On-Chip Lumped-Distributed Filters With Bandstop Stubs Based on Spoof Surface Plasmon Polaritons

One on-chip low-pass filter (LPF) and two on-chip bandpass filters (BPFs) with bandstop stubs are presented by virtue of spoof surface plasmon polaritons (SSPPs). Three differently patterned SSPPs are realized by reusing multiple stubs in lumped-distributed structures. In addition, bandstop stubs are loaded on the outside open stubs of the lumped-distributed structures to enhance high-band rejections. To elucidate the filtering characteristics of the proposed filters, the dispersive properties of different SSPP unit cells are investigated and discussed. To verify the feasibility of the proposed designs, three on-chip filters, all with a small area of only 2.56 mm², are fabricated and measured using glass-based integrated passive device (IPD) technology. The experimental results show that all three proposed on-chip filters have wide upper stopbands of $15.3~f_{c}$ , $8.2~f_{0}$ , and $4.4~f_{0}$ , respectively, which are very attractive in integrated systems.