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## 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 Z_{0}=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)