Allen Telescope Array - Overview

Overview

The ATA is a centimeter-wave array that pioneers the Large-Number Small-Diameter concept of building radio telescopes. Compared to a large dish antenna, large numbers of smaller dishes are cheaper for the same collecting area. However, to get similar sensitivity, the signals from all telescopes must be combined. This requires high performance electronics, and has been prohibitively expensive until now. However, due to the declining cost of the electronic components, the required electronics are now practical, resulting in a large cost saving over telescopes of more conventional design. This is informally referred to as "replacing steel with silicon".

The ATA has four primary advantages for scientific studies over all major radio telescopes built to date: a very wide field of view (2.45° at λ = 21 cm), complete instantaneous frequency coverage from 0.5 to 11.2 GHz, multiple simultaneous backends, and active interference mitigation. The instantaneous area of sky imaged is 17 times that of the Very Large Array. The instantaneous frequency coverage of more than four octaves is unprecedented in radio astronomy and is the result of a unique feed, input amplifier, and signal path design. Active interference mitigation will make it possible to observe even at the frequencies of many terrestrial radio emitters.

Because all-sky surveys are an important part of the science program, the efficiency of the ATA will be increased by doing radio astronomy and SETI searches simultaneously. The telescope will do this by splitting the signals in the control room prior to final processing. Simultaneous observations are possible because for SETI, several target stars will lie within the large field of view afforded by the 6 m dishes wherever the telescope is pointed. Thus, by agreement between the RAL and the SETI Institute, the needs of conventional radio astronomy will determine the pointing of the array.

The ATA is planned to comprise 350 six-meter dishes and will make possible large, deep radio surveys that were not previously feasible. The telescope design incorporates many new features, including hydroformed antenna surfaces, a log-periodic feed covering the entire range of frequencies from 500 MHz to 11.2 GHz, and low-noise, wide-band amplifiers with a flat response over the entire band making it possible to amplify the sky signal directly. This amplified signal, containing the entire received bandwidth, is brought from each antenna to the processing room on optical fiber cables. This means that as electronics improve and wider bandwidths are feasible, only the central processor needs to change, and not the antennas or feeds.

The instrument was operated and maintained by the UC Berkeley Radio Astronomy Laboratory (RAL) until the array's hibernation in 2011. The RAL worked hand in hand with the SETI Institute during design and prototyping and was the primary designer of the feed, antenna surfaces, beam forming, correlator and imaging system for radio astronomy observations.

The astronomy decadal panel, Astronomy and Astrophysics in the New Millennium, endorsed SETI and recognized the ATA (then called the 1-Hectare Telescope) as an important stepping stone to the Square Kilometer Array (SKA). The most recent Decadal Survey recommended ending US financial support of the SKA.

The ATA aspires to be among the world's largest and fastest observing instruments. It will also permit astronomers to search for many different target stars simultaneously. If completed as originally envisioned, it will be one of the largest and most powerful telescopes in the world.

Although cost estimates of unbuilt projects are always dubious, and the specs are not identical (the conventional telescopes have lower noise temperature, but the ATA has a larger field of view, for example), the ATA has potential promise as a much cheaper radio telescope technology for a given effective aperture. For example, the amount spent on the first ATA-42 phase, including technology development, is roughly 1/3 of the cost of a new copy of a Deep Space Network 34 meter antenna of similar collecting area. Similarly, the estimated total cost of building the remaining 308 dishes is estimated (as of October 2007) at about $41 million. This is about a factor of 2 cheaper than the $85 million cost of the last large radio astronomy antenna built in the USA, the Green Bank Telescope, of similar collecting area. The contractor filed for a $29 million overrun, but only $4 million of this was allowed.