Applicability and limitations of redundancy cal. in phased array stations Parisa Noorishad, Stefan Wijnholds, Arnold van Ardenne & Thijs van der Hulst YERAC2011, Manchester, 18 th -20 th July. 2011

A few words about new radio telescopes

Introduction & Motivation

[1] J. E. Noordam & A. G. de Bruyn, Nature, 14 oct [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?

Introduction & Motivation Redundancy in HBAs

Beam identicalness: CAESAR: Computationally Advanced and Efficient Simulator for Arrays [Rob Maaskant et al.]

When redundancy fails:

When redundancy holds:

Checking the influence of non-identical sidelobes

The systematic error due to non-identical sidelobes

The potential calibrator sources for RS208, on 24th of Nov 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:

The plots of the residuals for corrected redundant visibilities

Introduction & Motivation Redundancy cal. Quality

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.

Introduction & Motivation Redundancy cal. Limitations

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:

Station configuration and the condition of redundancy calibration

One more point

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 & Conclusion

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.