A PESA contrasts with an active electronically scanned array (AESA) antenna, which has a separate transmitter and/or 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.
The transmitter elements were typically klystron tubes or magnetrons, which are suitable for amplifying or generating a narrow range of frequencies to high power levels.
To scan a portion of the sky, a non-PESA radar antenna must be physically moved to point in different directions.
It was a large two-dimensional phased array with beam steering controlled by computers instead of requiring mechanical motion of the antenna.
PESAs took a signal from a single source, split it into hundreds of paths, selectively delayed some of them, and sent them to individual antennas.
The
Mikoyan MiG-31
combat aircraft with nose fairing removed, showing its
Zaslon
passive electronically scanned array radar antenna.
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 (
superpose
) in front of the antenna to create a
plane wave
, a beam of radio waves travelling in a specific direction θ. 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 θ to the antenna. The computer can alter the phase shifters to steer the beam to a new direction, very quickly. The velocity of the radio waves is shown slowed down enormously.
