The central ray of each composite illumination beam is directed to be {TAIL ~ incident} upon a separate preselected location on {HEAD ~ the subreflector} 
The central ray of each composite illumination beam is directed to be { TAIL ~ incident } upon a separate preselected location on { HEAD ~ the subreflector }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD