# Mumbai University Previous year question papers

## Microwave devices and Circuits

N.S. (1) Question No.1 is compulsory.

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

(3) Assume suitable data if necessary.

(b) Differentiate between TE and TM modes in a rectangular waveguide. Why is TMo1Or TM1Qmode not possible in a rectangular waveguide?

(c) What is Velocity Modulation? How Velocity Modulation is utilised in Klystron amplifier?

(d) Explain intermodel dispersion in Optical Fiber System.. .

(e) ComparebetweenLEDand LASERdiode.

2.(a) Explain with a suitable sketch the Mechanism of Propagation of an E-M wave through a rectangular waveguide.. . .

(b) Give the reasonwhy there are different modes of propagation and a cutoff freq. for a perticular waveguide having definite geometry.

(c) What is the dominant mode? What are the phase velocity and the group velocity of an EM wave in a waveguide? Explain.

3. (a) What are cross field devices? How does a magnetron sustain its os~illations using this crossfield? Assume7t modefor explainingthe same.

(b) A two Cavity Klystron is operated at 10 GHz with

Vo =1200 V, 10= 30 mA, d = 1 mm, L = 4 m and RSh= 40 KO neglecting beam loading, Calculate

(i) Input RF voltage V, for a maximum output voltage

(ii) Voltage gain (Hi) Efficiency.’

4.(a) In a H-plane Tee junction 20 mW power is applied to Port (1) that is perfectly matched to the junction. Calculate the power delivered to the load 60 0 and 75 n connected to Port (1) and Port (2).

(b) What is’a directional coupler? What are its characteristics?

(c) Differentiate between

(i) TWTA and Klystron

(ii) IMPATTdiode and Gunn diode.

5.(a) Describe different types of modes that are supported by an optical fiber. What is the significance of cuttoff no.of fiber? –

(b) With the help of neat block diagram. Explain the major elements of an optical fiber transmission link.

(c) Calculate the cross sectional area of amultimode stepindex fiber with a V no., V = 100 and a N.A. = 0.30. This fiber fiber will be used in a data link with a 0.82 Ilm LED.(Take n1.= 1.458)

6. (a) Distinguish between Spontanous Emission and Stimulated Emission.

(b). Explain splices and connections in optical fibers.

(c) Explain anyone method of measuring each of the following :-

(1) Dispension in optical fiber

2) Attenuation in optical fiber.

7. Write short notes on any four :-

(a) MagicTee

(b) S-matrix

c) Cavity resonators