Ultrathin and flexible directional coupler with arbitrary coupling level using s-shaped spoof surface plasmon polariton coupled-line

Abstract

Here, we study the coupling effect between two identical ultrathin plasmonic waveguides and present an ultra-flexible directional coupler by printing a pair of corrugated metallic strips with mirror symmetry on the top of an ultrathin dielectric substrate. The proposed coupler supports the transmission and coupling of spoof surface plasmon polariton waves efficiently. We experimentally demonstrate that the coupler possesses excellent flexibility, arbitrary coupling level and wide bandwidth simultaneously. Hence, the proposed coupler paves the way to develop flexible plasmonic devices, conformal circuits, human body sensors and wearable devices in microwave and terahertz frequencies.