Beam Refraction with an Isotropic and Ultrathin Huygens' Metasurface

We propose an isotropic and ultrathin Huygens' metasurface that can refract normally incident electromagnetic waves efficiently to a predefined angle at 25 GHz. The phase gradient of the surface is controlled by five subwavelength (with dimensions of 0.5 lambda(0) x 0.5 lambda(0), lambda(0) is the freespace wavelength at 25 GHz) non-resonant spatial phase shifters, which have metallic structures etched on both sides of an ultrathin dielectric substrate (with the thickness of 0.07 lambda(0)). The peak value of the transmission efficiency of the device approaches 60%. The proposed metasurface may find applications in designing various electromagnetic lenses, or beam-steerable devices.