BroadBand spoof surface plasmon polaritons coupler based on dispersion engineering of metamaterials

The dispersion curves of spoof surface plasmon polaritons (SSPPs) are typically asymptotically nonlinear, with only one single intersection point with the dispersion curves of couplers. This means that wave-vector matching can be achieved only at a single frequency, leading to a narrow bandwidth of SSPP couplers. In this letter, we propose to achieve broadband SSPP couplers through dispersion engineering of metamaterials. To this end, we investigated the dispersion properties of a metallic patch array (MPA) that supports the propagation of TE-mode SSPPs at microwave frequencies. After this, we designed a planar metamaterial lens that can provide additional tangential wave-vectors to free space waves. By dispersion engineering, the dispersion curve of the coupled waves overlaps with that of SSPPs on the MPA in a broadband, resulting in high-efficiency broadband coupling of SSPPs. As an example, we demonstrated a broadband SSPP coupler with more than a bandwidth of 1 GHz in the X band. The method can be readily extended to millimeter-wave, terahertz, and other higher frequencies.