Each composite illumination beam is directed to be {HEAD ~ incident} upon {TAIL ~ a separate predetermined location} on the subreflector which directs the illumination beams towards the main reflector 
upon
Each composite illumination beam is directed to be { HEAD ~ incident } upon { TAIL ~ a separate predetermined location } on the subreflector which directs the illumination beams towards the main reflector
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH