Model Questions on RF & Microwave Engineering

(Paper code: EC601)

Choose the correct alternatives

1. Which of the following modes does not exist in a rectangular waveguide?
(a) TE (b) TM (c) TEM (d) TE & TM
2. When electromagnetic waves are propagated in a waveguide, they
(a) travel along the broader walls of the guide.
(b) are reflected from the walls but do not travel along them.
(c) travel through the dielectric but do not travel along them
(d) travel along four walls of the waveguide.
3. The dominant mode in a waveguide is characterized by
(a) longest cutoff wavelength (b) shortest cutoff wavelength
(c) infinite attenuation (d) Zero attenuation
4. The cut-off frequency for the dominant mode in a rectangular waveguide with ID: 4cmX
2.5cm is
(a) 7.5 GHz (b) 6 GHz (c) 4.5 GHz (d) 3.75 GHz
5. When electric component of an electro magnetic wave is in the direction of propagation, the
resulting mode is
(a) transverse electric (b) transverse magnetic
(c) longitudinal (d) transverse electromagnetic.
6. The wavelength of a wave in a waveguide is
(a) equal to the broad dimension of the waveguide
(b) less than the free space wavelength
(c) greater than the free space wavelength
(d) inversely proportional to the operating frequency.
7. The propagation in a hollow waveguide below cutoff is not possible at a frequency below the
cutoff frequency, because
(a) copper loss is prohibitively large
(b) waveguide dimension becomes unmanageable
(c) wave impedance is imaginary
(d) wave impedance is negative.
8. The wave impedance offered by the waveguide to the propagating mode is
   
  (b)
(a) (c) (d)
    
9. The phase velocity at a frequency f for mode with cut-off frequency as f c (in hollow
waveguide) is
2
(a) v p  c 1   f  (b) v p  c
 fc  2
1   f 
 fc 
2
(c) v p  c 1   c 
f
(d) v p  c
 f 2
1   c 
f
 f

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 1

Model Questions on RF & Microwave Engineering
(Paper code: EC601)
10. Out of three types of mode: TEM, TE and TM, hollow waveguide supports
(a) TEM, TE and TM (b) TEM and TE (c) TEM and TM (d) TE and TM.
11. Waveguides are used mainly for microwave signals because
(a) the depend on straight line propagation which applies to microwaves only.
(b) losses would be too heavy at lower frequencies.
(c) there is no generators powerful enough to excite them at lower frequencies.
(d) they would be too bulky at lower frequencies.
12. The wavelength of a wave in a waveguide
(a) is greater than in free space.
(b) depends only on the waveguide dimensions and free-space wavelength.
(c) is inversely proportional to the phase velocity.
(d) is directly proportional to the group velocity.
13. The main difference between the operation of transmission lines and waveguides is that
(a) the later are not distributed, like transmission lines.
(b) the former can use stubs and quarter-wave transformers, unlike the later.
(c) transmission lines do not suffer from low-frequency cutoff.
(d) terms such as impedance matching and standing-wave ratio cannot be applied to
waveguide.
14. When a particular mode is excited in a waveguide, there appears an extra electric
component, in the direction of propagation. The resulting mode is
(a) transverse-electric (b) longitudinal
(c) transverse-magnetic (d) transverse-electromagnetic
15. When electromagnetic waves are reflected at an angle from a wall, their wavelength along
the wall is
(a) the same as in free space
(b) the same as the wavelength perpendicular to the wall
(c) shortened because of the Doppler effect
(d) greater than in the actual direction of propagation
16. As a result of reflections from a plane conducting wall, electromagnetic waves acquire an
apparent velocity greater than the velocity of light in free space. This is called the
(a) velocity of propagation (b) normal velocity (c) group velocity (d) phase velocity
17. A signal propagated in a wave guide has a full wave of electric intensity change between
the two further walls, and no component of the electric field along the direction of
propagation. The mode is
(a) TE11 (b) TE10 (c) TM22 (d) TE20
18. For some applications, circular waveguides may be preferred to rectangular ones because of
(a) the smaller cross section needed at any frequency (b) lower attenuation
(c) freedom from spurious modes (d) rotation of polarization
19. Indicate which of the following cannot be followed by the word “waveguide”
(a) Elliptical (b) Flexible (c) Coaxial (d) Ridged
20. In order to reduce cross-sectional dimensions, the waveguide to use is
(a) circular (b) ridged (c) rectangular (d) flexible
21. For low attenuation, the best transmission medium is
(a) flexible waveguide (b) ridged waveguide (c) rectangular waveguide (d) coaxial line

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 2

Model Questions on RF & Microwave Engineering
(Paper code: EC601)
22. Waveguide is a/an
(a) band pass filter (b) high pass filter (c) low pass filter (d) all pass filter.
23. Which of the following wave guide tuning components is not easily adjustable?
(a) Iris (b) Stub (c) Screw (d) Plunger.
24. Distance between maxima and minima of a standing wave is
 3 
(a) (b)  (c) (d)
2 4 4
25. The dominant mode in a rectangular wave guide is
(a) TE01 (b) TM01 (c) TE10 (d) TM11
26. The dominant mode in a waveguide is characterized by
(a) longest cutoff wavelength (b) transverse electromagnetic
(c) infinite attenuation (d) zero attenuation
27. In a rectangular cavity resonator having a= width, b=height and d = length for a>b<d, the
dominant mode is
(a) TE101 (b) TM101 (c) TE110 (d) TM110
28. In a circular waveguide with radius ‘r’, the dominant mode is
(a) TM01 (b) TE01 (c) TM11 (d) TE11
29. The degenerate modes in a wave guide are characterized by
(a) same cutoff frequencies but different field distribution
(b) same cutoff frequencies and same field distribution
(c) different cutoff frequencies but same field distribution
(d) different cutoff frequencies and different field distribution
30. Which of the following is not possible in a circular wave guide?
(a) TE10 (b) TE01 (c) TE11 (d) TE12
31. For TE or TM modes of propagation in bounded media, the phase velocity
(a) is independent of frequency (b) is a linear function of frequency
(c) is a non linear function of frequency
(d) can be frequency-dependent or frequency independent depending on the source
32. A waveguide operated below cut-off frequency can be used as
(a) a phase shifter (b) an attenuator (c) an isolator (d) directional coupler
33. If the height of the waveguide is halved, its cut-off wavelength will
(a) be halved (b) be doubled (c) remain unchanged (d) be ¼ of the previous value
34. In order to couple two generators to a waveguide system, one could not use a
(a) rat-race (b) E-plane T (c) hybrid ring (d) magic T.
35. Waveguides are not feasible at low frequencies because the
(a) circuit dimensions are small compared to a wavelength
(b) circuit dimensions are large compared to a wavelength
(c) circuit dimensions are comparable to the wavelength
(d) circuit dimensions do not come into picture
36. A cavity may be considered as
(a) low-pass filter (b) high-pass filter (c) band-pass filter (d) band-reject filter
37. Electromagnetic cavity resonators as energy store devices are used in
(a) Klystron (b) TWT (c) BWO (d)

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 3

Model Questions on RF & Microwave Engineering
(Paper code: EC601)
38. Microwave semiconductor devices are basically
(a) positive resistance device (b) positive differential device
(c) negative resistance device (d) negative differential resistance device.
39. A Traveling Wave Tube (TWT) is basically
(a) an oscillator (b) a tuned amplifier
(c) a wideband amplifier (d) both amplifier and oscillator
40. The cavity magnetron uses strapping to
(a)prevent mode jumping (b) improve the phase focusing effect
(c) ensure bunching (d) prevent cathode back-heating
41. A transmission line has a VSWR of 2. The reflection coefficient is
(a) 1/3 (b) 0 (c) 3 (d) ½
42. The advantage of TWT over multicavity klystron is that it
(a) has a greater bandwidth (b) is more efficient
(c) has a higher number of modes (d) produces higher output power.
43. Microwave components can be characterized by
(a) h-parameter (b) y-parameter (c) s-parameter (d) z-parameter.
44. A matched termination is a
(a) tapered capacitive load (b) tapered inductive load
(c) tapered resistive load (d) tuned circuit load.
45. One of the reasons why vacuum tubes eventually fail at microwave frequencies is that their
(a) noise figure increases (b) transit times becomes too short
(c) multiple or coaxial leads are used (d) the anode voltage is made larger
46. The multicavity klystron
(a) is not a good low-level amplifier because of noise
(b) has a high repeller voltage to ensure a rapid transit time.
(c) is not suitable for pulsed operation
(d) needs a long transit time through the buncher cavity to ensure current
modulation
47. The TWT is some times preferred to the multi cavity klystron amplifier, because it
(a) electrons are accelerated by the gap voltage on their return
(b) returning electrons give energy to the gap oscillations
(c) it is equal to the period of the cavity oscillation
(d) the repeller is not damaged by striking electrons.
48. The transit time in the repeller space of a reflex klystron must be n  3 / 4 cycles to ensure
that
(a) electrons are accelerated by the gap voltage on their return
(b) returning electrons give energy to the gap oscillations
(c) it is equal to the period of the cavity oscillations
(d) the repeller is not damaged by striking electrons
49. The cavity magnetron uses strapping to
(a) prevent mode jumping (b) prevent cathode back-heating
(c) ensure bunching (d) improve the phase focusing effect

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 4

Model Questions on RF & Microwave Engineering
(Paper code: EC601)
50. A parametric amplifier must be cooled
(a) because parametric amplification generates a lot of heat
(b) to increase bandwidth
(c) because it can not operate at room temperature
(d) to improve the noise performance
51. In Gunn diodes, electrons are transferred from
(a) high to low mobility energy bands (b) low to high mobility energy bands
(c) valley to domain formation (d) domain to valley formation
52. Helix is used in TWT
(a) reduces the band width (b) acts as a coaxial line
(c) reduce inductance/unit length (d) increase phase velocity
53. Klystron operates on the principle of
(a) amplitude modulation (b) frequency modulation
(c) pulse modulation (d) velocity modulation
54. In a traveling-wave tube, the phase velocity of the axial component of the field on the slow
wave structure is kept
(a) equal to the velocity of the electrons
(b) slightly less than the velocity of electrons
(c) slightly more than the velocity of electrons
(d) equal to the velocity of light in free space
55. In laboratory experiments the output from reflex klystrons are modulated by square waves
because
(a) it is easy to generate a square wave
(b) crystal diode operates in the square law region of the I-V characteristics
(c) it prevents frequency modulation
(d) detector circuit is less complicated
56. The kinetic energy of beam remains unchanged in the interaction between an electron beam
and an RF wave in a
(a) multi-cavity klystron (b) crossed-field amplifier
(c) traveling-wave tube (d) gyrotron
57. Which one of the following is a transferred electron device?
(a) BARITT diode (b) IMPATT diode (c) Gunn diode (d) Step recovery diode
58. One of the following is not used as a microwave mixer or detector:
(a) crystal diode (b) schottky-barrier diode (c) Gunn diode (d) PIN diode
59. Which one of the following can be used for amplification of microwave energy?
(a) Travelling wave tube (b) Magnetron (c) Reflex klystron (d) Gunn diode
60. In a reflex klystron, the velocity modulation
(a) occurs near the reflector (b) occurs in the resonator gap
(c) occurs near the accelerating grid (d) does not occur at all
61. As an ideal local oscillator for microwave frequency measurements, the most suitable
microwave source is a
(a) Multi-cavity magnetron (b) Reflex klystron
(c) Double cavity klystron (d) Travelling wave tube
62. One of the following microwave diodes is suitable for very low-power oscillators only
(a) Tunnel (b) avalanche (c) Gunn (d) IMPATT

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 5

Model Questions on RF & Microwave Engineering
(Paper code: EC601)
63. The transferred electron bulk effect occurs in
(a) germanium (b) gallium arsenide (c) silicon (d) metal semiconductor junction
64. A parametric amplifier sometimes uses a circulator to
(a) prevent noise feedback
(b) allow the antenna to be used simultaneously for transmission and reception
(c) separate the signal and idler frequencies
(d) permit more efficient pumping
65. 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

66. The biggest disadvantage of the IMPATT diode is its

(a) lower efficiency than that of the other microwave diodes (b) high noise
(c) inability to provide pulsed operation (d) low power handling ability
67. A backward-wave oscillator is based on the
(a) a rising sun magnetron (b) crossed-field amplifier
(c) co-axial magnetron (d) traveling-wave tube
68. Which one of the following can be used for amplification of microwave signals?
(a) Gunn diode (b) Magnetron (c) Reflex klystron (d) double cavity klystron
69. The Secondary cavity in a two cavity klystron is called
(a) Catcher cavity (b) Buncher cavity (c) velocity modulation cavity (d) multi cavity
70. The modes in a reflex klystron:
(a) give the same frequency but the different transit time
(b) result from excessive transit time across the resonator gap
(c) are caused by spurious frequency modulation
(d) are just for theoretical consideration
71. Magnetron is a
(a) High power amplifier (b) Low power amplifier
(c) high power oscillator (d) Low power oscillator.
72. Cylindrical cavity resonators are not used with klystron because they have
(a) Q that is too high (b) too heavy losses (c) harmonically related resonant frequencies
(d) a shape whose resonant frequency is too difficult to calculate
73. The following device is suitable for very low power oscillator circuits only:
(a) Gunn diode (b) Tunnel diode (c) IMPATT diode (d) TRAPATT diode
74. The behavior of which of the following device is governed by bulk effect?
(a) PIN diode (b) Gunn diode (c) Tunnel diode (d) IMPATT diode
75. Magic Tee is a combination of
(a) one H and one E plane tee (b) Two Hs and one E plane tee
(c) one H tee and two Es plane tee (d) two Hs and two Es plane tee.
76. Tees and junctions constitute:
(a) single port network (b) two port network
(c) three port network (d) three or more port network

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 6

Model Questions on RF & Microwave Engineering
(Paper code: EC601)
77. If the peak transmitted power in a RADAR system is increased by a factor of 16, the
maximum range will be increased
(a) 2 times (b) 4 times (c) 8 times (d) 16 times.
78. Microwave ovens operates at a frequency of
(a) 1.37 GHz (b) 2.15 GHz (c) 3.37 GHz (d) 22 GHz
79. A multihole directional coupler is preferred to two-hole directional coupler
(a) because it is more efficient (b) to increase coupling of the signal
(c) to reduce spurious mode generation (d) to increase the bandwidth of the system.
80. Radar cross-section of a target has the unit of
(a) time (b) area (c) speed (d) volume.
81. A disadvantage of microstrip compared with stripline is that microstrip
(a) does not readily lend itself to printed circuit technique
(b) is more likely to radiate
(c) is bulker
(d) is more expensive and complex to manufacture
82. The transmission system using two ground plane is
(a) microstrip (b) elliptical waveguide (c) parallel-wire line (d) stripline
83. 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
84. Indicate which of the following diodes does not use negative resistance in its operation:
(a) Backward (b) Gunn (c) IMPATT (d) Tunnel
85. Attenuator is a
(a) pure resistance network producing a constant attenuation
(b) pure resistance network producing a variable attenuation at variable frequencies
(c) pure resistance producing a constant attenuation at all frequencies
(d) pure resistance producing a constant attenuation at low frequencies
86. In Faraday’s induction phenomenon, a changing magnetic field is accompanied by an
electric field. Which of the following equation represents it?
 
    B  E
(a) .E  (b) .B  0 (c)   E   (d)   B  
 t t
87. Cassegrain feed is used with a parabolic reflector to
(a) increase the gain of the system
(b) increase the beam width of the system
(c) reduce the size of the main reflector
(d) allow the feed to be placed at a convenient point
88. For microwave propagation through microstrip lines, there will be
(a) radiation, eddy current and dielectric losses
(b) dielectric, ohmic and hysteresis losses
(c) dielectric, ohmic and radiation losses
(d) ohmic, hysteresis and eddy current losses
89. The position of the probe for half power points in the slotted line of a microwave bench
are interpreted to measure
(a) guide wavelength (b) load impedance (c) source frequency (d) high SWR

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 7

Model Questions on RF & Microwave Engineering
(Paper code: EC601)
90. The intrinsic impedance of free space is known to be 377Ω. The intrinsic impedance of a
medium with relative permittivity and permeability of 4 and 1 respectively will be
(a) 75 Ω (b) 94 Ω (c) 188 Ω (d) 377 Ω
91. “Double minimum” method is relevant to the measurement of
(a) low attenuation constant (b) high attenuation constant
(c) high VSWR (d) low VSWR
92. In a VSWR measurement, a square law detector is used to detect the signal level. The
voltmeter reads maximum and minimum as 64mV and 16mV respectively. The VSWR of
the system will be
(a) 2 (b) 4 (c) 8 (d) 16
93. In a line the VSWR of a load is 6dB. The reflection coefficient will be
(a) 0.033 (b) 0.33 (c) 0.66 (d) 3.3
94. The maximum theoretical output circuit efficiency of a double resonator klystron amplifier is
(a) 25% (b) 50% (c) 58% (d) 85%
95. A two-port non-reciprocal device which produces a minimum attenuation to electro
magnetic wave propagation in one direction and a very high attenuation in opposite
direction is generally known as
(a) phase shifter (b) isolator (c) polarizer (d) circulator

96. A metal probe inserted into a rectangular waveguide through broader wall of the guide will
provide a property across the guide. This property is a
(a) shunt (b) reactance (c) reverberation (d) resonance
97. In a microwave measurement set-up, the power reaching to the load is found to be 50mW. If
a 3dB coupler is placed before the load, the power to the load will be
(a) 50mW (b) 25mW (c) 12.5mW (d) 62.5mW
98. Which transmission line is ideal for handling high powers?
(a) co-axial line (b) microstrip (c) strip line (d) rectangular waveguide
99. One of the following is not use as a microwave mixer or detector
(a) crystal diode (b) schottky diode (c) backward diode (d) PIN diode
100. Which of the following is not an advantage of stripline over microstrip?
(a) higher Q
(b) lower tendency to radiate
(c) higher isolation between the adjacent circuits
(d) easier integration with semiconductor devices
101. Microstrip is similar to the
(a) rectangular waveguide (b) circular waveguide
(c) microwave cavity resonator (d) flat co-axial transmission line

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 8

Model Questions on RF & Microwave Engineering
(Paper code: EC601)

Short Answer Type Questions

1. What does the cut-off frequency of a waveguide mean? Deriving the necessary equation
discuss the different factors on which the cut-off frequency of a rectangular waveguide
depend? 1+4
2. An air filled rectangular waveguide of inside dimensions 7X3.5 cm operates in the dominant
TE10 mode.
(i) Find the cut-off frequency (ii) Determine the guided wavelength of 3.5GHz.
3. Define the term ‘Dominant Mode’ and explain why wave propagation in a hollow metallic
waveguide is preferred in this mode. 2+3
4. Draw the electric and magnetic field configurations in the (i) transverse cross-section (ii) over
a longitudinal section of the rectangular waveguide for the dominant mode.
5. Explain with neat sketches including field distributions how a rectangular waveguide in
dominant mode is excited by a coaxial line
6. Define quality factor Q of a resonator, what does unloaded, loaded and external Q mean 2+3
7. Describe critical coupling, over-coupling and under-coupling. Draw the variation of VSWR
with coupling coefficient. 3+2
8. Describe the operating principle of H-plane and E-plane Tee
9. Derive the scattering matrix of Magic Tee.
10. Describe the operation of four-port microwave circulator
11. Write down the limitations of conventional vacuum tubes over the microwave tubes.
12. With the aid of a schematic diagram, describe the traveling wave tube.
13. Determine the spacing between 2-holes in a 2-hole directional coupler made in rectangular
waveguide version with I.D 2.286cm X 1.00cm at 9GHz.
14. Draw the power vs repeller voltage and frequency vs repeller voltage characteristics of a
reflex klystron. Explain qualitatively.

15. Short notes

(a) Cavity magnetron
(b) Reflex klystron
(c) Industrial application of microwaves
(d) Techniques used for microwave power measurement

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 9

Model Questions on RF & Microwave Engineering
(Paper code: EC601)

Long Answer Type Questions

1. Derive the electromagnetic field equations in rectangular waveguide for TE mode. Hence,
obtain the cut-off frequency for TE10 mode in terms of waveguide dimension. Explain why
TE10 is called dominant mode. 10+3+2
2. Derive the electromagnetic field equations in rectangular waveguide for TM mode. Determine
the expression of the wave impedance. Explain why TM10 or TM01 is not possible in
rectangular waveguide. 10 + 3+2
x  jz
3. Given for propagating TE 10 mode in a rectangular waveguide a  b  , H z  A cos e A/m,
a
where symbols have their usual meanings, find the expressions of E y and H x . Hence,
determine the expression of the wave impedance. Explain why a rectangular waveguide is
preferred over a square waveguide for usual microwave transmission. 10 + 5
4. Derive the expressions of the electromagnetic field equations in cylindrical waveguide with
circular cross section for TE mode. Determine the expression of the wave impedance 10+5
5. Derive the expressions of the electromagnetic field equations in cylindrical waveguide with
circular cross section for TM mode. Determine the expression of the wave impedance 10+5
6. Define the cutoff frequency and guide wavelength in a rectangular waveguide. Derive the
expression of the guide wavelength in terms of the relevant parameters. Determine the values
of the cut off frequency, characteristic wave impedance and the guide wavelength in a hollow
rectangular wave-guide with inside dimensions 2.286 x 1.00 cm at 9GHz for the dominant
mode. 4+4+7
7. (a) Discuss the various considerations in choosing the cross sectional dimensions of a
rectangular waveguide
x
(b) Given E y  A sin e  jz v/m to be the electric field in the transverse cross-section of the
a
of the hollow metallic rectangular waveguide with inside dimensions as ‘ax b’. Derive the
expression for the power transported in the dominant mode.
(c) If a=2.286 cm, b=1.0 cm, and A=2 v/m then calculate the power in the dominant mode at
9 GHz. 3+6+6
8. A 6 GHz electromagnetic wave propagates in a rectangular waveguide, the separation between
the planes being 3cms. Determine the cutoff wavelength of the dominant mode, the guide
wavelength of the dominant mode, the corresponding group as well as phase velocities, and
the characteristic wave impedance. 15
x  jz
9. (a) Starting from H z  A cos e , Derive an appropriate for the power transported through
a
a hollow metallic rectangular waveguide in the dominant mode.
(b) Explain the causes responsible for attenuation of the wave power in a rectangular
waveguide. 9+6

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 10

Model Questions on RF & Microwave Engineering
(Paper code: EC601)
10. (a) Derive an expression for the electric field inside a rectangular cavity ( a  b  l ) made of a
rectangular waveguide with I.D ( a  b ) in TE101 mode.
(b) Explain with neat sketches including field distributions the mode TE101 in a rectangular
cavity made of a rectangular waveguide carrying dominant mode and closed at two ends
by shorting plates.
(c) Discuss how you can determine the ‘Q’ factor of the cavity. 7+5+3
11. (a) Derive an expression for the resonant frequency of a rectangular cavity ( a  b  l ) with
a  b  l and hence obtain the dominant mode of resonance.
(b) Define ‘Q-factor’ of a cavity. Discuss the steps involved in determining ‘Q-factor’ of the
cavity. Distinguish between ‘loaded Q’ and ‘unloaded-Q’ of the cavity. 7+(2+3+3)
12. (a) Discuss the working principle of a ‘Magic-T’
(b) Obtain the scattering matrix equation of a ‘Magic-T’ by using the necessary properties of
the scattering matrix
(c) Explain why ‘scattering Matrix’ representation of a microwave network is preferred over
Z-matrix or Y-matrix representation 5+7+3
13. (a) Describe an ideal ‘Directional coupler’ and write its ‘Scattering Matrix’. Define
‘Coupling’ and ‘Directivity’ in the context of a directional coupler.
(b) Explain the design of a 2-hole directional coupler in rectangular wave-guide version for a
given coupling. Mention the principal shortcoming of such a directional coupler. Discuss
how this shortcoming can be overcome.
14. (a) Compare and contrast the bunching operation in a two cavity klystron and reflex klystron.
(b) What is a slow wave structure? Why does the TWT need such a structure? Explain the
beam& RF interaction in such a tube.
(c) What is the function of magnetic field in a traveling wave tube? 5+(2+2+3)+3
15. Draw the neat diagram of a two cavity Klystron. Show all voltages with proper polarities.
Explain the phenomenon of bunching with the help of the Applegate diagram. 6+9
16. Describe the operation of microwave isolator. What are parametric amplifiers? How are they
differing from conventional amplifiers? 5+8+2
17. (a) What are the different measurement techniques for measuring microwave power?
(b) How can you measure the microwave peak power from average power?
(c) Explain clearly an experimental setup to measure the high value of microwave power.
(d) Define the terms directivity and coupling factor of a directional coupler 3+2+5+2+3
18. (a) Discuss the working principle of an ‘Absorption type wave meter’
(b) Describe the various means of measuring frequency of a microwave signal using a
microwave bench. 5+10
19. (a) Explain the slotted line method for the measurement of unknown impedance.
(b). Explain the basic blocks in a VSWR meter. Describe the procedure for measuring
(i) VSWR (<10) and (ii) VSWR (>10) using a VSWR meter in a microwave bench. 7+8

20. (a) Explain the working principle of a reflex klystron oscillator

(b) Explain what is meant by ‘velocity modulation’ and how this phenomenon is used in the
operation of a klystron tube.
(c) Draw the power vs repeller voltage and frequency vs repeller voltage characteristics of a
reflex klystron. Explain qualitatively. (5+5+5)

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 11

Model Questions on RF & Microwave Engineering
(Paper code: EC601)

Numerical
1. Calculate the propagation constants and phase velocities for the TE10 and TE11 modes for
a rectangular waveguide with inside dimensions 7.214cm x 3.404cm operating at 5 GHz.
2. An air filled cylindrical waveguide of internal diameter 5 cm supports the TE11 mode.
Determine the cut-off frequency, guide wavelength and wave impedance at 3 GHz.
3. A rectangular waveguide is characterized by a=6 cm and b=3 cm. Find the cut-off
frequency, guide wavelength and phase shift constant for the dominant mode.
4. Determine the length of a cavity which will resonate at 10 GHz. The cavity is made from
WG16 of the shortest length. Calculate the Q factor.
5. A rectangular cavity has cross-section 0.38 x 0.76 cm. If it oscillates in the TE102 mode at
50 GHz, calculate the length (l) of the cavity with air dielectric. Are there other modes
with the same resonant frequency?

Prepared by Dr. Sunandan Bhunia, CIT, Kokrajhar 12