Dual-band trapping of spoof surface plasmon polaritons and negative group velocity realization through microstrip line with gradient holes

In this letter, dual-band trapping of spoof surface plasmon polaritons (SSPPs) is realized by a simple surface plasmon waveguide (SPW), which takes the form of a microstrip line with periodic holes. A tapered microstrip line with periodic gradient holes is built for efficient mode conversion between the quasi-transverse electromagnetic waves in the common microstrip line and the SSPPs on the SPW. It is interesting to note that negative group velocity can be clearly observed on the first high-order mode of such SPW due to the strong coupling between the corrugated microstrip line and ground. A curved SPW of the same form is also investigated for testing its field confinement and circuitry function. Measurement results agree quite well with the simulation ones, which indicate this SPW can find potential applications in plasmonic integrated circuits at microwave and terahertz frequencies.