Propagation of low-frequency spoof surface plasmon polaritons in a bilateral cross-metal diaphragm channel waveguide in the absence of bandgap

In this work, spoof surface plasmon polaritons in a novel subwavelength periodic bilateral cross-metal diaphragm channel waveguide are theoretically and experimentally investigated. It is found that the propagation frequency range can be broadened due to the absence of the bandgap between the fundamental band and the second guiding band by tuning the geometric parameters. In addition, the dispersion curve of the second band can pass through the light line and then enter into the radiation region, leading to a frequency-based beam steering radiation. We also find that, below the light line, there exists an anomalous linear dispersion such that the guiding mode propagation length can be extended up to around 200\lambda. Good agreement has been achieved between experimental and numerical results.