Some Calculations on Coupling Between Satellite Communications and Terrestrial Radio-Relay Systems Due to Scattering by Rain

Interference coupling due to rain is an important factor in coordinating the shared use of frequencies between satellite-communications and terrestrial microwave radio-relay systems. Calculations of the coupling between a satellite ground station and a radio-relay station due to scattering by rain are given for the frequencies 4, 6, 11, 18.5 and 30 GHz. Several models of the rain environment are considered, one in which the rain falls uniformly over the path, and others involving localized showers in the earth-station beam. The beam of the earth-station antenna is taken to be elevated 30° above the local horizon. Interstation distances from 5 km to 200 km and rain rates up to 400 mm/hr are considered. The analysis includes the near field of the earth-station antenna and shows that attenuation by the rain on the path plays an important role at the higher frequencies. The greatest coupling occurs when the beam of the earth-station antenna is pointed opposite to the azimuth of the relay station. In that case, when the radio-relay antenna response in the direction of the earth station is isotropic, the maximum couplings are −132 dB and − 164 dB at 4 GHz with separations of 5 km and 200 km respectively, for a rain rate of 400 mm/hr.