| Description: | Compared to the relatively easy assembly of the Low Band Antennas, the placement of the High Band Antenna (HBA) tiles (which operate between 120 and 240 MHz) is a considerably more complicated procedure. The antennas are pre-assembled at a production facility in Exloo and transported one by one to the field on a trailer. A crane then hoists the tiles, which weigh 150 kg each and measure 5m x 5m, into place. The tiles are fixed to the ground with deep anchors, to ensure that they can resist high winds. Each of the “black boxes” actually contains 16 antenna elements, laid out in a 4x4 grid, whose signals are combined in a time-delay beamformer inside the tile. The HBA’s are covered by a uv-resistant flexible polypropylene foil that protects the interior of the tile from the elements.
The stations in the Netherlands will each have 48 HBA tiles. On the LOFAR stations in- or close to the core the HBA’s are equally divided over two fields. In observations, these two fields act as individual stations, which therefore contribute to a significantly better uv-coverage and improve the imaging quality of the inner part of LOFAR. Outside the core area, all 48 HBA’s are placed in a single field. The international LOFAR stations each have 96 HBA’s.
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