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.