A 10-183 GHz common aperture antenna with a quasioptical frequency multiplexer

A multifrequency coboresighted antenna would be cost effective because many wavelengths utilizing different receiver technologies would be observed with one instrument. Because the size of quasioptical components is determined by wavelength, filtering the lowest frequencies from the beam first allows the system to be compact. Two calibration schemes are then possible, a conventional method for the microwave frequencies and a quasioptical method for the shorter wavelengths. The brassboard instrument described in this paper consists of an offset Cassegrain antenna with a 60×65 cm aperture and a quasioptical frequency multiplexer with 7 distinct channels at 10, 18, 22, 37, 50-58, 90, and 183 GHz. The frequency selective surfaces (FSS) include 1 dual frequency bandpass filter and 4 perforated ellipsoidal mirrors, which are high pass filters in the band of interest and focusing elements below the cutoff frequency. With the main reflector and subreflector this system is contained in a volume 175×155×68.3 cm. The multiplexer by itself has dimensions of 100×155×32 cm, which include all feeds, lenses, and fss components. In each band the power is coupled to waveguide via a scalar feed and a lens. In all channels the authors measured beam patterns, gain, cross polarization, return loss, and interchannel isolation