Self-Calibration of the Horus All-Digital Phased Array Using Mutual Coupling

Calibration of digital phased array radars is of crucial importance for future radar surveillance systems, especially for high-accuracy polarimetric measurements needed for weather observations. Mutual coupling calibration (or self-calibration) leverages the coupling between antenna elements to derive alignment weights, and can be applied both at system start-up and in real-time during operations to initialize and maintain radar calibration. An operational implementation of mutual coupling calibration has been developed to calibrate the fully digital Horus radar system, and has now been fielded many times to support a variety of data collection experiments. This paper discusses our implementation and summarizes results from several experiments aimed at assessing calibration quality. Our results confirm the efficacy of the methods through ground-truth experiments at different array scales. It also validates beamforming post-calibration through precise far-field patterns measured from an uncrewed aerial system (UAS) which strongly agree with simulated patterns to within $\pm 0.15 \text{dB}$ dB at boresight. We believe that this is the first demonstration of holistic experiments assessing mutual coupling calibration performance in a large digital array.