GEO SAR Systems with Array-fed Reflector Antenna

Geosynchronous Earth Orbit Synthetic Aperture Radar (GEO SAR) provides high temporal resolution and persistent wide-area observation, which is highly valuable for applications such as disaster monitoring and ocean surveillance. However, traditional reflector antennas lack beam agility, while full phased arrays are constrained by high mass, cost, and thermal load. To address these limitations, this paper proposes an offset reflector antenna fed by a phased array for GEO SAR system. The radiation field is modeled using the Physical Optics method, and beam synthesis is achieved via a projection-matrix-based optimization. A focused feed structure is introduced to enhance beam scanning continuity and gain uniformity. Simulation results demonstrate that the system can flexibly synthesize pencil beams within a ±3° scanning range. Furthermore, a phase-only excitation strategy is adopted for transmission to maintain aperture efficiency and avoid thermal issues associated with amplitude tapering. The proposed scheme offers an efficient and practical antenna solution for future GEO SAR missions.