A radar antenna for a guided missile is calibrated in flight using a point source of microwave radiation and a lens to emulate a far field source. The microwave source and lens fit behind a metal cap at the leading end of the radome and so do not adversely affect the radar. A variety of techniques to power the point source are disclosed, and a variety of lens arrangements are disclosed. The invention allows a radar antenna to be calibrated in flight, and so insures against mis-calibration due to aging components as well as the heat and mechanical forces associated with storage and/or launch of the missile.
