## ANTENNAS AND WAVE PROPAGATION JNTU previous years question papers

2011

ANTENNAS AND WAVE PROPAGATION

( Common to Electronics & Communication Engineering and Electronics & Telematics)

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

1. (a) Define the terms:

i. Beam Width

ii. Side Lobe Level

iii. Polarization

iv. Effective Aperture Area.

(b) What is the effective length of an antenna. Determine the effective length of a half wave dipole antenna. [8+8]

2. (a) Assuming the expression of radiation fields for alternating current element,find out its radiation resistance. Explain the significance of the term Rr.

(b) An antenna whose effective height is 100 meters at a frequency of 60KHz radiated 100KWof power. Determine the strength of the electric field at a distance of 100km from the antenna. Neglect the ground effect and atmospheric losses.

[8+8]

3. (a) Compute the principle beam width for broadside and end fire array.

(b) A uniform linear array consisting of isotropic radiators spaced half wavelength apart has 10 elements, each element carries 0.5 amperes. Calculate the width of principle beam and maximum power radiated if operated as

i. Broadside array

ii. End fire array. [10+6]

4. (a) Explain the construction of Rhombic Antenna with balloon and termination.

Draw the radiation pattern of rhombic antenna

i. over perfectly conducting plane.

ii. in the presence of earth.

(b) Derive electric field expression for Non Resonant antenna. [8+8]

5. (a) For what mouth diameter and capture area of a paraboloid reflector is a BWFN of 120 obtained when it is operated at 2.5 GHz.

(b) Describe the cassegrain feed mechanism of a parabolic reflectors. [8+8]

6. (a) What is an electromagnetic horn antenna? What are its applications? The length of an E-plane sectoral horn is 15cms. Design the horn dimensions such that it is optimum at 10GHz.(b) Calculate the minimum distance required to measure the field pattern of an antenna of diameter 2m at a frequency of 3GHz. Derive the necessary equa-

tion. [8+8]

7. (a) Show that MUF of ionized layer is given by fcp1+(D/2h)2 for flat earth.

(b) Discuss the following:

i. Ionospheric Storms.

ii. Sudden Ionospheric Disturbances. [8+8]

8. A television transmitting antenna mounted at a height of 120m radiates 15kw power equally in all directions in azimuth at a frequency of 50MHz. Calculate

(a) the maximum LOS range.

(b) the field strength at a receiving antenna mounted at a height of 16m at a distance of 12km.

(c) the distance at which the field strength reduces to 1mv/m. Derive the formulas used.