Antenna and Microwave Engineering

Experiment list

1) To set up the Antenna trainer with motorized control.

2) a) To study the radiation pattern of λ/2 dipole. b) To study the radiation pattern of 3λ/2 dipole.

3) To study the radiation pattern of folded dipole.

4) a) To study the radiation pattern of end-fire antenna array with the spacing between the two elements is λ/2. b) To study the radiation pattern of end-fire antenna array with the spacing between the two elements is λ/2 and length of the dipoles is λ.

5) a) To study the radiation pattern of 7-element Yagi-Uda antenna for active element Is half wave dipole. b) Comparison of 5-element Yagi-Uda antenna with 7-element Yagi-Uda antenna for active element is half wave dipole. c) Comparison of 5-element Yagi-Uda antenna with 3-element Yagi-Uda antenna for active element is folded dipole.

6) To study the radiation pattern of log periodic dipole array.

7) Obtain the field pattern of helical antenna.

8) To Study the Microwave Test bench and Various Microwave Components.

9) To measure the calibration of the given attenuator.

10) To measure the polar diagram of a wave-guide horn.

11) To Determine the Standing Wave Ratio and Reflection Coefficient.

12) To determine the frequency of reflex Klystron.

13) To measure the radiation pattern of wireless link using horn antenna and parabolic reflector.14) To study about the microstrip Trainer.

15) a) To study microwave antennas like log periodic dipole antenna, log spiral antenna, patch antenna inset fed and patch antenna transformer fed. b) To study Ring resonator, half wave resonator

EXPERMENT:-1

Objectives: To set up the Antenna trainer with motorized control.

Equipments: Antenna Trainer ST2261. Motorised Antenna Unit ST2261A. Accessories (i.e. Patch cord, CRO probes, 5pin DIN cable)

Figure: Set-up for the ST2261, ST2261A and detector units.

Procedure:1. Install the given software in your PC.2. Connect the RS232 cable with your PC and the other end to the Motorised

Antenna Unit ST2261A as shown in the figure.3. Connect the RF output of the Antenna Trainer ST2261 to the Motorised

Antenna Unit ST2261A, with the BNC cable as shown in the figure.4. Connect the output of the detector to the Motorised Antenna Unit ST2261A,

with 5 pin DIN cable as shown in the figure.5. Connect the output of the tone generator to the input of the RF modulator in

the Antenna Trainer ST2261 with the help of patch cord as shown in the figure.

6. Connect the supply cable of both the unit and adaptor of the detector unit.7. Switch on both the unit.

EXPERIMENT:-2

PART-A

Objectives: To study the radiation pattern of λ/2 dipole. To conclude its application(s). To measure its directive gain. To measure its half power beamwidth. To measure its front to back ratio.

Equipment: Antenna Trainer ST2261. Motorised Antenna Unit ST2261A. λ/2 dipole.

Figure: Half Wave Dipole

Theory:

It is assumed that the antennas are symmetrically fed at the centre by a balanced two wire transmission line. The antennas may be of any length, but it is assumed that the current distribution is sinusoidal. Current distribution measurements indicate that this is a good assumption provided that the antenna is thin, i.e. when the conductor diameter is less than say λ/100. Thus the sinusoidal current distribution approximates the natural distribution on these antennas.

Referring to figure let us now proceed to develop the far field equations for a symmetrical, thin, linear, centre-fed antenna of length L. The retarded value of the current at any point z on the antenna referred to a point at a distance s is

[ I ] = Io sin[2π/ λ (L/2±z) ] ejw[t-(r/c)]

Far fields of center-fed dipole,

HΦ = j[Io]/2 πr [{cos[(βL cosθ)/2]-cos(βL/2)}/sinθ]Eθ = j60[Io]/r [{cos[(βL cosθ)/2]-cos(βL/2)}/sinθ]

Procedure:1. Arrange the Set up as given in Experiment: 1.2. Run necessary Software.3. Mount λ/2 dipole on the transmitting mast.4. Bring the detector assembly near to main unit and adjust height of both

transmitting and receiving antenna same.5. Keep detector assembly away from main unit approximately 1.5 in. and align

both of them. Ensure that there is no reflector sort thing in the vicinity of the experiment such as steel structures, pipes, cables etc.

6. Keep the RF level and FS Adjust to minimum and directional coupler switch to FWD.

7. Keep detector level control in the centre approximately.8. Increase RF level gradually and see that there is display in the detector meter.9. Adjust RF level and detector level so that the display in detector meter is

approximately 30-35 μA.10. Align arrow mark on the disk with zero of the goniometer scale.11. Click Configure and Reset button in the software.12. Click Plot button in the software and save the pattern with appropriate name.13. Measure the various parameters of the pattern with the help of software.

Conclusion: Draw your own conclusion(s) based on the objectives.

Assignment:1. What is the effect on the radiation pattern if the length of the dipole is

changed? 2. Draw the current and the voltage distribution for the half wave dipole.3. Draw the current and voltage distribution for the end fed dipole antenna.

PART-B

Objectives: To study the radiation pattern of 3λ/2 dipole. To conclude its application(s). To measure its directive gain. To measure its half power beamwidth. To measure its front to back ratio.

Equipment: Antenna Trainer ST2261. Motorised Antenna Unit ST2261A. 3λ/2 dipole.

Figure: Radiation pattern and current distribution of 3λ/2 dipole.

Theory:

It is assumed that the antennas are symmetrically fed at the centre by a balanced two wire transmission line. The antennas may be of any length, but it is assumed that the current distribution is sinusoidal. Current distribution measurements indicate that this is a good assumption provided that the antenna is thin, i.e. when the conductor diameter is less than say λ/100. Thus the sinusoidal current distribution approximates the natural distribution on these antennas.

Referring to figure given in the Experiment: 2 let us now proceed to develop the far field equations for a symmetrical, thin, linear, centre-fed antenna of length L. The retarded value of the current at any point z on the antenna referred to a point at a distance s is

[ I ] = Io sin[2π/ λ (L/2±z) ] ejw[t-(r/c)]

Far fields of centre-fed dipole,

HΦ = j[Io]/2 πr [{cos[(βL cosθ)/2]-cos(βL/2)}/sinθ]Eθ = j60[Io]/r [{cos[(βL cosθ)/2]-cos(βL/2)}/sinθ]

Procedure:1. Arrange the Set up as given in Experiment: 1.2. Run necessary Software.3. Mount 3λ/2 dipole on the transmitting mast.4. Bring the detector assembly near to main unit and adjust height of both

transmitting and receiving antenna same.5. Keep detector assembly away from main unit approximately 1.5 in. and align

both of them. Ensure that there is no reflector sort thing in the vicinity of the experiment such as steel structures, pipes, cables etc.

6. Keep the RF level and FS Adjust to minimum and directional coupler switch to FWD.

7. Keep detector level control in the centre approximately.8. Increase RF level gradually and see that there is display in the detector meter.9. Adjust RF level and detector level so that the display in detector meter is

approximately 30-35 μA.10. Align arrow mark on the disk with zero of the goniometer scale.11. Click Configure and Reset button in the software.12. Click Plot button in the software and save the pattern with appropriate name.

13. Measure the various parameters of the pattern with the help of software.

Conclusion: Draw your own conclusion(s) based on the objectives.

Assignment:1. Draw the radiation pattern of 5λ/2 dipole antenna.2. Draw the current and voltage distribution on the 3λ/2 dipole antenna.3. What is the effect on the major lobe of radiation pattern if the length of dipole

is increased?

EXPERIMENT:-3

Objectives: To study the radiation pattern of folded dipole. To conclude its application(s). To measure its directive gain. To measure its half power beamwidth. To measure its front to back ratio.

Equipment: Antenna Trainer ST2261. Motorised Antenna Unit ST2261A. Folded dipole.

Figure: Current distribution over the folded dipole

Theory:

A simple compensating network for increasing the bandwidth of a dipole antenna is shown in figure. The LC circuit is parallel-resonant at the half wave dipole resonant frequency. At this frequency its impedance is, therefore, a high resistance, not affecting the total impedance seen by the transmission line. Below this resonant frequency the antenna reactance becomes capacitive, while the reactance of the LC circuit becomes inductive. Above the resonant frequency the opposite is true, the antenna becoming inductive, and the tuned circuit capacitive. Over a small frequency range near resonance, there is thus a tendency to compensate for the variations in the antenna reactance, and the total impedance remains resistive in situations in which the impedance of the antenna alone would have been heavily reactive. This compensation is both improved and widened when the Q of the resonant circuit is lowered. Moreover, it can be achieved just as easily with a short-circuited quarter wave transmission line. The folded dipole provides the same type of compensation as the transmission line version of this network.

The folded dipole is a single antenna, but it consists of two elements. The first is fed directly while the second is coupled inductively at the ends. The radiation pattern of the folded dipole is the same as that of a straight dipole, but its input impedance is greater, in two elements folded dipole with equal diameter arms input impedance is 4x72 = 288 Ohms. It has many another advantages like greater bandwidth and impedance matching.

Procedure:1. Arrange the Set up as given in Experiment: 1.2. Run necessary Software.3. Mount folded dipole on the transmitting mast.4. Bring the detector assembly near to main unit and adjust height of both

transmitting and receiving antenna same.5. Keep detector assembly away from main unit approximately 1.5 in. and align

both of them. Ensure that there is no reflector sort thing in the vicinity of the experiment such as steel structures, pipes, cables etc.

6. Keep the RF level and FS Adjust to minimum and directional coupler switch to FWD.

7. Keep detector level control in the centre approximately.8. Increase RF level gradually and see that there is display in the detector meter.9. Adjust RF level and detector level so that the display in detector meter is

approximately 30-35 μA.10. Align arrow mark on the disk with zero of the goniometer scale.11. Click Configure and Reset button in the software.12. Click Plot button in the software and save the pattern with appropriate name.13. Measure the various parameters of the pattern with the help of software.

Conclusion: Draw your own conclusion(s) based on the objectives.

Assignment:1. What are the advantages of the folded dipole over the simple dipole?2. What will be the impedance of the folded dipole with the tree elements?