Antennas & Propagation - Jun 2013

Electronics & Communication (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. 1 (a) Define the following terms with respect to antenna:
i) Directivity
ii) Beam solid angle
iii) Radiation resistance(9 marks) 1 (b) State and prove Friis transmission formula.(5 marks) 1 (c) Show that maximum effective aperture of short dipole is 0.119 λ².(6 marks) 2 (a) State and prove power theorem and its application.(5 marks) 2 (b) Show that the directivity for unidirectional operation is 2(n+1) for an intensity variation of U-U_mcosⁿθ.(5 marks) 2 (c) Derive an expression and draw the field pattern for isotropic point source of the same amplitude and same phase.(10 marks) 3 (a) Starting from electric and magnetic potentials, obtain the far field components for a short dipole.(12 marks) 3 (b) Derive an expression for radiation resistance of a short electric dipole.(8 marks) 4 (a) Derive an expression for far field components of a loop antenna.(10 marks) 4 (b) The radius of a circle loop antenna is 0.02λ. How many turns of the antenna will give a radiation resistance of 35Ω.(5 marks) 4 (c) Write a note on slot antenna.(5 marks) 5 (a) Explain the features of an helical antenna and the practical design considerations of the helical antenna.(10 marks) 5 (b) Write note on: i) Ultra wide band antenna,
ii) Lens antenna.(10 marks) 6 (a) Explain: i) Yagi-Uda antenna, ii) Parabola reflectors(10 marks) 6 (b) Write short notes on:
i) Turnstile antenna
ii) Antennas for ground penetrating radar.(10 marks) 7 (a) Discuss the propagation characteristics of radio waves for different frequencies.(10 marks) 7 (b) Explain the principle of surface wave propagation. Obtain an equation for tilt angle α of the wave.(10 marks) 8 (a) Draw and explain different ionized layers an ionospheric propagation.(10 marks) 8 (b) A distance of 1500 km one is to be covered along earth surface using a communication link of the reflection region of ionosphere has f_c 6MHz and f_MUF 7.5 MHz, calculate the height of the region.(5 marks) 8 (c) Write a note on skip distance.(5 marks)