Reducing SKA-LOW Station Calibration Errors by Wideband Gain Model Fitting

Accurate calibration of the low-frequency aperture array stations of the Square Kilometre Array (SKA-LOW) is essential to achieve its ambitious science goals. Significant efforts have therefore been invested in characterising the response of the antennas within the station as well as the components of the analog receive paths between the antennas and digitisers resulting in experimentally validated models for the embedded element patterns (EEPs) and the receive path gains. In this contribution, these models are combined to build a realistic simulation of station calibration under the assumption that EEP variations can be ignored. It is found that fitting a simple gain model to the gain calibration solutions using weights proportional to frequency can reduce calibration errors to a level that permits over 99% beamformer efficiency. This suggests that wideband gain fitting is a powerful technique to improve robustness to errors in either the instrument or the source model used for calibration.