A Dual‐Loss‐Suppression Meta‐Unit for Low‐Loss Continuously Tunable Spoof Surface Plasmon Polaritons

Abstract

ABSTRACT Dynamic tuning of spoof surface plasmon polaritons (SSPPs) is typically accompanied by substantial loss, which mainly originates from two sources: parasitic loss in tunable semiconductor components and dielectric loss dominated by the substrate. Here, we propose a continuously phase‐tunable low‐loss SSPP waveguide based on dual‐loss‐suppression meta‐units that simultaneously addresses both limitations. For semiconductor loss suppression, a composite‐varactor network is introduced to reduce the equivalent parasitic resistance of the tunable elements while preserving the effective tuning range. For dielectric loss suppression, an inverted SSPP architecture is employed to redistribute the electromagnetic field from the lossy substrate into the air region, thereby reducing substrate‐induced loss. A prototype operating at 8.5 GHz is designed, fabricated, and experimentally characterized on a high‐loss FR‐4 substrate with tan δ = 0.025. The proposed waveguide achieves a continuous phase tuning range of 300° and an attenuation constant as low as 0.019 dB/mm, corresponding to a 64% reduction compared with a typical tunable SSPP waveguide. This work provides a systematic approach to overcoming the loss limitations of tunable SSPPs and advances the development of high‐performance tunable devices and systems.