NEC-LIST: Ansoft HFSS vs NEC etc.

Hello,
I would appreciate whatever insights anyone can provide on the best
software choice for the following problem:
For precise global positioning, knowledge of the phase center of an antenna
or antenna array (in the presence of adaptive beamforming) is critical. To
begin to understand this problem I need to know the magnitudes and phases
at the feed points for each element in an array (obviously including mutual
coupling effects) for an incident plane wave from a given angle. This is
the reverse of the typical antenna pattern calculation. I am a novice at
computational E&M and the software that I have been using (Ansoft HFSS)
does not seem to make it easy to do this calculation (but I may just be
ignorant of some aspect of HFSS).
Comments both on the problem and on the best choice of software would be
welcome.
Thanks very much!

John A. Orr
Professor of Electrical and Computer Engineering
Worcester Polytechnic Institute
Visiting Professor of Aero and Astro Engineering
Stanford University
Stanford tel: 650-724-2464
WPI tel: 508-831-5273
orr_at_wpi.edu, jorr_at_stanford.edu

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