针对传统3 dB 双频分支线耦合器频率比范围窄的问题，提出了一种加载阶梯阻抗枝节线的新型双频分支线耦合器的设计方法．引入阶梯阻抗枝节线后增加了设计自由度，减小了物理实现阻抗范围的限制，从而能设计出宽频率比( 1. 7 ～ 6. 3) 的3 dB 双频分支线耦合器．为验证设计方法的正确性，仿真并加工了一个工作在2. 4 和5. 8 GHz 的WLAN 频率的3 dB 微带分支线耦合器．与传统的Ⅱ型双频分支线耦合器相比，该耦合器的枝节尺寸减小了25. 1%．仿真结果与测试结果吻合较好，说明文中方法是可行的．

As the conventional 3dB dual-band branch-line coupler is of narrow operation frequency ratio,the method to design a novel dual-band branch-line coupler loaded with stepped impedance stub lines is presented. The adoption of stepped impedance stub lines increases the design degree of freedom and reduces the restriction from the physical realization of impedance range. Thus,a 3 dB dual-band branch-line coupler with wide-range frequency ratio ( 1. 7 ～ 6. 3) can be obtained. Moreover,a 3 dB microstrip branch-line coupler operating at 2. 4 /5. 8 GHz WLAN bands is simulated and fabricated to verify the proposed design method. The results show that,as compared with the conventional Ⅱ-shaped dual-band branch-line coupler,the novel coupler achieves a stub-size reduction up to 25. 1%. The simulated results accord well with the measured ones,which means that the proposed design method is feasible.