According to one definition, antenna phase center is the center of sphere on which the phase of the radiated field has the minimum change over certain elevation angle (θ) and azimuth angle (Φ) ranges. In case when the phase center of the radiated field is needed to be considered, the commercial electromagnetic simulation software can be utilized to obtain the phase pattern so as to find out the phase variation of the radiated field over the interested angular range. This paper will compare the simulated phase pattern obtained from different simulation software with the calculated result and will discuss the relationship between antenna phase pattern and phase center by modeling a simple patch antenna in the simulation software.