Tunable Attenuator Based on Hybrid Metal-Graphene Structure on Spoof Surface Plasmon Polaritons Waveguide

Introduction

In the past few years, Spoof Surface Plasmon Polaritons (SSPPs) have attracted increasing attention due to their exceptional capability of guiding electromagnetic waves, flexibility enhancement and mutual coupling reduction (Chen et al., 2018; Tang et al., 2019). Several groups developed many microwave components and devices based on SSPP concept, such as antennas, waveguides, sensors, filters, splitters and couplers (Kianinejad et al., 2015; Kianinejad et al., 2018; Zhang et al., 2017). A reconfigurable SSPP waveguide attenuator is a fundamental component for the microwave applications. Graphene, as a two-dimensional material with its several interesting characteristics, has been widely used in the manufacture of microwave and terahertz components. In fact, it is considered to be an electronically tunable component thanks to one of its key characteristics which is its ability to change its conductivity. A number of graphene-based tunable attenuators have been proposed in (Zhang et al., 2019a; Zhang et al., 2019b; Zhang et al., 2018; Zhang et al., 2019). Similarly, the tunable substrate integrated waveguide attenuator using graphene mentioned in (Zhang et al., 2018), were obtained by depositing two graphene sandwich structures inside a Substrate Integrated Waveguide (SIW). The attenuator in reference (Zhang et al., 2019a) consists of a microstrip line and two graphene sandwich structures. In fact, these graphene sandwich structures are placed on the substrate of the micro strip line, close to the signal strip over the propagation direction. Reference (Zhang et al., 2019) has proposed and realized a flexible and tunable attenuator construct on graphene-based spoof surface plasmon polaritons waveguide. This attenuator is built by making a graphene sandwich structure on a SSPP waveguide. All of these structures operate in the bands 7-14, 10-40 and 6-9 GHz, respectively. However, though it has not been developed a terahertz tunable attenuator is a fundamental device for an RF system. To our knowledge, no work has been developed a tunable attenuator based on SSPP designs in THz band. In this work a novel type of tunable attenuator based on hybrid metal-graphene structure on spoof surface plasmon polaritons waveguide is proposed, this type of attenuator is developed to operate in terahertz band. The theoretical analysis of the graphene-based attenuator demonstrated that the attenuation can be adjusted by adding graphene cells over the SSPP waveguide and by varying the graphene chemical potential. In order to validate the accuracy and efficiency of our study, the extracted analytic results are comprehensively compared with the simulated results with Wave Concept Iterative Process (WCIP) method and CST simulator. This paper is organized as follows. In section II, the theoretical analysis of the structures and some theoretical aspects about the graphene and WCIP method are presented. Subsequently, numerical results are introduced in section III to demonstrate the effect of graphene chemical potential variation and the number of cells on attenuation. Eventually, conclusions are provided at the end of this paper.