By Christopher Lovers
Let’s examine current AESA defence developments for the maritime environment. How does AESA address persistency, all-weather, night and day capabilities far from shore, and what are the existing SeaPower capability gaps? But firstly what are AESA?
AESA are Active Electronically Scanned Array based radar whose transmit/receive functions are generated from multiple solid-state Transmit-Receive Modules or TRMs. AESAs emit microwaves from many transmitter modules, a big improvement on Passive Electronically Scanned Arrays or PESAs, which couldn’t spread their RF emissions across sufficiently wide-bandwidth. The historic development of AESA architecture is illustrated in figure 1. Passive Electronically Scanned Arrays or PESAs were developed first in the 1960s, followed by introduction of Gallium Arsenide (GaAs) microelectronics, which reduced module size significantly in the 1980s, and followed by development of transmitter MESFETS, creating very small TRMs, for effective maritime applications.
Figure 1: left: PESA architecture, middle: AESA with analogue beam-forming, right: AESA with digital beam-forming.
Why use AESA?
AESA systems are the co-ordinated computer response to a threat environment using multiple TRM modules, able to emit a wide variety of frequencies and patterns, controlled by powerful software algorithms. Radar echoes are analysed with complex computing to provide radar pictures, with additional layers of information. AESA now apply to the military and paramilitary markets- from short to long-range for land, sea, air, and space-based applications, and are ideal for small target detection, tracking, and monitoring. AESA make it easier to spread RF frequencies across wide bandwidths with chirp methods, and without fixed PRF characteristics, making them harder to jam in the littoral environment.
Although Night and Day, All-Weather and Persistency aren’t specifically AESA capabilities, or just a feature of naval maritime operations, it is assumed that AESA enhances persistency, as no single transmitter failure deteriorates overall radar performance significantly, but rather results in what is termed graceful degradation, a slow and generally correctable deterioration in system performance. These factors are deemed significantly important after discussion with some 30 naval and maritime professionals (figure 2).
Figure 2 Night and Day Capabilities, from 30 military and maritime-related AESA questionnaire respondents.
Typical AESA mission purposes are varied and cross boundaries in the maritime environment into roles that have been considered the exclusive domain of air forces, namely: air to air, air-interdiction or surveillance, Ballistic Missile Defence or BMD, missile guidance and control, ground and sea-based air-defence, weapons location, gun-fire support; battlefield, border and coastal surveillance, and counter Unmanned Aircraft Systems (UAS). For air-defence modern AESA typically exceed 1TB per hour data-rates, which are processed in real-time (or near real-time) to generate plots and tracks.
Active Electronically Scanned Arrays enables simultaneous air and sea-surveillance, as well as accurate threat tracking. Recent rapid AESA panel cost reductions has led to much lower cost technologies (GaN, SiGe, RF-on-PCB technologies) being achieved. However, cost reductions are relative, e.g. the October 2014 Navy award of £41M to Raytheon provided 15 AN/APG-79 aircraft radar systems, which are expensive for marine radar systems generally.
How may AESA systems are currently in maritime service? Actually there are many sea-based arrays using Monolithic Microwave Integrated Circuit (MMIC) transmitters including: the Zumwalt-class destroyer or DD(X), SPY-3, and BAE systems SAMPSON. SAMPSON is the Royal Navy’s latest multi-function dual-face AESA radar produced by BAE Systems Maritime. SAMPSON is constructed out of high-carbon steel and is covered with an anti-radar reflecting paint to minimise radar detection.
SAMPSON is the fire control radar component of the Sea Viper naval air defence system, previously designated Principal Anti Air Missile System PAAMS(S) to distinguish it from EMPAR’s Franco-Italian Horizon Class destroyer PESA PAAMS system. SAMPSON’s multi-functional radar is reported to detect all current target types to a distance of 400km, and track hundreds of targets simultaneously. Sea Viper uses detailed target information to assess and command target priorities, and calculate optimum launch time for both missile variants (Aster 15, and 30). A wide-range of airborne MMICs are deployed or are under-development for potential maritime operations, including: F-18, F-22, JSF, F-16, GRIPEN-E, and CAPTOR-E. Some arrays use digital beam-forming such as SMART-L (also found on the Type 45), AMSAR, and SAMPSON.
AESA aviation for potential maritime applications
Saab now offers Gallium Nitride (GaN) and Silicon Carbide (SiC) AESA’s for aviation with the latest exciter/receiver and processors, Gallium Arsenide (GaAs) and Indium Phosphide (InP) low noise amplifiers, and low cost Silicon Germanium (SiGe) TRMs. GaN and SiC provide ten times more power than current GaAs systems (providing a 33:1 bandwidth improvement), which when combined provides coherent combination of 2 radars to achieving +9dB (8 fold) sensitivity increase.
Saab’s Erieye radar was recently installed on the Brasilian Embraer E-99 for maritime surveillance over 500, 000 km2 areas at a cruising altitude of 60000 ft. Sea cover is reported as horizon-limited in the detection of fighter aircraft, helicopters, cruise missiles and jet ski-sized targets. S-band for search operations (2-4GHz) ensures performance in all-weather conditions with air/sea-surveillance, and multi-mission capabilities (figure 3). GlobalEye provides air, maritime, and ground-surveillance with Synthetic Aperture Radar (SAR), identifying objects with Erieye small target capabilities.
Figure 3 Saab 2000 Erieye AEWC (Photo Peter Karlsson).
Saab provides a broad AESA range from variants suited to small patrol ships with just surface surveillance, to ship-augmented UAV air-surveillance delivering E-F NATO air-pictures in real-time with 70o vertical coverage, 360o air-surveillance, and 470km range. At the same time Saab’s Giraffe 1X maritime self-defence AESA radar for surface and air surveillance offers lightweight 3D X-band AESA with over 70o elevation coverage, 60 RPM, a modest 75km platform range, weight under 300kg, and 2.3kW consumption. In 2014 Saab launched its GaN Giraffe series of 3D-AESAs in the X-band (I/J NATO bands), and recently partnered with Ericsson in 5G technology developments (2015).
The USAF aims to improve its B-1 and B-52 bomber fleet performance with AESA to conduct wide-area maritime surveillance and target surface ships. Fitting AN/ASQ-236 Dragon’s Eye, first deployed on the F-15E in Afghanistan (2009), couples long-range and endurance for potent capability in the marine environment. Given Northrop Grumman and Raytheon are key USAF AESA suppliers they will likely both be involved in the acquisition, providing modular architecture for performance enhancements. The F-16s AN/APG-80 all-weather precision targeting offers situational awareness and detection, ultra-high resolution SAR, precision targeting, and long-range detection for air-to-air survivability.
Leonardo is currently contracted to the US Coastguard to provide Seaspray 7500 surveillance radars for the US Coastguard’s HC-130H aircraft. Their AESAs range includes the lightweight airborne surveillance PicoSAR, which provides unrivalled all-weather capability, the Vixen 500E and 1000E, and the RAVEN system which provides fully digitised multi-channel exciter/receivers and processor units. The Seaspray series: 5000E, 7000 and 7500E, is being superseded by the maritime high-performance Osprey series. Seaspray 5000E is the smallest, best-suited to small naval helicopters, and twin maritime surveillance aircraft, or tactical UAVs, whilst PicoSAR is better suited to compact light aircraft and tactical UAVs.
The first Osprey’s E-scan customer is the AW101 Norwegian All Weather Search and Rescue Helicopter fleet (NAWSRH) currently undergoing operational testing. Osprey (figure 4) and developed from previous Vixen, Seaspray and PicoSAR algorithms, providing improvements in processing power and functionality, bringing air-to-air technology into surveillance, and multi-mode missions over land and sea with air-to-air capabilities, into a deceptively small 6kg processor.
Figure 4. Osprey radar, three panel configuration © Leonardo.
Panels are arranged around the airframe to provide full 360o cover, with 3 antennas feeding a central processor capable of managing 4 arrays, like the Arleigh Burke. Such a configuration allows SAR imaging in one region, whilst conducting maritime surveillance elsewhere, and offers search pattern flexibility. Contract delivery will extend until 2020 for 16 helicopters, with option for 6 more. Leonardo has successfully brought low-cost distributed fixed-face AESA technology for maritime applications to fruition.
With its GaAs TRMs, Seaspray has matched marketed cleverly for its price and performance niche. The decision to stay with GaAs rather than adopting more efficient and higher power GaN reflects shrewd product positioning. Companies must look at what the market wants in terms of cost vs. capabilities. GaN may be more efficient and ideal for high power fire-control, but it is a costly technology and generates a large amount of waste heat. GaAs TRMs on the other hand are lower power and cost, and importantly can be air-cooled, ideal if you don’t need GaN efficiency gains. Fixed arrays weigh in at only 11.3kg.
Saab leads the pan-European EuroRADAR Typhoon’s Captor-E radar development with over 1400 TRMs, simultaneous tasking, cued search, search-while-track, weapon support, and high-resolution SAR. The UK is currently committed to full Captor-E Typhoon integration, with 20% more TRMs than other aircraft such as the F/A-18E/Fs and F-35s, and 40% more than Rafale’s RBE2-AA, giving greater range and resolution, as well as 120o cover. With F-16, F/A-18E/F, Gripen-E, and Rafale AESA all marketed at lower cost than the Typhoon, the latter’s selling point of exceptional air-superiority is undermined without addition of Captor-E integration. It is no accident Saudi Arabia recently stipulated Captor-E integration was an essential requirement for further orders to take place.
Figure 5 Typhoon Captor E open nose (photo credit: Saab).
The Royal Navy’s AW 159 Lynx Wildcat Maritime surveillance and attack helicopter, has the Seaspray 7000E fitted, a multi-mode I-band system providing ISAR and SAR, to the upgraded Lynx platform.
Mid-2016 Leonardo was confirmed as the MQ-8C AESA award choice over rival company Telephonics, who famously protested and lost the appeal. The two-panel Osprey, 240 o FOV with long-range and short-range: ISAR, SAR, weather, and air-to-air targeting won a 5.8M$ contract to supply 5-kit radars to NAVAIR with option for 12 more. 40 MQ-8Cs will also receive a maritime search radar fit, ‘Fire Scout’ a rotary-wing UAS providing situational awareness and precision target support for USN on land and sea (figure 6). The new MQ-8C variant, provides double the endurance and triple the MQ-8B payload. Leonardo’s integration of maritime search with increased situational awareness and targeting, wide-area capability and BriteStar II’s electro-optical/IR laser package expands MQ-8Cs surveillance.
Figure 6 MQ8C Fire Scout (photo credit: US Navy, Wikimedia).
The US Triton MQ-4C persistent maritime UAS, (a 360o X-band 2D AESA with maritime, air, and ground modes for long-endurance surveillance, flies at 50000 ft., covering vast oceans), and will provide world-wide coverage (start FY18) with upgrade capabilities planned until 2021 for MTI, weather modes, maritime surface surveillance, ground and stationary target SAR and ISAR for ship platform classification.
Selex Galileo now supplies Italy’s ATR72 Maritime Patrol and 4 Maritime surveillance versions, integrating Seaspray 7300, which will provide persistent surveillance (figure 7).
Figure 7. Seaspray 7500 © Leonardo.
UK’s Sampson multi-function AESA has multiple target search and precision tracking capabilities, weapons control and variable tracking data-rates. S-band enables high search rates in significant clutter environments, whilst GaAs TRMs provides digital phase control, beam-steering of its two 2000+ element arrays for accurate 3D target data, as well as sophisticated anti-jamming capabilities, complemented by the S1850M L-band GEC-Marconi long-range Type 45 search radar or SMART(L).
Thales latest AESA for the Royal Danish Navy is its X-band multi-function APAR successor, with digital beam-forming and GaN amplifiers. Thales SeaMaster400 is a non-rotating 4-faced S-band (E-F) volume search radar for air and surface surveillance, helicopter control, and weapons control, exploiting multi-beam and Doppler processing which shares technologies with other AESA such as Rafale’s combat aircraft RBE2-AA. Selected for France’s ATL2 maritime patrol aircraft, it extends capabilities beyond maritime search and ASW to multi-role, weighing in at 75kg, it is well-suited for UAVs, helicopter, and mission aircraft. Thales is providing upgraded NS200 multi-beam radar for naval platforms using GaN.
Raytheon recently received a $92M Navy contract for the US Ford-class carrier and amphibious warships, based on Raytheon’s current SPY-6 S-band AMDR, with X-band horizon search and 30 times target sensitivity over SPY-1D(V) with GaN (at 34% GaAs costs). Flat panels offer further advantages against rotating systems which wear out, and require less maintenance. Patriot $400M upgrades (2012) make its IT state-of-the-art, and with GaN a fully-digitised 360o coverage 2015.
3, 4 and 6 faced ship systems include: Zumwalt’s 3-faced SPY-3/VSR, 4-faced AEGIS (SPY-1), and Australia’s 6-faced CEAFAR. CEA Technologies provide units for maritime/land environments, target illumination and missile uplink for multiple simultaneous semi-active homing missiles. Recently Kelvin-Hughes revealed plans for its ‘Boxer’ concept to develop an AESA-like ‘Sharp-Eye’ in resolution terms, applying Sharp-Eye context to phased-array technology.
Chinese maritime developments are hard to verify but the UHF JY-26 Skywatch Digital 3D Long Range Air-Surveillance and 800km range Tactical Missile Defence, and the Type 346 array comprising 1524 TRMs on a Luyang II destroyer, is reported as a liquid-cooled system instead of air, suggestive of GaN arrays, and the Type 055 destroyer, under construction, will have 4 AESA for 360o situational awareness, unlike the dual-faced Type 052C destroyer.
Airbus’s TRS-4D (AESA) multi-mode naval C-band radar uses GaN, with advanced high-priority targeting for extended missions, whilst Germany’s F125 frigate, equipped with the TRS-4D, provides benefits only previously seen in expensive systems. Airbus fields the TRS-4D and Spexer ranges, Cobra radar and Eurofighter Captor-E (figure 8), ranging from 40kg (border security) to several tonnes for long-range with 4000+ transmitters, and hundreds of kWs power consumption, and will provide the Freedom LCS variant’s AESA capability.
Figure 8. Captor-E radar on Eurofighter Typhoon Courtesy Leonardo.
Future challenges:
The wish list for future maritime AESA systems is extensive: better sensitivity and range with advanced waveforms, fully digital arrays and multiple beam-forming for greater clutter rejection and interference mitigation. Further integration of RF-technologies with electrical/optical signals on the same chip, digitation of receiver RF-signals closer to the antenna, networking radars to act as one sensor, cognitive radar with resource management, and automatic environmental adaptation in real-time with wider bandwidth.
Many European companies now go a considerable way to filling many of the US capability maritime market gaps, driven by the need for higher power, higher efficiency components and subsystems to deliver customer improvements, and retrofitting to extend platform life-times, e.g. the Typhoon and B52. AESA will provide state-of-the-art radar for future decades, enhancing military, para-military and civil operational benefits. Current solid-state material advances in manufacturing are currently determined by the communications and automotive industry, leading to low-cost technologies, and operational capabilities at an affordable price.
Image Sourced : Saab