Need algorithm to calculate phase center of antenna

I am working in an algorithm to calculate the phase center of an antenna (or the effective phase center). But the papers i have found have not been very useful.
The idea is to be able to obtain the phase center from the radiated far fields (E field) amplitude. (obtained in HFSS analisys.). I have passed more than tree weeks trying to find some previous attempts or some feedback in this topic. But I have not suceeded. (I have to build a matlab program)

First I need this algorithm and then I have to extend it to find a "surface" in order to find the possible positions (because it moves with the frequency change) of the phase center of an UWB antenna.

I know that the phase center will depend on the type of antenna, the geometry, the polarization, frequency. But to beguin I just need a first step to go from a general algorithm to a mor specific one.

I hope someone has an idea.

Thanks in advance.

:D:D:D