TRB PG Assistant - Microwave generation - klystron, magnetron, travelling wave tubes, waveguides - rectangular and cylindrical, antenna characteristics - short dipole radiation, antenna gain, directivity, radiation resistance, radiation intensity Question Bank with Options

1. The efficiency of an antenna is the ratio of power radiated to the:

A) Net power accepted by the antenna

B) Total power delivered to the antenna

C) Power gain

D) Power density

2. Which of the following is a characteristic of the TE10 mode in a rectangular waveguide?

A) Electric field has a component in the direction of propagation.

B) Magnetic field has a component in the direction of propagation.

C) Both electric and magnetic fields are transverse to the direction of propagation.

D) It is the dominant mode and has no cutoff frequency.

3. The radiation resistance of an antenna is influenced by its:

A) Physical size and shape

B) Operating frequency

C) Surrounding environment

D) All of the above

4. The directivity of an antenna measures its ability to concentrate power in a specific direction compared to an isotropic radiator. This statement is:

A) True

B) False

C) True only for directional antennas

D) True only for omnidirectional antennas

5. What is the term for the power radiated by an antenna per unit solid angle in a particular direction?

A) Antenna Gain

B) Directive Gain

C) Radiation Intensity

D) Radiated Power

6. Which of the following is a primary application of magnetrons?

A) Satellite communication amplifiers

B) Radar transmitters

C) Broadband signal amplifiers

D) FM radio transmitters

7. In a TWT, the slow-wave structure can be a helix or a series of coupled cavities. The purpose of this structure is to:

A) Increase the electron beam voltage

B) Reduce the speed of the RF wave to match the electron beam speed

C) Generate the initial RF signal

D) Focus the electron beam

8. The anode block in a magnetron contains multiple resonant cavities arranged in a circular pattern around the cathode. This arrangement is crucial for:

A) Focusing the electron beam

B) Generating high-power oscillations

C) Modulating the electron velocity

D) Extracting the amplified signal

9. Which component in a klystron is responsible for introducing a small RF signal to initiate the velocity modulation process?

A) Catcher cavity

B) Drift tube

C) Input cavity

D) Repeller electrode

10. The radiation resistance of a half-wave dipole antenna is approximately:

A) 73 Ohms

B) 36.5 Ohms

C) 15 Ohms

D) 100 Ohms

11. If an antenna has a directivity of 10 and an efficiency of 0.8, what is its gain?

A) 12.5

B) 8

C) 10

D) 0.8

12. The gain of an antenna is always greater than or equal to its directivity. This statement is:

A) True

B) False

C) True only for lossless antennas

D) True only for isotropic antennas

13. Which parameter of a short dipole antenna is directly related to the average power radiated per unit solid angle?

A) Radiation Resistance

B) Directivity

C) Radiation Intensity

D) Gain

14. A circularly polarized wave can be generated using a:

A) Rectangular waveguide with a single probe

B) Circular waveguide with two probes excited 90 degrees out of phase

C) Rectangular waveguide with a single loop

D) Circular waveguide with a single loop

15. What is the condition for propagation in a waveguide?

A) The signal frequency must be equal to the cutoff frequency.

B) The signal frequency must be greater than the cutoff frequency.

C) The signal frequency must be less than the cutoff frequency.

D) The signal frequency can be any value.

16. Which of the following is NOT a mode of propagation in a waveguide?

A) TE (Transverse Electric)

B) TM (Transverse Magnetic)

C) TEM (Transverse Electromagnetic)

D) EE (Electric-Electric)

17. In a rectangular waveguide, if the larger dimension 'a' is twice the smaller dimension 'b' (a=2b), the cutoff frequency for the TE10 mode is given by c/(2a), where c is the speed of light. This statement is:

A) True

B) False

C) Depends on the dielectric

D) Depends on the mode

18. What is the primary function of the 'catcher' in a TWT?

A) To generate the initial RF signal

B) To collect the spent electron beam

C) To extract the amplified RF signal

D) To focus the electron beam

19. The 'reflex klystron' is a type of klystron that uses a single cavity and a:

A) Velocity modulating grid

B) Reflector electrode

C) Buncher cavity

D) Magnetic focusing system

20. Which microwave tube can be used as both an amplifier and an oscillator?

A) Klystron

B) Magnetron

C) Travelling Wave Tube (TWT)

D) Backward Wave Oscillator (BWO)

21. In a magnetron, the resonant cavities are part of the:

A) Cathode structure

B) Anode structure

C) Electron collector

D) Output coupler

22. Which of the following antenna characteristics quantifies how well an antenna concentrates radiated power in a particular direction?

A) Radiation Resistance

B) Bandwidth

C) Directivity

D) Efficiency

23. The maximum radiation intensity of a short dipole antenna occurs:

A) Along its axis

B) Perpendicular to its axis

C) At an angle of 45 degrees to its axis

D) In all directions equally

24. What is the relationship between gain (G) and directivity (D) of an antenna?

A) G = D * Efficiency

B) D = G * Efficiency

C) G = D / Efficiency

D) G = D + Efficiency

25. The radiation resistance of an antenna represents the equivalent resistance that would dissipate the same amount of power as the antenna radiates, when the same current flows through it. This statement is:

A) True

B) False

C) Partially true

D) Depends on the antenna type

26. An antenna with a radiation pattern that is uniform in all directions has a directivity of:

A) 0

B) 1

C) Infinity

D) Depends on the frequency

27. Radiation intensity (U) is defined as the power radiated per unit:

A) Volume

B) Area

C) Solid angle

D) Length

28. For a short dipole antenna of length 'l' much smaller than the wavelength 'λ', the radiation resistance is approximately proportional to:

A) l/λ

B) (l/λ)^2

C) (l/λ)^3

D) l^2/λ

29. Directivity of an antenna is the ratio of the radiation intensity in a given direction to the average radiation intensity over all directions. This average is calculated assuming:

A) A uniformly radiating source

B) A point source

C) The same total radiated power

D) The same input power

30. Antenna gain is defined as the ratio of the radiation intensity in a given direction to the radiation intensity of a reference antenna when both are fed with the same:

A) Voltage

B) Current

C) Input power

D) Frequency

31. What is the term for the total power radiated by an antenna in all directions?

A) Radiation Intensity

B) Directive Gain

C) Radiation Resistance

D) Radiated Power

32. The characteristic impedance of a waveguide is defined as the ratio of:

A) Electric field to magnetic field

B) Voltage to current

C) Transmitted power to reflected power

D) Waveguide height to width

33. In a rectangular waveguide, the electric field lines are parallel to the shorter dimension for the TE10 mode. This statement is:

A) True

B) False

C) Depends on the frequency

D) Depends on the dielectric material

34. What is the purpose of the 'helix' in a helix-type TWT?

A) To provide a magnetic field for focusing

B) To act as a slow-wave structure, matching the electron velocity to the RF wave velocity

C) To collect the spent electron beam

D) To modulate the electron beam

35. The magnetron uses crossed electric and magnetic fields to achieve:

A) Electron beam focusing

B) Velocity modulation

C) Microwave generation through electron oscillation

D) Signal amplification

36. The 'bunching' of electrons in a klystron occurs in which section?

A) Input cavity

B) Drift tube

C) Catcher cavity

D) Electron gun

37. Which mode has the lowest cutoff frequency in a standard rectangular waveguide?

A) TE10

B) TE11

C) TM11

D) TE01

38. What is the primary advantage of using a circular waveguide compared to a rectangular waveguide for certain applications?

A) Lower attenuation for the dominant mode

B) Easier to fabricate

C) Supports a single dominant mode (TE11) over a wider frequency range without mode degeneracy

D) Higher power handling capacity

39. What happens to a signal whose frequency is below the cutoff frequency of a waveguide?

A) It propagates with very low attenuation.

B) It is amplified.

C) It is attenuated exponentially and does not propagate.

D) It is reflected back to the source.

40. In a rectangular waveguide, the cutoff frequency is determined by the dimensions of the waveguide and the:

A) Permittivity of the dielectric material

B) Permeability of the dielectric material

C) Mode of propagation

D) Signal frequency

41. The dominant mode in a standard rectangular waveguide is:

A) TE10

B) TM11

C) TE20

D) TE01

42. Which type of waveguide is most commonly used for transmitting microwave signals due to its simpler manufacturing and lower attenuation?

A) Circular waveguide

B) Rectangular waveguide

C) Elliptical waveguide

D) Ridged waveguide

43. What is the typical operating frequency range for devices like klystrons, magnetrons, and TWTs?

A) Audio frequencies (20 Hz - 20 kHz)

B) Radio frequencies (3 kHz - 300 MHz)

C) Microwave frequencies (300 MHz - 300 GHz)

D) Infrared frequencies (300 GHz - 400 THz)

44. A key advantage of the Travelling Wave Tube (TWT) over a klystron for broadband amplification is its:

A) Higher efficiency

B) Simpler construction

C) Use of a single resonant cavity

D) Continuous interaction mechanism

45. Which component in a Magnetron is responsible for the interaction between the electron beam and the RF field, leading to oscillation?

A) Cathode

B) Anode block with resonant cavities

C) Focusing magnets

D) Output loop

46. What is the primary function of the 'catcher cavity' in a two-cavity klystron?

A) To modulate the electron beam velocity

B) To generate microwaves

C) To collect the bunched electron beam and extract energy

D) To focus the electron beam

47. In a Travelling Wave Tube (TWT), the electron beam interacts with the RF signal over the length of a:

A) Cavity resonator

B) Delay line

C) Magnetic field

D) Anode grid

48. The Magnetron is typically used for generating which type of microwave signals?

A) Low-power continuous wave (CW) signals

B) High-power pulsed signals

C) Low-frequency radio waves

D) Audio frequency signals

49. Which vacuum tube device is primarily used for amplifying microwave signals by using velocity modulation?

A) Magnetron

B) Klystron

C) Travelling Wave Tube (TWT)

D) Backward Wave Oscillator (BWO)

Microwave generation - klystron, magnetron, travelling wave tubes, waveguides - rectangular and cylindrical, antenna characteristics - short dipole radiation, antenna gain, directivity, radiation resistance, radiation intensity - Question Bank