# Mumbai University Previous year question papers

## Microwave devices and Circuits

Question NO.1 is compulsory.

(2) Attempt any four questions from remaining six questions. 2-‘-30

(3) Figures to the right indicate full marks.

1. Answer any four of the following :-

(a) Why TEM mode does not exist in hollow waveguide?

(b) Compare p-i-n and p-n photodiode.

(c) Draw refractive index profile diagram of step Index and graded Index fiber.

(d) What is dispersion in optical fiber? How does it affect the performance of optical fiber?

(e) Describe stimulated emission in Laser.

2. (a) DifferentiatebetweenTWTAmplifierand KlystronAmplifier.

(b) Draw the schematic diagram of cylinderical mode of magnetron and explain it’s 1principle of operation. Explain phase bunching process.

3. (a) A rectangular waveguide has the following characteristics :-

a = 3 cm, b = 1.5 cm, Jlr = 1, 8r = 2.25

Calculate: (i) the cut-off frequency for TE10 mode.

(ii) the cut-off wavelength for TE10mode.

(iii) the guided wavelength at a frequency of 4 GHz.

(b) Discuss the methods of exciting TE10and TE20mode’s in a rectangular waveguide. 10

4. (a) Discuss the limitations of conventional Vacuum tube’s at microwave frequencies.

(b) Describe the operation of Gunn diode.

(c) Compare E-Teeand H-Tee.

(d) Give the significance of coupling factor’s and directivity of directional Coupler.

5. (a) The quantum efficiency of a particularA.P.D is 0.8 for the detection of radiation at a wavelength of 0.9 Jlm.When the incidentpower is 0.5 Jlw, the output current from the device is 11 JlA.

Determine: (i) the responsivity of photodiode.

(ii) photo current in photo diode.

(iii) multiplication factor of photodiode.

(b) Compare LED and LASER optical source.

(c) What is the cut-off wavelength as applied to optical fibers?

(d) State the requirements for a good connector.

6. (a) With the help of neat diagram explain anyone method of fabricating an opti”calfiber. 10

(b) Explain various types of Splicing techniques. 10

7. (a) Discuss homojunction and hetrojunction structures. 5

(b) With the help of neat diagram explain the operation of surface emitting LED and edge emitting LED.

(c) Explain anyone method of measuring attenuation in optical fiber. 5