Scattering Characteristics of Vortex Electromagnetic Waves by Symmetrical Targets

Vortex electromagnetic (EM) wave, which carries orbital angular momentum (OAM), possesses a spiral wavefront phase distinct from traditional plane waves. As a signal source, it can convey more information about the target, presenting novel possibilities for radar detection and target recognition. With the development of electromagnetic vortex radar systems and electromagnetic vortex imaging techniques, research on the backward scattering characteristics of vortex EM waves has become a focal point. This study focuses on the investigation of the backward scattering characteristics of symmetric targets under vortex EM wave. Utilizing the angular spectrum expansion method, the Bessel form of vortex EM waves of symmetrically incident targets are decomposed into a series of plane sub-waves propagating in different directions, maintaining symmetrical relationships in their incident directions. Subsequently, the target scattering characteristics of vortex EM waves are analyzed through the theory of plane waves. Combining the physical optics approximation, the scattering of individual plane sub-waves is calculated and superimposed to obtain the total backward scattering field of the target. The analysis indicates that, unlike plane waves, due to the unique phase distribution, the backward scattering results for axisymmetric targets illuminated by the same vortex EM wave are unequal. However, symmetrically irradiating an object with the vortex EM waves possessing of opposite topological charges yields identical backward scattering results. Finally, the backscattering characteristics of vortex EM wave on symmetric targets were simulated and validated using electromagnetic simulation software CST, confirming the accuracy of the conclusions. This research provides great significance for target detection and recognition in vortex EM wave radar applications.