In this paper, an improved common-mode antenna model is proposed to quickly predict a common-mode excitation and radiation of printed circuit boards (PCBs). The improved common-mode antenna model is based on a common-mode potential distribution over the two-dimensional plane. Although the original common-mode antenna model explains the common-mode excitation well by introducing a "current division factor (CDF)" of a one-dimensional parameter which represents a degree of imbalance of a transmission line, but it is applicable for limited cases of PCB shapes. To remove the shape limitation, the improved model proposed here uses a "common-mode potential conversion factor (CPCF)." The CPCF is a two-dimensional parameter expanded from the CDF. The improved common-mode antenna model attains good accuracy with experimental measurements and numerical calculations using FDTD method in terms of electromagnetic interference (EMI). The calculation done using this model was extremely fast compared to that with the real structure.