新型高选择性双模宽带带通滤波器设计

首先利用阶梯阻抗谐振器和交叉耦合馈线结构设计了一种带宽达73．2％新型双模带通滤波器。该谐振器在通带内产生两个可调模式，馈线结构在阻带对称产生两个传输零点。接着在馈线上加载短路线，使原有的两个传输零点向截止频率靠近，并在上阻带新增一个零点，从而在保持原滤波器通带性能的同时提高了频率选择性和上阻带特性。通过对比两个滤波器S参数进一步验证改进效果。最后制作测试了该短路线加栽的滤波器，仿真和实测结果吻合良好。

Novel High Selectivity Dual-mode Broadband BPF Design

In this paper, a novel dual-mode broadband bandpass fiher （BPF） with fractional bandwidth 73.2% is proposed using stepped-impedance resonator （SIR） and cross-coupling feed structure at first. The resonator can generate two modes in the desired band which can be easily adjusted to satisfy the bandwidth of the BPF. The feed structure can symmetrically generate two transmission zeros in the stopband. Then one short stub is loaded at the feed structure to move two transmission zeros closer to the cut-off frequencies, thus enhancing the selectivity of the primary filter while maintaining passband performance. Additional transmission zero is created in the upper stopband by the short stub to gain deeper stopband. The S-parameters between the two filters are contrasted to further demonstrate the improvement. Finally, one short stub loaded filter prototype is fabricated and measured, and good agreement between simulated and measured results is achieved.