JNTU question papers B -Tech IInd Sem – Microwave engineering – Aug/Sep 2008

JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008


( Common to Electronics & Communication Engineering and Electronics &



1. (a) Mention different microwave regions & band designations.

(b) Discuss the war and peace time applications of microwaves.


2. (a) Discuss the power transmission in circular wave guides.

(b) An air filled circular wave guide of 2 cm inside radius is operated in the TE01 mode.

i. Compute the cut off frequency

ii. If the guide is to be filled with a dielectric material of 2r = 2.25, to what value must its radius be changed in order to maintain the cut off frequency at its original values.


3. (a) Sketch a 4 port hybrid junction and justify that it is a basically a 3 dB directional coupler.

(b) A matched generator with a power of one watt is connected to the H arm of magic tee C (port 4). The E arm (port 3) is match terminated and the length of the coplanar arms is the same. Compute the power delivered to the termination at port 1, 2 and 3 and the power reflected at port 4 when ports 1 and 2 are match terminated.


4. (a) What is Faraday rotation? Explain how a three port circulator operates.

(b) Write short notes on “Properties of S – matrix”.


5. (a) A reflex klystron operates at the peak mode of n = 2 with

Beam voltage V0 = 300v

Beam current I0 = 20mA

Signal Voltage V1 = 40v.


i. Input power in walts.

ii. Output power in walts.

iii. The efficiency.

(b) Derive the relation between accelerating voltage V0 , repeller voltage VR & repeller space L.


6. (a) A TWT operates under following parameters:

Beam Voltage Vo=3KV, Beam current Io = 30mA, characteristic Impedance

of helix Zo=10 ,circuit length , N=50 & frequency f =10 GHz. Determine

i. Gain parameter

ii. output power gain in dB & all

iii. four propagation constants .

(b) Explain why there are four propagation constants in TWT & derive equations to these propagation constants.


7. (a) Am IMPATT diode has drift length of 2 ?m. Determine

i. Drift time of the carriers

ii. Operating frequency of IMPATT diode.

(b) Compare IMPATT and TRAPATT diodes.


8. (a) The cablibrated power from a generator as read at the power meter is 25mw.

When a 3dB attenuator with a VSWR of 1.3/1 is inserted between the generator and detector what value should the power meter read.

(b) Compare the power ratio and RF substitution methods of measuring attenuation provided by the microwave component.

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