OAM-focal shift coupling effect and its application in wideband RCS reduction metasurface

A new method, to our knowledge, in designing a metasurface with wideband and angularly stable radar cross section (RCS) reduction based on the coupling effect of orbital angular momentum (OAM) and focal shift (FS) is proposed. Through the analytical discussion of both an ideal scattering model and a practical array model, it is found that the effect of OAM-FS coupling can control the scattering wavefronts efficiently with an optimal arrangement in backward field and ‘homogenization’ reflected field, indicating RCS reduction in both monostatic and bistatic directions. To verify this method, by combining three phases (geometric phase, gradient phase, and divergent phase), the OAM-FS coupling metasurface is designed and its performance in RCS reduction is tested in simulation and experimentally. The unit cell of the metasurface, constructed with arcs and lines, can provide arbitrary phase compensation and polarization conversion performance within a fractional bandwidth of 115.4%. Our results show that the proposed metasurface achieves a 10 dB reduction in both monostatic and bistatic RCSs over 8–32 GHz and has angular stability under 0°−30° oblique incidence of plane waves, and the measured results are in good agreement with the simulations. Our findings not only reveal a coupling effect in scattering waves of metasurfaces, but also offer a new perspective in manipulation of reflection and RCS reduction, which has potential applications in stealth technology.