Upper-bounds to the near- and far-end conversion loss in unbalanced differential lines

In this work, piece-wise linear upper bounds to the near- and far-end conversion loss in unbalanced differential lines are cast as function of geometrical parameters of the line cross-section. To this end, the measurement setup exploiting a four-port Network Analyzer is modeled in the modal domain, and the mixed-mode scattering parameters at the line terminations are derived resorting to the assumption of weak imbalance of the line cross-section. The obtained upper bounds allow for quick estimate of the amount of differential mode into common mode conversion occurring in unbalanced differential lines, and put in evidence the relevant parameters at the basis of mode conversion.