Silicon Micromachined Waveguide Quadrature-Hybrid Coupler at Terahertz Frequency Band

摘要

A waveguide quadrature-hybrid coupler operating from 350 to 410 GHz is designed and fabricated using the deep reactive ion etching (DRIE) silicon micromachining technique. The four-port branch-line coupling configuration with five branches is used as the basic structure of the coupler. The size of the coupler is about 6.3 mm x 6.3 mm x 1 mm, which is much smaller than the flange used in the vector network analyzer (VNA). Because it is difficult to measure all the characteristics of a four-port coupler with a small size using the two-port VNA with big-size flanges, four testing topologies with different bended input/output waveguide ports are designed for measurements. The terahertz (THz) wedged-type absorbing material is adopted as the replacement of the conventional waveguide matching load because the size of the conventional waveguide matching load is too large to use. Measured results of the proposed coupler are in good agreement with simulated results, indicating that the average insertion loss is 0.9 dB and the isolation is better than 20 dB. Effects of the DRIE process on the coupler's performance are discussed in detail.