Ultra-low-loss spoof surface plasmon polariton waveguides using substrate-free technology

Spoof surface plasmon polaritons (SSPPs) enable strong electromagnetic field confinement, which, however, inherently increases the dielectric losses, creating a contradiction between strong confinement and low loss. To mitigate this contradiction, a substrate-free technology is proposed for single-conductor (SC) and double-conductor (DC) SSPPS, which can reduce the dielectric losses. Experimental results demonstrate significantly reduced attenuation, achieving as low as 0.016 dB/mm for SC-SSPP and 0.017 dB/mm for DC-SSPP at 30 GHz, which correspond to 68% and 66% reductions of losses, respectively. Moreover, substrate-free DC-SSPP pairs maintain consistently lower coupling than the microstrip lines from 20 GHz to 30 GHz, with a maximum difference of 15 dB.