基于MPCL结构的小型化微带带通滤波器设计

Design of miniaturized microstrip bandpass filter based on modified parallel coupled-line structure

提出了一种改进型平行耦合线(Modified Parallel Coupled-line)结构,利用等效电路模型和奇偶模原理对该结构进行详细分析,并基于MPCL结构设计了两款高选择性微带带通滤波器。第一款滤波器利用半波长开路谐振器的基模和高阶模式实现了三通带响应特性,并在通带附近产生7个传输零点,显著提高了滤波器的带外选择特性。第二款滤波器则利用3阶谐振器的基模进行平行交叉耦合,分别于上下阻带各产生1个传输零点,从而获得更高的选择性和阻带抑制度。实验结果与仿真结果吻合良好,验证了设计理论的可行性。

In this paper,a modified parallel coupled-line(MPCL)structure is presented and analyzed by the equivalent circuit model and even-odd mode methods.Two high selectivity microstrip bandpass filters(BPFs)have been designed based on the MPCL structure.The first tri-band BPF is realized by using the fundamental mode and high-order modes of the half-wavelength open-circuit resonator.Seven transmission zeros(TZs)near the passbands are generated,which improved the out-of-band selectivity significantly for the filter.The second designed filter is implemented by using the fundamental modes of the three resonators for parallel cross-coupling,and two TZs are located at the upper-stopband and lower-stopband respectively,resulting in higher selectivity and stopband rejection.The experimental results are well agreed with the simulated ones,which verified the design theory.