## 1 Introduction  
As critical components in wireless communication systems, filters face technical challenges in 5G applications, including high-frequency operations, broadband requirements, and multi-sub-band (such as n257 (26.5 GHz-29.5 GHz), n258 (24.25 GHz-27.5 GHz), and n261 (27.5 GHz-28.35 GHz) frequency bands) coordination [1]. To address these constraints, novel design frameworks are being developed to enhance spectral efficiency, improve multi-sub-band interference rejection, and facilitate device integration. SIWs and SSPPs demonstrate exceptional electromagnetic field manipulation capabilities, offering promising pathways for developing advanced filtering solutions. The advantages of SIWs include low loss, effective out-of-band suppression, fabrication simplicity, and compatibility with planar microwave circuits [2]. In microwave integrated system design, SIW-based filters are widely employed in components and systems such as power dividers [3,4], couplers [5], amplifiers [6,7], phase shifters [8,9], oscillators [10], and antennas [11,12]. In summary, the inherent high-pass characteristics of SIW structures make them particularly suitable for microwave frequency filtering applications. As a periodic artificial structure, SSPPs emulate surface plasmon polaritons (SPPs) by etching a periodic structure array on the top conducting layer, enabling low-pass characteristics at sub-optical frequencies [13]. Benefiting from strong field confinement and low crosstalk, SSPPs find applications in microwave/RF systems, including antennas [14,15], couplers [16], sensors [17], and power dividers [18]. Particularly, their inherent high-frequency suppression capability facilitates low-pass implementation in bandpass filter designs through upper cutoff frequency control, making SSPPs promising for advanced filtering applications [19]. The exploitation of the high-frequency microwave spectrum enables substantial bandwidth enhancement. By merging the high-pass filter characteristics of SIWs and the low-pass filter characteristics of SSPPs, the resultant SIW-SSPP wide bandpass characteristics must be dealt with to obtain the expected filtering responses of the filters, establishing a new paradigm for high-efficiency microwave filters. To address multi-sub-bands' filtering requirements in broadband applications, many innovative design methodologies have been proposed and demonstrated using the new artificial structure of narrow bandpass with new combinations of elements such as hybrid resonators [20], stepped-impedance resonators [21], and meta-surface loading techniques, like CSRR. The integration of these approaches with SIW and SSPP technologies has been particularly effective for developing high-frequency broadband multi-bandpass filters, including SIW-based designs [22,23], SSPP-configured filters [24,25], and up-and-coming hybrid SIW-SSPP filters [26,27]. Furthermore, metastructure loading techniques, like CSRR, have been successfully employed to implement multiband operations through electromagnetic coupling control [28, 29, 30]. However, current research on SIW-SSPP multi-band filters remains insufficient, with unresolved technical challenges in achieving low insertion loss while maintaining a miniaturized multiband design [31], such as the complex dispersion phenomenon caused by the modes of SIWs and SSPPs within the wide bandpass. In this article, these complex problems are studied, and the corresponding designs and fabrication methods are developed. A novel SSPP structural unit is introduced to ensure a wide band, and the unit achieves the flexible tuning of cutoff frequencies in bandpass filters through integration with conventional SIW technology. The incorporation of Archimedean spiral configurations significantly enhances stopband rejection while maintaining excellent bandpass filter characteristics. To enable frequency selectivity for wireless communication systems, CSRR-loaded structures are implemented to realize multi-bandpass filters with low return loss, low insertion loss, and compact dimensions.