A low-loss bandpass filter with a nonresonant node (NRN) based air-filled substrate integrated waveguide (SIW) is proposed in this study. It is based on a second-order inductive diaphragm-coupled filter with an additional NRN to introduce a transmission zero (TZ) in the upper stopband. Measured results show that the filter has a center frequency of 32.27 GHz with the bandwidth of 0.9 GHz. The insertion loss in the passband is 1.2 dB, and the return loss is better than 24 dB. Due to the presence of TZ in the upper sideband, the AFSIW filter has a sharper transition performance and achieves good selectivity.

中文翻译：

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具有非谐振节点结构的新型充气衬底集成波导带通滤波器

本研究提出了一种基于非谐振节点 (NRN) 的充气衬底集成波导 (SIW) 的低损耗带通滤波器。它基于带有附加 NRN 的二阶电感膜片耦合滤波器，以在上阻带中引入传输零 (TZ)。实测结果表明，该滤波器的中心频率为32.27 GHz，带宽为0.9 GHz。通带插入损耗为1.2dB，回波损耗优于24dB。由于上边带中存在 TZ，AFSIW 滤波器具有更锐利的过渡性能并实现了良好的选择性。