JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III ANTENNAS AND WAVE PROPAGATION Previous Question Paper (November/December - 2017 - R13)
Part A is compulsory (25 Marks). Answer all questions. Part B consists of 5 Units. Answer any one full question from each unit (10 Marks each).
PART - A
What is quarter wave monopole?
Answer
A quarter wave monopole is an antenna consisting of a straight conductor of length approximately one-quarter of the operating wavelength, mounted vertically over a conducting ground plane. The ground plane acts as a mirror, creating an image of the antenna that effectively doubles its length to form a half-wave dipole, resulting in a radiation pattern that is identical to the upper half of a half-wave dipole.
Write the relation between effective aperture and Directivity.
Answer
The relationship between the effective aperture (Ae) and directivity (D) of an antenna is given by the following expression:
In this formula, λ represents the operating wavelength of the antenna. This relation demonstrates that the effective aperture is directly proportional to the directivity of the antenna, meaning that as an antenna becomes more directive, its ability to capture power from an incident electromagnetic wave increases proportionally.
Draw the structure of helical antenna with a coaxial line feed.
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What is the spacing between elements of Yagi - Uda antenna
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What are the disadvantages of lens antennas?
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Write short notes on horn antenna.
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What is the main disadvantage of binomial array?
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Draw uniform linear array.
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Derive the expression for refractive index of ionosphere.
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Explain the concept of super refraction.
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PART - B
Derive an expression for the radiation resistance of a Half wave dipole antenna.
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What is meant by the effective area of an antenna? How is it related to the gain?
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Discuss about loop antenna. What are the disadvantages of loop antenna? What are applications loop antennas?
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Write short notes on Yagi-Uda array Antenna and its applications, advantages and drawbacks.
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Discuss different types of horn antennas with neat sketches.
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With neat sketch, explain the operation of helical antenna.
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Explain the geometry of paraboloidal reflector with neat diagram.
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Calculate the 3dB beam width and power gain of a parabolic antenna at a frequency of 1.6GHz with 2.4 meter diameter and 48% antenna efficiency?
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Compare UHF and VHF antennas.
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What are the various feeds used in reflectors?
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Discuss broadside array and end fire array with neat diagrams.
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Derive expression for antenna array factor.
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An end fire array consisting of several half wave length long isotropic radiators having directive gain of 30. Find the length of array for broad side antenna?
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A broadside array of identical antennas consists 8 isotropic radiators separated by distance λ/2. Find radiation field in a plane containing the line of array showing directions of maxima and null.
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Briefly describe the following terms connected with sky-wave propagation: a) Virtual height b) Critical frequency c) Maximum usable frequency d) Skip distance.
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Describe the troposphere and explain how ducts can be used for microwave Propagation.
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Write a short note on Multi-hop propagation.
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