3D Sparse ISAR Imaging With Multiple Plane Spiral OAM Electromagnetic Waves

Vortex electromagnetic (EM) waves carrying orbital angular momentum (OAM) have a helical phase front and a field strength with a singularity along the axial center, which is expected to obtain resolutions beyond the Rayleigh limit for imaging systems, and provide new instruments for accurate radar targets imaging. However, since the vortex EM beams feature a doughnut-like intensity profile with a central dark zone and the inconsistent divergence angles of the main lobe, it is difficult to simultaneously illuminate the target for vortex EM beams with different OAM mode, which results in limited echo energy. In addition, the restricted elevation resolution hinders the acquisition of target spatial information, which limits the development of the OAM-based radar detection technique. This contribution offers a new set of ideas and solutions for achieving the 3D ISAR imaging using the superposition of different plane spiral OAM (PSOAM) waves. First, eigenmode beam steering techniques based on radio PSOAM waves is introduced. Subsequently, the PSOAM-based ISAR imaging model for maneuvering targets is derived and the echo characteristics are analyzed. Third, the effective imaging method, based on the amplitude phase compensation and fast Tensor-SL0 reconstruction algorithm, is proposed to solve the 3D sparse imaging problem in a tensor way. Finally, simulations are carried out to verify that the proposed method not only significantly reduces the computational complexity of the image reconstruction, but also generates the 3D image with sidelobes and artifacts removed remarkably from sparse measurements.