Active Electronically Scanned Array (AESA) Radars: In Focus

[Lankan Ranger]

Active Electronically Scanned Array (AESA) Radars: In Focus

An Active Electronically Scanned Array (AESA) is a type of phased array radar whose transmitter and receiver functions are composed of numerous small solid-state transmit/receive modules (TRMs).

AESAs aim their "beam" by broadcasting radio energy that interfere constructively at certain angles in front of the antenna. They improve on the older passive electronically scanned radars by spreading their broadcasts out across a band of frequencies, which makes it very difficult to detect over background noise.

AESAs allows aircrafts to broadcast powerful radar signals while remaining stealthy.

List of existing AESA Radars

Northrop Grumman/Raytheon AN/APG-77, for the F-22 Raptor

Northrop Grumman AN/APG-80, for the F-16E/F Block 60 Fighting Falcon

Northrop Grumman AN/APG-81, for the F-35 Joint Strike Fighter

Northrop Grumman Multirole AESA, for the Boeing Wedgetail (AEW&C)

Northrop Grumman APY-9, for the E-2D Advanced Hawkeye

Northrop Grumman SABR, for F-16 Fighting Falcon upgrades

Raytheon AN/APG-63(V)2 and AN/APG-63(V)3, for the F-15C Eagle & Republic of Singapore's F-15SG

Raytheon APG-79, for the F/A-18E/F Super Hornet and EA-18G Growler

Raytheon AN/APQ-181 (AESA upgrade currently in development), for the B-2 Spirit bomber

AMSAR, research from the European GTDAR consortium, for Eurofighter and Rafale fighter Radar

Captor-E CAESAR (CAPTOR Active Electronically Scanning Array Radar)

RBE2-AA Radar à Balayage Electronique 2 - Active Array

SELEX Seaspray 7000E, for helicopters

SELEX Vixen 500E

Mitsubishi Electric Corporation J/APG-1, AESA for the Mitsubishi F-2 fighter

Ericsson Erieye AEW&C

Ericsson PS-05/A MK-5 for JAS 39 Gripen. Will be available by 2012.

Phazotron NIIR Zhuk-AE, for MiG-35

Tikhomirov NIIP Epaulet-A

Elta EL/M-2083 aerostat-mounted air search radar

Elta EL/M-2052, for candidate for HAL Tejas. Also, suitable for F-15, MiG-29 & Mirage 2000

Elta EL/M-2075 radar for the IAI Phalcon AEW&C system

NRIET-designed (Nanjing Research Institute of Electronic Technology)
radar mounted on the KJ-2000 AEW&C system

Toshiba HPS-106, air & surface search radar, for the Kawasaki P-1 maritime patrol aircraft, four antenna arrays.

Mitsubishi Electric Corporation HPS-104, for the Mitsubishi SH-60

 

[Lankan Ranger]

Advantages of AESA Radars

AESA's add many capabilities of their own to those of the PESAs. Among these are: the ability to form multiple beams, to scan without mechanical steering, to use each TRM for different roles concurrently, like radar detection, and, more importantly, their multiple wave and scanning frequencies create multiple difficulties for traditional, correlation-type radar detectors.

Low Probability of Intercept

AESA Radar systems work by sending out a signal and then listening for its echo off distant objects. Each of these paths, to and from the target, is subject to the inverse square law of propagation.

That means that a radar's received energy drops with the fourth power of distance, which is why radar systems require high powers, often in the megawatt range, in order to be effective at long range.

The radar signal being sent out is a simple radio signal, and can be received with a simple radio receiver. It is common to use such a receiver in the targets, normally aircraft, to detect radar broadcasts.

Unlike the radar unit, which has to send the pulse out and then receive its reflection, the target's receiver does not need the reflection and thus the signal drops off only as the square of distance.

This means that the receiver is always at an advantage over the radar in terms of range - it will always be able to detect the signal long before the radar can see the target's echo. Since the position of the radar is extremely useful information in an attack on that platform, this means that radars generally have to be turned off for lengthy periods if they are subject to attack; this is common on ships, for instance.

Turning that received signal into a useful display is the purpose of the "radar warning receiver" (RWR). Unlike the radar, which knows which direction it is sending its signal, the receiver simply gets a pulse of energy and has to interpret it.

Since the radio spectrum is filled with noise, the receiver's signal is integrated over a short period of time, making periodic sources like a radar add up and stand out over the random background.

Typically RWRs store the detected pulses for a short period of time, and compare their broadcast frequency and pulse repetition frequency against a database of known radars.

The rough direction can be calculated using a rotating antenna, or similar passive array, and combined with symbology indicating the likely purpose of the radar - airborne early warning, surface to air missile, etc.

This technique is much less useful against AESA radars. Since the AESA can change its frequency with every pulse, and generally does so using a pseudo-random sequence, integrating over time does not help pull the signal out of the background noise.

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. Traditional RWRs are essentially useless against AESA radars.

High jamming resistance

Jamming is likewise much more difficult against an AESA. Traditionally, jammers have operated by determining the operating frequency of the radar and then broadcasting a signal on it to confuse the receiver as to which is the "real" pulse and which is the jammer's. This technique works as long as the radar system cannot easily change its operating frequency.

When the transmitters were based on klystron tubes this was generally true, and radars, especially airborne ones, had only a few frequencies to chose among. A jammer could listen to those possible frequencies and select the one being used to jam.

Since an AESA changes its operating frequency with every pulse, and spreads the frequencies across a wide band even in a single pulse, jammers are much less effective. Although it is possible to send out broadband white noise against all the possible frequencies, this means the amount of energy being sent at any one frequency is much lower, reducing its effectiveness.

In fact, AESAs can then be switched to a receive-only mode, and use these powerful jamming signals instead to track its source, something that required a separate receiver in older platforms.

AESAs are so much more difficult to detect, and so much more useful in receiving signals from the targets, that they can broadcast continually and still have a very low chance of being detected.

This allows such radar systems to generate far more data than traditional radar systems, which can only receive data periodically, greatly improving overall system effectiveness.

Other advantages

Since each element in a AESA is a powerful radio receiver, active arrays have many roles besides traditional radar. One use is to dedicate several of the elements to reception of common radar signals, eliminating the need for a separate radar warning receiver.

AESA's are also much more reliable than older designs. Since each module operates independently of the others, single failures have little effect on the operation of the system as a whole.

Additionally, the modules individually operate at low powers, perhaps 40 to 60 watts, so the need for a large high-voltage power supply is eliminated.

AESA's can help reduce an aircraft's overall radar cross-section (RCS).

 

[Lankan Ranger]

The Difference Between AESA and PESA

In a passive electronically scanned array (PESA), the microwave feed network in the back of the antenna is powered by a single radio frequency (RF), sending its waves into phase shift modules (usually digitally-controlled), which, in turn, feed the numerous emitting elements.

An Active Electronically Scanned Array (AESA), instead, has an individual RF source for each of its many transmit/receive elements, making them "active". This provides for a graceful degradation, so that many T/R modules may fail and the radar would not stop functioning.

AESA radars replace the traditional radars

Which usually require extremely high operating voltage and power, with multiple solid state RF sources operating at low voltage (40 to 60 volts).

Solid state electronics use silicon or gallium arsenide based power amplifier technology and benefit to some extent from mass production techniques developed for consumer electronics.

 

[Last Hope]

We have got a thread dedicated to it. Please look for that. Thanks.

 

[nomi007]

tell me also about chinese AESA radars
2nd tell me Lankan Ranger
about any anti stealth technology
i m finding articles but can't find
please help me

 

[Lankan Ranger]

tell me also about chinese AESA radars
2nd tell me Lankan Ranger
about any anti stealth technology
i m finding articles but can't find
please help me

See the link

http://homepage.mac.com/ardeshir/Anti-StealthTechnology.pdf

 

[nomi007]

thank u dear lankan ranger for this informative post