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Applicability and limitations of redundancy cal. in phased array stations
Parisa Noorishad, Stefan Wijnholds, Arnold van Ardenne & Thijs van der HulstYERAC2011, Manchester, 18th -20th July. 2011
[1] J. E. Noordam & A. G. de Bruyn, Nature, 14 oct. 1982
[2] M. Wieringa, PhD thesis, Leiden Univ., 1991
Introduction:
• Independent of a sky model,
• Less sensitive to RFIs,
• Computationally cheap and fast,
• Simple to implement (important for SKA),
• Could also be used as a diagnostic tool.
• Regularity in a station configuration e.g. in MWA, HBA, EMBRACE.
Why redundancy?
Beam identicalness:
CAESAR: Computationally Advanced and Efficient Simulator for Arrays [Rob Maaskant et al.]
The potential calibrator sources for RS208, on
24th of Nov. 2009 at 21:29:04 UTC and the
systematic errors in the amplitudes and the
phases of the redundant visibility due to the
contribution of other strong sources through
non-identical sidelobes.
Quantifying that systematic error:
CRB and the actual variance of the estimated parameters:
We tracked CasA on 24th November 2009 from 15:25:43 UTC until 22:12:19 UTC.
• Station configuration
• Mutual coupling between the station elements which leads to:
– Non-identical beams of the station elements
– Presence of baseline dependent noise
• SNR of the observed sky
Limitations of the redundancy calibration method:
• The mutual coupling seems to be a non-dismissible effect (for phased array stations).
• We need beam model of each individual station elements e.g. each tile at HBAs.
Model based cal. method:
[1] Wijnholds & van der Veen, 2009
[2] Wijnholds & van der Veen, 2010
• Summary:– Applicability and limitations of the redundancy cal. for phased
array station was investigated.
• Conclusions:– Redundancy cal. is a stand-alone gain cal. method.– Using redundancy requires taking into account the parameters
which affects its applicability and performance.– Identical beam; Mutual coupling seems to be a non-dismissible
effect, no matter which method we use.
• Next Step:– To do more rigorous CRB and Monte-Carlo analysis for two
existing implementations of the redundancy method.– To evaluate the merit of the redundancy in UVW-space at the
whole array level using SKA configuration.