Dynamically Tunable Attenuator on a Graphene-Based Microstrip Line

In this paper, a novel type of dynamically tunable attenuator based on graphene is proposed. This type of attenuator is composed of one or two graphene sandwich structures (GSSs) and a microstrip line. The GSSs are spread on the substrate of microstrip line near the signal strip along the direction of propagation to dissipate electromagnetic field. By the application of biased voltage, the surface impedance of graphene can be tuned, and consequently, the insertion loss of microstrip line can also be adjusted while the return loss maintains relatively low level. A transverse equivalent network and a closed form of attenuation of each attenuator are also proposed, which can be utilized to analyze the performance of attenuator with different critical parameters of graphene in detail. According to the analysis, there is a maximum value of the attenuation as the surface impedance of graphene rises from 0 to 3000 Omega/square. As an example, a prototype of each tunable microstrip line attenuator operating at gigahertz frequencies is fabricated and measured. The fabricated attenuator present favorable attenuation ranges from 3 to 15 dB, at the operating frequency from 9 to 40 GHz, and with a stable wideband attenuation corresponding to bias voltage changing from 0 to 4.0 V.