Combined radar altimeter, radiometer sensor employing multiport feed

Abstract

A remote sensing apparatus for conducting (spaceborne) measurements of ocean geophysical parameters integrates a radar altimeter subsystem with a radiometer subsystem through the use of a shared antenna feed horn that permits each subsystem to have the same viewing aperture, so that each subsystem sees the same location on the ocean. The horn is a multiport, multifrequency horn having a throat and a tapered sidewall portion extending from the throat to the outer edge of the horn. A first sidewall port is coupled to the transmit/receive channel of the radar altimeter. A second sidewall port is coupled to a first receive channel of the radiometer, and a third sidewall port is coupled to a second receive channel of the radiometer. A throat port is coupled to a third receive channel of the radiometer. The tapered sidewall portion has a first, generally linear shape adjacent to the throat, a second, conic (elliptical) shape at its outer edge, and a third, blending shape disposed between and joining together the generally linear shape and the conic shape at the outer edge. The blending shape is preferably a sinusoidal function and serves to blend the first shape into the second shape in such a manner that the horn presents, over the entirely of the surface of the sidewall portion, an effectively continuous surface to the E plane of an electromagnetic wave emitted or received by the horn. The distance over which the sidewall portion is tapered to effect the blending function is preferably no greater than two wavelengths of the lowest frequency of electromagnetic waves emitted or received by the horn.