The first 42 elements of the Allen Telescope Array (ATA-42) are beginning to deliver data at the Hat Creek Radio Observatory in Northern California. Scientists and engineers are actively exploiting all of the flexibility designed into this innovative instrument for simultaneously conducting surveys of the astrophysical sky and conducting searches for distant technological civilizations. This paper summarizes the design elements of the ATA, the cost savings made possible by the use of COTS components, and the cost/performance trades that eventually enabled this first snapshot radio camera. The fundamental scientific program of this new telescope is varied and exciting; some of the first astronomical results will be discussed.
Deep Dive into The Allen Telescope Array: The First Widefield, Panchromatic, Snapshot Radio Camera for Radio Astronomy and SETI.
The first 42 elements of the Allen Telescope Array (ATA-42) are beginning to deliver data at the Hat Creek Radio Observatory in Northern California. Scientists and engineers are actively exploiting all of the flexibility designed into this innovative instrument for simultaneously conducting surveys of the astrophysical sky and conducting searches for distant technological civilizations. This paper summarizes the design elements of the ATA, the cost savings made possible by the use of COTS components, and the cost/performance trades that eventually enabled this first snapshot radio camera. The fundamental scientific program of this new telescope is varied and exciting; some of the first astronomical results will be discussed.
HE Allen Telescope Array (ATA) is a "Large Number of Small Dishes" (LNSD) array designed to be highly effective for commensal surveys of conventional radio astronomy projects and SETI (search for extraterrestrial intelligence) targets at centimeter wavelengths.
The importance of surveys in astronomy is well illustrated by the great successes of programs such as the Sloan Digital Sky Survey [1], and the ATA is planned to follow that example. It is well known [2] that for surveys requiring multiple pointings of the array antennas to cover a large solid angle in a fixed amount of time, the resulting point source sensitivity is proportional to ND, where N is the number of dishes, and D is the dish diameter, rather than ND 2 , the total collecting area. Reasonable expectations for antenna and electronics costs then lead to the LNSD array as the optimum. The ATA will consist of 350 6m-diameter dishes when completed, which will provide an outstanding survey speed and sensitivity. In addition, the many antennas and baseline pairs provide a rich sampling of the interferometer uv plane, so that a single pointing snapshot of the array of 350 antennas yields an image in a single field with about 15,000 independent pixels. This number, the ratio of antenna beam width to array pattern beam width, is much smaller than the number of baselines and shows the large redundancy of the array. The goal is good image quality and high brightness sensitivity. Other important features of the ATA include continuous frequency coverage over 0.5 GHz to 10 GHz and four simultaneously available 600-MHz bands at the back-end which can be tuned to different frequencies in the overall band. Within these bands there are both 100-MHz spectral-imaging correlators and beamformers. The correlators have 1024 channels with adjustable overall bandwidths which permit high spectral T 0117-SIP-2008-PIEEE resolution. Up to 32 separate beams may be formed to feed either SETI signal detectors or, for example, radio transient processors.
The ATA is a joint project of the SETI Institute in Mountain View, CA, and the Radio Astronomy Laboratory of the University of California, Berkeley. The initial design grew out of planning meetings at the SETI Institute summarized in the volume “SETI 2020” [3]. The design goals were (a) continuous frequency coverage over as wide a band as possible in the range 0.5 -10 GHz for both SETI and conventional radio astronomy, (b) an array cost improvement approaching a factor of 10 over current array construction practices, (c) large sky coverage for surveys, (d) a collecting area as large as one hectare for a point source sensitivity competitive with other instruments, (e) interference mitigation capability for both satellite and ground based interference sources, and (f) both imaging correlator and beamformer capability with rapid data reduction facilities. An important realization at the planning meetings was that a very wideband inexpensive receiver could be built based on a MMIC chip that would have a very low noise temperature when cooled to only 60K (Weinreb, personal communication). A feed to accompany such a wideband receiver was clearly an important requirement, and some version of a log-periodic feed was an obvious choice. A simple cost optimization suggests that the antenna should cost about the same as the feed and receiver. An inexpensive antenna will be small, and the LNSD concept is a natural consequence. Finally, construction of large numbers of antennas and feeds that utilize commodity components and mass manufacturing techniques will lower the cost. A grant from the Paul G. Allen Family Foundation enabled the detailed hardware design and initial phase of array construction.
The ATA is now complete to 42 antennas and in operation. In the following sections, we describe the antenna design and operation, the feeds and receivers, the signal transport, the frequency adjustable bands, and the beamformers and correlators. We also discuss particular properties of the small array and the anticipated intermediate and final arrays. Highlights of the system are the frequency agility, the low background and sidelobes of the antennas, the wideband feed and input receiver, the analog fiber optical system, the large spatial dynamic range, the backend processing systems and the overall low cost.
The ATA is located at the Hat Creek Radio Observatory (HCRO) of the University of California Berkeley in northern California. Figure 1 shows an artist’s conception of the anticipated 350-element array at the Observatory.
The antenna is an offset Gregorian design that allows a larger secondary with no aperture blockage for good low frequency performance and also provides a clear aperture with lower sidelobes in the antenna pattern and lower thermal background. Having lower sidelobes is particularly important with the increasing level of satellite interference. The primary is an approximately 6m diameter section of a paraboloid, and t
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