RF Modelling and Antennas - Dec 2013

Electronics & Telecomm. (Semester 5)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1 (a) What is antenna, draw and explain all parts of radiation patterns of antenna ?(5 marks) 1 (b) Describe the concept of near field and far field radiation.(5 marks) 1 (c) Explain effective aperture of antenna.(5 marks) 1 (d) What is polarization, how circularly polarized wave can be produced?(5 marks) 1 (e) Derive FRIIS transmission equation.(5 marks) 2 (a) Derive expression for radiation power density, directivity and effective aperture of infinitesimal dipole antenna.(10 marks) 2 (b) Draw and explain folded dipole antenna and λ/2 length with appropriate expressions. (10 marks) 3 (a) Derive array factor of N-element linear array, where all elements are equally fed and spaced.(10 marks) 3 (b) An array of n=8 in phase isotropic sources spaced λ/2 apart, is to have a side-lobe level 26dB below the main lobe maximum. Find the amplitude distribution fulfilling this requirement that produce the minimum beamwidth between first nulls?(10 marks) 4 (a) With suitable diagram, explain log-periodic antenna and derive its essential parameters.(10 marks) 4 (b) Draw and explain microstrip antenna, also derive its design parameters.(10 marks) 5 (a) Describe normal mode helical antenna and derive axial ratio. What is the effect of the value of diameter D and spacing between each turns S of the same antenna.(10 marks) 5 (b) Describe basic geometry of single reflector antenna, also explain how radiation pattern of the same antenna can be modified.(10 marks) 6 (a) Draw and explain experimental set up of polarization measurement with appropriate patterns.(10 marks) 6 (b) Explain the mechanism of Ionospheric propagation. Define critical frequency.(10 marks) 7 (a) Ground wave propagation.(5 marks) 7 (b) Directivity of antenna.(5 marks) 7 (c) Radiation intensity.(5 marks) 7 (d) Rectangular horn antenna.(5 marks) 7 (e) Sleeve dipole.(5 marks)