Miniaturized Spoof Surface Plasmon Polaritons Load for Planar Terahertz Circuit Application on Thick Substrate

In this brief, we present a miniaturized spoof surface plasmon polaritons (SPPs) load for planar terahertz (THz) circuit application on thick substrate. The proposed SPP cell consists of a groove-shaped structure integrated with a folded stub. The coupling between the stub and the grooves enlarges the capacitance, reduces the cutoff frequency, and miniaturizes the SPP size. The strong field confinement of the SPP waveguide leads to tremendous insertion loss near the cutoff frequency. Furthermore, due to the low conductivity and high permeability, the SPP structures made of nickel (Ni) metal increase the metallic loss to 40 folds that of the aluminum (Al) case, effectively absorbing the propagating electromagnetic wave. Therefore, the tapered SPP structure made of Ni metal can operate as a load with a compact size of 1.7 λg × 0.23 λg (λg is the guided wavelength at 300 GHz). The reflection coefficient of this compact SPP load is below -20 dB in the 195 -500 GHz band. Finally, this SPP load is utilized in an equal-power two-way Goubau-line divider, with 0.194 λg substrate thickness, operating in 220-325 GHz band. The simulated and experimented results are consistent, indicating that the proposed compact SPP load could serve as a matching load for THz multiple-port circuit application on thick substrate.