Graphene-Based Dynamically Tunable Attenuator on a Coplanar Waveguide or a Slotline

In this paper, we propose a novel type of dynamically tunable graphene-based attenuator fabricated on a coplanar waveguide (CPW) or a slotline. We obtain this type of attenuator by depositing a graphene sandwich structure (GSS) on a CPW or a slotline. The fabrication of this type of attenuator is much easier than that of another GSS-based attenuator. The attenuation of the attenuator can be controlled by the surface impedance of graphene which can be tuned by a bias voltage. To investigate the performance of the attenuator, a closed-form equation of attenuation based on a transverse equivalent network is derived. It can be manifested from the closed-form equation that there exists a maximum attenuation when the surface impedance of graphene reaches a certain value. It is very different from other types of attenuators. To verify the closed-form equation, we manufactured and tested a prototype of each attenuator. The measure results manifest that the attenuation can be varied from 3 to 15 dB at 9-40 GHz while the bias voltage increases from 0 to 4 V; meanwhile, the magnitude of S11 can always be smaller than -15 dB across the operating frequency. The test results also validate the role of the length of graphene and the spacing between the CPW and the GSS in the attenuator.