The antenna current Green's function (ACGF) can be used to consider the mutual coupling effect between multiple arrayed antennas. To obtain the ACGF of antennas, numerical simulations such as moment method (MoM) are mainly used. However, these numerical simulations require large memory and it is time consuming to obtain a solution. The computer-aided design (CAD) model for the numerical simulation should be accurately designed. Therefore, we propose an alternative method for obtaining the ACGF based on infinitesimal dipole modeling (IDM). The IDM is a technique to model antennas with a distribution of theoretically expressed dipoles. The infinitesimal dipoles have the form of a current distribution, the same as that of the ACGF. The IDM can be optimized with the radiation pattern of the modeled antenna, which can be measured without a numerical simulation. The CAD model is not required, and only an approximate dimension of the antenna is used. A CAD model of a seven-patch array antenna with a large platform and a manufactured single Yagi antenna are used to verify the proposed scheme. For verification, we calculate the active element pattern (AEP) based on the ACGF for the antennas. These AEPs calculated, based on the ACGF obtained by MoM, are compared with those calculated on the basis of the IDM. The AEPs represent a sufficient coincident tendency and the phase values are even more accurate than the existing scheme.