Antenna and Wave Propagation - Jun 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.
Answer any one question from Q1 and Q2
1 (a) What is polarization of wave? Explain the polarization of three types of wave with the help of relevant diagram?(8 marks)
1 (b) Write a short note on
i) Ionospheric abnormalities
ii) Multihop propagation(6 marks) 1 (c) A lossless resonant λ/2 dipole antenna with input impedance of 73Ω is to be connected to a transmission line whose characteristic impedance is 50Ω. Assuming that the pattern the antenna is given approximately by U = Bo sin3?. Find the overall maximum gain of this antenna.(6 marks) 2 (a) What is Poynting vector? What is its significance? Derive an expression for Poynting vector?(6 marks) 2 (b) Explain antenna radiation mechanism in detail.(6 marks) 2 (c) Calculate the mean excess delay, RMS delay spread, and the maximum excess delay (10dB) for the multipath profile given in the figure below. Estimate the 50% coherence bandwidth of the channel. (8 marks)
Answer any one question from Q3 and Q4
3 (a) Derive the expression for radiation resistance of Infinitesimal Dipole.(9 marks) 3 (b) Derive the expression for radiation resistance of small dipole antenna.(9 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.(8 marks) 4 (b) Derive mathematical expression for power density and radiation intensity of half wave dipole antenna and draw radiation pattern of half wave dipole antenna in E and H plane.(10 marks)
Answer any one question from Q5 and Q6
5 (a) Write a short notes on
i) Pattern Multiplication.
ii) Binomial Array.(8 marks) 5 (b) 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.(8 marks) 6 (a) Explain planar array. State its advantages and applications.(6 marks) 6 (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.(5 marks) 6 (c) Give the comparison of broadside and End fire antenna array.(5 marks)
Answer any one question from Q7 and Q8
7 (a) Give structure details, radiation pattern, specification and application of Super-turnstile Antenna.(5 marks)
7 (b) What is meant by Rhombic Antenna? Explain its construction and operating principle.(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) Lens Antenna(6 marks) 8 (a) Write short notes on the following antennas.
i) Whip antenna
ii) Slot Antenna
iii) Microstrip patch antenna(12 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)