JNTU
JNTU B.Tech III ANTENNAS AND WAVE PROPAGATION Previous Question Paper (May - 2018 - R13)
Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks.
Part A
Define an antenna and mention the necessity of antenna.
Answer
An antenna is a metallic device used to transform electromagnetic energy in a transmission line into free-space electromagnetic waves or vice versa. It is necessary as a transducer to facilitate wireless communication, acting as the interface between the guided waves in a circuit and the unguided waves in space.
How the radiation is accomplished in a two wire antenna?
Answer
Radiation in a two-wire line occurs when the wires are flared out, preventing the cancellation of fields. As the wires diverge, the currents no longer flow in opposite directions with identical phases at every point, allowing the electric and magnetic fields to detach from the conductors and propagate as electromagnetic waves into space.
Mention the advantages of folded dipole.
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While measuring the gain of horn antenna the gain oscillator was set for 9 GHz frequency and attenuation inserted was found to be 9.8 dB. Calculate the gain of horn. The distance between the two horn was 35cm.
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Estimate the diameter of a paraboloidal reflector required to produce a beam of 5 degrees width at 1.2 GHz.
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What are the merits and demerits of lens antenna?
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Calculate the directivity of given linear end fire, uniform array of 10 elements with a separation of λ/4 between the elements.
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Describe the principle of end-fire array.
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Find the maximum range of tropospheric for which the transmitting antenna height is 100 ft and receiving antenna height is 50 ft.
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Briefly explain about D-region.
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Part B
Explain the following terms with proper expressions: Directivity, Field pattern, Half power beam width, Beam efficiency.
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State and prove Frii’s transmission formula.
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With the help of Maxwell’s equation, explain how the radiation and reception of EM waves takes place.
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Describe about the following: Folded – dipole antenna, Yagi-uda antenna.
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Find length L, H plane aperture and flare angles θE and θH of a pyramidal horn for which E plane aperture is 10 λ. Horn is fed by a rectangular waveguide with TE10 mode. Assume δ = 0.2 λ in E plane and 0.375 λ in H plane. Also find E plane and H plane beam widths and directivity.
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Write short notes on helical antenna.
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Describe in detail about the cassegrain method of feeding a paraboloid reflector, with the help of the geometry of this feeding arrangement.
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Explain briefly about features of microstrip antennas.
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Compare the performance of parabolic reflector and corner reflector.
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Explain zoning in lens antenna.
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What is broadside array? Draw the pattern. Obtain the expressions for directions of peaks, nulls, sidelobes and BWFN.
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Explain the method of measuring impedance of an antenna.
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Calculate the directivity of an antenna, which has half power beam widths of 60 degrees and 75 degrees in vertical and horizontal planes respectively.
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Explain in brief about the following terms with respect to wave propagation: Critical frequency, MUF, Skip distance, Virtual height.
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Discuss the salient features of ground wave propagation.
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Calculate the wave tilt in degrees of the surface wave over an earth of 6mm conductivity and relative permittivity of 12 at 2 MHz.
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