Scattering characteristics of electrically large arbitrarily shaped targets illuminated by an off-axis vortex electromagnetic beam

Abstract

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.

Scattering Field Intensity and Orbital Angular Momentum Spectral Distribution of Vortex Electromagnetic Beams Scattered by Electrically Large Targets Comprising Different Materials

“…The receiving field intensity distributions corresponding to the different polarizations were similar. This conclusion is consistent with the results of previous research [39,41]; that is, for symmetric targets, when the polarization of the receiving field is the same as that of the transmitting field, the topological charge of the scattering field is the same as that of the incident field. When x-linear polarization incidence occurs, other modal components also occupy a portion of the proportion.…”

“…The receiving field intensity distributions corresponding to the different polarizations were similar. This conclusion is consistent with the results of previous research [39,41]; that is, for symmetric targets, when the polarization of the receiving field is the same as that of the transmitting field, the topological charge of the scattering field is Subsequently, the scattering electric field intensity and OAM spectral distribution in the x, y, and z directions of the receiving plane illuminated by vortex EM beams with different polarizations were investigated. The incident frequency was set to 5 GHz, the topological charge was l = 1, and θ 0 = 5 • .The target parameters were consistent with Figure 6.…”

“…We found that when the off-axis degree of the beam or the topological charge carried by the beam increased, the scattering field was distorted and the OAM spectrum was aliased. For asymmetric targets, spectral aliasing occurred even when the beam was on the incidence axis [41].…”

Detection accuracy of target accelerations based on vortex electromagnetic wave in keyhole space

“…[23] Very recently, it was reported that the off-axis vortex waves illuminate electrically large conductors of different shapes. [24] These results indicate that the OAM spectrum spreading due to inhomogeneous transmission environment will inevitably bring negative influence on the application of vortex beam. However, as a unique feature of vortex electromagnetic wave, the rotating Doppler effect and its application in detecting a rotating target have been studied mostly within the ideal line-of-sight scenarios until now.…”

“…[20,21] On the other hand, in the radio frequency range, the transmission of vortex electromagnetic wave is more obviously affected by the scattering of obstacles. [22][23][24] The scattering of high-order Bessel vortex electromagnetic waves on dielectric spheres was studied. [22] Fortunately, the OAM spectrum maintains well after the vortex electromagnetic wave has transmitted through conductor sphere and cone.…”