Low-Loss Spoof Surface Plasmon Slow-Wave Transmission Lines With Compact Transition and High Isolation

The symmetric spoof surface plasmon (SSP)-based slow-wave transmission line (SW-TL) with compact transition, low ohmic loss, and low crosstalk between SW-TLs is proposed and investigated. First, the SSP cells are modeled by equivalent circuit elements. The proposed equivalent circuit model is appealing for the integration of SW-TLs with other microwave circuits. With the symmetricity, the SW-TLs are readily realized by a compact mode converter providing gradual impedance, momentum, and polarization matching from guided waves to spoof microwave plasmons. Then, simulation studies and experiments verify that the proposed SSP SW-TL features as low as half the ohmic loss of the traditional counterparts. After that, the low mutual coupling between the proposed SSP SW-TLs is numerically and experimentally substantiated and showed to be up to 10 dB lower than that between conventional microstrip TLs. The proposed low loss, highly isolated and compact SW-TL along with the reliable circuit model enables the further exploitation of promising spoof plasmon modes in microwave technology.