Method of operation of a detection radar using Doppler modes and associated detection radar

Abstract

Method for operating a Doppler-mode detection radar and associated detection radar. The present invention relates to a method for operating a target detection radar using Doppler modes, the method comprising the implementation of several repetitions of a signal transmission / reception step (110), each Nth repetition of said step (110) comprising the following substeps: + generation (111) of two consecutive pulses associated with different Doppler modes; + transmission (112) of the pulses in different frequency bands; + reception (113) in a common time window of the pulse echoes. Figure for the abstract: Figure 4

Description

Title of the invention: Method for operating a detection radar using Doppler modes and associated detection radar

[0001] The present invention relates to a method of operating a detection radar. The present invention also relates to a detection radar implementing such a method.

[0002] The technical field of the invention is that of the management of the detection and identification time budget by radar systems.

[0003] Traditionally, a radar system can be used in a "single-task" manner, meaning a single Doppler operating mode throughout the mission. This is the case, for example, with a maritime surveillance mode (known as "MMTI," from the English "Maritime Moving Target Indicator") or a land surveillance mode (known as "GMTI," from the English "Ground Moving Target Indicator") which is adapted to a given altitude and target type. This adaptation includes, for example, the use of a fixed space scanning logic, waveforms, and processing. In other words, in such a case, the frame does not vary over time, as long as the operator does not change the mission or mode. The time budget is then associated solely with this task and with technical tasks for radar self-calibration.

[0004] For many years, radar operators have sought to broaden the range of applications for radar detection systems and have requested that they become "multi-tasking." For example, for a single radar system, it is advantageous to simultaneously have a maritime tactical situation (MMTI), an air situation (known as "AIR"), and possibly weather condition feedback. The radar system must then define the time budget to be allocated to each of the tasks to be performed.

[0005] Obviously, the more time a task is allocated, the more effective it will be, for example in terms of detection and / or discrimination capacity. Managing and optimizing the time budget therefore appears crucial for new radar systems.

[0006] Traditionally, radar systems employ "short-time" (at the processing block level) or "long-time" (at the scan level) interleaving strategies to perform their various tasks. A time budget is allocated to each of these tasks based on a performance trade-off for each function taken individually (refresh time, detection range, etc.).

[0007] Radar block interleaving is then a technique which temporally orders tasks that are not simultaneous.

[0008] To achieve simultaneous tasks, a known technique consists of decomposing the radar antenna system into several sub-arrays and allocating a task to each sub-array to perform what is called a color transmission. This operation is found mainly in MIMO (Multiple Input Multiple Output) radar systems.

[0009] The simultaneous emission of several orthogonal waveforms is thus achieved to color the space, that is to say, to associate a {sub-array, waveform] pair with a {azimuth-elevation} direction. Colored emission makes it possible either to obtain a complete view of the environment by considerably reducing or improving the refresh time of a task, or to perform several tasks simultaneously.

[0010] This decomposition of the antenna space into sub-arrays and colored emission are not necessarily available or desirable for every radar architecture. Indeed, such a type of emission can degrade the performance of a radar system, particularly in terms of range.

[0011] The present invention aims to solve this problem and thus provide a solution for implementing a multitasking radar system while using a refresh rate equivalent to that of a single-tasking system. This makes it possible to adapt the radar system to any architecture while maintaining system performance.

[0012] To this end, the invention relates to a method for operating a target detection radar using Doppler modes, the method comprising the implementation of several recurrences of a signal transmission / reception step, each Nth recurrence of said step comprising the following sub-steps:

[0013] + generation of two consecutive pulses associated with Doppler modes different;

[0014] + emission of pulses in different frequency bands;

[0015] + reception in a common time window of pulse echoes.

[0016] According to other advantageous aspects of the invention, the radar comprises one or several of the following characteristics, taken individually or in all technically possible combinations: - the process further includes a preliminary step of selecting a number M corresponding to an ambiguity rank to be treated in a beam of signals emitted / received by the radar, the number M varying between 0 and a maximum number of ambiguity ranks in the beam:

[0017] during the substep of the emission of each Nth recurrence, at least one of the pulses, called the phase-shifted pulse, being emitted with a random phase associated with the number N;

[0018] during the sub-step of receiving each Nth recurrence, the phase shift of the received echoes being compensated by the frequency band of the phase-shifted pulse, by the random phase associated with the number NM. - each pulse is emitted with a random phase associated with the corresponding frequency band. - the reception sub-step includes the compensation of the phase shift of the echoes received in each frequency band, by the random phase associated with the NM number and that frequency band.

[0019] - the pulses are emitted with a frequency deviation greater than the width of each of the said frequency bands

[0020] - the frequency gap is chosen to be able to distinguish the frequency bands different upon receiving the echoes.

[0021] - during the emission substep, the pulses associated with the radar modes different ones are emitted using different slopes of chirps used to emit them.

[0022] - during the reception substep, echoes associated with different radar modes are distinguished by determining the slopes of the corresponding chirps.

[0023] - during the emission substep, the pulses associated with the radar modes different ones are emitted using different polarizations.

[0024] - during the reception substep, echoes associated with different radar modes are distinguished by determining their polarizations.

[0025] The invention also relates to a target detection radar comprising technical means configured to implement the method as defined above.

[0026] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0027] - [Fig. 1] [Fig. 1] is a schematic view of a detection radar according to the invention;

[0028] - [Fig.2] [Fig.3] Figures 2 and 3 are schematic views illustrating different applications of the radar of the [Fig.1];

[0029] - [Fig.4] [Fig.4] is a flowchart of a method for operating the radar of the [Fig.l];

[0030] - [Fig.5] [Fig.6] [Fig.7] [Fig.8] Figures 5 to 8 are different views illustrating the implementation of the process of [Fig.4].

[0031] Figure 1 illustrates a detection radar 10 according to the invention. This radar 10 is intended, for example, to be mounted on a mobile platform moving in the air and / or on a land surface and / or on a sea surface. Advantageously, the radar 10 is intended to be mounted on a carrier moving through the air, such as an aircraft. Alternatively, the radar 10 is fixedly mounted.

[0032] The radar 10 allows the detection of targets according to at least two radar modes. Each radar mode corresponds to a specific Doppler mode, defining a waveform emitted towards a target. In other words, each radar mode allows the detection of targets of a particular type located or moving in a specific medium relative to the radar. For example, when radar 10 is mounted on a platform moving through the air, each radar mode allows the detection of targets moving at a specific relative speed in the air or on a land or sea surface.

[0033] Advantageously, the radar 10 allows the detection of targets following at least two different radar modes.

[0034] Figures 2 and 3 illustrate the implementation of a first radar mode called "AIR" and a second radar mode called "GMTI" when the radar 10 is mounted in an aircraft 12.

[0035] The AIR mode thus makes it possible to detect other aircraft 14 moving in the vicinity of the aircraft 12. The pointing direction applied by the radar 10 in such a case is at substantially zero site.

[0036] In the example in [Fig. 2], the two aircraft 12, 14 represent airplanes, for example fighter jets, moving with a relative speed that can vary (for example, from 0 to several Mach numbers). In the example in [Fig. 3], each aircraft 12, 14 represents a helicopter or a drone, such that their relative speed is moderate or low (for example, less than 200 km / h).

[0037] The GMTI mode allows the detection of objects 16 (such as vehicles) moving on the land surface. Alternatively, the second radar mode can correspond to the MMTI mode for detecting objects (such as boats) moving on a sea surface. The pointing direction applied by the radar 10 in such a case is negative elevation.

[0038] Alternatively, the two modes implemented by the radar 10 are identical but correspond to different pointing directions. For example, the first mode may correspond to the "AIR" mode at positive sites and the second mode may correspond to the "AIR" mode at negative sites. A similar example with different pointing directions can also be applied to each of the GMTI and MMTI modes.

[0039] With reference to [Fig.1], the radar 10 comprises an array of elementary antennas 21 enabling the emission of signals in the form of pulses and the reception of signals corresponding to echoes of these pulses.

[0040] The radar 10 further comprises a transmission unit 22 for generating the pulses to be emitted by the antenna array 21 and a reception unit 23 allowing the processing of echoes received by the antenna array 21 in order to deduce the presence of a target and possibly, a speed and a distance to that target.

[0041] Each of the units 22, 23 is implemented, for example, as a programmable circuit of the FPGA (Field Programmable Gate Array) type and / or of the ASIC (Application-Specific Integrated Circuit) type. In addition or alternatively, each of these units 22, 23 is implemented at least partially as software executable by a processor and stored in memory.

[0042] The operating method of radar 10 will now be explained with reference to [Fig.4] showing a flowchart of its steps.

[0043] It is considered that this method is implemented to perform a scan or image of the surroundings of the carrier carrying the radar 10, according for example to a direction of movement of the carrier.

[0044] This process includes in particular the implementation of several recurrences of a step 110 of signal transmission / reception.

[0045] The repetition frequency of these recurrences is chosen based on the repetition frequencies associated with the radar modes. The repetition frequency of each radar mode is chosen according to the application selected for the radar 10.

[0046] Thus, when the radar 10 is used according to the application explained with reference to [Fig. 2] (i.e., the speeds in "AIR" mode varying considerably), referred to as the first application, a repetition frequency Fri is chosen for the first radar mode and a different repetition frequency Fr2 is chosen for the second radar mode. In such a case, it is considered that Frl = kFr2, where k is an integer, and therefore the first frequency Fri is greater than the second frequency Fr2. Furthermore, in this application, the repetition frequency of each recurrence is chosen based on the higher frequency, i.e., based on Fri. The duration TR of each recurrence is then equal to 1 / Frl, as illustrated in [Fig. 5].

[0047] When the radar 10 is used according to the application explained with reference to [Fig. 3] (i.e., the speed variations in "AIR" mode are small or moderate), referred to as the second application, the same repetition frequency Fr is chosen for both radar modes. In such a case, this same repetition frequency Fr is chosen for each recurrence so that the duration TR of each recurrence is equal to 1 / Fr, as illustrated in [Fig. 6].

[0048] Each Nth recurrence of step 110 includes the implementation of substeps 111 to 113 explained in detail below.

[0049] During substep 111, the emission unit 22 generates two consecutive pulses associated with different radar modes and different emission directions.

[0050] In particular, during this substep, the emission unit 22 generates a first pulse Ii associated with the first radar mode and a second pulse I2 associated with the second radar mode.

[0051] Each pulse is associated with an emission direction defined, for example, by a pair of angular values. These angular values ​​correspond, for example, to the emission elevation (or site) and azimuth, hereafter denoted respectively by Eh and Az;. In all that follows, the subscript i=1 denotes the first radar mode and i=2 denotes the second radar mode.

[0052] The pulses are generated in an emission window Te in which each pulse has a width Li and is spaced from the other pulse and from one of the boundaries of the emission window Te by a time gap TGAP.

[0053] In the frequency domain, the pulses share the same frequency support Brec, with a frequency gap FGap between the corresponding carriers Fi greater than the frequency bands Bi of these pulses. The frequency gap FGAP is chosen to be sufficient to distinguish echoes of these pulses at the receiver. In what follows, a frequency band is defined by a center frequency and a bandwidth. Advantageously, in what follows, all frequency bands have the same bandwidth. Furthermore, the frequency gap FGAP is measured between a pair of corresponding center frequencies and is greater than the bandwidth of each frequency band.

[0054] The frequency band Bi of the first pulse L, that is, the pulse associated with the first radar mode (AIR mode), is chosen to be the same for each recurrence. Advantageously, this choice is independent of the application of the radar 10. This is illustrated schematically in Figures 5 and 6, which show several consecutive recurrences of the first and second applications of the radar 10, respectively. Thus, the same center frequency Fei is chosen for the first pulse in each recurrence in each application.

[0055] The frequency band of the second pulse I2, i.e. of the pulse associated with the second radar mode (GMTI or MMTI mode for example), is chosen according to the application of the radar 10.

[0056] In particular, for the first application, the same frequency band, and more specifically the same center frequency, for the second pulse I2 is chosen in each k-th recurrence. This technique can be viewed as a barrel mechanism, where at each instant TR, a center frequency is chosen in the barrel modulo k. In other words, in such a case, k different center frequencies are chosen alternately for the second pulses I2 in k consecutive recurrences. In the example in [Fig. 5], when k=2, two frequency bands B2 and B3 (i.e. two center frequencies) are then chosen alternately for each second pulse I2.

[0057] For the second application, the same frequency band B2 for the second pulse I2 is chosen in each recurrence, as illustrated in [Fig.6].

[0058] During substep 112, the transmission unit 22 emits the pulses generated during the previous substep in the corresponding frequency bands.

[0059] During substep 113, the receiving unit 23 receives echoes corresponding to the pulses emitted within a common reception time window. The duration of this common reception window is equal to the total duration of the recurrence Tr minus the duration of the transmission window Te. During reception, the echoes corresponding to the different pulses are distinguished by their different frequency bands, for example, using bandpass filters. Spatial filtering of the FFC type can also be applied in the direction associated with said band.

[0060] In a subsequent step 120, implemented after the N recurrences of step 110, the receiving unit 23 performs coherent processing of the echoes corresponding to the pulses associated with the first radar mode and the pulses associated with the second radar mode. Such coherent processing consists of applying filtering adapted to the waveform of the detection mode, for example, pulse compression on the short time axis (within a recurrence) and Doppler processing on the long time axis (from recurrence to recurrence).

[0061] In a subsequent step 130, implemented only when the radar 10 is operating according to its first application, the receiving unit 23 further implements non-coherent processing of the outputs of the coherent processing of the pulses associated with the second radar mode.

[0062] Such non-coherent processing performs the power average of the signals received on each frequency band in the same direction (after coherent processing).

[0063] In some embodiments, this step is implemented systematically (i.e. independently of the radar application) insofar as k = 1 the average is directly the signal.

[0064] In a subsequent step 140, the receiving unit 23 transmits all the outputs of the coherent processing and possibly of the non-coherent processing, to any interested system allowing for example to implement a resolution of ambiguity in distance and / or in speed.

[0065] These outputs can then be used to detect one or more targets according to different radar modes, possibly with speeds and distances associated with these targets.

[0066] In some embodiments, the operating method as explained above further includes the implementation of at least one technique for separating the different radar modes and / or rejecting from consideration certain echoes that are not necessary or are ambiguous in distance to reconstruct a complete image of the surroundings according to at least one of the radar modes.

[0067] Figure 7 illustrates an example of such a case according to the GMTI radar mode. According to this For example, the radar beam emitted by the radar 10 from the carrier 12 covers several portions on the Earth's surface, the echoes of which overlap as the carrier moves along the direction D. To avoid processing all the echoes from the footprint of the beam on the ground, a first technique consisting of choosing and processing only one rank of ambiguity within the beam is implemented.

[0068] According to this first technique, the operating method of the radar 10 further comprises a preliminary step 105 consisting of selecting a number M corresponding to an ambiguity rank to be addressed in the beam of signals emitted / received by the radar. This number M then varies between 0 and a maximum number of ambiguity ranks in the beam. The maximum number depends in particular on the aperture of the radar beam. As illustrated in [Fig. 7], the ambiguity rank M can correspond to the central part of the radar beam.

[0069] In some embodiments, during this step, several numbers M corresponding to several ambiguity levels to be addressed are chosen. In this case, it is subsequently assumed that the technique described below is applied in relation to each chosen number M. The processing is carried out, for example, in parallel.

[0070] During the implementation of the Nth recurrence of step 110, and in particular during the emission substep 112, the emission unit 22 selects one of the pulses, for example the first pulse, and adds a random phase $iN to that pulse. Advantageously, the emission unit 22 adds a different random phase $iN to each of the pulses. The pulse or pulses having an added random phase are hereafter referred to as a phase-shifted pulse.

[0071] It should be noted that the choice of the pulse to be phase-shifted remains the same for each recurrence of this substep 112. In other words, when only one pulse is phase-shifted during this substep, the same pulse is phase-shifted in each recurrence of this step. When both pulses are phase-shifted during this substep, these pulses are also phase-shifted in each recurrence of this substep.

[0072] It should also be noted that the value of the random phase $iN for the or each pulse is then stored for at least M subsequent recurrences of step 110.

[0073] It should also be noted that when this first technique is implemented, the echoes received during the first P recurrences, called "dead time," are, for example, rejected. This number P is related to the maximum instrumented distance, to the maximum delay resulting from the most distant echo that the waveform can reach. The number P is therefore related to the maximum ambiguity rank of the radar mode; it is thus an upper bound of M: M < P.

[0074] Then, during the reception substep 113, the receiving unit 23 compensates for the phase shift of the received echoes in the frequency band of the or each phase-shifted pulse, by the random phase associated with the number NM. In other words, the phase shift is performed by subtracting the value $iN_M from the band corresponding to the index i.

[0075] Thus, during the subsequent processing, only the echoes corresponding to ambiguity rank M can be processed coherently. The phase shift of the other echoes cannot be performed correctly, so they are considered white noise.

[0076] This principle is illustrated schematically in Figure 8. According to the example in this figure, the number M is equal to 2 and the maximum number of ambiguity ranks is equal to 3. Thus, during the Nth recurrence of step 110, in order to select only the signals corresponding to the ambiguity rank M=2, the value is used to compensate for the phase shift in the corresponding frequency band.

[0077] Other techniques for resolving ambiguities in distance and speed and / or according to at least one pointing direction are also possible, for example by employing several repetition frequencies associated with an extraction process.

[0078] Furthermore, it is also possible to obtain better isolation of the echoes corresponding to the different radar modes during their reception.

[0079] Thus, according to a second technique, during the implementation of the Nth iteration of step 110, and in particular during the emission substep 112, the emission unit 22 uses different slopes for the chirps used to emit the pulses associated with the different radar modes. In other words, during this substep 112, the emission unit 22 emits the pulses using either an ascending or a descending slope depending on the radar mode associated with each pulse. The same slope is then used for all pulses of this type in all iterations of step 110.

[0080] For example, for all recurrences, an upward slope is chosen for the impulses associated with the first mode and a downward slope is chosen for the impulses associated with the second mode.

[0081] Then, during the reception substep 113, the receiving unit 23 receives echoes having different frequency slopes. This receiving unit 23 therefore determines the received slopes (using, in particular, suitable filters) in order to isolate the echoes corresponding to the different radar modes.

[0082] According to a third technique that also provides better isolation of the echoes corresponding to the different radar modes during their reception, during the implementation of the Nth iteration of step 110, and in particular during the transmission substep 112, the transmission unit 22 uses different polarizations for the waves used to emit the pulses associated with the different radar modes. In other words, during this substep 112, the transmission unit 22 emits the wave carrying each pulse with a polarization chosen according to the radar mode associated with that pulse. This same polarization is chosen for this type of pulse for all iterations of step 110.

[0083] For example, two polarizations, namely vertical polarization and horizontal polarization, can be chosen for the pulses emitted during substep 112. According to other examples, 45° or circular polarization can be used. For example, left-hand circular polarization can be associated with the AIR mode and right-hand circular polarization can be associated with the GMTI or MMTI mode.

[0084] Then, during the reception substep 113, the receiving unit 23 receives echoes having different polarizations. This receiving unit 23 therefore determines the polarizations of the received echoes (using, in particular, suitable filters) in order to isolate the echoes corresponding to the different radar modes.

[0085] In certain embodiments, the aforementioned techniques are combined to be implemented simultaneously. Furthermore, a technique for resolving ambiguities in distance and speed and / or along at least one pointing direction can also be used in combination with the second or third technique, as described above.

[0086] It is therefore understood that the present invention has a number of advantages.

[0087] First, the invention allows the two radar modes to be processed simultaneously, enabling operation with a common refresh rate in each radar application. This offers a clear advantage for target tracking applications.

[0088] In addition, a modern radar architecture makes it possible to implement a particular configuration (frequency, direction) of each pulse in the emission window Te.

[0089] Simultaneous processing of both modes also offers an advantage in terms of false alarm detection and management. For example, typically, an AIR mode displays echoes present in its side lobes on its detection maps. Side Lobe Suppression (SLS) processing can then be used to filter these echoes to avoid detecting moving targets on Earth. Conversely, in the context of simultaneous AIR and GMTI (or MMTI) modes, this information can be useful for correlating any targets detected in the side lobes of one mode and forwarding them to the other.

[0090] Furthermore, the technique of selecting the desired ambiguity rank(s) allows only the signals corresponding to that rank(s) to be retained, thus avoiding unnecessary processing. This technique also provides a strong additional isolation between the AIR mode signals and the GMTI (or MMTI) mode signals.

[0091] Other techniques for resolving ambiguities in distance and speed and / or along particular directions can also be used, for example by employing several repetition frequencies associated with an extraction process.

Claims

Demands

1. Method of operating a radar (10) for detecting targets using Doppler modes, the method comprising the implementation of several recurrences of a signal transmission / reception step (110), each Nth recurrence of said step (110) comprising the following sub-steps: + generation (111) of two consecutive pulses associated with different Doppler modes; + transmission (112) of the pulses in different frequency bands; + reception (113) in a common time window of the echoes of the pulses.

2. A method according to claim 1, further comprising a preliminary step (105) of selecting a number M corresponding to an ambiguity rank to be dealt with in a beam of signals emitted / received by the radar (10), the number M varying between 0 and a maximum number of ambiguity ranks in the beam; during the substep of the emission (112) of each Nth recurrence, at least one of the pulses, called the phase-shifted pulse, being emitted with a random phase associated with the number N; during the substep of the reception (113) of each Nth recurrence, the phase shift of the received echoes being compensated in the frequency band of the phase-shifted pulse, by the random phase associated with the number NM.

3. A method according to claim 2, wherein each pulse is emitted with a random phase associated with the corresponding frequency band.

4. A method according to claim 3, wherein the reception substep (113) includes compensating for the phase shift of the received echoes in each frequency band, by the random phase associated with the NM number and that frequency band.

5. A method according to any one of claims 1 to 4, wherein the pulses are emitted with a frequency gap greater than the width of each of said frequency bands.

6. Method according to claim 5, wherein the frequency gap is chosen to be able to distinguish the different frequency bands at the reception of the echoes.

7. A method according to any one of claims 1 to 6, wherein, during the emission substep (112), the pulses associated with the Doppler modes are emitted using different slopes of the chirps used to emit them.

8. A method according to claim 7, wherein, during the reception substep (113), echoes associated with Doppler modes are distinguished by determining the slopes of the corresponding chirps.

9. A method according to any one of claims 1 to 8, wherein, during the emission substep (112), the pulses associated with the Doppler modes are emitted using different polarizations.

10. A method according to claim 9, wherein, during the reception substep (113), pulses associated with Doppler modes are distinguished by determining their polarizations.

11. Target detection radar (10) comprising technical means (21, 22, 23) configured to implement the method according to any one of claims 1 to 10.

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