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Commissioning of the ASKAP antennas has revealed that the system
temperatures of the Phased Array Feeds (PAFs) are not quite as low as
had been expected. Two possible contributing factors are blockage of
the dish surface by the feed legs (which support the PAF in the focal
plane), and scattering of extraneous radio emission from the feed legs
onto the PAF. In order to investigate the effects of these, one ASKAP
antenna has had its steel feed legs replaced by legs constructed from
a non-conducting, fibre-glass composite material, which are
effectively transparent at radio wavelengths and will result in less
blockage and scattering. The image above shows the process of
replacing the existing feed legs with the new materials, a process
(including the removal of the PAF in advance of feed leg changeover,
and subsequent reinstallation) which took several days. Observations
are now underway to characterise the improvement in performance.
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