JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008
(Electronics & Communication Engineering)
1. (a) What is velocity modulation? Explain how amplification takes place in a two cavity Klystron amplifier.
(b) What is transit time? How it is made use of in realization of microwave tubes.
2. (a) What is a backward wave oscillator? Write brief notes on its configuration and characteristics.
(b) Describe the merits and demerits of helix as a slow wave structure.
3. (a) What are disadvantages of strapping? Show the cross section of a magnetron anode cavity system that does not require stapping.
(b) What is critical magnetic field as it is used in connection with magnetron?
Derive an expression for cut off magnetic field in linear magnetron.
4. (a) Describe a non-degenerate negative resistance parametric amplifier.
(b) An N type Ga As GUNN diode has the following specification
Threshold field: 3KV/m
Applied field 3.5KV/m
Device length 10 micrometers
Doping Constant 1014 electron/ Cm3
Operating freq. 10 GHz Calculate the current density and (-Ve) electron mobility in the device, explaining the relations used.
5. (a) A rectangular wave-guide has a cross section of 1.5 cm x 0.8 cm, ?=0, ?= ?0
and 2= 420. The magnetic field component is given as
Hx = 2Sin ????_xa _ cos ????3_yb _ Sin (? × 1011t ? ? z) A/m
i. The mode of operation
ii. The cut off frequency
iii. The phase constant
iv. The propagation constant
v. The wave impedance.
(b) Write short notes on “Rectangular resonant Cavity”.
6. (a) Explain the working of two hole directional coupler with a neat diagram.
(b) Explain about E plane Tee junction with a neat sketch. Why it is called a series Tee?
7. Write short notes on:
(a) Properties of S matrix.
(b) Gyrator and its applications.
8. Explain with a neat black diagram how VSWR and impedance can be measured using a slotted line in X band. Name the types of sources used and list out the precautions to be taken.