UAV-based measurement of sharp spectral resonances in mutually coupled SKA-low elements

Strong mutual coupling between antennas can have detrimental effects in very sensitive radio telescopes based on aperture arrays. For the low-frequency instrument of the square kilometer array, narrowband perturbations in the radiation patterns of the inner elements have been predicted through electromagnetic simulations. This phenomenon deteriorates the spectral smoothness properties and disturbs the station calibration at very specific frequencies. In this letter, we present a new unmanned aerial vehicle (UAV)-based methodology to experimentally characterize such narrowband phenomena with a high-frequency resolution by means of independently-sweeping transmitting and receiving equipment. This solution does not add complexity to the system (e.g., by tethering the UAV). Results and predictions are in good agreement confirming both the presence of spurious resonances and the validity of the simulation approach.