EP3213111A1 - Système de détection d'intrusion du périmètre, bistatique, à balayage - Google Patents

Système de détection d'intrusion du périmètre, bistatique, à balayage

Info

Publication number
EP3213111A1
EP3213111A1 EP15718950.7A EP15718950A EP3213111A1 EP 3213111 A1 EP3213111 A1 EP 3213111A1 EP 15718950 A EP15718950 A EP 15718950A EP 3213111 A1 EP3213111 A1 EP 3213111A1
Authority
EP
European Patent Office
Prior art keywords
signal
baseline
target
node
received
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP15718950.7A
Other languages
German (de)
English (en)
Inventor
Peter LUDLOW
George Redpath
Stephen Seawright
David Graham
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sensurity Ltd
Original Assignee
Sensurity Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sensurity Ltd filed Critical Sensurity Ltd
Publication of EP3213111A1 publication Critical patent/EP3213111A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/003—Bistatic radar systems; Multistatic radar systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/04—Systems determining presence of a target
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/886—Radar or analogous systems specially adapted for specific applications for alarm systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • G01S7/415—Identification of targets based on measurements of movement associated with the target
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
    • G08B13/181—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems
    • G08B13/187—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems by interference of a radiation field
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S2013/0236—Special technical features
    • G01S2013/0245—Radar with phased array antenna

Definitions

  • This invention relates to perimeter intrusion detection systems and, more particularly, to those that utilise a bistatic radar topology.
  • Microwave perimeter intrusion detection systems generally have one of two basic configurations, comprising either a bistatic or monostatic radar system.
  • the IEEE defines bistatic radar as 'a radar system that uses antennas at different locations for transmission and reception'. In the case of the angle between transmitter and receiver being equal to 180° the system may be described as a forward scatter (FS) radar.
  • FS forward scatter
  • a fixed beam antenna element or antenna array is used to transmit or receive at each node, for example as detailed in US Patent 3,877,002.
  • the strength of the reflected signal from an object is dependent on the scattering properties of the object at the radar operating frequency, i.e. its radar cross section (RCS).
  • the FS RCS of objects that are electrically large at a given frequency is significantly enhanced (relative to the backscattered or BS RCS) due to the effect of Babinet's principle. This effect may be observed for transmitter-target or receiver-target angles within ⁇ 10° of the baseline between transmitter and receiver.
  • a common problem in microwave bistatic radar perimeter intrusion detection systems is the false alarms that may result if processing of the received signal is not able to adequately distinguish an intruder from other fading effects. Also multipath signals may be difficult to observe in the presence of a large direct signal.
  • a first aspect of the invention provides an intruder detection system as claimed in claim 1.
  • a second aspect of the invention provides a method as claimed in claim 40.
  • false alarm reduction is achieved, and greater target information gathered, through the implementation of an electronically scanned bistatic radar system, which preferably uses a phased antenna array for transmission or reception at each side of the link being protected.
  • each detection node is electronically switched between a plurality of scan angle configurations, preferably with a frequency greater than 2n times that of the maximum frequency content of the received multipath signal, where n is the number of scan angle configurations implemented.
  • using an electronically scanned bistatic radar enables simultaneous, or like-for-like, comparisons to be made with stored intrusion signatures for each scan angle configuration, thereby ensuring that the probability of false alarms being triggered is significantly reduced, and detection probability increased, compared with a typical bistatic radar link.
  • correlation of time domain intruder signatures from a plurality of scan angle configurations enables a longer target visibility time and hence improves the received signal-to-noise ratio of multipath target signatures, thereby enabling more accurate application of pattern recognition algorithms.
  • the preferred electronically scanned bistatic radar system helps to resolve a target's baseline crossing point or direction of movement more precisely through switching between a plurality of scan angle configurations focussed along a locus of points running substantially parallel to, or perpendicular to, the link, respectively.
  • Knowledge of the exact baseline crossing point is useful with regard to interception of the target by on-site security as it pinpoints the exact location/direction of movement of the intruder, which may be especially useful for links that have a long baseline length. Determining the target's direction of movement reduces the likelihood of potential false alarm events due to movement or people or vehicles within the perimeter being protected.
  • the preferred electronically scanned bistatic radar system helps to discriminate between movement parallel to, and movement perpendicular to, the link through switching between a plurality of scan angle configurations focussed along a locus of points running substantially perpendicular to the link. This reduces the likelihood of false alarms due to large reflectors, with high RCS, such as cars, moving parallel nearby to the link.
  • a threshold process is advantageously used to determine if objects with RCS above a certain level have been detected within any of the detection zones, and in particular focus regions, formed by the plurality of scan angle configurations of the link. If the variation in the RSSI (Received Signal Strength Indication) signal level is above this threshold then the target parameter/classification process may be triggered; also if a video camera, or other equipment, is linked to the system then recording of video footage of the link will commence. This means that the computational resources used by the system are minimised and current consumption thereby reduced, which is especially important for remotely positioned/battery powered nodes.
  • RSSI Receiveived Signal Strength Indication
  • Figures 1 (a)-(c) are alternative schematic views of an electronically scanned bistatic radar system scanning along a locus of points running perpendicular to the link, the system embodying one aspect of the invention and being suitable for use as an intruder detection system embodying another aspect of the invention;
  • Figures 2(a)-(c) are alternative schematic views of the bistatic radar system scanning along a locus of points running parallel to the link;
  • Figure 3 is a schematic view of an electronically scanned bistatic radar system where both transmit and receive detection nodes are directed along the baseline of the link to be protected;
  • Figure 4(a)-(c) are block diagrams of a transmitter detection node, a receiver detection node and a phased antenna array respectively, being suitable for use in the electronically scanned bistatic radar system or intruder detection system of Figures 1 (a)-(c) and Figures 2(a)-(c);
  • Figure 5(a)-(b) shows typical time-domain and frequency domain plots of RSSI variation as an intruder passes through an electronically scanned bistatic radar link which is scanned through a locus of points running perpendicular to the link baseline, for example of the intruder detection system of Figures 1 (a)-(c);
  • Figure 6(a)-(b) shows typical time-domain and frequency domain plots of RSSI variation as an intruder passes through an electronically scanned bistatic radar link which is scanned through a locus of points running parallel to the link baseline, for example of the intruder detection system of Figures 2(a)-(c);
  • Figure 7 illustrates a preferred target detection method suitable for use in the in
  • Figure 8 illustrates a preferred method of target crossing point evaluation in the intruder detection system of Figures 1 (a)-(c) and Figures 2(a)-(c) or other system supporting an electronically scanned bistatic radar link
  • Figure 9 illustrates a preferred method of target direction of movement evaluation in the intruder detection system of Figures 1 (a)-(c) and Figures 2(a)-(c) or other system supporting an electronically scanned bistatic radar link;
  • Figure 10 (a)-(b) shows typical time-domain and frequency domain plots of RSSI variation as a relatively large reflector moves parallel to an electronically scanned bistatic radar link which is scanned through a locus of points running perpendicular to the link baseline, for example of the intruder detection system of Figures 1 (a)-(c); and
  • Figure 1 1 illustrates a preferred method of discriminating between movement parallel with, or perpendicular to, the intruder detection system of Figure 1 (a)-(c) or other system supporting an electronically scanned bistatic radar link.
  • the system 10 comprises first and second spaced apart detection nodes 12, 14, each node comprising a respective transmitter and/or receiver (or transceiver) for sending or receiving wireless signals 13 to or from the other node.
  • the system may be described as bistatic.
  • the bistatic angle between the nodes 12, 14 (when their respective transmitter/receiver are scanned to a 0° angle) is 180°.
  • systems having other bistatic angles may be implemented.
  • Each node 12, 14 is configured to create a scanned wireless link between the nodes 12, 14, i.e.
  • the transmitting node is configurable to direct wireless signals selectably in any one of a plurality of transmit directions
  • receiving node is configurable to receive wireless signals selectably from any one of a plurality of receive directions.
  • Means for controlling the nodes 12, 14 is provided such that wireless signals 13 are directed between the nodes along a plurality of alternative main signal paths in succession, each signal path corresponding to a respective one of the transmit directions and a corresponding respective one of the receive directions.
  • This action is referred to herein as scanning and the corresponding link between the nodes 12, 14 is referred to as a scanned link.
  • the scanning is preferably performed repeatedly and continuously, at least while the system 10 remains in one or other of its operational modes,
  • a respective suitably controlled phased antenna array (also known as a phased array antenna) is provided in each node 12, 14 to create the scanned wireless link between the nodes.
  • the angle of maximal transmitter or receiver radiation is electronically controlled, and hence the system 10 may be described as an electronically scanned bistatic radar system.
  • any other conventional antenna that is capable of adjusting its transmit/receive direction may be used instead of a phased antenna array, e.g. an antenna mounted on a mechanically movable structure.
  • phased antenna arrays are preferred not least because of the speed at which transmit/receive direction can be changed.
  • the nodes 12, 14 operate as a pair and, although Figures 1 and 2 illustrate a single pair, other embodiments of the system may comprise more than one pair of detection nodes.
  • alternative embodiments of the system 10 may support more than one electronically scanned wireless link.
  • Signals that travel directly between the nodes 12, 14, i.e. without deflection, may be referred to as direct signals and may be said to travel along a baseline between the nodes 12, 14.
  • Signals that reach the receiving node after deflection from an object in a detection zone 16 defined between the nodes 12, 14 may be referred to as multipath signals.
  • the signals comprise electromagnetic signals, typically in the radio frequency or microwave frequency range, and so the link may be described as a radar link.
  • the preferred intruder detection system 10 may therefore be said to comprise an electronically scanned bistatic radar system.
  • a continuous wave (CW) wireless signal is transmitted between the nodes 12, 14, meaning that in a FS configuration (e.g. where the link between nodes 12, 14 is scanned to angles within ⁇ 10° of the baseline between the transmitter and receiver) a received signal will typically comprise a relatively strong direct signal and a weaker multipath signal, which modulates the amplitude and phase of the direct signal.
  • a received signal will typically comprise a relatively weak direct signal and a weaker multipath signal, which modulates the amplitude and phase of the direct signal.
  • node 12 acts as the transmitting node and so comprises transmitter circuitry (for example as shown in Figure 4(b)), while node 14 acts as the receiving node and so comprises receiver circuitry (for example as shown in Figure 4(a)).
  • each node 12, 14 may comprise both transmitter and receiver circuitry, e.g. by means of a transceiver.
  • the respective transmitter/receiver circuitry of each node 12, 14 comprises a respective phased antenna array 18 ( Figure 4(c)), the respective phased antenna arrays 18 of each node 12, 14 being aligned with each other to define the detection zone 16.
  • the antennas of bistatic radar systems typically have a relatively narrow beam width, for example having a 3 dB beamwidth of less than or equal to approximately 12°.
  • the receiver node 14 is sensitive to, i.e. is capable of detecting, multipath signals scattered from a target 20 ( Figure 3) in the zone 16.
  • the ratio of the strength of a direct signal between the nodes 12, 14 to the strength of multipath signals scattered from the target 20 is typically less than a given threshold, for example approximately 30-40 dB.
  • the shape and dimensions of the detection zone 16 are a function of any one or more of: (i) target RCS, as an electrically larger target will have a higher value/narrower beamwidth FS RCS lobe, (ii) target height, as propagation loss for target scattering is inversely related to (target height) for ground links, (iii) link length, as the propagation loss for target scattering is proportional to (link length) A 8 in a ground link, and (iv) phased antenna array gain, as a narrow beam width/low side lobe level transmit or receive antenna will focus transmitted signals or be sensitive to multipath scattered signals, respectively, within a narrower volume of space, (v) phased antenna array scan angle, as this will change the angle at which the antenna's main lobe is oriented and hence the orientation, relative to the transmitter or receiver node, of the volume of space in which the antenna focuses transmitted signals or is sensitive to multipath scattered signals.
  • an object e.g. target 20
  • the detection zone 16 interferes with the electromagnetic field associated with the bistatic radar link and this results in detectable changes (which may be referred to as a signature) in the output signal from the phased antenna array 18 at the receiving node.
  • detectable changes which may be referred to as a signature
  • the target 20 moves through the detection zone 16 a unique signature is detectable in the receiving phased antenna array 18 output, typically as a result of amplitude and phase modulation caused in the received signal by the object's movement.
  • the signature may be evaluated using analogue and/or digital signal processing techniques to determine if an intrusion has occurred.
  • the instantaneous Doppler frequency f d (t) of the scattered multipath signal created as the target 20 moves through the detection zone 16 of the bistatic radar system 10 is determined by the target's speed, v, the wavelength, A, of the continuous wave signal used in the system, the angles from transmitter to target, a h (t), and from receiver to target, ⁇ ), and the baseline crossing angle, ⁇ .
  • phased antenna array switching time is the speed of the digital control interface used to change scan angles in digital phase shifters.
  • FIG. 4(a) shows receiver circuitry suitable for use in the detection nodes 12, 14.
  • detection node 14 comprises the receiver circuitry.
  • the receiver circuitry comprises the phased antenna array 18, which is capable of sending and receiving signals via the wireless link between the nodes 12, 14, a receiver 22, filter 24 and a processor 26.
  • the receiver 22 is coupled to the phased antenna array 18 such that it may receive signals.
  • the receiver 22 comprises a superheterodyne receiver and, as appropriate, is operable to downconvert radio frequency (RF) signals to intermediate frequency (IF) signals.
  • RF radio frequency
  • IF intermediate frequency
  • the receiver 22 is preferably configured to produce an output signal comprising an RSSI (Received Signal Strength Indicator) signal.
  • RSSI Receiveived Signal Strength Indicator
  • the output of the receiver 22 is provided to the filter 24 for removing unwanted components of the receiver output.
  • the filter 24 typically comprises a high-pass filter (to eliminate low-frequency clutter signals from, for example, vegetation or rainfall) and a low pass filter (usually with a cut off frequency more than twice that of the maximum frequency content of the scattered multipath signal, thereby preventing aliasing from occurring during sampling of the signal).
  • An analogue-to-digital converter (ADC) is usually provided for sampling the (filtered) output signal.
  • ADC analogue-to-digital converter
  • the resulting digitised received output signal is provided to analysing means, typically comprising a suitably programmed processor 26, for analysis.
  • the processor 26 may comprise a suitably programmed microprocessor, microcontroller or other digital signal processing (DSP) device. As is described in more detail hereinafter, the processor 26 is configured to detect the presence of an intruder in the detection zone 16.
  • FIG. 4(b) shows transmitter circuitry suitable for use in the detection nodes 12, 14.
  • detection node 12 comprises the receiver circuitry.
  • the transmitter circuitry comprises a transmitter 28, which may take any convenient conventional form, a processor 30 and the phased antenna array 18.
  • the processor 30 may comprise a suitably programmed microprocessor, microcontroller or other digital signal processing (DSP) device.
  • DSP digital signal processing
  • FIG. 4(c) shows a preferred embodiment of the phased antenna array 18, which in this example comprises an architecture well known to one skilled in the art.
  • transmit RF signals are input to a power divider network 32.
  • the N outputs from the power divider network 32 are input to a respective digital phase shifter 34, which may be conventional.
  • the magnitude of the phase shift, ⁇ , applied to the RF signal at each digital phase shifter 34 may be incremented digitally using a typical digital control interface, such as the l 2 C or SPI protocols.
  • the RF phase shift may be applied in the order of nanoseconds, however the speed at which switching between phase states may occur is limited by the speed of the digital control protocol, which is typically > 10 MHz in the case of the SPI protocol. Therefore switching may typically occur in the order of ⁇ 100 microseconds.
  • An alternative embodiment of the system may use analogue phase shifters, which have a voltage control line to allow switching between phase shift angles over a continuous range.
  • the voltage control line of the phase shifter may be driven from a digital-to-analogue converter on a processor to enable convenient switching of phase shift angles.
  • Each digital phase shifter 34 is connected to a respective antenna element or antenna sub-array 36. When used for receiving, the operation of the phased antenna array 18 is reciprocal to that described for transmitting, as would be apparent to a skilled person.
  • the steering angle, ⁇ 0 of the main beam of the phased antenna array 18 is dependent on the RF phase shift applied at each phase shifter 34, ⁇ , and the electrical spacing, d/A 0 , between each antenna element, or antenna sub-array 36, measured in wavelengths.
  • 9 n sin [2]
  • the receiver detection node 14 may distinguish a received multipath signal from a received direct signal by using variations in RSSI levels to evaluate intrusions. For example, for a direct signal the RSSI remains at a relatively high and constant level, whereas for multipath signals the RSSI level varies.
  • the processor 26 may be programmed or otherwise configured to perform such analysis of the received signals.
  • the filter 24 may be configured to remove the dc content in the RSSI signal in order that only variations in RSSI level are analysed.
  • each node 12, 14 is configured to implement low bitrate amplitude shift keying (ASK) or frequency shift keying (FSK) modulation to uniquely pair the, or each, pair of transmitter and receiver nodes 12, 14 present in the system 10 via transmission of a unique identifier code between paired nodes.
  • ASK amplitude shift keying
  • FSK frequency shift keying
  • the phased antenna array 18 of the respective transmitter and receiver nodes 12, 14 of a pair switch at intervals between operating at any one of a plurality of scan angle configurations and operating at the next of the scan angle configurations. Typically, the switching is performed until all supported scan angle configurations have been implemented and is then repeated. In preferred embodiments, switching between scan angle configurations occurs continuously, irrespective of whether a target 20 is present in the detection zone 16.
  • the respective processors 26, 30 control the switching between scan angle configurations. In the embodiment shown in Figure 4(c) the respective processor 26, 30 provides the digital control signals to the digital phase shifters 34 for this purpose.
  • the system 10 may have a first operating state (illustrated in Figure 1 (a)) in which transmit and receive phased antenna arrays 18 are adopt a first scan angle configuration (T R-i) to focus on a region 40 on one side of the baseline, a second operating state (illustrated in Figure 1 (b)) in which transmit and receive phased antenna arrays 18 are directed along the baseline, i.e.
  • a first operating state illustrated in Figure 1 (a)
  • T R-i first scan angle configuration
  • a second scan angle configuration (T 2 , R 2 ) where T 2 , R 2 are equal to 0°, to focus on a region 42, and a third operating state (illustrated in Figure 1 (c)) in which transmit and receive phased antenna arrays 18 adopt a third scan angle configuration, (T 3, R 3 ), to focus on a region 44 on the opposite side of the baseline to the first scan angle configuration.
  • the scan angle configurations are selected such that, as the system 10 switches operating state to the next, the focus region 40, 42, 44 where the transmit and receive directions intersect moves along a locus oriented substantially perpendicularly to the baseline.
  • the focus regions 40, 42, 44 are substantially equidistant from the nodes 12, 14 although this need not necessarily be the case in alternative implementations.
  • three operating states are shown although more generally two or more operating states may be supported.
  • the system 10 may have a first operating state (illustrated in Figure 2(a)) in which transmit and receive phased antenna arrays 18 adopt a first scan angle configuration, (T a , R a ), to focus on a region 46 that is closer to the transmit node 12 than the receive node 14, a second operating state (illustrated in Figure 2(b)) in which transmit and receive phased antenna arrays 18 adopt a second scan angle configuration, (T b , R b ), to focus on a region 48 midway between transmitter 12 and receiver 14, and a third operating state (illustrated in Figure 2(c)) in which the transmit and receive phased antenna arrays 18 adopt a third scan angle configuration, (T c , R c ), to focus on a region 50 that is closer to the receiver 14 than the transmitter 12.
  • the scan angle configurations are selected such that, as the system 10 switches operating state to the next, the focus region 46, 48, 50 where the transmit and receive directions intersect moves along a locus oriented substantially parallel with the baseline.
  • the focus regions 46, 48, 50 are substantially equidistant from the baseline although this need not necessarily be the case in alternative implementations.
  • three operating states are shown although more generally two or more operating states may be supported.
  • the switching between scan angle configurations is conveniently performed periodically, preferably at a frequency greater than 2n times that of the maximum frequency content of the received multipath signal, where n is the number of scan angle configurations implemented in the system 10.
  • n is the number of scan angle configurations implemented in the system 10.
  • the transmitter and receiver nodes 12, 14 may communicate with one another by any convenient means (not shown) to synchronise switching between different scan angle configurations.
  • the nodes may be linked by Ethernet in which case the Precision Time Protocol, defined in the IEEE 1588 standard, may be used for synchronisation of switching. This allows sub-microsecond synchronisation.
  • a GPS module (not shown) may be provided in each transmitter or receiver node 12, 14 to allow synchronisation with atomic clocks on GPS satellites, which means synchronisation accuracy at the GPS module of typically 100 nanoseconds or less. Either of these techniques, or any other convenient technique, may be implemented in the system 10 using readily available off-the-shelf components.
  • the processor 26 may be programmed to perform pattern recognition (and/or other analysis) on the receiver output signals, and in particular in respect of the target signatures included in the output signals.
  • the target signatures may be represented as plots (or other representation) of signal power, conveniently normalised received signal power, versus target frequency, conveniently Doppler frequency (where Doppler frequency describes the variation in the frequency of the received multipath signals over time), as shown in Figure 5(b), for the system configurations shown in Figures 1 (a)-(c).
  • the signal power values may be normalised to the maximum power level in the signal.
  • the instantaneous Doppler frequency defined in equation [1] above corresponds to a single point on the x-axis of this plot which, for a target 20 moving at a certain speed and for a known radar operating wavelength, will correspond to the position of a target relative to the transmitter 12 and receiver 14.
  • the normalised signal power amplitude depends on the amplitude of the received multipath signal for this target position, which is dependent on target RCS/target height/link length/phased array antenna gain/phased array antenna scan angle.
  • the characteristics of the frequency domain, or Doppler frequency, plots used for pattern recognition are dependent on the feature extraction technique used.
  • the frequency characteristics may be assigned automatically using for example Principle Component Analysis, which reduces the dimensionality of the frequency domain signatures down to Principle Components, the number of which may be chosen by the user.
  • the characteristics may be manually extracted, e.g. first main lobe width, second main lobe width, and/or number of lobes below a set threshold frequency.
  • the lobe widths and number of lobes are primarily affected by variations in the received signal level due to how the radar cross section of the target varies for particular target-receiver angles, /3 h ffJ - radar cross section nulls occur at particular angles, corresponding to nulls at particular instantaneous Doppler frequencies as each
  • instantaneous Doppler frequency corresponds to a target position relative to transmitter/receiver.
  • target detection may be performed using threshold analysis, e.g. determining if the movement of the target through the direct path of the link has led to a drop greater than a threshold value in the amplitude of the received signal in the time domain, conveniently the RSSI amplitude, meaning that a target with an RCS greater than a threshold value has passed through the link. It is noted that the target does not necessarily have to cross the baseline of the link for it to cause a drop in the RSSI greater than the threshold value set at the receiver 14 for target detection.
  • threshold analysis e.g. determining if the movement of the target through the direct path of the link has led to a drop greater than a threshold value in the amplitude of the received signal in the time domain, conveniently the RSSI amplitude, meaning that a target with an RCS greater than a threshold value has passed through the link. It is noted that the target does not necessarily have to cross the baseline of the link for it to cause a drop in the RSSI greater than the threshold value set at the receiver 14 for target detection.
  • the RSSI may drop by an amount greater than the threshold value (which is typically set for smaller targets, such as people, with smaller RCS moving through the baseline of the link).
  • a simple threshold detection method is vulnerable to false alarms since multipath signals received from outside of the direct path may also cause signal amplitude drops of greater than the threshold value. Also, relatively subtle changes in the received signal caused by movement of a low RCS target, such as a crawling person, through the link may not be detected.
  • RSSI RSSI
  • threshold analysis is used to trigger subsequent target detection, for example application of signal processing algorithm(s), in order to classify the target that caused the RSSI change with greater accuracy and fewer false alarms.
  • the processor 26 is programmed to implement one or more pattern recognition algorithms. This may involve comparing one or more characteristics of the received multipath signal(s) (which may be said to be represented by a signature of the respective signal) with one or more of a plurality of stored comparable signatures (i.e. data representing one or more corresponding characteristics of a plurality of reference signals) that represent respective identifiable events, such as intrusion events or false alarm events.
  • the stored signatures may be stored in local memory (not shown) in the node 14.
  • Multipath signals caused by movement of a target between the transmitter and receiver nodes 12, 14 are received in the time domain with a "signature" amplitude and phase variation.
  • a "signature" amplitude and phase variation For the purposes of analysis, it is convenient to convert time domain multipath signals to the frequency domain, e.g. using FFTs, thereby creating a corresponding frequency signature for the target.
  • the stored signatures for comparison with the frequency signatures obtained from the received multipath signal conveniently also comprise corresponding frequency domain signatures that facilitate comparison by signal processing.
  • the frequency signatures preferably comprise Doppler frequency signatures.
  • pre-processing of the received frequency signatures is advantageously performed to normalise them to a reference target speed and also to the maximum power level in the received signal.
  • the baseline crossing point/angle is preferably evaluated to reduce the number of stored frequency domain signatures with which comparison is to be made, i.e. for particular intervals of baseline crossing point/crossing angle, frequency domain signatures of target types are stored.
  • the pre- processing may involve an autocorrelation process, which compares the phase variation in the received time domain signal with that expected for a particular target speed, baseline crossing point and baseline crossing angle.
  • Pattern recognition algorithms well known to one skilled in the art, for example involving a neural network approach or a principle component analysis/K-nearest neighbour approach, may be used.
  • the use of pattern recognition algorithms enables determination of intrusion with a high level of accuracy.
  • Using an electronically scanned bistatic radar link enables simultaneous comparisons to be made with the stored database of intrusion signatures for each scan angle configuration, thereby further reducing the probability of false alarms, and increasing detection probability, compared with a typical bistatic radar link using a fixed beam antenna array.
  • the target's frequency signature in particular its Doppler signature, is dependent on its speed, baseline crossing point and baseline crossing angle.
  • the processor 26 prior to any comparisons with reference intruder signatures stored in the database, the processor 26 performs a pre-processing process to normalise the received Doppler signatures to a selected (or reference) target speed. The processor 26 also determines a baseline crossing point and baseline crossing angle for the target. This allows the number of database signatures that the detected signature should be compared with to be reduced.
  • the stored reference signatures comprise respective Doppler signatures for a plurality of target types (e.g.
  • a person running, walking, jumping, commando rolling, crawling on hands and knees or belly crawling and optionally one or more anticipated false alarm Doppler signatures (e.g. representative of a small animal walking or a bird/flock of birds flying through the link, especially when close to either node, or a car moving parallel to the link), respective such reference signatures preferably being stored for respective intervals of baseline crossing point/crossing angle.
  • Doppler signatures e.g. representative of a small animal walking or a bird/flock of birds flying through the link, especially when close to either node, or a car moving parallel to the link
  • Figure 7 shows a flow chart of the preferred detection process used by the, or each, receiver node 14 in the evaluation of received signals for each scan angle configuration, the process conveniently being performed by the respective processor 26.
  • the received signal which in this example is assumed to have been filtered and digitised, is provided to the processor 26. It is also assumed in this example that the received signal is provided as, or at least comprises, an RSSI signal.
  • the received signal is subjected to a threshold analysis to determine if a target 20 with an RCS above a certain level has been detected within the detection zone 16 of the link supported by the nodes 12, 14.
  • the threshold analysis involves comparing a characteristic, typically the amplitude, of the received signal (in this case the RSSI signal, in particular the filtered RSSI level since it is the RMS amplitude of the ac content in the RSSI signal that is assessed in the preferred embodiment) against a threshold value. It is preferred to analyse variations in the multipath signal strength (RSSI level in this example) using RMS values. If the RMS amplitude exceeds the threshold value for a given measurement period of, for instance, 0.1 seconds then it is assumed that an object has been detected in the detection zone 16.
  • a characteristic typically the amplitude
  • the target analysis process is initiated (703 to 705), otherwise it is determined that no object is detected (706).
  • the system 10 includes one or more activatable detection or monitoring devices, for example one or more video cameras for monitoring the detection zone (or elsewhere), such devices may be activated in response to the detection of an object.
  • the computational resources used by the system 10 are minimised and current consumption thereby reduced, which is especially important for remotely positioned and/or battery powered nodes 12, 14.
  • the preferred target analysis process involves a transform, conveniently a Fast Fourier Transform
  • (704) is then employed to normalise the speed and baseline crossing point/angle to reference values, to facilitate comparison of the received signal with the stored signatures.
  • This may involve the use of conventional pattern recognition algorithms such as neural network analysis or principle component/K-nearest neighbour analysis.
  • a decision is made, based on the result of this process, to determine whether to cause an alarm signal to be rendered to an end user via any suitable interface (707) (e.g. comprising one or more visual and/or audio output device).
  • any suitable interface e.g. comprising one or more visual and/or audio output device.
  • Figures 5(a)-(b) and Figures 10(a)-(b) show respective typical time-domain and frequency domain plots of the received signal for each scan angle configuration shown in Figures 1 (a)-(c), i.e. (T 1: R-,), (T 2 , R2) and (T 3 , R 3 ), respectively.
  • Figures 6(a)-(b) show typical time-domain and frequency domain plots of the received signal for each scan angle configuration shown in Figures 2(a)-(c), i.e. (T a , R a ), (T b , R b ) and (T c , R c ), respectively.
  • the plots in particular show variations in the RSSI signal as an intruder (target 20) walks through the electronically scanned link between the nodes 12, 14.
  • the time at which the intruder crosses the baseline of the link equates to the time at the origin of the plot.
  • the intruder crosses the baseline at the midpoint of the link in Figures 6(a)-(b) the intruder crosses the baseline at a point perpendicular to the focus region 46 of scan angle configuration (T a , R a ).
  • the plots show variations in RSSI signal as an object, for example a relatively large reflector such as a car (not shown), moves parallel to the electronically scanned link between the nodes 12, 14, passing through focus region 40 of Figure 1 (a).
  • objects are not considered to be valid targets and it is desirable that the system 10 can distinguish between them and valid targets.
  • a valid target 20 may for example be an object that crosses or at least moves in a direction towards the baseline between the nodes 12, 14.
  • the time at which the large reflector passes through focus region 40 of Figure 1 (a) equates to the time at the origin of the plot.
  • the amplitude envelope of the time-domain signal varies according to any one or more of: the propagation loss (which is greater for lower target height, a longer link length and, in the case where the target crosses the baseline, baseline crossing points closer to the link centre), target RCS, phased antenna array beamwidth and phased antenna array scan angle.
  • the phase shift of the time-domain signal is due to the varying propagation path (from transmitter 12 to target 20 to receiver 14) length, as detailed in equation [1 ], as the target 20 moves through the detection zone 16.
  • the frequency resolution is equal to the sampling or observation time divided by the sampling rate.
  • the significant increase in intruder RCS that occurs as they cross through the link baseline means that the amplitude envelope is still of a significant magnitude, despite the lower phased antenna array gain along the baseline, as while the absolute direct and multipath signal levels are at a reduced level, the ratio of received multipath and direct signals will be of a similar magnitude to the case where the phased antenna array scan angle configuration is focussed along the baseline.
  • the visibility time of the target 20 corresponds to the signal- to-noise ratio of the target's time domain signature. Hence by increasing the target visibility time it is possible to detect or classify targets with greater accuracy.
  • the amplitude envelope is significantly lower. This is due to the scan angle of the phased array antenna being focussed away from the movement of the large reflector, such that it illuminates said reflector less strongly and is less sensitive to multipath signals generated by said reflector.
  • the scan angle of the phased array antenna being focussed away from the movement of the large reflector, such that it illuminates said reflector less strongly and is less sensitive to multipath signals generated by said reflector.
  • the amplitude is significantly higher (e.g. higher by more than a threshold amount, where the threshold may be an absolute value but more typically a percentage value) for one or more scan angle configuration corresponding to a respective focus region on one side of the link than it is for one or more scan angle configuration corresponding to a respective focus region on the other side of the link (or closer to the link but on the same side)
  • the processor 26 is illustrated by way of example in Figure 1 1.
  • FIG. 1 1 there is shown a flow chart of a process that may be used, conveniently by processor 26, to evaluate whether a detected object is moving parallel with the baseline of the link, or through the baseline of the link.
  • the respective time domain signatures, and in particular the respective amplitude, captured as the system 10 scans along a locus of points running substantially perpendicular to the baseline, for example as shown in Figures 1 (a)-(c), are compared with one another.
  • a threshold process (1 12) which may be similar to that described above, to evaluate if the RSSI variation in the received signal increases beyond a threshold value, for example a preset RMS value, for respective scan angle configuration(s) on one side of the baseline compared to respective scan angle configuration(s) on the other side. If the difference in amplitude is sufficiently great, then it may be concluded that the detected object is a parallel-moving non-target (1 13) in which case no further action may be taken, otherwise it may be determined that the object is a potentially baseline-crossing target (1 14), and any relevant further analysis may be performed.
  • a threshold value for example a preset RMS value
  • the scanned link is scanned through multiple scan angle configurations with focus regions 46, 48, 50 in a locus running parallel to the baseline.
  • the amplitude envelope of the corresponding time domain signatures shown in Figure 6(a) increases in magnitude as the intruder moves closer to the baseline. This is due to the intruder's FS RCS increasing considerably here due to Babinet's principle (assuming their cross section is electrically large at the radar operating frequency).
  • the time domain signature of the target 20 becomes visible in each plot at different times, i.e. for the scan angle configuration focussed closer to the transmitter node 12, in Figure 2(a), the time domain target signature is visible at an earlier time compared with the plots of Figure 2(b) or 2(c).
  • This is due to the varying shape of the detection zone 16 for each scan angle configuration, as shown in Figures 2(a)-(c), whereby the transmit or receive phased array antennas18 focus, or are more sensitive to, signals in particular regions of space for each configuration.
  • an intruder passing close to the transmitter node 12 is visible at an earlier time for the scan angle configuration focussed close to the transmitter node 12 and so on.
  • an autocorrelation process may be employed, typically by the processor 26, to correlate an expected phase variation in the received signal as a target 20 moves through the detection zone 16 with a given speed and baseline crossing point/angle (as predicted in equation [1]) with that observed.
  • Expected phase variation may be obtained from any one or more of a plurality of reference signal data. This pre-processing process can only determine that an intrusion occurred at a certain distance from the midpoint of the baseline of the link, as the phase variation in the time domain for targets moving symmetrically with respect to the midpoint is identical.
  • FIG. 8 shows a block diagram that illustrates this process, as may be performed by the processor 26.
  • an evaluation of the distance of an intrusion from the baseline is made using a first technique, namely correlating an expected phase variation in the received signal as a target 20 moves through the detection zone 16 with a given speed and baseline crossing point/angle (as predicted in equation [1]) with that observed.
  • FIG. 8 shows a flow chart of a process that may be used, conveniently by processor 26, to evaluate the target's direction of movement through the link.
  • the time domain signatures of the electronically scanned link as it is scanned along a locus of points running substantially perpendicular to the baseline, for example as shown in Figures 1 (a)-(c), are compared with one another.

Landscapes

  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Electromagnetism (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Burglar Alarm Systems (AREA)

Abstract

L'invention concerne un système radar bistatique à balayage électronique comprenant un réseau d'antennes réseau à commande de phase pour la transmission ou la réception à chaque nœud d'une liaison qui est protégée. Chaque nœud est électroniquement commuté entre une pluralité de configurations d'angle de balayage. Un point de croisement de ligne de base ou une direction de mouvement est déterminé de manière plus précise par commutation entre une pluralité de configurations d'angle de balayage focalisées le long d'un lieu de points s'étendant sensiblement parallèlement ou perpendiculairement à la liaison. Le système réduit l'incidence de fausses alarmes et permet à plus d'informations cibles d'être rassemblées.
EP15718950.7A 2014-05-06 2015-05-01 Système de détection d'intrusion du périmètre, bistatique, à balayage Withdrawn EP3213111A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1407958.6A GB2525867A (en) 2014-05-06 2014-05-06 Scanning bistatic radar perimeter detection system
PCT/EP2015/059629 WO2015169709A1 (fr) 2014-05-06 2015-05-01 Système de détection d'intrusion du périmètre, bistatique, à balayage

Publications (1)

Publication Number Publication Date
EP3213111A1 true EP3213111A1 (fr) 2017-09-06

Family

ID=50980646

Family Applications (1)

Application Number Title Priority Date Filing Date
EP15718950.7A Withdrawn EP3213111A1 (fr) 2014-05-06 2015-05-01 Système de détection d'intrusion du périmètre, bistatique, à balayage

Country Status (3)

Country Link
EP (1) EP3213111A1 (fr)
GB (1) GB2525867A (fr)
WO (1) WO2015169709A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3206044B1 (fr) * 2016-02-12 2023-09-13 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Dispositif de détection d'un objet et procédé correspondant
CN105929377B (zh) * 2016-05-16 2018-05-11 武汉大学 一种基于单极子交叉环天线的高频雷达船舶方位角估计方法
US11467278B2 (en) 2017-06-29 2022-10-11 Sensing Management Pty Limited System and method of detecting objects
CN112180326B (zh) * 2020-09-21 2023-11-21 南昌大学 一种基于大规模天线阵的分层分布式定位和测速方法
CN116996133B (zh) * 2023-09-27 2023-12-05 国网江苏省电力有限公司常州供电分公司 电力线载波通信设备身份认证及窃听定位方法

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4967183A (en) * 1988-05-18 1990-10-30 Eastman Kodak Company Method of intrusion detection over a wide area
US4952939A (en) * 1989-02-16 1990-08-28 Seed Willian R Radar intrusion detection system
US5200755A (en) * 1989-12-06 1993-04-06 Mitsubishi Denki Kabushiki Kaisha Bistatic radar system
JP3521899B2 (ja) * 2000-12-06 2004-04-26 オムロン株式会社 侵入物検知方法および侵入物検知装置
JP3643871B2 (ja) * 2002-02-26 2005-04-27 防衛庁技術研究本部長 マルチスタティック・レーダ装置
JP2004085363A (ja) * 2002-08-27 2004-03-18 Omron Corp 侵入物体検出装置及びその設定装置、設定方法、並びにその設定確認方法
JP3903221B2 (ja) * 2005-06-24 2007-04-11 オプテックス株式会社 防犯センサ
GB0719995D0 (en) * 2007-10-12 2007-11-21 Qinetiq Ltd Radar method and apparatus suitable for use in multipath environments
US8456349B1 (en) * 2009-03-19 2013-06-04 Gregory Hubert Piesinger Three dimensional radar method and apparatus
KR101257061B1 (ko) * 2011-05-24 2013-04-22 주식회사 에스원 다중 안테나 기반 침입 감지 시스템 및 방법

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
None *
See also references of WO2015169709A1 *

Also Published As

Publication number Publication date
WO2015169709A1 (fr) 2015-11-12
GB2525867A (en) 2015-11-11
GB201407958D0 (en) 2014-06-18

Similar Documents

Publication Publication Date Title
US20160178741A1 (en) Bidirectional bistatic radar perimeter intrusion detection system
EP3213111A1 (fr) Système de détection d'intrusion du périmètre, bistatique, à balayage
US4952939A (en) Radar intrusion detection system
US6275180B1 (en) Collision warning system
US6400307B2 (en) System and method for intrusion detection using a time domain radar array
US6218979B1 (en) Wide area time domain radar array
US9857462B2 (en) Detection of concealed object on a body using radio frequency signatures on frequencies and polarizations
WO2013175558A1 (fr) Dispositif de radar et procédé de vérification d'angle
US20060267764A1 (en) Object detection sensor
CN108291959A (zh) 具有交错串行发射和并行接收功能的雷达系统
US8477063B2 (en) System and method for obstacle detection and warning
Andrews et al. Active millimeter wave sensor for standoff concealed threat detection
KR101507238B1 (ko) 레이더 장치
JP2015190777A (ja) 歩行者検出装置
Narayanan et al. A multifrequency radar system for detecting humans and characterizing human activities for short‐range through‐wall and long‐range foliage penetration applications
JP4754292B2 (ja) レーダ装置
JP5678692B2 (ja) レーダ装置
RU2455692C1 (ru) Способ обнаружения нарушителя в контролируемой зоне
DE102005049772A1 (de) Bewegungssensor sowie Verfahren zu seinem Betrieb
Inomata et al. Wide-area surveillance sensor with leaky coaxial cables
Kohlleppel et al. Enhancement of along-track interferometry for ground moving target indication
Rezgui et al. Standoff detection of concealed handguns
RU2215303C2 (ru) Способ контроля воздушного пространства
Caruso et al. An X-band FMCW radar for airports' perimeter surveillance
Bouhlel et al. FMCW radar system for transponder identification

Legal Events

Date Code Title Description
STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE INTERNATIONAL PUBLICATION HAS BEEN MADE

PUAJ Public notification under rule 129 epc

Free format text: ORIGINAL CODE: 0009425

PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: REQUEST FOR EXAMINATION WAS MADE

17P Request for examination filed

Effective date: 20161206

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: EXAMINATION IS IN PROGRESS

17Q First examination report despatched

Effective date: 20190220

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: EXAMINATION IS IN PROGRESS

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 20211201