Design methodology for graphene tunable filters at the sub-millimeter-wave frequencies

Abstract

Tunable components and circuits, allowing for the fast switching between the states of operation, are among the basic building blocks for future communications and other emerging applications. Based on the previous thorough study of graphene based resonators, the design methodology for graphene tunable filters has been devised, outlined, as well as explained through an example of the fifth order filter. The desired filtering responses can be achieved with the material loss not higher than the loss corresponding to the previously studied single resonators, depending mostly on the quantity of graphene per resonator. The proposed design method relies on the detailed design space mapping; obtained data gives an immediate assessment of the feasibility of specifications with a particular filter order, maximal passband ripple level, desired bandwidth, and acceptable losses. The design process could be further automated by the knowledge based approach using the collected design space data.

Tuning the Filter Responses with Graphene Based Resonators

“…The collected data sets were utilized to determine the geometrical loci of points (combinations of insert lengths and graphene lengths) with the desired gains, K. Also, based on the collected data, the appropriate quantity of graphene to achieve the desired tunability can be determined. This is explained in much more detail in [5].…”

“…Namely, the equivalent circuit of a combined graphene-metal resonator can be conveniently represented using the K-inverter circuit with an equivalent gain K, and an equivalent electrical length at ports, ϕ. For the chemical potential between 0.2 eV and 1.0 eV, parameter K ("gain") predominantly depends on the insert length [5]. The equivalent electrical length, ϕ, strongly depends on the material properties.…”

“…A particular curve is adopted as a solution based on an estimated tunability. For more detailed explanation, as well as the graphical representation, please see [5].…”

“…Due to the nonlinear frequency dependence, around the desired central frequency, of the equivalent analytical models of E-plane discontinuities as well as pronounced losses in graphene, an accurate analysis required the full-wave EM numerical computations [4]. The state-of-the-art commercial software package HFSS has been employed in the design procedures relying on the extensive design space mapping [5]. The variable surface conductivity of graphene has been modeled, in the considered frequency range where the spatial-dispersion effects are negligible, using the Kubo formalism of statistical physics [6]:…”

“…Here, we outline the general design procedure, described in detail in [5], and illustrate the design of graphene tunable filters by using several examples of filters at 400 GHz. Obtainable filter responses mostly depend on the required bandwidth and tunability in combination with the acceptable insertion loss.…”