基于耦合模理论的强阻带抑制带通滤波器设计

Design of microstrip bandpass filter with enhanced stopband rejection based on coupled-mode theory

为了实现射频收发系统中相邻通道间的信号收发隔离,运用时域耦合模理论设计具有较强的阻带抑制的微带带通滤波器.该滤波器由1个奇偶双模微带谐振单元和1个偶模微带谐振单元构成.3个谐振模式相互耦合,在通带低频侧形成1个传输零点,在高频侧形成2个传输零点.可以实现较高的频率选择性和带内平坦度,在通带的高频侧实现较强的阻带抑制.以C波段的三模耦合微带带通滤波器为例,通过时域耦合模理论对滤波器的滤波特性进行准确计算,得到各个谐振模式之间的耦合关系.通过特征模电磁仿真完成满足该耦合关系的滤波器结构设计.对该滤波器进行实物加工与测试.测试结果与理论计算结果吻合良好.结果表明,该滤波器可以有效地应用于射频收发系统收发通道间的隔离.时域耦合模理论可以实现多模耦合滤波器的高效设计,快速得到系统所需的滤波特性.

A microstrip bandpass filter with enhanced stopband rejection was designed based on the temporal coupled-mode theory in order to realize the signal isolation between transmitter and receiver（TR）channels in radio frequency（RF）transceiver systems.The filter consisted of two microstrip resonators,one supports an odd and an even mode,and the other supported an even mode.These three resonant modes coupled with each other,producing a transmission zero at low frequency below the passband,and two transmission zeros at high frequency above the passband.High frequency selection,passband flatness,and good stopband rejection above the passband were achieved.A C-band triple-mode microstrip bandpass filter was taken as an example.The characteristics of the filter with enhanced high-frequency stopband rejection can be accurately calculated by using temporal coupled-mode theory,and the coupling relationship among the three resonant modes can be obtained.The filter structure which satisfies the coupling relationship can be finished by using electromagnetic eigenmode simulation.The proposed filter was fabricated and tested.The test results matched the theoretical prediction well.Results show that the filter can be effectively applied in the isolation between TR channels in RF transceiver systems.The temporal coupled-mode theory can highly improve the design efficiency of filters with multi-mode coupling,whichcan achieve the required filter response of the system with high speed.