微带滤波器级间耦合系数的计算方法

通过在耦合微带谐振器对称面加电壁和磁壁法、用网络的转移矩阵计算插入损耗L(ω)法、以及滤波器谐振时回路的阻抗虚部为零的方法,推导了滤波器级间耦合系数的计算公式。用微波全波仿真软件建立了发卡耦合微带滤波器模型,用上述三种方法分别计算了滤波器在不同间距下的级间耦合系数,给出了计算结果曲线,从计算公式和曲线图分析比较了以上三种方法的关系以及适用情况。结果表明:加电壁磁壁法适用于计算机软件仿真计算,插入损耗法适用于窄带滤波器,阻抗虚部为零法则适用于工程应用。

Calculation of interstage coupling coefficient of microstrip filter

The formula of interstage coupling coefficient of microsrip filter was deduced in this paper. The first method calculated the interstage coupling coefficient by adding the electric wall and magnetic wall in the symmetry plan and calculated their resonant frequency. The second way was accounted the insertion-loss by the transfer matrix of the network, and found three strange points on the locus of insertion-loss. The third way was deduced from the equation that the imaginary part of resistance is zero when it is resonance. The relation of the three methods was analyzed by the results of the full-wave simulation. The results show that adding electric wall and magnetic wall is applicable for the computer simulation, the insertion-loss technique is applicable for the interstage coupling coefficient of narrow hand filter, and the resistance zero imaginary part technique is more widly used in engineering.