For the application of vortex electromagnetic (EM) beams in practical detection scenes, the scattering characteristics of electrically large arbitrarily shaped targets illuminated by an off-axis Laguerre–Gaussian (LG) vortex beam are investigated and compared to the on-axis incidence case. The vector potential method is used to extract the electric and magnetic field components of the LG beam in different polarization states. The physical optics algorithm is adopted to calculate the scattering fields of four typical targets with the shape of a sphere, NASA almond, blunt cone, and blade model. The results revealed that as the beam center offset and the topological charge of the incident vortex beam increase, the scattering field distorts, and the obvious orbital angular momentum (OAM) spectrum mixing occurs. In addition, OAM spectrum aliasing occurs for asymmetric targets, even at on-axis incidence. These results elucidate the mechanism of vortex EM scattering and provide a reference for applying vortex beams for target detection and recognition.

We implement an algorithm, termed parallel-processing physical optics, providing an efficient high-frequency approximation method to characterize the scattering of Laguerre–Gaussian (LG) vortex electromagnetic (EM) beams by electrically large-scaled complex targets. The incident beam is described by vector expressions in terms of electric and magnetic fields, and it is combined with rotation Euler angles to achieve an arbitrary incidence of the vortex beam. The validity and capability of the proposed method are illustrated numerically, and the effects of various beam parameters as well as target geometric models such as a blunt cone and Tomahawk-A missile on monostatic and bistatic radar cross section distributions are investigated. Results show that the scattering features of the vortex beam vary significantly with the parameters of the vortex beam and the target. These results are helpful to reveal the scattering mechanism of LG vortex EM beams and provide a reference for the application of vortex beams to detect electrically large-scaled targets.

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