Characterization of PCB dielectric properties using two striplines on the same board

Signal integrity (SI) and power integrity (PI) modelling and design require accurate knowledge of dielectric properties of printed circuit board (PCB) laminate dielectrics. Dielectric properties of a laminate dielectric can be obtained from a set of the measured S-parameters on a PCB stripline with a specially designed through-reflect-line (TRL) calibration pattern. In this work, it is proposed to extract dielectric properties from the measurements of S-parameters on the two 50-Ohm stripline structures of the same length, but different widths of the trace, designed on the same layer of a PCB. The dielectric properties on these two lines should be identical. However, an application of the simplest “root-omega” technique to extract dielectric properties of the substrate would lead to the ambiguity in the extracted data. This is because the conductor surface roughness affects the measured S-parameters and is lumped in the extracted dielectric data. This problem of ambiguity in the dielectric properties extraction can be overcome using the approach analogous to the recently proposed method to separate dielectric and conductor losses on PCB lines with different widths and roughness profiles [1].