Anti-drone systems and transponders for drones

After the events at Gatwick Airport, where repeated drone sightings led to a massive loss of flights for almost 32 hours, there is one apparent and urgent question: How can such a massive disruption caused by a drone be prevented in the future?

There is already a clear legislation that it is illegal to fly a drone close to an airport – but how can it be enforced? There are different approaches and ideas on how to fight back against illegal drone flights.

In contrast to large passenger aircraft, drones do not carry transponders on board that actively transmit their position and are visible to air traffic control. Initial efforts are being made to integrate civilian drones into air traffic control, for example the “Unmanned Aerial Traffic Management” (UTM)-System from Airmap, which is currently being implemented in Switzerland. However, most of these systems are not based on transponders, but on the registration of the drones via the app and the transmission of the position based on the GPS signal and thus require the cooperation of the drones pilot – the system cannot actively prevent sabotage or terrorism.

Transponder for drones

The obligatory introduction of a transponder for drones is also frequently discussed in industry. One conceivable option is ADS-B transponders that can be retrieved from the ground (for example from air traffic control or the police) using appropriate devices. Alternatively, a transponder could also be permanently online and actively transmit its position to the Internet. The problem with all transponder solutions: For drone manufacturers to be able to integrate an appropriate system into all their models, the legislation would have to be based on a single technical implementation – ideally worldwide. In addition, it would still be relatively easy to bypass the system with a toy drone or a do-it-yourself drone without a transponder – the hurdle for unruly drone pilots would merely be raised, but it is not impossible to circumvent this requirement.

Passive detection of drones

In principle, the airport radar would be technically capable of making a drone visible. In practice, however, small objects are deliberately filtered out, because otherwise each and every bird would be visible on the screen and too much information would be poured into the controllers. In order to depict small objects such as drones sensibly, a much finer resolution or a different scale on the screens would be necessary than is used today.

There are some systems that work stand-alone and can be used locally. The company Dedrone sells a “Drone-Tracker” that uses cameras, sound and ultrasonic sensors, and a WLAN sensor to detect drones. With the WLAN sensor also the MAC addresses of the devices can be read, whereby certain drone models can be identified. WLAN signals can be detected up to 300 meters.  For an extra charge, it is also possible to integrate an RF sensor to detect the drone’s remote control signals and radar data.

An alternative system that relies more on radar data is the SharpEyeâ„¢ by Kelvin Hughes Ltd. It consists of one or more mobile radar systems and can also be supplemented with optical cameras. According to the company, the product should also be able to detect drones in bad weather conditions.

Active drone defense systems

In many cases it is not sufficient to notice and identify a drone. In cases of imminent danger and massive disruption at Gatwick Airport, solutions are sought to force the drone to land or to shoot it down. In most countries, it is not permitted to shoot down a drone over private property. Taking a drone violently down is a big risk to anyone on the ground and also has the potential to cause substantial damage, as the drone will crash down uncontrollable.

The police did not shoot down the drone during the disturbance at Gatwick airport. The risk of endangering third parties is high and the probability of a successful hit is considerably lower than you might assume: It may still be possible for experienced shooters to hit a drone from a very short distance. To hit a drone at a distance of 200-300 metres during flight is probably a masterstroke, depending on the size and flight behaviour of the drone.

There are several drones defense systems on the market that promise to catch drones. For example, the Swiss start-up Droptec, that offers a kind of pistol that shoots a 2×2 meter net at the drone. However, the system is only suitable for close range and can retrieve drones from a maximum height of 50 metres from the air.

The “Dropster” crashes a drone. Image source:

The Dutch police is testing to bring down drones with the help of eagles. In cooperation with the company Guard From Above the eagles are trained to catch the drone in mid-flight. Currently, the project is still in the pilot phase.

Image source:

Airbus is working on defence systems with interfering transmitters that are particularly suitable for securing airports, industrial plants and nuclear power plants. The Airbus Counter UAV System consists of various sensors such as radar and infrared cameras and a jamming transmitter and is connected to a database in order to analyse the signals.

The Italian company Selex ES follows a similar approach. Although the company does not disclose any details about the exact functioning of the drone, according to the available information, it is a targeted electronic malfunction of the drone.

All solutions which aim at disturbing or interrupting the radio connection to the drone (so-called “jamming”) are not suitable for continuous use in close proximity of airports: The radio interferences could also disturb the radio connections of airliners.

Boeing, on the other hand, is researching a somewhat more rigorous method: a mobile laser cannon to shoot drones. A laser beam is directed at the drone for a few seconds, setting it on fire and crashing it. The Compact Laser Weapon should be able to detect the drone itself and align the laser beam.

The “Compact Laser Weapon” from Boing for launching drones. Image source: Boing.

However, almost all active defence systems are still in a test phase or are only in use in very specific areas. For the time being, it remains a challenge for airport operators to deal with the threat posed by illegal drone flights.

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