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C6802 Pages: 2

PART C

Answer any two full questions, each carries 20 marks.
Explain the axial mode and normal mode of operation of a helical antenna.
A television transmitting antenna mounted at a height of 120m radiates 15kW of
power equally in all directions in azimuth at a frequency of 501/1117 .Calculate (1)
maximum line of sight range (ii) the field strength at a receiving antenna mounted
at a height of 16 m at a distance of 12 km and (iii) distance at which the field
strength reduces to 1൩7൩.
Explain Tropospheric scatter propagation.
Design a rectangular microstrip antenna using a substrate with a dielectric
constant of 2.25 and operating at 9 GHz. Take Height of Substrate (h = 0.16 cm).
Derive an expression for the LOS distance in km when the antenna heights above
ground are h, and h, respectively for the transmitter and receiver Antenna.
Differentiate between critical frequency and maximum usable frequency.
With the help of neat diagrams explain the principle of operation of Log Periodic
Antenna.
What are the requirements for an antenna used in a mobile handset? Give some
typical antennas used in cellular handsets.

Explain the diversity techniques employed in wave reception.

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