## RF Modelling and Antennas - May 2014

### 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) ** Explain the terms Insertion Loss, Ripple factor and Band -width related to filter design. (5 marks)

** 1 (b) ** Compare Microstriplines with striplines. (5 marks)

** 1 (c) ** Explain Simplified Eber's-moll model, for forward active mode of transister. (5 marks)

** 1 (d) ** Draw equivalent circuit representation of two wire transmission line. Explain primary and secondary parameters for the same. (5 marks)

** 2 (a) ** Explain Richards transformation and kurodas Identity. How they are used in realization of RF Filter? (10 marks)

** 2 (b) ** Explain the role of scattering parameter and its's properties at RF and microwaves. (10 marks)

** 3 (a) ** Derive power consideration for transmission line when.

(i) Load Impedance Z_{L} & source Impedance Z_{S} are mathched.

(ii) Z_{L} is matched and Z_{S} is mismatched. (10 marks)

** 3 (b) ** A transmission line of characteristics Impedance Z_{0}=50 Ω and d=0.15 λ is terminated with a load impedance of Z_{L}=(25-j 30) Ω.

Find reflection coefficient, input impedance at distance 'd' and VSWR by using Z-smith chart. (10 marks)

** 4 (a) ** Explain in brief the principle operation of HEMT and MESFET along with their construction. (10 marks)

** 4 (b) ** Find the attenuation of 4 element, 2.5 dB ripple, low pass chebyschew filter at $$ \dfrac {W}{W_C}=2.5 $$ (10 marks)

** 5 (a) ** Explain different types of diode model's (RF) and differentiate them with respect to junction capacitance, band gap energy and conductance. (10 marks)

** 5 (b) ** Explain what is skin depth? Calculate the skin depth for copper and aliminium at 1GHz and 10 GHz and Find the resistance of 10cm wire with diameter of 1mm

$$ 6_{CU}=64.516 \times 10^6 s/m, 6_{Al}=40 \times 10^6 s/m. $$ (10 marks)

** 6 (a) ** Derive expression for internal, external and loaded quality factors for standard series and parallel resonant circuit. (10 marks)

** 6 (b) ** For a transmission line circuit involving source and load terminations of Z_{G}=60 Ω and Z_{L}=50 Ω respectively and Z_{0}=75 &Omgea;. Compute the input power and power delivered to load. Assume length of line to be [ dfrac {lambda}{4} ] with source of V_{G}=8V (10 marks)

### Write short note on :-

** 7 (a) ** Schottky contacts(7 marks)

** 7 (b) ** Equivalent circuit of Resistor's, Inductor and capacitor(7 marks)

** 7 (c) ** ABCD parameter(6 marks)