# Mumbai University Previous year question papers

## Microwave devices and Circuits

N.B. (1) Question No.1 is compulsory,

(2) Attempt any four questions from remaining six questions.

(3) Figures to the right indicate full marks,

1. Attempt any four :- 20

(a) Explain group velocity and phase velocity in rectangular waveguide.

(b) What is back heating? How can it be avoided?

(c) Explain Gunn effect using two valley theory.

(d) What are the advantages of microwave frequencies over low frequency?

(e) Explain Rat-Race junction.

2. (a) Compare the multicavity Klystron and TWT from the point of view of basic construction, performance and applications.

(b) A pulsed cylindrical magnetron is operated with the following parameters :- 10

Anode voltage = 25 kV, Beam current = 25A

Magnetic flux density = 0.34 wb/m2 ~ Ra = 5 cm, Rb = 10 cm.

Calculate

(i) Angular frequency

(ii) The cut off voltage

(iii) Cut off magnetic flux density.

3. (a) Derive the wave equation for a TM wave and obtain all the field components in a rectangular waveguide.

(b) A TE11 mode is propagating through a circular waveguide having an air dielectric and a radius of 5 cms. Calculate the cut off frequency, guide wavelength and the wave impedance.

4. (a) (i) For TE101 mode in a rectangular cavity resonator of width ‘a’, height ‘b’ and length ‘d’. Show that the frequency of resonance is given by –

(ii) For a = 2cm, b = 1 cm, choose d so that cavity will resonate at 10 GHz for TE101 mode.

(b) Why is hybrid Tee is referred as magic Tee? Derive the scattering matrix for the same.

(c) Explain the operation of microwave isolator. 5

5. (a) Describe the operation of IMPATT diode compare it with TRAPATT diode. 1 0 ~

(b) Explain RF substitution method for measuring attenuation.20 db is used to monitor the power delivered to the load ZI’ Bolometer 1 introduces VSWR 2.0 on arm 4. Bolometer 2 is matched to arm 3. If Bolometer 1 reads 8 mW and bolometer 2 reads 2 mW.

Find (i) the amount of power dissipated in the load Z,.

(ii) VSWR on arm 2.

(b) Explain the construction and working principle of Refiex Klystron. 10

7. Write short notes on any four :- 20

(a) Working of circulator

(b) Strapping in Magnetron,

(c) Double minimum method for measuring VSWR

(d) Excitation in Waveguides