In this chapter, we propose a calibration method for an array antenna, which includes electromagnetic coupling between antenna elements. Conventional methods such as the rotating element electric field vector (REV) method for elements of an array antenna do not take into account the electromagnetic coupling between elements. If the antenna calibration is not properly performed, the radiation pattern of the radio waves in the undesired directions will increase and interfere with the other satellites that are not intended. To overcome this drawback, a model of an array antenna including the mutual coupling between antenna elements has been constructed. Using this model, the estimation problem of the effect of the mutual coupling is formulated as a formulation problem. Finally, a calibration method based on the solution of the optimization problem is derived and shows the effectiveness of the method through some numerical examples.