Near-field calibration of SKA-Low stations using unmanned aerial vehicles

The low frequency part of the Square Kilometre Array (SKA-Low), currently in development, will need accurate calibration [1]. A self-calibration is widely used in the radio astronomy literature and allows the calibration of several SKA pathfinders. However the increased sensitivity and the very large number of antennas of the SKA-Low reduce the hope for relying only on self-calibration. Research involving artificial sources carried by an unmanned aerial vehicle (UAV) has already led to successful far-field calibrations of radio telescopes [2], [3]. In this work, we show a characterization of the embedded element patterns (EEPs) carried out in the near field on a SKA-Low station composed of 256 log-periodic antennas. Two antennas mounted on a UAV act as calibration sources. Several flight strategies are studied with uncertainties on the UAV position and attitude. Using simulations, we show that near-field calibration enables to correctly model the array pattern. An advantage of near-field calibration is the lower required altitude which reduces the covering area of the UAV flight.