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Plasma-based GHz tunable bandstop filter

Tunability is an important feature for the filter. As a special electromagnetic medium, the plasma has its permittivity being altered in a wideband range. In this work, based on the surface plasmon polaritons of plasma–dielectric–plasma waveguides, we propose a double-stubs structure submerged in a gaseous discharge plasma medium to realize tunable filtering properties in the giga-hertz (GHz) regime. The finite element method is applied to numerically compute filtering properties. The coupled mode theory and orthogonal design method are introduced to verify simulation results and estimate the effect of simulation parameters on the filtering properties. It is shown that the height of two stubs has the most important influence on filtering performance. Although once the filter is fabricated, its size cannot be modified, one can, nevertheless, vary the plasma frequency to effectively adjust the plasma frequency for the best filtering. Thus, such a plasma-modified filter provides a feasible scheme to dynamically adjust the filtering frequency.