Research on A Miniaturized Wide Stopband Folded Substrate Integrated Waveguide Filter

KE Rongjie; WANG Hongbin; CHENG Yujian

doi:10.11999/JEIT250869

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KE Rongjie, WANG Hongbin, CHENG Yujian. Research on A Miniaturized Wide Stopband Folded Substrate Integrated Waveguide Filter[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250869

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KE Rongjie, WANG Hongbin, CHENG Yujian. Research on A Miniaturized Wide Stopband Folded Substrate Integrated Waveguide Filter[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT250869

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Research on A Miniaturized Wide Stopband Folded Substrate Integrated Waveguide Filter

doi: 10.11999/JEIT250869 cstr: 32379.14.JEIT250869

University of Electronic Science and Technology of China, Chengdu 611731, China

Accepted Date: 2025-12-29
Rev Recd Date: 2025-12-29

Available Online: 2026-01-05

Abstract

Abstract

To meet the requirements of 5G/6G communication systems for miniaturization, high integration, and wide stopband, a fourth-order bandpass filter based on the eighth-mode folded substrate integrated waveguide (FSIW) is proposed in this paper using high-temperature co-fired ceramic (HTCC) technology. The miniaturization advantages of folded SIW are combined with the three-dimensional integration characteristics of HTCC in this filter. Size reduction is achieved through the eighth-mode FSIW cavity structure, with a size of 0.29λg × 0.29λg, where λg is the waveguide wavelength corresponding to its center operating frequency (f₀). High-order mode coupling is suppressed using metal vias, transmission zeros are introduced by loading a bent microstrip line, and the high-frequency response is optimized through the addition of an L-shaped stub. As a result, three controllable transmission zeros are formed in the upper stopband, with a wide stopband characteristic of 20 dB@3.73f₀ achieved. The measured results show that the filter has a center frequency of 6.4 GHz. Although it exhibits a certain amount of frequency deviation and insertion loss, compared with existing research, it demonstrates distinct advantages in terms of miniaturization, stopband width, and the number of transmission zeros, holding promising potential for applications in high-density integrated communication systems. Objective With the rapid advancement of 5G/6G communication systems, there is an urgent demand for radio frequency (RF) microwave devices that combine miniaturization, high integration, and wide stopband performance. As a core component of RF transceiver front-ends, bandpass filters play a critical role in transmitting useful signals and suppressing interference. Traditional substrate integrated waveguide (SIW) filters suffer from limitations such as large size, restricted stopband extension, and insufficient controllability of transmission zeros, which hinder their application in high-density integrated communication systems. To address these challenges, this paper proposes a miniaturized wide stopband fourth-order bandpass filter based on eighth-mode folded substrate integrated waveguide (FSIW) and high-temperature co-fired ceramic (HTCC) technology, which aims to achieve a balance between compact size and broad stopband. Methods The proposed filter integrates the miniaturization advantage of folded SIW with the three-dimensional integration capability of HTCC technology. First, an eighth-mode FSIW cavity structure is designed by modifying the quarter-mode FSIW cavity. The square patch is replaced with a triangular patch (i.e., eighth-mode cavity I), and slots are further etched in the triangular patch (i.e., eighth-mode cavity Ⅱ). Second, a fourth-order bandpass filter is constructed by symmetrically designing two triangular metal patches for each cavity type and stacking them vertically, with a common metal layer (fifth layer) featuring coupling windows to enable coupling between upper and lower cavities. To optimize performance, three key techniques are employed: metal vias to suppress high-order mode coupling, bent microstrip lines to introduce transmission zeros, and an L-shaped stub to improve high-frequency response. Finally, parameter scanning analysis is conducted on critical dimensions (d₂, s₄, s₆) to verify the controllability of transmission zeros, and the filter is fabricated using HTCC technology, employing the Al₂O₃ substrate with relative permittivity 9.8 and loss tangent 0.0002. Results and Discussions The measured results indicate that the proposed filter achieves a center frequency of 6.4 GHz. Although processing and assembly errors lead to slight frequency deviation and increased insertion loss, the filter exhibits outstanding performance compared to existing designs (Table 2). In terms of miniaturization, the filter achieves a size of 0.29λg×0.29λg, which is significantly smaller than most reported SIW filters. Regarding stopband performance, the upper stopband extends to 20dB@3.73f₀, which is superior to that of filters with comparable sizes. Three controllable transmission zeros are generated in the upper stopband, with parameter scanning verifying their flexibility (Fig.13). Conclusions A miniaturized wide stopband fourth-order bandpass filter based on eighth-mode FSIW is successfully designed in this paper. The key achievements are summarized as follows. For one thing, the eighth-mode FSIW cavity structure combined with HTCC technology delivers a compact size of 0.29λg×0.29λg, meeting the high integration demands of 5G/6G systems. For another, the integration of metal vias, bent microstrip lines, and L-shaped stubs realizes a wide stopband of 20 dB@3.73f₀ along with three controllable transmission zeros, which enhances interference suppression capability. Additionally, parameter adjustment allows for flexible tuning of transmission zero positions without influencing the passband, improving design flexibility for different interference conditions. Overall, these innovations collectively overcome the challenges of miniaturization, stopband performance, and design flexibility in SIW filters, offering a practical and competitive solution for the RF front-ends of next-generation high-density integrated communication systems.
- Bandpass filter,
- Folded substrate integrated waveguide,
- Miniaturization,
- Wide stopband,
- HTCC

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References(19)

References

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