rameshpkd@gmail.com

CHARACTERISTICS OF REFLEX KLYSTRON (MODES)

Aim

To obtain mode curves, peak output for different modes, frequency variation of any one mode of a Reflex Klystron.

Components Required

Microwave bench set up, VSWR meter.

Block Diagram

Arrangement of microwave bench to study the characteristic of reflex klystron

Theory

Reflex Klystron makes use of velocity modulation to transform a continuous electron beam into microwave power. Electron emitted from the Cathode are accelerated and passed through the positive resonator towards negative reflector, which retards, and finally, reflects the electron and the electron turns back through the resonator. The accelerated electrons leave the resonator at an increased velocity and the retarded electrons leave at the reduced velocity. The electrons leaving the resonator will need different time to return, due to change in velocities. As a result, returning electrons group together in bunches.

Procedure:

1) Set up the microwave test bench as in the block diagram.2) Before switching ‘ON’ klystron power supply make sure the beam

voltage knob should be minimum and repeller voltage knob should be in maximum position.

3) ‘ON’ the KPS, and cooling fan.4) Vary the negative repeller voltage in step starting from the

maximum voltage. At each step note down repeller voltage.

Experiment: #213 Feb 2014

Batch I: EE13M131 DHANESH C. V

EE13M132 MEGNA MOHAMMEDEE13M134 RAMESH K

5) Repeat the steps 4 and 5 for various modes (repeller voltage from -250V to -40V) and tabulate.

6) Plot output current versus the repeller-voltage which gives repeller mode characteristics of a Reflex Klystron.

ObservationVRep

(V)Po (dB)

Po (uW)

-245.00 -55.00 3.16-240.00 -55.00 3.16-233.00 -47.00 19.95-225.00 -43.50 44.67-219.00 -43.00 50.12-200.00 -67.00 0.20-195.00 -69.08 0.12-175.00 -45.88 25.85-165.00 -53.50 4.47-160.00 -68.07 0.16-157.00 -56.00 2.51-150.00 -52.50 5.62-140.00 -47.55 17.59-130.00 -66.00 0.25-125.00 -68.00 0.16-123.00 -67.00 0.20-110.00 -54.00 3.98-105.00 -52.28 5.92-92.00 -50.00 10.00-85.00 -67.00 0.20-70.00 -55.45 2.85-60.00 -52.50 5.62-50.00 -68.00 0.16-40.00 -69.00 0.13

Result

The mode characteristic of reflex klystron has been verified. The first mode has the maximum power and is equal to 44.67µW.

Department of Engineering and Design IIT Madras