Editing Phased array (section)

{{Short description|Array of antennas creating a steerable beam}}
{{Use American English|date=May 2023}}
[[File:Phasearray.gif|thumb|upright=1.3|Animation showing the [[radiation pattern]] of a phased array of 15 antenna elements spaced a quarter wavelength apart as the [[phase shift|phase difference]] between adjacent antennas is swept between −120 and 120 degrees. The dark area is the beam or [[main lobe]], while the light lines fanning out around it are [[sidelobe]]s.]]

In [[antenna (radio)|antenna]] theory, a '''phased array''' usually means an '''electronically scanned array''', a computer-controlled [[Antenna array|array of antennas]] which creates a [[radio beam|beam of radio waves]] that can be electronically steered to point in different directions without moving the antennas.<ref name="Milligan">{{cite book
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 | title  = Modern Antenna Design, 2nd Ed.
 | publisher = John Wiley & Sons
 | date   = 2005
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 | isbn   = 0471720607
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 | title  = Antenna Theory: Analysis and Design, 4th Ed.
 | publisher = John Wiley & Sons
 | date   = 2015
 | pages  = 302–303
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 | title  = Antenna Theory and Design
 | publisher = John Wiley & Sons
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 | url    = https://books.google.com/books?id=xhZRA1K57wIC&q=%22phased+array%22&pg=PA315
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In a phased array, the power from the transmitter is fed to the radiating elements through devices called ''[[phase shifter]]s'', controlled by a computer system, which can alter the phase or signal delay electronically, thus steering the beam of radio waves to a different direction.  Since the size of an antenna array must extend many wavelengths to achieve the high gain needed for narrow beamwidth, phased arrays are mainly practical at the high [[frequency]] end of the radio spectrum, in the [[ultrahigh frequency|UHF]] and [[microwave]] bands, in which the operating wavelengths are conveniently small.

Phased arrays were originally invented for use in military [[radar]] systems, to detect fast moving planes and missiles, but are now widely used and have spread to civilian applications such as [[5G]] [[MIMO]] for cell phones. The phased array principle is also used in [[acoustics]] is such applications as [[phased array ultrasonics]], and in optics. 

The term "phased array" is also used to a lesser extent for unsteered [[array antenna]]s in which the radiation pattern of the antenna array is fixed,<ref name="Visser"/><ref>{{FS1037C MS188}} [http://glossary.its.bldrdoc.gov/fs-1037/dir-027/_3979.htm Definition of Phased Array] {{webarchive|url=https://web.archive.org/web/20041021132428/http://glossary.its.bldrdoc.gov/fs-1037/dir-027/_3979.htm |date=2004-10-21 }}. Accessed 27 April 2006.</ref> For example, AM broadcast radio antennas consisting of multiple [[mast radiator]]s are also called "phased arrays".