Design and preparation methods of a 0.4 terahertz multilayer hole array directional coupler

•A miniaturized, highly directional, and low-loss T-type terahertz multi-aperture coupled directional coupler is presented.•A process for the preparation of directional couplers for porous coupled waveguides based on UV-LIGA technology is presented.•Samples of directional couplers with good steepness and high aspect ratios were prepared.•The sacrificial layer technique of PDMS was used to improve the timeliness and accuracy of the cavity structure preparation.