A low-cost 77/79-GHz ladder-type forward-wave directional coupler (FWDC) is proposed based on microstrip and substrate integrated waveguide (SIW) for frequency modulated continuous wave (FMCW) radar application in this article. The SIW structures are periodically loaded between two parallel microstrip lines. In the circuit topology of the proposed FWDC, the impedance matching between the even/odd modes is achieved. Meanwhile, an approximate constant phase difference (about 12°) between the even and odd modes is designed within 76-81 GHz. The proposed FWDC is modeled by the Bloch-Floquet theorem, and the design procedure is given. Besides, the full-microstrip ladder-type FWDC is discussed and its theoretical analysis demonstrates that such an FWDC with a weak coupling cannot be obtained using the full-microstrip topology. Finally, the proposed FWDC is fabricated by the PCB technology. To measure its performances, W-band fin-line microstrip-waveguide transition and waveguide package are utilized, and three waveguide packaging cases are measured and discussed. Good agreement between the simulations and measurements is achieved.

中文翻译：

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适用于 FMCW 雷达应用的基于微带线和 SIW 的 77/79GHz 前向波定向耦合器组件


本文提出了一种基于微带和基板集成波导 (SIW) 的低成本 77/79 GHz 梯型前向波定向耦合器 (FWDC)，用于调频连续波 (FMCW) 雷达应用。 SIW 结构周期性地加载在两条平行微带线之间。在所提出的 FWDC 的电路拓扑中，实现了偶/奇模式之间的阻抗匹配。同时，在76-81GHz范围内设计偶模和奇模之间近似恒定的相位差（约12°）。所提出的 FWDC 通过 Bloch-Floquet 定理进行建模，并给出了设计过程。此外，还讨论了全微带梯型FWDC，其理论分析表明，使用全微带拓扑无法获得这种弱耦合的FWDC。最后，所提出的FWDC是通过PCB技术制造的。为了测量其性能，利用了W波段鳍线微带波导过渡和波导封装，并对三种波导封装情况进行了测量和讨论。模拟和测量之间达到了良好的一致性。