Electronic Warfare
JSF EW capabilities – sensor fusion the key.
Byline: Frederick Haddock

As is now common knowledge, the F-35 JSF is still fighting its critics on numerous fronts and in the process it has collected many supporters and many detractors across the world, with Australia represented in both camps. In mid-March, Lockheed Martin representatives were given a comprehensive grilling by the Joint Parliamentary Committee on Foreign Affairs, Defence and Trade.
As we write it would be difficult to decide whether the optimists or pessimists will be proven correct, but it is noteworthy to report that most recently in December, Japan has opted to join a growing list to buy the aircraft to replace its ageing fleet. This came after a comprehensive evaluation in a competition against the Super Hornet and the Eurofighter.
It is interesting to record that the JSF is now in its 11th year of development – not including the industry competition period that included the production of two flying prototypes. Yet, the list of defects arising from the developmental testing program is growing rather than diminishing and Lockheed Martin is taking a financial “bath”. No one appears to be willing to make a reliable forecast on availability of a fully qualified aircraft or its final price, though recently Lockheed Martin representatives expressed confidence in a long-term figure of approximately US $75 million per aircraft in 2011 dollars.
Furthermore, there does not appear to be a spiral evolution program in motion – which is a bit surprising for this huge international program, even accepting that the maturity of aircraft is still some way off. Some critics continue to argue that the programme is destined to fail – and certainly there will be tough times ahead if later this year further dramatic cuts to US defence spending are triggered by a Congressional failure to agree on deficit reduction measures.
Meanwhile, the US DoD is funding the further development of the F-22 and an Unmanned Combat Air Vehicle (UCAV) aircraft to the Technology Development stage – eliminate the pilot and the game is altogether different.
A major issue is that technology is not waiting for the JSF. Development of military technology continues at a pace that Industry and the US DOD can afford and it might be said that the JSF is missing – or has missed the technology “boat” – in a number of cases. There are quite a few technology carry- overs as well as a number of new systems.
So when we look at the capabilities of the EW suite in the JSF, we have to ask ourselves “which generation and which environment?”
Although the world is awash with EW systems that are tailored to meet a very complex range of threat environments and the performance of the aircraft that carry them, the EW suite on the JSF appears to be standard for all users. All customers get what the USAF/ USN/ USGC determine.
The JSF is described as a fifth generation multi-mission aircraft with air combat and ground attack roles. It is equipped with both active (RF) and passive (E-O) self-defence systems designed to counter air-launched and ground-launched weapons that use these techniques.
One- on- one air-air warfare is relatively unlikely today compared to the air – ground warfare environment. All other things being equal, success in the air will go to the aircraft that has the highest speed, longest range, most capable radar and longest-ranges weapons. But today, low observability (stealth) to reduce detectability of an aircraft in defensive and attacking roles has come into the superiority equation and has become a frequent factor in military aircraft design.
Additionally, if a defending force has the benefit of superior AEW&C assets that could make a significant difference. These contribute to the depth and capability of a networked force and therefore can provide early warning of an approaching hostile force before it is in position to do damage. This means the balance of power may change significantly, providing the attacking force is not very stealthy. The fact is that today’s military aircraft are an element of a much larger force structure and need to be considered in that context.
In the case of air-to-ground warfare the re-development of the WW11 concept of a layered ground-based air defence system has emerged, but with infinitely more capability than the original approach. New Integrated Air Defence (IAD) systems typically use networked C3 nodes with multiple radars and weapons that may be widely dispersed to provide both spread and depth. For an attacking airforce , success against an IAD requires the capability to rapidly launch a number of long range (>100km) homing weapons that saturate it , and the ability to leave the zone very quickly. On the other side of the coin most modern IADs have the considerable advantage of mobile elements, rather than being in a fixed and known location. This gives them a “shoot and scoot” capability that promotes confusion in an attacking force without necessarily disrupting integrated defence operations.
IADs are likely to operate a number of different radar and weapon systems, to cover all aspects of possible engagements, with deployment of both short range weapons, using EO homing, and long range weapons using radar mid-course guidance and EO terminal homing. An additional feature of IADs is that they often deploy long-range high power jammers to make engagement more difficult.
In these environments an attacking aircraft needs a full quiver of RF and EO self-defence systems to cope with air and ground-launched weapons. In addition the critically important features of an enveloping all-attitude, very low- observable (stealth) capability, high manoeuvrability, and supersonic dash need to be present. The JSF does not appear to have a full measure of these capabilities with known “holes” in its stealth envelope, a quite short tactical range and a single large engine, compared with the supersonic, high stealth level performance of the twin-engined F-22A.
This paper describes publicly available information on the currently known EW sensors and system capabilities of the F-35.
Integrated Avionics Suite (IAS)
On paper the F-35 appears to have the most comprehensive avionics suite that is available today for an aircraft of its class. The principal components are the APG-81 multi-function Active Electronically Scanned Array (AESA) radar, and three EW systems. These are the AAQ-37 Distributed Aperture System (DAS), the Electro Optical Targeting System (EOTS) and the ASQ-AAQ-37 Integrated Defensive Avionics Suite (RWR).
Of the above systems the radar is by far the most complex as, in addition to providing a very diverse set of ”radar functions”, it provides a significant EW jamming function – as well an RF data link (Multifunction Advanced Data Link (MADL). MADL is an ultra high bandwidth data link provided by selected directed radar beams enabling target and other situational awareness data to be shared with own-force assets, without compromising the source platform’s low observability.
The F-35’s electronic warfare systems are intended to first detect hostile aircraft using sensors operating in the RF spectrum, which can then be scanned with the electro-optical system. This enables the optimised detection and identification, followed by engagement or evasion of the target. This capability is achieved using full sensor data fusion provided by the IAS function.
IA Suite architecture
All major components of the aircraft’s IAS are functionally integrated using multiple COTS Freescale Power PC processors, Integrity DO-178B RTOS and a discrete industry standard open architecture network. The pilot is connected into this system by an HMDS to facilitate target selection and tracking and a cockpit-mounted colour MFD to facilitate weapon selection. All software is written using C++. The amount of code being developed steadily increases and, reportedly, by the time it is all qualified is likely to exceed estimates of 8.6 million lines, resulting in the familiar method of successive Block releases.
The above architecture facilitates real time sharing of data between systems connected to the IAS allowing contribution to Situational Awareness, Command and Control and Network-Centric Warfare.
Such a configuration is colloquially referred to as an “OODA (Observe, Orient, Decide, Act) loop” capability where stealth and advanced sensors aid in Observation (while being difficult to Observe), automated target tracking helps in Orientation, sensor fusion simplifies Decision making, and the system controls allow the pilot to maintain his focus on targets and act on them rather than focussing on his aircraft controls.
Individual sensors
APG-81 AESA radar
This 5th Generation multi-role all solid state Active Electronically Scanned Array (AESA) provides the main air-air and air-ground sensor and weapon engagement capability of the F-35. It is a frequency agile, scanning radar that provides an exceptional range of capabilities including Air-Air multiple target detection and fire control (cloned from the F-22 APG -77 radar ), air-to- ground modes, including and ground tracking (SAR and ISAR) high resolution mapping, multiple ground moving target detection and track.
On 22 June 2010 the Project Office said: “The radar met and exceeded its performance objectives successfully tracking long-range targets as part of the first mission systems test flights of the F-35 Lightning II BF-4 (Development) aircraft”
The radar also provides electronic warfare functions (RWR and RF Jammer) and the RF elements of the Multifunction Advanced Data Link (MADL) – that is an ultra high bandwidth data link. This provides communications between own force assets to allow development and sharing of situational awareness data and networked force operations.
The radar is a successor to the F-22’s AN/APG-77 and includes selected features of it. Conversely, the APG-77v1, the current radar for the F-22A, uses APG-81 hardware and software features for its advanced air-to-ground capabilities that were a more recent addition to that aircraft.
From the EW perspective the APG-81 provides the following capabilities:
• A steerable, precisely focussed, jamming signal that can be transmitted to any point in space within the radar’s field of regard (FOR). The duration of the jamming signal is selectable and it is frequency agile.
• Detecting and locating in-band RF radiations from a remote source that is contained within the radar’s FOR to provide an EW RWR capability.
Similarly, AESA radars are inherently jam resistant as these types are able to change operating frequency with every pulse, and spread the frequencies across a wide band even in a single pulse. Although jammers are available that generate broadband white noise covering the entire operating frequency of a radar, AESAs can be selected to operate on a receive-only basis to locate the jamming transmission.
Electro-Optical Targeting System (EOTS)
This multi-functional day/night sensor has been developed by Lockheed Martin to provide a precision air-to-air and air-to-surface targeting capability. EOTS is integrated in the IAS with the EW RF sensors. Based on proven Sniper XR technology, the EOTS sensors are installed on a stabilised, steerable platform, which is carried internally and pointing forward under the aircraft’s nose.
EOTS comprises a third generation FLIR camera, a laser, and a CCD-TV camera. The system provides target detection and identification at greatly increased stand-off ranges, high resolution imagery, automatic tracking, infrared search and track (IRST), laser designation and range finding, and laser spot tracking.
The EOTS is fully integrated with the IAS using a fibre optic interface and is designed to compliment the operation of the Northrop Grumman DAS, described below.

AN/AAQ-37 Distributed Aperture System (DAS)
DAS is an electro-optical warning system that is optimised to detect, track and process video of multiple missile launches and their in-flight tracks and approach track to the pilot. The system comprises an array of six wide field- of -view mid-wave IR sensors that are distributed around the fuselage. Collectively they provide a spherical field of regard of the surrounding airspace, allowing the pilot to “see” through the fuselage. Each sensor operates independently and continuously. Video imagery from all sensors is fused simultaneously to provide a continuous, seamless picture , analogous to the aircraft being in the centre of a bubble. The system displays EO countermeasures deployment, passive air-to-air radar, off-axis targeting for air-to-air missiles, and wide field-of-view day/night pilot vision including imagery of other own force aircraft. With off-axis targeting the pilot can assign a target of interest to the HMDS, point his head to the intended target, designate and shoot.
AN/ASQ-239 (Barracuda) Electronic Warfare System.
The AN/ASQ-239 Barracuda is based on the F-22 Raptor’s AN/ALR-94 suite, but is reportedly many times more sensitive than previous generations of RWR. The ten sets of RF antennae are distributed on the both wing leading and trailing edges and rear edges of the horizontal tail surfaces of the aircraft to collectively provide forward and aft Band 2,3,4 coverage. These locations provide excellent, almost spherical, spatial coverage allowing detection and geolocation of threats. Public data about this system is limited.
On paper the EW suite appears to be a good match for the overall performance of the aircraft. Sensor fusion and data sharing within the IAS and offboard to another asset is smart and undoubtedly will reduce the pilot’s workload and improve the effectiveness of the aircraft’s combat capability. The architecture of the EW suite lends itself to evolution, weight permitting. Notably, it appears that the aircraft does not have a decoy capability, such as a towed RF/EO decoy (FOTID) or flares.




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