Autofocusing and imaging algorithm for moving target by vortex electromagnetic wave radar

Abstract

Electromagnetic (EM) vortex imaging, which combines with spiral wavefront phase modulation and computational imaging concept introduced by orbital angular momentum (OAM), has demonstrated superior performance in target information extraction and two-dimensional (2-D) or even three-dimensional (3-D) imaging capability in forward-looking observation geometry. However, due to the unknowns and complexity of target motion, the translational component will lead to the disturbance of echo phase, which hinders the motion compensation between target echo pulses and causes imaging defocus. In this paper, a high-resolution imaging algorithm based on Fourier ptychography (FP) is proposed for moving target autofocusing imaging by vortex electromagnetic forward-looking radar (VEMFLR). Firstly, based on the spatial geometric model and echo model of VEMFLR, high-order phase terms caused by target motion are derived, which provides a theoretical basis for applying FP phase retrieval to autofocusing imaging; Then, the spectrum information in FP sub-aperture is obtained; Thirdly, the imaging method, based on FP phase retrieval, is exploited to compensate phase error and obtain a well-focused image. Simulation results show that this method can achieve fine imaging performance without estimating target motion parameters.