COMMUNICATION LAB(MICROWAVE EXPERIMENTS)
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
PREREQUISITIES
• Applied Electromagnetic Theory• Digital Communication Techniques• Microwave Engineering
A microwave test bench
Microwave Sources used in Lab
• Reflex Klystron• Gunn Diode
Reflex klystron
Reflex klystron – cross section
Klystron Power supply
Klystron power supply (contd…)
Two sections of KPS
• High voltage section• Modulation section (LV)
SAFETY PRECAUTION
• Before switching ON, ensure that REPELLER VOLTAGE is MAXIMUM and BEAM VOLTAGE is MINIMUM
• Ensure this conditions before switching OFF also
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
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
Block diagram
Mode curves
Slotted line section
Standing waves
Frequency meter
Horn antenna
Study of Horn Antenna
Directional Coupler
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
Calculations
• Coupling coefficient = P1 – P2
• Insertion loss = P1 – P3
• Directivity = P1 – P4
Measuring guide wavelength
VSWR Measurement
• VSWR
• (In theory, VSWR = Vmax/Vmin)
min
max
VV
Impedance Measurement
Calculations
• Shift in minima, d = 4.2 – 2.72 = 1.48cm = 0.37g
• VSWR = 1.5
djVSWRdjVSWRZZ L
tantan1
0
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