Time:  Three Hours                     Maximum : 100 Marks

Answer All The Questions

PART - A (2 x 10 = 20 Marks)

1.  With the help of electronic admittance diagram explain the modes of a reflex
klystron oscillator.

2.  A two-cavity klystron operates at 10 GHz with I0 = 3.6 mA, V0 = 10KV. The
drift space length is 2 cms, the output cavity total shunt conductance is Gsh = 20 µ
mho and the beam coupling coefficient ß2  = 0.92. Find the maximum voltage

3.  Explain the use of a PIN device as a single switch and a double switch circuits.

4.  Give the comparison between IMPATT, TRAPATT and BARITT diodes
considering their performance characteristics and applications.

5.  Establish the relation between Z and S matrices of a two-port network.

6.  Derive the scattering matrix of a H plane T.

7.  Explain the concept of choke flange and how it is realized in microwave joint. 

8.  Explain the use of magic T in a balanced microwave mixer.

9.  Explain the principle of the power meter double bridge circuit for microwave
power measurement.

10.  A crystal detector generates a signal of 10 m V for an incident microwave power
of -25 dBm. What is the detector sensitive in mV/ mW ? Why is the microwave
signal amplitude modulated by a 1 KHz square wave before it is applied to a
crystal detector?

 PART - B (5 x 16 = 80 Marks)

11.   Derive the expressions for power output and efficiency of a reflex klystron


 A reflex klystron operators at frequency 5 KHz with repeller space L =- 0.5 cm,
dc beam voltage V0 =300V, beam current I0 = 20 mA, repeller voltage - VR volt
for 1¾ mode. Calculate (i) maximum power output (ii) repeller voltage, (iii) the
bandwidth for the range of .VR = 1V, (iv) efficiency.

12.a)  Explain with the help of neat diagram the construction and amplification process
in TWTA. Draw the rf power output and gain characteristic curves.

 A helix TWT operates at 5 GHz under a beam impedance 8KV and beam current
400 mA. The helix impedance is 20 ohm and the interaction length is 25 cm. Find
the output power gain in dB.

 (OR )

12.b)   Draw the schematic diagram of a cylindrical magnetron tube oscillator. If a & b
are outer & inner radii of the cathode and anode cylinders respectively, derive the
expression for the cut off magnetic field Bc. Give three important application of
magnetron with power and frequency specifications. 

 A cylindrical magnetron with 16 resonators is operated at 1 GHz with a = 3 cm,
b= 5 cm, V0= 20 KV, B0 = 0.1 Tesla. Find the Hartree voltage.

13.a)  Draw the electrical equivalent circuit of a Gunn diode explaining the parameters.
Explain with diagram how a Gunn diode oscillator can be designed using
rectangular waveguide in X-band. Give typical power output and frequency
tuning range achievable. What is the difficulty in obtaining very high power?
The drift velocity of electrons is 3 x107 cm/s, through the active region of length
20 x 10-4 cm. Calculate the natural frequency of the diode and the critical voltage
for GaAs. Critical field for GaAS is 3.2 KV / cm.

13.b)  Explain how Varactor diode is used as frequency multiplier, State and explain
Man1ey Rowe relations with the help of the circuit diagram.

A sinusoidal input signal at frequency fs and pump signal at frequency fp are
applied across a varactor diode. If the output circuit is a bandpass filter with
resistive series load at frequency fs + fp, calculate the power gain.

14.a)  What are the properties of S parameters of a perfectly matched, lossless,
reciprocal microwave network?

 A matched magic-T is terminated at collinear ports 1&2 and difference port 4 by

impedances of reflection coefficients G1 = 0.5, G2 = 0.6 & G4 = 0.8 respectively. If
I-watt power is fed at a sum port 3, calculate the power reflected at port 3 &
power transmitted to other three ports.

14.b)  Explain with a schematic diagram. The working principle of a four part circulator
  and how it is achieved. A three port circulator has an insertion loss of dB,
  isolation 30 dB and VSWR = 1.5. Find the S-matrix.

15.a)  Why VSWR> 20 is not measured directly by VSWR meter? Explain the theory
of double minimum method of experimentally determining high VSWR of a load
by using w/g-slotted line. What are the possible errors in the slotted line method?


15.b)  Define antenna test ranges. Explain with a schematic diagram the antenna gain
measurement with three-antenna method. How do you predict about the
polarization of the signal from the measured output voltage pattern?

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