Microwave & Radar Engineering - May 2012

Electronics & Telecomm. (Semester 7)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1 (a) Solution for magnetic vector potential (5 marks) 1 (b) Microstrip transmission lines.(5 marks) 1 (c) Power dividers(5 marks) 1 (d) Gryotrons.(5 marks) 2 (a) Derive plane wave equations and explain the significance(10 marks) 2 (b) Derive the expression for reflection and transmission coefficient of finite length (10 marks) 3 (a) Derive the electro magnetic equations for TE modes in rectangular waveguide.(10 marks) 3 (b) A TE₁₁ mode propogating through a circular waveguide. The radius of the guide is 5 cm and the guide contains a air dielectric.
(i) Determine the cut off frequency
(ii) Determine the guid wavelength for an operating frequency of 3 GHz
(iii) Determine the wave impedance in the guide(10 marks) 4 (a) Explain various types of microwave solid state devices along with their applications(10 marks) 4 (b) A Silicon n-p-n bipolar transistor operates in common-base mode at 300°K and has the following parametes:
Silicon instrinsic density : n₁=1.5 ×10¹⁰ cm^-3
Acceptor density in base region : N_a=5 ×10¹⁶ cm^-3
Donor density in emitter region : N_d=5 × 10¹⁸ cm^-3
Hole Lifetime : ?_p=1 ?s
Electron Lifetime : ?_n = 1 ?s
Cross Section : A= 10^-4 cm²
Base width : w=10^-3 cm
Emitter length : L_E = 10^-2 cm
Determine : -
(i) The mobilities μ_n and μ_p
(ii) The diffusion coefficients D_n and D_p
(iii) The emitter efficiency factor y
(iv) The transport factor β
(v) The current gain α(10 marks) 5 Explain various avalanche transit-time devices with reference to construction, operation and applications.(20 marks) 6 (a) A two cavity amplifier Klystron has the following characteristics :
Voltage gain : 15 dB
Input power : 5 mW
Total shunt inpedance of input cavity R_sh : 30 k?
Total shunt impedance of output cavity R_sh : 40 ?
Load impedance at o/p cavity R_L : 40?
Determine :-
(i) The input Voltage (Vms)
(ii) The output Voltage (Vms)
(iii) The power delivered to the load in watts(10 marks) 6 (b) Explain the concept velocity madulation and explain cylindrical magnetron.(10 marks) 7 (a) Microwave filters (5 marks) 7 (b) Travelling wave tube(5 marks) 7 (c) Measurement of impedance .(5 marks) 7 (d) Hybrid junctions.(5 marks)