  In this paper, the displacement of the phase centers of multi-mode antennas
is investigated. A mathematical approach is applied in order to calculate the
positions of the phase center for each mode. Using electric far field samples
obtained from electromagnetic field simulation data, the coordinates of the
shifted positions of the phase center relative to the physical center of the
antenna are determined for each mode. Numerical results show the dependency of
the phase centers of an antenna prototype as a function of the considered angle
of observation.
