A 650 GHz broadband 3dB coupler using a bridged PPDW

In this paper, a 650GHz broadband 3dB directional coupler with very flat coupling based on bridged parallel plate dielectric waveguide (PPDW) is presented. In the uniform coupling section, a bridge structure between the two PPDWs is employed to obtain accurate coupling value and achieve a broadband coupling. And in the transition sections, two quarter-circle bend arms are introduced to achieve strong isolation between the adjacent ports and reduce the power reflection in all ports. It is found that this new type of bridged coupler exhibits excellent performance at terahertz frequencies. Calculated results show that return loss is greater than 18dB, isolation is better than 27dB, and the average coupler loss is 1.3dB, over a percentage bandwidth of 6.2% at 650GHz. Compared to the conventional PPDW coupler, the bridged PPDW coupler shows significantly greater bandwidth (about 2.3 times), compact and mechanically stable with a much shorter uniform coupling length (reduced about 56%), which may have potential applications for terahertz integrated circuits and systems.