External parasitic inductance in microstrip and stripline geometries of finite size

An external parasitic ground (return) plane inductance, or a mutual inductance associated with fringing magnetic fields in planar transmission line structures, is the culprit of common-mode voltage (ground plane noise) that leads to parasitic radiation of the corresponding unintentional "antennas" in high-speed electronic equipment. Mutual inductance of this sort in microstrip and stripline structures is studied here using an analytical quasi-magnetostatic approach and FDTD modeling. Closed-form expressions for mutual inductance in symmetrical and asymmetrical microstrip and stripline structures are presented.