The Rafale EW suite, known as Spectra, is one of the most powerful systems installed on a fighter aircraft and is intimately associated with the unique approach to stealth and survivability designed into the Rafale. Dassault executives describe the Rafale as discreet rather than being stealthy in the sense of a F-22. To avoid detection, it combines avionics, tactics, and reduced radar reflectivity with some techniques that have not been directly revealed and are apparently unique.
The first element of discretion is that Spectra's receiver system and the FSO help detect and track targets without using radar. Spectra incorporates a radio-frequency (RF) detection system, a missile-approach warning sensor, and a laser-warning system and provides full 360-degrees coverage. The RF detection subsystem uses prominent square-section antennas, mounted on the lower corners of the engine inlets and in the rear of the fin-top pod, covering 120 degrees each. The receiver antennas use interferometric techniques to measure a signal's angle of arrival within less than 1 degree and are designed so that they do not have a large radar-cross-section (RCS) contribution.
The Rafale is also designed to use terrain masking, particularly at night or in bad, weather when visually cued short-range surface-to-air weapons are less effective. With its maneuverability and a high degree of cockpit automation, the fighter is designed to fly a terrain-avoidance/threat- avoidance profile at 5.5 g and 100 feet in altitude. The RBE2 and a terrain-referenced navigation system, using stored terrain data, are used to provide redundant flight guidance.
Rafale makes extensive use of radar-absorbent material (RAM) in the form of paints and other materials, Dassault engineers have said. RAM forms a saw-toothed pattern on the wing and canard trailing edges, for instance. The aircraft is designed to so that its untreated radar signature is concentrated in a few strong "spikes," which are then suppressed by the selective use of RAM.
Spectra's active jamming subsystem uses phased-array antennas located at the roots of the canards. Dassault has stated that the EW transmit antennas can produce a pencil beam compatible with the accuracy of the receiver system, concentrating power on the threat while minimizing the chances of detection.
But there is more to Spectra than conventional jamming. Pierre-Yves Chaltiel, a Thales engineer on the Spectra program, remarked in a 1997 interview that Spectra uses "stealthy jamming modes that not only have a saturating effect, but make the aircraft invisible... There are some very specific techniques to obtain the signature of a real LO [low-observable] aircraft." When asked if he was talking about active cancellation, Chaltiel declined to answer.
Earlier this year, Thales and European missile-builder MBDA disclosed that they were working on active-cancellation technology for cruise missiles and had already tested it on a small unmanned aerial vehicle, using a combination of active and passive techniques to manage radar signature. This revelation makes it considerably more likely that active cancellation is already being developed for Rafale.
Active cancellation is a LO technique in which the aircraft, when painted by a radar, transmits a signal which mimics the echo that the radar will receive - but one half-wavelength out of phase, so that the radar sees no return at all. The advantage of this technique is that it uses very low power, compared with conventional EW, and provides no clues to the aircraft's presence; the challenge is that it requires very fast processing and that poorly executed active cancellation could make the target more rather than less visible.
The complexity of active cancellation could account for Spectra's high price tag, estimated in 1997 as "several billion francs" (equivalent to the high hundreds of millions of US dollars) for research and development. One of four Rafale prototypes was dedicated to Spectra tests, along with a Falcon 20 flying testbed. Four new large anechoic chambers were built to support the Spectra project, including one which is large and well equipped enough to operate the complete system in a fully detailed electromagnetic environment.
Spectra's RF systems are backed up by a laser-warning system, an optical missile-launch-warning system, and a full range of expendable countermeasures. There is no towed decoy system.