A Generalized Lossy Transmission-Line Model for Tunable Graphene-Based Transmission Lines with Attenuation Phenomenon

Abstract

To investigate the frequency shift phenomenon by inserting graphene, a generalized lossy transmission-line model and the related electrical parameter-extraction theory are proposed in this paper. Three kinds of graphene-based transmission lines with attenuation phenomenon including microstrip line, double-side parallel strip line, and uniplanar coplanar waveguide are analyzed under the common conditions where different chemical potentials are loaded on graphene. The values of attenuation constant and phase constant, and the real and imaginary parts of the characteristic impedance of transmission lines are extracted to analyze in details. When the attenuation constant and the reactance part of the characteristic impedance are approximately equal to zero, this kind of transmission line has low or zero insertion loss. On the contrary, the transmission line is under the radiation mode with obvious insertion loss. The phase constant changes linearly under the transmission mode and can be varied with changing of chemical potentials which attributes to the property of frequency tunability. Furthermore, a bandwidth reconfigurable uniplanar coplanar waveguide power divider is simulated to demonstrate that this theory can be applied to the design of three-port devices. In summary, this work provides a strong potential approach and design theory to help design other kinds of terahertz and mid-infrared reconfigurable devices.

Modeling and Analysis of Sub-Millimeter-Wave Graphene Switches for On-Wafer Coplanar Transmission Lines

“…Namely, in [47] an equivalent model is used to extract the graphene sheet impedance values from the measured Sparameters of a microstrip attenuator. Moreover, in [48], an equivalent model approach is exploited to identify the losses in GL TLs, by carrying out full-wave simulations and then using the ABCD parameters to extract the complex TL characteristics (complex-propagation constant and -characteristic impedance) for different frequencies. Finally, in [49] a one-port GL device is proposed and an equivalent model is used to extract the graphene sheet impedance values without investigating the effects of patch geometry on device performance.…”

“…Graphene is modelled as a distributed admittance of ΔGgr=2NL/Zgr,sheet. The propagation constant and Z0 of the GL-CPW are given by [48] (6) where ΔL and ΔC are the distributed CPW components obtained by [52]. Thus, the ABCD parameters of the GL-CPW switch are [55] (7) To validate the accuracy of the proposed model, we compare the analytical model results with full-wave simulations, as shown in Fig.…”

Modeling and Analysis of Sub-Millimeter-Wave Graphene Switches for On-Wafer Coplanar Transmission Lines

“…Graphene is modelled as a distributed admittance of ΔGgr=2NL/Zgr,sheet. The propagation constant and Z0 of the GL-CPW are given by [48]   To validate the accuracy of the proposed model, we compare the analytical model results with full-wave simulations, as shown in Fig. 10.…”

Physics-Based Analytical Engineering Models of Graphene Micro- and Nanostrip Lines

“…are not seen in this formula, the influence of anisotropy of conductivity remains in hybrid nature of the main mode caused by this conductivity, and it needs to be considered in the theory of graphene microstrip line if its conductivity is anisotropic that is in correspondence to the conclusion of [18]. For calculation of the characteristic impedance for the main mode, the boundary equations (6) and 7should be solved if the propagation constant z k is found from (9) or (10). Then, this parameter is found as a relationship between the graphene current and line voltage.…”

“…An attractive feature of graphene components is their low signal delay and the possibility of tuning of their parameters using the electric or/and magnetic biasing of graphene's chemical potential and the conductivity of graphene layers [4], [5]. For instance, even loss of graphene interconnects can be decreased, tuning the chemical potential that is shown in measurements and simulations [6], [7]. Many linear and nonlinear graphene devices are published for analog microwave integrations [2], [4], [8], [9].…”