Low-Loss Spoof Surface Plasmon Polariton Based on Folded Substrate Integrated Waveguide

Spoof surface plasmon polariton (SSPP) features highly confined field confinement and subwavelength operational scale. However, at the low-frequency region, SSPP usually suffers from a poorly confined field, and a relatively large loss resulted from the mode conversion. Folded substrate integrated waveguide (FSIW) is a compact version of substrate integrated waveguide. However, FSIW suffers from a large guided wavelength and hence is not preferred for compact antennas. In this letter, we propose a combination of FSIW and SSPP, which has the benefits of both FSIW and SSPP. Compared with the pure SSPP, FSIW-SSPP significantly improves the field confinement and transmission loss at the low-frequency region due to the closed structure. At the same time, FSIW-SSPP reduces the guided wavelength by 67% due to the slow-wave feature of SSPP. A prototype of FSIW-SSPP was fabricated and measured. The simulated and measured results validate the expected performance. This new structure has potential applications in the antenna miniaturization.