Antenna and Wave Propagation - Dec 2015

Electronics & Telecom Engineering (Semester 6)

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.

Solve any one question from Q1 and Q2

1 (a) What is Poynting vector? What is its significance? Derive an expression for Poynting vector?(6 marks) 1 (b) Derive the fundamental equation for free space propagation and explain its parameter(6 marks) 1 (c) A lossless resonant λ/2 dipole antenna with input impedance of 73 Ω is to be connected to a transmission line whose characteristics impedance is 50Ω. Assuming that the pattern of the antenna is given approximately by U=Bosin ³θ. Find the overall maximum gain of this antenna.(8 marks) 2 (a) State Maxwell's field equation with their significane and derive the wave equation foe lossless dielectric medium.(6 marks) 2 (b) Derive vector potential A for an magnetic current source J.(6 marks)

Explain the following wireless channel characteristics

2 (c) (i) Coherence bandwidth(4 marks) 2 (c) (ii) Coherence time(4 marks)

Solve any one question from Q3 and Q4

3 Find the following terms for half wave Dipole:
a) Specify the current
b) Vector magnetic potential
c) Far field components of Electric & Magnetic fields
d) radiation density, radiation intensity
e) radiated power, radiation resistance
f) Directivity
g) draws the radiation pattern(18 marks) 4 (a) Calculate the radiation resistance of a double turn and an eight turn small circular loop when radius of loop is λ/10 and the medium is free space. Calculate its efficiency if loss resistance is 25Ω.(6 marks) 4 (b) Derive the expression for radiation resistance of Infinitesimaldipole.(6 marks) 4 (c) Derive the expression for input impedance of small dipole.(6 marks)

Write short notes on:

5 (a) (i) Pattern Multiplication(4 marks) 5 (a) (ii) Binomial Array(4 marks) 5 (b) An Endfire array with element spaced at λ/2 and with axes of elements at right angles to the line of array is required to have directivity of 36. Determine - the array length and the width of major lobe.(8 marks) 6 (a) Design a broad side Dolph-Tschebhysheff array of five elements with half wavelength spacing between elements and with major to minor lobe ratio to be 19dB. Find the excitation coefficients & array factor.(6 marks) 6 (b) Give the comparison of broadside and End fire antenna array.(5 marks) 6 (c) Explain planar array. State its advantages and applications.(5 marks)

Solve any one question from Q7 and Q8

7 (a) What is Microstrip patch antenna? Give structure details, radiation pattern, specification and application of such antenna.(5 marks) 7 (b) What is meant by Rhombic Antenna? How it is constructed? Explain how unidirectional pattern is obtained in properly terminated Rhombic Antenna.(5 marks) 7 (c) Write a short notes on following antennas with respect to structural details, radiation pattern, features and applications.
i) Hertz antenna
ii) Whip antenna(6 marks)

Write a short note on the following antennas

8 (a) (i) Lens Antenna(4 marks) 8 (a) (ii) Resonant Antenna(4 marks) 8 (a) (iii) Super - turnstile Antenna(4 marks) 8 (b) A paraboloidal reflector antenna with diameter 20m is designed to operate at frequency of 6 GHz and illumination efficiency of 0.54. Calculate the antenna gain in decibels.(4 marks)