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Submitter: Michiel Brentjens
Description: The Dutch LOFAR core stations have two HBA antenna fields with 24 antenna tiles each. The remote stations have one HBA field with 48 tiles. The idea is to increase the uv-coverage (and the field-of-view) for the short baselines. This should improve our chances to detect, and perhaps image, evidence of the Epoch of Reionisation (EoR), shortly after the Big Bang. This is a question of great cosmological importance, and a major plank in the scientific case for LOFAR.

Because the remote HBA fields are larger, their station beams are smaller. This is no problem when observing specific target sources near the field centre, but it complicates the reduction of wide-field data. Therefore, for wide-field projects, LOFAR supports an "INNER" HBA mode, in which the remote stations only use their innermost 24 tiles, so their beams are the same size as the core station beams.

The figure shows a beam scan in HBA_DUAL mode (top) and HBA_DUAL_INNER mode (bottom). White dots mean that data was missing, for example due to interference. You can see that the beam sizes are now the same for core and remote stations, approximately 3.8 degrees FWHM at 150 MHz, versus 2.5 degrees for RS106 in the top row.

The data were reduced by Wilfred Frieswijk with beam mapping software provided by George Heald.
Copyright: (c) ASTRON 2012
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