Empty Substrate Integrated Waveguide Coupler and Transition Structure to WR-3 Waveguide

This paper proposes a sub-THz Riblet coupler based on the empty substrate integrated waveguide (ESIW) and a transition structure between ESIW and a WR-3 rectangular waveguide. The ESIW is fabricated through laser engraving and electroplating processes. The transition is achieved simply by a rectangular cavity and can be modeled by two coupled notch filters. The measured insertion loss of a single transition is 1.25 dB from 250 to 313 GHz. The amplitude imbalance of the coupler is about 2 dB and the phase difference is between 87 deg and 101 deg from 250 to 290 GHz.