A ultra low-loss silica-based transformer between microstrip line and post-wall waveguide for millimeter-wave antenna-in-package applications

We fabricated a post-wall waveguide (PWW) into silica substrate having thickness of 520 μm and integrated a transformer between microstrip transmission line (MSL) and the PWW. The estimated loss of the transformer associated with the mode conversion and the measured loss of the PWW is 0.06 dB and 0.017 dB/mm at 60 GHz, respectively. This work would be a first attempt to apply silica substrate for microwave waveguide, to our knowledge.