Graphene-Based Plasmonic Tunable Low-Pass Filters in the Terahertz Band

We propose the concept, synthesis, analysis, and design of graphene-based plasmonic tunable low-pass filters operating in the terahertz band. The proposed structure is composed of a graphene strip transferred onto a dielectric and a set of polysilicon dc gating pads located beneath it. This structure implements a stepped impedance low-pass filter for the propagating surface plasmons by adequately controlling the guiding properties of each strip section through graphene´s field effect. A synthesis procedure is presented to design filters with desired specifications in terms of cutoff frequency, in-band performance, and rejection characteristics. The electromagnetic modeling of the structure is efficiently performed by combining an electrostatic scaling law to compute the guiding features of each strip section with a transmission line and transfer-matrix framework, approach further validated via full-wave simulations. The performance of the proposed filters is evaluated in practical scenarios, taking into account the presence of the gating bias and the influence of graphene´s losses. These results, together with the high miniaturization associated with plasmonic propagation, are very promising for the future use and integration of the proposed filters with other graphene and silicon-based elements in innovative terahertz communication systems.