直线型端口类盒型拓扑结构微带滤波器设计

针对微波带通滤波器小型化、高性能的应用需求，研究了基于双模方形环谐振器的直线型端口的两阶带通滤波器响应特性，进一步提出使用单模谐振器和双模谐振器相结合设计直线型端口的高阶微带带通滤波器。提出的直线型端口双模方形环微带滤波器具有类盒型拓扑结构，能够实现灵活的频率响应特性，而且传输零点的位置可调，能够满足不同的应用需求。由于存在寄生的对角交叉耦合路径，提出的类盒型拓扑结构微带滤波器可以实现一个额外的传输零点。为了验证结构和设计方法的可行性，设计了两款中心频率为5.2 GHz的三阶和五阶带通滤波器，最后进行加工和测试。耦合矩阵响应、仿真和测试结果一致性较好，表明了该结构实现高性能滤波器的可行性。

In-line ports microstrip bandpass filters in box-like coupling schemes

According to the miniaturization and high performance, the characteristic of a second-order bandpass filter (BPF) with in-line ports based on dual-mode square-shaped resonator is researched, and higher-order BPFs with in-line ports using single-mode resonators and dual-mode resonators are proposed. The proposed filters can be modeled by the box-like coupling scheme, which can realize flexible frequency responses. Moreover, the positions of transmission zeros (TZs) can be easily adjusted to satisfy different applications. An additional TZ can be achieved by the proposed filter in box-like topology for the parasitic coupling in the diagonal cross-coupling path. To verify the proposed structure and design method, third-order and fifth-order filters with center frequency of 5.2 GHz are designed, fabricated and measured. The responses of coupling matrix, simulated and measured results are in good agreement, which demonstrates the feasibility of the proposed filters with high performance.