A monolithic low-cost 3-dB directional coupler based on silicon image guide (SIG) technology at millimeter-wave band

A low-cost and low-loss directional coupler implemented in the Silicon Image Guide (SIG) platform for high-end millimeter-wave and THz integrated systems is proposed. A novel idea of supporting beams is used for facilitating the high precision fabrication of such a monolithic structure. A 3-dB coupler is designed and simulated for working at the centre frequency of 150 GHz. The simulated average phase unbalance of the coupler within the range of 145–155 GHz is less than 1 degree. The proposed coupler is fabricated using a fast and mask-free laser micro-machining process. The measured insertion loss and 1-dB bandwidth of the coupler are <0.4 dB and 8 GHz, respectively.