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ECE : Microwave Communication - Quiz(MCQ)
A)
increases
B)
decreases
C)
remain the same
D)
decreases or remains the scheme

Correct Answer : Option (A) :   increases


Explanation : Charging current and MVAR are proportional to frequency.

A)
input cavity
B)
output cavity
C)
intermediate cavity
D)
Both (A) and (B)

Correct Answer : Option (C) :   intermediate cavity


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.

A)
Cavity match
B)
Waveguide match
C)
Direct coax-helix match
D)
All of the above

Correct Answer : Option (D) :   All of the above

A)
Low-pass filters
B)
The shortest possible time
C)
A long time constant
D)
The restricted high-frequency response

Correct Answer : Option (B) :   The shortest possible time

A)
current
B)
voltage
C)
electrical size
D)
circuit elements

Correct Answer : Option (C) :   electrical size


Explanation : Circuit theory assumes physical dimensions of the network smaller than electrical wavelength, while transmission lines may be considerable fraction of wavelength.

A)
active
B)
distributed
C)
lumped
D)
None of the above

Correct Answer : Option (B) :   distributed


Explanation : Since no lumped elements like resistors, capacitors are used at microwave frequencies, only transmission lines are used. Hence they are called distributed parameter network.

A)
1 conductor
B)
2 conductors
C)
3 conductors
D)
bunch of conductors

Correct Answer : Option (B) :   2 conductors


Explanation : With a single conductor, transverse electromagnetic wave propagation is not possible. Hence we need a minimum of 2 conductors.

A)
1°
B)
30°
C)
70°
D)
90°

Correct Answer : Option (A) :   1°


Explanation : For ideal dielectric loss angle is zero. For good quality cables, loss angle is very small, about 1° only.

A)
isolation (dB) equals (coupling) (directivity)
B)
coupling (dB) equals isolation plus directivity
C)
directivity (dB) equals isolation plus coupling
D)
isolation (dB) equals coupling plus directivity

Correct Answer : Option (D) :   isolation (dB) equals coupling plus directivity


Explanation : Isolation equals coupling plus directivity.

A)
skin effect
B)
temperature
C)
relative permittivity of dielectric
D)
None of the above

Correct Answer : Option (C) :   relative permittivity of dielectric


Explanation :

r of a dielectric changes with humidity.