Online Electronics and Communication Engineering Test - Microwave Communication Test



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Instruction:

  • This is a FREE online test. DO NOT pay money to anyone to attend this test.
  • Total number of questions : 20.
  • Time alloted : 30 minutes.
  • Each question carry 1 mark, no negative marks.
  • DO NOT refresh the page.
  • All the best :-).


1.

Microwave resonators are used in

A.
microwave oscillators
B.
microwave narrow band amplifier
C.
microwave frequency metres
D.
all of the above

Your Answer: Option (Not Answered)

Correct Answer: Option D

Explanation:

They are used in all the devices.

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2.

Assertion (A): The phenomenon of differential mobility is called transferred electron effect.

Reason (R): GaAs exhibits transferred electron effect.

A.
Both A and R are correct and R is correct explanation of A
B.
Both A and R are correct but R is not correct explanation of A
C.
A is correct but R is wrong
D.
A is wrong but R is correct

Your Answer: Option (Not Answered)

Correct Answer: Option B

Explanation:

A Gunn diode uses GaAs which has a negative differential mobility, i.e., a decrease in carrier velocity with increase in electric field.

This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms.

A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement to couple RF power to load.

Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers.

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3.

Assertion (A): The condition of minimum distortion in a transmission line is L = RC/G.

Reason (R): Line loading means addition of inductance to satisfy the condition L = RC/G.

A.
Both A and R are correct and R is correct explanation of A
B.
Both A and R are correct but R is not correct explanation of A
C.
A is correct but R is wrong
D.
A is wrong but R is correct

Your Answer: Option (Not Answered)

Correct Answer: Option B

Explanation:

Oscillator circuits using vacuum tubes (triodes, pentodes) have the following limitations at very high frequencies (microwave region).

The stray capacitances and inductances become important and affect the operation of the circuit.

At low frequencies the transit time between cathode and anode is a small fraction of period of oscillation.

However, at microwave frequencies this transit time becomes comparable to time period of oscillations.

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4.

In a backward wave oscillator the wave

A.
travelling along the line winds itself back and forth
B.
progresses only in forward direction
C.
progresses only in backward direction
D.
either (a) or (c)

Your Answer: Option (Not Answered)

Correct Answer: Option A

Explanation:

It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.

It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.

The growing RF wave travels in opposite direction to the electron beam.

The frequency of wave can be changed by changing the voltage which controls the beam velocity.

Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.

It features are:

1. Frequency range - 1 GHz to 1000 GHz.

2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).

It is used as signal source in transmitters and instruments.

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5.

If antenna diameter is increased four times, the maximum range is increased by a factor of

A.
2
B.
2
C.
4
D.
0.2

Your Answer: Option (Not Answered)

Correct Answer: Option C

Explanation:

Range of radar is proportional to antenna diameter.

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6.

A line has an attenuation of 0.054 Np/m. The attenuation in decibels is

A.
4.7 dB/m
B.
0.47 dB/m
C.
0.54 dB/m
D.
5.4 dB/m

Your Answer: Option (Not Answered)

Correct Answer: Option B

Explanation:

0.054 x 8.68 = 0.47 dB/m.

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7.

A wave Em cos (bx - ωt) is a backward wave.

A.
True
B.
False

Your Answer: Option (Not Answered)

Correct Answer: Option B

Explanation:

It is a forward wave because as t increases, x increases.

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8.

For matching over a range of frequencies in a transmission line it is best to use

A.
a balun
B.
a broad band directional coupler
C.
double stub
D.
a single stub of adjustable position

Your Answer: Option (Not Answered)

Correct Answer: Option C

Explanation:

Double stub is useful for matching over a range of frequencies.

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9.

In the given figure forward voltage wave has a magnitude

A.
90 V
B.
60 V
C.
30 V
D.
10 V

Your Answer: Option (Not Answered)

Correct Answer: Option C

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10.

In a klystron amplifier the bunching effect

A.
converts velocity modulation into current modulation of beam
B.
converts current modulation into velocity modulation of beam
C.
both (c) and (b)
D.
neither (a) nor (b)

Your Answer: Option (Not Answered)

Correct Answer: Option A

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.

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11.

In a circular waveguide with radius r, the dominant mode is

A.
TM01
B.
TE01
C.
TM11
D.
TE11

Your Answer: Option (Not Answered)

Correct Answer: Option B

Explanation:

Some applications require dual polarization capability. Circular waveguide has this capability.

These analysis uses cylindrical coordinates.

In circular waveguide TE11 mode has the lowest cut off frequency and is the dominant mode.

If D is diameter of waveguide

λc = 1.706 D for TE11 mode

λc = 1.029 D for TE21 mode

λc = 0.82 D for TE01 mode

λc = 1.306 D for TM01 mode.

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12.

If 'a' is the width of rectangular wave guide and 'λ' is the wave length, then

A.
B.
C.
D.

Your Answer: Option (Not Answered)

Correct Answer: Option B

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13.

Radar is essentially an echo ranging system

A.
True
B.
False

Your Answer: Option (Not Answered)

Correct Answer: Option A

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14.

Fibers have numerical aperture (NA) in the range of 0.15 to 0.4 Fibers with higher NA value would have

A.
reduced losses
B.
high bandwidth
C.
reduced losses and low bandwidth
D.
more losses and low bandwidth

Your Answer: Option (Not Answered)

Correct Answer: Option D

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15.

Assertion (A): For a reciprocal microwave junction the S matrix is symmetrical.

Reason (R): In a symmetrical matrix Sij = Sji.

A.
Both A and R are correct and R is correct explanation of A
B.
Both A and R are correct but R is not correct explanation of A
C.
A is correct but R is wrong
D.
A is wrong but R is correct

Your Answer: Option (Not Answered)

Correct Answer: Option B

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16.

A TEM wave is incident normally on a perfect conductor. The E and H fields at boundary will respectively be

A.
minimum and maximum
B.
minimum and minimum
C.
maximum and minimum
D.
maximum and maximum

Your Answer: Option (Not Answered)

Correct Answer: Option A

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17.

Assertion (A): In rectangular waveguide TE01 mode is just TE10 mode rotated by 90°.

Reason (R): When a rectangular waveguide is rotated by 90°, the broad and narrow dimensions get interchanged.

A.
Both A and R are correct and R is correct explanation of A
B.
Both A and R are correct but R is not correct explanation of A
C.
A is correct but R is wrong
D.
A is wrong but R is correct

Your Answer: Option (Not Answered)

Correct Answer: Option A

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18.

Assertion (A): Hollow waveguides are frequently used as transmission lines at microwave frequencies.

Reason (R): Waveguide has high power handling capacity, low loss and simple structure.

A.
Both A and R are correct and R is correct explanation of A
B.
Both A and R are correct but R is not correct explanation of A
C.
A is correct but R is wrong
D.
A is wrong but R is correct

Your Answer: Option (Not Answered)

Correct Answer: Option A

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19.

Which of the following modes cannot exist in rectangular resonant cavity?

A.
TE110
B.
TE011
C.
TM110
D.
TM111

Your Answer: Option (Not Answered)

Correct Answer: Option A

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20.

A waveguide twist is used to change the plane of polarization.

A.
True
B.
False

Your Answer: Option (Not Answered)

Correct Answer: Option A

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