Radio-Relay Antenna Pointing for Controlled Interference with Geostationary Satellites

When radio-relay and communication satellite systems share frequency bands, as they do at 4 and 6 GHz, it is necessary to impose restrictions on both systems so that interference is not excessive. The CCIR (International Radio Consultative Committee) recommends that radio-relay antennas maintain a specified angular separation with respect to the geostationary (stationary equatorial) orbit or, where this is not practicable, the application of power limitations to terrestrial radio transmitters involving reception at the satellite. While the above restrictions protect satellites, designers of terrestrial systems should be aware of possible interference into radio-relay systems from satellite radiation arriving at low elevation angles and close to the on-beam directions of receiving antennas. Because the dielectric constant of the earth's atmosphere varies with altitude, the radio-relay beam is not straight, and atmospheric refraction must be considered when computing the directions of radio beams for which the restrictions apply. l.i Simplified Exposure Model Figure 1 introduces the geometry of the problem and illustrates significant trends and limits. Radio-relay site P located at North Latitude