Abstract: In an antenna system for tracking a satellite, a prediction of the angular orientation of the satellite relative to the antenna as a function of time is obtained from the orbital parameters of the satellite. The mechanisms for controlling the angular position of the entire antenna structure then "drive" the entire structure so as to point the antenna beam towards the predicted position of the satellite as the satellite progresses in its orbit. The "drive" instructions are perturbed slightly so as to cause the antenna beam to "dither" slowly about the predicted satellite positions. The variations in signal strength produced by the dither are then used to determine the azimuth and elevation errors. The orbital parameters upon which the predictions are based are then adjusted so as to minimize the observed azimuthal and elevation errors. Because any error in the orbital parameters changes only very slowly, a relatively slow "dither" and a long time constant can be used in the correction process.

Abstract: A monopulse antenna feed system utilizing multiple modes within the feed. A TEM mode and two TE.degree..sub.11 modes that are orthogonal and in phase quadrature are utilized in the antenna feed system to provide tracking information and data communication from a far-field source of circularly polarized radiation. The output from a port that is responsive to the TEM mode is compared with the output from a port that is responsive to the TE.degree..sub.11 modes to obtain tracking information and the output from the latter port also provides a channel for communication of data. The phase of the TEM mode relative to the phase of the TE.degree..sub.11 modes is indicative of the angular rotational position of a far-field source relative to the axis of the feed system and the relative amplitude of the TEM mode is indicative of the angular displacement of the far-field source away from the axis of the feed system.