Super-resolution performance studies for orbital-angular-momentum-based imaging radar

Abstract

ABSTRACT Vortex electromagnetic (EM) wave carrying orbital angular momentum (OAM), whose unique wavefront distribution exhibits angular diversity characteristics, which provides a richer degree of freedom for information modulation. Although several works have reported that the EM vortex imaging has superior performance in target detection and imaging with azimuthal super-resolution, the underlying physical mechanism needs to be further developed. This article offers a solution to significantly refine the imaging resolution for conventional real-aperture imaging radar (CRAIR) using multiple OAM-carrying beams. Firstly, it is deduced that the various spatial frequency distributions and time-varying phase wavefront distributions of OAM beams promote the realization of OAM-based imaging radar (OAMIR) super-resolution imaging. Secondly, a scheme for adjusting the directivity of EM vortex beam is proposed, which can effectively acquire most spatial frequency components of the probed target, resulting in the target can be illuminated simultaneously by the main lobes of various beams carrying different topological charges. Thirdly, the point-spread function (PSF) comparison for CRAIR and OAMIR is carried out by theoretical analysis and numerical simulation, and the spatial azimuth resolution for OAMIR is derived. Finally, the signal mathematical model for OAMIR is established and analysed. Simulation results validate that the proposed OAM-based imaging paradigm breaks through the Rayleigh limit associated with conventional real-aperture imaging technology and achieves imaging performance superior to OAMIR in previous works.