Low-loss post-wall waveguide and broadband transition to microstrip line realized in 0.6 mm-thick liquid crystal polymer-substrate for millimeter-wave application

We realized a post-wall waveguide (PWW) with transformers connected to microstrip line in liquid crystal polymer substrate as thick as 0.6 mm to reduce transmission loss, for the first time. Matching to 50 Ω impedance is mainly accomplished by designing anti-pads carefully. The measured bandwidth of the transformer for a reflection smaller than −15 dB is more than 15 GHz, which fully covers the unlicensed 60 GHz band. The estimated loss associated with the mode-conversion and the measured loss of the PWW is 0.2 dB and 0.047 dB/mm at around 60 GHz, respectively.