# VTU Previous Exam Paper BE EC 6th Sem Antenna and Propagation Jan 08

Note : Answer any FIVE full questions.

1 a. Define the terms Normalized field pattern, Beam efficiency, Aperture efficiency, Directivity. Effective height of an antenna.

b.  Write brief notes on – Antenna Field Zones.

2 a.Derive the expression for total field, in case of two isotropic point sources with same amplitude and opposite phase. Plot the relative field pattern when these two isotropic sources are spaced — apart.

b.  Find the directivity for the source with sine – squared (Doughnut) power pattern. (05 Marks)

c.   Illustrate the principle of pattern multiplication with suitable example.

3 a. Derive the expression for Array factor in case of linear array of ‘n’ isotropic

point sources of equal amplitude and spacing.

b.  Derive the expression for radiation resistance of short dipole with uniform current.

4 a.  Derive the expression for instantaneous electric field and magnetic field at a large distance ‘r’ from a loop antenna of radius ‘a’.

b.  Compare the far fields of small loop and a short dipole.

5 a. Give the brief account of design considerations of Log – periodic Array.

b.  State and explain Rumsey’s principle.

c.   “Helical antennas are indispensable for space communication applications”. Justify the statement in brief.

6 a.  Describe the important features of Pyramidal Horn Antenna.

b.  Write notes on i) Adaptive base station antennas of terrestrial mobile communications

ii)  Whip antennas.

7 a. Discuss the salient features of ground wave propagation.

b.  Distinguish between E – layer and Sporadic E – layer of ionosphere.

c.   What are the effects of earth’s magnetic field on propagation of radio waves through the ionosphere?

8 a. Explain the following terms in connection with sky wave transmission and indicate briefly the factors on which they depend : i) Maximum usable frequency ii) Critical Frequency

iii)  Skip distance.

b.  Distinguish between Virtual height and Actual heights of an ionized layer.