The antenna of the MPA-4 target tracking radar used with the US Air Force MIM-3 Nike Ajax anti-aircraft missile, in service from 1954 through the 1960s. It is a Fresnel lens antenna, composed of a lattice of parallel strips of metal. Microwaves from a feed horn below pass through the lens, which focuses them into a beam which tracks the target aircraft. Exhibit in the National Electronics Museum, 1745 West Nursery Road, Linthicum, Maryland, USA. All items in this museum are unclassified. The museum permitted photography without restriction.