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Posted By: Sra1 Member Level: Diamond Posted Date: 28 May 2008
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2007 Jawaharlal Nehru Technological University B.Tech Electronics & Communications Engineering ANTENNA AND WAVE PROPAGATION (Supplimentary Examinations, November 2007) Question paper
Set No 4
----------------------
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1. (a) As related to antennas, define and explain the following terms:
i. Gain
ii. directivity
iii. radiation resistance
iv. effective area
v. effective length
vi. efficiency
vii. beam width
viii. bandwidth.
(b) Evaluate the directivity of
i. an isotropic source, and
ii. source with bi-directional cos ? power pattern. [8+8]
2. (a) Define and account for the presence of
i. Radial power flow
ii. Radiation resistance for a short dipole,
iii. Uniform current distribution
(b) Obtain the relative amplitudes of radiation, induction and electro-static fields at a distance of 2? from a short current element having an uniform current of 1 mA along its length. [8+8]
3. (a) What is array factor? Find the array factor of two element array?
(b) For an array of two identical infinitesimal dipoles oriented with a separation of D and phase excitation difference B between the elements, find the angles of observation where the nulls of the array occur. The magnitude of excitation of the elements is same. [8+8]
4. Write notes on:
(a) Parasitic elements and their reference
(b) Terminated antennas
(c) Applications of Rhombic Antenna.
(d) Multi director Yagi Antenna. [4+4+4+4]
5. (a) Sketch the typical geometry of a helical antenna radiating in axial mode, and list out all its parameters and basic characteristics. List out the expressions for HPBW, BWFN, directivity and axial ratio.
(b) With a neat sketch, explain the image formation and field calculation for the case of a 600 corner reflector. [10+6]
6. (a) Determine the axial length, H-plane aperture dimension and the total flare angles in E and H 0.35?. Calculate its beam widths and directivity.
(b) List out and explain the set of principal plane patterns required for a circularly
polarized antenna. [8+8]
7. (a) For vertical incidence, determine the critical frequency for reflection by the ionosphere if maximum value of electron density is 1.24 x 106/cc. What happens if the angle of incidence is changed to 600 Establish the relations used?
(b) Describe any two types of fading normally encountered in radio wave propa-
gation. How are the problems of fading overcome? [8+8]
8. With neat diagrams, explain the important features of different types of space wave propagation of electromagnetic waves over long distance even beyond the horizon. For what frequency range this is applicable and why? [16]
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