Animation 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, without turning the antenna.  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 moving 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 they 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.  By progressively delaying the phase of each antenna going up the line, the phase shifters cause the beam of radio waves to be emitted at an angle to the plane of the antennas.  By changing the phase shifts the computer control system can instantly steer the beam to any direction over a wide angle in front of the antenna.  Th velocity of the radio waves is shown slowed down enormously.
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<span class="int-own-work" lang="en">Own work</span>