Radar-absorbing materials are used in stealth technologies for concealment of an object from radar detection. Resistive and/or magnetic composite materials are used to reduce the backscattered microwave signals. However, nontunable characteristics or the required complex structure hampered the application of these materials. Here, multilayer graphene-based frequency selective surfaces (MLGFSS), which reach a size of 150 mm $x$ 150 mm, are designed and fabricated. By properly changing the growth temperature of MLG using the chemical vapor deposition approach and designing the pattern of graphene layer, the impedance matching condition can be satisfied at different frequencies. As a result, two kinds of absorbers with different working bandwidths are realized. The performances of the proposed absorbers are analyzed using full-wave simulation and are also tested with experimental results. Our method of fabricating large-area MLGFSS avoids the direct contact between the stencil mask and graphene, and guarantees the integrity and quality of patterned graphene structure. A good agreement between simulation and measurement results demonstrates that such ultrathin MLGFSS is very useful in the design of graphene-based functional devices at microwave frequencies.

In this paper, a dynamically tunable substrate-integrated-waveguide (SIW) attenuator using graphene is first presented. Two graphene sandwich structures are placed inside an SIW, which serve as conductivity-tunable E-plane septum. By applying biased voltage to the graphene, the attenuation can be dynamically changed; meanwhile, the reflection can still keep at a relatively low level. A closed form of the attenuation is also proposed, and the mechanism of the attenuator is theoretically analyzed in detail. Furthermore, a prototype operating from 7 to 14.5 GHz has been fabricated and measured. Both the theoretical calculation and the numerical simulation results have a good agreement with the experimental results, which present the attenuation ranges from 2 to 15 dB with a stable 7.5-GHz wideband while the bias voltage changing from 0 to 4 V.

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 Ω /□. 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.

In this article, to reduce the operating frequency and the size of the spoof surface plasmon polariton (SSPP) attenuator and introduce the filtering function into the graphene attenuator, we propose a tunable graphene filtering attenuator, namely the graphene-based effective SSPP (ESSPP) attenuator. It consists of an ESSPP waveguide and a graphene sandwich structure (GSS). The effect of GSS on the attenuation and dimensions of the ESSPP waveguide on the passband are analyzed in detail, and the closed form of the attenuation is proposed. Finally, five prototypes of the graphene filtering attenuator are fabricated and measured. The experimental results show that not only the attenuation of this attenuator can be tuned but also that the upper and lower cutoff frequencies can be adjusted independently, which means that this filtering attenuator demonstrates expected filtering and attenuation performance.

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.