A Broadband Graphene-Based THz Coupler with Wide-Range Tunable Power-Dividing Ratios

A wide-band coupler based on the graphene with inherent DC-block function and adjustable power-dividing ratios is proposed. This coupler uses three sections of the two-line coupled lines, four sections of the three-line coupled lines, and four graphene stubs (two U-shaped stubs and two rectangular stubs). The graphene stubs allow the coupler to own dynamic surface conductivity, which could be tuned by altering the chemical potentials. The tunable power-dividing ratios could be achieved by varying the chemical potentials applied to the U-shaped graphene stubs and the rectangular graphene elements, respectively. In addition, the widths of two-line coupled lines in the proposed coupler are analyzed to affect the power-dividing ratios in detail. Finally, the power-dividing ratios of the proposed coupler have a variation range from 5.4 to 9.56 dB at 1.75 THz with a flat 90° phase shift. The minimum −10 dB impedance bandwidth is 44 % from 1.47 to 2.3 THz, thus indicating a wide-band performance.