In 2008, CSIRO commissioned Patriot Antenna Systems to build a single, 12-metre diameter antenna at Parkes Observatory. Although the functional specification and design of the antenna differs from that of the actual ASKAP antennas, it provides a single dedicated platform to test successive generations of phased array feeds (PAFs) and other systems being developed for ASKAP.
The antenna is equipped with a feed rotator at the prime focus to allow the PAF to maintain a constant parallactic angle during observations. This ‘de-rotation’ (‘parallactification’) of the sky means that the data stream from the PAF is significantly easier to process in the imaging software.
The original beamformer electronics were housed in a shielded (RFI-tight) cabinet in the antenna pedestal. An underground fan-duct system was installed to provide naturally-cooled forced air to the pedestal to determine if this type of system would be suitable for ASKAP in Western Australia. (Ultimately this design was not pursued).
The new antenna is located approximately 400 metres east of the 64-m Parkes ‘dish’ parallel to the east-west interferometer track, on a level area of land previously leased for farming. The antenna was controlled from a refurbished RFI-shielded room in the Parkes ‘Woolshed’ containing a simple correlator, which allowed the signals from the 12m and 64m telescopes to be correlated.
A major milestone was reached on 24 July 2008 when the first prototype PAF (of a “5×4” design) was hoisted onto the antenna. On 29 July 2008 the ASKAP team captured signals from eight of the PAF’s 40 ports and ‘first light’ was declared.
In July 2011 a full-size PAF with 188 ports was installed on the 12-metre antenna. The beam-former and other electronics for this antenna was housed in a demountable building adjacent to the antenna known as “Harold’s Hut” (after an errant sheep that was discovered nearby). This full-size PAF and associated electronics were electrically identical to the six Mark-I systems built for BETA, the Boolardy Engineering Test Array which effectively became the prototype for ASKAP.
The 12-m with its full-sized PAF was linked with the 64m telescope to form a powerful interferometer. This was used to make sensitive measurements of the PAF performance and acquire experience with the process of beam-forming that proved invaluable in the development of BETA and ASKAP.
Further Information
See the ATNF Parkes Test Bed Archive for more detail (CSIRO internal access only)