PSU MCQs on Microwave Engineering

1. A reflex Klystron fuctions as
a) Microwave oscillator
b) Microwave amplifier
c) Both as Microwave amplifier and oscillator
d) A high gain cavity

Ans: Option a)

2. The modes in a reflex Klystron
a) give the same frequency but different transit times
b) result from excessive transit time across the resonator gap
c) are caused by spurious frequency modulation
d) are just for theoretical considerations

Ans: Option a)


3. Klystron operates on the principle of
a) Amplitude Modulation
b) Frequency Modulation
c) Pulse Modulation
d) Velocity Modulation

And: Option d)

4. In Microwave we take the elements as
a) Lumped circuit elements
b) Distributed circuit elements
c) Both a) and b)
d) None of the above

Ans: Option b)

5. Short term fading in microwave communication links can be overcome by
a) Increasing the transmitted power
b) Changing the antenna
c) Changing the modulation scheme
d) Diversity reception and transmission

Ans: Option d)

6. For handling large microwave power, the best medium is
a) Coaxial line
b) Rectangular waveguide
c) Stripline
d) Circular waveguide

Ans: Option b)

7. A Microwave tube amplifier uses an axial magnetic field and radial electric field. This is the
a) Reflex Klystron
b) Coaxial Magnetron
c) Travelling wave magnetron
d) CFA-Crossed Field Amplifier

Ans: Option d)

8. A disadvantage of microstrips with respect to stripline circuit is that the former:
a) Do not let themselves to be printed-circuits
b) Are more likely to radiate
c) Are bulkier
d) Are more expensive and complex to manufacture

Ans: Option d)

9. Most of the power measuring microwave devices measure
a) Average power
b) Peak power
c) Instantaneous power
d) None of these

Ans: Option a)

10. HEMT used in microwave circuit is a
a) Source
b) High power amplifier
c) Detector
d) Low noise Amplifier

Ans: Option d)

11. Ionospheric preparation is not possible for microwaves because
a) Microwaves will be fully absorbed by the ionospheric layers
b) There will be an abrupt scattering in all directions
c) Microwave will penetrate through the ionospheric layers
d) There will be dispersion of microwave energy

Ans: Option c)

12. A waveguide section in a microwave circuit will act as a
a) Low-pass filter
b) Band-pass filter
c) High-pass filter
d) Band-reject filter

Ans: Option c)

13. The biggest advantage of the TRAPATT diode over the IMPATT diode is its
a) Low noise
b) Higher efficiency
c) Ability to operate at higher frequencies
d) Lesser sensitivity to harmonics

Ans: Option b)

14. A varactor diode may not be useful at microwave frequencies
a) For electronic tuning
b) for frequency multiplication
c) as an oscillator
d) As a parametric amplifier

Ans: Option c)

15. The negative resistance in a tunnel diode
a) is maximum at the peak point of the characteristic
b) is available between the peak and valley points
c) is maximum at valley point
d) may be improved by the use of reverse bias

Ans: Option b)

16. Which one of the following is a transferred electron device?
a) BARITT diode
b) IMPATT diode
c) Gunn diode
d) Step recovery diode

Ans: Option c)

17. A PIN diode is suitable for use as a
a) Microwave switch
b) Microwave mixed diode
c) Microwave detector
d) None of these

Ans: Option a)

18. The semiconductor diode which can be used in switching circuits at microwave range is
a) PIN diode
b) Tunnel diode
c) Varactor diode
d) Gunn diode

Ans:  Option a)

19. Microwave antenna aperture efficiency depends on
a) Feed Pattern
b) Antenna Aperture
c) Surface losses
d) Low side lobe level

Ans: Option b)

20. The noise produced in a microwave tube due to random nature of emission and electron flow is called
a) Partition noise
b) Shot noise
c) Johnson noise
d) Shannon noise

Ans: Option b)

21. A duplexer is used
a) To couple two different antennas to a transmitter without mutual interference
b) To allow one antenna to be used for reception or transmission without mutual interference
c) To prevent interference between two antennas when they are connected to a receiver
d) To increase the speed of the pulses in pulsed radar

Ans: Option b)

22. One of the reasons why vacuum tubes eventually fail at microwave frequencies is that their
a) Noise figure increases
b) Transit time becomes too short
c) Shunt capacitive reactances become too large
d) Series inductive reactances become too small

Ans: Option a)

23.A magic-Tee is nothing but
a) A modification of E-plane tee
b) A modification of H-plane tee
c) A combination of E-Plane and H-Plane
d) Two E-plane tees connected in parallel

Ans: Option c)

24. Which of the following can be used for amplification of microwave energy?
a) Travelling wave tube
b) Magnetron
c) Reflex Klystron
d) Gunn diode

Ans: Option a)

25. In microwave power measurements using bolometer, the principle of working is the variation of
a) Inductance with absorption of power
b) Resistance with absorption of power
c) Capacitance with absorption of power
d) Cavity dimensions with heat generated by the power

Ans: Option b)

26. In π mode operation of magnetron, the spokes due to phase focusing effect rotate at an angular velocity corresponding to
a) One pole/cycle
b) Two poles/cycle
c) Four poles/cycle
d) Six poles/cycle

Ans: Option b)

27. For Gunn diodes, gallium arsenide is preferred to silicon because the former
a) Has a suitable empty energy band, which silicon does not have
b) Has a higher ion mobility
c) Has a lower noise at the highest frequencies
d) Is capable of handling higher power densities

Ans: Option a)

28. For best low-level noise performance in the X-band an amplifier should use
a) A bipolar transistor
b) A Gunn diode
c) A step recovery diode
d) An IMPATT diode

Ans: Option c)

29. Travelling wave parametric amplifiers are used to
a) provide a greater gain
b) reduce the number of varactor diodes required
c) avoid the need for cooling
d) provide a greater bandwidth

Ans: Option d)

30. The major advantage of TWT over Klystron
a) higher gain
b) higher frequency
c) higher output
d) higher bandwidth

Ans: Option d)

31. Microwave frequency range extends from
a) 3 MHz to 30 MHz
b) 30 MHz to 300 MHz
c) 300 MHz to 3000 MHz
d) 500 MHz to 30000 MHz

Ans: Option d)

32. Due to curvature of earth, microwave repeaters are placed at a distance of about
a) 10 Km
b) 50 Km
c) 150 Km
d) 250 Km

Ans: Option b)

33. At microwave frequencies the size of the antenna becomes
a) Very large
b) Large
c) Small
d) Very Small

Ans: Option d)

34. Which of the following noise becomes important at microwave frequencies
a) Shot noise
b) Flicker noise
c) Thermal noise
d) Transit time noise

Ans: Option d)

35. The phenomenon of microwave signals following the curvature of earth is known as
a) Faraday effect
b) Ducting
c) Wave tilt
d) Troposcatter

Ans: Option b)

36. The front end of an amplifier chain in manufacture of a communication system is kept immersed in liquid nitrogen to
a) Dissipate heat generated by amplifier
b) Expand the frequency response
c) Improve its noise figure
d) reduce the distortion by the amplifier

Ans: Option c)

37. In microwave communication links, the rain drop attenuation experienced is mainly due to
a) Absorption of microwave energy by water vapour
b) resonance absorption of atomic vibration in water molecules
c) scattering of microwaves by collection of water drops
d) refraction of microwaves through liquid-drop lenses formed by rain

Ans: Option a)