Punjab Technical University 2008-5th Sem B.Tech Electronics and Communications Engineering Antenna & Wave Propagation- -e - Question Paper

Paper ID[EC303]
B.Tech.(Sem-5th )
ANTENNA & WAVE PROPAGATION(EC-303)
Time:03 Hours Maximum Marks:60
Instructuions to Candidates:
1) Section-A is Compulsory.
2) Attempt any 4 ques. from part – B.
3) Attempt any 2 ques. from part –C.

part – A
Q1)
a) Draw the charge and current distribution for a chain of Hertizan dipoles and how they contribute for radiation.
b) Draw the 2 dimensional top view and side view of omni directional and isotropic radiation trend.
c) Define directive gain of antenna. Write expressions of radiation resistance of a dipole antenna.
d) How do reflections from the ionosphere effect the transmission?
e) A rectangular aperture with a constant field distribution , with a=3? and b=2?, is mounted on an infinite ground plane. calculate FSLBW and FSLMM in the E-plane.
f) What is virtual height and how is this important in transmission or receiving signals.
g) Define field equivalence principle.
h) Differentiate ranging from planar and linear array.
i) What is critical frequency and write expression for the critical frequency in terms of ionization density.
j) Define superdirectivity. What will be the value of directive gain(in dB) for a super directive antenna?


part –B
Q2) discuss the concept of polarisation in antennas.What are the conditions for the various kind of polarisations? Also show that circular polarization is a condition of elliptical polarization.
Q3) The maximum radiation intensity of a 90% efficiency antenna is 200mW/unit solid angle. obtain the directivity and gain (dimensionless and in dB) when the
a) Input power is 125.66mW.
b) Output power is 125.66mW
Q4)How does E and H field components vary in near, intermediate and far field, for an infinitesimal current carrying dipole.
Q5) If the antenna enters the ionosphere, what modifications will occur in the performance of antenna. Does earth’s magnetic field affect it? If yes, how.
Q6) discuss self amd mutual impedance. What is the importance of impedance in antennas.

Section-C
Q7) A half wave dipole radiator is elevated 50ft above the ground. A receiving dipole two miles distant is elevated 15ft. Determine the sapce and surface wave fields strengths at the receiving antenna. When the transmitting antenna carries a current of one ampere at a frequency of 50MHz. Assuming an avg. earth having er=15 and s=5x10-3.
a) For vertical half wave dipole and
b) For horizontal half wave dipole.
Q8) define the working of Slot and reflector antenna. Derive the expressions for the radiation resistance of these antennas.
Q9) elaborate the various kinds of arrays? Derive the expression for the directivity of an element ordinary end fire linear array.

Earning:   Approval pending.