## RF Modelling and Antennas - Dec 2011

### 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.

### Write short notes on following :-

**1 (a)** Chip components(5 marks)
**1 (b)** Microstrip lines and strip lines(5 marks)
**1 (c)** Large signal FET model(5 marks)
**1 (d)** ABCD Parameters(5 marks)
**2 (a)** Explain what is Skin depth? Calculate the skin depth for copper and aluminium at 0.86 and 1.2 GHz? Also find the resistance of an 8 cm wire with diameter of 1.5 mm? $$ \sigma_{CU}=64.516 \times 10^6 (s/m), \ \sigma_{Al}=40\times 10^6 (s/m) $$(10 marks)
**2 (b)** Explain with the equivalent circuits the Radio frequency behavior of Resistor, Inductor and Capacitor?(10 marks)
**3 (a)** Explain the folllowing terms related to the filter Design? Insertion Loss, Ripple Factor, Bandwidth(6 marks)
**3 (b)** Explain why the ideal filter response cannot be realized?(4 marks)
**3 (c) ** Design the Butterworth High pass filter having cutoff frequency of 250 MHz and -15dB response at 200 MHz?(10 marks)
**4 (a) ** Plot the following Impedance points on the smith chart? Z_{0}=50Ω

23+j 42Ω, 12-j 109Ω, 72+j 42.5Ω and 115-j 22Ω

Calculate their equivalent admittance using smith chart?(8 marks)
**4 (b)** Calculate the input impedance of the Transmission line using equations and the smith Chart, for Z_{0}=50Ω, Z_{1}=110+j 22Ω, ε_{r}=1.0, length of the line = 20 cm and operating frequency equal to 1.8 GHz?(12 marks)
**5 (a) ** Explain the equivalent circuit of the transmission line?(5 marks)
**5 (b)** Derive the input impedance equation of Transmission line of length 'I'>(5 marks)
**5 (c) ** Using the input impedance equation of Transmission line, derive the input impedance equation for shorted and open circuit transmission line and draw their voltage, current and impedance waveform?(10 marks)
**6 (a)** Define and derive AC parameter for BJT and FETs?(10 marks)
**6 (b)** Write short notes on,

(i) High Electron Mobility Transistor

(ii) Small signal BJT model?(10 marks)
**7 (a)** How the capacitor and inductors are realized using the sections of transmission line? Explain the same using the smith charts ?(6 marks)
**7 (b)** What are Kuroda Identities? How they are used in realization of RF filters?(10 marks)
**7 (c) ** Explain what are Schottky Contacts?(4 marks)