为了得到高选择性、小尺寸、低损耗和低成本的射频带通滤波器,提出了一种具有4个传输零点的源负载耦合滤波器的设计方法.该滤波器采用二分之一波长T形多模谐振器,以减小滤波器尺寸和方便带宽设计.同时,根据信号的多路径传输产生零点原理,在滤波器的输入和输出端口之间加入可控耦合元件,为信号的传输提供多条路径,使得该滤波器可产生4个独立于带宽和中心频率的可控零点.文中最后设计和制作了一个带内最小测量插损为1.4 dB、相对带宽为10%、具有4个传输零点的小型微带滤波器,并对其进行了测试,测试结果与仿真结果吻合良好,说明这种设计方法是有效的.

In order to obtain bandpass filters with high selectivity,small size,low loss and low cost,a compact source-load coupling filter with four transmission zero points is presented,which uses a half-wavelength multi-mode T-shaped resonator to reduce the filter size and to facilitate the bandwidth design.Then,based on the generation mechanism of transmission zero points,a controllable coupled element is inserted in the region between the input and the output ports to generate multiple paths for signal transmission.Thus,four controllable zero points independent of bandwidth and central efficiency are generated.Moreover,a compact microstrip bandpass filter with four transmission zero points is designed and fabricated,with the insertion loss and the bandwidth respectively reaching 1.4 dB and 10%.Finally,the filter is tested and the results accord well with the simulated ones.It is thus concluded that the proposed design method is feasible.