BriteCloud is a new-generation anti-missile countermeasure developed in the UK (Picture: Leonardo).
By David Hambling, technology expert
The RAF is now testing BriteCloud, a new type of decoy to give Typhoon fighters improved protection against radar-guided missiles.
Such missiles are the greatest threat to fast jets, a point underlined by the shooting down of a US drone by an Iranian surface-to-air radar-guided missile last month.
The RAF claims the distinction of fielding the very first anti-radar countermeasures during the Second World War. Even as British boffins were developing ‘Home Chain,’ the radar system that was to provide vital early warning in the Battle of Britain, they realised how such radar might be countered.
Radar works by reflecting a beam of radio waves from an aircraft, like a searchlight illuminating a target.
If the target emits the right radio signal, it can blind the radar by drowning out the radar return with a stronger signal on the same frequency. This is possible because only a tiny fraction of the radar signal is reflected back.
The radar may be putting out tens of kilowatts, but only a fraction of a watt is reflected back, so a low-power jammer can out-shout a powerful radar.
When the Germans developed their own early warning radar, the RAF was ready with Mandrel, a jammer developed by the Telecommunications Research Establishment (TRE) and fielded in 1942.
Mandrel could only jam radio of one frequency and the Germans employed several different types of radar, so eventually, one RAF bomber would have to carry eight different Mandrels tuned to different frequencies. Over 30,000 Mandrel sets were built during the war.
The TRE also invented ‘chaff’, bundles of metallic strips which formed the radar equivalent of a smoke screen.
The original chaff was made of coarse black paper with metallic foil glued to it, cut into strips exactly 27 centimetres long, corresponding to the wavelength of the German WurzBurg ground-based radar.
Pathfinder bombers going ahead of the main force dropped a bundle of over 2,000 strips each minute, timed with a stopwatch. The bundles were dropped via chutes normally used for the illuminating flares which guided bomber formations.
Such countermeasures work because a strip of metal of the right length will resonate like a radio aerial and produces a powerful reflection. A few such strips will produce more of a radar return than a bomber, and a cloud of them show up as a gigantic blob on radar screens, screening any actual aircraft.
The first use of chaff was during a night raid on Hamburg in 1943 and was spectacularly successful. German night fighters failed to locate the bombers, radar-guided anti-aircraft guns fired at random and radar-guided searchlights were useless.
Since then, chaff dispensers have become standard kit; rather than having dedicated chaff-dropping planes, everyone carries their own chaff for self-defence. Similarly, many aircraft carry their own jammers.
However, the attackers have also become more sophisticated. The jammer itself is effectively a bright radio beacon and modern anti-aircraft missiles have a ‘home on jam’ function: they stop trying to look for radar reflections, and home in on the source of the jamming. Instead of protecting the aircraft, the jammer actually leads the missile to it.
This is especially an issue for stealth aircraft like the F-35 which keep their radio emissions to a minimum to remain effectively invisible.
The new BriteCloud is known as an Expendable Active Decoy. Made by Leonardo Aerospace in Luton, Bedfordshire, it is an ingenious way of fooling home-on-jam, and the latest in a series of such devices developed by the company.
It is a small device about the size of a soft drinks can which fits into the dispensers normally used to drop chaff.
BriteCloud is ejected when an incoming missile is detected. On release, small aerofoil wings pop out of BriteCloud and it starts gliding away from the launch aircraft.
As it does so, its electronics package – what the makers call a Digital Radio Frequency Memory jammer - detects the frequency of the radar, and it broadcasts a strong jamming signal on the same frequency. So, unlike the Mandrel, the same jammer will work against all sorts of different radar.
The jammer means that the missile can no longer see the target aircraft. It can see the BriteCloud though, and will home in on the jamming signal. As it does so, the launch aircraft slips away unscathed.
BriteCloud is completely self-contained and can be deployed rapidly. The fast launch means that it can be well away from the launch aircraft as soon as possible, creating a large ‘miss distance’ between the missile and the aircraft. It is effective against both surface-to-air missiles and air-to-air missiles.
The current tests in which RAF Typhoons dispense BriteCloud rounds against a series of simulated battlefield threats are intended to demonstrate that they can be launched safely from the Typhoon as well as confirming their effectiveness.
Further tests are planned from helicopters and the C-130 Hercules transport aircraft. The Ministry of Defence says that if the trials are successful, the decoy will be available for deployment by the end of the year.