The antenna of the MPA-4 target tracking radar used with the US Air Force <a href="https://en.wikipedia.org/wiki/MIM-3_Nike_Ajax" class="extiw" title="w:MIM-3 Nike Ajax">MIM-3 Nike Ajax</a> anti-aircraft missile, in service from 1954 through the 1960s.  It is a <a href="https://en.wikipedia.org/wiki/Fresnel_lens" class="extiw" title="w:Fresnel lens">Fresnel lens</a> antenna, composed of a lattice of parallel strips of metal.  Microwaves from a <a href="https://en.wikipedia.org/wiki/feed_horn" class="extiw" title="w:feed horn">feed horn</a> below pass through the lens, which focuses them into a beam which tracks the target aircraft. For more information see <a rel="nofollow" class="external text" href="http://ed-thelen.org/ifc_track.html#mtr">IFC-Tracking Radars page, Ed Thelen's Nike Missile website</a>
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/93452909@N00">brewbooks</a>
CC BY-SA 2.0
<a href="//commons.wikimedia.org/wiki/Flickr" class="mw-redirect" title="Flickr">Flickr</a>: <a rel="nofollow" class="external text" href="https://www.flickr.com/photos/93452909@N00/2367040493">NIKE AJAX  Anti-Aircraft Missile Radar</a>