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Printed Pages: 2
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Paper Id: 130501
Sub Code: REC 051
Roll No.
B.TECH.
(SEM V) THEORY EXAMINATION 2018-19
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ANTENNA AND WAVE PROPAGATION
Time: 3 Hours
Total Marks: 70
Note: 1. Attempt all Sections. If require any missing data; then choose suitably.
SECTION A
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1. Attempt all questions in brief. 2 x 7 = 14
- a) Give reason why does retardation potential take place?
- b) A thin dipole antenna is ?/15 long if its loss resistance is 1.5 O. Find radiation resistance and efficiency?
- c) What is end-fire array and broad-side array?
- d) Define the gain of antenna?
- e) Define virtual height and skip distance?
- f) Estimate the distance & effective aperture of a paraboloid reflector antenna required to produce Null beam width of 10º at 3GHz.
- g) Find the radiation efficiency of a 1m diameter loop of diameter copper wire at 10MHz.
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SECTION B
Attempt any three of the following: 7 x 3 = 21
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- a) Calculate the effective aperture for an antenna of length 2cm at a 1.2 GHz. What will be the power received for an incident power density of 2mW/m²?
- b) Sketch the horizontal and vertical plane radiation pattern of Centre fed dipole for the following length- (i) ?/2 dipole (ii) 3?/2 dipole (iii) 2? dipole
- c) What is folded dipole antenna? Describe Yagi-Uda antenna and explain its operation?
- d) Explain the principle of operation of parabolic dish? Why is the parabolic shape is used?
- e) Explain the phenomenon of Duct Propagation. What are the Ionospheric conditions under which duct propagation can take place?
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SECTION C
Attempt any one part of the following: 7 x 1 = 7
- a) Discuss about antenna impedance and temperature?
- b) How the directivity of any antenna is related and what is the relationship between directivity and gain of the antenna?
Attempt any one part of the following: 7 x 1 = 7
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- a) Explain the principle of pattern multiplication. Obtain the radiation pattern of 4 element fed in-phase, spaced ?/2 apart using pattern multiplication.
- b) Define the isotropic sources? N-isotropic sources are arranged in a uniform linear array. Derive an expression for the array factor?
Attempt any one part of the following: 7 x 1 = 7
- a) A linear broad-side array consists of four equal isotropic in-phase point source width ?/2 spacing. Find the directivity, BWFN and HPBW of the array?
- b) An end fire array consisting of several half wavelength isotropic radiators has a directive gain of 30. Find the array length and width of the major lobe. What will be the value for broadside array?
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Attempt any one part of the following: 7 x 1 = 7
- a) Explain with suitable diagram log periodic antenna? What are practical application of these antenna?
- b) A loop antenna consists of 10 turns, each having an area of 1 m². A radio wave having a frequency of 1 MHz induces a sinusoidal emf of 100 mV(rms) in this antenna when it is oriented for maximum response. Calculate the peak value of the magnetic field intensity of the RF wave. (µo=4px10-7h/m)
Attempt any one part of the following: 7 x 1 = 7
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- a) Assume that reflection take place at a height of 350km & that the maximum density in the ionosphere corresponds to a 0.8 refractive index at 15 MHz what will be range for which the MUF is 20MHz. Assume flat Earth.
- b) Derive expression for refractive index of ionosphere µ = v(1 - 81N / f²)
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