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An offset Cassegrainian antenna with essentially zero aperture blockage is expected to support closely spaced well-isolated beams suitable for earth stations and satellites. Each beam is fed with a separate small-flare-angle corrugated horn and has good area efficiency over a 1.75:1 bandwidth. Each beam also has good cross-polarization properties. The antenna is compact, and the design appears practical for a 4-and 6-GHz earth station, a 20-and 30-GHz earth station, and a 20-and 30-GHz satellite.

By adding a square wave of noise to the input of an ultra‐low‐noise receiver via a directional coupler, a radiometer with a sensitivity greater than a Dicke type can be achieved when the basic system temperature is less than 18°K. A noise‐adding radiometer is compatible with a communications receiver and has been used (i) to measure and monitor the absolute system temperature and (ii) to check the boresighting of a space communications antenna by detecting and tracking radio stars.