# Mumbai University Previous year question papers

## VI Sem Electronics Examination June 2005

## Antena and Wave Propogation

N.B. (1) Question NO.1 is cor.lpulsory.

(2) Answerany four from the remainingsix questions.

(3) Figures to the right indicate marks.

(4) Assume any suitable data whenever required.

1. (a) Derive the wave equation in terms of vector potential from the Maxwell’s Equation~. Also find the solution of wave equation for infinitesimal dipole.

(b) Explainthe mechanism of ionospheric propagation. Define the terills criticalfrequency and MUF.

The maximum electron density of the ionospheric layer at 10 MHzoccurs when the refractive index is 0.92. Find the range ifMUFis 10 MHzand the height of the ray reflection point on the ionospheric layer is 400 400 km. Assume flat earth and negligible effect of earth’s magnetic field.

2. (a) When a linear dipole is cailed a infinitesimaldipole or a small dipole or a finite length dipole? Compare infinitesimal dipole, small dipole and halfwave length dipole in terms of current distribution, radi’3tion resistance, effective length and directivity.

(b) ‘DeriVethe expressions for electric and magnetic field for a small loop antenna. Compare them with thyse of infinitesimal electric dipole.

3. (a) Define the terms directivity, radiation resistance, radiation efficiency and polarization loss factor of an antenna. An antenna having a gain of 6 dB over a reference antenna is radiating 700 watts. Calculate the power the reference antenna must radiate in order to be equally effective in most preferred direction.

(b) The normalised radiation intensity of an antenna is given by U=sin 0 sin2 cp for 0 ~ 0 ~ 7t , 0 ~ cp~ 7t =0 elsewhere

Find (i)Exact directivity in dtB. {“

(ii) Arimuthal and elevation HPBW in degrees.

4. (a) Twopoint sources carrying current of same phase and magnitude are placed with a distance Abetween them. Find the total far field expression, directions of maxima and directions of minima. Plot the pattern.

(b) State and explain principle of pattern multiplication.

Using lhe above principle plot the pattern for an array of four isotropic sources with a distance of A,’2 between adjacent elements.

5. (a) Explain the different types of feeds for paraboloidal reflector antenna.

A paraboloidal reflector is required to have a power gain of 1000 at a frequency of 03 Ghz. Determine the mouth diameter and beamwidth of the antenna.

(b) Explain the structure of microstrip antenna. Find its effective heig~.: and directivity. Discuss its applications.

6. (a) Explain differeht types of horn antennas. What are the applications of horn antennas?

Determine the length L. H plane aperture and flure angles 8e and 8Hfor a pyramidal horn. Eplane aperture aE=10 A. (delta)E =0.5 A. (delta)H =0,375 A.

Find the beam width and directivities.

(b) Compare –

(i) Logperiodic and Yagi Uda array.

(ii) Rhombic and Loop antenna.

7. (a) Explain space wave propagation. Determine the radio horiton of a space wave propagation if the

height * ota *tr~nsmitting antenna is 60 mts and that of receiving antenna is 6 mts. Assume standard atmosphere. ‘

(b) Write short notes on :

(i) Sleeve dipole

(ii) Troposp~eric scatter propagation.