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

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