Instrument Details
The ATA-42 configuration will provide a maximum baseline of 300 m (and ultimately the ATA-350, 900 m). A cooled log-periodic feed on each antenna is designed to provide a system temperature of ~45K from 1 GHz to 10 GHz, with reduced sensitivity in the range 0.5 GHz to 1.0 GHz and 10 GHz to 11.2 GHz. Four separate frequency tunings (IFs) are available to produce 4x100 MHz intermediate frequency bands. Two IFs support correlators for imaging; two will support SETI observing. All tunings can produce four dual polarization phased array beams which can be independently pointed within the primary beam and can be used with a variety of detectors. The ATA can therefore synthesize up to 32 phased array beams.
The wide field of view of the ATA gives it an unparalleled capability for large surveys (Fig. 4). The time required for mapping a large area to a given sensitivity is proportional to (ND)2, where N is the number of elements and D is the diameter of the dish. This leads to the surprising result that a large array of small dishes can outperform an array with smaller number of elements but considerably greater collecting area at the task of large surveys. As a consequence, even the ATA-42 is competitive with much larger telescopes in its capability for both brightness temperature and point-source surveys. For point source surveys, the ATA-42 is comparable in speed with Arecibo and the Green Bank Telescope (GBT), but slower by a factor of 3 than the Very Large Array (VLA). The ATA-350, on the other hand, will be an order of magnitude faster than the Very Large Array for point-source surveys and is comparable to the Expanded VLA (EVLA) in survey speed. For surveys to a specified brightness temperature sensitivity, the ATA-98 will exceed the survey speed of even the VLA-D configuration. The ATA-206 should match the brightness temperature sensitivity of Arecibo and the GBT. The ATA, however, provides better resolution than either these single dish telescopes.
The antennae for the ATA are 6.1 m × 7.0 m hydroformed offset Gregorian telescopes, each with a 2.4-meter subreflector with an effective f/D of 0.65. (DeBoer, 2001). The offset geometry eliminates blockage, which increases the efficiency and decreases the sidelobes. It also allows for the large subreflector, providing good low frequency performance. The hydroforming technology used to make these surfaces is the same hydroforming technique used to generate low-cost satellite reflectors by Andersen Manufacturing of Idaho Falls, Idaho. The unique, interior frame rim-supported compact mount allows excellent performance at a low cost. The drive system employs a spring-loaded passive anti-backlash azimuth drive train. Many concepts and designs originated from a SETI affiliated company in Antioch, California, Minex Engineering Corp. (Matt Fleming and others), including the compact mount and drive train.
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