AN/PPS-4 Portable Ground Surveillance Radar
U.S. Army
<a rel="nofollow" class="external text" href="https://babel.hathitrust.org/cgi/imgsrv/download/pdf?id=uiug.30112106755439;orient=0;size=100;seq=68;attachment=0">Military Review</a>, January 1957, Page 66