Broadband spoof surface plasmon polariton couplers based on transmissive phase gradient metasurface

In this paper, we propose the design of broadband spoof surface plasmon polariton (SSPP) couplers based on transmissive phase gradient metasurfaces (TPGMs). Due to the large parallel phase gradient, transmitted waves through the TPGM are converted to driven surface waves (DSW). By placing the TPGM above a square patch array, the DSW can be coupled to an eigenmode SSPP in a broadband. High efficiency can be achieved since there is no initial reflection and SSPP decoupling effect in such SSPP couplers. A SSPP coupler was demonstrated in a microwave regime. Both the simulated and measured results show that the SSPP coupler can operate effectively in 7.0-9.9 GHz under normal incidence. Our finding may pave the way for broadband applications of SSPP.