The Central Redundant Array Megatile.

The Central Redundant Array Mega-tile (CRAM) is a specially built double-size (8×8 dipoles) MWA tile that is located in the centre of the MWA’s south hexagon.

The CRAM is primarily aimed at supporting the MWA’s EoR science program, and is designed to:

  • Improve the characterisation of the MWA Phase II hexagon tile beam patterns, and
  • Improve foreground characterisation and excision for Epoch of Reionisation (EoR) science at Curtin University.

Because the CRAM is in the centre of the MWA’s southern hex tiles, it forms redundant baselines with the regular hexagon tiles. By using the coherent information obtained by simultaneous, co-redundant hexagon-CRAM baselines, contaminating signals from the field edge can be coherently removed, improving the relative EoR-signal-to-foreground-signal ratio.

The CRAM is twice the size of a regular MWA tile, so normal MWA beamformers cannot be used for it. Instead, the CRAM uses a custom-built zenith-pointing two-stage beamformer, which adds the signals collected by the CRAM dipole antennas and transmit the summed signals to the correlator via optical fibre links.

The CRAM was co-designed and built as part of a Masters of Engineering project by ICRAR/UWA student Gurashish Singh. Curtin PhD student Aishwarya Selvaraj is using observations with the CRAM to understand the statistics of near-horizon foregrounds for the MWA EoR experiment.

Lead investigators of this project are A/Prof. Randall Wayth and Prof. Cathryn Trott.

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