New Active Electronically Scanned Array radar overview
Air and naval forces around the globe are launching new Active Electronically Scanned Array (AESA) radars, which they claim will see further and will be able to detect smaller targets at greater ranges than ever thought. Mönch takes a closer look at the technology and what the market has to offer.
Conventional radars, with rotating antennas, operating on fixed frequencies or with limited frequency agility, usually perform only one function, with separate units required for surveillance, tracking, and targeting. AESA radars, however, are capable of carrying out several functions simultaneously. The AESA radar antenna does not move but consists of a matrix of small, solid state transmit/receive modules (TRM). Each TRM is capable of generating and radiating its own independent signal, allowing the AESA to produce radar pulses on different frequencies with interleaved pulse streams carrying out several functions simultaneously.
The use of multiple frequencies creates difficulties for Electronic Surveillance (ES) systems and radar warning receivers. The AESA radar can change its frequency with every pulse and generally does so using a random sequence so it is very difficult for an ES system to de-interleave pulses from a specific radar. Additionally, it does not need to have a fixed pulse repetition frequency, making an AESA radar a Low-Probability of Intercept (LPI) radar.
A major advantage of AESA radars is their resistance to jamming. Traditional radars are vulnerable to jamming as jammers determine the frequency of the radar and then broadcast a signal at the same frequency to confuse the radar receiver. As AESA radars can easily change their frequencies with every pulse, this technique is no longer effective.
The Next-Generation AESA Goes Airborne
AESA radar is an essential sensor for fighter aircraft, and is increasingly deployed on surveillance platforms, such as Australia’s E-7A WEDGETAIL AEW aircraft (based on a Boeing 737-700, with the addition of an advanced Multi-Role Electronically Scanned Array [MESA] radar and 10 mission crew consoles) and Japan’s Kawasaki P-1 MPA.
Key providers in the US are Northrop Grumman and Raytheon, while in Europe these are Thales and Leonardo-Finmeccanica. Russian and Chinese systems are also under development, and Israel Aerospace Industries (IAI) Elta provides systems for aircraft operating in a variety of countries.
Northrop Grumman’s AN/APG-77 AESA radar is installed on the F-22 RAPTOR. With an antenna composed of 1,956 TRMs, it can perform near-instantaneous beam steering. The radar provides 120° degrees field-of-view (FOV) in azimuth and elevation, the highest possible value for a flat phased array antenna. It is specified to achieve an 86% probability of intercept against a 1sqm target at a detection range of 240 kilometres. More than 100 AN/APG-77 AESA radars have been produced and much of the technology developed for the AN/APG-77 is being used in the AN/APG-81 radar for the F-35 Joint Strike Fighter (JSF). Over 3,000 AN/APG-81 AESA radars are expected to be ordered with production to run beyond 2035. Capabilities of the AN/APG-81 include the AN/APG-77’s air-to-air modes, plus air-to-ground modes, including high-resolution mapping, multiple ground moving target indication, and target identification and tracking.
Raytheon has developed the AN/APG-79 for the F/A-18E/F SUPER HORNET and EA-18G GROWLER. With its beam steering capability operating at nearly the speed of light, the AN/APG-79 optimises situational awareness in both air and ground domains. The agile beam enables the radar to interleave modes so that pilot and crew can use both modes simultaneously. In production for the US Navy and Royal Australian Air Force, the AN/APG-79 demonstrates reliability, image resolution, and tracking range significantly greater than that of the previous mechanically scanned array F/A-18 radar. Replacing a mechanically scanned array with a fixed AESA mount helps reduce an aircraft’s overall radar cross-section (RCS).
It is not only fixed-wing aircraft that take advantage of AESA technology. In May 2016, Leonardo-Finmeccanica unveiled its OSPREY AESA radar employing multiple fixed antennas distributed around the aircraft, each antenna panel containing 256 TRMs and providing 120° coverage. An advantage of OSPREY is that its antenna arrays can be mounted higher on an aircraft fuselage than traditional mechanically scanned antennas. On rotary-wing aircraft, mechanical antennas normally have to be mounted on the underside of the fuselage limiting the size of the antenna due to ground clearance restrictions. OSPREY has been purchased by Norway for its 16 AW101 helicopters and Leonardo-Finmeccanica, manufacturer of the aircraft, has also secured contracts for OSPREY in the US.
In November 2015, France completed testing of the RAFALE’s new RBE2 AESA radar during missions over Iraq. RBE2, developed by Thales, is compatible with the latest-generation air-to-air missiles, including MBDA’s METEOR Beyond Visual Range Air-to-Air Missile (BVRAAM). RBE2 is capable of tracking up to 40 aircraft and engaging eight of them during air-to-air combat operations. In addition, the radar can provide submetric Synthetic Aperture Radar (SAR) imagery.
Thales also developed the SEARCHMASTER maritime surveillance radar, which derived from the RBE2 to provide surface surveillance and ASW capability. The combination of a rotating antenna and electronic scanning in the vertical plane gives 360° coverage and enables simultaneous short-range and long-range surveillance. This radar has been selected by France for the upgraded ATLANTIQUE 2 MPAs.
IAI recently expanded its best-selling Maritime Surveillance Radar family, and presented two new additions to the market: The ELM-2022ES radar and the ELM-2022ML lightweight radar. The ELM-2022ES radar, developed by IAI’s subsidiary Elta Systems, provides optimal maritime and ground surveillance and imaging capabilities, in addition to simultaneous air surveillance. Over 250 ELM-2022 radars have been sold to customers in over 25 countries worldwide, with the radar currently operated on many platforms: Lockheed Martin P-3 ORION; Bombardier DASH-8; Airbus Defence & Space (DS) C-295 and Airtech (joint venture of Airbus DS and IPTN) C-235; RUAG Dornier 228 MPA; maritime helicopters; and IAI’s HERON 1 maritime UAS.
The ELM-2022ML radar uses a unique front-end design in which most of the radar components are installed directly on the mechanical antenna array. Weighing only 50kg, this radar is suitable for the growing market of small to medium UAS, as well as light reconnaissance aircraft and helicopters.
Russia’s first fighter-mounted AESA radar, the ZHUK-AE, contained 652 TRMs and was unveiled in 2007. A more recent Russian development by Tikhomirov-NIIP, the AESA-N050 radar mounted on Sukhoi’s new T-50 (PAK-FA) stealth fighter. It has about 1,500 TRMs and operates in the L-band. AESA-N050 radar can detect a 1sqm target at a range of 260km, making it comparable in performance with the AN/APG-77 on the F-22.
It is likely that the J-10, which achieved IOC in October 2014, is the first Chinese fighter to feature an AESA with about 1,200 TRMs. Images of the J-11D, the most advanced version of the Chinese FLANKER aircraft, have recently appeared on the internet. The J-11D is speculated to have an AESA radar inside its upwardly canted radar dome to make best use of the PL-10 air-to-air missile, Pl-12/PL-15 beyond visual range missiles, and the YJ-12 supersonic anti-ship cruise missile.
An Indian fighter, the TEJAS Light Combat Aircraft, designed by the Aeronautical Development Agency and Hindustan Aeronautics Ltd. (HAL) for the Indian Air Force and Navy, is equipped with a version of the EL/M-2052 AESA radar being developed jointly by IAI Elta and HAL. The EL/M-2052 is capable of tracking up to 64 targets simultaneously, and can provide very high-resolution SAR imagery. Interestingly, the TEJAS Mk2 will feature an Indian-developed AESA fire control radar named UTTAM.
Retrofitting Existing Aircraft
While new aircraft typically have AESA radars as part of the original design, there is an increasing demand for pod-mounted AESA to be fitted to existing aircraft. Northrop Grumman has developed the AN/ASQ-236 pod weighing around 500kg as an externally mounted self-contained unit. It is fitted to the F-15E STRIKE EAGLE and consists of an antenna, inertial navigation, and cooling systems. It provides SAR images for detailed surveillance, coordinate generation, and bomb impact assessment purposes.
The Lockheed Martin VIGILANCE Pod contains the Northrop Grumman AN/APG 81 AESA radar. Two such pods are carried on either side of a platform to provide 360° coverage. Operator consoles can be fitted inside the aircraft, although the pod can be operated in an entirely self-contained mode.
The AN/APG-81 is the radar deployed on the F-35, enabling data sharing among other aircraft within the same battlespace via the VIGILANCE pods. Lockheed Martin has suggested fitting the pods to C-130 or CN-235 transport aircraft, as well as AW101 MERLIN or Mi-17 helicopters.
AESA for UAS
In 2011, Raytheon began development of the Dismount Detection Radar (DDR) system to be deployed on the MQ-9 REAPER Block 5 for the USAF. The new radar provides operators with the ability to find and track individuals and vehicles. Mounting such a system in a pod allows it to be moved between individual platforms, and possibly platform types, to match mission requirements.
Russia’s Phazotron-NIIR Corporation is working on a new AESA radar whose first applications will be on future Russian UAVs. The new system is a 3D radar, so the TRMs are arranged not on the usual two-dimensional surface but in several progressively elevated layers. The radar will have a range of 200km and will provide high-resolution imagery.
AESA Technology Boosts Naval Operations
The first shipboard AESA radar was the OPS-24 fire control radar mounted on the Japanese destroyer HAMAGIRI (DD 155) launched in 1988. Developed by Mitsubishi, OPS-24 operated in the L-band (1-2GHz) and had 360° azimuth coverage. A more recent development for the Japanese Maritime Self Defense Force (JMSDF) is the FCS-3 integrated naval weapon system. This multifunction AESA radar has two sets of antennas: The larger one operates in the C-band (4-8GHz) for surveillance and tracking, the smaller one is an X-band (8-12GHz) fire control radar. FCS-3 was introduced in 2007 with an enhanced version, FCS-3A, being installed on the AKIZUKI-class (19DD) destroyers.
One of the first AESA radars to be deployed on a European warship is the Active Phased Array Radar (APAR), a multifunction, 3D radar developed by Thales Nederland. It has four fixed sensor arrays mounted on a pyramidal structure, each array consisting of 3,424 TRMs operating in the X-band. APAR can track over 200 air targets to a range of 150km and over 150 surface targets to a range of 32 kilometres. It can carry out horizontal search out to 75km and a volume search out to 150 kilometres. Thirty-two semi-active radar homing missiles can be guided simultaneously, including 16 in the terminal guidance phase. APAR is installed on four Royal Netherlands Navy frigates, three Royal Danish Navy frigates, and three German Navy Type F124 frigates.
Germany has also selected the TRS-4D/NR (Non-Rotating) system developed by Airbus DS for four new Type F125 frigates, with an Initial Operating Capability (IOC) in 2016. The TRS-4D/NR, operating in the C-band, is installed with four fixed antenna panels mounted on the ships’ two main masts. TRS-4D/NR can carry out several reconnaissance tasks simultaneously. It can do a long-range scan of the sea surface and airspace while tracking individual targets, operating in both ‘blue water’ and littoral environments.
The RAN-40L, a 3D, L-band search radar produced by Leonardo-Finmeccanica, is used for long-range maritime air surveillance and early warning, and is capable of detecting and tracking aircraft or UAS up to 400km away. Radar coverage is obtained by phase scanning in elevation, while mechanically rotating an antenna in azimuth. RAN-40L is deployed on the Italian aircraft carrier CAVOUR (C 550).
The Italian manufacturer also unveiled a new version of its KRONOS multifunction AESA radar in 2014. It can perform surveillance, tracking, threat evaluation, and fire control against multiple threats, simultaneously and automatically, at all altitudes. The radar has been designed to detect even very small maritime threats, and can provide missile guidance. It links surveillance to air defence, covering all threats from low-level supersonic cruise missiles to small UAVs.
In operation on-board the UK Royal Navy’s Type 45 destroyer, the SAMPSON radar is at the core of the SEA VIPER naval air defence system. A dual-face AESA radar produced by BAE Systems Maritime, it provides surveillance and dedicated tracking of hundreds of targets, enabling the Type 45 to defend itself and other ships in its company from attack. SAMPSON is compatible with both active and semi-active homing missile systems, providing mid-course guidance, and it operates in the S-band (2-4GHz) with a power of 25kW and a range of 400 kilometres.
In August 2005, Australia and the US signed an agreement to develop AESA technology in Australia. CEA Technologies in Australia and Northrop Grumman in the US jointly developed CEAFAR as part of Australia’s project to make its ANZAC frigates survivable against supersonic cruise missile attacks. CEAFAR is an S-band AESA radar, designed to be supplemented with the X-band CEAMOUNT solid-state Continuous Wave Illuminator. The combined system of radar and illuminator allows the generation and maintenance of more than 10 simultaneous fire control channels.
IAI has developed MF-STAR (ELM-2248) for use on naval platforms. It delivers a high-quality situation picture and weapon support under severe target/environmental conditions. MF-STAR incorporates a lightweight antenna with four active arrays operating in the S-band that can be tailored to fit even relatively small ships. Additionally, it can provide guidance for anti-air missiles and automatically initiates tracking for low-flying attacking missiles at ranges of 25km and for high-flying fighter aircraft at more than 120 kilometres. Hundreds of targets can be tracked simultaneously. It is currently installed on the Indian Navy’s VIKRANT-class aircraft carrier and KOLKATA-class destroyers, as well as the Israel Navy’s EILAT-class (SA’AR 5) corvettes.
The Type 346 radar, with an antenna array comprising 1,524 TRMs, is installed on-board two PLAN-operated LUYANG II-class (Type 052C) destroyers. The PLAN’s aircraft carrier LIAONING (16), formerly constructed for the Soviet Navy, has a similar radar using technology characterised by high-energy consumption that requires special cooling equipment. A new AESA system being installed on the new-generation LUYANG III-class (Type 052D) destroyers has a liquid cooling system for the antenna instead of the air cooling system in the Type 346 radar. As a liquid cooling system has larger cooling capacity and the contact area is bigger in the antenna array, it must be assumed that the new radar has greater power and better performance than the Type 346.
Continuing Advances
In 2015, Thales Nederland unveiled the NS100 3D Naval Air and Surface surveillance radar. Different types of targets put different requirements on the radar: fighters require long-range; high-diving missiles require elevation coverage; sea skimming missiles require fast reaction time; and hovering helicopters and UAVs require good clutter suppression. The NS100 detects this wide variety of targets in one single mode. The radar can be scaled by adding TRMs to meet the diverse requirements and operational needs of navies. The same basic radar can be optimised for different ship classes, leading to fleet-wise logistic advantages.
Saab has introduced its new solid-state naval radar system, the SEA GIRAFFE 4A, which is an S-band AESA radar featuring a 360° rocket, artillery and mortar (RAM) locator and target tracking for long-range surface-to-air missiles. Capable of classifying both hovering and moving helicopters, the radar can also detect and classify UAVs. SEA GIRAFFE 4A, scheduled to be delivered in 2016, will be incorporated on-board the US Navy’s INDEPENDENCE variant Littoral Combat Ship (LCS).
The Air and Missile Defense Radar (AMDR aka AN/SPY-6[V]) is the US Navy’s next-generation air and missile defence radar. Developed by Raytheon, it will be deployed initially on the DDG-51 Flight-III destroyers, and will enhance the ships’ ability to detect air and surface targets and ballistic missile threats.
AMDR is constructed with individual building blocks, called Radar Modular Assemblies (RMA). Each RMA is a self-contained radar in a box measuring 60.96cm cubed. Individual RMAs are stacked to form any size array to fit the mission requirements of any ship, making AMDR the Navy’s first truly scalable radar. For the ARLEIGH BURKE-class destroyers, AMDR will feature 37 RMAs, giving a 15dB advantage over the AN/SPY-1D(V) currently installed on US destroyers. AMDR’s performance and reliability are the result of more than 10 years investment in the production of high-powered GaN semiconductors. AMDR’s GaN components cost 34% less than traditional GaAs alternatives, deliver higher power density and efficiency, and have a meantime between failures of 100 million hours.
Lessons from the Mess
With the launching of two new S-and X-band classes of the GIRAFFE surface radar on 12 May 2014, Saab continues to embark on multifunction radar options, providing a unique capability to nearly all military and security missions. Based on gallium nitride (GaN) semiconductor technology, the new radars include the X-band GIRAFFE 1X and S-band GIRAFFE 4A systems, as well as GIRAFFE 8A which is also operating in the S-band. The two new classes also include Sea GIRAFFE 1X and Sea GIRAFFE 4A as naval variants.
With a detection range of 350km, the latter exceeds twice the detection range of the earlier Sea GIRAFFE system found aboard the Royal Swedish Navy’s VISBY-class corvettes and US Navy’s INDEPENDENCE variant LCS. Saab EDS quotes this radar’s simultaneous detect and classify capacity at more than 1,000 tracks.
Sea GIRAFFE 4A combines air surveillance, air defence, sense and warn, and weapon locating capabilities in a single, low-footprint AESA radar, the company noted. Saab also explained that the GIRAFFE 8A radar is the surface-based variant of the company’s ERIEYE AEW&C radar system, exceeding a range of over 450 kilometres. It is also suitable for the TBMD role.
The GaN semiconductor technology used in the five new GIRAFFE options allows for a much higher output level, providing the radars with a longer range and a capability to detect and track very small objects in the air over distances of over 100 kilometres. Each of the five radars will be relatively cheap to operate and potentially capable of operating in a dense, complex Electronic Countermeasures (ECM) environment and under the harshest climatic conditions. Compared to gallium arsenide (GaAs), which is not wideband and robust enough, GaN is extremely useful for detecting very small airborne targets, including RAM targets, and offers a larger bandwidth, according to Saab. GaN offers smaller chip sizes (12sqmm) when compared to GaAs whose chip size is usually greater than 15 square millimetres. Three of the radars, operating in the S-band, address advanced applications in medium- to long-range air defence and air surveillance applications.
The demand for 3D AESA radars will continue to grow worldwide. Developments in airborne AESA technology are likely to include the creation of so-called smart skins, i.e. integration of new-generation TRMs into the platform’s fuselage, allowing for a larger number of antenna elements.
Dr. Sue Robertson
