This letter presents the design of mixed quarter- and one-eighth modes substrate integrated waveguide (SIW) bandpass filter (BPF). The transmission zeros (TZs) of the proposed SIW BPF can provide wide stopband response and high selectivity characteristics by using different mode SIW cavities. For validation, two- and three-stage SIW BPFs with Chebyshev response were designed at a center frequency ( $f_{0}$ ) of 8 GHz. The measured results are consistent with the simulations. For two-stage BPF, the insertion loss smaller than 0.9 dB is measured within the passband of 0.65 GHz (7.75–8.4 GHz). The return loss higher than 19.7 dB is measured within the same passband. The spurious is produced at around 18 GHz ( $ < 2.25f_{0}$ ). The stopbands are attenuated more than 17.31 dB from the dc to 5.68 GHz ( $0.71f_{0}$ ) and from 9.28 GHz ( $1.16f_{0}$ ) to 16.67 GHz ( $2.08f_{0}$ ). The TZs are produced at 10 GHz and around 18 GHz due to a small cross-coupling between source/load and the interaction of the higher resonant modes of cavities, respectively. For three-stage BPF, the $\vert S_{21}\vert $ and $\vert S_{11}\vert $ smaller than −1.3 dB and −18 dB are measured within the passband of 7.57–8.45 GHz fractional bandwidth (FBW = 11%), respectively. The TZs are produced at 1.102, 1.9, and $2.39f_{0}$ and provide higher selectivity and attenuation compared to two-stage BPF.

中文翻译：

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使用混合四分之一模腔和八分之一模腔的紧凑型宽阻带基板集成波导带通滤波器

这封信介绍了混合四分之一和八分之一模式的衬底集成波导 (SIW) 带通滤波器 (BPF) 的设计。通过使用不同模式的 SIW 腔，所提出的 SIW BPF 的传输零点 (TZ) 可以提供宽阻带响应和高选择性特性。为了验证，在中心频率下设计了具有切比雪夫响应的两级和三级 SIW BPF（ $f_{0}$ ) 的 8 GHz。测量结果与模拟一致。对于两级 BPF，在 0.65 GHz (7.75–8.4 GHz) 通带内测得的插入损耗小于 0.9 dB。高于 19.7 dB 的回波损耗是在同一通带内测得的。杂散产生于 18 GHz 左右（ $ < 2.25f_{0}$ ）。阻带从直流到 5.68 GHz 衰减超过 17.31 dB（ $0.71f_{0}$ ) 和从 9.28 GHz ( $1.16f_{0}$ ) 至 16.67 GHz ( $2.08f_{0}$ ）。TZ 分别在 10 GHz 和 18 GHz 左右产生，原因是源/负载之间的小交叉耦合和腔的更高谐振模式的相互作用。对于三级 BPF， $\vert S_{21}\vert $ 和 $\vert S_{11}\vert $ 分别在 7.57–8.45 GHz 分数带宽 (FBW = 11%) 的通带内测量到小于 −1.3 dB 和 −18 dB 的信号。TZ 在 1.102、1.9 和 $2.39f_{0}$ 并提供比两级 BPF 更高的选择性和衰减。