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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 3
----------------
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1. (a) Define the term input “impedance” of an antenna. Show that the input impedance of an antenna used in a transmitting mode is the same as the input impedance if it is used in receiving mode. Clearly mention the assumptions made in proving this relation.
(b) Define and derive a relation for effective length ‘le’ of an antenna. Find ‘le’ or a short dipole antenna. [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) A linear broad side array consists of four equal in phase point sources with ?/3 spacing. Calculate and plot the field pattern. Also find directivity and beam width.
(b) Distinguish between ordinary EFA and an EFA with increased directivity and compare them. [10+6]
4. (a) Compare the requirements and radiation characteristics of resonant and non-resonant radiators?
(b) Determine the lengths and spacing requirements for a 3-element Yagi -Uda antenna array at 500 mHz, and explain its characteristics. [6+10]
5. (a) Establish and explain the gain and beam width relations for a parabolic reflector and account for its beam shaping considerations.
(b) Write short notes on: Cassegrainian antennas. [8+8]
6. (a) Distinguish between sectoral, Pyramidal and Conical Horns, with neat sketches. List out their utility and applications.
(b) With neat set up, explain the absolute method of measuring the gain of an antenna. [8+8]
7. (a) Describe the effect of terrain and earth’s curvature on ground wave propagation.
(b) Explain the terms
i. Virtual height and
ii. Multihop transmission
iii. sporadic E layer with reference to sky wave propagation. [6+10]
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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