Closeup of the antenna elements of the US <a href="https://en.wikipedia.org/wiki/PAVE_PAWS" class="extiw" title="w:PAVE PAWS">PAVE PAWS</a> (Phased Array Warning System) ballistic missile defense radar located at Cape Cod Air Station, Technical Facility-Scanner Building &amp; Power Plant, Massachusetts Military Reservation, Sandwich, Barnstable County, Massachusetts, USA.  Constructed beginning in 1978, it was one of the first <a href="https://en.wikipedia.org/wiki/phased_array_radar" class="extiw" title="w:phased array radar">phased array radars</a>.   Each of the elements is a crossed <a href="https://en.wikipedia.org/wiki/dipole_antenna" class="extiw" title="w:dipole antenna">dipole antenna</a>.  The drive current from the transmitter to each antenna passes through a <a href="https://en.wikipedia.org/wiki/phase_shifter" class="extiw" title="w:phase shifter">phase shifter</a> controlled by a computer system.  The <a href="https://en.wikipedia.org/wiki/radio_wave" class="extiw" title="w:radio wave">radio waves</a> (microwaves) from each individual antenna combine in front of the antenna to create a narrow beam in a specific direction.  By changing the phase shifts the computer can instantly steer the beam in any direction, scanning it across the sky to detect and track missiles.  This large antenna produced a narrow "pencil" beam of microwaves only 2.2° wide
Historic American Engineering Record (HAER), creator
2012-02-04
Daderot