Compact filters with adjustable multi-band rejections based on spoof surface plasmon polaritons

Abstract

Owing to the gorgeous features of planar design, strong field confinement, and compatibility with traditional microwave devices, spoof surface plasmon polaritons (SSPPs) have been developing at a rapid pace in modern microwave technologies. Band-rejection filters, especially multi-band rejection filters, are a significant ecosystem of SSPPs to be designed. Here, we firstly propose compact multi-band rejection filters, including dual-band and triple-band, through the addition of interdigital capacitance loaded loop resonators (IDCLLRs) into the grooves of the corrugated SSPP transmission line (TL). Compared to traditional metamaterial particles like split ring resonators (SRRs) and complementary SRRs (CSRRs) with the same size, IDCLLRs possess excellent merits of lower resonant frequency, larger dynamic range, and more tunable parameters, which enable the proposed device to be more compact and have more freedom for adjusting bandwidths. Both the simulated and experimental results demonstrate the high performance of two multi-band rejection filters, which can provide wide stop-bandwidth (a maximum relative bandwidth of up to 9.5% for the dual-band filter and 8.8% for the triple-band filter) and high isolation (the isolation of both filters can be less than -30 dB and the maximum isolation of up to -60 dB for the dual-band filter and -58 dB for the triple-band filter). The compact SSPP filters with adjustable multi-band rejections may greatly advance progress towards SSPP-based devices and integrated systems.