In this article, we present the first demonstration of distributed and symmetrical all-band quasi-absorptive filters that can be designed to arbitrarily high orders. The proposed quasi-absorptive filter consists of a bandpass section (reflective-type coupled-line filter) and absorptive sections (a matched resistor in series with a shorted quarter-wavelength transmission line). Through a detailed analysis, we show that the absorptive sections not only eliminate out-of-band reflections but also determine the passband bandwidth (BW). As such, the bandpass section mainly determines the out-of-band roll-off and the order of the filter can be arbitrarily increased without affecting the filter BW by cascading more bandpass sections. A set of 2.45-GHz one-, two-, and three-pole quasi-absorptive microstrip bandpass filters are designed and measured. The filters show simultaneous input and output absorption across both the passband and the stopband. Measurement results agree very well with the simulation and validate the proposed design concept.

中文翻译：

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高阶双端口准吸收微带线耦合带通滤波器

在本文中，我们首次展示了可设计为任意高阶的分布式对称全频带准吸收滤波器。所提出的准吸收滤波器由带通部分（反射型耦合线滤波器）和吸收部分（与短的四分之一波长传输线串联的匹配电阻器）组成。通过详细分析，我们表明吸收部分不仅消除了带外反射，而且还决定了通带带宽 (BW)。因此，带通部分主要决定带外滚降，通过级联更多的带通部分，可以在不影响滤波器带宽的情况下任意增加滤波器的阶数。设计并测量了一组 2.45 GHz 单极、二极和三极准吸收微带带通滤波器。滤波器在通带和阻带上同时显示输入和输出吸收。测量结果与模拟非常吻合，并验证了所提出的设计概念。