Since its first introduction in 1966, the Finite Difference Time Domain (FDTD) method has been widely used as a tool for solving complex electromagnetic problems. For FDTD, Maxwell’s equations are discretized in space and time and it is very flexible in modeling complex structures. The first applications of the FDTD were mainly broadcast. In this paper, the authors apply the numerical method of Finite Difference Time Domain (FDTD) for modeling a rectangular patch antenna via a MATLAB code using UPML (Uniaxial Perfectly Matched Layer) formulation for absorption boundary conditions.