We investigate the application of vortex beams carrying different orbital angular momentum (OAM) modes to SAR systems. For the traditional OAM-carrying wave, the inconsistent divergence angles exhibit that it is difficult to simultaneously illuminate the target with different OAM beams, resulting in limited echo energy or deterioration of the imaging capability. In this work, an enhanced SAR imaging method is proposed, which exploits plane spiral OAM (PS-OAM) to form a pencil beam and eliminates the above negative effects. First, the echo signal model for conventional vortex SAR is derived. Second, the feasibility of PS-OAM-based beamforming techniques for high-resolution SAR imaging is analyzed. Third, in light of the echo model of the proposed vortex SAR, an improved chirp scaling (CS) algorithm is provided by considering amplitude correction and phase compensation. Finally, the numerical simulations demonstrate the proposed method can achieve high-precision focusing processing in comparison with the traditional algorithm.

Vortex beams, plane spiral OAM (PS-OAM), SAR imaging, Beamforming technique