Countering Drones with Drones – CUAS using cUAVs

This article is work in progress.

Introduction

In 2013, when DJI launched its first drone, the “Phantom 1”, many people from the general public, for the first time, were able to see an actual drone in real life and up close. I remember that when I did my first test flights of my DIY drone people who were just passing by took the time and stopped to watch me sending my noisy quadcopter up into the sky. Some were even asking if that device was a “drone”, because they have never seen one in real life.
Until then, it was the hobbyists who built them for racing, the students and researchers who explored new ways or the military that spent billions to create these heavy-lifting and remotely controllable machines.

11 years later in the year 2024, everyone knows about drones. Most people have seen them flying and some might even be able to recognize one that is hovering 100m above them by the buzzing sound-signature they still create. Although you can still hear them, they have become much quieter over the years. However, what evolved the most is their electronics and software. They now carry cameras with massive 1″ sensors, optics with multiple zoom factors, night vision and have the ability to operate almost fully autonomously. The electronics have gotten much cheaper and more integrated, up to the point where a 500€ drone that only weighs 250g and that is slightly bigger than the size of your hand can produce actual good 4k video.

Motivation

While this is all great and fascinating it’s not just the good guys that took a closer look at what these little devices can do for their cause. Every major public event must nowadays have a security concept on how to counter unwanted UAVs in the sky. Airports struggle to monitor the airspace for these little devices and to keep the area free of them. Cartels and other criminal organisations seek and find new ways of smuggling their goods undetected across borders, all without having to risk their men thanks to the autonomous features of UAVs. Military bases no matter where have to protect themselves from attacks and espionage. Likewise, drones of all sizes have secured their place in modern conflicts. Countless articles on the internet investigate the impact these drones have on the conflict that emerged because of the Russian invasion of Ukraine.

As a consequence militaries from all over the world have taken notes and are thinking about ways how to integrate these new systems into their arsenal. However, more importantly, they are thinking about ways how to protect their assets from this newly emerged threat. In 2024, all it takes to disable a vehicle with a multimillion-dollar price tag is a 500-1000€ drone. No direct line of sight is required. Till recently the focus was on getting very few but also very sophisticated drones that could stay airborne for hours and monitor the area. The problem with these systems is, they only are effective once one has air superiority. From their looks and behaviour, they resemble past and existing threads, so there are also countermeasures available to deal with them. This makes them a relatively easy target. Just look at the career of the Turkish Bayaktar. While low-cost UAVs monitor the movements on the frontline 24/7, the Bayaktar mainly gets deployed in airspace that is under friendly control with only little threads to the system.

In 2024 it’s the small, unmanned and affordable drone platform that makes the most impact. It’s because the technological advances in the past years have allowed even these small systems to have reasonable practical use. Even more importantly since it is a completely new development: There is currently no way of properly defending against these kinds of systems.

These small handheld drones can spot enemy activity within seconds and identify & locate enemy assets very quickly and with high precision.
The Iranian drone “Shahed” might not be the most effective system in use, but with a price tag of an estimated 20.000-30.000 USD per unit, they are very effective in keeping far more expensive air defence systems busy. More importantly, thanks to their range and relatively small size, they may appear anywhere in big numbers and the air defence must be designed rather dense to spot and counter them.

What to expect

Let’s take a quick look at what types of UAVs we are dealing with and how they will evolve according to their role within the next few years.

FPV-Dones

  • Guerilla and terrorists will keep using today’s versions that are cheap, low-tech and based on consumer hardware
  • Improved versions that do not require an FPV data link up to the impact but get a picture of the target and will do the final approach on their own based on object tracking.
  • Swarm capable versions
  • More or less a tool like artillery, anti-tank rockets and mortar
  • Will continue to require a spotter, ideally in the sky

Reconnaissance

  • One of the pillars of modern battlefield intelligence
  • Short Range MAVIC Mini Style: silent, small, light, good optics, used per squad basis, cheap, shorter flight time (<1h), vertical take-off
  • Medium Range: thermal and better optics, higher endurance, still cheap, operated and launched by local command, direct fire support of local troops, relay of information to them.
  • Long Range, endurance, higher altitude, low radar cross-section & good optics, for long-range weapon systems

Offensive

  • Bayraktar and other type of gunships, Loitering UAVs, Shahed, Improvised versions (long range autonomous FPV), Lancet
  • The bigger they are, the more offensive firepower they have
  • Alternative to traditional anti-tank systems when the enemy is still far away
  • Underwater Mini-Submarines and UA like speedboats, underwater cruise missiles

While offensive UAVs and FPV drones will continue to gain importance, it will be the reconnaissance UAVs that will have the biggest impact. You can only target what you are aware of and reconnaissance UAVs make it easier than ever to setup a dense 24/7 surveillance system.
Furthermore, most drones will not use jet engines because they shall remain affordable and easy to use. This means their cruising speed will remain rather low.

Existing ways of countering UAVs

  • Jamming GNSS & Data
  • Nets & Cages
  • Air-Burst ammunition with stationary or mobile platforms
  • Lasers
  • Traditional MANPADS and short-range ground-to-air missile systems

Jamming GNSS & Datalinks will continue to work on consumer drones and “low-tech” improvised DIY drones. It is the cheapest way to ensure a small perimeter remains clear and requires minimal effort. It can be used for civil and military purposes.
The problem with jammers is that they jam everyone (you are also jamming yourself) and they are limited to a particular frequency band. While the frequency band for GNSS will not change so quickly, other applications might switch to a free band automatically when they detect interference. Some jammers might be able to jam a specific protocol in the future but those will be expensive. More expensive and sophisticated jammers are directional and only jam a frequency band in a defined direction.
GNSS antennas of UAVs can be designed to be less prone to jamming. Ultimately autonomous features can render any form of jamming completely obsolete. While jamming makes it harder to operate UAVs, it can never guarantee full protection because it can not physically stop the UAV from approaching.

Nets & Cages are only effective in a few use cases. One of them might be protecting stadiums from rogue drones trying to fly to the inside via the hole in the roof. Police might continue to use them for catching low-flying drones and to bring them to the ground with a small parachute so that any surrounding people are not harmed. In most other cases they will simply not work.

Air-Burst ammunition has proven to be very effective against the Shahed drones. The German anti-aircraft tank “Gepard” works wonders in that regard. It detects the drones using its own radar and only requires a few shots to take them down. While such platforms themselves are on the more expensive side, the cost per shot is quite low. Such systems are great for defending corridors, bases or mobile high-value assets. They can only be used in a military context. Besides the initial cost, the firing rate and range are the limiting factors.

The newest tool on the horizon is the high-power laser weapons. Militaries have been experimenting with them for a few years now. They are very much comparable to air-burst ammunition when it comes to their use against drones. However, their initial cost is much higher while the cost per shot can almost be neglected. Because of the cost and size laser weapons, even in the years to come, will not be in use in great numbers. These systems also have to prove their effectiveness first. Ceramic tiles (think of the heatshield on the Space Shuttle) or reflective coatings might render lasers useless because it takes too long to burn through the outer shell. This may be a critical disadvantage in the case of an attacking drone swarm. Since the laser must be focused on a very small spot many kilometres away I’d imagine that it is most effective against targets with a predictable flight path.
Just like air-bursting ammunition, the military will be the sole customer for lasers.

In the military, MANPADS do a great job defending against areal threads. While their range is very limited, they can be deployed directly at the frontline keeping enemy units at a distance. All MANPADS are currently designed to be used against rather big, fast or hot targets. They often incorporate a heat seeker to track the target or require a visual line of sight for the duration of flight. Their initial cost is almost equal to the cost per shot and compared with other air defence systems they do not cost as much. However, they might only be used against more valuable targets of a certain size.

As a reaction to the thread that drones like the “Lancet” pose against tanks and other mobile equipment, companies like MBDA & Diehl started adapting their newest platforms trying to provide an answer. With their quick reaction time and lower price point, they will do a good job defending bases against drone swarms and equipment in the field against guided or autonomous drones. Since these systems will be more expensive, they can be considered the premium defence solution. Their use will be limited to protecting high-value assets like tanks or bases against strikes. They are not economically for use against far cheaper reconnaissance UAVs that can be produced in far greater numbers.

Drones to counter Drones!

So what to do? What kind of ground-to-air system could make a valuable addition to future air defence and law enforcement?
You might have guessed it already: How about drones against drones?

A counter-drone (CUAV) comes in roughly at around the same price tag as the UAVs we are trying to defend against. cUAVs must not be as fast as missiles, since reconnaissance drones pose no immanent threat and even offensive drones will remain rather slow compared to state-of-the-art rocket-propelled weapon systems. This is good news because it means that the electronics can be slower and thus cheaper. Latest innovations in the area of millimeter wave- and automotive radar allow the detection and localisation of small objects from hundreds of meters away. Artificial Intelligence improves detection and tracing even more. It can be applied to camera, radio or radar vision-based systems.

A possible future cUAV system would not look much different compared to today’s air defence solutions.

  • Detection of incoming UAVs using signal intelligence, millimeter wave radar or decentralized mobile (man-portable) tracking systems
  • Mobile (man-portable) or stationary launch platforms for the counter-UAV
  • The counter UAV itself, capable of quickly intercepting the target

The long-range detection system like a radar is used to detect and track any possible threats as early as possible. Commercial UAVs can be localized using their broadcasted DroneID or by analyzing the radio traffic. Such systems already exist and have proven effective.
As an alternative, a decentralized spotting and tracking system could be implemented. Police units or soldiers on the ground could point a mobile tracking device at the UAV. The tracking device will determine the rough geolocation of the UAV based on the position of the tracker, tracking angle, distance to the UAV and other parameters. Multiple trackers pointing at the UAV from different angles would improve the localisation accuracy. Such trackers can be expected to be the size of a bottle. While radar and signal intelligence will be struggling in urban environments with high-rise buildings and lots of noise, these mobile trackers could offer an affordable solution to further enhance detection and localisation.

Once the rough location of the rogue UAV is known a counter UAV (cUAV) is launched to catch or intercept it. The geolocation of the rogue UAV is not precise enough to make a direct hit with a cUAV possible. The determined location may be off by 100m. The chances of a miss are very high in that case. Only systems using the DroneID are likely to have good enough tracking of the rogue drone since the DroneID generally contains the exact GPS position of the drone.
For all other tracking systems, the cUAV needs to conduct some detection and tracking on its own to directly hit its target. The idea is that the cUAV gets launched in the direction of the UAV to intercept. When the cUAV comes close to the expected position of its target, it switches to a self-guided mode where it searches for the target using its sensors. This is not a new idea. Missiles for example have used “active radar homing” for a very long time.
Modern automotive radars are very capable, compact and comparably cheap. These chips could be used to build an affordable radar homing for cUAVs. Alternatively, cameras and object-tracking algorithms have come a long way and could be used instead. Another idea is to detect and lock onto the radio emissions of the rogue drone. No matter the design and use case of a UAV, it always uses a radio link to relay its information back to the ground. Without it drones and especially reconnaissance UAVs are totally useless. So-called anti-radiation missiles can detect and home in on radar emissions. The same idea could be implemented with drones. Since cUAVs would fly a lot slower, the electronics used to detect and track emissions can be made a lot cheaper.
Since UAVs are highly agile they can be used in urban environments and in between high-rise buildings. Obstacle avoidance and complex flight paths pose no problem to such systems. 3D maps of the area can be used to determine the perfect interception path.

Finally, when the cUAV has reached its target it can deploy its payload to either destroy or catch the rogue drone. For police, it could be interesting to use a net-throwing mechanism that catches the drone mid-air and a parachute to guide it down to the ground safely. Such net launchers are already tested and seem to work great against flying targets.

How do CUAVs compare

Compared to all other solutions a cUAV can be used by civil and military entities. It is the only solution that can physically remove the rogue drone from the sky while remaining affordable and cost-effective. Such a system can be scaled up and down to fit any need and to cover areas from a few hundred meters to many square kilometres. From stadiums, events and government buildings to borders and conflict areas that stretch many kilometers, cUAVs can be used to protect the skies from small to medium-sized drones.

To be continued …

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