Board Thread:Speculation House/@comment-1323841-20140829235316/@comment-1323841-20140831180009

My understanding was something of a combination of both our comments; that the AT-field was a projection of the soul's ego in order to keep the soul a discreet individual, and that the angels were capable of projecting their AT-fields outside of their bodies to use in various ways.

The EVAs capable of this as well because they were made from angels, but since they were soulless, they required human souls be implanted in them. Although the AT-fields were emitted by this soul, it was the will of the pilot that powered them.

Unfortunately, all I have to back any of this is my (admittedly poor) memory of the show and while the EVAgeeks wiki does state "A.T. Fields are actually generated by the human soul contained within the Eva", this claim is not sourced.