设计了一种结构紧凑、工作频带较宽、耦合平稳、高方向性的“十字形”多孔耦合的太赫兹波导定向耦合器。基于多孔耦合原理, 利用HFSS软件对太赫兹波导定向耦合器进行了模型仿真和结构优化。仿真结果表明: 在325~475 GHz带宽范围内, 该多孔耦合太赫兹波导定向耦合器耦合度达到7.5±0.8 dB, 隔离度达到30 dB, 即方向性优于20 dB, 各端口回波损耗小于-20 dB。通过对该波导定向耦合器进行高温高压模拟仿真, 确定了使用负性光刻胶SU-8作为结构材料的可行性, 提出应用MEMS工艺在硅衬底上进行加工, 将牺牲层工艺应用到波导腔结构的制作中。利用光刻在直通波导和耦合波导公共宽壁上形成的"十字形"等间距排列耦合孔结构, 可以实现较宽的带宽和良好的耦合平坦度。该方法提高了耦合孔尺寸和位置的精度, 减小了反射损耗, 为太赫兹波导结构的加工提供了新思路。

A "cross-shaped" multi-hole terahertz waveguide directional coupler was designed. This compact structure has a large frequency band, stable coupling value and high directivity. The terahertz waveguide directional coupler structure was simulated and optimized with professional electromagnetic simulation software high-frequency structure simulator(HFSS) based on multi-hole coupling principle. The results show that the coupling degree of the terahertz waveguide directional coupler is 7.5±0.8 dB, the isolation is 30 dB, that is, the directivity is higher than 20 dB, and the return loss of each port is less than -20 dB in the range of 325 GHz to 475 GHz. Through high temperature and pressure simulation of the waveguide directional coupler, negative photoresist SU-8 is considered as a suitable material for structure fabrication. The directional coupler is fabricated by micro-electro-mechanical system(MEMS) technology, at the same time, sacrifice layer technology is applied to form the waveguide cavity structure. The uniformly-spaced coupling holes on the common wall of straight waveguide and coupling waveguide can be achieved by photolithography, therefore a wider bandwidth and a good coupling flatness of the directional coupler were obtained. This method improves the accuracy of the size and position of the coupling holes, reduces the reflection loss, and thus provides a new idea for the processing of terahertz waveguide structures.