Design of multi-hole terahertz waveguide directional couplers

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 7.50.8 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.