"M*A*S*H" corporal (7)
'mash corporal' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for radar that I've seen before include "Method of detection" , "Locator of plane" , "Instrument to detect and track distant objects" , "Equipment for locating objects" , "System for detecting objects with radio waves" .)