JNTU B.Tech II Semester Examinations, MICROWAVE ENGINEERING, Apr/May 2008

( Common to Electronics & Communication Engineering and Electronics &

Telematics)

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

SET-I

1. (a) Derive the expression for guide wave length of TEmn mode in rectangular wave guide.

(b) What are the advantages of dominant mode propagation? [8+8]

2. (a) What are TEnm and TMnm modes w.r.t a circular wave guide. Sketch the dominant modes.

(b) A cylindrical wave guide has a inner radius of 2 cm. Find the cut off frequency for the guide operating in TE11 mode. Calculate ? g and ZTE at 10 GHz (?0= 3 cm). [8+8]

3. Write short notes on:

(a) Wave guide Irises

(b) Rat ? Race hybrid

(c) Dielectric phase shifters. [16]

4. (a) Explain the characteristics of ferrite materials.

(b) Derive the S – matrix for 4 port directional coupler when the coupling factor is 3dB. [8+8]

5. (a) A reflex klystron operates under the following conditions:

V0 = 600v, I0 = 11.45mA, L = 1mm.

Rsh = 15k ? 2, fr = 9GHZ.

The tube is oscillating at fr at the peak of n = 13

4 mode.

Assume ?1

i. The microwave gap voltage.

ii. Repeller Voltage for the mode 134 .

(b) Draw the equivalent circuit of reflex klystron & explain about the electronic admittance of it. [8+8]

6. (a) A helix travelling wave tube is operated with a Beam current of 300mA, beam Votage of 5KV, characteristic Impedance of 20. What length of helix will be Selected to give an output power gain of 500db at 10GHz.

(b) Explain the construction & working of TWT. [8+8]

7. (a) Derive the criterion for classifying the modes of operation for Gunn effect diodes

(b) An n-type GaAs Gunn diode has following parameters

Electron drift velocity Vd = 2.5 × 105m/s

Negative Electron mobility |?n| = 0.015 m2/ v s

Relative dielectric constant ?r = 13.1

Determine the criterion for classifying the modes of operation. [8+8]

8. (a) How are microwave measurements different from low frequency measurements.

(b) What is the average power of a periodicwave if the peak power is 1300 W and

the pulse width is .56 and periodic frequency of the wave is 1500 Hz. [8+8]