Applicability and limitations of redundancy cal. in phased array stations Parisa Noorishad, Stefan...
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Transcript of Applicability and limitations of redundancy cal. in phased array stations Parisa Noorishad, Stefan...
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.