Design of Vortex Forward-Looking SAR Imaging using OAM Beam Modulation

Forward-looking synthetic aperture radar (SAR) systems often suffer from low resolution and blurred imaging in the azimuthal direction due to the limited variation in Doppler frequency. To address this issue, this paper proposes a novel forward-looking SAR imaging technique leveraging vortex electromagnetic waves and orbital angular momentum (OAM) modulation. The core innovation lies in introducing a new azimuthal Doppler frequency component by establishing a linear relationship between the OAM mode number and slow-time, significantly enhancing azimuthal resolution. The method employs a transceiver system comprising a uniform circular array for transmission, with a single antenna at the center of the array for reception. Additionally, the traditional Range-Doppler (RD) algorithm is optimized to suppress motion-induced azimuthal Doppler interference and isolate mode-induced Doppler effects. Simulation results demonstrate that the proposed method effectively expands the azimuthal Doppler bandwidth, resolving left-right target ambiguity and substantially improving azimuthal imaging quality in forward-looking SAR systems.