MSc Map Antennas and Propagation module exam 2002 (DJJ question)

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Antennas notes.

Question 1.

Define the terms numerical gain, boresight, polarisation, null, and isotropic radiator. Illustrate your answers with diagrams and write notes where needed.


A certain antenna, ANT, consists of a number of parallel straight rods. It has numerical gain 8.4 with respect to a practical half-wave dipole. The practical half-wave dipole is specified to have gain in decibels, after accounting for losses, of 2.06 dBi. What is the numerical gain of ANT with respect to an isotrope? Express this gain also in dBi and indicate two directions in space where nulls must lie. You may ignore any residual radiation from the feed.


Distinguish between the terms omnidirectional and isotropic. Explain how a loop antenna in combination with a dipole, may be used to generate omnidirectional circular polarisation in a horizontal plane. Sketch the radiation pattern in an elevation plane.



Calculate the maximum range at which two co-polarised lambda/2 dipoles can communicate in free space. Assume a system noise temperature of 100K. Express your answer in terms of the transmitter power P watts, the system bandwidth B Hz, and the wavelength lambda metres.


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