Microwave Devices & Circuits - May 2013

Electronics Engineering (Semester 6)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks. 1 (a) What are the applications of Microwaves? (5 marks) 1 (b) Can TEM mode exist in hollow waveguide? Justify your answer. (5 marks) 1 (c) What are O-type and M-type devices in microwave? (5 marks) 1 (d) Explain the terms: Cut-off frequency, Dominant mode, Phase velocity, Group velocity. (5 marks) 2 (a) Derive wave equation for TE wave and obtain all the field components in a rectangular waveguide. (10 marks) 2 (b) Explain the action of isolator and circulator using ferrites, mention their typical applications. (10 marks) 3 (a) Draw a neat diagram of two cavity Klystron amplifier and explain the bunching process. Derive the equation of velocity modulation.(10 marks) 3 (b) An X-band pulsed cylindrical magnetron has the following parameters:
Anode voltage: Vo = 2.6x10⁴V
Beam current: Io=27A
Flux density: Bo=0.336Wb/m²
Radius of cathode cylinder: a=5 cm
Radius of vane edge to centre: b=10 cm
Compute the cyclotron angular frequency
the cut off voltage for a fixed B and
the cut off magnetic flux density for a fixed Vo. (10 marks) 4 (a) Draw and explain two-hole directional coupler. Define coupling factor, directivity and isolation. Derive S matrix for the same.(10 marks) 4 (b) Explain Gunn Effect with the two valley model of Gunn diode. What are the criteria that a semiconductor must satisfy in order to exhibit negative resistance?(10 marks) 5 (a) What are slow wave structures? Explain how helical TWT does amplification. (10 marks) 5 (b) Describe the types of strip lines in brief. (5 marks) 5 (c) Explain the excitation of modes in circular waveguides.(5 marks) 6 (a) Explain the methods used for power measurement in microwaves.(10 marks) 6 (b) With the help of sketch distinguish between IMPATT and TRAPATT diode.(10 marks)

Write short notes on any three:-

7 (a) Limitations of conventional tubes at microwave frequencies. (7 marks) 7 (b) Waveguide attenuators.(7 marks) 7 (c) Measurement of VSWR.(7 marks) 7 (d) Microwave transistors.(7 marks)