In this letter, a new technique to design wideband bandpass filters (BPFs) is proposed. It is based on the classical filter topology formed by shunt short-circuited stubs connected by transmission lines, where the $\lambda /4$ connecting lines are replaced by $\lambda /2$ lines. In this way, the connecting lines have a double functionality: to control the coupling between resonators and to add additional poles, increasing the filter order up to $2N-1$ , where $N$ is the number of short-circuited stubs. In addition, their function as inverters is, theoretically, for all spectrum, avoiding the limitation of the $\lambda /4$ lines working as inverters or the coupled-line coupling mechanisms of classical configurations, which are of narrowband nature. Design equations are provided with up to $N$ degrees of freedom, which allows for a proper selection of impedance values for the filter design. As a verification, a fifth-order BPF of fractional bandwidth 50% centered at 2.5 GHz and with a Chebyshev response is implemented, fullfiling the expections and validating, in this way, the proposed approach.

中文翻译：

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基于短路短截线的宽带带通滤波器的系统设计 λ/2 传输线

在这封信中，提出了一种设计宽带带通滤波器 (BPF) 的新技术。它基于由传输线连接的并联短路短截线形成的经典滤波器拓扑结构，其中 $\λ/4$ 连接线被替换为 $\λ/2$ 线。通过这种方式，连接线具有双重功能：控制谐振器之间的耦合和添加额外的极点，将滤波器阶数增加到 $2N-1$ ， 在哪里 $N$ 是短路短截线的数量。此外，它们作为逆变器的功能理论上适用于所有频谱，避免了限制 $\λ/4$ 作为逆变器工作的线路或经典配置的耦合线耦合机制，具有窄带性质。设计方程式最多提供 $N$ 自由度，允许为滤波器设计正确选择阻抗值。作为验证，实施了以 2.5 GHz 为中心并具有切比雪夫响应的分数带宽 50% 的五阶 BPF，满足了预期并以这种方式验证了所提出的方法。