JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008
(Electronics & Communication Engineering)
1. (a) What are the applications of microwave frequencies? Discuss in detail.
(b) Explain the principle of operation of a reflex Klystron oscillator and derive an expression for the bunching parameter.
2. (a) What are the desirable properties of slow wave structures to be used in TWT amplifiers.
(b) Draw a neat sketch of traveling wave tube and explain its principle of operation with bunching diagrams.
3. (a) Draw the sketches of different types of magnetron anodes.
(b) Explain Hatree conditions. Derive the voltage under this condition for 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) Derive the expression for the attenuation of TE10 mode of a rectangular waveguide with finite conductivity.
(b) An air filled rectangular cavity with brass walls has ? = 1.54 × 107 (s/m) and the following dimensions a= 4 cm, b = 3 cm and d = 5 cm.
i. The dominant mode and its resonant frequency for this cavity.
ii. Find the Q and the time average stored electric and magnetic energies at resonant frequency, assuming H0 to be 0.1 A/m.
6. (a) Sketch a 4 port Hybrid junction. Justify that it is basically a 3 dB directional coupler.
(b) A 20-mw signal is fed into the series arm of a loss less Magic Tee junction. Calculate the power delivered through each port when other ports are terminated in matched load.
7. (a) What are ferrites? What property do they have different from ordinary conductors or insulators?
(b) Describe any one microwave component which make use of Faraday rotation principle, with neat sketches.
8. (a) What are the precautions to be taken while setting up microwave bench for measurement of various parameters.
(b) How do you measure microwave power using a Bolometer.