1.2 Meter Shielded Cassegrain Antenna for Close-Packed Radio Interferometer

摘要

Interferometric millimeter observations of the cosmic microwave backgroundand clusters of galaxies with arcmin resolutions require antenna arrays withshort spacings. Having all antennas co-mounted on a single steerable platformsets limits to the overall weight. A 25 kg lightweight novel carbon-fiberdesign for a 1.2 m diameter Cassegrain antenna is presented. The finite elementanalysis predicts excellent structural behavior under gravity, wind and thermalload. The primary and secondary mirror surfaces are aluminum coated with a thinTiO$_2$ top layer for protection. A low beam sidelobe level is achieved with aGaussian feed illumination pattern with edge taper, designed based on feedhornantenna simulations and verified in a far field beam pattern measurement. Ashielding baffle reduces inter-antenna coupling to below $\sim$ -135 dB. Theoverall antenna efficiency, including a series of efficiency factors, isestimated to be around 60%, with major losses coming from the feed spilloverand secondary blocking. With this new antenna, a detection rate of about 50clusters per year is anticipated in a 13-element array operation.