# JNTU Previous Questions Papers B Tech Year 3rd Year Microwave Engineering Apr/May 2008

JNTU B.Tech year-III MICROWAVE ENGINEERING, Apr/May 2008

( Common to Electronics & Communication Engineering and Electronics &

Telematics)

Time: 3 hours Max Marks: 80

SET-II

All Questions carry equal marks

1. (a) What are TEM, TE, TM and HE modes. Sketch the field patterns for dominant modes in a rectangular wave guides.

(b) A rectangular wave guide has a = 4 cm, b = 3 cm as its sectional dimensions.

Find all the modes which will propagate at 500 MHz. [8+8]

2. (a) Derive the Q for TM111 mode of rectangular cavity assuming lossy conducting walls and lossless dielectric.

(b) The quality factor of micro strip line is reciprocal of the dielectric loss tangent ? and is relatively constant with frequency. Prove this statement. [8+8]

3. (a) Show the attenuation produced by rotary vane attenuator is given by – 40

log(sin?).

(b) Describe in detail about linear phase changer. [8+8]

4. (a) Describe microwave component which makes use of Faraday rotation principle.

(b) What are the advantages of scattering matrix representation over impedance or admittance matrix representation? [8+8]

5. (a) Explain the gain Bandwidth product limitation & Transit angle effects in

conventional tubes at microwave frequencies.

(b) A reflex klystron operates under the following conditions

V0 = 900v, L = 1mm

Rsh = 25k ? 2, e

m = 1.759 × 1011, fr = 9GHZ

The tube is oscillating at fr at the peak of n =2 mode or 134 mode. Assume that the transit time through the gap & beam loading can be neglected.

i. Find the value of repeller voltage Vr.

ii. Find the D.C. current necessary to give a microwave gap voltage of 100v.

iii. What is the electronic efficiency under this condition. [8+8]

6. (a) The linear magnetron has the following parameters:

Vo =32KV, Io = 60A, f=10GHz, Bo= 0.01Wb/m2, d=6cm.

Find

i. Electron velocity at the hub space.

ii. Phase velocity for synchronization.

iii. Hartree anode voltage.

(b) Describe the effect of DC axial field on the electrons traveling from cathode to anode of a magnetron &describe the combined effect of the axial magnetic field & radial DC field .define the cutoff field. [8+8]

7. (a) A Ku-band IMPATT diode has a pulse operating voltage of 100v and a pulse

operating current of 0.9 A. The efficiency is about 10%. Calculate

i. The output power

ii. The duty cycle if the pulse width is 0.01ns and frequency is 16 GHz.

(b) Describe the principle of operation of IMPATT diode. [8+8]

8. (a) Describe various techiques of measuring unknown frenquency of a microwave

generator.

(b) A slotted line is used in association with an X-band microwave source, When the line is terminated by a short circuit, adjacent nulls are found at position which are shown as 9.27cm and 11.05 cm. What is the value of the guide wavelength. [8+8]