Active electronically scanned array
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.
Bell Labs proposed replacing the Nike Zeus radars with a phased-array system in 1960, and was given the go-ahead for development in June 1961.
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.
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.
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.
[citation needed] US based manufacturers of the AESA radars used in the F-22 and Super Hornet include Northrop Grumman[7] and Raytheon.
[9][10] In 2016 the Congress funded a military industry competition to produce new radars for two dozen National Guard fighter aircraft.
[11] Radar systems generally work by connecting an antenna to a powerful radio transmitter to emit a short pulse of signal.
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.
In earlier systems the transmitted signal was originally created in a klystron or traveling wave tube or similar device, which are relatively large.
Shrinking the entire assembly (the transmitter, receiver and antenna) into a single "transmitter-receiver module" (TRM) about the size of a carton of milk and arraying these elements produces an AESA.
This allows the AESA to produce numerous simultaneous "sub-beams" that it can recognize due to different frequencies, and actively track a much larger number of targets.
The rough direction can be calculated using a rotating antenna, or similar passive array using phase or amplitude comparison.
The direction to the source is normally combined with symbology indicating the likely purpose of the radar – airborne early warning and control, surface-to-air missile, etc.
Since the AESA (or PESA) can change its frequency with every pulse (except when using doppler filtering), and generally does so using a random sequence, integrating over time does not help pull the signal out of the background noise.
[12] Nor does the AESA have any sort of fixed pulse repetition frequency, which can also be varied and thus hide any periodic brightening across the entire spectrum.
Modern RWRs must be made highly sensitive (small angles and bandwidths for individual antennas, low transmission loss and noise)[12] and add successive pulses through time-frequency processing to achieve useful detection rates.
AESAs can also be switched to a receive-only mode, and use these powerful jamming signals to track its source, something that required a separate receiver in older platforms.
Obtaining a range and a target vector requires at least two physically separate passive devices for triangulation to provide instantaneous determinations, unless phase interferometry is used.
The same basic concept can be used to provide traditional radio support, and with some elements also broadcasting, form a very high bandwidth data link.
The F-35 uses this mechanism to send sensor data between aircraft in order to provide a synthetic picture of higher resolution and range than any one radar could generate.
In 2007, tests by Northrop Grumman, Lockheed Martin, and L-3 Communications enabled the AESA system of a Raptor to act like a WiFi access point, able to transmit data at 548 megabits per second and receive at gigabit speed; this is far faster than the Link 16 system used by US and allied aircraft, which transfers data at just over 1 Mbit/s.
[19][20] The first AESA radar employed on an operational warship was the Japanese OPS-24 manufactured by Mitsubishi Electric introduced on the JDS Hamagiri (DD-155), the first ship of the latter batch of the Asagiri-class destroyer, launched in 1988.
