Diagram showing how a <a href="https://en.wikipedia.org/wiki/phased_array" class="extiw" title="w:phased array">phased array</a> antenna works. A phased array is a computer controlled antenna which produces a beam of radio waves that can be steered electronically to point in different directions. They are widely used in military <a href="https://en.wikipedia.org/wiki/radar" class="extiw" title="w:radar">radar</a>.  The phased array consists of an array of multiple identical antenna elements <i>(A)</i>, driven by a <a href="https://en.wikipedia.org/wiki/transmitter" class="extiw" title="w:transmitter">transmitter</a> <i>(TX)</i>   The feed current for each antenna passes through a device called a <a href="https://en.wikipedia.org/wiki/phase_shifter" class="extiw" title="w:phase shifter">phase shifter</a> <i>(φ)</i> which is controlled by a computer control system <i>(C)</i>. The red lines show the wavefronts (surfaces of constant phase) of the radio waves emitted by each antenna.  The waves of the individual antennas are spherical, but combine (<a href="https://en.wikipedia.org/wiki/superposition" class="extiw" title="w:superposition">superpose</a>) in front of the antenna  to make a <a href="https://en.wikipedia.org/wiki/plane_wave" class="extiw" title="w:plane wave">plane wave</a>, a beam of radio waves traveling in a specific direction.   The phase shifters progressively delay the phase of radio waves by a fixed amount going up the line of antennas so each antenna emits its wavefront after the antenna below it, creating a beam of radio waves directed at an angle <i>θ</i> to the plane of antennas.  By changing the phase delay of the phase shifters the computer control system can instantly steer the beam to any direction over a wide angle in front of the antenna. Actual phased arrays use a two dimensional plane array of antennas rather than the line of antennas shown here.
<a href="//commons.wikimedia.org/wiki/User_talk:Chetvorno" title="User talk:Chetvorno">Chetvorno</a>
<span class="int-own-work" lang="en">Own work</span>