Development of a Ka-band UAV-Borne Phased-Array SAR and Imaging Validation for Large Radio-Astronomy Facilities: A Case Study at the Mingantu Observing Station

Synthetic aperture radar (SAR) is an active microwave imaging sensor that enables dayand-night, all-weather Earth observation. When integrated on unmanned aerial vehicles (UAVs), SAR provides high-resolution imaging with small size, low cost, and high maneuverability, while shortening deployment and data turnaround. Focusing on large astronomical facilities, this paper presents the design and validation of a Ka-band UAV-borne phased-array SAR system. The payload adopts a modular, lightweight architecture compatible with multirotor, fixed-wing, and compound-wing airframes. The short wavelength of Ka-band millimeter-wave signals enhances sensitivity to fine linear features and complex metallic structures, making it well suited for precise geometric mapping, array-layout calibration, structural health monitoring, and perimeter inspection of astronomical facilities. We conducted multiple day-andnight flight experiments at the Mingantu Observing Station and acquired high-resolution two-dimensional (2-D) SAR images of the Chinese Meridian Project Phase II interplanetary scintillation (IPS) phased-array telescope, MingantU SpEctral Radioheliograph (MUSER) spiral array, and surrounding infrastructure. Point targets and distributed scenes show well-focused impulse responses with distinct mainlobes and suppressed sidelobes, confirming the imaging quality of the system. These results indicate that the Ka-band UAV-borne SAR enables rapid, fine-grained, and repeatable monitoring of large astronomical equipment and sites. The system also shows promise for broader applications, including geohazard assessment, mining subsidence, major civil-infrastructure monitoring, power-line and pipeline inspection, and environmental monitoring.