beam width is a measure of directivity of an antenna. antenna beamwidth is defined as the

angular separation between two half power points on the radiation pattern pattern of an

antenna.

Ques2: Define radiation intensity.

Ans: Radiation intensity is quantity which does not depend upon the distance from the radiator.

radiation intensity is defined as power per unit solid angle.

Ques3: What is radiation intensity ?

Ans: Unit of radiation intensity is watt/ steradian.

Ques4: What is HPBW.

Ans: HPBW is the angular width between the angular points half power below thats half power.

Ques5: Define skip distance ?

Ans: Skip distance is the shortest distance from a transmitter,measured along the surface of the earth

at which a sky wave of fixed frequency( more than fc) will be returned to earth.



(EC-604)

EXPERIMENT–5

AIM:

To find the radiation pattern, beam width and standing wave ratio of loop antenna.

APPARATUS REQUIRED:

Experimental set and Loop antenna.

THEORY:

This antenna consists of single or multiple loop arrangements. The total loop perimeter is generally half

wavelength long or multiple.In the basic configuration this antenna has very low impedance so that it is

used only for reception for the reasons of matching efficiency. In order to rise the impedance our loop

antenna uses a radiating element and a two conductor strip line loop shaped. The current in the opposite

side of the arm of the loop add up and subtracts the effects the effects to the radiated wave, so that the

radiation diagram appears to have a rather odd unexpected pattern. Normally the loop is circular but in our

case it is a square loop.

PROCEDURE:


2. Mount the loop antenna on the transmitting mast.





(EC-604)4. Keep detector assembly away from main unit approximately 1.5m and align both of them Ensure


cables etc.


6. Keep detector level control in the center approximately.



µA.



assembly.

11. Convert the µA reading of detector assembly into dB's with the help of conversion chart.

12. Plot the polar graph in degrees of rotation of antenna against level in the detector in dB's.


FOR SWR MEASUREMENT:

1. The SWR is the index of mismatch existing between the load and the feeding line. Adjust RF level

and detector level for the optimum indication on detectors meter.

2. Remove the transmitting antenna and fix BNCT and BNC cable to stub line.

3. Mount the antenna over BNCT.

4. Keep the stub at zero of the scale.

5. You will observe that the reading on the detector meter has already gone down with the connection

of the stub. however you can increase RF output level and detector level slightly to suit

measurement.

6. Keep the coupler switch to REV Position.



(EC-604)7. Start moving stub knob from right to left slowly and observe the reading on the meter on the main

unit.

8. You will observe that the meter has maxima and minima at some point. The maxima point indicates

that the reverse power is maximum and line is mismatched.

9. Choose the first minimum point while going from right to left. this position indicates that the line is

matched.

10. Note this reading in µA, on main unit.

11. Turn the switch to FWD,which gives the reading of the forward power.

12. SWR can be calculated as under.

SWR= (FWD+REV)/ (FWDREV).

CALCULATIONS:

BEAMWIDTH:




3. Measure the angle CAD. This angle is 3 dB beam width.






3. G=AA'/1 dB.

STANDING WAVE RATIO:



(EC-604)SWR= (FWD+REV)/ (FWDREV).

RESULT:

PRECAUTIONS:


pipes, cables etc.







(EC-604)

VIVA VOICE

Ques1: What is the relation between directivity and length of the Nelement

broadside linear array ?

Ans: D=2(L/ ).λ

Ques2: Define radiation resistance ?

Ans: Radiation resistance of an antenna is the equivalent resistance which would dissipate the same

amount of power as the antenna radiates when the current in that resistance equal the input

current at the antenna terminals.

Ques3: Which type of error in loop antenna.

Ans: There are two type of errors are seen in loop antenna

1. Vertical effect error.

2. Polarization error.

Ques4: What do you mean by the Directivity of loop antenna.

Ans: The directivity of an antenna is defined as the ratio of maximum radiation intensity to the

average radiation intensity.

Ques5: What do you mean by sense antenna.

Ans: A sense antenna is a small vertical antenna and radio wave induces voltage in it in phase where

as voltage induced at the centre of the loop is 90 degree out of phase with electromagnetic field

as seen.



(EC-604)

EXPERIMENT–6

AIM:

To find the radiation pattern , beam width and standing wave ratio of a Yagi Uda 5 element antenna.

APPARATUS REQUIRED:

Experimental set and Yagi uda 5 element antenna.

THEORY:

Yagi – Uda antenna with folded or non folded dipoles are widely used antennas. Behind the dipoles they

have a reflector and in front they have directors 135 etc.

The theoretical impedance of this antenna is 75 ohms.This is very important antenna for unidirectional

transmission and widely used in TV reception. A yagi Uda antenna has a folded dipole rerounded by

director and reflector. The number of directors can be 1,3,5,7,9 etc the polarization is horizontal.

PROCEDURE:


2. Mount Yagi uda 5 element folded dipole antenna on the transmitting mast.





cables etc.







µA.



assembly.

11. Convert the µA reading of detector assembly into dB's with the help of conversion chart.











measurement.


7. Start moving stub knob from right to left slowly and observe the reading on the meter on the main

unit.





(EC-604)9. Choose the first minimum point while going from right to left. this position indicates that the line is

matched.



12. SWR can be calculated as under

SWR= (FWD+REV)/ (FWDREV)

CALCULATIONS:

BEAMWIDTH:


2. Draw bore sight maximum line AA' mark3dB from maximum on the bore sight line point B.

3. Draw an arc of radius AB.


5. Measure the angle CAD. This angle is 3 dB beam width.






3. G=AA'/1 dB


SWR= (FWD+REV)/ (FWDREV)



(EC-604)RESULT:

PRECAUTIONS:


pipes, cables etc.







(EC-604)

VIVA VOICE

Ques1: Explain yagiuda antenna ?



(EC-604)

Ans: A YagiUda array, commonly known simply as a Yagi antenna, is a directional antenna

consisting of a driven element (typically a dipole or folded dipole) and additional parasitic

elements (usually a socalled reflector and one or more directors). The reflector element is

slightly longer ( typically 5% longer) than the driven dipole, whereas the socalled directors are

a little bit shorter. This design achieves a very substantial increase in the antenna's directionality

and gain compared to a simple dipole.

Ques2: What is maximum usable frequency ?

Ans: Critical frequency is the maximum frequency of the radio wave which is returned through a

ionized layer at vertical incidence.

Fmuf = fc seci.

Ques3: Define null beam width ?

Ans: This is the angular separation from which the magnitude of the radiation pattern decreases to

zero (negative infinity dB) away from the main beam.

Ques4: What is the range of frequency in VHF band ?

Ans: 30300 MHZ.

Ques5: Define critical frequency ?

Ans: Critical frequency of an ionized layer of the ionosphere is the limiting frequency at or below

which a radio wave is reflected by an ionospheric layer at vertical incidence. this frequency is

different for different ionospheric layers.

EXPERIMENT–7 & 8



(EC-604)AIM:

To find the radiation pattern , beam width and standing wave ratio of half wave length phase Array End

fire and broad side array antenna.

APPARATUS REQUIRED :

Experimental set and phase Array End fire and broad side array antenna.

THEORY:

PHASE ARRAY:

The two element antenna has the appearance of two half wave dipoles connected the parallel. The spacing

of the dipole is one half the wave length.This antenna is also called end fire antenna. The signal leaving

dipole D1 will reach dipole D2 after ½ period since distance between D1 and D2 is /2.

The signal going through the feed line to D2 will also reach dipole D2 after ½ period so that the twowave

contribution of D1 and D2 will add up in forward direction. With the similar reasoning we can show that

the contribution of D1and D2 in the reverse direction also add up. This antenna is horizontally polarized.

BROAD SIDE ARRAY:

The simplest array consists of a number of dipoles of equal size equally spaced along a straight line (i.e.

collinear), with all dipole fed in the same phase from the same source. Such an arrangement is called a

broadside array. The broadside array is strongly directional at right angles to the plane of the array, while

radiating very little in the plane.

PROCEDURE:


2. Mount the (End fire or Broad Side array) antenna on the transmitting mast.





(EC-604)4. Keep detector assembly away from main unit approximately 1.5m and align both of them Ensure


cables etc.





µA.

9. Align arrow mark on the disk with zero of goniometric scale.


assembly.



13. Calculate the beamwidth. front to back ratio and the gain of the antenna with the help of this graph.









measurement.




(EC-604)7. Start moving stub knob from right to left slowly and observe the reading on the meter on the main

unit.



9. Choose the first minimum point while going from right to left. this position indicates that the line is

matched.



12. SWR can be calculated as under

SWR= (FWD+REV)/ (FWDREV).

CALCULATIONS:

BEAMWIDTH:


line point B Draw an arc of radius AB


3. Measure the angle CAD. This angle is 3 dB beamwidth.



isotropic antenna with same power input)



3. G=AA'/1 dB.




(EC-604)SWR= (FWD+REV)/ (FWDREV).

RESULT:

PRECAUTIONS:


pipes, cables etc.





BROAD SIDE ARRAY



(EC-604)

PHASE ARRAY



(EC-604)

VIVA VOICE



(EC-604)

Ques1: What is the relation between directivity and length of the Nelement broadside linear array ?

Ans: D=2(L/ ).λ

Ques2: Define pattern multiplication ?

Ans: The field pattern of an array of non isotropic but similar sources is the product of the individual

sources pattern and the pattern of an array of isotropic point sources each located at the phase

centre of the individual source and having the same relative amplitude and phase, while the

total phase pattern is the sum of the phase pattern,of the individual source and the array of

isotropic point sources.

Ques3: What is binomial array ?

Ans: In binomial array amplitudes of the radiating sources are arranged according to the coefficient

of successive terms of the following binomial series.

Ques4: What is the height for D layer in ionospheric layers ?

Ans: 5090 km above the earth surface.

Ques5: What is FNBW for broad side array ?

Ans: (2 ) / (Nd) where d= spacing between the elements.λ



(EC-604)

EXPERIMENT9

AIM:

To find the radiation pattern, beam width and polarization of Rhombus antenna.

APPARATUS REQUIRED:

Experimental set and Rhombus antenna.

THEORY:

Rhombus antenna is also a loop antenna and made in the Rhombus from. It is a nonresonant antenna

capable of operating over very wide range because the characteristics do not change with frequency. This

is used mostly for point to point working. The impedance varies form 650 to 700 ohms.

PROCEDURE:


2. Mount the antenna on the transmitting mast.





cables etc.





µA.




(EC-604)10. Start taking reading at the interval of 5 or 10 degrees and note the deflection on the deflection

assembly.


12. Plot the polar graph in degrees of rotation of antenna against level in the detector in dB s.


14. For polarization test, turn the detector box at 90 degree by fixing the screw at the back of detector

box Note the readings again. Rotate the transmitting antenna from 0 to 360 degree gradually and

take the readings.

CALCULATIONS:

BEAMWIDTH:
















(EC-604)2. We presume here that maximum radiation intensity of isotropic antenna is 1 DB and is 100%


3. G=AA'/1 dB.

RESULT:

PRECAUTIONS:


pipes, cables etc.







(EC-604)RHOMBUS ANTENNA



(EC-604)

VIVA VOICE

Ques1: Are rhombus antennas ever used for TV reception ?

Ans: You probably could, but they would be huge. The TV band runs from 50 MHz to 700 MHz.

Even if you restrict it to VHFHigh plus UHF, it would go as low as 175 MHz. UHF starts at

470 MHz. If you want to experiment with TV DX'ing fine, but it's not a real practical antenna

for a wide range of frequencies. It might work for UHF only.

Ques2: Why it is called rhombus antennas.

Ans: It is named after its "rhombic" diamond shape, with each side typically at least one wavelength

(λ) or longer in length. Each vertex is supported by a pole, typically at least one wavelength

high.

Ques3: when rhombic antenna required large area ?

Ans: A rhombic requires a large area of land especially if several antennas are installed to serve a

variety of geographic regions at different distances or directions or to cover widely different

frequencies.

Ques4: What is radiation efficiency of rhombic antenna in percentage ?

Ans: Typical radiation efficiency is in the order of 4050%.

Ques5: How to improve the efficiency ?

Ans: It is possible to improve efficiency by recirculation of power wasted in the termination

resistance of unidirectional rhombics. Use of a recirculating termination system can move

efficiency into the 7080% range by combining power that would have been wasted in the

termination with the transmitter power. Such systems bring a lowloss balanced line back from

the termination end to the feed point through a matching and phasing system. Energy that would

otherwise dissipated in the termination resistance is applied inphase with the excitation.


http://en.wikipedia.org/wiki/%CE%9B


(EC-604)

µ A to Db µ A conversion chart

Db µA µA Db µA µA Db µA µA

0 1.00 19 8.91 38 79.4

1 1.12 20 10.0 39 89.1

2 1.26 21 11.2 40 100

3 1.41 22 12.6 41 112

4 1.58 23 14.1 42 126

5 1.78 24 15.8 43 141

6 2.00 25 17.8 44 158

7 2.24 26 20.0 45 178

8 2.51 27 22.4 46 200

9 2.82 28 25.1 47 224

10 3.16 29 28.2 48 251

11 3.35 30 21.6 49 282

12 3.98 31 35.5 50 316

13 4.47 32 39.8

14 5.01 33 44.7

15 5.62 34 50.1

16 6.31 35 56.2

17 7.08 36 63.1

18 7.94 37 70.8


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LAB MANUAL EC-604 A&WP

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