Design of compact and broadband filtering balun based on N-shaped spoof surface plasmon polaritons

Abstract

This paper presents a novel compact and broadband filtering balun using N-shaped spoof surface plasmon polaritons (SSPPs). The N-shaped SSPP unit cell's lateral size has a 48% reduction compared to the rectangle-shaped counterpart. The proposed filtering balun is constructed by periodically etching N-shaped and mode-matching SSPP unit cells into the slotline balun consisting of the microstrip-toslotline transition (MST) structures. The combination of the N-shaped SSPP unit cells and slotline balun realize the compactness and the broadband bandpass filtering response. Moreover, we can individually adjust the passband's lower and upper cut-off frequencies. Due to the larger phase constant of the N-shaped SSPP unit cell, the field-confined ability of the proposed filtering balun is enhanced. The proposed design is fabricated and measured. It has advantages in bandwidth, stopband performance, size, and degree of design freedom compared with existing SSPP filtering baluns.

Compact balanced filter with high common mode suppression using hybrid microstrip and slotline spoof surface plasmon polaritons

“…Recently, spoof surface plasmon polariton (SSPP) structure such as corrugated metal constructed by periodic array can also support surface wave alike the SPPs at terahertz and microwave frequency [2]. And the SPP-like surface wave shows similar propagation characteristics [3,4]. In view of the advantages of local-field enhancement and stronger field confinement of the SSPPs, in recent years, the SSPP structures are widely used for designing microwave filters.…”