This paper presents a three-dimensional (3D) full time-domain modeling of the time reversal process for the localization of a dielectric obstacle in free space using an array of transceivers made of electric dipoles. The main purpose of this study is to propose a localization method and analyze the influence of the density of dipoles in the Time Reversal Array (TRA) on the accuracy of the localization in a given electromagnetic configuration. A Generalized Finite Difference (GFD) method and a leapfrog time discretization are used to get the numerical results.