High-efficient and low-coupling spoof surface plasmon polaritons enabled by V-shaped microstrips

We propose a novel variety of V-shaped microstrips for highly efficient and strongly confined spoof surface plasmon polaritons (SSPPs) propagation. We analyze the dispersion characteristics of the V-shaped SSPPs microstrip units and find that the asymptotic frequency of the dispersion curve can be significantly reduced by adding the folded stub without increasing the lateral dimension of the structure. The V-shaped microstrip possesses the advantage of being compatible with a conventional microstrip without the need for complicated and bulky mode conversion structures in other typical grooved SSPP waveguides. Then, broadband transitions with a tapered microstrip and an array of graded height V-shaped units with good impedance matching and high mode conversion efficiency are designed. The simulated and measured results demonstrate that the proposed V-shaped microstrip has excellent broadband lowpass filter characteristics with the reflection coefficient (S₁₁) less than -10 dB and the transmission coefficient (S₂₁) higher than -3 dB in the frequency range from 0 to 10.3 GHz. Furthermore, the coupling characteristics of the parallel and symmetrically arranged V-shaped microstrips are investigated. Compared to conventional parallel microstrips with a separation of 2.8 mm, the proposed parallel V-shaped microstrips with 2 mm inner-overlapping have significantly lower coupling effects in the frequency ranging from 0 to 10 GHz. The low coupling, strong field confinement, and flexible dispersion manipulation of the proposed microstrip make it possible to achieve device miniaturization and noise interference suppression, which may have great potentials in the development of various highly integrated microwave plasmonic circuits, devices, and systems.