Mode Conversion Path Vias in Differential Via Pairs in ANSYS HFSS

This signal integrity video explores unwanted mode conversion, from differential signal to common signal, due to unbalanced ground return current via paths in a multilayer differential pair simulated in HFSS 3D Layout. Starting at 1:35, the video shows how to move a differential pair, including the port, from one lower layer up to another layer in one operation. At 2:46 the video describes the engineering relation between asymmetry and mode conversion in terms of mixed mode S-parameters. The HFSS 3D Layout unbalanced (asymmetric) design, with a ground return path via missing, is created after 4:58. The change to an HFSS fully arbitrary 3D (FA3D) design starts at 7:19, with the symmetrical S-parameters shown at 8:34. The asymmetrical (unbalanced) FA3D design consideration starts at 9:14