Attempt all questions. Full Mark: 100 All questions carry equal marks

Time: 3 Hours
Jan 2016
Attempt all questions.
Full Mark: 100
All questions carry equal marks.
Q1: (a) Write definitions of:
i- Radiation power intensity
ii- Beam solid angle
iii- Directivity of an antenna
iv- radiation resistance of an antenna
v- Polarization of an antenna.
(b) The radiation field of a small single turn circular loop antenna of radius a and uniform
current of rms value I amperes in free space is given by: E, = 30TT (~a)2 I sineS) e-i13r/r.
(E, 0, Ee= 0.)
i- Determine the radiation resistance, the beam solid angle, and the directivity of the
antenna. What would be these parameters if the loop is made of n turns?
ii- What is the type of polarization of the small loop antenna?
02: (a) Two antennas are separated by a distance r in free space. Write expression relating
the power at output the terminals of the receiving antenna to the input power delivered
to the transmitting antenna.
(b) Discuss the principle of working of Parabolic Reflectors. What factors do degrade the
directivity of parabolic reflector antennas?
(c) A satellite transmits electromagnetic waves at 12 GHz via an antenna of gain 56 dB.
The input power to the satellite antenna is 20 W. Determine the magnitude of the
electric field at a point A on the earth distant 37000 km from the satellite. The receiving
antenna at A is a parabolic dish of aperture diameter 6 m, aperture efficiency 90%, and
radiation efficiency 80%. What is the gain of this antenna in dB and what is the power at
its output terminals?
03: (a) Give three examples of broad-band wire antennas and explain briefly why they are
(b) Outline the radiation mechanism of microstrip patch antennas What are the main
advantages and limitations of these antennas?
What are the effects of substrate
thickness and dielectric constant on the impedance bandwidth of the antenna?
04: (a)What are the reasons for using antenna arrays?
(b) Determine the main beam-width and the level of the first side lobe relative to the main
beam of an n = 6 elements uniform forward endfire array with element spacing M2. Vvhat
would be these parameters if n is made very large?
(c) A 3-elel1'ent linear array is made up of equally spaced parallel short elect ic dipole"
oriented in free space in the z direction. The element currents are such that 11 : b : I~ =
1. : 2 : 1. If the array is placed at height h above a perfectly ground plane, what would be
the far zone electric field?
(Hint: make use of the principal of pattern multiplication)
Q5: Write short notes on: i- Ground wave propagation
ii- Propagation in the ionosphere
iii- Line of sight communication.
v- Diversity reception.
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