In the study, a novel implementation of the coupled-line co-directional (CL-COD) coupler is proposed for the first time, and the wideband realizations are also demonstrated. The CL-COD coupler, which is composed of inductor loaded parallel coupled line and a pair of open-circuited stubs, has the advantages of smaller size and inherent harmonics suppression compared with the traditional λ/4 branch line coupler. Design equations of the single-section CL-COD coupler are derived by the even-odd mode decomposition analysis and a prototype is designed for validation. The experimental results indicate that compared with the traditional single-section λ/4 branch line coupler, the designed single-section CL-COD coupler shows a size reduction of 64.1%, a bandwidth enhancement of 13%, and a second harmonic suppression of more than 20 dB. By cascading multi-sections of the CL-COD couplers, wideband CL-COD coupler with harmonics suppression is also realized. A computer-aided program is applied for solving the circuit parameters of the multi-section cascaded CL-COD coupler. Besides, the two- and three-section cascaded 3-dB CL-COD couplers are designed for guidance. Finally, a 3-dB three-section cascaded CL-COD coupler is fabricated and measured. Compared with the traditional three-section cascaded λ/4 branch line coupler, the prototype shows a size reduction of 61.9% with an additional second order harmonic suppression.

在这项研究中，首次提出了耦合线同向 (CL-COD) 耦合器的新实现，并且还演示了宽带实现。CL-COD耦合器由负载电感的并联耦合线和一对开路短截线组成，与传统的λ/4支线耦合器相比，具有体积更小和固有谐波抑制等优点。通过奇偶模态分解分析推导出单节CL-COD耦合器的设计方程，并设计原型进行验证。实验结果表明，与传统的单段λ/4支线耦合器相比，所设计的单段CL-COD耦合器尺寸减小64.1%，带宽提高13%，二次谐波抑制率更高。小于 20 分贝。通过将多段CL-COD耦合器级联，也实现了宽带CL-COD耦合器的谐波抑制。应用计算机辅助程序求解多段级联CL-COD耦合器的电路参数。此外，两段和三段级联的 3-dB CL-COD 耦合器专为引导而设计。最后，制造并测量了一个 3-dB 三段级联 CL-COD 耦合器。与传统的三段级联 λ/4 支线耦合器相比，该原型的尺寸减小了 61.9%，并具有额外的二阶谐波抑制。两段和三段级联 3-dB CL-COD 耦合器专为引导而设计。最后，制造并测量了一个 3-dB 三段级联 CL-COD 耦合器。与传统的三段级联 λ/4 支线耦合器相比，该原型的尺寸减小了 61.9%，并具有额外的二阶谐波抑制功能。两段和三段级联 3-dB CL-COD 耦合器专为引导而设计。最后，制作并测量了一个 3-dB 三段级联 CL-COD 耦合器。与传统的三段级联 λ/4 支线耦合器相比，该原型的尺寸减小了 61.9%，并具有额外的二阶谐波抑制功能。