An active electronically scanned array (AESA) is a type of phased array antenna, which is a computer-controlled antenna array in which the beam of radio waves can be electronically steered to point in different directions without moving the antenna. In the AESA, each antenna element is connected to a small solid-state transmit/receive module (TRM) under the control of a computer, which performs the functions of a transmitter and/or receiver for the antenna. This contrasts with a passive electronically scanned array (PESA), in which all the antenna elements are connected to a single transmitter and/or receiver through phase shifters under the control of the computer. AESA's main use is in radar, and these are known as active phased array radar (APAR).
The Eurofighter Typhoon combat aircraft with its nose fairing removed, revealing its Euroradar CAPTOR AESA radar antenna
ZMAR concept sketch, 1962
An aerial view of the three domes of the Multifunction Array Radar prototype, surrounded by a clutter fence, at White Sands Missile Range, N.M.
Sketch of the FLAT TWIN antiballistic missile radar
A passive electronically scanned array (PESA), also known as passive phased array, is an antenna in which the beam of radio waves can be electronically steered to point in different directions, in which all the antenna elements are connected to a single transmitter and/or receiver.
The largest use of phased arrays is in radars. Most phased array radars in the world are PESA. The civilian microwave landing system uses PESA transmit-only arrays.
The Mikoyan MiG-31 combat aircraft with nose fairing removed, showing its Zaslon passive electronically scanned array radar antenna.