A Broad Dual-Band Bandpass Filter Design Based on Double-Layered Spoof Surface Plasmon Polaritons

Lingyun Liu,Xiaohua Jin,Zhuo Li,Yun Liu,Yubo Tian

doi:10.3390/electronics11050697

Abstract

In this work, a broad dual-band bandpass filter is designed by applying double-layered spoof surface plasmon polaritons (DLSSPPs) as the main transmission line (MTL) and loading combined-stub dual-mode resonators (CSDMRs) onto the MTL with certain spaces. Each CSDMR consists of an open stub and a short stub that are connected in parallel. Efficient mode conversion between the quasi-transverse electromagnetic waves in the microstrip line and the spoof surface plasmon polaritons (SSPPs) on the double-layered surface plasmon waveguide is realized using gradient double-layered metal gratings and via the sector structure impedance matching technique. A parametric study of the CSDMR demonstrates that center frequencies and bandwidths can be controlled by varying the stub lengths and widths of the CSDMRs. A second-order dual-band filter is designed and fabricated, and simulated and experimental S-parameters agree well. A lower loss of the passband is achieved compared with the filters that apply single-layered SSPPs. The space between two CSDMRs is shortened because of the slow-wave effect of the DLSSPPs. The lowpass performance of the DLSSPPs exhibits good rejection from the cutoff frequency above.

Highlights

Surface plasmon polaritons (SPPs) are surface electromagnetic waves that propagate along the interface between two materials with opposite permittivity and whose electromagnetic fields exponentially decay in the transverse direction [1]
Thanks to the tight confinement of electromagnetic waves between metal layers, a relatively lower loss can be achieved with double-layered spoof surface plasmon polaritons (DLSSPPs) than with solutions based on single-layered spoof surface plasmon polaritons (SSPPs) (SLSSPPs)
Double-layered SSPPs with comb-shape units are used for the main transmission line to realize broad dual-band bandpass filters

Summary

Introduction

Surface plasmon polaritons (SPPs) are surface electromagnetic waves that propagate along the interface between two materials with opposite permittivity and whose electromagnetic fields exponentially decay in the transverse direction [1]. A highly efficient conversion from conventional guided waves to SPPs is achieved in the broadband by using ultrathin corrugated metallic strips with a transition with gradient grooves. Using such strips allows the realization of combined devices and circuits of guided waves and SSPPs, especially surface plasmonic bandpass filters with SSPP structures [28,29,30,31,32,33,34,35]. Thanks to the tight confinement of electromagnetic waves between metal layers, a relatively lower loss can be achieved with DLSSPPs than with solutions based on single-layered SSPPs (SLSSPPs). The center frequencies and bandwidths can be controlled by varying the parameters of the CSDMRs

Materials and Methods

Structure of a Second-Order Dual-Band Bandpass Filter and Simulation Results

Conclusions