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Sunday, 27 October 2013

Electromagnetic waves and radiating systems - model question paper for B.Tech



1(a) Explain Ampere’s Force law. (4 Marks)
(b) Show that the capacitance of an isolated sphere of radius R is 4πε0R Farad. (6 Marks)
(c) What is Dirac Delta? Draw approximate form and symbolic representation. (6 Marks)
(d) Verify that the expression for the potential due to an electric dipole satisfies the Laplace equation. (4 Marks)
2 (a) Write Maxwell’s equations. (5 Marks)
(b) Explain linear, elliptical and circular polarization. (6 Marks)
(c) Write notes on surface impedance and skin effect. (4 Marks)
(d) Sketch the planes of zero magnetic field strength, zero EZ, and zero EY for the case of oblique reflection with E parallel to plane of incidence. (5 Marks)
3 (a) State and explain Poynting’s theorem. (6 Marks)
(b) Write a note on attenuation in parallel-plane guides. (6 Marks)
(c) What is attenuation factor? (4 Marks)
(d) Show that a coaxial line having an outer conductor of radius ‘b’ will have minimum attenuation when the radius ‘a’ of the inner conductor satisfies the ratio b/a=3.6 (4 Marks)
4(a) Explain Child-Langmuir law. (4 Marks)
(b) Write a note on frequency response of dielectric materials. (6 Marks)
(c) Deduce the expression for the power radiated through a spherical surface by the dipole of half-length H. (6 Marks)
(d) Determine the distance from a 60-cycle circuit where the radiation field ia almost equal to the induction field. (4 Marks)
5 (a) Explain Thevinin’s theorem. (4 Marks)
(b) What are the directional properties of dipole Antennas? (4 Marks)
(c) Write a note on practical antennas and methods of excitation. (8 Marks)
(d) A uniform cross section tower antenna is 400 ft high and 7 ft square. Determine the base impedance at a frequency of 1300 kHz. (4 marks)
6 (a) Explain Tchebyscheff distribution. (8 Marks)
(b) Design a six element broadside array having a spacing d=λ/2 between adjascent elements. The pattern is to be optimum, with the side-lobe level 20 db down. (6 Marks)
(c)Write a note on slotted cylinder antennas. (6 Marks)
7 (a) What are biconical antennas? Explain the two methods for the calculation of terminal impedance. (8 Marks)
(b) Write the expression for the reactance of a monopole antenna. Explain the terms. (4 Marks)
(c) Draw and explain average characteristic impedance for cylindrical antennas. (4 Marks)
(d) Using Schelkunoff’s method, calculate the input impedance of a uniform cross section tower antenna at 1300 kHz. The tower is 400 ft high and 6.5 ft square. The base-insulator capacitance is 30 pf. (4 Marks)
8 (a) What is antenna bandwidth? Explain. (4 Marks)
(b) What is LUHF? Mention any 3 factors on which it depends. (4 Marks)
(c) Explain Michelson-Morley experiment. (8 Marks)
(d) Derive electromagnetic relations from theory of special relativity. (4 Marks)

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