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This document contains questions related to antennas and electromagnetic waves. It covers topics such as: 1. The Friss transmission formula, directivity of antennas, calculating directivity from radiation patterns, deriving radiation resistance of dipoles, and relationships between effective aperture and beam area. 2. Deriving expressions for radiation patterns of end-fire arrays and calculating total radiated power and directivity from given radiation intensity distributions. 3. Dolph-Chebyshev distribution for linear arrays and its properties for minimizing sidelobes for a given beamwidth. Comparing radiation patterns of linear arrays using uniform, binomial, and other amplitude distributions.

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Raj
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69 views3 pages

1

This document contains questions related to antennas and electromagnetic waves. It covers topics such as: 1. The Friss transmission formula, directivity of antennas, calculating directivity from radiation patterns, deriving radiation resistance of dipoles, and relationships between effective aperture and beam area. 2. Deriving expressions for radiation patterns of end-fire arrays and calculating total radiated power and directivity from given radiation intensity distributions. 3. Dolph-Chebyshev distribution for linear arrays and its properties for minimizing sidelobes for a given beamwidth. Comparing radiation patterns of linear arrays using uniform, binomial, and other amplitude distributions.

Uploaded by

Raj
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Printed Pages-4 NEC-504

(c) Edge distribution (d) Optimum


Roll No:
distribution
HI-Tech Institute of Engineering and Technology
(c) Explain the field of a short dipole at very low B.Tech (EC, V SEM)
Pre-University test, 2017-2018
frequencies. Antenna & Wave Propagation

Name of Faculty: Raj Gopal Mishra

Time: 3 hours Total Marks: 100


SECTION A
Note : The answers are expected to be in maximum 30 words.
1. Attempt all parts of this question: (2 x 10 = 20)

a) Explain Friss Transmission formula.


b) What is directivity of antenna? Relate directivity and
gain of antenna.
c) Calculate the directivity for a unidirectional source
whose pattern is =m ?
d) A source has a cosine radiation intensity given by
U=Um . The radiation intensity has value only in
upper hemisphere. Fin the total power radiated and its
directivity.
e) Derive the radiation resistance of a short electric
dipole.
f) Evaluate the radiation resistance of antenna length antenna. Draw its radiation pattern and
element operating at a frequency of 10 MHz. calculate HPBW.
f) What is end-fire array? Deduce an expression for
g) Derive relationship between effective aperture and radiation pattern of an end-fire array with vertical
beam area of an antenna. dipoles.
h) What is the importance of retarded potential? g) (i) A source has a cosine radiation intensity given by
U = Um Sin2. The radiation intensity has a value
i) Evaluate the radiation resistance of an element of
only in upper hemisphere. Find the total radiated
length l=1 m at an operating frequency of 10 MHz. power and its directivity.
j) Find the radiation resistance of Hertzian dipole of (ii) A ground vertical antenna fed at the bottom with
an rms current of 32 ampere at 1 MHz produces field
length m in free space.
strength of 9mV/meter at a distance of 100 Km.
SECTION B
Evaluate the effective height of such antenna
2. Attempt any five parts of the following. (10 x 5 = 50)
SECTION C

a) Calculate the radiation resistance of short electric 3. Attempt any two parts of the following. (15 x 2 = 30)
dipole.
(a) What is meant by Dolph-Chebysev Distribution for a
b) Write short notes on: (i) Antenna Temperature
(ii) Radiation Intensity linear array? Show that such a distribution gives a
(iii) Isotropic antenna minimum side lobe level for a given beam-width of
c) Explain array of two isotropic point sources of equal
major lobe.
amplitude and opposite phase.
d) What is pattern multiplication? Draw the radiation (b) Explain linear broad side arrays with non-uniform
pattern of four sources using multiplication of pattern. amplitude distribution. Compare following four
e) Design a four element broad side array of amplitude distributions
spacing between elements. Consider unit element as (a) Uniform distribution (b) Binomial
distribution

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