# Microwave Communication MCQ Questions & Answers

Microwave Communication MCQs : This section focuses on the "Microwave Communication". These Multiple Choice Questions (MCQs) should be practiced to improve the Microwave Communication skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.

Question 1

A 10 km long line has a characteristic impedance of 400 ohms. If line length is 100 km, the characteristic impedance is

A. 4000 Ω
B. 400 Ω
C. 40 Ω
D. 4 Ω

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Question 2

A line has a phase constant of 29.8 rad/m. At 1000 MHz the wavelength is

A. 29.8 m
B. 2.98 m
C. 2.1 m
D. 0.21 m

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Question 3

A line has Z0 = 300 ∠ 0° Ω. If ZL = 150 ∠ 0° Ω, reflection coefficient is

A. 0.5
B. 0.3333
C. -0.3333
D. -0.5

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Question 4

A line is excited by a 100 V dc source. If reflection coefficients at both ends are 1 each then

A. there will be no oscillations on line
B. there will be only 1 or 2 oscillations on line
C. there will be a finite number of oscillations on line
D. the oscillations will continue indefinitely

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Question 5

A loss less line of characteristic impedance Z0 is terminated in pure reactance of -jZ0 value. VSWR is

A. 10
B. 2
C. 1
D. infinity

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Question 6

A matched generator (Zg = Z0) with 1 Ω available. If all ports are matched, the power delivered at ports 1, 2, 3 respectively are

A. 0.5 W, 0.5 W, 0 W
B. 0 W, 0 W, 1 W
C. 0.33 W each
D. 0 W, 0.25 W, 0.25 W

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Question 7

A quarter wave line open circuited at far end behaves as

A. inductance
B. L and C in parallel
C. capacitance
D. L and C in series

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Question 8

A resistive microwave load with ZL = 150 Ω is connected to 50 Ω coaxial line. SWR is

A. more than 3
B. less than 3
C. equal to 3
D. either (a) or (c)

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Question 9

A waveguide section in a microwave circuit acts as

A. LP filter
B. Bandpass filter
C. HP filter
D. Band stop filter

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Question 10

As the frequency is increased, the charging MVAR in a cable

A. decreases
B. increases
C. remain the same
D. decreases or remains the scheme

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Question 11

Assertion (A): A backward wave oscillator has an internal positive feedback.Reason (R): A positive feedback is necessary for sustained oscillations.

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

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Question 12

Assertion (A): A coaxial line is a non-radiating line.Reason (R): In a coaxial line the electric and magnetic fields are confined to the region between the concentric conductors.

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

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Question 13

Assertion (A): Artificial transmission lines are frequently used in laboratories.Reason (R): An artificial transmission line can be used to represent an actual line and can also be used as a delay circuit, as attenuator, as filter network etc.

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

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Question 14

Assertion (A): The impedance of a matched load is equal to characteristic impedance of line.Reason (R): A matched termination absorbs all the power incident on it.

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

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Question 15

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

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Question 16

Assertion (A): The reverse saturation current in a semiconductor diode is 4nA at 20°C and 32 nA at 50°C.

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

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Question 17

Assertion (A): The reverse saturation current in a semiconductor diode is 4nA at 20°C and 32 nA at 50°C.Reason (R): The reverse saturation current in a semiconductor diode doubles for every 10°C rise in temperature.

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

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Question 18

Both Impatt and Trapatt devices use avalanche effect

A. TRUE
B. FALSE

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Question 19

For a 50 Ω resistor for 3 GHz application, the stray capacitance should be less than

A. 1 μF
B. 1 nF
C. 1 pF
D. 0.1 pF

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Question 20

Impedance level of Impatt diodes is generally lower than that of Gunn diodes

A. TRUE
B. FALSE

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Question 21

In a backward wave oscillator the wave travelling along the line winds itself back and forth

A. TRUE
B. FALSE

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Question 22

In a circular waveguide the dominant mode is

A. TE01
B. TE11
C. TE20
D. TE21

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Question 23

In a directional coupler

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

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Question 24

In a klystron amplifier dc electron velocity is v0 and dc electron charge density is r0 the dc beam current is

A. r0v0
B. r0/v0
C. v0/r0
D. (v0/r0)2

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Question 25

In a klystron amplifier the input cavity is called

A. buncher
B. catcher
C. Pierce gun
D. collector

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Question 26

In a microstrip transmission the signal can be easily redirected by changing the centre strip.

A. TRUE
B. FALSE

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Question 27

In a three cavity klystron amplifier, the oscillations are excited in

A. input cavity
B. output cavity
C. intermediate cavity
D. both (a) and (b)

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Question 28

In a travelling wave tube distributed interaction between an electron beam and a travelling wave takes place

A. TRUE
B. FALSE

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Question 29

In a turnstile antenna two-half wave resonant wire radiators are placed at 90° to each other in the same plane and are excited

A. in phase
B. in phase opposition
C. 90° out of phase with each other
D. 45° out of phase with each other

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Question 30

In a TWT the amplitude of resultant wave travelling down the helix

A. increases exponentially
B. increases linearly
C. decreases exponentially
D. is almost constant

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Question 31

Microwave resonators are used in

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

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Question 32

Reflex klystron oscillator is essentially a low power device

A. TRUE
B. FALSE

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Question 33

Skin effect is more pronounced at high frequencies.

A. TRUE
B. FALSE

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Question 34

The action of backward wave oscillator is similar to that of

A. klystron amplifier
B. reflex klystron oscillator
C. TWT
D. magnetron

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Question 35

The diagram to show distance time history of electrons in klystron amplifier is called

A. apple gate diagram
B. asynchronous diagram
C. bunching diagram
D. velocity modulation diagram

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Question 36

The fabrication of microstrip line is done by

A. photo etching
B. printed circuit technique
C. oxidation
D. cladding

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Question 37

The frequency of oscillation in a backward wave oscillator can be changed by

A. varying the voltage which controls beam velocity
B. varying the beam current
C. both by varying the beam current and by light varying the voltage which controls beam velocity
D. changing the rate of thermionic emission

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Question 38

The reflection coefficient on a line is 0.2 ∠45°. The SWR is

A. 0.8
B. 1.1
C. 1.2
D. 1.5

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Question 39

The velocity factor of a transmission line depends on

A. temperature
B. skin effect
C. relative permittivity of dielectric
D. none of the above

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Question 40

The width of a radio beam from a 1 m diameter parabolic antenna at 10 GHz is about

A. 100°
B. 50°
C. 5°
D. 1°

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Question 41

Which of the following devices uses a helix?

A. Klystron amplifier
B. Klystron oscillator
C. TWT
D. Both (a) and (b)

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Question 42

Which of the following devices uses a slow wave structure?

A. Klystron two cavity amplifier
B. Klystron multicavity amplifier
C. Reflex klystron oscillator
D. TWT

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Question 43

Which of the following is not a travelling wave?

A. e = Em sin (βx - ωt)
B. e = Em cos (βx - ωt)
C. e = Em sin (ωt - βx)
D. e = Em sin (βx)

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Question 44

Which of the following lines is non-radiating?

A. Open two wire
B. Coaxial
C. Both
D. None of the above

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Question 45

Which of the following parameters is negligible in transmission lines?

A. R
B. L
C. C
D. G

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Question 46

Which TM mode in rectangular waveguide has lowest cutoff frequency?

A. TM11
B. TM01
C. TM10
D. TM21

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