Elevation angle dependence of the SMA antenna focus position

Satoki Matsushita; Masao Saito; Kazushi Sakamoto; Todd R. Hunter; Nimesh A. Patel; Tirupati K. Sridharan; Robert W. Wilson

doi:10.1117/12.670642

27 June 2006 Elevation angle dependence of the SMA antenna focus position

Satoki Matsushita, Masao Saito, Kazushi Sakamoto, Todd R. Hunter, Nimesh A. Patel, Tirupati K. Sridharan, Robert W. Wilson

Author Affiliations +

Proceedings Volume 6275, Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III; 62751W (2006) https://doi.org/10.1117/12.670642
Event: SPIE Astronomical Telescopes + Instrumentation, 2006, Orlando, Florida , United States

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.

Citation Download Citation

Satoki Matsushita, Masao Saito, Kazushi Sakamoto, Todd R. Hunter, Nimesh A. Patel, Tirupati K. Sridharan, and Robert W. Wilson "Elevation angle dependence of the SMA antenna focus position", Proc. SPIE 6275, Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III, 62751W (27 June 2006); https://doi.org/10.1117/12.670642

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