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APERTIF Beamforming

Submitter: Boudewijn Hut for the APERTIF team
Description: Continuing the '300 MHz of ... ' series (300MHz Fringe, 300MHz Pulsar Detection), we demonstrate that the ALPHA-3 hardware can simultaneously form 37 beams, each with a bandwidth of 300 MHz.

The image on the left shows the distribution of compound beams. During the actual measurement, the seven highlighted ones were measured. Their shape was determined by a single scan over a bright source.

The image on the right shows the result for 300 MHz for two of these compound beams (top and bottom panels). This illustrates the Phased Array Feed concept: it is possible to form multiple compound beams at the same time, by using just a single telescope.

For this measurement, the 61 APERTIF receiver chains (LNA, DCU, LOG, ADU and UniBoard) were used. Each compound beam was formed by adding the receiver signals in the beamformer with suitable weights. The beamformer input datarate is 61 x 800e6 x 8 = 390 Gbps. The total bandwidth of 300 MHz is built up from 384 subbands which also had to be weighted. So, for all 37 compound beams, 61 [receiver chains] x 384 [subbands] x 37 [compound beams] = 866688 weight values need to be determined. This was done by performing a so called 'hot/cold' measurement on the supernova remnant Cassiopeia A, followed by the max-snr algorithm.
Copyright: ASTRON, 2014 - 2015
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