On-sky calibration of a SKA1-low station in the presence of mutual coupling

Abstract

This paper deals with the calibration of the analogue chains of a Square Kilometre Array (SKA) phased aperture array station, using embedded element patterns (one per antenna in the array, thus accounting for the full effects of mutual coupling) or average element patterns to generate model visibilities. The array is composed of 256 log-periodic dipole array antennas. A simulator capable of generating such per-baseline model visibility correlation matrices was implemented, which allowed for a direct comparison of calibration results using Statistically Efficient and Fast Calibration (StEFCal) with both pattern types. Calibrating the array with StEFCal using simulator-generated model visibilities was successful and thus constitutes a possible routine for calibration of an SKA phase aperture array station. In addition, results indicate that there was no significant advantage in calibrating with embedded element patterns, with StEFCal successfully retrieving similar per-element coefficients with model visibilities generated with either pattern type. This can be of significant importance for mitigating computational costs for calibration, particularly for the consideration of real-time calibration strategies. Data from the Aperture Array Verification System 1 prototype station in Western Australia was used for demonstration purposes.