Tunable band-notched coplanar waveguide based on localized spoof surface plasmons

This Letter proposes a simple band-notched coplanar waveguide (BNCPW), which consists of a coplanar waveguide (CPW) and an ultra-thin periodic corrugated metallic strip that supports spoof surface plasmon polaritons (SSPPs) with defect units on the back of the substrate. By introducing a defect unit or multiple defect units into the strip, a narrow stopband or multiple narrow stopbands would be generated flexibly and conveniently. The band-notch function is based on the idea that a defect mode, which exists in the bandgap between the fundamental and the first higher mode of the SSPPs, can be introduced to form a stopband. Thus, the SSPPs field is localized around the defect units, which is another form of localized spoof surface plasmons (LSSPs). By properly tuning the dimensions of each defect unit, the absorption level and center frequency of the stopband could be adjusted independently. We offer theoretical analysis and experimental results to validate our idea and design. In this framework, a variety of band-notched devices and antennas in the microwave and terahertz (THz) frequencies can be easily designed without additional band-stop filters.