English: Diagram showing how a phased array 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 radar. The phased array consists of an array of multiple identical antenna elements (A), driven by a transmitter (TX) The feed current for each antenna passes through a device called a phase shifter (φ) which is controlled by a computer control system (C). 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 (superpose) in front of the antenna to make a plane wave, 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 θ 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.