Retro-directive ground-terminal antenna for communication with geostationary satellites in slightly inclined orbits

Abstract

A retro-directive antenna for communicating with a geostationary satellite autonomously detects the direction from which a signal is received, and transmits a beam that points back along the same direction. An array feed is used to illuminate a parabolic reflector. Each feed element of the retro-directive antenna is associated with a unique pointing direction of the beam in the far field. As the transmit energy is switched to different feed elements, the far-field beam is scanned, making it possible to track a geostationary satellite in a slightly inclined orbit. This eliminates the need for mechanical tracking and maintains high antenna gain in the direction of the geostationary satellite. The use of a toroidal reflector with multiple linear array feeds spaced in the azimuth direction enables multi-beam operation, allowing multiple geostationary satellites, spaced by up to fifteen beam widths in azimuth, to be tracked simultaneously and independently.