# Transmission Lines and Antennas June-July 2009

PART – A

1    a. Obtain the required condition for a transmission line to have neither frequency nor delay distortion.

b. A generator of 1-0 volt, 1kHz supplies power to 100 km open wire line terminated in Zo and having following parameters. R = 10.4 ohms / km ; L = 0.00367 henry per km ; G-0.8xl0′6mhosperkm C = 0.00835 |iF per km.

Find, characteristic impedance, Propagation constant, wavelength of the

propagating wave, sending end current.

2 a. Comment with Justification on the correctness of the statement – “Standard reference antenna for the directive gain is the istropic antenna”.

b.  Comment with justification on the correctness of the statement – “A quarter wave section of the line may be thought of as a transformer to match a load and to a source impedance”.

c.   A line of characteristic impedance 200 ohms is terminated in a load of 80 – J100 ohms. Determine the location and length of the single stub matching section. The characteristic impedance of stub is same as that of line.

3  a. Derive Frii’s Transmission formula.

b. Define Stray factor, Effective length, Effective Aperture. State the expressions, notations used.

a.     T and n equivalent to lines.

b.     Telephone cables.

c.     Antenna Field Zones.

PART – B

5    a. Find the directivity for the source with unidirectional cosine squared power pattern.

b. Illustrate the principles of pattern multiplication.

c.   Derive the expression for an N-element uniform array. Further show that the peaks of this array factor are given by the solution of the equation. N.tan(\j//2) = tan (N y/2).

6  a. Derive the expressions for Electric and magnetic fields of a short dipole.

b. Give the properties of Horn Antenna.

c. Illustrate – Babinet’s Principle.

7 a. Derive instantaneous electric field at a large distance V from a loop antenna of radius ca.

b.  Give the properties of Parabolic reflector. How a parabolic reflector servers the purpose of transmitting and receiving antenna? Discuss in detail its short comings.

8  Write short notes on :

a.   Broad side array with non uniform amplitude distribution.

b.  Lens antenna.

c.   Plasma antenna.