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Thursday, 26 June 2014

Antenna-Theory and Practice-Model question paper for Electronics and Communication Engineering

1(a) Define the terms power density and radiation intensity. (4 Marks)
(b) Derive an expression for electric field of electric current element whose current varies arbitrarily with time. (6 Marks)
(c) Show that when the relaxation time for a material is little as compared to the period of the time-harmonic field, the displacement current may be neglected in comparison with the conduction current. (6 Marks)
(d) A sheet of glass having a relative dielectric constant of 8 and negligible conductivity is coated with a silver plate. Show that at a frequency of 100 MHz, the surface impedance will be less for a 0.001 cm coating than for a 0.002 cm coating. (4 Marks)
2(a) Write a detailed note on current distribution on the cylindrical conducting antenna. (6 Marks)
(b) Write a note on bioconical antenna. (4 Marks)
(c) Derive the array factor of a bionomial array of 7 isotropic point sources. (4 Marks)
(d) Assume that the current distribution on a 3/4(wavelength) thin layer antenna is sinusoidal. Calculate and plot the radiation pattern in the plane of the antenna. (6 Marks) 
3(a) If a small square loop is considered equivalent to 4 short dipoles, calculate the far-field pattern. Show that the pattern in the loop is a circle. (8 Marks)
(b) Explain terminal impedance of Helix. (4 Marks)
(c) A helix has 8 turns. The diameter is 2.5 cm. The turn spacing is 15 cm. Assume increased directivity and calculate the phase velocity. Calculate the field pattern at 600 Mc and plot the pattern, (8 Marks)
4(a) Explain Babinets' principle. (6 Marks)
(b) Write a note on slot arrays on waveguides. (6 Marks)
(c)What are the dimensions of a slot antenna whose terminal impedance is (70+j0) ohms? The slot is open on both sides. ( 8 Marks)
5(a) Write a note on different type of Horns. (6 Marks)
(b) For the parabolic cylinder, the line source is isotropic in a plane perpendicular to its axis. Explain. (8 Marks)
(d) Calculate the gain of the horn antenna of length l = 12 cms, a = 12 cms and b varying between 5 and 10 cms in steps of 1 cm. Plot gain versus b. (6 Marks)
6(a) Write notes on delay lens and Lubeburg lens. (4 Marks)
(b) Solve the electromagnetic boundary-value problem of a dielectric sphere embedded in free-space and derive the characteristic equation. (8 Marks)
(c) What are self-complementary log-periodic antennas? (4 Marks)
(d) Write some important features of Dolph-Chebyshev optimization method. (4 Marks)
7(a) What are radomes? (4 Marks)
(b) Write a note on antennas used for medical applications. (6 Marks)
(c) What is a Smith Chart? Why it is used? (4 Marks)
(d) Explain reciprocity theorem for antennas. (6 Marks)
8 (a) What is free-space transmission ratio? Explain. (4 Marks)
(b) Write a note on formation of ducts and mode theory of duct propagation. (6 Marks)
(c) Discuss the different causes of attenuation and fading in tropospheric propagation. (6 Marks)
(d) An electromagnetic wave of frequency 12.73 kHz is incident in the F-layer at an angle of 45 degrees which is equal to the critical frequency of the layer. Calculate the MUF and skip distance. (4 Marks)

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