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