Retro-reflective metasurfaces for backscattering enhancement under oblique incidence

In this letter, we propose the design of retro-reflective metasurfaces for enhancing backscattering under oblique incidence. Through reflective phase profile design along the surface, an equivalent wave-vector can be generated, with double magnitude but opposite direction to the parallel component k|| of the wave-vector k0 of incident waves. Due to this artificial parallel wave-vector, the main lobe of reflective waves can be reoriented backwards. As an example, we demonstrate an X-band retro-reflective metasurface that can operate effectively under oblique incidence θ=20°. A modified metallic square loop structure is used to achieve the required phase profile under oblique incidence. Through the phase gradient design, the metasurface can reflect incident waves backwards at 9.8GHz under transverse electric (TE) polarizations. A prototype was fabricated and measured. Both the simulation and experiment results verify the good retro-reflection performance of the metasurface.