Combatting the growing threat of UAVs

The UK's Civil Aviation Authority (CAA) has responded to the trend with guidance about their use. Noting the wider use of UAVs, the CAA says such aircraft are likely to be operated in a way that may pose a greater risk to the general public.

Accordingly, it is illegal in the UK to fly UAVs over congested areas or near to airports and airfields. They must not be flown within 50m of people nor overhead of groups of people at any height. And commercial activity has to be approved in advance by the CAA. How closely these rules are being observed is open to debate.

But the opportunity exists for UAVs to be used by those with darker motives. In February 2015, UAVs were seen at five locations in Paris – including the US Embassy and the Eiffel Tower – but authorities still have no idea of who was flying them and why. With flights over Paris illegal at altitudes of less than 6000m, these UAVs were flying in a forbidden zone and potentially hostile.

In 2013, a small quadcopter flew within feet of German Chancellor Angela Merkel. While Chancellor Merkel appeared to be amused by the UAV, her security team wasn't and it was pointed out that even a small amount of explosive on the UAV could have been fatal.

So it is no surprise to see that three British technology companies –Blighter Surveillance Systems, Chess Dynamics and Enterprise Control Systems (ECS) – have developed an Anti-UAV Defence System (AUDS). The system, say the partners, has been designed to combat what they see as the growing threat posed by malicious UAVs.

Mark Radford, Blighter's CEO, said: "We formed the AUDS team in 2014 as we were each acutely aware of the urgent operational requirement from our customers for an effective and affordable anti UAV system.

"Working in partnership, we have developed some clever technology that integrates the different sensors, effector and electro-mechanical positioning systems to disrupt and bring down any malicious drone in a phased and controlled manner."

Dave Morris, business development director with ECS, explained the challenge. "UAVs are becoming an issue, particularly those used by hobbyists, who don't always realise they are causing problems. While there are many responsible users who will stop when they realise what they're doing, there are others who won't."

Morris noted the AUDS system is intended to deal with commercially available UAVs. "We're not looking to deal with military class devices," he continued.

The AUDS systems has two parts: detection, performed using a Doppler radar; and disruption or inhibition, performed using three directional antennas. The disruption part of the system also features electro optical and infra red cameras.

"The radar is a 2D Doppler system from Blighter," Morris said. "It scans through 180° with a 10° or 20° vertical field. It explores azimuth and range, but not elevation.

"Blighter is good at detecting slow moving targets," Morris continued, "and these are the growing issue. Once the target is detected, the data is passed to the camera/disruptor system."

The camera/disruptor system 'nods' up and down until it detects the target, after which it locks on. "The disruption system is targeting the UAV's command and control links," Morris noted, "with the possibility of disrupting its GPS system. Various techniques can be used and the system can inhibit selected channels or all channels at once."

UAVs respond in different ways to interruption of the GPS signal. "Some tend to climb until they regain the signal," Morris explained, "while others will head in a particular direction. Some will turn around and go home because the owner will want them back. If you can force a suspicious UAV to go home, you can track it."

The AUDS system is designed to be operated by one person, but it's likely those using the system will put a commander alongside the operator. "It's important to have an operator in the loop," Morris contended. "The system could also be configured to operate automatically, but we wouldn't recommend that."

Multiple targets could be detected simultaneously and it is here the operator plays an important role. "What's detected by the radar may not be a threat," Morris explained. "It could be a large bird, for example, or a police UAV. When multiple targets are seen, the operator can select which to track."

Because the system is intended to be disruptive, rather than destructive, there is a degree of flexibility available. "You might only want to disrupt channels for a few seconds to see if that has an effect," Morris said. "But the aim is to stop the UAV, make it turn around and go away or bring it down safely somewhere. But the best solution is to make it go home and then to track it."

The AUDS system operates over a reasonably compact area: the Blighter radar has a range of about 8km. "However, the UAVs we're most worried about are quadcopters," Morris said, "and we can detect them at up to 5km.

"Doppler radar requires movement, but Blighter will detect a UAV moving as slowly as 0.2km/hr. Even if the UAV is hovering, Blighter will detect the rotors moving. Command and control links can be disrupted at distances of up to 3km."

Chess Dynamics provides the camera system, while ECS has contributed its knowledge of operating data links and how to exploit their vulnerabilities. "We are all UK based SMEs and experts in our respective fields," Morris pointed out. "We complement each other and, because we don't compete, we make an effective team and our agility has been key."

The AUDS project started in mid 2014, when the issues began to come into focus and potential customers had been identified. "By the end of 2014, we had demonstrated a working system," Morris added.

Peter Williams, ECS' engineering director, outlined the disruption element of the AUDS system. "All the frequencies used in AUDS are standard; we are targeting the most commonly used. For example, the antennas can disrupt GPS communications at 1.3GHz, control transmissions at 2.4GHz and telemetry at 433MHz in Europe and 913MHz in the US. If other bands are being used, we can disrupt those.

"The system is modular when it comes to antennas and customers can select the appropriate antenna and frequency for their needs."

While the AUDS system is targeted, it can't be guaranteed not to affect other systems. "You can't guarantee that," Morris concluded, "it's all about physics, so denying GPS to a UAV will also deny GPS to other systems, which is why GPS is an option. But the system will generally be on and off within 15s."