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Added animation showing how a passive phased array works |
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[[File:DN-ST-92-02246.JPEG|thumb|[[Zaslon]] Passive electronically scanned array on [[Mikoyan MiG-31]]]]
[[File:Phased array animation 10 frames 371x400px 100ms.gif|thumb|upright=1.2|Animation showing how a passive electronically scanned array works. It consists of an array of antenna elements ''(A)'' powered by a single [[transmitter]] ''(TX)''. The feed current for each antenna passes through a [[phase shifter]] ''(φ)'' controlled by a computer ''(C)''. The moving red lines show the wavefronts of the radio waves emitted by each element. The individual wavefronts are spherical, but they combine ([[superposition|superpose]]) in front of the antenna to create a [[plane wave]], a beam of radio waves travelling in a specific direction. The phase shifters delay the radio waves progressively going up the line so each antenna emits its wavefront later than the one below it. This causes the resulting plane wave to be directed at an angle to the antenna. The velocity of the radio waves is shown slowed down enormously.]]
A '''passive electronically scanned array''' (PESA), also known as '''passive phased array''', is a [[phased array]] [[radar]] which has a single ''central'' [[radio frequency]] source (such as a [[magnetron]], a [[klystron]] or a [[travelling wave tube]]), sending energy into the multiple [[phase shift module]]s, which then send energy into the individual emitting elements in the front of the [[antenna (radio) |antenna]]. This contrasts with [[active electronically scanned array]] (AESA) devices, which have a separate radio frequency source for each phase shifter/emitting element. A PESA radar is therefore simpler to construct than an AESA.
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