Enhanced passive coherent location techniques to track and identify UAVS, UCAVS, MAVS, and other objects

[0001] The present invention relates to the field of aircraft tracking. In particular, the present invention is directed to a method and apparatus using passive coherent techniques to track aircraft, aircraft and other objects.

Background of the invention [0002] In a report published on October 9, 2006,

Teal Group (<a href="http://www.tealgroup.com/">www.tealgroup.com</a>) predicted that the global Unmanned Aerial Vehicle (UAV) market will exceed USD 54 billion, and that UAV spending will more than triple in the next decade compared to current UAV spending around the world, from

USD 2.7 billion per year to USD 8.3 billion over the decade, approaching a total of USD 55 billion over the next ten years. The analysis concludes that the US will have a 77% share in global spending on research and development of UAV technology in the next decade and about 64% in supply. These US expenditures represent a larger share of the aviation and space market than overall global defense spending, with the Teal Group accounting for a 67% share of total global research and development spending on defense, and 37% in supply expenditure.

[0003] An article by Charlotte Adams, published in Avionics Magazine in September 2001, provides an overview of the development of UAVs at that time. The article indicates that the UAV wingspan is in the range of six inches (15 cm) to 247 feet (75 meters). In flying mode, they include fixed

57P33505PL00

Wings, spinning wings, vertical takeoff and landing (VTOL) type MV-22 Osprey and structures fluttering wings like birds. The flight altitude range is from 50 feet (12.24 meters) to 100,000 feet (30,480 meters), and in terms of mission, UAVs are used for intelligence, surveillance and reconnaissance (ISR) - (Intelligence, Surveillance and Reconnaissance), as well as for firing weapons. The article describes avionics and sensor sets on various vehicles, which are listed below for reference:

• Infrared sensors without cooling (IR) • "Spherical" electro-optical sensors (E / O) • Laser radar (ladar) - Jigsaw • Ku band, over-horizontal satellite communication • Radios ARC210 Collins (HF Rockwell radio systems)

Collins ARC210 AM / FM / UHF / satcom) • Radar sensors with synthetic aperture • Ultra wideband sensors (UWB) - (Ultra wideband) [0004] These devices generally emit about 0.25 watts of instantaneous power in impulse and about 750 microwatts (million watt part) of medium power, ensuring low probability of interception / detection and high interference resistance. The sensors described in the article operate in the range of 6 to 6.5 GHz.

[0005] Although it is generally accepted that future UAVs operating in a controlled space will contain avionics adapted to air traffic control, for example transponders, in general such aircraft use different avionics and sensors. With the advent of new technologies to track aircraft in space, it can be

57P33505PL00

It is necessary to provide means for reliable UAV tracking etc., in order to prevent collisions with passenger aircraft and other aircraft, as well as to avoid collisions with buildings and other objects. In addition, passive coherent techniques offer the ability to detect secret enemy aircraft at high and high altitudes. It therefore remains in demand to provide means for tracking UAVs and other aircraft using passive location techniques.

[0006] Traditional systems in small radar fields include a third and directly spaced transmitter and receiver that typically share the same antenna for transmitting and receiving. The impulse signal is transmitted and the time needed for the impulse to travel the path to the object and back again allows you to determine the distance to the object. Passive Coherent Location (PCL) - (Passive Coherent Location) is a passive radar system in which there is no dedicated transmitter. The receiver, on the other hand, uses existing hand emitters that measure the difference in the time it takes to receive the signal from the transmitter and the signal reflected from the object.

This allows you to specify a bi-static distance from the object. In addition to the two-static distance, passive radar usually also measures the two-static Doppler echo shift as well as the direction from which it is received. This allows you to calculate the location, direction of flight and speed of the object. In some cases, many transmitters and / or receivers can be used to perform several independent measurements of bi-static distance, Doppler shift and flight direction, thereby significantly increasing the final tracking accuracy.

[0007] The PCL system includes a bi-static radar that measures elliptical distance and Doppler shift

57P33505PL00

EP 1 992 963 B1. Works with random (CW) - (Continuous Wave) transmitters, which means that it uses electromagnetic radiation originally intended for other purposes, such as terrestrial radio or television. It is necessary to detect at least two (ideally three or more) direct signals from the transmitters in order to correctly determine the position of the target, as shown in Figure

1. Figure 1 is a diagram illustrating a typical PCL configuration according to the current state of the art.

[0008] According to the principles of PCL methodology, all targets interacting with an electromagnetic field (having specific wavelengths) can be detected. In practice, all flying objects that are heavier than air are constructed of certain metal materials, carbon composites, or at least contain some metal parts or ducts, thus meeting this requirement.

[0009] Traditional stealth aviation technology is not designed for the frequency bands used by PCL. Stealth technology is designed to minimize the cross section of an effective radar target (RCS) - (Radar Cross Section) and is based on obtaining anti-reflection coverage on the plane surface and the shape of the fuselage from the RCS mono-static point of view. These "stealth" features are lost for lower frequency bands, such as Very High Frequency (VHF) - Frequency Modulation (FM) - (Frequency Modulation). Compared to traditional main radar, PCL relies on a much lower, equivalent isotropic radiation power (EIRP) - (Equivalent Isotropically Radiated Power). This inconvenience is offset by the use of long

57P33505PL00

The integration period in the receiver correlation detector because the reference signal is present with a sufficient signal-to-noise ratio. Weather conditions, such as rain, snow, hail, fog, etc., have little effect on the frequency bands used by PCL.

[0010] The PCL system should be able to detect extremely small changes in the signal, scattered by the targets, which are caused by the interaction of the random transmitted signal with the target. The changes of the scattered signals are about 100 dB smaller than the direct signal. In addition, ground interference is about 10 to 50 dB higher in the received signals than the reflected signals, depending on the terrain.

[0011] PCL represents technological challenges that must be solved from the point of view of both a precise antenna and reception techniques, but mainly by using sophisticated digital signal processing methods. As a consequence, detailed system simulations must be performed before deploying the system to investigate known effects and processes affecting the functionality of the PCL system. Extremely high sensitivity is available due to the relatively long signal integration period (0.1 - 1.0 seconds) for coherent processing of CW signals. Detection of those signals that are 100 dB smaller is possible thanks to improved antennas and signal processing.

[0012] In December 2006, there were several PCL systems at various stages of development or implementation:

• PCL Silent Sentry system in Lockheed Martin (USA), which uses FM radio transmissions. Apparently, there are two different variants of antennas available: an antenna that provides 360 azimuth coverage⁰ with 4 different beams

57P33505PL00

The system was developed by Angewandte (Adcock matrix) and a variant that provides an azimuth range of 100⁰ with six different beams (linear matrix). It has a range of up to about 100 nautical miles (185.2 kilometers), depending on the variant used, and a number of receiving nodes at different locations can be combined to provide increased range (<a href="http://www.dtic.mil/ndia/">http://www.dtic.mil/ndia/</a> jaws / sentry.pdf).

Celldar is a British system, jointly by Roke Manor and BAE Systems, a PCL sensor that can use GSM signals, currently in the 900 MHz band, but in the future will also be able to use the 900 MHz and 1800 MHz bands simultaneously. The sensor can track targets in two dimensions in sector 100⁰ with a range of up to about 60 km. Celldar is a low level / surface surveillance system, adapted to achieve good coverage below 10,000 feet (3,048 meters) (<a href="http://www.roke.co.uk/skills/radar/)">http://www.roke.co.uk/skills/radar/)</a>.

CORA is a German PCL sensor, developed by FGAN (Die Forschungsgesellschaft fur Naturwissenschaften eV), which uses Digital Video Broadcast Terrestrial (DVB-T) and Digital Audio Broadcast (DAB) transmissions. Cristal is a PCL sensor developed by Thales that uses FM radio transmissions to track targets. In addition to the Cristal sensor, Thales is thought to have a PCL system prototype that uses analogue TV or DAB transmissions.

One of the PCL systems developed by ERA Systems Corporation, the assignee of this application (<a href="http://www.rannoch.com/">www.rannoch.com</a>) uses eight elements

57P33505PL00

The circular antenna matrix as shown in Figure 2. The system uses a block of analog variable power (VF) - (Variable Power) (receiver and beam forming circuits) with a large dynamic range and linearity. The digital conversion block uses high-quality 24-bit A / D converters (bandwidth (BW) up to 100 kHz). The DSP engine block (digital signal processor) uses a parallel multiprocessor cluster as shown in Figure 3.

[0013] Estimated parameters of one of the ERA PCL unit prototypes, based on 3 FM transmitters, and a target from an effective radiolocation target (RCS) (Radar Cross Section) of the order of 0 dBsm (1 m²) for 100 MHz are as follows:

System delay time, &lt;2 seconds (which depends on the actual computing power of the DSP engine)

Study area: 200 x 200 km, 360 degree coverage. Position accuracy: H - 250 m, Z - 550 m. Horizontal speed accuracy: 2 m / s. Accuracy of determining vertical speed: 8 m / s. Up to 50 targets can be tracked simultaneously.

[0014] To demonstrate how important PCL is for security, the US Government's Request for Information (RFI) has recently been forwarded to the industry (<a href="http://www.hsarpabaa.com/%20Solicitations/MPCL-SOURCES-SOUGHT-NOTICE_final.pdf)">http://www.hsarpabaa.com/</a><a href="http://www.hsarpabaa.com/%20Solicitations/MPCL-SOURCES-SOUGHT-NOTICE_final.pdf)">Solicitations / MPCL-SOURCES-SOUGHT-NOTICE final.pdf)</a>. This request from Homeland Security Advanced Research Projects Agency (HSARPA) from the Department of Homeland Security, Science and Technology Directorate (DHS S&amp;T) was

57P33505PL00

EP 1 992 963 B1 sent for information on Passive Coherent Location (PCL) techniques for detecting surface targets on water and land. In RFI, HSARA stated that they are looking for new and innovative technical solutions for detection and tracking using multi-static locations using PCL, where targets include small and large vessels in coastal waters, ports and waterways as well as ships and people crossing borders .

[0015] HSARA further stated that the system sought should be able to meet the following requirements:

• Be able to provide coverage of either the main port or marina area (such as Miami, New York,

Hampton Roads, or Puget Sound), or along an enlarged shoreline (such as the Florida Keys, Gulf Coast and long Island Sound).

• Be able to detect a 25-foot (7.62 meter) boat (estimated radar cross-section from -5 to dBsm) with a speed of 3 knots (5.556 km / h) or a jet ski with a speed of 10 knots (18.52 km / h).

• Be able to distinguish between surface targets and low-flying aircraft with fixed and rotating wings.

• Be able to track the target better than

100 m.

• Be able to separate and distinguish cells 50 meters apart from each other.

• Be able to develop and maintain a complete tracking image of the area in your area.

57P33505PL00

EP 1 992 963 B1

10 Be able to refresh data less than seconds with a delay less than 5 seconds.

[0016] Many military and security agencies around the world are investigating the utility of PCL. In the Chinese research report presented in the Taipei Times (<a href="http://www.taipeitimes.com/News/archives/1999/11/30/0000013001/wiki">http://www.taipeitimes.com/News/archives/1999/11/30/000001</a><a href="http://www.taipeitimes.com/News/archives/1999/11/30/0000013001/wiki">3001 / wiki</a>) it was found in 1999 that China is close to deploying a defensive anti-aircraft system that uses technology so advanced that it even tracks stealth military aircraft. According to a recent Newsweek article, US analysts are expressing concerns about whether the new early warning defense system could overcome current US Air Force tactics against enemy air defense.

[0017] An article in Newsweek states that defense systems use radar to track incoming aircraft today, but the signals generated can be detected disturbed or decommissioned.

The passive "technology that China probably has at its disposal, detects aircraft by monitoring interference to radio and television signals and is virtually undetectable commercial," reports Newsweek. Technology that can defeat American stealth aircraft, including the F-117 bomber and maybe even the futuristic F-22 fighter, alerted the defense community so that top military and industrial experts were called to discuss strategic implications. At that time, however, a Taiwanese military said it was unlikely that China's PCL technology would go beyond the theoretical stage.

[0018] The patents and published patent applications listed below describe various methods and extensions,

57P33505PL00

EP 1 992 963 B1

11for passive coherent location using a receiver subsystem that receives reference signals from an uncontrolled transmitter and diffuse transmissions, originating from an uncontrolled transmitter and scattered by the object.

[0019] US Patent No. 7,012,552 describes a system of passive coherent awareness of the state of an object, approaching air objects, a receiver subsystem for receiving reference signals from an uncontrolled transmitter and distributed transmissions, originating from an uncontrolled transmitter and diffused by approaching air objects. The leading processing subsystem determines the radial speed of the object based on received transmissions and buffers the digital copy forms of received transmissions. The internal processing subsystem receives digital copies of received transmissions and estimates the state of the object based on the determined radial speed. The leading processing subsystem and the internal processing subsystem are located away from each other. Patent 7,012,552 describes a method of determining when an object is at a predetermined distance from the ground locator. [0020] US Patent No. 7,019,692 describes a system for processing narrowband pre-detection signals for a coherent location passive application. The apparatus receives an input signal containing the target signal and the reference signal. The reference signal is received from the direct path of the uncontrolled transmitter along with the target signal which contains the reference signal reflected from the target. The received signals are sent over two paths for parallel processing. Each path, respectively, contains a target channel and a reference channel for the target signal and the reference signal, and one of the paths is used for the location, which increases in order to track several

57P33505PL00

EP 1 992 963 B1

12 processing correlation signals. Patent 7,019,692 claims a method of processing narrowband pre-detection signals for a passive coherent location application. According to the method, an input signal is received, including the target signal, reflected from the target. The coherent processing time interval is selected. The system performs motion compensation by accepting the tracking device's feedback for the target. Motion compensation is performed over the time of coherent processing. [0021] US Patent No. 6,839,026 describes a system and method for processing a narrowband pre-detection signal for a passive coherent location application. The method includes the steps of receiving the first reference signal and the first target signal, filtering the first reference signal against the first target signal using a filter to form the first reference output signal and combining the first reference output signal with the first target signal to form the first target signal output. receiving a second reference signal and a second target signal, updating the filter relative to the difference between the first target signal and the second target signal, filtering the second reference signal using the updated filter to form a second reference output signal, and combining the second reference output signal with the second target signal to form a second target signal output.

[0022] US Patent No. 6,798,381 describes a system for measuring the association of zone data in passive coherent location applications. The patent describes how to associate a detection report, including measurement results, with a line trace, where the line trace is

57P33505PL00

EP 1 992 963 B1

13 correlated with the reflected source transmitted from the coherent signal, the target and detected by the system of passive location. The method comprises the steps of estimating the line trace state vector based on measurements using a Kalman filter set, the measurement results being at least partially obtained by comparing the signal with the reference transmission from the accidental source and initiating the line trace. Patent 6,798,381 describes a system for measuring the association of detection report data with a trace of a line within a passive coherent location system. Detection reports are correlated with target signals transmitted from an adventitious source, reflected from the target and received by the system of passive coherent location. The system includes means for estimating the state to associate new detection reports with existing line traces and to estimate update states for extending the line traces, with the new detection reports being at least partially obtained by comparing the target signal with a reference signal from an accidental source, means of connecting the trace lines, to connect line traces, means of terminating the line trace, used for terminating line traces according to specific means of initiating a line trace, a servant for new line traces for non-associated detection reports.

[0023] US Patent No. 6,738,021 describes and extracts features in location applications that includes a method for detecting and extracting target information during a coherent processing time interval in a passive coherent location system. The patent describes a method, including the steps of forming a surface ambiguity having data surface ambiguity for a time interval of coherent processing, identifying criteria and initiating a system for passive coherent detection

57P33505PL00

EP 1 992 963 B1

14 packs from the previous pairing of ambiguity packs from the coherent in the system The method includes the steps of the ambiguity surface, from the previous surface the data of the current ambiguity surface and identifying new packages for new target echoes within the ambiguity surface. Patent 6,738,021 also describes a method of detecting and extracting target data for purposes within a time interval for processing a passive coherent location of generating ambiguity surfaces, associating packages from an ambiguity surface, forming detection maxima based on packages and many old packages from a previous ambiguity surface, maximum detections are correlated with target echoes within the coherent processing time interval and estimation of target parameters based on detection maxima.

[0024] US Patent No. 6,710,743 describes a system for central mating and tracking in passive coherent location applications that uses a method of associating a line trace with a target for a passive coherent location system, wherein the passive coherent location system uses comparative data from direct and reflected signals, emitted from one or more transmitters, geographically separated from the receiver. The system receives a detection report, at least partially obtained from a data comparison, the detection report having a line trace corresponding to the target. The target condition is calculated using line trace measurements; calculating state covariance using line trace measurement. The track of the line is obtained according to the covariance of the state of the target and the track of the line is assigned to the target track according to the obtained values.

57P33505PL00

EP 1 992 963 B1

15 or more geographically from the receiver [0025] Patent 6,710,743 also describes a method for associating and tracking target data in a passive coherent location system, where the target data includes measurements of direct and reflected signals, emitted from one transmitter, separated. Target status and target covariance are calculated as based on measurements, wherein the measurements are at least partly a comparison of data from direct and reflected signals. The line track is assigned by correlating the target data with the target track, depending on the target state and state covariance, respectively. The target track is initiated and the filter is initialized according to the target state and state covariance. The target track is tracked using the filter and the target data is extrapolated from the target track.

[0026] US Patent No. 6,703,968 describes a system and method for alleviating interference in a common channel in passive coherent location applications. The system identifies the main illuminator signal from the main illuminator, the main illuminator signal comprising a frequency modulated carrier with a given frequency. The main illuminator signal is regenerated and isolated from the common channel signals. The secondary illuminator signal is identified as being derived from the secondary illuminator, the secondary illuminator signal comprising a frequency-modulated carrier with a given frequency. The secondary illuminator signal is regenerated and isolated from common channel signals.

[0027] US Patent No. 6,522,295 describes a system of passive coherent location to increase awareness of the condition of an object. The receiver subsystem receives a reference signal from an uncontrolled transmitter and distributed transmissions from an uncontrolled one

57P33505PL00

EP 1 992 963 B1

- 16 transmitter and diffused by the object. The leading processing subsystem determines the radial speed of the object based on received transmissions and buffers digital copies of received transmissions. The internal processing subsystem receives digital copies of the transmission and estimates the state of the object based on the determined radial speed.

[0028] US Patent No. 6,522,295 describes a method for determining an updated estimate of an object's condition. The reference transmission is received from the uncontrolled transmitter, along with the distributed transmission that comes from the uncontrolled transmitter and has been dispersed by the object. Received transmissions are compared to determine the receiving frequency difference and the previous status estimate is updated based on the established receiving frequency difference. Digital replicas of received transmissions are buffered, with the digital replicas being received by the internal processing subsystem.

[0029] Published US Patent Application 2003/0001778 describes a system for detecting and determining features in passive coherent location applications. The system includes generating an ambiguity surface and associating packages with an ambiguity surface. The method also includes detecting the formation of maxima in packets, wherein the maxima detection is correlated with target echoes during the coherent processing time interval. The method further includes estimating target parameters based on the detection of maxima.

[0030] US Patent No. 6,930,638 describes a passive object detection method. The receiver receives the first signal transmitted by the cellular base station along with the second signal containing the first signal transmitted by the cellular base station after

57P33505PL00

EP 1 992 963 B1

17bounce it from the object. The first and second signals are compared to obtain data related to the position or speed of movement of the object. The method further includes providing a plurality of cellular base stations that transmit a signal such that when an object moves from the range of one base station, it falls within the range of another, while the distance of the object from the base station, used to determine the position of the object, remains substantially constant, while the distance between the object and the receiver changes, thus improving the received power and range.

SUMMARY OF THE INVENTION [0031] The invention is defined in claim 1. Particular embodiments of the invention are set out in the dependent claims.

[0032] System and technique have been described that have the ability to track and identify, in real time, various airplanes and objects, including Unmanned Aerial Vehicles (UAV) - (Unmanned Aerial Vehicles), Unmanned Combat Aircraft (UCAV) (Unmanned Combat Aerial Vehicles) and Miniature Aircraft (MAV) - (Micro Aerial Vehicles). The system uses a combination of techniques, including traditional automatic dependent surveillance (ADS-B) (Automatic Dependent Surveillance Broadcast), hyperbolic surveillance (multirateration) using a transpoder, hyperbolic surveillance using a broadband emitter, main radar and secondary radar and passive coherent location . A number of extensions to traditional passive coherent location (PCL) have been described - (Passive Coherent Location). The use of the extended PCL system for tracking and categorizing these and other purposes has been described, along with

57P33505PL00

EP 1 992 963 B1

18 integrating tracking data and distinguishing data from other sources.

[0033] According to a first aspect, the present invention includes a system for tracking an object by receiving a reference transmission from a controlled or uncontrolled transmitter and a distributed transmission that originates from a controlled or uncontrolled transmitter and has been dispersed by the object, comparing the received transmissions to determine the difference in reception frequency, thus establishing a track or tracks for an object or objects and updating each track with a set period and forwarding each track to a system processing unit for filtering and display. Broadcasts may contain one or more elements of a group including FM radio signals,

Digital Video Broadcst Terrestrial (DVB-T), Digital Audio Broadcast (DAB) and General System for Mobile Communications (GSM).

[0034] The system includes a Passive Coherent Location (PCL) receiver system that is connected to a stationary system. The stationary system is connected to the passive emitter tracking (PET) receiver system (Passive Emitter Tracking) and to the ELINT channel.

[0035] According to a second aspect, the present invention also includes a system for processing narrowband pre-detection signal for a passive coherent location application. Input signals include a target signal and a reference signal, wherein the reference signal is received from a direct path from a controlled or uncontrolled transmitter, and the target signal includes a reference signal reflected from the target. The target signal and reference signal are correlated in the processing unit

57P33505PL00

EP 1 992 963 B1

19 signals using a database of signals taken a priori as illuminator signals to distinguish reference signals from target signals.

[0036] According to a third aspect, the present invention also includes a method of mitigating interference in a common channel in passive coherent location applications. The database is used to store a priori known near-illuminator signals, with the illuminator signals being part of a group of FM radio signals, Digital Video Broadcast Terrestrial (DVB Digital Audio Broadcast)

DAB) and Global System for

Mobile Communications (GSM). Illuminators are then generated from a database and used to isolate the illuminator signals from common channel signals to remove interference in the common channel.

[0037] According to a fourth aspect, the present invention includes a system and method for continuously detecting and extracting target information using a series of samples in a passive coherent location system. An ambiguity surface is formed, having ambiguity surface data for a number of samples, ambiguity surface, dedicated target information to the processor for comparison with a database of characteristics of a predetermined target type.

[0038] According to a fifth aspect, the present invention also includes a method of associating detection with a line trace, wherein the line trace is correlated with the signal of a controlled or uncontrolled source, target and detected by the passive transmission system.

Mentioned then the central system broadcast with a reflection of the coherent location. The line trace vector is determined based on a series of measurement results using an adaptive set or other filters, with measurement results

57P33505PL00

EP 1 992 963 B1

20 are at least partially obtained by comparing the signal with a reference transmission from a controlled or uncontrolled source. A path is generated, comparable to traditional air traffic control radar systems, containing two states of the tracking device regarding the air traffic control of the path and the sea shore.

[0039] In certain example embodiments of this invention, Passive Emitter Tracking (PET) and PCL receiving systems use the same antenna masts, power supply, connectivity and infrastructure.

[0040] In another embodiment of the present invention, PET includes searching the direction using the phase difference of received target emissions and time difference of arrival (TDOA) for received target emissions.

BRIEF DESCRIPTION OF THE DRAWINGS [0041]

Figure 1 is a diagram illustrating the configuration of PCL according to the current state of the art.

Figure 2 illustrates an eight-element circular antenna matrix used in one of the PCL systems developed by ERA Corporation, the assignee of this application.

Figure 3 is a block diagram of an analogue and digital conversion radio frequency (RF) signal (Radio Frequency) used in a PCL system according to the current state

57P33505PL00

EP 1 992 963 B1

- a technique developed by ERA Systems Corporation, the assignee of this application.

Figure 4 is a block diagram of a first embodiment of the present invention.

Figure 5 is a block diagram of a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION [0042] With reference to Figure 4, in a first embodiment of the present invention, the PCL tracking and identification system is provided as an autonomous system. With reference to Figure 4, the reference signal antenna 1000 transmits various reference signals to the signal conditioning system 1010. The beam forming antenna 1015 transmits the reflected signals through the beam forming system 1020 to the signal conditioning system 1030. Like most passive radar systems that use simple antenna arrays with several antenna elements and conversion to digital form at element level, this allows you to calculate the direction of echo reception using standard radar beam forming techniques such as mono-pulse amplitudes that use a series of overlapping constants bundles, or more sophisticated, adaptive bundling.

[0043] Signal conditioning systems 1010 and 1030 perform some transmitter-specific signal conditioning prior to processing according to a cross-correlation. Conditioning includes analogue signal filtering using a bandpass filter, equalization, to improve the quality of the reference signal and removal of unwanted structures from digital signals, in order to

57P33505PL00

EP 1 992 963 B1

22 improved radar ambiguity function. The main measure in distance detection in most passive radar systems is the signal-to-interference ratio, due to the strong and constant direct signal received from the transmitter. Adaptive filter 1040, using the reference emitter 1100, removes the direct signal, ensuring that the direct signal side flaps used for measuring distance and Doppler shifts will not mask weak echoes in the 1050 cross-correlation step. [0044] The cross-correlation function 1050 acts as a matched filter as well as provides an estimate of the bi-static distance and bi-static shift

Doppler for each target echo. Because analog and digital broadcast signals are inherently high noise and only correlate with each other, 1050 cross-correlation processing uses a bank of matched filters, each matched to a different Doppler shift for the target. Effective implementation of cross-correlation processing based on discrete Fourier transform, as described in the document "Using Reconfigurable HW for High Dimensional CAF Computation", whose authors are A. Hermanek, M. Kunes and M. Kvasnicka from the Institute of Information Theory and Automation, can be used Academy of Sciences of the Czech Republic, Prague, Czech Republic 2003.

[0045] Targets are detected on the cross-correlation surface by applying an adaptive threshold and declaring all returns above that surface as the targets. The standard algorithm of averaging the constant false probability (CFAR) - (Constant False Alarm Rate), or more advanced algorithms, as presented in block 1060. The line tracking function 1070 tracks target returns from specific targets as a function of time in space.

57P33505PL00

EP 1 992 963 B1

23 distances in the Doppler shift function obtained by processing cross-correlation. The standard Kalman filter can be used to remove most false positives in this processing step.

[0046] For tracking function 1080, a simple two-static configuration using one transmitter and one receiver can be used, or the target state (position, direction of flight, speed) can be obtained from a set of results of measurements of two-static distance, bearing and offset Doppler using a non-linear filter, such as an extended Kalman filter. When multiple transmitters are used from the database, the target can be detected by each transmitter and target returns can occur for different values ​​of the two-static distance and Doppler shift for each transmitter, and therefore it is necessary to associate the returns from each transmitter. The target is located exactly in the process that combines the measurement results for each transmitter using a non-linear filter, such as an extended Kalman filter.

[0047] Element 2000 extraction feature processing function for detecting the purpose of target parameters on the basis of uses and determining the ambiguity data surface. The system may use the crest / noise discriminator to compare previous ambiguity surface data with current ambiguity surface data and to update packets correlated with previous ambiguity surface data. The 2010 classification of the goal is done by comparing the distinguished features, e.g. information about the rotorcraft, with the 2000 database.

[0048] With reference to Figure 5, in a second embodiment of the present invention, tracking and identification

57P33505PL00

EP 1 992 963 B1

24PCL is combined with other sources. This embodiment shows the use of PCL when integrated with other surveillance sources that include ADS-B, hyperbolic surveillance, broadband emitter tracking, or Passive Emitter Tracking (PET) as well as identification information from all sources, including electronic intelligence (ELINT) - (Electronic Intelligence). The aircraft 100 flies with a set of hyperbolic / ADSB surveillance receivers and broadband PET receivers, shown as combined receivers 150 for this embodiment. [0049] The data of hyperbolic surveillance sensors / ADS-B / PET are transmitted to central server 250 using various communication media, including fiber optics, telephone lines, wireless as well as satellite communication 200.

[0050] The PCL channel consists of a reference antenna and a beam forming network and is shown separately as 450, but in practice it can be located with other sensors 150. The PCL information is processed to provide trace and classification of the target 450 and data sent to the central server. Finally, the ELINT channel, which provides electronic "fingerprints" associated with PET tracking, provides data on the types of data emitted by each target. Thus, in the central server 300, tracking consists of a fusion of the following sources, if available:

both with connectivity • ADS-B • Hyperbolic supervision • Broadband PET • PCL • SSR • Main radar

57P33505PL00

EP 1 992 963 B1

[0051] Target identification consists of the following data, if available:

• ADS-B / Mode S identification • Mode A / C transpoder code • ELINT PET fingerprint and emitter classification • PCL target separation and fusion classification

57P33505PL00

EP 1 992 963 B1