Low-coupling reflective metasurfaces for accurate near-field focusing

Metasurface is a 2D metamaterial which manipulates electromagnetic wavefront by carefully designing the transmissive or reflective responses of the planar subwavelength structures. Despite various emerging new functionalities, one of the limitations of metasurfaces in practical applications is the lack of control accuracy of its local amplitude and phase responses. This is in part caused by the discrepancy between the periodic EM simulated responses of unit cells and the actual non-periodic metasurfaces when functionality-determined amplitude and phase gradients are introduced. Under such conditions, the focusing capabilities of metasurfaces can be greatly affected. In this paper, we address this problem by introducing a slotted ground plane metasurface design which reduces the above-mentioned discrepancy by limiting the mutual coupling effects of a unit cell with its surrounding elements. An offset-fed near-field focusing reflective metasurface is designed and fabricated to verify the performance of the proposed design. Both the EM simulated and measurement results demonstrate the advantages of the proposed design in terms of sidelobe level and transfer efficiency.