lab manual ec-604 a&wp
DESCRIPTION
THE QUICK BROWN FOX JUMPS RIGHT OVER THE LAZY DOGTRANSCRIPT
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.
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(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
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(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
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(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:
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(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.
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(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.
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(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
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(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
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(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
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(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.
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(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
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(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.
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(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:
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(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.
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(EC-604)
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(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.
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(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).
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(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.
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(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.
isotropic antenna with same power input).
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.
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(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:
1. Arrange the set up.
2. Mount folded dipole antenna ( /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.
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(EC-604)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.
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:
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(EC-604)1. G=(Maximum radiation intensity) /(Maximum radiation intensity form a reference antenna i.e.
isotropic antenna with same power input).
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.
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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.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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:
1. Arrange the set up.
2. Mount the log periodic antenna 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.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)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.
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.
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:
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 beamwidth.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)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).
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 as steel structure,
pipes, cables etc.
2. Don't place your hand between transmitting antenna and receiving antenna.
3. Antenna should be property mounted on the transmitting mast.
4. Conversion of µA to dB µA should be correct.
5. Distance between main unit and the detector unit should not exceed 1.5 meters.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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:
1. Arrange the set up.
2. Mount the cut paraboloid reflector antenna without reflector 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 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.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)9. The New readings show the effect of paraboloid reflector.
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 beamwidth.
GAIN OF THE ANTEN:
1. G=(Maximum radiation intensity) /(Maximum radiation intensity form a reference antenna i.e.
isotropic antenna with same power input).
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 as steel structure,
pipes, cables etc.
2. Don't place your hand between transmitting antenna and receiving antenna.
3. Antenna should be property mounted on the transmitting mast.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)4. Conversion of µA to dB µA should be correct.
5. Distance between main unit and the detector unit should not exceed 1.5 meters.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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:
1. Arrange the set up.
2. Mount the loop antenna on the transmitting mast.
3. Bring the detector assembly near to main unit and adjust the height of both transmitting and
receiving antenna same.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)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 center 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.
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 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.
13. Calculate the beam width. front to back ratio and the gain of the antenna with the help of this graph.
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.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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:
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 3 dB beam width.
GAIN OF THE ANTENNA:
1. G=(Maximum radiation intensity) /(Maximum radiation intensity form a reference antenna i.e.
isotropic antenna with same power input).
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.
STANDING WAVE RATIO:
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)SWR= (FWD+REV)/ (FWDREV).
RESULT:
PRECAUTIONS:
1. Ensure the there are no reflector sort things in the vicinity of the experiment such as steel structure,
pipes, cables etc.
2. Don't place your hand between transmitting antenna and receiving antenna.
3. Antenna should be property mounted on the transmitting mast.
4. Conversion of µA to dB µA should be correct.
5. Distance between main unit and the detector unit should not exceed 1.5 meters.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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:
1. Arrange the set up.
2. Mount Yagi uda 5 element folded dipole antenna 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.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)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.
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 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 dBs.
13. Calculate the beam width. front to back ratio and the gain of the antenna with the help of this graph.
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.
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.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)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:
1. look for main lobe.
2. Draw bore sight maximum line AA' mark3dB from maximum on the bore sight line point B.
3. Draw an arc of radius AB.
4. This arc will intersect main lobe at C and D.
5. Measure the angle CAD. This angle is 3 dB beam width.
GAIN OF THE ANTENNA:
1. G=(Maximum radiation intensity) /(Maximum radiation intensity form a reference antenna i.e.
isotropic antenna with same power input).
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
STANDING WAVE RATIO:
SWR= (FWD+REV)/ (FWDREV)
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)RESULT:
PRECAUTIONS:
1. Ensure the there are no reflector sort things in the vicinity of the experiment such as steel structure,
pipes, cables etc.
2. Don't place your hand between transmitting antenna and receiving antenna.
3. Antenna should be property mounted on the transmitting mast.
4. Conversion of µA to dB µA should be correct.
5. Distance between main unit and the detector unit should not exceed 1.5 meters.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)
VIVA VOICE
Ques1: Explain yagiuda antenna ?
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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:
1. Arrange the set up.
2. Mount the (End fire or Broad Side array) antenna on the transmitting mast.
3. Bring the detector assembly near to main unit and adjust the height of both transmitting and
receiving antenna same.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)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.
9. Align arrow mark on the disk with zero of goniometric 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 beamwidth. front to back ratio and the gain of the antenna with the help of this graph.
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.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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:
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 3 dB beamwidth.
GAIN OF THE ANTENNA:
1. G=(Maximum radiation intensity) /(Maximum radiation intensity form a reference antenna i.e.
isotropic antenna with same power input)
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.
STANDING WAVE RATIO:
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)SWR= (FWD+REV)/ (FWDREV).
RESULT:
PRECAUTIONS:
1. Ensure the there are no reflector sort things in the vicinity of the experiment such as steel structure,
pipes, cables etc.
2. Don't place your hand between transmitting antenna and receiving antenna.
3. Antenna should be property mounted on the transmitting mast.
4. Conversion of µA to dB µA should be correct.
5. Distance between main unit and the detector unit should not exceed 1.5 meters.
BROAD SIDE ARRAY
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)
PHASE ARRAY
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)
VIVA VOICE
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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:
1. Arrange the set up.
2. Mount the antenna 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.
9. Align arrow mark on the disk with zero of goniometer scale.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)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 dB s.
13. Calculate the beam width. front to back ratio and the gain of the antenna with the help of this graph.
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:
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).
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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 as steel structure,
pipes, cables etc.
2. Don't place your hand between transmitting antenna and receiving antenna.
3. Antenna should be property mounted on the transmitting mast.
4. Conversion of µA to dB µA should be correct.
5. Distance between main unit and the detector unit should not exceed 1.5 meters.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(EC-604)RHOMBUS ANTENNA
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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.
LAB MANUAL AND WORKBOOK 40
ANTENNA AND WAVE PROPAGATION
(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
LAB MANUAL AND WORKBOOK 40