Analysis and optimization of the recessed probe launch for high frequency measurements of PCB interconnects

Measurements of internal printed circuit board (PCB) structures such as striplines and vias face the problem of launching clean test signals into the device under test (DUT). Traditionally, coaxial connectors or surface probing with high frequency microprobes are used to provide interfaces to test equipment. Both approaches have to be carefully optimized in order to give adequate results for the multi-GHz range. This paper discusses a different access technique, the recessed probe launch (RPL), which was previously used by the authors for measurements up to 40 GHz. Full-wave 3D electromagnetic modeling is applied to analyze the parasitics of the proposed launch technique and to find strategies for its optimization. Comparison to measurement shows that the models are able to predict the major physics of the launch but several details still need to be explored, e.g. accurate modeling of the microprobes, material parameters, and network analyzer calibration.