In order to determine the position of equivalent phase centers of pyramidal horn antenna, which keep the phase of the antenna’s field relative invariable in some range of the antenna’s main lobe, an approach to analyze the equivalent phase centers of pyramidal horn antenna is presented in this paper.

By analyzing and calculating the phase center and equiphase surface of the antenna with the method of moving reference point, the phase center and the width of equiphase surface of pyramidal horn, and the relationship of deviation of phase between the phase center and equiphase surface are obtained in this paper.