Site shielding of earth-station antennas

This paper concerns interference in satellite earth stations, due to microwave links sharing the same frequency band, and its solution by site shielding. The uniform theory of diffraction (UTD) has been used to analyze the near field of a parabolic-reflector antenna. An extension of the UTD, in which the influence of the surface impedance is taken into account, has been applied, to calculate the diffraction from the top of the barrier. The theoretical model has been verified in a field-measurement exercise, using a three-meter earth-station antenna, located behind an existing free-standing concrete wall, with a simulated source of interference. The undesirable effects of the barrier on the gain, noise temperature, and the radiation pattern have been studied, and criteria for the clearance of the main beam have been established. Methods of improving shielding effectiveness using absorbing materials and, also, specially shaped diffracting edges have been studied, as well. Laboratory measurements of the diffraction loss of absorbers have been made, and relative advantages are presented. Design guidelines have also been given.<
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