Compact lowpass filters using GCPW-based spoof surface plasmon polaritons

In this paper, a new type of spoof surface plasmon polaritons (SSPPs) is proposed to construct lowpass filters based on grounded coplanar waveguide (GCPW) transmission lines. Compared with the conventional SSPP-based lowpass filters, the proposed lowpass filters using GCPW-based SSPPs only need two transition unit cells to achieve mode conversion from GCPW to SSPPs, which significantly reduce the circuit size. In addition, the cutoff frequency of the filter can be independently controlled by modifying the corresponding structural parameters. In order to further decrease the cutoff frequency of the lowpass filter, another improved SSPP structure is constructed by periodically adding L-shaped grooves on the SSPP unit cells. The experimental results show that the measurement results are in good agreement with the simulation results, which validate the correctness of the proposed structures and design method.