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Added blurb about hybrid PESA/AESA which are extremely common in lower cost modern terminals |
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The largest use of phased arrays is in [[radar]]s. Most phased array radars in the world are PESA. The civilian [[microwave landing system]] uses PESA transmit-only arrays.
A PESA contrasts with an [[active electronically scanned array]] (AESA) antenna, which has a separate [[transmitter]] and/or [[radio receiver|receiver]] unit for each antenna element, all controlled by a computer; AESA is a more advanced, sophisticated versatile second-generation version of the original PESA phased array technology. Hybrids of the two can also be found, consisting of subarrays that individually resemble PESAs, where each subarray has its own [[RF front end]]. Using a hybrid approach, the benefits of AESAs (e.g., multiple independent beams) can be realized at a lower cost compared to true AESAs.
Radar systems generally work by connecting an antenna to a powerful radio transmitter to emit a short pulse of signal. The transmitter is then disconnected and the antenna is connected to a sensitive receiver which amplifies any echos from target objects. By measuring the time it takes for the signal to return, the radar receiver can determine the distance to the object. The receiver then sends the resulting output to a [[Radar display|display of some sort]]. The transmitter elements were typically [[klystron tube]]s or [[magnetron]]s, which are suitable for amplifying or generating a narrow range of frequencies to high power levels. To scan a portion of the sky, the radar antenna must be physically moved to point in different directions.
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