Method of operation of a target detection radar and associated detection radar

Abstract

Method of operating a target detection radar and associated detection radar. The present invention relates to a method of operating a target detection radar, comprising the following steps: - determination (140) within a cone of visibility of a plurality of active tracks, each active track presenting a target to be tracked; - for each active track, determination (150) of a waveform enabling its detection and tracking; - determination (160) of the compatibility of the active tracks by comparing the waveforms determined for these tracks to form at least one set of compatible active tracks; - for the set or sets of compatible active tracks, transmission / reception (110) of a communalized wave comprising consecutive pulses, each pulse being associated with one of the active tracks of said set. Figure for the abstract: Figure 2

Description

Title of the invention: Method of operating a target detection radar and associated detection radar

[0001] The present invention relates to a method of operating a target detection radar.

[0002] The present invention also relates to a detection radar implementing such a method.

[0003] The technical field of the invention is that of radar systems embedded for example on board aircraft, boats, submarines or satellites, implementing target detection / identification.

[0004] The general problem solved by the invention is the management of the time budget in view of the increasing demand for new detection and identification functionalities required of radar systems.

[0005] Traditionally, a radar system can be used in a "single-task" manner, that is to say, a single "mode" of operation throughout the mission, for example when using a maritime surveillance mode adapted to a given altitude and type of target.

[0006] In particular, in a "single-task" mode, the radar employs a space scanning logic that 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.

[0007] 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, simultaneously providing a maritime tactical situation, an air situation, and possibly weather conditions feedback. The system must then define the time budget to be allocated to each of the tasks to be performed.

[0008] Obviously, the more time a task is allocated, the more effective it will be (better detection or discrimination capabilities, for example). Managing and optimizing the time budget therefore appears crucial for new radar systems.

[0009] Traditionally, radar employs "short-time" (at the processing block level) or "long-time" (at the scan level) interlacing strategies to perform its 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.).

[0010] Radar block interleaving is then a technique which temporally orders tasks that are not simultaneous.

[0011] To achieve simultaneous tasks, the method known to those skilled in the art consists of decomposing the radar antenna system into several sub-arrays and allocating a task to each sub-array to perform what is called color emission. This operation is found primarily in MIMO (Multiple Input Multiple Output) radar systems. The simultaneous emission of several orthogonal waveforms is thus achieved to color the space, that is, to associate a {sub-array, waveform} pair with a {azimuth-elevation} direction. Color emission makes it possible either to obtain a complete view of the environment by drastically increasing the refresh time of a task, or to perform several tasks simultaneously.

[0012] However, this decomposition of the antenna space into sub-arrays and coloured emission are not necessarily available or desirable in terms of budget for a given radar architecture.

[0013] Active tracking is a radar function that ensures optimal visibility and detectability of a tracked target by applying dedicated illuminations in the direction of the target, with one or more waveforms calculated to optimize visibility in the area (distance, speed) where the track is located. During active tracking, an evaluation of an estimated equivalent radar area (also called SER) and the target's distance is available.

[0014] As a general rule, active tracking Doppler waveforms are designed by choosing the repetition frequency or frequencies Fr, the associated wavelength(s) A, and the number of repetitions per Fr to minimize the associated time budget while maintaining a very comfortable Signal-to-Noise Ratio (SNR) for target detection. Such an algorithm, named {A, Fr}, is known to those skilled in the art.

[0015] A radar scheduler then integrates the active tracking tasks with regard to the relative priorities with respect to the watch counts and maintenance tasks.

[0016] A time budget, fixed or dynamic, is allocated to active tracking tasks, limiting in practice either the number of active tracks or the monitoring capacity that can be maintained, depending on the desired trade-off: maintaining monitoring at the expense of active tracking, or maintaining active tracking at the expense of monitoring. Optimizing the time budget allocated to active tracking therefore presents a significant challenge in radar budget management.

[0017] The present invention aims to address this problem and therefore to propose means of optimizing the time budget allocated to active pursuit.

[0018] To this end, the invention aims at a method of operation of a target detection radar, the detection radar implementing a scan forming a cone of visibility;

[0019] the process comprising the following steps:

[0020] - determination within the cone of visibility of a plurality of active tracks, each active track presenting a target to pursue;

[0021] - for each active track, determination of a waveform enabling its detection and prosecution;

[0022] - Determination of the compatibility of active tracks by comparing waveforms determined for these tracks to form at least one set of compatible active tracks;

[0023] - for the or each set of compatible active tracks, transmission / reception of a commonized wave comprising consecutive pulses, each pulse being associated with one of the active tracks of said set.

[0024] According to other advantageous aspects of the invention, the method comprises one or more of the following features, taken individually or in all technically possible combinations:

[0025] - the method further comprising for each active track not belonging to any set of compatible active tracks, transmission / reception of a simple wave comprising a single pulse;

[0026] - each waveform defines a visibility domain of a wave having that form;

[0027] - each visibility domain comprises a distance domain and a domain in speed of an active track;

[0028] - two active tracks are compatible when they are in the same visibility domain with a probability greater than a predetermined threshold;

[0029] - each waveform is defined by a wavelength, respectively a emission frequency, and a repetition frequency of a wave having this shape;

[0030] - the compatibility of the active tracks is verified by testing different values ​​of wavelength and / or repetition frequency;

[0031] - the compatibility of the active tracks is determined for each pair of tracks active;

[0032] - the impulses of the same commonized wave are associated with directions different emission methods;

[0033] - each nth recurrence of the communalized wave transmission / reception step includes the following sub-steps:

[0034] + generation of at least two consecutive pulses associated with active tracks different from the same set of compatible active tracks;

[0035] + emission of pulses in different frequency bands;

[0036] + reception in a common time window of the echoes of the pulses;

[0037] - each pulse is emitted with a random phase associated with the band corresponding frequency;

[0038] - the reception sub-step includes compensation for the phase shift of the echoes received in each frequency band, by the random phase associated with that frequency band;

[0039] - during the emission substep, the corresponding pulses are emitted in using different slopes of chirps used to emit them;

[0040] - during the reception sub-step, echoes associated with tracking points different actives are distinguished by determining the slopes of the corresponding chirps;

[0041] - during the emission substep, the corresponding pulses are emitted in using different polarizations;

[0042] - during the reception sub-step, echoes associated with tracking points different active materials are distinguished by determining their polarizations;

[0043] - a polarization is emitted for each pulse or a set of polarizations forming a signature is emitted for each pulse.

[0044] The invention also relates to a target detection radar comprising technical means configured to implement the method as defined above.

[0045] 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:

[0046] - [Fig. 1] [Fig. 1] is a schematic view of a detection radar according to the invention;

[0047] - [Fig.2] [Fig.2] is a flowchart of a method for operating the radar of the [Fig.l];

[0048] - [Fig.3] [Fig.4] [Fig.5] Figures 3 to 5 are different views illustrating the implementation work of the process of [Fig.2].

[0049] 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 platform moving in the air, such as an aircraft. Alternatively, the radar 10 is fixed in place.

[0050] The radar 10 enables the detection of targets according to one or more watch modes. By "watch mode" is meant an observation mode consisting of regular pointing. An example of such a mode is a Doppler mode of the MMTI (Maritime Moving Target Indicator), GMTI (Ground Moving Target Indicator), AMTI (Aerial Moving Targets), etc. type.

[0051] 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.

[0052] The radar 10 further includes a transmission unit 22 for generating the pulses to be emitted by the antenna array 21 and a reception unit 23 for processing the echoes received by the antenna array 21 in order to deduce the presence of a target and possibly a speed and distance to that target.

[0053] 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.

[0054] The operating method of radar 10 will now be explained with reference to [Fig.2] showing a flowchart of its steps.

[0055] This method is considered to be implemented during an electronic scan of the space around the radar 10. In particular, this method includes the iterative implementation of at least steps 110 and 120 described below for each pointing position of the radar 10. Each iteration of these steps is called a recurrence.

[0056] It is further considered that the pointing positions follow one another in a predetermined direction of rotation and each defines an angular opening dependent on the pointing angle known to those skilled in the art. The set of pointing positions defines an available visibility cone of the radar 10. In other words, the term "visibility cone" refers to the set of different pointing positions during a single sweep performed by the radar 10.

[0057] Figure 3 illustrates such a visibility cone C. In the example in this figure, the visibility cone C is formed by the angles +65° and -65° with respect to the normal direction D to the antenna array 21. Thus, this visibility cone C forms an opening angle of 130°. To cover a larger opening angle, for example, an opening angle of 360° (i.e., to form a complete turn in space), an antenna panel receiving the antenna array 21 can be mounted on a mechanical pedestal.

[0058] The mechanical rotation of the pedestal allows the position of the panel's visibility cone to be continuously modified. This mechanical rotation allows the antenna to cover an angular domain of 360°, for example. In this architecture, the electronic azimuth scanning allows radar pointings to be positioned "ahead" or "behind" relative to the antenna normal in order to accommodate the radar tasks sequenced by the scheduler.

[0059] A second solution for covering 360° visibility with a single panel consists of replacing the pedestal with a positioner. The latter positions the normal antenna on a few angular values, for example 90°+, -90° and 180° so that the electronic scanning of the panel is sufficient to cover all positions.

[0060] Once positioned, the antenna array 21 thus electronically scans its cone of visibility, then the positioner locks onto a new position (stops transmission) and the electronic scanning resumes until all positions are covered.

[0061] A final solution consists of structuring as many fixed antenna panels as possible so that the sum of their visibility cones allows a 360° domain to be covered.

[0062] The process described below is adaptable to each of the architectures mentioned.

[0063] Inside, the cone of visibility defines a plurality of visibility domains traversed successively during the scanning of the radar 10.

[0064] Each visibility domain corresponds to a geographical area in which a target having a certain speed is detectable by a wave sent from the radar 10. Thus, each visibility domain is determined by a waveform sent from the radar 10. In addition, each visibility domain is defined by a range domain measured from the radar 10 and a speed domain of the target.

[0065] In other words, as illustrated in [Fig.4], each visibility domain can be defined by a probability that a target located at a particular distance from the radar 10 and having a particular speed will be detected by a Doppler waveform sent from the radar 10. The probability therefore varies from 0 to 1.

[0066] Each waveform is defined by a wavelength X and a repetition frequency Fr of a wave having this shape. In other words, each waveform is defined by a pair of values ​​{X, Fr}.

[0067] With reference to [Fig. 1], each nth recurrence of step 110 includes an emission / reception of signals in the corresponding pointing position.

[0068] In particular, during this step, the transmitting unit 22 of the radar 10 emits signals having a particular waveform and the receiving unit 23 receives echoes of these signals.

[0069] This signal transmission / reception step 110 comprises several substeps, the implementation of which depends on the type of signals chosen. These substeps will be explained in detail later. This step 110 also includes filtering and detection processing, as will be explained later.

[0070] During each nth iteration of the following step 120, the radar 10, and in particular its receiving unit 23, performs an analysis of the received signals. In particular, this step 120 includes, for example, turn-by-turn extraction processing or any other processing enabling the identification of targets in a standby mode.

[0071] A target is considered to be detected when, at the end of this processing, the radar 10 concludes that such a target is present in the area considered.

[0072] A target is considered definitively detected when, after several iterations of steps 110 and 120, at least K detections are present and correlate within the same area over a horizon of N iterations of these steps. In this notation, the number K represents the number of steps 120 during which the target was considered detected. The coefficient K / N can then be compared with a threshold called the target extraction threshold.

[0073] During the following step 130, implemented after several recurrences of steps 110 and 120, a request to pursue one or more targets considered to have been definitively detected during step 120 is acquired, for example by the receiving unit 23 of the radar 10.

[0074] Such a request may, for example, come from a user or an external system connected to radar 10.

[0075] Each target for which such a request is received is considered an active track, and active tracking is therefore implemented for that target. This active tracking includes, in step 110, the transmission / reception of signals of a specific waveform to each active track, as will be explained later. In particular, unlike standby mode, active tracking consists of irregular tracking points. Active tracking involves supplementing the standby mesh with tracking points associated with specific waveforms, calculated on the fly. These tracking points are dedicated to detecting the tracked target, unlike standby tracking points, which seek to detect the maximum number of potential targets.

[0076] During the next step 140, the transmission unit 22 determines a plurality of active tracks in the instantaneous visibility cone, i.e. in the visibility cone defined by the antenna array 21 without taking into account any possible mechanical scanning.

[0077] This plurality of active leads corresponds, for example, to the set of targets for which a pursuit request was received during the previous step.

[0078] In the next step 150, the emission unit 22 determines a waveform for each active track. As previously stated, such a waveform is defined by a pair {X, Fr}.

[0079] To achieve this, an algorithm of the type {X, Fr], known per se, can be implemented. Such an algorithm also makes it possible to maintain a Signal-to-Noise Ratio (SNR) necessary to detect a plot and feed the active track of interest, while minimizing the illumination time required for this detection. To this end, the algorithm of the type {X, Fr] further determines a number of recurrences Nrec compatible with detection for each active track.

[0080] During the next step 160, the transmission unit 22 determines the compatibility of the active tracks identified during the previous step.

[0081] Active tracks are said to be compatible when there exists the same waveform, called a compatible waveform, which can be used for tracking each of these active tracks. In other words, active tracks are compatible when they are located within the same visibility range defined by the corresponding compatible waveform, with a probability greater than a predetermined threshold. This threshold may, for example, be close to 1. It may, for example, be approximately equal to 0.90 or 0.95.

[0082] Fig. 4 illustrates a case where two active tracks, namely active tracks PI and P2, are in the same visibility domain with a probability close to 1. These active tracks therefore form a set of compatible tracks.

[0083] To implement this step, according to an exemplary embodiment, the transmission unit 22 performs a compatibility test for each pair of compatible active tracks determined in the previous step. For example, when M active tracks have been determined in the previous step, the transmission unit 22 performs at most Mx(Ml) compatibility tests.

[0084] Each compatibility test then includes a comparison of two pairs {X, Fr] defining the waveforms determined for the corresponding active tracks, in order to determine, if possible, a pair {X, Fr] compatible with the first two pairs. This latter pair {X, Fr] defines a compatible waveform for the two active tracks, which can then be considered compatible. This compatible waveform may potentially reduce the initial SNR for each track. However, this SNR remains acceptable for continuing the corresponding active tracks.

[0085] When a compatible waveform has been determined by the test, the corresponding active tracks are therefore compatible. Otherwise, these tracks are incompatible.

[0086] According to one embodiment, the compatibility test is performed on each previously chosen Fr value by cross-referencing the X values ​​defined for each track and testing the {distance, speed} positions (i.e., the visibility domain) of each track. A compatibility matrix is ​​then defined to determine which tracks and which pairs {X, Fr} (or triplets {X, Fr, Nrec}) are compatible or incompatible.

[0087] In particular, before implementing such a compatibility test, it is assumed that the triplets {X, Fr, Nrec] are calculated for each track. Then, the X values ​​are cross-referenced, taking the triplet {X1, Fr2, Nrec2] for the first track and the triplet {X2, Fri, Nrecl} for the second track. The triplet {X2, Fri, Nrecl] is compatible with the detection of the second track if:

[0088] - the probability of visibility of the second runway is satisfactory with the value Fri;

[0089] - the RSB required for the detection of the second track is satisfactory with the value Nrecl.

[0090] Then, the accounting of the triplet {XI, Fr2, Nrec2] at the detection of the first track is analyzed in the same way.

[0091] The compatibility matrix can aggregate two or three notes.

[0092] When the compatibility matrix aggregates two scores, the first score is the compatibility of the two X values ​​with each other. In particular, to implement the communalized wave emission technique as described below, the X values ​​must be sufficiently spaced to accommodate the emitted bands, and close enough to remain within the instantaneous band of the radar 10.

[0093] The second note is the visibility note of the active track number n with its own value X and the value Fr corresponding to that of the active track number k.

[0094] When the compatibility matrix aggregates three notes, the third note signifies compatibility in terms of detection balance (RSB).

[0095] The search for X is imposed, whether we operate with a constant ambiguous velocity waveform (V amh = X x Fr / 2) or with a constant ambiguous distance (D amh = cx Tr / 2).

[0096] The search principle works in both cases.

[0097] In one embodiment, the search is performed by testing only the X values ​​already associated with the tracks. Conversely, it is possible to perform a more complex and costly search around the compatible X values ​​of target number n to be applied to target number k.

[0098] At the end of this step 160, at least one set of compatible tracks is formed. This set consists, for example, of a pair of compatible active tracks. For example, at the end of this step, K active tracks are considered compatible and K / 2 pairs of tracks compatible with each other are formed.

[0099] The other active tracks (i.e. MK active tracks) are then considered incompatible.

[0100] The compatibility / incompatibility of each active track defines how to implement the transmission / reception step 110 of signals to that track during the next occurrences of steps 110 and 120.

[0101] In particular, for each incompatible active track, this step 110 comprises a substep 111 for generating a pulse, a step 112 for emitting this pulse in a frequency band corresponding to the waveform determined for this active track, a step 113 for receiving an echo of this pulse in a time window of predetermined duration, and a substep 114 for preprocessing received echoes including for example appropriate filtering and appropriate detection processing (for example in power or contrast).

[0102] In other words, for each incompatible active track, this step 110 includes the transmission / reception of a simple wave according to techniques known per se.

[0103] On the contrary, for each set of compatible active tracks, this step 110 includes a transmission / reception of the same commonized wave.

[0104] Each communalized wave comprises at least two consecutive pulses associated with compatible active tracks belonging to the same set. For example, each pulse is associated with a transmission direction corresponding to the active track associated with that pulse.

[0105] In such a case, during substep 111, the transmitting unit 22 of the radar 10 generates consecutive pulses associated with compatible active tracks. For example, during this substep, at least two pulses are generated. In particular, the number of pulses corresponds to the number of corresponding compatible active tracks.

[0106] According to this example, the emission unit 22 generates a first pulse h and a second pulse I2, illustrated in [Fig.5].

[0107] Each pulse is associated, for example, with a particular emission direction. This emission direction can be 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 El; and Az;. In all that follows, the subscript i=1 denotes any value relating to the first pulse and i=2 denotes any value relating to the second pulse.

[0108] The pulses are generated in an emission window Te in which each pulse has a width Li and is separated from the other pulse and from one of the boundaries of the emission window Te by a time gap TGAp. The pulse widths Li are advantageously chosen to be identical to obtain the same pulse compression processing for both targets and the same processing gain.

[0109] 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. This frequency support is defined by the compatible waveform corresponding to the compatible active tracks. 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 width of each frequency band.

[0110] The frequency bands Bi and B2 of the first pulse h and the second pulse I2 respectively are advantageously chosen to be the same for each recurrence of step 110. Thus, the same center frequency Fei and the same center frequency Fe2 are chosen respectively for the first pulse and for the second pulse in each recurrence of step 110.

[0111] These Fei and Fe2 values ​​correspond to the X values ​​chosen for the active tracks compatible with each other. In particular, A, = dFe i with c the speed of light. Thus, the associated emission frequencies Fei and Fe2 are chosen to be close enough to fall within the radar's reception band 10 and far enough apart to contain, without overlap, the emitted bands associated with each pulse.

[0112] During substep 112, the transmitting unit 22 emits the pulses generated during the previous substep in the corresponding frequency bands.

[0113] During substep 113, the receiving unit 23 receives echoes corresponding to the pulses emitted within a common reception time window. The duration Tr of this common reception window is equal to the total duration of the recurrence TR (i.e., the observation time of the corresponding pointing for one recurrence) minus the duration of the transmission window Te. During reception, the echoes corresponding to the different pulses are distinguished by different frequency bands, for example, by using suitable bandpass filters. Spatial filtering of the FFC type can also be applied in the direction associated with said band.

[0114] During substep 114, the receiving unit 23 performs preprocessing of the received echoes including for example suitable filtering and suitable detection processing (for example in power or contrast).

[0115] The results of such pretreatment are used as inputs to step 120.

[0116] It is therefore understood that the process according to the invention has a number of advantages.

[0117] In particular, according to the method according to the invention, the emission of communalized wave type signals for at least two active tracks is particularly advantageous because it saves time budget when the radar is used in active tracking.

[0118] Despite a loss on the energy budget linked to the cutting of the emission window into sub-pulses, this technique remains particularly advantageous compared to MIMO and colored emission techniques allowing the complete balance of the antenna to be preserved (transmitted power and transmission / reception gains).

[0119] In certain embodiments, the operating method as explained above further includes the implementation of at least one technique enabling better separation, during the transmission / reception of communalized waves, of echoes of pulses corresponding to different active tracking points and / or of rejecting the consideration of certain echoes which are not necessary or are ambiguous in distance.

[0120] According to a first technique, 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 (p.^) to this pulse. Advantageously, the emission unit 22 adds a different random phase 0 to each of the pulses. The pulse or pulses having a random phase (p) added are hereafter called a phase-shifted pulse.

[0121] It should be noted that the choice of the pulse to be phase-shifted can remain 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.

[0122] 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 corresponding random phase. In other words, the phase shift is performed by subtracting the value (p) in the band corresponding to the index i. This phase shift corresponds to the known distance ambiguity rank of the active track. Advantageously, the random phase compensation processing combined with Doppler processing provides suitable filtering for all echoes originating from the same ambiguity rank as the active track. This allows for advantageous isolation from other target echoes, and even the rejection of some of the ground or sea clutter.

[0123] Thus, during the subsequent processing, only the echoes corresponding to the ambiguity rank of the active track being sought are processed coherently. The phase shift of the other echoes cannot be performed correctly, so they are considered to behave as white noise.

[0124] Other techniques for obtaining better isolation of echoes corresponding to different active tracking points upon their reception are also possible.

[0125] Thus, according to a second usable technique, during the implementation of the nth recurrence of step 110 and in particular during the emission substep 112, the emission unit 22 implements different slopes of the chirps used to emit the pulses associated with different active tracking points. In other words, during this substep 112, the transmitting unit 22 emits the pulses using either an ascending or descending slope depending on the active track associated with each pulse. The same slope is then used for all pulses of this type in all iterations of step 110.

[0126] For example, for all recurrences, an upward slope is chosen for the pulses associated with a particular active track and a downward slope is chosen for the pulses associated with another active track.

[0127] Then, during the reception substep 113, the receiving unit 23 receives echoes with 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 active tracking points

[0128] According to a third usable technique that also provides better isolation of the echoes corresponding to different active tracking points upon reception, during the implementation of the nth recurrence 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 active tracking points. In other words, during this substep 112, the transmission unit 22 emits the wave carrying each pulse with a polarization chosen according to the active track associated with that pulse. This same polarization is chosen for this type of pulse for all recurrences of step 110.

[0129] For example, two polarizations, namely a vertical polarization and a horizontal polarization, can be chosen for the pulses emitted during substep 112. According to other examples, a 45° or circular polarization can be used.

[0130] Then, during the reception substep 113, the receiving unit 23 receives echoes with 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 active tracking points

[0131] The principle just described can be refined by using several polarizations in the same pulse.

[0132] In such a case, each pulse has a specific polarization signature. Such a signature corresponds to a polarization code.

[0133] This technique thus makes it possible to color the different impulses in space and to obtain an additional rejection of 20 to 30 dB.

[0134] In some embodiments, the aforementioned techniques are combined with each other to be implemented simultaneously.

Claims

Demands

1. Method of operating a target detection radar (10), the detection radar (10) implementing a scan forming a visibility cone; the method comprising the following steps: - determination (140) in the visibility cone of a plurality of active tracks, each active track presenting a target to be tracked; - for each active track, determination (150) of a waveform enabling its detection and tracking; - determination (160) of the compatibility of the active tracks by comparing the waveforms determined for these tracks to form at least one set of compatible active tracks, active tracks being compatible when there is the same waveform usable for tracking each of these active tracks;- for the or each set of compatible active tracks, transmission / reception (110) of a communalized wave comprising consecutive pulses, each pulse being associated with one of the active tracks of said set.;

2. Method according to claim 1, further comprising for each active track not belonging to any set of compatible active tracks, transmission / reception (110) of a simple wave comprising a single pulse.

3. A method according to any one of the preceding claims, wherein each waveform defines a visibility domain of a wave having that form.

4. Method according to claim 3, wherein each visibility domain comprises a distance domain and a speed domain of an active track.

5. A method according to claim 3 or 4, wherein two active tracks are compatible when they are within the same field of view with a probability greater than a predetermined threshold

6. A method according to any one of the preceding claims, wherein each waveform is defined by a wavelength, respectively an emission frequency, and a repetition frequency of a wave having that shape.

7. A method according to claim 6, wherein the compatibility of the active tracks is verified by testing different values ​​of wavelength and / or repetition frequency.

8. A method according to any one of the preceding claims, wherein the compatibility of the active tracks is determined for each pair of active tracks.

9. A method according to any one of the preceding claims, wherein the pulses of the same communalized wave are associated with different emission directions.

10. A method according to any one of the preceding claims, wherein each nth recurrence of the communalized wave transmission / reception step (110) comprises the following substeps: + generation (111) of at least two consecutive pulses associated with different active tracks of the same set of compatible active tracks; + transmission (112) of the pulses in different frequency bands; + reception (113) in a common time window of the pulse echoes.

11. A method according to claim 10, wherein: - each pulse is emitted with a random phase associated with the corresponding frequency band; - the reception substep (113) includes compensating for the phase shift of the echoes received in each frequency band, by the random phase associated with that frequency band.

12. A method according to any one of claims 10 to 11, wherein: - during the transmission substep (112), the corresponding pulses are emitted using different slopes of the chirps used to emit them; - during the reception substep (113), echoes associated with different active tracking points are distinguished by determining the slopes of the corresponding chirps.

13. A method according to any one of claims 10 to 12, wherein:

14.

15. - during the emission substep (112), the corresponding pulses are emitted using different polarizations; - during the reception substage (113), echoes associated with different active tracking points are distinguished by determining their polarizations. A method according to claim 13, wherein a polarization is emitted for each pulse or a set of polarizations forming a signature is emitted for each pulse. Target detection radar (10) comprising technical means (21, 22, 23) configured to implement the method according to any one of the preceding claims.

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