MNRF Upgrade: Antenna surface Extension | |
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The SystemFor 3mm (100 GHz) observations the current surface of the Narrabri antennas is only useable to 15 metres diameter. The outer section of the antenna has perforated panels which are largely transparent at wavelengths below 5mm (60 GHz). This results in reduced gain and increased system temperature at small wavelengths, compared to a non-transparent 22 metre antenna.The antenna surface extension project involves replacing the existing outer perforated panels with solid panels, giving 22 metre reflectors useable to beyond 100 GHz. Modelling of the static and dynamic wind loading effects on the extended antennas indicates that satisfactory pointing performance can be obtained at these high frequencies in winds < 15 km/hr, the usual situation at Narrabri during weather conditions likely to be suitable for millimetre-wave observing. Thus the extension will significantly improve the scientific capabilities of the antennas. The shape of the current surface will be retained. This is the simpler engineering solution, although it carries the penalty of reduced off-axis performance. The extension will approximately double the sensitivity to point sources, and will allow mosaicing of the full primary beam; an important consideration for sources of extended emission. The StrategyFollowing the preliminary investigations outlined in the 1997 MNRF annual report (PDF file), the ATNF has successfully carried out a specification, tendering and tender evaluation process. Two bids were received for the panel manufacture and installation; Evans Deakin Engineering (EDE) P/L was the successful tenderer. EDE will manufacture the panels using a vacuum forming and epoxying technique, a method developed by CSIRO for the initial Australia Telescope Compact Array construction and since transferred to Australian industry. For historical reference, a report of progress as at August 20, 1998, presented to the 3-mm science team meeting on August 14, 1998 together with the two figures presented with the report, Figure 1 and Figure 2 are available. First panels installedThe first set of panels, delivered by EDE for a six-month evaluation by the ATNF, were installed in September, 1998 and are now being tested. A report on testing results up to February 26, 1999 is available here. Present indications are that final panel surface errors will be in the range 50-100 microns, making the ATNF goal of a 125 micron root-mean-square antenna surface error (corresponding to > 40% aperture efficiency at 100 GHz) appear reasonable.Results of tests on the first antenna fitted with new panels indicate that the panels and installation are satisfactory and the remaining ATCA antennas will be outfitted in the first half of 1999. After panel installation by EDE, the ATNF will carry out the final, precise panel adjusments. Related Information
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Last update by Michelle Storey. 18/3/99
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