宽带定向耦合器的设计与应用

Design and Application of Wideband Directional Coupler

对耦合线定向耦合器进行理论分析，对于对称型，首先求得多节定向耦合器的耦合度通用表达式，然后利用二项式（最平坦）响应前n-1阶导数为零的条件，计算出各节耦合系数。对于非对称型，利用四分之一波长耦合器与四分之一波长阶梯阻抗滤波器等效，通过切比雪夫多项式及理查德变换综合出阶梯阻抗滤波器的归一化阻抗，此即为耦合器的偶模阻抗，然后计算出各节耦合系数。实例计算比较4-20GHz的两种耦合器：二项式响应耦合器具有最平坦的带内特性；与二项式响应相同节数的切比雪夫响应耦合器具有更大的带宽比。最后用厚度为0．254mm的Rogers5880微带板制作了6-18GHz的两节微带线耦合器，并应用在某组件中。

The paper analyses the coupled-transmission-line directional coupler. For the symmetric, the universal expression of multi-element directional coupler is obtained and then the couple coefficient of every element by the condition that the forward （n-1） steps derivative of Binomial response（the most fiat response） is calculated. For the asymmetric, normalization impedance of step-impedance filter by Chebyshev polynomial and Richard transform are synthesized. This is the same as theeven mode impedance of multi-element asymmetric directional coupler, because the 1/4 wavelength coupler and 1/4 wavelength step-impedance filter are equivalent. Then the couple coefficient of Chebyshev response can be obtained. In thepaper, the two kinds couplers are designed, whose frequency is from 4 GHz to 20 GHz. The frequency response of Binomial response coupler is the most fiat. The bandwidth ratio of Chebyshev response coupler is larger than Binomial response coupler. Finally, two-element micro-strip coupler made with Rogers 5880 micro-strip, 0.254 mm thickness, is applied in module.