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ANTENNA :- Important questions

Q1. (a) Explain antenna action. Define any of its four parameters.
(b) An antenna has an effective height of 10m and the current at the base is 450A (rms) at 50 kHz. Calculate the power radiated. If the total resistance of the antenna system is 1.5 ohm find out the efficiency of the antenna.
(c) How retarded potentials are useful in deriving the radiated field due to any antenna?
(d) Show that the directivity of an alternating current element is 1.76dB.
(e) Find the Gain, beam width and capture area for a parabolic antenna with a 6 m diameter dish and dipole fixed at a frequency of 10 GHz.
Q2. (a) Classify various type of antenna array with example.
(b) Derive and draw the radiation pattern of two isotropic sources separated by a distance  with an initial phase of 90 degree.
(c) With the help of pattern multiplication draw the radiation pattern of 4 element isotropic array separated by  with the initial phase of 0 degree among them.
(d) Design Yagi-Uda antenna of 6 elements of provide gain of 10 dB if the operating frequency is 200 MHz
(e) Derive the radiation resistance of a  antenna.
(f) Derive the field component of short electric dipole.
Q3. (a) Design a helical antenna operating in the axial mode that gives a directivity of 14 dB at 2.4 GHz. For this antenna, calculate the input impedance, half power beamwidth, BWFN, and the axial ratio.
(b) Determine the directivity of a loop antenna whose radius is 0.5m, when it is operated at 0.9MHz. Explain two of its applications.
(c) Design a log periodic dipole array having a τ = 0.895 and σ =0.166 over a frequency range of 10 MHz to 30 MHz
Q4. (a) Why we use term modified refractive index in propagation of radio waves. In which type of propagation it is valid and what is its value?
(b) Explain the structure of ionosphere. Explain any two parameters of sky wave propagation.
(c) What is troposphere? Explain the mechanism of wave propagation in this region.

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