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A phased array, in antenna theory, is an array of antennas in which all of the phases of each signal that feeds each antenna are set in such a way that the effective radiation pattern of the entire array is set toward the desired direction and that the signals emanating toward undesired directions are suppressed. It is a way to direct waves of radiation toward a desired direction.
A phased array is also known as a phased antenna system.
A phased array antenna has multiple radiating elements, each having a phase shifter of its own. The beams are then formed through the shifting of the signal's phase that is emitted from each radiating element; this serves as constructive interference toward the desired direction for the waves and as destructive interference for undesired directions. The main beam in a phased array antenna always points in the direction of the increased phase shift.
Because of the phase shifting and directional nature of the application, a phase array antenna usually has a flat surface that can be moved, unless it is meant as a stationary antenna, in which case it always broadcasts in a single direction. These antennas are often large installations, with some of them being as large as buildings. Mobile installations can be found on warships where the phased array antenna is used for radar systems in the detection and tracking of planes, ships and even missiles. These radar installations are also used to steer a missile during the mid-course phase of its flight.
Phased array antennas are used in AM broadcasting to provide more power and range, and so that they will only serve their area of license and not interfere in others. The Messenger spacecraft mission to Mercury in 2011 to 2015 was the first deep-space mission to use a phased array antenna for communication. Phased array antennas are also used in weather research and tracking of storms.