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Design and test of submillimeter array (SMA) chopping subreflector

The Smithsonian Astrophysical Observatory (SAO) is constructing an array of antennas that is expected to be placed on Mauna Kea and operated at submillimeter wavelengths. To facilitate calibration work in single dish mode, each antenna is equipped with a subreflector that chops about its center of mass. In addition to chopping, the subreflector's position is controlled by three actuators permitting the mirror position to be corrected for the effects of temperature and pointing elevation. This paper discuses the specifications, design, fabrication, and performance testing of the chopping subreflector system.