This article reports a compact microstrip dual-band bandpass filter (DBBPF) using two pairs of λ/4 short-circuited stepped impedance resonators (SSIRs) and a stub-loaded triple-mode resonator (STR). The first and fourth λ/4 SSIRs not only couple with the second and third SSIRs to form the lower passband, but also serve as the feeding structure and provide source-load coupling for the higher passband, formed by the STR. As a result, a compact filter size can be achieved, and two extra transmission zeros are created for the higher passband to enhance the passband selectivity. Meanwhile, both the center frequency and bandwidth of each passband can be controlled independently. Furthermore, the impedance and length ratios of the two pairs of λ/4 SSIRs are dissimilar to achieve wide stopband. A fourth/third order DBBPF prototype centered at 1.575 GHz (GPS) and 3.5 GHz (WiMAX) is ultimately implemented to demonstrate the design concept, and the measurements match the simulations with good consistency.

中文翻译：

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具有独立可控通带的紧凑型四/三阶双带带通滤波器

本文报告了一种紧凑型微带双带带通滤波器 (DBBPF)，它使用两对 λ/4 短路阶梯阻抗谐振器 (SSIR) 和一个短线负载三模谐振器 (STR)。第一个和第四个 λ/4 SSIR 不仅与第二个和第三个 SSIR 耦合以形成较低的通带，而且还用作馈电结构，并为由 STR 形成的较高通带提供源-负载耦合。因此，可以实现紧凑的滤波器尺寸，并为更高的通带创建两个额外的传输零点，以提高通带选择性。同时，每个通带的中心频率和带宽都可以独立控制。此外，两对 λ/4 SSIR 的阻抗和长度比不同，以实现宽阻带。以 1 为中心的四/三阶 DBBPF 原型。