RF Modelling and Antennas - May 2013

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 significance of directivity and radiation pattern of antenna.(5 marks) 1 (b) Describe the concept of near field and far field radiation.(5 marks) 1 (c) Discuss the voltage and current distribution of a half wave dipole antenna. Can we say the antenna is resonant?(5 marks) 1 (d) Differentiate between broadside and end fire array.(5 marks) 2 (a) Explain the significance of the term Effective Area of an Antenna. Derive the relation between effective area and directivity of any antenna.(10 marks) 2 (b) Describe parabolic reflector and its use of microwave frequencies. Discuss Cassegrain method of feeding the parabolic reflectors. (10 marks) 3 (a) State and derive FRIIS transmission equation.(10 marks) 3 (b) What is the maximum power received at a distance of 0.5 km over a free space 1 GHz circuit consisting of a transmitting antenna with a 25 dB gain and a receiving antenna with a 20dB gain. The transmitting antenna is fed with 150 W of power.(10 marks) 4 (a) Explain V antenna and rhombic antenna. List their advantages and disadvantages. Mention their applications.(10 marks) 4 (b) Explain and derive equations for total electric field, directivity, half power beam width in case of two isotropic point sources of same amplitude but opposite phase.(10 marks) 5 (a) Explain the difference in driven and parasitic elements in an antenna array. Differentiate between a director and a reflector.(10 marks) 5 (b) Explain the formation of inversion layer in the troposphere and the phenomenon of duct propagation. What factors help in the formation of duct?(10 marks) 6 (a) Derive the expression for vector potential wave equation.(10 marks) 6 (b) Explain different types of horn antennas. Find the directivity and beamwidth. (10 marks) 7 (a) Ionospheric propagation.(5 marks) 7 (b) Log periodic antenna.(5 marks) 7 (c) The equivalent noise temperature of an antenna.(5 marks) 7 (d) Folded dipole and its applications.(5 marks)