Planar tunable graphene based low-pass filter in the terahertz band

In this paper, design and analysis of planar graphene-based low-pass filters in the terahertz band are proposed. Using the proposed approach, it is possible to design plasmonic low-pass filters with the desired properties in the form of open stubs. The transfer matrix method is used based on the transmission line model for analyzing filters. The propagation constant and characteristic impedance required for this method are obtained according to the electrostatic scaling law and power-current approach, respectively. A typical fifth-degree low-pass filter is designed and analyzed according to the mentioned process. The frequency response of the low-pass filter indicates insertion loss of less than 2 dB, roll-off rate of 17 dB/THz, return loss higher than 10 dB, and constant group delay of 0.3 ps. The results of the full-wave simulation confirm the analytical ones. Also, the theory of graphene equivalent circuit variation to the different chemical potentials is expressed so the filter frequency response can be explicitly predicted for any bias value. These filters, due to their compact structure and integrated electrical and physical shape, are the suitable choice for use in full-integrated planar circuits of terahertz systems.