Low Transmission Loss Solder Ball Waveguide and Transmission Line to Waveguide Transition Using Loop Antenna Structure in PCB

This paper proposes Solder Ball Waveguide (SBW) and its transition (transmission line to waveguide) for low-loss signal transmission that can be applied to 77 GHz automotive radar application. The SBW was implemented using two PCB substrate ground planes, with solder balls placed in the space between them, to form a waveguide. The structure of the transition was designed in the form of a loop antenna in cavity using vias and stripline within the substrate. For smooth impedance matching between the cavity and the waveguide, and stepped ground structure was implemented using conductive vias. To evaluate the performance of the proposed SBW, HFSS simulation was conducted at 77 GHz band. The proposed SBW including the transition showed the extremely low insertion loss per unit length at copper roughness of 0 um and 1 um, with values of 0.01 dB/mm and 0.018 dB/mm, respectively.