Electronics and Communication Engineering - Microwave Communication

21. 

Out of modes TE20 and TE30 of propagation of electromagnetic engery

A. both have the same cutoff frequency
B. TE20 has lower cut off frequency as compared to TE30
C. TE30 has lower cutoff frequency as compared to TE20
D. either (a) or (c)

Answer: Option B

Explanation:

No answer description available for this question. Let us discuss.

22. 

A TE10 rectangular waveguide is to be designed for operation over 25-35 GHz and the band centre is 1.5 times the cutoff frequency. The dimension of broadside is

A. 15 mm
B. 10 mm
C. 9 mm
D. 7.5 mm

Answer: Option D

Explanation:

No answer description available for this question. Let us discuss.

23. 

In a klystron amplifier the force on all electrons

A. causes acceleration of all electrons
B. causes retardation of all electrons
C. causes acceleration of some electrons and retardation of others
D. none of the above

Answer: Option C

Explanation:

A Klystron is a vacuum tube used for generation/amplification of microwaves.

An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.

As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.

The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

The input is fed at buncher cavity and output is taken at catcher cavity.

In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.

The features of a multicavity klystron are :

1. Frequency range - 0.25 GHz to 100 GHz

2. Power output - 10 kW to several hundred kW

3. Power gain - 60 dB (nominal value)

4. Efficiency - about 40%.

A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.


24. 

If load impedance ZL >> Z0, then

A. Z0 = ZL (VSWR)
B. ZL = Z0 (VSWR)
C. ZL = Z0 (VSWR - 1)
D. ZL = Z0 VSWR

Answer: Option B

Explanation:

If ZL >> Z0, |rv| and VSWR . Therefore ZL = Z0(VSWR).


25. 

The inductance of a twin feeder used to connect antenna to TV receiver is about

A. 0.2 μ H/m
B. 0.6 μ H/m
C. 1.6 μ H/m
D. 10 μ H/m

Answer: Option C

Explanation:

No answer description available for this question. Let us discuss.