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.