High frequency (HF) integrated circuits (ICs) generate millimeter-wave (MMW) signals such as those used for automotive radar (from 76 GHz to 81 GHz). Planar transmission lines on a substrate, such as a printed circuit board (PCB), carry the MMW signal from one location on the PCB to another location. For example, a planar transmission line may carry a MMW signal from one MMW IC to another IC on the PCB, from a MMW IC to a radiating element or antenna, or from a MMW IC to a waveguide transition built into the PCB (a PCB waveguide transition). The PCB waveguide transition couples the MMW signals from the planar transmission line on the PCB into an external waveguide. Alternatively, the PCB waveguide transition can couple an incoming MMW signal from an external waveguide onto the planar transmission line on the PCB.
PCBs are formed of dielectric materials and layers of conductive metal separated by dielectric layers. A PCB waveguide transition is formed by etching a PCB waveguide through the PCB, coating the sidewalls of the PCB waveguide with a conductive material, attaching a waveguide termination to one end of the PCB waveguide, and attaching a probe to the end of the planar transmission line on the PCB. The probe is positioned in the PCB waveguide to couple the MMW signal from a planar transmission line on the PCB to the external waveguide. PCB waveguide transitions require complex manufacturing including: substrate etching; sidewall plating; and manual probe positioning and attachment. These processes are not compatible with high volume and low cost PCB manufacturing.
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