Microwaves & RADAR - Dec 2015

Electronics & Communication (Semester 5)

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) Derive the transmission line equations by the method of distributed circuit theory.(10 marks) 1 (b) A 300 Ω line is terminated in a load of (600+j300) Ω operating at 600 Hhz. Find the of SWR and design a single stub matching system.(10 marks) 2 (a) Using Helmholtz equation, derive the field equation for TM mode in rectangle waveguide.(10 marks) 2 (b) What is circulator? Explain the working of a 4-port circulator using magic tees and write S-matrix.(10 marks) 3 (a) What is GUNN diode? Explain LSA and TT modes.(10 marks) 3 (b) What are the difference between microwave transistor and TEDs? Give few examples.(5 marks) 3 (c) An IMPATT diode with nominal frequency 10 GHz has C_j=0.5 pF, L_p=0.5 nH C_p=0.3 pF at breakdown bias of 80 V and bias current 80 mA. The RF peak current 0.65 A for R_d= -2 Ω. Find i) Resonant frequency ii) Efficiency.(5 marks) 4 (a) State and prove symmetric property of S-matrix.(8 marks) 4 (b) What are S-parameters? Explain the S-parameters for two port network.(8 marks) 4 (c) The S-parameters of a 2 port network are given by S₁₁=0.2∠0, S₂₂=0.1∠0, S₁₂= 0.6∠90° and S₂₁=0.6∠90°. Is the network reciprocal? Lossless?(4 marks) 5 (a) What is attenuator? Derive its S-matrix.(8 marks) 5 (b) Write a note on: i) phase shifter ii) Coupling loop.(6 marks) 5 (c) A 20 mW signal is fed into one of the collinear port 1 of a lossless H-plane T Junction. Calculate the power delivered through each port when other ports are terminated in matching load.(6 marks) 6 (a) Write a note on lossless in the microstrip line.(8 marks) 6 (b) Explain co-planar strip lines and shielded strip line.(6 marks) 6 (c) A shielded strip has the following parameter ε_r=2.56, strip width =25 mils, Strip thickness = 14 mils and shield depth = 70 mils. Calculate i) the k-factor ii) friction capacitance ii) Impedance of the line.(6 marks) 7 (a) Derive the basic radar range equation.(10 marks) 7 (b) Write a note on: i) Origin of radar ii) Applications of radar.(4 marks) 7 (c) A 10 GHz radar has the following characteristics P₁= 250 kW, Prf=1500 PPS, P-width = 0.8 μs, power gain of antenna = 2500, S_min = 10^-14W, A_c=10 m², σ=2 m². i) R unambiguous ii) Maximum possible range iii) Duty cycle iv) Average power.(6 marks) 8 (a) What is blind speed? How can we eradicate it?(8 marks) 8 (b) Explain digital MTI processing.(8 marks) 8 (c) A CW radar operates at frequency of 10 Ghz. What is the Doppler frequency produced i) an aeroplane plying at a speed of 250 kmph ii) a man crawling at 2.5 cm/sec. What you understand?(4 marks)