Microwave experiments Reflex Klystron Characteristics Study of Horn Antenna Study of Directional Coupler Frequency and wavelength measurement VSWR Measurement Impedance Measurement Study of Isolator Gunn diode characteristics

1. COMMUNICATION LAB
(MICROWAVE EXPERIMENTS)

2. LIST OF EXPERIMENTS
• Reflex Klystron Characteristics
• Study of Horn Antenna
• Study of Directional Coupler
• Frequency and wavelength measurement
• VSWR Measurement
• Impedance Measurement
• Study of Isolator
• Gunn diode characteristics

3. PREREQUISITIES
• Applied Electromagnetic Theory
• Digital Communication Techniques
• Microwave Engineering

4. A microwave test bench

5. Microwave Sources used in Lab
• Reflex Klystron
• Gunn Diode

6. Reflex klystron

7. Reflex klystron – cross section

9. Klystron Power supply

10. Klystron power supply (contd…)

11. Two sections of KPS
• High voltage section
• Modulation section (LV)

12. SAFETY PRECAUTION
• Before switching ON, ensure that
REPELLER VOLTAGE is MAXIMUM and
BEAM VOLTAGE is MINIMUM
• Ensure this conditions before switching
OFF also

13. How to energize Klystron?
• Initial settings
– Mod- Switch : AM
– Beam Voltage Knob : Fully anticlockwise
– Reflector Voltage Knob : Fully clockwise
– AM-Amplitude Knob : Mid Position
– AM-Frequency Knob : Mid Position
• Turn on Power switch, HT switch and
cooling fan

14. How to energize Klystron?
• Increase beam voltage to about 300 V,
ensure beam current between 15 to 20
mA
• Obtain square wave on CRO
• Maximize o/p of square wave using
– Variable Attenuator
– Plunger of klystron mount
– Repeller voltage knob
– AM amplitude and frequency knob

15. Block diagram

16. Mode curves

17. Slotted line section

18. Standing waves

19. Frequency meter

20. Horn antenna

21. Study of Horn Antenna

22. Directional Coupler

23. Observations
• Initial reading, P1
• Power reading in coupled port in forward
direction, P2
• Power reading in through port in forward
direction, P3
• Power reading in coupled port in reverse
direction, P4

24. Calculations
• Coupling coefficient = P1 – P2
• Insertion loss = P1 – P3
• Directivity = P1 – P4

25. Measuring guide wavelength

26. VSWR Measurement
• VSWR
• (In theory, VSWR = Vmax/Vmin)
min
max
V
V
=

27. Impedance Measurement

29. Calculations
• Shift in minima, d = 4.2 – 2.72 = 1.48cm =
0.37λg
• VSWR = 1.5






−
−
=
djVSWR
djVSWR
ZZL
β
β
tan
tan1
0