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.
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