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Proceedings Paper

Elevation angle dependence of the SMA antenna focus position
Author(s): Satoki Matsushita; Masao Saito; Kazushi Sakamoto; Todd R. Hunter; Nimesh A. Patel; Tirupati K. Sridharan; Robert W. Wilson
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Paper Abstract

We report the measurement results and compensation of the antenna elevation angle dependences of the Submillimeter Array (SMA) antenna characteristics. Without optimizing the subreflector (focus) positions as a function of the antenna elevation angle, antenna beam patterns show lopsided sidelobes, and antenna efficiencies show degradations. The sidelobe level increases and the antenna efficiencies decrease about 1% and a few %, respectively, for every 10° change in the elevation angle at the measured frequency of 237 GHz. We therefore obtained the optimized subreflector positions for X (azimuth), Y (elevation), and Z (radio optics) focus axes at various elevation angles for all the eight SMA antennas. The X axis position does not depend on the elevation angle. The Y and Z axes positions depend on the elevation angles, and are well fitted with a simple function for each axis with including a gravity term (cosine and sine of elevation, respectively). In the optimized subreflector positions, the antenna beam patterns show low level symmetric sidelobe of at most a few%, and the antenna efficiencies stay constant at any antenna elevation angles. Using one set of fitted functions for all antennas, the SMA is now operating with real-time focusing, and showing constant antenna characteristics at any given elevation angle.

Paper Details

Date Published: 27 June 2006
PDF: 10 pages
Proc. SPIE 6275, Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III, 62751W (27 June 2006); doi: 10.1117/12.670642
Show Author Affiliations
Satoki Matsushita, Academia Sinica Institute of Astronomy and Astrophysics (Taiwan)
Harvard-Smithsonian Ctr. for Astrophysics (United States)
Masao Saito, National Astronomical Observatory of Japan (Japan)
Harvard-Smithsonian Ctr. for Astrophysics (United States)
Kazushi Sakamoto, National Astronomical Observatory of Japan (Japan)
Harvard-Smithsonian Ctr. for Astrophysics (United States)
Todd R. Hunter, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Nimesh A. Patel, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Tirupati K. Sridharan, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Robert W. Wilson, Harvard-Smithsonian Ctr. for Astrophysics (United States)


Published in SPIE Proceedings Vol. 6275:
Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III
Jonas Zmuidzinas; Wayne S. Holland; Stafford Withington; William D. Duncan, Editor(s)

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