A Silicon-chip-based Waveguide Directional Coupler for Terahertz Applications

We propose a waveguide directional coupler design with weak coupling using silicon-based suspended coupling microstrip probes and the split-block type of construction common in integrated millimeter wave components. WR4.0 coupler prototypes with standard UG-387 flanges were fabricated and measured. The simulation and measurement results show that this design achieves a coupling of around −18 dB, with a typical $\pm$ 2-dB variation across the band from 210 to 270 GHz, while the isolation is better than 30 dB. Tolerance studies confirm that this design could be scaled up to terahertz frequency with modern computer numerical control (CNC) machining and silicon chip fabrication technology.