RF Modelling and Antennas - May 2013

Electronics & Telecomm. (Semester 5)

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) Draw the lumped element circuit model for a transmission line. Derive the expression for voltage and current travelling waves.(5 marks) 1 (b) Explain simplified Ebers-Moll model for forward active mode of a transistor.(5 marks) 1 (c) Explain current flow in p-n junction and give the expression for I_diff in terms of diffusion constant and V_diff in terms of doping concentration. (5 marks) 1 (d) Discuss terminations used for microstrip lines.(5 marks) 2 (a) Prove the first three Kuroda s Identities by computing appropriate ABCD matrices. (10 marks) 2 (b) Explain construction and functionality of HEMT. (10 marks) 3 (a) Discuss power considerations in transmission line when
i) Source and Load impedances are matched
ii) Load impedance is matched and source mismatched. (10 marks) 3 (b) Explain with equivalent circuits the RF behavior of resistor,inductor and capacitor. (10 marks) 4 (a) Explain Insertion loss, Ripple factor and bandwidth in relation to filter design. Why ideal filter response cannot be realised?(10 marks) 4 (b) if Z₀=50Ω, plot the following impedances on Smith Chart.
23+j42Ω, 12-j109Ω, 72+j42.5Ω & 115-j22Ω
Find corresponding admittances and VSWR.(10 marks) 5 (a) Define and derive AC parameters for BJT and FET. (10 marks) 5 (b) Explain the role of scattering parameters and its properties at RF and microwaves. (10 marks) 6 (a) Explain Schottky contact with help of energy band diagram for metal semiconductor contact. (10 marks) 6 (b) Derive expression for internal, external and loaded quality factors for standard series and parallel resonant circuit. (10 marks)

Write short notes on:

7 (a) Realization of capacitors and inductors using sections of transmission lines. (7 marks) 7 (b) Microstrip transmission lines. (7 marks) 7 (c) Butterworth filter.(6 marks)