ELECTRICAL ENGINEERING DEPARTMENT
EP603 : MICROWAVE DEVICES
Lab 5: To study Rhombus Antenna and Yagi-Uda 5-Element Antenna
COURSE LEARNING OUTCOME (CLO):
CLO3
:
Handle systematically the related microwave communication equipment in performing
the assigned practical work
Objective
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To study Rhombus Antenna
To study Yagi-Uda 5-Element Antenna
Background / Preparation
Rhombus antenna is also a loop of antenna and made in the rhombus form. It is a non-resonant
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 from typically 650-700Ω.
The theoretical impedance for Yagi-Uda 5 element impedance’s is 75 Ω. This is very important
antenna for unidirectional transmission and widely used in TV reception. Behind the dipole they have a
reflectors and in front they have directors. The polarization pattern of this antenna is horizontal.
Basic operation of transmit and receive antennas.

Transmission - radiates electromagnetic energy into space

Reception - collects electromagnetic energy from space
In two-way communication, the same antenna can be used for transmission and reception.
The following apparatus will be required:
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Antenna Trainer
Transmitting Mast
Receiving mast
RF Detector
L shape BNC connector
Rhombus Antenna
Yagi-Uda 5-Element Antenna
Part A (i): Arranging the trainer and performing the functional checks
Procedure:
1. Install a transmitting mast, place it beside the main unit and connect it to the main unit’s ‘RF OUT”
using a BNC to BNC cable of 25’ long.
2. Install Receiving mast and keep it at some distance from the Transmitter mas.
3. Place RF detector Unit beside the Receiving mast and connect it to the Receiving mast using a BNC
to BNC cable of 25’ long.
4. Keep the base of Transmitting mast such that the ‘0’ degree position of the Goniometer should be
directed towards the RF Detector and also align the marker of the mast with “0” degree position.
5. Install Detector antenna on the Receiving mast.
6. Install Rhombus Antenna on the Transmitting mast. Keep its direction towards the Receiving mast by
rotating it in counter clockwise direction.
7. Switch ON the main unit and check the display in DPM of Directional Coupler. It will show some
reading according to its level knob at starting.
8. Connect a +9V Adapter to the RF Detector unit, switch it ON and keep the Level knob at middle
position. It will show some reading according to its level knob at starting.
9. Now vary the FS Adjust pot of Directional Coupler to make the display reading 100 Micro Amp and
then adjust the Level of RF detector to show the ¾ reading of the main unit’s display.
10. Rotate the transmitting antenna between 0-360 degrees and observe the display at RF Detector. The
variation in reading indicates that the transmitter and receiver are working and radiation pattern is
formed.
Part A (ii) : Adjustment of level RF Generator
Procedure:
In case of low reading ( for low gain antennas 0, set the RF level Pot of main unit to maximum
position. Also the reading of DPM of Directional Coupler can be set to 50 Micro Amp for these antennas
and then adjust the level of RF detector to show ¾ reading of the main unit’s display.
Part A (iii): Adjustment of level RF Generator
The distance between the transmitting mast and the Receiving mast may be adjusted for receiving
optimum radiations at RF Detector.
Part A (iv): Plotting the Polar Graph for Normalized Reading.
One can also plot the polar graph against normalized readings of the RF Detector. The procedure to
convert the Micro Amp in the normalize reading is given as follows.
Consider the maximum reading say N (When the RF Detector receives maximum radiations) as db.
Let say it is N = 50micro Amps,
Convert next reading taken at the interval (5 or 10 degrees) say N1 by the following formula:
Ln N1/N = reading in dB
Part B : Rhombus Antenna
1. Mount the Rhombus Antenna on the transmitting mast as Figure below.
RF Detector
Receiving Mast
Transmitting mast
Antenna trainer
2. Rotate the transmitting antenna between 0-360 degrees and observe the display at RF Detector. The
variation in reading indicates that the transmitter and receiver are working and radiation pattern is formed.
Convert the reading of RF position meter (Micro Amp) to dB before plot the graph.
Result Part B
Angle
(Degree)
RF position
meter
RF position
meter
(Micro Amp)
(dB)
Angle
(Degree)
0/360
180
10
190
20
200
30
210
40
220
50
230
60
240
70
250
80
260
90
270
100
280
110
290
120
300
130
310
140
320
150
330
160
340
170
350
Table 1
Plot the graph of antenna at antenna radiation graph.
RF position
meter
RF position
meter
(Micro Amp)
(dB)
Part C : Yagi-Uda 5-Element Antenna
Setup the apparatus as same as Part B but replace the Transmitting antenna with Yagi-Uda
5-Element Antenna directly to the BNC connector.
Result Part C
Angle
(Degree)
RF position
meter
RF position
meter
(Micro Amp)
(dB)
Angle
(Degree)
0/360
180
10
190
20
200
30
210
40
220
50
230
60
240
70
250
80
260
90
270
100
280
110
290
120
300
130
310
140
320
150
330
160
340
170
350
RF position
meter
RF position
meter
(Micro Amp)
(dB)
Table 2
Plot the graph of antenna at antenna radiation graph.
Part D : Reflection
What types of radiation pattern occur for both antennas? Explain each of that type. Compare your
views with your classmate.
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Suggested answer;
Rhombus antenna; Bidirectional radiation pattern
Part E : Discussion
Part F : Conclusion