In this study, a series of rat-race couplers with bandpass filtering responses and impedance transforming characteristics are presented based on novel coupled-line structures. Firstly, a novel filtering rat-race coupler core circuit is proposed by introducing coupled-line structures into conventional rat-race coupler. Then, a series of rat-race couplers with enhanced filtering responses and stopband rejections are constructed by employing various types of impedance transformers. The even- and odd-mode methods are adopted to explain the operating mechanisms. Finally, a filtering rat-race coupler prototype with a fractional bandwidth of 35.2% is designed and measured. The measured results show high passband selectivity, good out-of-band rejection and isolation performances, which is attractive for practical application.

中文翻译：

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基于端接耦合线结构对具有阻抗变换特性的鼠类耦合器进行滤波

在这项研究中，基于新颖的耦合线结构，提出了一系列具有带通滤波响应和阻抗变换特性的鼠类耦合器。首先，通过将耦合线结构引入常规的大鼠种族耦合器中，提出了一种新颖的滤波大鼠种族耦合器核心电路。然后，通过使用各种类型的阻抗变压器来构建一系列具有增强的滤波响应和阻带抑制性能的鼠类耦合器。采用偶数和奇数模式来解释操作机制。最后，设计并测量了带宽为35.2％的滤波鼠类耦合器原型。测量结果显示出高通带选择性，良好的带外抑制和隔离性能，对于实际应用具有吸引力。