Understanding phase pattern discrepancies in UAV-based measurements of a SKA-low prototype

In-situ far-field phase pattern measurements of a prototype of the Square Kilometre Array known as Aperture Array Verification System 1.5 (AAVS1.5) are reported and discussed. Such phase patterns have been measured using a UAV as flying test source. This paper presents a preliminary analysis of discrepancies between the expected and the reconstructed phase patterns. These discrepancies are attributed to a position offset (with respect to the nominal position) common to all elements belonging to the same subarray. A method that estimates this position shift exploiting a combination of measurements and simulations is presented and applied. The resulting position shift could be due to both non-regularity (non-flatness) of the ground and installation errors.