English: Antenna of one of the first experimental US radars being developed during the late 1930s on the roof of the US Naval Research Laboratory, Anacostia, Washington DC. Operating at 200 MHz, it was the first rotating radar antenna. Research in radiolocation was started as early as 1922 by Naval radio engineers Albert Hoyt Taylor and Leo Clifford Young. In 1930 at the newly opened NRL, with another engineer Lawrence Hyland they began a research program. In 1934 they patented a radar system. This picture shows a "bedspring" antenna made of multiple dipole antennas which was needed to create a beam narrow enough to locate ships or planes. The antenna is mounted on a mast so it can rotate and also tilt to point up into the sky. The rotating mast extends through the roof to a large manual wheel in the room below which contains the radar equipment, so it can be rotated by hand.

Caption: Closeup of the antenna of the first complete radar, installed "topside" of a building at the Naval Research Laboratory, Anacostia, D. C. in the late 1930s. It is a "dirigible" antenna, meaning that it is so mounted that it can be turned to allow for around the compass search