A novel three-pole microstrip bandpass filter using mixed capacitor-loaded asymmetric quasi-combline and combline resonators is proposed. The equivalent circuit of the design is demonstrated and analyzed based on odd- and even-mode method in detail. According to the overall equivalent circuit, two transmission zeros can be introduced at both sides of the passband,which improves the selectivity significantly. The measured central frequency in the passband of the fabricated filter is 1.83 GHz,and the relative bandwidth is 9％. The insertion loss is only 1.45 dB with its return loss better than 14 dB. The measured results show good agreement with the simulated ones.%提出了一种基于电容加载4λ 梳状线谐振器和电容加载非对称2λ 准梳状线谐振器的三阶耦合滤波器拓扑结构.利用奇偶模方法,给出并分析了整个滤波器结构的等效电路,由导纳矩阵可以得出传输零点的位置.实际制作了一个中心频率为1.83 GHz的三阶微带带通滤波器,相对带宽为9％,带内中心插损仅为1.45 dB,回波损耗优于14 dB.传输响应在通带两侧分别存在一个传输零点,有利于提高滤波器的选择性.实验结果表明,测试结果与仿真结果基本一致.
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