# Mumbai University Previous year question papers

## Antena and Wave Propogation

N.S.: (1) Question No.1 is  compulsory.

(2) Attempt any four questions out of remaining six questions.

(3) Assume suitable data wherever required.

(4) Figures to the right indicate full marks.

1.(a) Explain the followingterms :-
(i) Critical frequency

(ii) Beam efficiency

(iv) Friss transmission formula

(v) Directivity.

‘(b ) Derive ~n expression for the near field and far field for a short electric dipole. Draw the field pattern.

2.. (a) When a linear dipole is called an infinitesimaldipole or a small dipole or a finite length dipole? Compare infinitesimal dipole, small dipole and halfwave length dipole in terms of current distribution, radiation resistance, effective length and directivity.

(b) What is an array factor (AF) ?

(c) List the parameters that decide the overall pattern of an antenna array.

3. (a) Why antenna array is required? Explain broadside and end-fire array in detail. 10

(b) Design a broadside Dolph-Tschebyscheff array of 10 elements with spacing d between the elements and with a major to minor lobe ratio of 26 dB. Find the excitation coefficient.

4.(a) Disc;:ussthe effect of ‘flare angle’ on aperture phase angle variation in microwave pyramidal Horn antenna. Also explain E-plahe & H-Plane Horn antenna.

(b) What is Vagi antenna? Explain its construction &properties with special reference to directivityand bandwidth.

5.(a) Descrioe space wave propagation and derive the relation for maximum distance between transmitting and receiving antenna. Earth is assumed to be flat.

(b) A radio communication link is to be established via ionosphere. Take maximurTl v;,~u&: 1D . height to be 100 km. at the mid-point of the path. Assume critical frequency to be 2 MHz and distance between stations to be 600 km. Find optimum working frequency (OWF) and angle of elevation of beam.

6.(a) Explain the working of loop antenna. Sketch its field pattern. Give applications.

(b) Explain the different types of feed~ for paraboloidal reflector antenna.

7.(a) Write details on the formation of ionised layer in the ionosphere and describe their importance in radio communication.

(b) Explain travelling wave antennas and their applications.