Gripen Sensors Claim Counter-Stealth Performance
By Bill Sweetman
Source: Aviation Week & Space Technology
March 17, 2014
Credit: Saab
New sensors being developed for the JAS 39E and close to starting flight tests on the JAS 39-7 Gripen Demo testbed will be able to detect low-radar-cross-section (RCS) targets, and will provide the pilots in a Gripen formation with a new level of situational awareness, according to Bob Mason, Selex-ES marketing director for advanced sensors.
The JAS 39E will have three Selex-ES sensors. The Raven ES-05 active, electronically scanned array radar (AESA), developed by the company's Edinburgh unit, will be the first production AESA to be mounted on a “repositioner,” a rotating mount that gives the radar a ±100-deg. field of view around the nose. The Skyward-G infrared search and track (IRST) system (from Nebbiano, Italy) is based on experience with the Eurofighter Typhoon's Pirate IRST and Selex-developed land- and sea-based IRSTs. The fighter also has a new identification friend-or-foe (IFF) system with three electronically steerable antenna arrays, which matches the radar's range and field of view.
The three main sensors will cue one another automatically to display to pilots a fused picture of airspace around the fighter; it will also be fused with the JAS's new electronic-warfare system. Finally, sensor data can be shared between Gripens in a flight via data link.
The IRST is capable of detecting low-RCS targets at distances compatible with a beyond-visual-range missile launch, Mason says. “We have seen them,” he responds when asked if Selex IRSTs have tracked low-RCS targets. “We are looking at very small delta-Ts [temperature differences between the target and the background]. Some infrared absorbent paints cause more friction than standard surfaces, and that causes kinetic heating that the IRST will pick up.” Skyward-G does not depend on a supersonic target—“skin heating at 300-400 knots is significant”—and detects heat radiating through the aircraft's skin from the engine, as well as skin friction and the exhaust plume.
The IRST uses a long-wave focal plane array sensor (a dual-band system, adding mid-wave capability, is a potential upgrade) with three fields of view. In its long-range search mode, the system is an IR telescope with a fast-moving scanning mirror (located in a transparent dome in front of the windshield) and “step-scans” through its search sector. It also has a single-target track mode, and in wide-field mode it provides a night-vision image on the head-up display. As a passive system, IRST does not have inherent range data, but it can perform “kinetic ranging”—the aircraft performs a weaving maneuver and the range is determined by the change in azimuth angle to the target—or the IRSTs on two aircraft can triangulate the target over the TAU-Link.
IRST hardware—the optics, detector and processor—has been improved since the development of Pirate started, but (according to Mason and other industry sources) the most important change has been the development of algorithms, based on operational experience and the analysis of real-world imagery, that look at IR signatures in detail, including variations of color and brightness within the target, in order to filter out false alarms caused by everything from birds to barbecue grills.
The IRST can give the radar a very accurate azimuth and elevation to the target, which allows it to focus its energy and increase the probability of achieving detection and track on a low-RCS target, Mason says. The AESA provides virtually instantaneous beam-steering within its ±70-deg. scan, but the repositioner is slower. One concept to be demonstrated will be the use of two Gripen radars and the TAU-Link to provide a wide-angle picture to both targets.
The new IFF is designed to provide low-latency coverage over the radar's entire field of view and to its maximum range, and is independent of the radar. That approach has been selected to furnish the best possible information on cooperating targets (such as friendlies and commercial traffic), allowing the IRST and radar to concentrate on potentially hostile aircraft.
Selex-ES is now delivering what it calls “C-model” sensors to Saab for installation on the Demo and the three JAS 39E development aircraft. These units are built to production standards, Mason says, but have not undergone the full range of tests required for full qualification. The C-Model IRST is expected to fly on the Demo imminently, the radar is being delivered to Linkoping and the IFF will arrive later in the year. c
