• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The present invention relates to a system (300) for reducing or concluding unwanted signals when detecting objects useful to a detection system (200). The detection system is an antenna-based system that uses 2 or more receive beams as an echo response to an emission signal. The system (300) for reducing or canceling unwanted signals consists of an input (310) adapted to obtain from the aforementioned antenna system (210) receive signals from a first receive beam and receive signals from at least one other receive beam. . In addition, it includes a coupler (320) adapted to couple receive signals from a first receive beam with receive signals from at least a second receive beam, so as to obtain a detection signal with suppressed unwanted signal contribution to better distinguish objects of interest.
    公开号:BE1019043A3
    申请号:E2009/0595
    申请日:2009-09-25
    公开日:2012-02-07
    发明作者:
    申请人:Intersoft Electronics Nv；Vanuytven Marcel P G；
    IPC主号:
    专利说明:

    Clutter reduction in detection systems
    Technical support of the invention:
    The present invention relates to the field of signal detection, such as, for example, radar or sonar detection. In particular, the invention influences the methods and systems for reducing or completely eliminating “dutter” in signal detection.
    Background of the invention:
    Detection of presence, position and / or speed of objects is common especially in traffic, such as for example civil and military air traffic control, parking guide systems, navigation or submarine detection of objects, etc. Various detection systems are known, most use a transmission signal and an antenna signal to focus energy on targets and measure the returning signals using the same antenna and a receiver to identify the targets and measure the associated parameters. Such systems can utilize the properties of sound waves in applications such as sonar or of electromagnetic signals in the case of radar or similar technologies.
    The range of such measuring systems is limited by the so-called “line of sight” rule, meaning that the antenna must be in a position with a view of the targets, since unwanted objects or objects that are not important but that occur located between the antenna and the target can disrupt or even prevent the detection of the target. Nevertheless, such unwanted objects can sometimes not be avoided and unwanted detection of these objects can make it difficult to trace the objects of interest. Unwanted detections are called “dutter” and must be rejected as they can obstruct the view of the observer. Clutter suppression is a very important but difficult aspect of signal processing. For example, in radar signal processing, the intensity of dutter caused by artificial structures, forests, hills, and mountains is often much stronger than the recurring signal from, for example, a small aircraft. Over the past 50 years, highly advanced techniques have been developed to minimize the impact of dutter on aircraft detection. Examples of these methods are the "ΜΊΊ" (Moving Target Indicator) technique and the "MTD" (Moving Target Detector) technique and techniques that use Doppler signal processing. As a result of the technological progress of computers, these methods have led to a clute level that is considered workable. On the hardware side, better antennas with lower side lobes have been developed to reduce ground-level exposure, from which most of the recurring clutter signals are received. Unfortunately, the level of side lobe reduction has practical limits that are caused by the cost of antenna size and the environment.
    A large number of solutions are aimed at filtering properties of the signals that are important. More specifically, the spectral content of the return signal is used to filter and reduce clutter intensity. The latter can be based on the fact that moving objects exhibit a Doppler shift.
    However, in this way also signals are rejected that come from objects with a low radial speed and that arrive at the receiver simultaneously with the clutter signal. Since the Doppler shift is proportional to the radial speed of the object, objects that perform a tangential flight above a clutter area have a considerably lower chance of being detected. In addition, most radars have a range requirement that limits their Doppler filter capabilities. Air Traffic Control (ATC) radars suffer from a problem known as "blind speed": if the sampling frequency of the radar is not high enough, under-sampling can take place making the target appear stationary to the radar, even on a radial flight. in this case the target will be rejected by the clutter filter. With a radar performance according to the current state-of-the-art techniques, a dutter reduction of 5 OdB is theoretically feasible. But the most important limitation of clutter filters based on the difference in spectral content of an object versus dutter signals lies in the fact that many dutter objects are also not stable at all. "Sea napter" in particular is a major challenge for a radar that illuminates the surface of the water since the reflectivity is high and the object (the sea) often moves erratic.
    Another problem for accurate detection is the distance dependency of dutter. At larger ranges where a radar or sonar is active, there is usually little nap as the curvature of the earth limits the number of objects within range. With smaller ranges, the dutter level rises considerably as evidenced by the path loss formula that has an inverse fourth-order power of the range. In fact, most airport radars must take extra measures to prevent their receiver from becoming saturated with too much nap. If saturation occurs, the MTI mechanism cannot work and the target is lost for all speeds. There are usually two methods available to keep the return signals in the dynamic range of the receiver.
    1. The vertical antenna pattern is designed asymmetrically so that there is a "roll-off" at a certain elevation angle; this reduces the number of retinal signs from a low elevation.
    2. Most antennas have 2 or more beams that point to a different elevation angle. For the first few hundred microseconds after the transmission, the High Beam (HB) is switched to the receiver. If the dutter return signals are lower than the saturation level, the Low Beam (LB) is used. To illustrate this effect, images FIG. 1a and 1b, the figures show a zoomed-in image that is available on the output of the receiver. FIG. 1 a shows the signals when the LB is in use and it can be seen that the view is completely cluttered with signals up to the saturation level. As a result, potential targets that are important are completely masked. The video from the HB reduces the number of blips and brings the signals within the dynamic range of the receiver allowing further signal processing.
    FIG. 2 illustrates a typical radar setup that is used to track air traffic. It shows a radar setup for a dual beam radar, an LB for tracking objects with lower azimuth and an HB for tracking objects with higher azimuth. The transmitter is usually connected to the LB with a circulator since most power is needed to illuminate targets at the greatest distance, suffering from the greatest path loss attenuation. After the emitter pulse has left the antenna, the receiver is first connected to the HB since targets are expected at high elevation angles and at a short distance the clutter is much too strong to aim lower. After some elapsed and programmable time, the receiver is switched to the lower beam since the target elevation angle is lower at greater distances (corresponding to longer response time) and the antenna direction angle must be lower to have sufficient gain at the target. A schematic representation of the processing system for processing signals according to this method is shown in FIG. 3 given.
    Switching between the two beams can be used as a raw filter. This provides approximately 20 dB clutter reduction to the disadvantage of a reduction in detection of low-flying targets. Switching the beams is often not sufficient to handle saturation and STC (Sensitivity Time Control) is usually used to attenuate signals that are too strong at a short distance. To allow such attenuation, azimuth / range maps are tuned on site to prevent the need to use all of these attenuation mechanisms over the full range to be scanned, as these attenuation mechanisms will also weaken the signals from the objects to be measured. Since the intensity and position of clutter is dependent on seasonal and weather effects, the current clutter suppression mechanisms, which require intensive manual fine-tuning, are adjusted for the worst conditions. As a result, they sometimes make it difficult to properly detect aircraft. All this leads to a situation where only the very strong (large) targets can be detected in areas with a lot of clutter.
    The signal from the receiver is forwarded to the processing module that can integrate the coherent responses of the targets to obtain processing gain whereby, if necessary, clutter is reduced by MTI and Doppler processing. These techniques are performed in the frequency domain. A disadvantage of these techniques is that detections are missed if the targets have similar Doppler properties as a clutter. False detections are created when the clutter has other spectral content that can be filtered. In addition, it is a disadvantage that false detection will raise the detection threshold for a certain area, thereby missing out on real targets of interest. Given the disadvantages of these clutter rejection filters, the probability of detection (Probability of Detection, Pd) of a typical dual frequency ATC PSR radar is rarely better than 90%. Most of the missed detection signals (10%) are due to strong clutter signals.
    It should be noted that, remarkably enough, little or no progress has been made in the last 20 years in all of this, with the exception of the use of particularly expensive "phased array" antennas, where the antenna technique is used to the maximum to avoid clutter areas are highlighted when tracking the horizon. This method still requires STC use to reduce signals received by side lobes at a short distance and thus masks the detection of low-flying objects when the horizon screening angle is high as in mountainous areas.
    Summary of the invention
    The purpose of the concrete elaboration of the present invention is to provide systems and methods for detecting important objects with a high probability of detection. The stated object is achieved by using the method and the device according to the present invention.
    The present invention relates to a system for suppressing unwanted signals when detecting objects of interest with a detection system consisting of an antenna system that has 2 or more receivebeams. The system consists of an input adapted for obtaining, via the above-mentioned antenna system, receive signals from the first receive beam and at least 1 other receive beam that can respond to the same emission signal, and from a link adapted to link receive signals from the first receive beam and at least 1 other receive beam to obtain signal detection of important objects by suppressing unwanted signals.
    The coupling can be adjusted to induce a local electronic zero in the place of an unwanted clutter signal. The local electronic zero can be generated by coupling the receive signals in the opposite phase.
    The detection signal can express a presence or property of an object as a function of an azimuth angle, elevation and range relative to the antenna system and the coupling can be adjusted to significantly reduce or disable the detection signal for a certain elevation angle.
    The link can be adjusted to link the receive signals differently depending on the range between an object for which the receive signal has been received and the antenna system. The coupling can be further adapted for coupling receive signals in phase with detection signals in which no unwanted signals are present.
    It should be noted that any azimuth / range cell can contain a dutter or can be clutter-free. The latter usually occurs because the cell is in the shadow of a tall object at a shorter distance. Thus, the system can also be modified, in addition to scanning dutter into cells containing dutter, to combine receive signals from both beams in phase to obtain an increased gain. This increases the sensitivity for the holes between dutter where in previous systems the gain was reduced by selecting only the high beam.
    The coupling may consist of vector modulators for modulating receive signals for the first beam and the receive signals of the second beam and a combiner for combining the modulated receive signals.
    The system may furthermore consist of a calibration processor to determine coupling parameters for coupling receive signals from the first beam to receive signals from at least 1 other receive beam, so as to obtain a detection signal of the desired object with suppressed, unwanted signal. The calibration processor can be adjusted to determine link parameters so that part of the receive signals from the first beam is combined with the receive signals from the second beam, the part from the receive signal from, the first beam introduces an unwanted signal on a predetermined location that is equal in amplitude but in reverse phase with an unwanted signal at that predetermined location that is present in the receive signals from the second beam.
    The coupling can be tuned to cancel unwanted signals by changing the coupling amplitude and phase.
    The coupling can be adjusted to provide coupling, taking into account that gain is a function of elevation azimuth and range.
    The present invention also relates to: • A detection system for detecting objects of interest; the detection system consists of an antenna system adapted to receive 2 or more receive beams and to determine a detection signal for objects of interest and a system for reducing or canceling unwanted signals in the detection signal of the objects as described above.
    • A calibration processor used in the system for reducing unwanted signals as described above, the processor is adapted to determine linking parameters for linking receive signals from the first receive beam and from the second receive beam.
    • A method for detecting objects of interest, the method is to send an emission signal to the objects of interest, to receive the receive signals in a first and a second beam (both are echo signals on link the same emission signal) and both receive signals to obtain a detection signal from the objects with suppressed unwanted signals.
    • A method for upgrading a detection system that consists of an antenna that uses 2 or more receive beams and means to switch between 2 or more receive beams, the method involves replacing the switching means with means to receive coupling signals from the first beam to those from a second beam to obtain a coupled signal that is a detection signal for objects with suppressed unwanted signals.
    The concrete implementation of the invention brings the following advantages: • Improvements are not based on adjusting the power of the transmitter since it is subject to physical limitations that apparently have already been achieved.
    • Improvements are not based on adjusting the sensitivity of the receiver since progress there is subject to physical limitations that apparently have already been achieved.
    • Improvements are not based on adapting antenna shapes since this can prove to be impractical and often very expensive.
    • The dutter signal is canceled at the start of the radar chain, thus saturation can be avoided and a strong STC action is no longer necessary.
    • Real time data is used to reduce or cancel the dutter since such designs are not dependent on instabilities in the antenna and / or in the dutter.
    • Clutter can be reduced, filtered and canceled. The latter results in a reduction or elimination of loss of detection of targets.
    • A system based on this principle does not suffer from blind speeds and / or problems with tangentially moving targets.
    • Coverage of the detection system for low-flying targets, for example close to an airport, can be very good.
    • Unstable clutter, such as sea clutter or signals from wind turbines, can also be reduced or eliminated.
    • A system based on this principle can continue to detect a helicopter or ULM while the dutter is reduced or avoided.
    • Accurate clutter reduction and / or canceling is achieved without the need for expensive radar designs, making it possible, for example, to use a microwave transmitter source, resulting in systems that are more cost efficient.
    • Initialization, maintenance and more generally site tuning of the radar can be reduced in time, this results in a reduced cost both in time and in expenses.
    • Tuning can be less dependent or even independent of the weather and seasonal effects.
    • A system based on this principle has been adapted to automatically reduce or suppress the effect of jammers.
    • It is possible to use this principle for different types of detection systems, such as radar, sonar, etc.
    Specific and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Functions of the dependent claims can be combined with functions of the independent claims and with functions of other dependent claims if necessary and not only when this is explicitly stated in the claims.
    The above and other features, functions and advantages of the present invention will be apparent from the following detailed description, together with the accompanying drawings, illustrating the operation of the principles of the invention, by way of example. This description is only given by way of example, without limiting the scope of the invention. The reference figures listed below refer to the attached drawings.
    BRIEF DESCRIPTION OF THE FIGURES FIG. la prior art, illustrates by way of example radar detection using the low beam for a switchable beam system, as used in radar detection systems according to prior art FIG. 1b - prior art, illustrates by way of example radar detection using the high beam for a switchable beam system, as used in radar detection systems according to prior art FIG. 2 - illustrates a schematic representation of a dual beam radar antenna setup, for example as used at airports, according to prior art FIG. 3 - illustrates a schematic representation of a signal processing circuit according to prior art for processing signals from a dual beam radar antenna setup FIG. 4 - illustrates a schematic representation of a system for detecting objects with dutter canceling according to the concrete embodiment of the present invention. FIG. 5 - illustrates a schematic representation of a possible calibration processing system that can be used according to the concrete embodiment of the present invention FIG. 6 - illustrates a schematic representation of the various steps in a possible method for dutter cancellation according to the concrete embodiment of the present invention FIG. 7 - prior art, describes a vertical antenna diagram showing gain versus elevation for a low receive beam and a high receive beam in an antenna that switches between the two beams according to prior art FIG. 8 - describes a vertical antenna diagram showing how the coupling of low and high beam receive signals can result in a significant reduction of dutter to an elevation of -0.5 degrees, as can be achieved according to the concrete embodiment of the present invention FIG. 9 - describes a vertical antenna diagram showing how the coupling of low and high beam receive signals can result in a significant reduction of dutter to an elevation of 0 degrees, as can be achieved according to the concrete embodiment of the present invention FIG. 10 - describes a vertical antenna diagram showing how the coupling of low and high beam receive signals can result in an increase in sensitivity in combination with a reduction in dutter
    In the different figures, the same reference symbols refer to the same or similar elements.
    Description of the schematic elaborations
    The present invention will be described in the light of certain applications and refer to certain drawings. No references in the claims will be construed as limiting the scope. The drawings that are described are only schematic and non-limiting. For illustrative purposes, the size of some elements in the drawings may be exaggerated and not drawn to scale. Where the term "containing" is used in the description and claims, it does not exclude other elements or steps. Where an indefinite or definite article is used in relation to a certain word, such as a, the, this also implies multiples thereof, unless explicitly stated otherwise.
    In addition, the terms "first", "second" and "de" as used in the description and in the claims, are used to distinguish between similar elements and not necessarily for describing a series, nor in time, space, order or in any other way. It is to be understood that the terms so used are interchangeable under the appropriate conditions and that the embodiments of the invention described herein may also operate in sequences other than those described or illustrated herein.
    References throughout this specification to "1 embodiment" or "an embodiment" means that a particular function, structure, or feature described with respect to the embodiment is included in at least 1 concrete embodiment of the present invention. So appearances of the sentences "in 1 version" or "in a version" at different places throughout this specification do not necessarily refer to the same version, but it may be so. Moreover, the specific functions, structures and features can be combined in any suitable manner, as will be apparent to all familiar with this matter, starting from some concrete elaborations. Similarly, it is clear that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped in one embodiment, figure or description to streamline this disclosure and to help understand 1 or more of the various inventive aspects. However, this method of disclosure should not be interpreted as a plan that requires more characteristics to the claimed invention than explicitly formulated in each claim. In addition, while some embodiments described herein include some but not all of the functions of other embodiments, combinations of functions of different embodiments are intended to be within the scope of the invention and to form other embodiments, as would be apparent to a person skilled in the art. .
    Several specific details are set forth in the description that this notice contains. However, it is clear that embodiments of this invention can be carried out without these specific details. In other cases, well-known methods, structures and techniques have not been described in detail in order not to complicate the understanding of this description.
    The following terms and definitions are intended solely to help you understand the invention.
    In the following description, the term "dutter" is used to refer to unwanted signals in a detection system, more particularly referring to unwanted echoes in electronic systems, such as, for example, with radars or sonars. Methods for reducing or canceling dutter according to the practice of the present invention can also be described as "VCC methods" or "Vanuytven Clutter Canceller methods". Systems for reducing or canceling dutter according to the practice of the present invention can also be described as "VCC systems" or "Vanuytven Clutter Canceller systems".
    In certain embodiments or examples, the terms "low beam" or "high beam" are used. The term low beam is used to refer to a receive beam that receives receive signals from an elevation interval that corresponds to a volume that is closer to the ground level than that of the high beam. Often the low beam is more under the influence of clutter than the high beam since there is usually more clutter closer to the ground level.
    According to a first aspect, the present invention relates to a system for reducing or canceling unwanted signals, also described as clutter, when objects of interest are to be detected in a detection system. Clutter can, for example, refer to signals that come back from soil, sea, rain, animals such as insects, atmospheric turbulences, environmental objects, etc. Clutter is a major problem in detection, such as radar or sonar detection, since it can cause serious performance problems with regard to the detection accuracy of objects. The system according to embodiments of the present invention includes an input adapted to receive receive signals from a first beam and receive signals from at least a second beam from an antenna that uses 2 or more receive beams in response to the same emission signal. In other words, embodiments according to the present invention use responses from at least 2 beams detected in response to the same emission signal, each of which records information from different elevation angle intervals. The system can therefore be suitable for connection to 2 receivers or a dual beam antenna or an antenna with several beams. For example, the system can be used in combination with a dual beam antenna, with a high and a low receive beam, as often used in radar applications. Optionally, the system for reducing or canceling unwanted signals can be included in a detection system. In embodiments of the present invention, the term "first beam" or "first receive beam" can be used to refer to a beam that contains receive signals with more dutter than a second receive beam used in the system or method and vice versa, the term "second beam" or "second receive beam" can be used to refer to a beam that contains receive signals with less dutter than another receive beam used in the system or method.
    Furthermore, the system includes a link adapted to link receive signals from a first beam with receive signals from at least a second beam to reduce the dutter in the detection image. Reduction of the dutter can therefore be achieved with the use of images from only the high beam or the low beam or by switching between both images. For this link, the link can store or use link information, such as link parameters that represent the link between the first and at least one second beam to be applied. The coupling information can include a coupling amplitude and / or a phase angle. The detection volume that is of interest can be subdivided into a plurality of sub-volumes characterized by a given range interval and a given azimuth angle interval, thus defining a plurality of azimuth-range cells that all together comprise the detection volume that of importance is described. The link information can thus contain link information for each azimuth-range cell of interest. The link information can thus contain a set of link parameter values for each azimuth-range cell of interest. It is therefore an advantage that embodiments according to the present invention allow dutter correction data based on a four-dimensional parameter space, which expresses gain as a function of azimuth, elevation and range, to be offered. The coupling can be adjusted to output an output signal based on a coupled signal from the first beam and a coupled signal from at least 1 other beam.
    The link information in the link can be presented as predetermined stored values or using the VCC calibration processor that makes it possible to determine the link information. Such link information can be determined by the VCC calibration processor at initialization, maintenance moments or at predetermined moments during the detection process for updating the dutter correction process to adjusted dutter conditions. The system can therefore be connected to a VCC calibration processor which is adapted to determine coupling factors for coupling receive signals from the first beam to at least receive signals from the second beam, but even more advantageously, the system is such a VCC calibration processor contains.
    These and other components of the system for reducing and even scanning unwanted signals is described in more detail with reference to FIG. 4, which shows an exemplary system according to a concrete embodiment of the present invention and which contains the standard and optional components of the system illustrates.
    The system 300 for reducing or canceling unwanted signals according to the embodiment of the present invention can be part of the complete detection system 200 and / or can be adapted to cooperate with an antenna system 210. The antenna system 210 can be an antenna 212 that can be positioned relative to a transmitter 214, such as, for example, a microwave, to send an emission beam, also referred to as an antenna beam, to a target as focused energy. The transmitter 214 can also be a Klystron or a solid state amplifier, although this is not necessary since the clutter does less reduction or canceling or does not require such strong emission intensities or strong coherent stability, as was often required in prior art systems.
    The antenna system 210 further comprises at least 2 receivers 216 for receiving the return signal, also known as the echo signal. The transmitter 214 can use the same or similar components as 1 or more of the receivers or can be integrated with it. The return signals or the receive signals must allow to identify targets and / or measure parameters such as presence, position and speed of objects.
    Note that when the current aspect describes cooperation with an antenna system or integration of the system for reducing or canceling unwanted signals in a detection system, based on 1 aspect, the present invention also refers to a complete detection system that has such a system for reducing or scanning unwanted signals in a detection system.
    It is to be noted that system 300 for reducing or canceling unwanted signals can be adapted to cooperate with antenna systems for various detection techniques, such as for example in detection techniques that use sound waves such as in sonar or in detection techniques that use electromagnetic waves as in radar or similar technologies. The system according to a concrete embodiment of the present invention is based on the detection of echo signals in response to a controlled signal.
    As indicated above, the system 300 is focused on reducing or canceling unwanted signals, also called clutter, that obstruct the view of the observer using the system. The system for reducing or canceling unwanted signals includes input 310 adapted to receive receive signals from a first beam and at least receive signals from a second beam. The input 310 may include 1 or more input ports to receive signals from the antenna system 200, for example, more particularly from receivers 216. The receive signals may be pre-processed to the input or before they are received.
    The system 300 further includes a link 320 adapted to link receive signals from a first beam with receive signals from at least a second beam. The first beam and at least 1 second beam are typically selected to receive signals from different angle intervals as a function of height. The latter can be achieved by varying the vertical angle with respect to the antenna in the antenna system. For example, in some embodiments the first beam may be referred to as the low beam, it receives information closer to the ground level and often contains a stronger clutter signal than at least 1 second beam, possibly called the high beam, that receives information from an elevation that is higher than the ground level. Coupler 320 is adapted to use the beam with the stronger clutter signal for a certain indicated detection volume, for example a certain azimuth range cell, to compensate for clutter in signals from the beam with a lower clutter signal and more target signal. Instead of not using the beam with the stronger clutter signal, as was previously done in systems that switch between different beams, in embodiments of the present invention, part of the receive signals from the beam with the stronger clutter signal may be added to the receive signal from the beam with the lower clutter signal to compensate for the clutter. The part to be added is determined by the size and phase of this link. The coupling 320 is adapted to couple the beams so that the dutter in the first beam is substantially equal in amplitude and vice versa in phase with the dutter in at least 1 other beam, the resulting sum for dutter on the target channel can be substantially zero, ie essentially canceled.
    In one embodiment, for a first beam that receives information that is more sensitive to dutter than the second beam such as, for example, a low beam that receives signals from a space closer to the ground level, the coupling of the first beam will use a sample that is equal is in amplitude to the dutter received from at least 1 second beam but shifted to the reverse phase and injected into the receive channel so as to scan the dutter signal and thus avoid degradation of the receive signal.
    The link 320 may contain the link information in a memory, for example based on stored values that have been experimentally determined or calculated, in a look-up table or receiving a processor via an input as will be discussed in more detail below. For example, such link information will include a link amplitude and phase angle to link receive signals from a first beam with receive signals from at least 1 other beam. The coupling parameters can be selected to generate an electronic zero so that dutter at a certain elevation is reduced or removed. By adjusting the coupling parameters, the electronic zero can be positioned or tuned to a different elevation. Thus, the parameters can be adaptively tuned to reduce or "zero" signals that are present for a long time, i.e., that can be more deaf. Thus, embodiments of the present invention can introduce an electronic zero into the received antenna diagram by mixing the received signals.
    The coupling information can be determined such that the nap is reduced or canceled at certain 3-dimensional positions. The link 320 can therefore be quite adaptable, for example through software control. As will be further explained, in valuable embodiments, the link may be adapted to link the first beam to at least 1 other beam and to use different link information for different range-azimuth cells of interest. It is an advantage for the embodiments according to the present invention that for detection range is seen as a parameter. It is thus an advantage for the embodiments according to the present invention that for detection a four-dimensional parameter space is represented which represents gain as a function of azimuth, elevation and range. To do this, the detection volume of interest can be subdivided into different azimuth-range cells, each in itself they are representative of a volume with boundaries determined by a certain azimuth interval and range interval. Working with a plurality of azimuth range cells makes it possible to provide an electronic zero for "zeros" at a predetermined elevation in the azimuth range cell, for each azimuth range cell. In this way, the most prominent dutter signal in the azimuth range cell can be reduced or canceled. It will be clear to experts that the quality of the reduction or canceling of the dutter will depend on the number of range-azimuth cells for which different coupling parameters can be selected, determined or adjusted. More range-azimuth cells that are used means higher resolution of the range-azimuth map for which different linking parameters can be selected and therefore more dutter signals that can be reduced or even canceled. Based on the combination of 2 signals, an electronic zero at a predetermined elevation can be obtained. When signals from more receive beams can be combined, more electronic zeros can be introduced, resulting in the possibility of blocking different dutter signals at different elevations in the same azimuth range, as will be understood by an expert.
    Since the “zeroing” of the dutter signal can happen at different elevations in the same range-azimuth cell, this also prevents targets from being “zeroed” at the same elevation angle but at a different range. Thus, using this system results in improved detection capability. It is an advantage of embodiments according to the present invention that embodiments according to the present invention use range and time of flight as a parameter. Clutter reduction can therefore be performed in a four-dimensional parameter space that sets gain as a function of azimuth, elevation and range.
    In some embodiments of the present invention, a particular selection of link parameters is made for range azimuth cells positioned in the shadow of an obstruction, i.e., in the shadow of a clutter object. In advantageous embodiments, coupling parameters of range-azimuth cells that do not contain clutter because they are in the shadow of an obstruction are determined so that they obtain maximum coupling in amplitude and phase. The latter can be performed because no clutter rejection is needed at that position. Using the first beam and at least 1 other beam for these non-clutter cells effectively improves the signal strength received, resulting in improved sensitivity. This can significantly improve the low elevation range of the radar and reduce cone-of-silence since the need for sensitivity time control (STC) can be reduced. The latter therefore results in a bonus effect as the radar coverage improves. In some embodiments according to the present invention, the beam coupling for clutter-free cells can thus be selected to obtain an improved maximum gain and low elevation range and thus to obtain an improved general target detection.
    In embodiments where different coupling information is used for different azimuth range cells, the system includes an azimuth encoder capable of accurately selecting or distinguishing different azimuth positions. The higher the accuracy of this azimuth encoder, the more corrections or improvements can be made.
    Coupling 320 has an output signal representing a detected image in which the clutter is reduced by combining, i.e. coupling, the received signals from the different beams.
    The output signal of the coupling can be further processed in the detection system with the aid of a processor 220. This processor can be adapted for the further processing of the image, for example by applying Doppler techniques, applying object recognition techniques to the image, this states enable us to perform further standard process steps, as is known to every initiate in this matter. The additional processing unit 220 can then be connected to the output 230 which allows the detection image to be represented with a reduced to fully eliminated clutter for the user. The output 230 can be any suitable output, such as via a monitor, a printer, etc., but the invention is not limited thereto.
    As described above, the link may receive its link information from the VCC calibration processor 330, which may form part of or reduce the connectivity of the dutter system 300. An advantage is that the VCC calibration processor 330 is part of the system 300, since this allows for easier adjustment of the dutter reduction or canceling at predetermined times during the lifetime of the detection system, so that it can adapt to a variable dutter situations. To determine the link information, the VCC calibration processor 330 can use information from the first beam and from at least a second beam that is simultaneously measured with the same antenna, identify dutter and determine link information based on it so that it is possible to receive the receive link signals from the first and second beams to reduce or cancel the dutter. The VCC calibration process can be performed during installation, during maintenance, at fixed times, etc. It can be performed in an automated and / or automatic manner. The VCC calibration processor 330 can determine the link information based on a predetermined algorithm, according to previously determined rules, based on a neural network, etc. The VCC calibration processor 330 can be adapted to determine the link information provided by the clutch 320 is used as explained above. In a particular embodiment of the present invention, the VCC calibration processor may include components for determining the link information as shown in FIG. 5. The VCC calibration processor 330 may consist of a receive component 332 that receives receive signals from the first beam and from at least one second beam, with the first beam suffering more from naps than the second. The latter can be performed via a direct connection to the input of the system 300, or via a direct connection of the VCC calibration processor 330 to the antenna system 210. The VCC calibration processor 330 can then consist of a dutter identification system 334 that is adapted to identify dutter based on the input received with the receive component. The latter may, for example, be based on a specific characteristic of the received signal, may be based on input received from an external source, such as, for example, a person identifying dutter, and / or may be based on comparison of previously obtained input signals with identification of objects that are present in the same place for a long time and can be considered a dutter in a system that detects objects of interest, such as moving objects. The processor may optionally also include a memory for storing the received information from an external source and / or previously received images. The processor can also be adapted with a link information extractor means 336 to derive link information based on the identified dutter in the received signals from the first beam and the received signals from the second beam. The latter may include means for comparing the dutter in the receive signals of the first beam and the second beam and means for deriving the comparison of the link parameters. Such parameters can be determined by calculating an amplitude and phase, so that the contribution of the first beam dutter in the combined signal is equal to but opposite to the dutter in the second bundle resulting in a reduction or cancellation of the dutter in the combined signal. For some parts of the signals, for example when they occur in clutter-free cells, the parameters can be chosen such that an optimum signal strength is obtained. Determination of the coupling parameters can be performed by comparing the combined signal with a predetermined signal and thus adaptively changing the parameters until a predetermined or optimum point is reached, fixed with predetermined criteria. The system can therefore be adapted to continuously receive the result of the combined signal as a reference or comparative signal, e.g. as a video input. The latter allows adaptive tuning. The processor also includes an output component 338 for outputting the link information to the link. Such processor components can be implemented in hardware or software.
    The system and method for reducing or canceling a dutter is particularly suitable for systems in which the ratio between the first and at least one second beam is stable in amplitude and phase, for example, in dual beam systems that use two beams to detect echo signals through a single antenna or systems that use more than two beams for detecting echo signals based on the same antenna.
    It is an advantage of the embodiment according to the present invention that the instability of the dutter due to movement of the dutter object (trees, waves or wind turbines) from pulse to pulse is not important, because both channels have the same degree of amplitude. and show phase changes for the same clutter cell in space. Therefore, it is only necessary to slightly tune the link parameters by means of an iteration from scan to scan to maintain a zero in that clutter cell. Because the adjustment of the parameters is only required when the relationship between the two antenna beams changes, the time constant for adjusting the clutter correction can be in the order of minutes or hours. In fact, this should make it possible for a wind turbine not to be seen while a floating helicopter is still being seen and reported.
    The methods and systems according to the embodiments of the invention can also be applied to "swept" frequency radars. With the help of software processing on the data of the two channels after pulse compression, the coupling parameters in range can be timed with a very fine resolution since dutter from different range also comes from different angle angles. Since 1 beam position probably touches multiple dutter objects with different return amplitude and phase, the counted vectors can vary very rapidly in azimuth and range.
    By way of illustration, a more specific example of a system for the reduction or elimination of unwanted signals is described. The example shown in FIG. 6, shows a system that receives input signals from an antenna system by using two receive beams to receive an echo signal on input 310, in which a programmable link 320 is provided to combine the signals from both receive beams.
    The programmable link 320 can be programmed to link the received signals from the first and at least a second beam based on a predefined reference table or look-up table that contains predetermined values or is based on values for minimizing dutter and maximizing of the gain obtained with a VCC calibration processor 330 to determine the coupling amplitude and phase angle, for example based on an amount of dutter that was sampled for each azimuth range cell, e.g. using a logic circuit. Fig. 6 shows an example where the VCC calibration processor is housed in the system 300 and the link 320 includes the vector modulators 322 so that the receive signals from the first and at least a second beam can be modulated. The vector modulators 322 are driven by the output of the VCC calibration processor 330. The modulated signals are then combined in the combiner 324 and passed to the receiver 326. In accordance with some embodiments of the present invention, the vector modulator can be in a high beam receive channel can be used to block the channel for distant ranges since it can be expected that it only adds noise and not a useful signal because for large distances it is assumed that all targets are at a low elevation.
    While the previous example illustrates how the VCC coupling unit and the VCC calibration processor are implemented in hardware, one or more components may be implemented in software in a more general processing means. If a "chirp" pulse is used, the VCC calibration processor may be designed so that it does not start to act until the received signals have been compressed. This function usually happens after a digitization step. The implementation is especially useful for systems in which compression and digitization of the signal occurs and / or when both beams are sampled simultaneously.
    It is an advantage of the embodiment according to the present invention that annoying jammers can be suppressed. Jammers can occur unintentionally, for example due to the presence of wireless electronics and PCs that work with clock frequencies located in the radar band as well as consciously for military purposes by inducing hostile signals to disrupt the operation of detection systems. Special measures must limit the degradation of the target detection. If a jamming signal is present then the VCC system will detect this as a form of damper and will place a zero at that elevation angle. This results in a reduction in the dutter suppression for that specific azimuth angle as used by the jammer.
    Either the jammer or the dutter is suppressed, depending on which is the most dominant for the given range of azimuth cells.
    According to an embodiment according to the present invention, the detection system can be combined with a Doppler filter technique, because it reduces the noise by distributing the noise energy over all frequencies while the energy of the target is accumulated in 1 single Doppler bin to simplify the detection. Some embodiments may use terrain elevation data to help the adaptive tuning mechanisms that control the coupling factors so that timing is started with parameters that are closest to the notch of the dutter while maximizing the gain of the target above it. Indeed, if there are different settings for making a notch, the solution with maximum target strength must be chosen.
    An advantage of the embodiments according to the present invention is that methods and systems for reducing or even glancing the dutter according to embodiments according to the present invention can be applied to different types of detection systems, e.g. different types of ATC radar systems.
    It should be noted that for systems according to embodiments according to the present invention, detection of a target present at exactly the same elevation for the same range-azimuth cell is not possible, since the signal is nullified in that range-azimuth cell for that elevation. It should be noted that the zero signals are detected in a four-dimensional space and not in the frequency-speed domain. In other words, a target may be decreased in strength when it is near the same elevation level as the dutter and in the same range and azimuth. The target only disappears from the radar when it is at the same position as the dutter and it is present before the radar before or after it is at this position.
    For all practical applications, a flying target would be in trouble anyway if it is at the same elevation, range, and azimuth as the dutter, and the use of the radar is most likely irrelevant. The latter nevertheless results in the fact that the VCC methods and systems are less suitable for detection systems that are intended to track targets at ground level (dutter) level.
    It is then possible that for a given range azimuth cell more than 1 object is involved at a different elevation angle. In this case, the strongest dutter reflection will be removed, but part of the signal will always be present. Nevertheless, it is to be expected that such types of dutter are very rare. When more than two antenna beams are available, a second VCC method can be switched stepwise for scanning the second elevation angle.
    It is an advantage of embodiments according to the present invention that, in contrast to the beam pointing techniques (3D radar), the target and the dutter object can be exposed simultaneously while the dutter is dynamically canceled in the receive channel alone.
    It should be noted here that while in the above description the system has been described with reference to the complete system for reducing or canceling dutter containing or connected to a VCC calibration processor, the present invention also relates to the VCC calibration processor as described above.
    According to another aspect of the present invention, the embodiments of the present invention relate to a method of detecting objects of interest. The method can make useful use of a dutter reduction system as described in the first aspect, although the invention is not limited thereto. The method may consist of a step for providing an emission signal or the response to it. A high intensity source may be required to provide an emission signal, although the present invention is not limited thereto. The method further comprises receiving receive signals in a first and a second beam that are responses to the same emission signal but contain different overlapping elevation intervals of the region to be covered. The detection system furthermore also comprises coupling receive signals from the first beam with receive signals from the second beam to obtain a output with a reduced dutter relative to the signals in the first beam and / or the signals in the second beam. The method can therefore consist of one or more steps that can be performed with a system for reducing or canceling a dutter as described in more detail above.
    In another aspect, the invention also relates to the method for determining coupling parameters for coupling signals from at least two receive beams as can be performed using the VCC calibration processor as described above.
    In yet another aspect, the embodiments of the present invention may also relate to a method of upgrading a detection system for detecting objects of interest. The method is particularly suitable for the improvement of detection systems consisting of an antenna with at least two receive beams and which are adapted for switching between the two beams. Such detection systems are well distributed on the market and often used for the detection of objects of interest at the moment, such as for example for air traffic control. The method for upgrading consists of replacing a switch for switching between at least two receive beams with a system for reducing clutter adapted for combining, e.g. coupling, signals from a first beam and at least a second beam . It is thereby an advantage that the detection system can be considerably improved with regard to accuracy, but that it is not required to replace the entire antenna. The dutter reduction or canceling system may be as described in the first aspect of the present invention. It is an advantage of the embodiments according to the present invention that the method for upgrading can be carried out quickly. The method can be particularly useful in the field of radar detection, although the embodiments of the invention are not limited thereto. It is also an advantage of the embodiments according to the present invention that they can help to extend the life of the detection systems.
    Some execution options are described above as systems, processors or parts thereof, the execution of a method or the combination of elements of a method. The respective method or method steps as can be obtained with the system, the processor or the components for performing the function are therefore also embodiments according to the aspects of the present invention.
    By way of example, embodiments of the present invention are not limited thereto, an example of the use of a VCC dutter reduction system and method is shown below. The example is based on a typical ATC radar, but it will be clear to a person skilled in the art that it can be applied mutatis mutandis for other detection systems based on echo detection and detection with at least two receive beams at different angles. This example in particular illustrates features and advantages of the embodiments according to the invention as can be used in the typical airport radar that uses a two beam antenna, as illustrated in FIG. 2. It is discussed with reference to FIG. 3 how conventional systems with a beam switch are used. In FIG. 7 - prior art, a typical vertical antenna diagram that can be obtained for a low receiver beam and a high receive beam, as used in prior art systems, as shown in FIG. 3. The diagram shows the gain as a function of the elevation angle. The red line 702 represents the antenna gain for the low beam (LB). It can be seen that there is a maximum gain of 34 dB at a height of approximately 1.5 degrees. This low beam intercepts the strong dutter which is usually between 0 and -0.5 degrees and has approximately 28 dB gain and will therefore saturate the receiver. At a short distance the prior art systems select the high beam (HB), indicated by the green line 704 and thus point upwards to place a notch at the expected location of the dutter. This weakens the gain of the dutter by 20dB in the ideal case, but since not all dutter are at the same height, an average improvement of about 15dB can be expected for this antenna. The dotted line 706 represents the difference in gain between the HB and the LB. In the dutter region there is a strong difference that can be used to remove the dutter in the HB.
    In embodiments of the present invention, the signals in the receive beams are coupled so that an improved reduction or even cancellation of a dutter is achieved. The following two figures show how in the example the coupling between a low and a high beam can be used for a significant reduction or even the removal of a dutter. FIG. 8 illustrates an example in which the coupling of signals in the low beam and the high beam results in canceling the dutter at a height of -0.5 degrees. The blue solid line 802 shows the new vertical receive diagram if the coupling for this antenna from the high beam to the low beam is -16dB and has a phase shift of 26 degrees. It can be seen that a sharp notch can easily be realized 40dB deeper than the original antenna notch. In addition, the receive pattern has not changed for targets at a greater height. If the coupling made is made stronger to -11 dB and has a phase shift of -81 degrees, the deep notch shifts to zero degrees of elevation, as seen in the blue curve 902 in FIG. 9. For this (relatively high altitude) dutter caused by obstacles at the same height as the radar antenna, the receive pattern for targets at higher altitudes is also affected, ie there is a reduction of approximately 2 dB loss in gain for the targets at higher altitudes height. The combined signal is represented by the blue curve 802.
    The current examples show how the reduction in dutter can be achieved. Calculations show that an improvement of 40dB can be achieved if the coupling is adjusted to be better than 1 / 10th of ldB and 1 degree accurate in phase. The coupling parameters can be estimated by measuring the antenna or using two coherent receivers to measure the difference in dutter on both channels. Adaptive tuning of the amplitude and phase of the coupling is expected to be the easiest and cheapest way to fully “note” the dutter.
    It is an advantage of the embodiments according to the present invention that combining the receive signals from a first beam with receive signals from a second beam not only allows reduction of the dutter, but moreover also increases the sensitivity of the detection system and / or expansion of its cover volume can be obtained.
    By way of example, FIG. 10 a coupling that places a notch at a lower dutter angle of -1 degree where the difference in amplitude between the two beams is very small, but given that both signals are in phase, a considerable gain can be obtained with large elevations while the dutter is still suppressed at low elevations. The coupling parameters for the results shown in FIG. 10 are a coupling of OdB with a phase correction of 63 degrees, resulting in a combined or coupled signal 1002 represented by the blue line.
    In the examples above, the first negative side lobe of the high beam was canceled using a signal from the low beam antenna. If clutter can result from even lower elevation angles then it may be possible that the second side lobe of the low beam must be suppressed. The latter can be carried out, for example, by reducing (weakening) the "weight" of the high beam, since the low beam is already fully coupled (0 dB).
    It is to be understood that, even though there are preferred embodiments, specific constructions and configurations, as well as materials, discussed herein for devices of the present invention, various changes or modifications in design and detail can be made without the scope of this invention as defined. in the attached claims. For example, while the above embodiments are often illustrated for radar detection systems, they can also be applied to sonar detection, or more generally for a system for detection of objects of interest based on detection of an echo signal in which at least two receive beams for receiving a reply from another angle are provided.
    TRANSLATION OF THE ENGLISH CONCEPTS IN THE FIGURES
    FIGURES 1 a and lb
    Range: Azimuth range: Azimuth FIGURE 2
    Rotating Radar: Rotating Radar Parabolle Antenna: Parabolic Antenna High Beam: High Beam Low Beam: Low Beam Obstructions, Clutter: Obstruction, Clutter Target: Target FIGURE 3
    Antenna: Antenna
    Transmitter: Transmitter
    High beam channel: High beam channel
    Low beam channel: Low beam channel
    Beam Switch: Jet switch
    Receiver: Receiver FIGURE 6
    High Beam channel: High Beam channel From Antenna: From Antenna Low Beam channel: Low Beam channel Combiner: Combinator Receiver: Receiver FIGURES 7-8-9-10
    Gain: Reinforcement Elevation angle: Elevation angle degrees: degrees
    权利要求:
    Claims (11)
    [1]
    A system (300) according to claim 1, the coupling (320) of which is adapted to induce a local electronic zero in the detection signal at a position of an unwanted signal contribution. 3. A system (300) according to the preceding claims, the detection signal of which expresses a presence or property of an object as a function of azimuth angle, elevation or range relative to the antenna system (210), the coupling (320) being adapted to substantially reduce or cancel the detection signal for a selected elevation angle.
    [2]
    A system (300) according to the preceding claims, the coupling (320) of which is adapted for otherwise coupling receive signals as a function of range between an object from which a receive signal has been received and the antenna system (210).
    [3]
    A system (300) according to the preceding claims, the coupling (320) of which is additionally adapted to phase-receive receive signals for detection signals in which there are no unwanted signals.
    [4]
    A system (300) according to the preceding claims, the coupling (320) of which comprises vector modulators for modulating the receive signals from the first beam and the receive signals from the second beam, and a combiner for combining modulated receive signals.
    [5]
    A system (300) according to the preceding claims, wherein the system (300) further comprises a calibration processor (330) for deriving coupling parameters for coupling receive signals from the first receive beam with receive signals from at least a second receive beam so as to obtain a detection signal, with a suppressed unwanted signal contribution, for objects of interest.
    [6]
    8, - A system (300) according to claim 7, the calibration processor (330) of which is adapted to determine coupling parameters so that a part of the received signals from the first beam is combined with received signals from the second beam, the part of the signal received from the first receive beam introduces an unwanted signal at a predetermined location that is equal in amplitude but in counter-phase to the unwanted signal present at that particular position in the received signals from the second beam. 9. A system (300) according to the preceding claims, the coupling (320) of which can be tuned adaptively to "zero" unwanted signals by adjusting the coupling amplitude and phase.
    [7]
    10. A system (300) according to the preceding claims, of which the coupling (320) is adapted to obtain a coupling taking into account gain as a function of azimuth elevation and range.
    [8]
    A detection system (200) for detecting objects of interest, the detection system includes an antenna system (210) adapted to receive 2 or more receive beams and for determining a detection signal of objects of interest and a system (300) for reducing or canceling unwanted signals in the detection signal of objects of interest according to any claim 1 to 10.
    [9]
    A calibration processor for use in a system according to any claim 1 to 10, the processor, the processor is adapted to determine linking parameters for linking receive signals from the first receive beam with receive signals from a second receive beam.
    [10]
    13. A method for detecting objects of interest, the method comprises: • sending an emission signal to objects of interest • receiving receive signals in a first beam and receive signals in a second beam, both of which echo responses are to the same emission signal • linking aforementioned receive signals from a first beam with aforementioned receive signals from a second beam to obtain a coupled signal such that for objects of interest a detection signal with suppressed unwanted signals is
    [11]
    14. A method for upgrading a detection system that includes an antenna that uses 2 or more receive beams and a means to switch between the 2 or more receive beams, the method includes: • replacing the switching means with a link to to couple the aforementioned receive signals from a first beam with the aforementioned receive signals from a second beam in order to obtain a coupled signal such that for objects of interest a detection signal with suppressed unwanted signals is
    类似技术:
    公开号 | 公开日 | 专利标题
    EP2342581B1|2015-02-25|Clutter reduction in detection systems
    Griffiths et al.2014|Radar spectrum engineering and management: Technical and regulatory issues
    US6531976B1|2003-03-11|Adaptive digital beamforming radar technique for creating high resolution range profile for target in motion in the presence of jamming
    EP2078213B1|2011-08-31|A moving target detector for radar systems
    Kingsley et al.1999|Understanding radar systems
    Picciolo et al.2008|Adaptive LFM waveform diversity
    US4041489A|1977-08-09|Sea clutter reduction technique
    US6680687B2|2004-01-20|Method to determine the azimuth of a target by means of a radar, especially of the ASR type
    DE69927242T2|2006-06-29|TARGET DETECTION DEVICE
    Ulander et al.2003|The VHF/UHF-band LORA SAR and GMTI System
    BE1019043A3|2012-02-07|CLUTTER REDUCTION IN DETECTION SYSTEMS.
    US4060807A|1977-11-29|Low angle radar
    Hao et al.2022|Advances in Adaptive Radar Detection and Range Estimation
    Baker et al.2000|Short-range surveillance radar systems
    RU2691771C1|2019-06-18|Method of detecting ground moving targets by onboard radar
    Abdallah et al.2017|Study and analysis of radar system
    Watts2019|ASV Mks. I and II, the First Airborne Maritime Surveillance Radars
    Kassotakis2014|Modern radar techniques for air surveillance & defense
    KR102053881B1|2019-12-09|Ground-based Array Antenna System and Method for Obtaining an Image of Detection Region in the Sky using the Ground-based Array Antenna System
    Vivek et al.2016|Simulation and performance prediction of an UWB radar for active protection system applications
    D'Addio et al.1985|Adaptivity and design criteria of a latest-generation MTD processor
    Singh et al.2013|Moving Target Indication Radar
    Doerry et al.2013|Compound radar waveforms with multiple frames
    Martín Gálvez2020|Radar jamming prevention through sidelobes cancellation
    Zainuddin et al.2019|Maritime radar: a review on techniques for small vessels detection
    同族专利:
    公开号 | 公开日
    GB0817885D0|2008-11-05|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US3720941A|1970-04-13|1973-03-13|Gen Electric|Automatic monopulse clutter cancellation circuit|
    WO2004077093A1|2002-12-20|2004-09-10|Telefonaktiebolaget Lm Ericsson |Adaptive ground clutter cancellation|
    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    GB0817885|2008-09-30|
    GB0817885A|GB0817885D0|2008-09-30|2008-09-30|Clutter reduction in detection systems|US13/121,045| US8599060B2|2008-09-30|2009-09-30|Clutter reduction in detection systems|
    EP20090760123| EP2342581B1|2008-09-30|2009-09-30|Clutter reduction in detection systems|
    PCT/EP2009/062672| WO2010037770A1|2008-09-30|2009-09-30|Clutter reduction in detection systems|
    [返回顶部]