counter-drone radar

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White Paper

QINETIQ/CF/CM/PUB2100003

Counter-Drone RadarOptimal Characteristics, for Effectiveness and Affordability

January 2021

2 Counter-Drone Radar – Optimal Characteristics for Effectiveness and Affordability - White Paper © QinetiQ Limited 2021QINETIQ PROPRIETARY

Table of Contents11. Introduction 13

12. Fundamental requirements of a Counter-Drone surveillance Radar 13

13. The Radar challenge: detecting small, slow moving objects with Radar 13

14. Currently-available Radar technologies 14

15. Choice of radar frequency and waveform 15

16. Designing a Radar specifically for drone detection 17

17. QinetiQ’s Obsidian Radar: designed specifically for the most demanding 18 counter-drone applications 1

18. QinetiQ’s Radar Heritage 10

10. Summary and conclusions 11

3Counter-Drone Radar – Optimal Characteristics for Effectiveness and Affordability - White Paper© QinetiQ Limited 2021 QINETIQ PROPRIETARY

1. Introduction

Having explored the effectiveness of the most commonly used drone-detection and tracking technologies in our previous paper – ‘Counter-Drone Technologies Evaluation’ – we concluded that Radar is the most effective and reliable ‘primary sensor’ in a counter-drone system. We also concluded that the most effective systems will combine the benefits of a highly-effective Radar, with those of other sensors, such as cameras, or Radio Frequency (RF) direction finding. When used in combination with the right Radar, these additional sensors can help reduce false alarms, overcome environmental challenges and underpin high levels of system automation.

Radars come in many shapes and sizes – each designed and optimised for a specific application and environment. In this document, we explore the characteristics of an ideal counter-drone Radar, based on specific customer and user requirements. This is not an academic study. QinetiQ has translated its research, insight and conclusions into development of its Obsidian counter-drone system, centred on a Radar specifically designed for counter-drone applications around the world.

2. Fundamental requirements of a Counter-Drone surveillance Radar

During 6 years of counter-drone research, QinetiQ worked closely with our customers to understand their objectives and their operational context and challenges.

With our customers, we concluded that, to be effective in a counter-drone solution, a Radar must be competent at the following:

— Reliably detect objects, whether moving fast, slow, or stationary, in a wide range of environmental conditions and cluttered environments;

— Unambiguously classify a detected target as a drone;

— Specify the tracked target’s position in 3D space (bearing, range and elevation), particularly to direct other sensors or effectors onto that target;

— Discriminate between multiple simultaneous tracked targets, of different types (e.g. drones, birds, other aircraft, people, vehicles, animals, etc.); and

— Operate without a dedicated human operator.

3. The big Radar challenge: reliably detecting small, slow moving objects

Radars are fantastically effective at detecting physical ‘stuff’. They are used reliably in a huge range of military, commercial and weather-tracking applications – even in the early detection of impending land-slips at open-cast mining facilities. Drones, however, represent a hugely challenging target for conventional Radar systems.

Small drones typically have a radar cross-section of between 0.1m2 and 0.01m2. This requires exceptional sensitivity from the Radar, to enable reliable detection. These drones exhibit similar size and speed to birds, often with similar flight characteristics such as erratic movement and rapid changes in direction. This creates a significant challenge to discriminating drones unambiguously and avoiding high numbers of false alarms.

Drones can also be slow-moving or hovering, which typically this puts them below the minimum Doppler velocity at which a conventional ground surveillance Radar will identify a target.

Fortunately, the unique micro-Doppler Radar reflection from a drone’s rotors and motors does allow for discrimination between a drone and another, similar-sized contact. However, the reflected energy is tens of dBs lower in power than the reflection from a drone’s or bird’s body, requiring a much more sensitive Radar technology to be able to receive and track this tiny reflection.

Counter-Drone Radar – Optimal Characteristics for Effectiveness and Affordability - White Paper © QinetiQ Limited 2021QINETIQ PROPRIETARY4

4. Currently-available Radar technologies

So, is there a Radar technology that will deliver these requirements and overcome the challenges? There are several types of Radar being marketed for counter-drone purposes - each designed using different engineering approaches.

Many Radar manufacturers have re-marketed their existing Radar systems for detection of drones. With relatively few exceptions, these Radar systems pre-date the rise of the drone threat and were designed for other purposes. Although they offer a degree of utility, they often suffer significant compromises around accuracy, usability, 3D location and unambiguous identification of drones.

4.1 Electronically scanning (e-scan) 2D Radars

A number of ground/battlefield surveillance systems have been re-tasked for Counter-Drone purposes. These e-scan (electronically scanning) Radars generally use flat panels to generate a single Radar ‘beam’, scanning through roughly 90° horizontally (azimuth) by 10°-20° vertically (elevation). This limited and static elevation capability means these Radars cannot measure a target’s elevation. These are often referred to as 2D Radars.

Importantly, the lack of elevation measurement on a 2D radar precludes automated set-on of other system assets such as cameras, or effectors (jammers, projectiles, nets, etc.). This leads to higher cost of ownership, as human system operators are required to achieve manual set-on.

The e-scan beam scans over a defined period of time, allowing only a brief time to apply consistent energy to the target, ‘painting’ the target only as it scans past.

A relatively narrow field of view for these Radars causes them to take longer to scan through 3600 – causing a trade-off between the speed of scanning and the effectiveness of each scan. A short observation time per scan gives the Radar very little opportunity to observe detailed Doppler characteristics of the target - necessary to discriminate slow-moving or even stationary targets from other Radar reflections.

Even with a relatively fast scan, the associated track update rate will be slow, causing tracks to be lost, as targets move, or to be missed altogether. This is particularly acute when trying to track multiple simultaneous targets, or swarms.

4.2 Mechanically scanning (m-scan) Radars

Before electronic scanning, there was mechanical scanning – using motors to steer an antenna, to transmit and receive. M-scan radars are similar in performance to e-scan and suffer similar drawbacks through their 2D nature and low dwell time on targets. Since they typically scan mechanically through 3600, they require clear line of sight in all directions from the Radar’s location and suffer from structures and other environmental obstructions.

This type of radar system is illustrated in Diagram 1, showing a single beam, mid-scan.

Diagram 1: illustration of coverage from a 2D e-scan Radar

Counter-Drone Radar – Optimal Characteristics for Effectiveness and Affordability - White Paper© QinetiQ Limited 2021 QINETIQ PROPRIETARY 5

4.3 ‘Staring’ Radars

‘Staring’ Radars don’t scan. They use beam-forming techniques to transmit a large number of continuous beams, each one in a continuous direction. Diagram 2 illustrates this approach. The Radar ‘stares’ permanently along a number of pre-formed beams, enabling it to detect high numbers of simultanous targets and to maintain consistent energy on target to enable detailed Doppler measurements and maintain tracking with confidence.

Staring Radars overcome the challenges of missing or losing a target while not looking in its direction, enabling detailed micro-Doppler measurements. They can also form beams in all directions simultaneously, and allow target measurement in 3D space.

4.4 3D Radars

3D radars transmit, or look, vertically, as well as horizontally. This allows them to determine elevation, as well as direction and range, enabling them to pinpoint and track a target in 3-dimensional space.

3D tracking is essential to automation of a counter-drone solution. For example, a 3D Radar can automatically set-on (point) a camera or other secondary sensor at a suspected target, to increase confirmation that it is truly a drone. It can also be used to accurately set-on the means of disabling, or destroying the drone, known as ‘effects’ – likely with the final disable/destroy command being taken by an alerted human. Fine 3D location measurement allows effects to be accurately targeted, minimizing the potential for these effects to cause collateral damage.

Diagram 2: ‘staring’ Radars permanently maintain energy in all target directions


5. Choice of radar frequency and waveform

Radar designers spend a great deal of time testing and determining the optimum shape, frequency and power of the radio waveforms transmitted, matching these to the Radar’s primary purpose. As with any other Radar application, the choice of waveform and transmission frequency band is key to maximizing operational performance against drones.

The radar transmission frequency is a critical consideration in terms of radar performance, interference with other radio sources (either suffered by the Radar, or caused by it), and compliance with regulatory spectrum-management rules in the location where it is to be deployed. Diagram 3, below, illustrates the trade-off between transmit frequency and received micro-Doppler power (y-axis) and bandwidth (x-axis) from drone propellers and motors.

At lower radar transmit frequencies more micro-Doppler receive power is achieved, which theoretically allows for greater detection range, however there is little bandwidth in the micro-Doppler return, rendering it difficult to discriminate from background clutter.

Higher transmit frequencies provide more Doppler bandwidth which can be used to discriminate drone targets, but this is at the expense of power and therefore range.

After extensive research and trials, QinetiQ found that the X-Band part of the radio spectrum offered the best balance between good range performance and the bandwidth required to characterise a drone’s specific micro-Doppler signature at operationally useful ranges.

Diagram 3: Obsidian Radar is designed at the optimum frequency to exploit the low-power micro-Doppler signature of drone propellers and motors.


6. Designing a Radar specifically for drone detection

So, to be effective in detecting drones, we need a Radar that has been designed with the above specific objectives in mind. QinetiQ’s own approach to this problem focused on creating a brand new Radar design, with the following characteristics:

— A 3D, staring Radar to achieve near-instantaneous coverage of a full 360° hemisphere (imagine a dome, centred on the Radar and detecting any and all drones as soon as they enter that air-space – Diagram 4 illustrates this), minimizing the opportunity for a drone to pass undetected;

— 3D parameterisation that provides the very highest measurement accuracy, in azimuth, range and elevation. This allows accurate and automated control, set-on and tracking of a camera or effector, for evidentiary recording, manual threat validation and/or mitigation of the drone threat;

— Use of X-band frequencies and power, to optimise detection range against accurate micro-Doppler discrimination;

— Real-time characterization of micro Doppler signatures from the moving parts of potential targets, to provide fast, effective identification of threats, with low false-alarm rates. This allows the counter-drone system to recognise, but treat as low-priority (or ignore, as required), Radar tracks from general background traffic including people, vehicles, trees, birds, foliage and any other moving structure; and

— Detection range from 20m to 2km, allowing continuous tracking of targets – including those moving very slowly, or hovering.

Advanced beam-forming techniques and algorithms, both in azimuth and elevation (horizontally and vertically), can be used to detect and continuously-track targets in 3D space. This also enables the Radar to detect targets with a very low minimum Doppler velocity – QinetiQ’s Obsidian Radar achieves well under 1 m/s (metre per second) - rather than the several m/s required by more generic Radar systems.

Finally, use of a staring Radar maintains energy on each target – including a high number of simultaneous targets – for long periods of time. This allows precise measurement of target characteristics, including the presence of spinning propellers and motors, which is the basis for true discrimination of drones from other contacts.

Such a Radar offers its users the highest possible levels of situational awareness – enabling precise tracking of multiple targets in all dimensions, thereby supporting automated and immediate set-on of other sensors and effectors.

Diagram 4: illustration of a staring 3D Radar’s volumetric coverage


7. QinetiQ’s Obsidian Radar: designed specifically for the most demanding counter-drone applications

QinetiQ’s detailed research into the optimum Radar technologies for counter-drone applications began in 2014. Using the research and conclusions noted in this paper, we designed a counter-drone system centred on a Radar designed from the ground up, for just this purpose. We called it Obsidian.

The Obsidian Radar is unique in the market, and provides optimised performance for drone detection and tracking. The Radar forms the core sensor within QinetiQ’s Obsidian Counter-Drone system, and has also been adopted by a number of global prime systems integrators, displacing legacy less-capable Radar systems. Diagrams 6 and 7 below show the specified and actual instantaneous Azimuth and Elevation coverage of a single Obsidian radar, providing 180° by 90° coverage.

Obsidian’s antenna arrays are entirely solid-state printed circuit boards, with no moving parts and low maintenance. Each Radar contains five such antenna arrays, staring in different directions to form a half-dome of coverage. Each of the five arrays generates 16 permanently-staring (not scanning) beams, to allow precise measurement of target location and range.

In order to minimise radio interference and to ease regulatory spectrum-management considerations, QinetiQ chose a low-power, non-pulsed FMCW (Frequency Modulated Continuous Wave) waveform, for Obsidian Radar transmissions. This is also central to QinetiQ’s approach to achieving a staring Radar. Obsidian’s operating frequency is approximately 10GHz, within the ideal, drone-optimised and openly-available, X-band part of the radio spectrum.

A single Radar provides instantaneous coverage of 180° azimuth and 90° elevation. Two Radars, mounted back-to-back, provide a full 360° dome of coverage, out to 2km.

This performance allows Obsidian to provide a high degree of protection of high value assets, whether these are Airports, Power Stations, or other Critical National Infrastructure (CNI) sites. Obsidian not only provides detection Horizontally, but also Vertically, preventing threats from approaching undetected from above. Diagram 8 below shows raw micro-Doppler detections (blue and green dots) over a period of several hours at an airport – with the colours relating to different types of micro-Doppler signature, extending in this case to a height of 1.2km above the airport. These micro-Doppler characterisations are used within Obsidian’s advanced processing to determine likely drones within a background of other moving targets.

Diagram 5: Obsidian Radar benefits from an extensive R & D programme to determine the optimum drone detection radar

Diagrams 6 & 7: Obsidian Radar provides a class-leading 180 x 90 degrees instantaneous coverage


When coupled with QinetiQ’s intelligent, sensor-data-fusing, track-management software, the Obsidian Radar has:

— Class-leading 3D positional accuracy, of 10 rms in Azimuth and Elevation and 3m range, out to 2km;— Wide Doppler range coverage, allowing accurate detection and tracking of slow moving quad-copters

and faster fixed wing UAVs;— High Doppler resolution to maximise Micro Doppler signature information and unambiguous

identification of drones;— Low false alarm rate, since drones can be distinguished from birds and other non-drone contacts; and— Continuous range coverage from 20m-2km – giving permanently-staring and fully-automated

monitoring of a volume of 17 cubic km of airspace.

The above performance brings significant operational benefits. High positional accuracy not only allows accurate target tracking and set-on of other system assets, it also allows discrimination of multiple targets in the environment. Similarly, high Doppler resolution and accuracy further allows separation of multiple targets in the environment. Diagram 9 below shows a single drone being automatically tracked in the presence of multiple birds and ground tracks:

Diagram 9: Example C2 output showing drones being automatically tracked

Diagram 8: Obsidian Radar provides high accuracy detection of micro-targets in 3D space around critical assets. (vertical axis is height in metres)


1942

Today

8. QinetiQ’s Radar Heritage

QinetiQ’s Radar teams at our Malvern site in Worcestershire, UK, have a long and distinguished history of Radar development, which has been conducted on our site since 1942, when the UK Government established the Radar Research and Development Establishment (RRDE) to develop truck mounted early warning Radars during the Second World War. Over the last eight decades, we have been involved in every Radar procurement for UK aircraft and supported a range of NATO activities, including trials and working groups. Today, we provide specialist Radar advice, consultancy, and development of Radars for specific threats, where other available Radars are often unable to provide effective performance.

Alarm

Developed specifically to detect, track and warn-of improvised rocket threats flying under conventional Radar and launched from short range at allied troops’ Forward Operating Bases.

Tarsier

Developed to detect dangerous runway debris, in the wake of the Concorde disaster in July 2000 – scans active runways and can detect objects as small as a bolt at 2km.

Obsidian

Designed and built to mitigate the modern drone threat – providing a unique 3D staring array that can accurately detect and track multiple small (low and slow) airborne targets simultaneously.


Summary and conclusions

While drones offer many benefits – both recreational and practical – they also present a number of increasingly worrying threats. As with the management of any potential threat, reliable and immediate situational awareness is vital. In order to respond to potential threats appropriately and in a timely manner, we need to know what we are dealing with; where it is; and not to be distracted by false alerts. We also need high levels of automation, to avoid errors caused by the human boredom and fatigue that are inevitable in most circumstances.

QinetiQ has been developing Radar systems at the leading edge of technology, for almost 80 years – working with the most demanding of customers to protect lives. This experience and bank of research has allowed us to develop a Radar that is uniquely capable of finding, identifying and tracking drones.

Drone technologies continue to advance, with autonomous and increasingly remote flight control techniques, plus use of multiple or swarming drones, making it increasingly difficult to detect and track drones using passive RF direction-finding, or optical techniques as the primary sensor method. So, Radar has emerged as the most reliable primary sensor, supported by secondary sensors for increasing levels of confidence and sophistication.

Often the first choice for any user is which level to enter at, it’s a balance between effectiveness and cost. 3D radar technology such as Obsidian provides the first building block, it’s an essential foundation technology needed to build a fuller and more reliable solution in the combat against drones.

For further information please contact:

Cody Technology Park Ively Road, Farnborough Hampshire, GU14 0LX United Kingdom

+44 (0)1252 392000 [email protected] www.QinetiQ.com © QinetiQ Ltd 2021QINETIQ/21/00225

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counter-drone radar

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