Active electronically scanned array

The Eurofighter Typhoon combat aircraft with its nose fairing removed, revealing its Euroradar CAPTOR AESA radar antenna

An active electronically scanned array (AESA), is a type of phased array antenna, that is a computer-controlled array antenna 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 AESA is a more advanced, sophisticated, second-generation of the original PESA phased array technology. PESAs can only emit a single beam of radio waves at a single frequency at a time. The AESA can radiate multiple beams of radio waves at multiple frequencies simultaneously. AESA radars can spread their signal emissions across a wider range of frequencies, which makes them more difficult to detect over background noise, allowing ships and aircraft to radiate powerful radar signals while still remaining stealthy.

History

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

Bell Labs proposed replacing the Nike Zeus radars with a phased array system in 1960, and were given the go-ahead for development in June 1961. The result was the Zeus Multi-function Array Radar (ZMAR), an early example of an active electronically steered array radar system.[1] ZMAR became MAR when the Zeus program ended in favor of the Nike-X system in 1963. The MAR (Multi-function Array Radar) was made of a large number of small antennas, each one connected to a separate computer-controlled transmitter or receiver. Using a variety of beamforming and signal processing steps, a single MAR was able to perform long-distance detection, track generation, discrimination of warheads from decoys, and tracking of the outbound interceptor missiles.[2] MAR allowed the entire battle over a wide space to be controlled from a single site. Each MAR, and its associated battle center, would process tracks for hundreds of targets. The system would then select the most appropriate battery for each one, and hand off particular targets for them to attack. One battery would normally be associated with the MAR, while others would be distributed around it. Remote batteries were equipped with a much simpler radar whose primary purpose was to track the outgoing Sprint missiles before they became visible to the potentially distant MAR. These smaller Missile Site Radars (MSR) were passively scanned, forming only a single beam instead of the MAR's multiple beams.[2]

The first Soviet APAR was developed in 1963-1965 as a part of the S-225 ABM system. After some modifications in the system concept in 1967 it was built at Sary Shagan Test Range in 1970-1971 and nicknamed Flat Twin in the West. Four years later another radar of this design was built on Kura Test Range, while S-225 system was never commissioned.[citation needed]

US based manufacturers of the AESA radars used in the F-22 and Super Hornet include Northrop Grumman[5] and Raytheon.[6] These companies also design, develop and manufacture the transmit/receive modules which comprise the 'building blocks' of an AESA radar. The requisite electronics technology was developed in-house via Department of Defense research programs such as MMIC Program.[7][8]

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