WBUT Question Papers B Tech EC Rf And Microwave Engineering Sem 7th 2008

WBUT Question Papers B Tech EC

 Rf And  Microwave Engineering Sem 7th 2008


Time : 3 Hours ]

GROUP-A (Multiple Choice Type Questions)

Choose the correct alternatives for any ten of the following :

1) A hollow waveguide behaves as

a)    Low Pass Filter   b) Band Pass Filter

c)    High Pass Filter  d) All Pass Filters.

H) If the height of the rectangular waveguide is halved, its cut-off wavelength for the dominant mode will  •

a)              be halved                              –

b)               remain unchanged

c)              be doubled

d) be ^ of its previous value, ill) The dominant mode of propagation in a circular waveguide is






iv)            In transmission through a waveguide, the maximum and minimum values of VSWR obtained under loaded conditions are     .


a) 1 and 0 c) Infinity and 1

b) Infinity and zero d) – 1 and + 1.




v)   A disadvantage of microstrip compared with strlpline Is that

a)  does not lend Itself rapidly to printed circuit technique

b)              is more likely to radiate

c)              is more complex to manufacture

d)              Is bulkier.

vi)            Microwave components are generally characterized by a) h-parameter

b) z-parameter c) s-parameter d) {/-parameter.

vli) A Travelling Wave Tube (TWT) is basically


 an oscillator b) a tuned amplifier

c) a Wideband amplifier   d) a transmission line.

viii) P-l-N diode is used as

a)  a phase shifter  b) an amplifier

c) an oscillator          d) an Isolator.

» ■ ■ ■, ■ . ix} In a VSWR measurement, a square law detector is used to detect the signal level. The current meter connected Jto the circuit reads 64 mA and 16 mA as maximum and minimum currents respectively, the VSWR is

a) 4                           b) 2

c) 0-25                   d) zero.

x)              Large mirowave power can be measured by


VSWR meter                  b) Bolometer                              *

c) Calorimeter-wattmeter  d) Thermistor.            |

xi)            Caseagraln Feed is used with a parabolic reflector to

a)              Increase the beam width of the system

b)              increase the gain of the system /

c)              allow the feed to be placed at a convenient point

d)              reduce the size of the main reflector.

xii)          The uplink and downlink frequencies of satellite communication are

a)              6 GHz, 4 GHz              ,b) 4 GHz, 6 GHz

c)    6 GHz, 6 GHz              d) 3 GHz, 5 GHz.    |

77103 (4/12)


GROUP -B ( Short Answer Type Questions)

/      Answer any three of the following.     3×5=15

  1. 2.             An air filled rectangular waveguide of Inside dimensions 7-0 cm x 3-5 cm operates in the dominant mode.

a)              Find the cut-off frequency

b)               Determine the guided wavelength at 1-5/ c, where fc is the cut-off frequency.

  1. 3.              From the properties of a Magic – T, derive the S – matrix of the ideal magic T.
  2. 4.              Distinguish between the basic principles of working of

a)              a Gunn diode and

b)              an Impatt diode.

  1. 5.              Derive the Radar Range Equation.
  2. 6.              Describe the operating principle of a precision type variable attenuator.

GROUP -C ( Long Answer Type Questions)

Answer any three questions.       3×15 = 45

  1. 7.              a) Define the term ‘Dominant Mode’ and explain why wave propagation in a hollow

metallic waveguide is preferred in this mode.

b)              Given for propagating TE 10 mode in a rectangular waveguide (axb),

H z = A cos ~ e~$z A/m, where symbols have their usual meanings, find the expressions of E „ and H „ . Hence, determine the expression of the wave

y                   x


c)              Explain why a pure TEM mode is not supported by hollow rectangular wave guide.

d)              Explain why a rectangular waveguide is preferred over p. square waveguide for usual microwave transmission.     4 + 6 + 2 + 3

  1. 8.              a) Derive an expression for the resonance frequency of a rectangular cavity

( a x b x I), made of a rectangular waveguide with I.D. ( a x b) in TE 101 mode.

b)              Define ‘Quality Factor’ of a cavity resonator. Discuss the steps involved in finding an expression for ‘0-factor’ of the cavity.

c)   Discuss how such a cavity is excited using a co-axial line. 5 + 2 + 6 + 2= 15


  1. 9.              a) Describe an ideal Directional coupler’. Define Coupling’ and Directivity’ in the

context of a directional coupler.  .

b)               Explain the design of a 2-hole directional coupler,in redt angular waveguide version for a given coupling. Mention the principal shortcoming of such a directional coupler. Discuss how this shortcoming can be overcome.

c)              A directional coupler has a coupling factor of 15 dB and directivity of 30 dB. If the power in the coupled port Is 32 microwave, find the power in the input port and insertion loss. 5 + 5 + 5

  1. 10.        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 theoperation of a klystron tube.

c)               Draw the power us repeller voltage and frequency us repeller voltage characteristics of a reflex kystron. Explain qualitatively.                                    5 + 5 + 5

  1. 11.        a) Discuss the various means of providing fixed and variable susceptances in

rectangular waveguide circuits.

b)               Describe the working principle of a Faraday Rotation Isolator.

c)               In microwave measurements, discuss the role of a slotted line.  6 + 6 + 3

  1. 12.        Write short notes on any three of the following :        3×5

a)               Industrial Application of microwaves

b)               Operating Principles of MTI radar

c)               Optimum length and Flare angle of a horn antenna

d)              Structural Characteristics of Microwave Transistors

e)              Tunnel Diode.


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