Wide-angle scattering cancellation from Pancharatnam-Berry metasurfaces with hybrid and combined hybrid phase OAM-profiles

In this paper, the phase mechanism of broadband wide-angle reduction of the radar cross-section (RCS), based on the use of non-absorbing Pancharatnam-Berry (PB) metasurfaces (MS) with the generation of orbital angular momentum (OAM) and a combination of different phase profiles is studied. Unit cells of the MS contain a thin shielded single-layer substrate and meta-particles in the form of perforated rectangular patches with a coded rotation angle. The aim of the work is to compare the scattering characteristics and the efficiency of scattered field cancellation of structural elements (modules) of the MS, consisting of the same number of meta-particles, but having different PB phase profiles. The scattering characteristics of the MS modules are studied using HFSS (finite element method) on a co- and cross-polarization in the case of irradiation with a normally incident left circular polarized plane wave. The simulation showed that the scattering patterns of the co-polarized field of the MS in all these cases have a funnel-shaped vortex character with a helical spiral phase front and OAM. The generation of OAM significantly cancelles the backscattering of the co-polarized field. The combination of OAM profiles and parabolic profiles increases the diffusion of broadband scattering, implements a wider-angle scattering of the resulting field, which is important for RCS reduction. Therefore, hybrid Pancharatnam-Berry MSs and combined hybrid MSs were designed and their scattering characteristics were studied. Hybrid MSs consist of two subblocks of different shapes, each of which is a fragment of antiphase OAM modules of a square shape. Combined hybrid MSs are constructed by superimposing a modified parabolic profile on the OAM profiles of the subblocks of the hybrid MSs. The validity of the holographic approach underlying the design of hybrid MSs is demonstrated, according to which a fragment (part) of a metasurface preserves the phase properties of the object wave of the entire metasurface. From a comparison of diffusion and wave cancellation by hybrid and combined hybrid metasurfaces it follows that combined hybrid MSs implement a wider-angle diffuse vortex funnel-shaped scattering of a co-polarized field with an angle of intense side lobes of up to 88°, whereas hybrid MFs of the same size have a funnel opening angle of about 55°.