To adjust the transmission band while keeping the width of a spoof surface plasmon polariton (SSPP) waveguide unchanged, periodic cells with T-shaped conductor branches on both sides are used. By controlling the top lateral strips of branches, the adjustable range of cutoff frequencies can reach approximately 3.5 GHz. Thus, compromised regulation of the field confinement and transmission loss is easily achieved, improving the transmission performance of SSPP modes. By loading open conductor rings onto T-shaped branches to construct a split ring resonator (SRR), a band-rejection filter is realized. When multiple SRRs with gradient lengths are loaded onto one side of the SSPP waveguide, a broad stop band with a relative bandwidth of 18% is achieved. The proposed structures are also advantageous for the miniaturization of microwave circuits.

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Negative group velocity (NGV) exists only in the anomalous dispersion band with resonance absorption. In this paper, it is verified that spoof surface plasmon polaritons (SSPPs) with spiral-shaped periodic units have the NGV characteristics near cutoff frequency. The negative group delay of this NGV SSPP can be used to achieve the compression of the pulse signal, and also to compensate the positive group delay with high efficiency. Of course, this group delay compensation scheme based on NGV may introduce an absorption loss, which is the characteristic of all passive negative group delay circuits.

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