Integration of geometrically different elements to design thin near-field metasurfaces

Phase-gradient metasurfaces, also known as phase-shifting surfaces, are used to steer the beam of medium-to-high gain antennas. Almost all such surfaces are made of cell elements that are similar in shape and only differ in dimensional parameters to achieve the required spatial phase gradient. A limitation of using the same geometry for the cell elements is that only limited phase shift range can be achieved while maintaining high transmission through each cell. A new strategy of integrating geometrically different cell elements, having different transmission phase and amplitude characteristics, is presented in this article. To demonstrate the concept, four different cell geometries are considered. The results indicate that the hybrid approach allows the designer to achieve the required phase shift range together with a high transmission with thinner metasurfaces having fewer dielectric and metal layers. When used to steer the beam of a microstrip patch array, the hybrid metasurface produced more accurate beam steering with 1.6° less steering error compared to a reference single-geometry metasurface.