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CYLINDRICAL ANISOTROPIC METASURFACES WITH PANCHARATNAM-BERRY PHASE BIGRADIENT HELICAL CODING AND ANOMALOUS SCATTERING

Scattering characteristics of anisotropic cylindrical phase-gradient metasurfaces (MSs) with various helical Pancharatnam-Berry phase (PB-phase) coding are studied. The efficiencies of the scattering field reduction of circularly polarized (CP) waves in the forward half-space is compared for three different MS models with the same PB-phase gradient in the azimuthal direction and different phase gradients in the axial direction. The metasurfaces are conformally located on semi-cylindrical metallic polyhedral prisms. The meta-particles are of the form of triple coupled split-ring resonators. Spiral coding of the PB-phase of MS unit cells in the azimuthal and axial directions is carried out by the rotation of the meta-particles. The effect of constant phase gradients on the frequency characteristics of backscattered fields and bistatic diagrams of scattering of CP-waves in the azimuthal and meridional planes is numerically estimated. It is shown that the axial phase gradient causes more efficient anomalous scattering of co- and cross-polarized CP-waves. It leads to the deviation of intense diffraction lobes from the normal in the meridional plane by a large angle, with a shift of the lobes in the azimuthal plane. Bigradient MSs provide the scattering field reduction of CP-waves by at least 10 dB in the band from 10-12 GHz to 18.5 GHz in almost the entire forward half-space in the azimuthal plane and in the sector of angles up to ±45° in the meridional plane.