the "patriot" isnt designed to score a direct hit on an incoming missile. the theory is that computers find, track and determine how sucessful a launch would be.
if the incoming missile were to be selected as a possable kill, the patriot system would launch a missile from its own battery.
this weapon would fly on a collision course and explode a fraction of a second before any impact... the patriot exploding would (in theory) destroy or divert the path of the incoming weapon.
it was used against aircraft in one of the Gulf wars. at least one British Tornado was lost to the patriot system, with the loss of both air men..
i think its design was primeraly for high flying weapons, not hand held or truck launched low altitude missiles.