GB2536043A - A counter-UAV system - Google Patents

Abstract

A Counter-UAV (Unmanned Aerial Vehicle) system integrates a number of sensor, effector and electro-mechanical positioning systems with software running on a computer system and combines the knowledge gained about the UAV from its sensors to most effectively disrupt the UAV's normal operation. A two-dimensional radar system 1 detects the UAV, an electro-optic infra-red (EO/IR) video camera system 7 tracks the UAV, and a RF jammer system 8 interferes with the wireless communications channel to the UAV resulting in the disruption of the UAV's planned mission. The system console 3 receives information from the radar and video systems to allow classification of a detected airborne object and selectively enables/disables the RF jammer system based on the classification.

Description

Intellectual Property Office Application No. GII1503759.1 Rum Date:14 August 2015 The following terms are registered trade marks and should be read as such wherever they occur in this document: Blighter WiFi Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo Title A counter-UAV system

Background of the invention

Unmanned Aerial Vehicles (an aircraft piloted by remote control or on-board computers), also known as UAVs, Drones, UAS (Unmanned Air Systems), RPA (Remotely Piloted Aircraft) and a variety of other names, are becoming increasingly prevalent on the open market place, meaning that they are accessible and affordable by many, including members of the general public. UAVs are available in a multitude of forms but they may be grouped into two general classes: 1) Fixed wing, where the lift is provided principally by the wings, and 2) Rotary wing, where the lift is provided principally the rotation of the rotors blades. Sizes of UAV range from palm sized devices through to aircraft with wingspans or rotor blade lengths of many metres. Such UAVs can be used for surveillance purposes, carrying camera systems to either record still pictures or video footage, or if fitted with wireless radio link, the possibility of transmitting live camera images or video. Likewise UAVs can be equipped to carry other payloads that could include weapons, toxic chemicals, explosives and other items that could be used for terrorism or nefarious activities. As a result of the ubiquity of UAVs, there is heightened concern within military, government, critical infrastructure and commercial security organisations that UAVs may be used to cause economic disruption, physical damage or terrorism, or for espionage purposes, or smuggling. There is therefore growing interest in being able to control the activities of UAVs in defined areas; including country borders, critical infrastructure sites, government buildings, military sites and other sites where UAVs are or are perceived to be a security risk. The invention describes a system that is able to detect, track, classify and disrupt UAVs, thereby helping security organisations to enhance their security capabilities.

Electronic systems exist that are capable of detecting UAVs. Radar detection, using the reflection of radio waves off the object, is one of the more effective methods and operates in the day and night time under most weather conditions. Ideally the radar would scan in all directions from the horizon upwards, forming a hemisphere of surveillance, with the ability to measure the precise location of the object in three dimensions; range, azimuth angle and elevation angle, all with respect to the radar performing the measurement. Such a radar would generally be termed a 3D (three dimensional) radar (for example the "Sea Giraffe AMB" from SAAB AB www.saabgroup.com) as it can accurately, typically better that 1%, measure object range, azimuth and elevation angles. However such 3D radars are generally expensive and until recently have been the preserve of the military. Additionally, many 3D radars are designed for long range air surveillance of large manned aircraft out to ranges of many tens or even hundreds of km. In general these long range radars are not capable of searching for small unmanned aircraft and at ranges of less than 10km. Also, there is a class of 3D radars capable of detecting ballistic airborne objects such as RPGs (Rocket Propelled Grenades) and mortars (for example the "AN/TPQ-S0 Counterfire Radar" from SRCTec, LLC., USA. www.srcinc.com), and while capable of detecting small objects also at short range, these systems cannot detect the relatively slow movement of unmanned air vehicles especially rotary winged UAVs which having one or more horizontally inclined rotors are able to hover in one location or move very slowly with respect to the radar. Additionally, most existing 3D radars, being designed to operate while looking upwards towards the sky, do not operate efficiently when trying to detect small UAVs flying close to the ground and or in urban areas where buildings, vehicles and other infrastructure can create large ground clutter reflections which can desensitise the radar or reduce its positional measurement accuracy.

Furthermore, even if a UAV can be detected there is still a remaining problem of how to react to the presence of the UAV. Ideally the UAV should be controlled in some way either by stopping it, catching it or diverting it from its operator's planned course.

To solve the problems of the poor effectiveness and high costs of 3D radar systems this invention combines the operation of two sensors, a two-dimensional (2D), non-rotating, Doppler ground surveillance radar and a moveable electro-optic/thermal imager camera system. A number of types of 2D, non-rotating, Doppler ground surveillance radars exist including; passive electronic scanning array ('PESA'), active electronic scanning array ('AESA') and 'Ubiquitous' staring-array type radars. Electronic scanning array antennas are described in a publication by Skolnik,M.; Introduction to Radar Systems, 3rd Edition, McGraw-Hill Co., New York. The Ubiquitous radar is described in a publication by Skolnik,M.; Systems Aspects of Digital Beam forming Ubiquitous Radar, Naval Research Laboratory, Report No. NRL/MR/5007-02-8625.

Additionally to effect control over or disruption of the UAV the invention includes a directional RE jammer system co-located with an Electro-Optic/InfraRed camera system that can block various system-critical wireless communication links to the UAV, including, but not exclusively, the GNSS (global navigation satellite system -a satellite navigation system with global coverage) signal and multitude of UAV wireless control channels. The three systems; radar, EO/IR cameras and RF jammer, operating together form the invention which is capable of detecting, tracking, classifying and then disrupting UAVs. This system is referred to herein as a 'Counter-UAV system'.

Summary of the invention

The invention is a Counter-UAV system that integrates a number of sensor, effector and electro-mechanical positioning systems with software running on a computer system that combines the knowledge gained about the UAV to most effectively disrupt its normal operation. The Counter-UAV system operation is summarised in figure 13. A radar unit 4, mounted on a radar tilting unit 6, scans, through its azimuth scan angle 203, the sky searching for UAVs 50c (and other flying objects). Once the radar unit detects a UAV 50d it passes the object position information (range and azimuth, but not elevation) to the system console 3 which initiates a vertical search for the same UAV by the Eo/IR system 7 at the radar supplied azimuth angle. The EWIR system performs a vertical search for the UAV 50e so that it can acquire and track the UAV. Once the EWIR system is tracking the UAV the pan/tilt unit 9 position is updated so as to maintain the UAV within the Eo/IR camera video frame. The UAV elevation angle is also sent back to the radar tilting unit 6 so that the radar unit is tilted at the best angle to continue detecting the UAV. Once the distance from the UAV 50f to the RF Jammer system 8 is less than a predetermined range then the RF Jammer system, co-mounted on the pan/tilt unit may be either automatically or manually enabled so as to jam one of more of the communications channels used by the UAV. The effect of the RF jamming signal is to disrupt the planned operation of the UAV 50g, shown as a sudden change in direction 901 of the UAV. The EWIR jammer system continues to track and disrupt the UAV for as long as required, resulting in the UAV either crashing, running out of fuel, or being brought down to the ground in a controlled manner. The Counter-UAV system includes an object classification process to allow appropriate decisions to be made about the use of the RF jammer system.

Detailed description

Figure 1 shows a logical block diagram of the counter-UAV system 0. The radar system 1 is used to detect and radar-track UAVs (objects). The radar system comprises a radar unit 4 mounted on a radar tilting unit 6 and a radar trackers to form tracks on any objects that are repeatedly detected by the radar unit.

The object output of the radar unit and the commands to it are provided through the system console 3 and specifically the radar console 10, which provides both the radar display 19 and the control console 20 for the operator. Information about the object or objects being detected by both the radar system and electrooptic/Infrared (EO/IR) Jammer System 2 are shared between the radar console 10 and the EO/IR Jammer Console 11.

The EO/IR Jammer system 2 comprises a number of sensors and effectors. The EO/IR System 7 comprises a number of camera or thermal imager systems. In the embodiment described in Figure 1, the EO/IR System includes EO/IR cameras 12 which are a daylight camera 13a and a thermal imager 13b, which provide the video channels to the video tracker unit 16, which detects and tracks one or more objects of interest on the video channels from both the daylight camera and thermal imager either individually or simultaneously.

The EO/IR system 7 optionally includes a laser ranger finder 14, commonly abbreviated to LRF, and one or more directional illuminators 15, which can provide a directional visible light or infrared illumination beam to point in the same direction as the daylight camera and thermal imager systems, thus providing enhanced illumination of the object (s) when it is being video tracked.

The EO/IR jammer system 2 also includes a RF (Radio Frequency) Jammer system 8 that itself consists of an RF jammer unit 17 and directional antennas 18.

Both the EO/IR system 7 and the RF jammer system 8 are mounted on a pan/tilt unit 9 that is able to alter the azimuth (pan) and elevation (tilt) position of the systems mounted on it. In an alternative embodiment the EO/IR system could be mounted on one pan/tilt unit and the RF Jammer system mounted on a separate pan/tilt unit with both pan/tilt units connected to the EO/IR jammer console 11.

The EO/IR System 7, the RF jammer system 8 and pan/tilt unit 9 are all logically connected to the EO/IR jammer console 11 allowing video from the EO/IR cameras 12, object information, commands and controls to be sent between the EO/IR jammer system 2 and the EO/IR jammer console 11.

Within the EO/IR jammer console 11 the EO/IR system display 21 allows one or more video channels and status information from the EO/IR jammer system to be displayed. The EO/IR system control console 22 provides a user interface for the operator to view and control the system components within the EO/IR jammer system 2.

The Radar System 1, the EO/IR jammer system 2 and the system console 3 may all be installed remote from one another. For installations where the radar system 1, the EO/IR jammer system 2 and the system console 3 are separated by less than about 10 metres then individual discrete interfaces may be used for each of the radar interfaces. In a typical embodiment the radar interface 25 may use a high speed serial interface, e.g. R5422, or Ethernet. The EO/IR system interface 26 may typically use coaxial or balanced differential cables for the video channels and RS422 or RS485 for the control and information signals. The RF jammer interface 27 would typically use a RS422 or R5485 serial interface. The pan/tilt interface 28 would typically use a R5422 or R5485 serial interface.

For installations where the radar system 1, the EO/IR jammer system 2 and the system console 3 are separated by greater than 10 metres then the system interfaces may be combined onto a common interface capable of supporting long range communications, for example Ethernet either over wire or fibre. It is common industry practice to convert discrete electrical interfaces such as composite video, RS232, RS422 R5485 and other short range interface standards to Ethernet and back again using converter boxes. Ethernet could also be used for system installation of less than ten metres but may increase the cost of the system.

With reference to figure 2, a non-rotating (commonly electronic-scanning) 2-Dimensional Doppler "Ground surveillance" radar 4 (for example the Blighter B400 series radar from Blighter Surveillance Systems, www.blighter.com) is used to scan a volume of the sky searching for UAVs. Ground surveillance radars (GSR) are a class of radar that is typically but not exclusively used by the military to detect moving objects on the ground. Ground surveillance radars typically detect ground based objects at ranges from 10 metres up to a maximum of 50km, but more typically a maximum of 10km or 20km. Ground surveillance radars typically measure object range 201 and position within the azimuth scan angle 203, but having a fixed elevation beamwidth 202, they do not include the means to measure the object vertical offset or object height so they can be considered to be two-dimensional (2D) radars. The azimuth/elevation cells 204 shown in figure 2 represent how the radar is able to finely measure azimuth position but only measure a single position in elevation. The physical size of ground surveillance radar antennas is typically less than 1 metre horizontally and less than 0.5 metres vertically. A typical ground surveillance radar is described in European patent number EP1934627 "Blighter -Short range radar system". Ground surveillance radars will usually employ Doppler frequency measurement allowing them to detect movement by virtue of the Doppler frequency shift of the reflected radar beam from moving objects. The Doppler frequency measurement also allows Ground Surveillance radars to filter out and remove significant amounts of radar signal power reflected from static objects on the ground including hills, static vegetation such as trees, buildings, and other fixed infrastructure, as described in US patent number 7,876,262 "Blighter Crawler Mode". The search volume of the ground surveillance radar is defined by the volume enclosed within the segment shape with sides formed by the range 201 of the radar, the azimuth scan angle 203 and the fixed elevation beamwidth 202 of the radar unit 4.

Referring for figures 3 and 4, the radar 4 may be mounted on a radar tilting unit 6(a & b) attached to a mounting structure 303 allowing the radar beam 301 (a & b) to be adjusted in elevation angle 302 such that the radar can either search for low altitude UAVs 50a close to the ground, as per figure 3, or high altitude UAVs 50b flying in clear sky as per figure 4. Referring specifically to figure 4, note how although the figure shows the UAV to be at a precise object elevation angle 304, the radar unit is not able to measure this angle. The most accurate measurement of elevation angle for UAV Sob that the radar unit can make is the radar tilt angle 302 plus or minus half of the elevation beamwidth 202, this is shown as the radar object elevation window 402. For example, if the radar tilt angle 302 is 15 degrees and the radar elevation beamwidth 202 is 20 degrees then that radar can only indicate that the UAV is in the radar object elevation window somewhere between +5 degrees and +25 degrees above the horizon. Note that the elevation boresight 305 is the chosen elevation reference point (zero degrees) for this radar unit, though any other reference point could be used.

The Doppler signal measurement capability of the radar unit allows static reflections from the ground (Ground clutter) to be effectively removed from the radar signal thereby allowing the small radar reflections from small sized UAVs to be detected by the radar. The use of a non-rotating Doppler ground surveillance radar provides advantages over traditional mechanically scanned radar systems including faster azimuth scanning and, in conjunction with Doppler signal processing, enhanced ground clutter discrimination and the ability to detect objects with very low radial velocity (as described in US patent number 7,876,262 "Blighter Crawler Mode") with respect to the radar, e.g. Rotary wing UAVs. The radar is able to detect UAVs and measure their location in range and azimuth with respect to the radar boresight. The non-rotating Doppler ground surveillance radar described does not have the ability to measure the object elevation angle 304 of the UAV other than by an assumption that the UAV is probably within the main elevation beamwidth of the radar unit as previously described. The non-rotating Doppler ground surveillance radar is able to measure the instantaneous Doppler velocity of objects and the instantaneous Radar Cross Sectional area (RCS) of the UAV, both of these object characteristics being useful for the object classification process described later in this document.

The radar system 1 can optionally include a radar trackers (for example the "SPx Tracking Server" from Cambridge Pixel Ltd. www.cambridgepixel.com) that allows tracks to be formed on sequences of individual detections of individual objects over a number of radar scan periods. For example, for a single UAV flying in a straight line and being detected by the radar on each radar scan (or object update period), over a period of seconds or tens of seconds then a sequence of radar detections each with changing range and azimuth measurements would be seen. The object tracker is able to associate the detections on each scan to create a track that follows the vector formed by the UAV's motion. Such a track can determine the relative ground speed and heading of the object based on the change of object position over a measured period of time. Use of object speed and heading is beneficial to the counter-UAV system as it allows the object location to be extrapolated from the previous and most recent positions to compensate for radar system object measurement latency, which is inevitable in such a system due to signal processing delays.

Information determined by the radar unit and radar tracker concerning the object can include some or all of: range, azimuth, approximate elevation, radar cross sectional area (commonly referred to by the industry as RCS), Doppler velocity, ground speed and heading. This information, in part or whole, can be used to assess if the measured object has the characteristics of a UAV that is likely to be of interest and especially a threat. Equally the same information can also determine if the object is likely to be some other type of object including ground based objects; vehicles, people, wind-blown vegetation, air conditioning fans etc., or other air based objects including: birds or larger commercial aircraft. An object filter in the radar console 10 can apply rules based on the aforementioned radar object information to exclude or include objects with specific characteristics. For example a small winged UAV may never fly slower than 20km/hr nor faster than 60km/hr. A simple filter based on these speed limits could be used to indicate an object having a speed of, for example, 50km/hr as being a small winged UAV. Equally, an object having a speed of 10km/hr would be excluded by the rule allowing that object to be ignored. The radar system land the radar console 10 are capable of detecting and then filtering many hundreds of possible objects per scan. This enables false alarms from objects of little interest to be dramatically reduced thereby reducing the operator burden of using the counter-UAV system.

Referring again to figure 1, once an object has been detected by the radar system 1 and radar console 10 then that object information is passed to the EO/IR Jammer console 11 over the object interface 29. The information from the radar may either be sent in its original radar format and coordinate system or converted to a format suited to the EO/IR System. For example the radar can either provide the object range and bearing with respect to the radar's own position, or convert it to be with respect to the EO/IR System's location, or alternatively convert it into an Earth referenced location, for example, latitude and longitude.

Referring to figures Sand 6, the radar unit 4 described is capable of measuring object range 404 and azimuth position 401 with a high accuracy of within about 1% but can only provide a crude assessment of elevation angle based on the elevation beamwidth 402 and tilt angle (not shown in diagram to avoid confusion) of the radar system. Note how the azimuth position 401 is shown with respect to the azimuth boresight angle 403 of the radar, the azimuth boresight being the chosen reference point (zero degrees) for this radar, though any other reference point could be used.

Referring to figure 7, the EO/IR System 7 is capable of measuring object position within the video frame 101 with high accuracy of approximately one pixel (pixel element) in the horizontal field of view (HFOV) 211 and vertical field of view (VFOV) 210 but not in range 404 as the daylight camera 13a and thermal imager 13b contain no method of directly determining range. Both the radar unit 4 and the EO/IR system 7 can be considered to be 2D (two dimensional) sensor systems, but with only one common dimension, the azimuth angle. As the radar system cannot provide a sufficiently accurate measurement of object elevation angle to point the EO/IR system directly at the object in elevation then the EO/IR system needs to search for the radar object in elevation based on the 2d spatial information, range and azimuth, provided by the radar system.

To perform a spatial search either the system operator (human) or the EO/IR Jammer console 11 must select one or more of the available EO/IR cameras 12 on the EO/IR jammer system. Referring to figure 8, the EO/IR jammer system can include a daylight camera 13a or Thermal Imager 13b or other imaging camera system (not shown), assuming that more than one is available. Typically, but not essentially, a visible wavelength daylight camera 13a would be used during daylight and a Thermal Imager 13b camera system would be used at night. A daylight camera can view distant objects due to reflection of visible or near visible light off the object, the light coming from either the sun, moon, manmade lighting or other sources of illumination including but not exclusively an optional directional illuminator 15 built into the EO/IR System 7. The Thermal Imager 13b can view (create a video representation of the object being pointed at by the sensor) distant objects due to the thermal emissions from the objects. Both cooled and uncooled thermal imaging cameras can be used, but for optimum detection ranges of small UAVs, cooled thermal imaging cameras are preferred. Cameras sensitive to other wavelengths may also be used, including for example MWIR (Medium wavelength Infrared) cameras. The EO/IR system 7 may also include a Laser Range Finder (LRF) 14 to measure the range from the LRF to the object. (examples of various EO/IR cameras and LRFs can be seen on the "Hawkeye system" from Chess Dynamics Ltd. www.chess-dynamics.com) Having received object information from the radar system 1 the system console 3 initiates a spatial search for the object, based on the object information provided by the radar system 1, using the EO/IR system 7 on its Pan/Tilt Unit 9. Referring to figure 8, the pan/tilt unit 9 allows the EO/IR system 7 and the RF jammer system 8 to be tilted 504 about its horizontal axis 503, i.e. moved in elevation so that the EO/IR jammer system can point down to the ground or up into the air. The pan/tilt unit 9 may also be panned 501 about its vertical axis such that the EO/IR jammer system rotates horizontally about its base 506, which is attached to some suitable secure mounting point 303, for example on a building, mast or a vehicle.

Once the EO/IR camera selection has been made, the EO/IR camera's horizontal fields of view (HFOV -the effective angle subtended by the horizontal extent of the camera image) of each EO/IR system is preset to a value such that 1) it exceeds the variability in the measurement of object azimuth position on the radar, and 2) it also provides sufficient magnification of the object for the video tracker unit 16 to detect and track the object at the pre-determined maximum range of engagement. The maximum range of engagement is the longest distance from the EO/IR system where it is expected that the E0/113 system will be able to detect and track a typical large UAV and beyond which no detection would be anticipated. For example, for a radar with azimuth measurement variability of +/-1 degree, the EO/IR camera HFOV should be set at a minimum of 2 degrees. However for the video tracker to detect and track an object at the maximum range of engagement it may be sufficient to use a HFOV of S degrees. In this instance the EO/IR camera would scan a greater volume of sky compared to the 2 degree HFOV, thereby increasing the probability of detection by the EO system and reducing the object acquisition time.

The EO/IR Jammer Console 11 then initiates an EO/IR System 2 search for the object by controlling the Pan/Tilt unit 9 in azimuth and elevation (Pan & tilt) on which the EO/IR system 2 is mounted. Referring to figures Sand 6, as the object is more likely to be at the range 404 and azimuth position 401 calculated by the radar system 1 and within the radar object elevation window 402 of the Radar unit then, referring to figure 9, the E0/113 jammer console 11 commands the Pan/tilt unit 9 to move the EO/IR System 7 so that it scans a vertical line 901 starting at the given azimuth position 401 and from one end of the radar object elevation window 402, e.g. 901a, through to the other end of the radar object elevation window 402. If no object is detected within the EO/IR video window 904 by the video tracker unit 16 then the EO/IR Jammer console 11 reverses the direction of the scan 901 and searches again. This up and down scan pattern may continue for as long as either the EO/IR Jammer console 11 or the operator decides. During the EO/IR System scan the azimuth position 401 may be updated by more recent radar system 1 object updates. Depending on both the radar characteristics and the EO/IR camera characteristics, the EO/IR Jammer console 11 may use a modified scan 903 to increase the volume of the sky being searched. For example it may be possible for the radar to detect a very large object (an object having a large radar cross sectional area capable of being detected on the radar unit's elevation beam sidelobes) outside of the main elevation beamwidth 202 and in one the radar antenna's elevation sidelobes. In this instance the extended elevation scan angle 906 would be increased to cover the extended sidelobe region of the radar. Equally the azimuth scan angle 907 of the EO/IR System could be extended in either direction to accommodate positional measurement or prediction errors within the radar system. In such a case, a modified scan 903 with the vertical search in one direction being set at one limit of azimuth and the return search in the other direction set at the other limit of the azimuth angle would allow the EO/IR video window 904 to search a greater volume of the sky. Other search patterns could also be used depending on the characteristics of the radar, EO/IR camera systems and the type of object anticipated. For example, if fast moving objects are anticipated then the volumetric search pattern may need to be extended to allow for object manoeuvres which result in non linear object motion and the exaggeration of system measurement errors of fast objects resulting from sensor and processing latency.

Once the video tracker unit has detected a potential object within a single video frame (one complete image acquisition period) on any of the EO/IR cameras 12, it searches, on the subsequent video frames, for additional detections of the object in the vicinity of the first detection allowing for sensor movement and object manoeuvres. The video tracker unit determines if the same object can be detected on a predefined percentage of the number of subsequent video frames. This object detection correlation process reduces the probability of falsely initiating a video track on sporadic EO/IR camera detections or video noise. Referring for figure 10, once the object is acquired (i.e. the video tracker has detected the object on sufficient video frames that it considers the detected object to be a candidate for continuing the video tracking process) the video tracker unit measures the object position 104 (vertical) and 105 (horizontal) within the video frame 101 to allow the angular offset of the E0 system to be calculated.

The object horizontal video offset 107 from video boresight 106 is the difference between object horizontal position 105 and video horizontal boresight 103. The object vertical video offset 108 from video boresight 106 is the difference between object vertical position 104 and video vertical boresight 102. Knowing the angular offset of the object within the video frame (which is easily derived from the horizontal and vertical video offsets 107 and 108 within known horizontal and vertical fields of view 211 and 210) and the absolute position of the EO/IR camera system on the Pan/Tilt unit allows the EO Jammer console to calculate the absolute angular position of the object in both azimuth and elevation with respect to the base of the Pan/Tilt unit, which is likely to be mounted on a known ground position reference. Note that the EO/IR camera system is not inherently capable of measuring range to the object.

In an alternative embodiment of the simple position based tracking system described above, a more sophisticated velocity based tracking system may be used. An example of this is a proportional-integralderivative controller (PID controller) which is a control loop feedback mechanism (controller) widely used in industrial control systems (for example the "DART Embedded Target Tracking Software" from Vision4ce Ltd. www.vision4ce.com). The coefficients within the PID controller are selected to provide zero error when tracking a target with constant angular velocity.

Once the video tracker unit has acquired the object, it sends the object azimuth and elevation offsets 107 and 108 to the Pan/tilt unit 9. This allows the video tracker unit to optimally place the object on the video frame 101 and to maintain it there by constantly tracking the object, measuring its position and/or motion and feeding positional offsets to the Pan/Tilt unit on a time interval that is typically a video frame update period. Note that this time interval will depend on the implementation of the video tracker unit and may require multiple video frame update periods in some instances. The process described beforehand is commonly referred to as closed-loop video tracking.

As described above, when the video tracker unit 16 is tracking the object, the object's elevation angle with respect to the ground is accurately known (refer to figure 4 item 304). This elevation angle can be passed back from the EO/IR jammer console 11 to the Radar Console 10 to enable the radar console to optimally change the tilt angle of the radar tilting unit 6. Normally the radar tilting unit 6 will tilt the radar such that the elevation boresight angle 305 is set to the measured object elevation angle, however, if the object is close to the ground then a minimum elevation limit (minimum tilt angle) may be set to prevent the radar from being tilted too low thereby preventing the radar transmission from illuminating too much of the ground. This minimum radar tilt angle ensures that ground clutter reflections and ground based object detections are reduced within the radar unit, which prevents unwanted information being presented to the operator on the radar control console 20.

When the video tracker unit 16 is tracking an object, the object's azimuth position on the EO/IR camera or cameras can be validated with the object's azimuth position from the unit radar. If the radar and camera azimuth angles do not agree, within tolerances defined by radar positional measurement errors, camera positional measurement errors and object dynamics and other systematic positional errors, then the EO/IR Jammer console can either stop tracking the object and/or alert the operator so that he can decide how to react to what the EO/IR jammer console believes to be mismatched radar and video objects (i.e. the object being tracked by the radar tracker is not the same as the object being tracked by the video tracker unit).

Assuming that the radar tracker and video tracker unit are both tracking the same object then the information on that same object from both the radar unit and the EO/IR system may be combined to improve the object location accuracy and provide both the EO/IR Jammer console and the operator with better object information. The EO/IR Jammer Console is able to use the combined object information from the radar unit and the EO/IR system to classify the object. Classification is the process of identifying unique or common characteristics of different type of objects. For example, by combining radar object azimuth position and range with EO/IR system object azimuth and elevation position, the precise location of the object in three-dimensional (3D) space can be determined, i.e. Range, azimuth and elevation. Additionally, knowing the exact 3D location and the object's radar cross sectional area (radar object size), and EO/IR camera object size in horizontal and vertical pixels, plus additional object dynamic information such as ground speed and heading can allow the object to be classified. For example, it may be possible to automatically identify (classify) the make and model of a specific UAV by analysing its radar range and RCS, video dimensions (EO/IR object size), and speed. Knowledge of the object type can allow the operator to assess the threat posed by that UAV, or other air object. Importantly the use of object classification allows for improved safety as the EO/IR jammer console should be able to warn the operator if the tracked object appears to have the characteristics of, for example, a manned helicopter or manned aircraft. It would be highly undesirable for the Counter-UAV system to automatically disrupt a manned flight due to potential loss of life.

Referring back to figure 8, when the object is being video tracked, an RF Jammer System 8 (for example the "Kestrel jamming system" from Enterprise Control Systems www.enterprisecontrol.co.uk) co-located on the same Pan/Tilt unit 9 as the EO/IR system 7, or in an alternative embodiment, mounted on a separate Pan/Tilt unit but controlled by the same EO/IR jammer console, can be pointed towards the same object. This allows the directional antennas 18 on the RE Jammer System 8 to optimally point towards the object to maximise the amount of jamming energy that may be transmitted towards the object.

The RF Jammer system 8 is able to produce high power radio transmissions at either single frequencies or over a range of frequencies (spectra). The RF Jammer may typically, but not exclusively, use three different spectra, each relating to key wireless communication channels typically used by UAVs. In the described system, the spectra include: the GNSS L-Band wireless link, the UAV control data link channels and the UAV WiFi data link channels (These communications channel will be described in more detail later). Other channels could include other UAV control uplink channels and other video and UAV status downlink channels. The aim of jamming the control and information wireless channels on the UAV is to deny control of the UAV to the original UAV operator(s) and to instead enable some level of control of the UAV to the Counter-UAV system operator.

Referring to figure 11, the RF Jammer system 8 comprises an RF Jammer unit 17 capable of producing a multitude of RF jamming spectra at high power levels and one or more, typically three, directional antennas 18 through which the RF jamming signals are broadcast. The RF Jammer unit comprises a waveform generator 801 that generates the required spectra and a series of power amplifiers, 802a, b & c that amplify the outputs of the waveform generator 801 to provide the high power transmissions for each unique spectra. The radio frequency power generated by each power amplifier depends on the system design and especially the radiated power required to exceed the radio transmission power being received by the UAV from the UAV operator(s) or other communication channels, especially if the UAV operator is using directional wireless communication links. Typically a power amplifier RF transmission power of between 1 Watt and 50 Watts may be used. The directional antennas 18 ensure that as much RF jammer power is sent in the direction of the object as practically possible, while minimising the amount of RF Jammer power being broadcast in the remaining space (outside of the main antenna beam). The directional antennas are designed to produce a transmission beamwidth 804 (the angle over which the power is not less than 3dB below the peak power) that is practical for deployment on the pan/tilt unit. A typical antenna beamwidth of between S degrees up to 40 degrees may be used and will typically be the same on both azimuth and elevation, though this symmetry is not essential as there may be merit in shaping the beamwidth to minimise the effect of the jamming system on the ground. Narrow beamwidths require physically large antennas and for this reason it is often necessary to compromise the beamwidth in favour of more compact antennas. Also, it is beneficial if all the directional antennas have similar beamwidths so that the effectiveness of the RF jammer system is consistent across all spectra being used. Note how the directional antennas 18a, b & c produce a series of transmission beams 803a, b& c that are nominally similar in shape and point in the same direction. Antennas with dissimilar beamwidths and directions could be used depending on the jamming requirements and antenna physical design. Minimising the residual jamming power outside of the main transmission beam reduces the risk of other local services that use the same RF spectra from being jammed also. For example, jamming the GNSS channel might stop local GPS based products from working, including Satellite navigation systems and other communication services that use precise GPS time references.

Referring to figure 12, the RF Jammer system 8 operates by over powering the radio frequency transmissions received by the UAV 50 from remote sources. The RF Jammer system prevents the UAV from receiving commands and positional information from the external sources by transmitting radio frequency energy along its jamming RF link 111 within the same spectra as used by the UAV receiver channels and with sufficient radiated power to exceed the power from the intended external transmission sources. These intended external sources include: the control data link 113 (example in UK 458.5MHz to 459.5MHz) from the remote control transmitter 52 used by the UAV ground pilot, the WiFi bi-directional data link 114 (example 2.4GHz or 3.5GHz or 5.8GHz WiFi spectra) used by the UAV programming unit 53, and the GNSS L-Band wireless broadcast 112 (example 1164MHz to 1610MHz) from the Global Navigation Satellite System (GNSS) satellite constellation 51, which include the American Global Positioning System (GPS) and the Russian GLONASS satellite systems. Object 115 is describing a notional cylinder in space with its long axis along the boresight of the directional antennas within which the RF Jammer System can successfully jam the UAV communications channels. The edge of the cylinder is deliberately vague (wavy) due to the variations in the effectiveness of the RF jammer system with respect to the UAV's external wireless communications channels.

It is possible for UAVs to use a diverse range of communications channels and therefore the three spectra described above are examples of what may be used. For example, it is common for the control datalink channel 113 to vary according to country, due to spectrum usage regulations. Equally there is no reason why the UAV operator might not choose a completely non standard frequency or spectra by which to communicate with his UAV. A number of new GNSS networks are also due to start operating in future years including the European Galileo satellite navigation system, which will use other channels within the GNSS L-Band spectrum. It is important to note that in many countries it is illegal to interfere with GNSS transmissions and other transmissions and therefore permissions must be sought before doing so.

While the UAV or other object is being tracked by both the radar system and the video tracker unit, the EO/IR Jammer Console has knowledge of the 3D position of that object in the air, including the range from RF Jammer System to the object. Beyond a pre-determined range defined by the likely ERP (Effective Radiated Power) of the remote UAV wireless communications channels and the ERP of the local RF Jammer system, the RF Jammer system may not be effective, and therefore, the EO/IR Jammer console inhibits the use of the RF Jammer system until the object is at a range, the maximum jamming range, where the object is most likely to be disrupted by the RF Jammer. Early use of the RF Jammer system may disclose to the UAV operators the characteristics of the RF Jammer system, enabling them to design counter-measures. For example, if the RF jammer system was transmitting continuously then the UAV operator could continue to fly the UAV until the point where control of the UAV was lost. This point would provide useful information about the relative jammer powers being used compared to the UAV control uplinks. Alternatively, if the RF Jammer system is deployed only when UAV denial is almost certain then the UAV operator will gain little knowledge of the RF Jammer system.

The proposed RF Jammer system includes three unique spectra selected to deny the UAV access to its primary GNSS L-band wireless broadcast 112, control data link 113 and WiFi bidirectional data link 114 channels. Other spectra may be used depending on UAV characteristics and the evolving counter measures used by the UAV operator. For example if may be found that just one radio channel will successfully prevent a UAV from completing its mission on the first attempt, but in time, additional and diverse control channels and intelligent on-board navigation systems may be used to prevent jamming, requiring more RF Jamming spectra to be used and with more elaborate waveforms to interfere with more complex wireless communication links, e.g. spread spectrum wireless communication links.

When the EO/IR System is tracking the object and the object range as measured by the radar system or other sensors (e.g. Laser Range Finder -LRF) is less than the maximum jamming range, then the EO/IR Jammer console may either automatically or under the control of the operator enable one or more RE Jamming spectra. Depending on the threat either all or just some of the available RF Jamming spectra may be used, with the remaining spectra being enabled only if required. For example, in an urban location, it may be undesirable to use the GNSS spectra due to collateral inhibition of other systems, so the control data link or WiFi bidirectional data link spectra may be tried first. If they do not appear to alter the behaviour of the UAV then the GNSS channel jamming may be enabled. This decision process could be automated by the EOPR jammer console but is more likely to be made by the Counter-UAV system operator.

The RF Jamming transmissions from the RF jammer system may be applied for as long it is felt necessary to take control of the UAV, which his could range from seconds to many minutes. One effect of RF jamming may be to make the UAV start to fall to the ground within seconds due to its loss of positional awareness (e.g. no GNSS channel). Alternatively, a jammed UAV may simply fly to or between pre-programmed waypoints (specific 3D spatial positions) waiting for a new instruction over its jammed control data link or WiFi bidirectional data link channels. In this instance the UAV would eventually run out of battery power or fuel and fall to the ground.

The effect of RF jamming is highly dependent on the type of communication channel being jammed and the way in which the UAV's computer software is programmed to operate. Denial of the GNSS channel is generally very effective at preventing the UAV from knowing where it is, though onboard inertial navigation systems can determine its location and heading for a period of time after GNSS is denied. The effect of jamming the UAV control uplink channels is more unpredictable as the UAV may already be pre-programmed with waypoint information meaning that denial of the use of the channel(s) is of no benefit unless the jamming signal can itself spoof typical control commands. It is proposed that the RI Jammer system could be sufficiently capable as to be able to send alternative commands to the UAV telling it, for example, to land in a different location where no harm can be done and the UAV retrieved by the protecting forces.

Claims (4)

1. Claims What is claimed is: 1. A counter-UAV system comprising a radar system, an electro-optic infra-red (ED/IR) video camera system and a radio frequency jammer system controlled by a system console (a computer based software application that interfaces to the system components and provides a human interface) to detect a UAV or other airborne object on the radar system and then conduct a localised search for and then video track the same object on the Eo/IR camera system and then disrupt the actions of the UAV by enabling the RF jammer system to transmit on the discrete frequencies or the spectra of frequencies within a wider band used by the UAV to receive wireless transmissions from remote sources, so as to deny the UAV access to the data on those wireless transmissions.
2. 2. A counter-UAV system according to claim 1, wherein the radar system comprises one or more non-rotating Doppler ground surveillance radars that can measure with respect to the radar the range and the azimuth angle of one or more objects in the sky, wherein the radar is either a passive electronic scanning array ('PESA'), or an active electronic scanning array ('AESA') or a 'Ubiquitous' staring array type radar wherein the radar is designed to detect objects both in range and over an azimuth extent exceeding 30 degrees and typically less than 180 degrees without movement of the radar system including its antenna(s).
3. 3. A counter-UAV system according to claim 1, wherein the electro-optic infra-red camera system (E0/IR system) comprises one of more electro-optic infra-red cameras (E0/IR camera) each capable of capturing moving images of remote scenes either in the visible light spectrum or the infra-red spectrum or both the visible light and infra-red spectrum simultaneously and outputting them in electronic format for storage, viewing or video processing
4. 4. A counter-UAV system according to claim 3, wherein one or more of the EWIR cameras include a mechanism by which the field of view of that camera may be altered in accordance with instructions from a system console, a computer based software application, so as to maintain the optimum field of view for detecting or tracking the UAV; such a mechanism may include selectable or adjustable lenses (zoom lens), or electronic zooming where the field of view is set to a smaller area of the original video image from the camera system, or other methods of adjusting the field of view.S. A counter-UAV system according to claim 3, wherein the video output from one or more EO/IR cameras is provided to one or more video tracker units that are capable of detecting a UAV within the video image and then tracking the UAV by measuring its position or motion within the video image and maintaining a tracking gate (an electronic window within which the object is expected to be detected) around the UAV and which is updated on subsequent video frames so as to follow the motion of the UAV as it moves through the sky.6. A counter-UAV system according to claim 3, wherein the Eo/IR cameras are mounted on a pan/tilt unit (an electro-mechanical device capable of adjusting the rotation (pan) and elevation angle (tilt) of an object mounted on it) such that the EWIR cameras may be pointed in the direction of interest to search for and/or track the UAV 7. A counter-UAV system according to claim 1, wherein a radio frequency (RI) jammer system, a device for producing high power radio frequency transmissions on one or more discrete frequencies or spectra and for transmission through one or more antennas, is configured to jam (block deliberate 3"d party wireless transmissions by means of radio frequency interference on the wireless communications channel(s)) the radio frequency communications frequencies or spectra used by the UAV.8. A counter-UAV system according to claim 7, wherein one or more of the antennas used by the RF jammer system are directional antennas such that a significant proportion of the transmitted power is directed in one direction and within a 3dB beamwidth (a measure commonly used within the industry to describe the angle at which the transmitted RF power is half that of the peak power at the centre of the transmitted beam) of forty degrees or less.9. A counter-UAV system according to claim 8, wherein the directional antenna or antennas are mounted on a pan/tilt unit (an electro-mechanical device capable of adjusting the rotation (pan) and elevation angle (tilt) of an object mounted on it) such that the directional antennas may be pointed towards the UAV so as to maximise the RF Jamming power transmitted in the direction of the UAV and minimise the residual RF jamming power, from the antenna sidelobes, thereby reducing the effect of the RF jamming transmission on local wireless services near the counter-UAV system.10. A counter-UAV system according to claims 6 and 8, wherein the EO/IR cameras and the directional antenna(s) of the RF jammer system are all mounted on the same pan/tilt unit and aligned so that the directional antennas have their axis of maximum transmission power nominally parallel to the boresight (centre of the video frame) of the EO/IR cameras such that the directional antennas inherently point towards the UAV when the UAV is within the field of view of the EO/IR camera system.11. A counter-UAV system according to claims 6 and 8, wherein the EO/IR cameras are mounted on one pan/tilt unit and the directional antenna(s) of the RF jammer system are mounted on another pan/tilt unit and where the system console controls the position of both pan/tilt units such that the directional antenna(s) are moved so that their axis of maximum transmission power is nominally parallel to the boresight (centre of the video frame) of the EO/IR cameras when a UAV is in the field of view of the EO/IR camera 12. A counter-UAV system according to claim 1, wherein the system console receives information about a specific airborne object from both the radar system and the EO/IR system and combines that information to enhance the spatial knowledge of that specific object, including some or all of: three-dimensional position in the air and speed, direction of travel and the size characteristics of that specific object as measured by both the radar(s) and EO/IR camera(s), to allow classification of that specific object, wherein the classification process in the system console compares the available characteristics of the specific object against a list of characteristics, commonly a database, of known objects, including UAVs and other airborne objects, such that it can select a known object(s) that is the closest match to the characteristics of the specific object in order to classify the specific object as a known object; the classification of the specific object may be presented on the system console for the operator (human) and may also be used to selectively enable or disable use of the RF jammer system depending on the object classification.13. A counter-UAV system according to claim 2, wherein each non-rotating Doppler ground surveillance radar unit is mounted on a radar tilting unit which allows the azimuth scanning plane of the radar unit to be adjusted in elevation (tilt) thereby allowing the radar unit to detect objects within its radar beam either in the sky, typically above the horizontal position, or close to the ground, typically near or below the horizontal position.14. A counter-UAV system according to claim 13, wherein the radar tilting unit also allows the radar unit to be rotated in azimuth, as commonly provided for by a pan/tilt unit, such that the radar unit can be rotated to allow it to detect objects within its azimuth extent in other directions.15. A counter-UAV system according to claim 3, wherein the EO/IR system includes a Laser Range Finder (LRF), an electro-optical device that uses a laser to measure range, such that the distance from the LRF to the object appearing in the EO/IR camera(s) field of view can be measured independent of or in collaboration with the range measurement from the radar system.16. A counter-UAV system according to claim 3, wherein the EO/IR system includes one or more directional illuminators aligned nominally parallel to the boresight of the EO/IR camera(s), wherein each directional illuminator provides a narrow beam, typically less than 5 degree beamwidth, of visible light or infrared energy with the wavelength of that light or energy matched to the characteristics of one or more of the EO/IR cameras such that the directional illuminator increases the illumination of the UAV thereby making the UAV more visible on the EO/IR camera and so increasing the probability of detecting and tracking that object on that EO/IR camera.17. A counter-UAV system according to claims 2 and 5, wherein the system console, on receipt of object information including range and azimuth angle from the radar system, sends positional or motion information to the pan/tilt unit on which the EO/IR system is mounted and initiates a vertical scan of the EO/IR camera at the horizontal direction of the object, the lower and upper vertical scan limits of the pan/tilt unit being calculated by the system console based on the three dimensional space within which the radar unit has detected the object, that three dimensional space being defined by the elevation beamwidth of the radar unit antennas adjusted by the angle at which the radar antenna(s) boresight is inclined (tilted) away from the horizontal.18. A counter-UAV system according to claim 17, wherein the video tracker unit(s) on scanning vertically through the object position first detects the object within the video image, then acquires the object by confirming detections on multiple video frames at which point it instructs the system console to stop the vertical scan and then tracks the object; the first video tracker to detect the object taking precedence for stopping the scan and initiating the video track in the case where multiple EO/IR cameras and video tracker units are being used.19. A counter-UAV system according to claim 18, wherein the pan/tilt unit scan is extended both in elevation (tilt) and azimuth (pan) in order to accommodate objects that have high velocities or rapid flight path changes and which are likely to move outside of the EO/IR camera field of view before the standard vertical scan in claim 17 is complete; the extended scan will typically be, but is not essentially, a rectangular scan with the four corners of the scan forming a rectangle shape outside of the vertical scan line described in claim 17.20. A counter-UAV system according to claim 2, wherein the system console contains a radar control console, a software application responsible for handling radar system control and information, and an EO/IR system control console, a software application responsible for handling EO/IR camera control and information, wherein the radar control console applies numerical filters to the object information being supplied by the radar system to restrict which objects the radar control console will pass onto the EO/IR console for tracking by the EO/IR cameras; by programming appropriate numerical filters into the radar control console the system operator can restrict Counter-UAV system activations to only those objects that have radar characteristics similar to UAVs thereby preventing unwanted system activations on other non UAV-like objects, for example but not exclusively birds, and reducing the risk of disrupting the actions of manned aircraft.21. A counter-UAV system according to claim 7, wherein the RF Jammer system is inhibited from transmitting by the system console if the distance from the RF jammer system to the object is measured by the radar system to be above a predetermined range, wherein the predetermined range is calculated to disrupt with certainty the actions of a typical UAV.22. A counter-UAV system according to claim 13, wherein the object elevation angle measured by the EO/IR system is used to control the tilt angle (elevation) of the radar tilting unit such that the radar unit elevation boresight is optimally angled towards the object.23. A counter-UAV system according to claims 10 and 13.24. A counter-UAV system according to claims 12 and 23.25. A counter-UAV system according to claims 17 and 24.26. A counter-UAV system according to claims 19 and 25.27. A counter-UAV system according to claims 20 and 24.28. A counter-UAV system according to claims 21 and 24.29. A counter-UAV system according to claims 22 and 24.30. A counter-UAV system according to claims 18, 19, 20, 21, 22 and 24.