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 day-and-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-and-night flight experiments at the Mingantu Observing Station and acquired high-resolution two-dimensional SAR images of the Chinese Meridian Project Phase II interplanetary scintillation phased-array telescope and surrounding infrastructure. Results exhibit generally well-focused impulse responses with clear mainlobes and controlled sidelobes, supported by quantitative metrics (e.g., resolution, peak sidelobe ratio, and integrated sidelobe ratio). 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.