Abstract: A spacecraft-based cellular communications system includes a spacecraft with transmit and receive antennas, each of which produces a plurality of spot beams which, together, provide coverage of the region served. In order to control the pointing of the spacecraft antennas, four mutually adjacent spot beams are centered over a particular "beacon" location, so that the beacon location lies between a pair of North and South spot beams, and between a pair of East and West spot beams. The transmit antenna is controlled by transmitting a beacon signal in time sequence over each of the four spot beams surrounding the beacon location, and decoding or desequencing the time-sequential signal received at the beacon location. The decoded signal is processed to provide a signal indicating the pointing error of the transmit antenna, and the error signal is used to control a gimbal which controls the pointing of the transmit antenna.

Abstract: A distribution network provides signals that are representative of the sum of the amplitudes of values of the first, second and third terms of a Fourier cosine series expansion of the discrete inverse Fourier transform of a desired pattern of excitation of a purality of radiators. The signals are coupled to an orthogonal beam matrix via a plurality of phase shifters to provide a signal representation of an approximation of the inverse transform. The matrix is connected to the radiators whereby the desired pattern of excitation is applied to the radiators.

Abstract: A radar antenna includes a plurality of radiators disposed near the focal point of a parabolic reflecting surface. The radiators are coupled to a sector horn waveguide via a plurality of phase shifters and a Butler matrix. The sector horn is concurrently excited in H.sub.10 and H.sub.12 modes of propagation to provide excitation to the radiators. Radiated energy from a radiator propagates to the reflecting surface and is reflected therefrom.