Method of operation of a target detection radar in maritime surveillance mode and associated detection radar

Abstract

Method for operating a target detection radar in maritime surveillance mode and associated detection radar. The present invention relates to a method for operating a target detection radar in maritime surveillance mode; the method comprising a step (140) of determining a false alarm level in each geographical sector; the method further comprising, for each geographical sector, the implementation of several repetitions of a step (110) of transmitting / receiving signals of a type selected from simple waves and communalized waves, according to the false alarm level determined for at least one of the geographical sectors; each communalized wave comprising at least two consecutive pulses associated with different transmission directions and / or different frequencies, and transmitted in different frequency bands; each simple wave comprising a single pulse. Figure for the abstract: Figure 2

Description

Title of the invention: Method for operating a target detection radar in maritime surveillance mode and associated detection radar

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

[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 a detection / identification of targets in maritime surveillance mode.

[0004] The general problem solved by the invention consists of remedying the stroboscopic effect of wave fronts in order to readjust the "turn-by-turn" type extraction treatments while maintaining or locally reducing the radar detection budget.

[0005] In the context of a maritime surveillance mode for which the detection criterion is made mainly (or even exclusively) in the presence of heavy sea clutter, i.e. for distances close to the radar, increasing the radar budget by coherent processing is not an appropriate solution to improve target detection, unlike the case of the presence of only thermal noise.

[0006] In this context, opting for a large pulse width to increase the pulse compression gain or opting for a longer observation time to increase the Doppler processing gain in Doppler mode is not necessarily an advantageous strategy.

[0007] When the clutter-to-noise ratio (CRN) is very high, for example at short range, the detection of small maritime targets is hampered by the presence of spikes, i.e., clutter echoes from a large radar cross-section (RCS) relative to an average RCS of the local clutter. Waves can cause such a phenomenon, for example.

[0008] To differentiate a target from a spike, which do not have the same correlation time, "turn-by-turn" (or scan-by-scan) treatments of the extractor type or even kinematic filtering are generally used to extract in time the contributions of the targets and surrounding spikes.

[0009] It is assumed for this reason that the spikes will "collapse" in power more rapidly than the coherence time of the targets, which is assumed to be longer. This is why This is why "K / N" type extractors are generally used to filter out false alarms related to spikes.

[0010] However, these "turn-by-turn" processing methods assume that spike contributions in a "distance-azimuth" macrocell are not replaced by other contributions. Yet, under atypical clutter conditions, this is not always the case: at high wave speeds, new physical contributions can migrate and replace the previous ones, thus undermining the extraction processes.

[0011] The present invention aims to remedy this problem and improve the quality of maritime target detection even under atypical clutter conditions.

[0012] To this end, the invention aims at a method of operating a target detection radar in maritime surveillance mode, the detection radar implementing a scan in a plurality of geographical sectors;

[0013] the method comprising a step of determining a level of false alarms in each geographical sector;

[0014] the method further comprising for each geographical sector, the implementation of several recurrences of a signal transmission / reception step of a type chosen from simple waves and communalized waves, depending on the level of false alarms determined for at least one of the geographical sectors;

[0015] each communalized wave comprising at least two consecutive pulses associated with different emission directions and / or different frequencies, and emitted in different frequency bands;

[0016] each simple wave comprising a single pulse.

[0017] 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:

[0018] - the communalized waves are chosen in a geographical sector when the the level of false alarms in at least one of the geographical sectors is above a predetermined threshold;

[0019] - the method further comprising an adaptation step depending on the level of false alarms in at least one of the geographical sectors of at least one of the parameters chosen in the group including:

[0020] - an observation time for each pointing position included in this sector geographical or in another geographical area;

[0021] - a target extraction threshold in this geographical area;

[0022] - a number of pulses emitted in each communalized wave in this sector geographical or in another geographical area;

[0023] - the geographical area in which the communalized waves are chosen, is chosen randomly or according to a predetermined rule, from among all geographical sectors where the number of false alarms has not exceeded the threshold;

[0024] - each geographical sector corresponds to a quadrant describing the sea clutter in wind function;

[0025] - each dial corresponds to a domain of the type "downwind", "upwind" and "crosswind";

[0026] - a false alarm is determined by applying a target density criterion by area and / or by analyzing the number of targets in an area according to external data;

[0027] - the method further comprising a step of analyzing the echoes of received signals including a "turn-by-turn" type extraction treatment;

[0028] - each nth recurrence of the communalized wave transmission / reception step includes the following sub-steps:

[0029] + generation of at least two consecutive pulses associated with directions of different emissions and / or at different frequencies;

[0030] + emission of pulses in different frequency bands;

[0031] + reception in a common time window of the echoes of the pulses;

[0032] - each pulse is emitted with a random phase associated with the band corresponding frequency;

[0033] - 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;

[0034] - during the emission substep, the corresponding pulses are emitted in using different slopes of chirps used to emit them;

[0035] - during the reception sub-step, echoes associated with emission directions and / or at different frequencies are distinguished by determining the slopes of the corresponding chirps;

[0036] - during the emission substep, the corresponding pulses are emitted in using different polarizations;

[0037] - during the reception sub-step, echoes associated with emission directions and / or at different frequencies are distinguished by determining their polarizations;

[0038] - a polarization is emitted for each pulse or a set of polarizations forming a signature is emitted for each pulse.

[0039] The invention also relates to a target detection radar comprising technical means configured to implement the method as defined above.

[0040] 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:

[0041] - [Fig. 1] [Fig. 1] is a schematic view of a detection radar according to the invention;

[0042] - [Fig.2] [Fig.2] is a flowchart of a method for operating the radar of the [Fig.l];

[0043] - [Fig.3] [Fig.4] Figures 3 and 4 are different views illustrating the implementation of the process of [Fig.2].

[0044] 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.

[0045] The radar 10 allows the detection of targets according to a maritime surveillance mode, for example a Doppler mode of type MMTI (from the English "Maritime Moving Target Indicator") or a non-Doppler mode.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The operating method of radar 10 will now be explained with reference to [Fig.2] showing a flowchart of its steps.

[0050] 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.

[0051] It is further considered that the pointing positions follow one another in a predetermined direction of rotation and each defines a dependent angular opening M is the number of different frequencies that must be emitted in a direction of the known pointing angle. The set of pointing positions covers the entire available field of view of the radar system. Without limiting the invention, this field of view forms, for example, a 360° rotation. Furthermore, an observation time Tr(i) is defined for each pointing position. This observation time corresponds to the time required to take measurements in the corresponding pointing position.

[0052] The time elapsed between two successive measurements in the same pointing position is called the Traf refresh time.

[0053] The calculation of this Traffic refresh time depends on the mode chosen for radar 10.

[0054] In particular, for a non-Doppler mode: 100551

[0056] where

[0057] Nh of pointing to perform a non-consistent integration (power mean);

[0058] Nb^i) is 'c number of pointings.

[0059] For a Doppler mode, the preceding formula takes the following form: 100601 T„f = ) X x Ti{i)

[0061] where

[0062] Nrec(i) is the number of recurrences treated consistently for the same frequency.

[0063] Each pointing position belongs to a geographical sector defined according to the environment in which the radar 10 operates. For example, four sectors, then called gimbals, can be determined around the radar 10 according to the wind. Each sector can thus correspond to a geographical area of ​​the type "leeward," "upwind," and "crosswind." Alternatively, the geographical sectors are defined in a more refined and possibly irregular manner. Their number can thus be strictly greater than 4. Generally, the number of geographical sectors is greater than or equal to 1.

[0064] Advantageously, a plurality of successive pointing positions correspond to the same sector.

[0065] Each nth recurrence of step 110 includes an emission / reception of signals in the corresponding pointing position.

[0066] In particular, during this step, the transmitting unit 22 of the radar 10 emits signals in a cone defined by the pointing position and the receiving unit 23 receives echoes of these signals.

[0067] 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.

[0068] 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 a turn-by-turn extraction process to identify maritime targets.

[0069] In a manner known per se, such treatment is carried out by considering a plurality of macro-cells capable of containing a marine target. An example of such a macro-cell C is illustrated in [Fig.3].

[0070] In particular, this [Fig. 3] illustrates the arrangement of a radar antenna panel 10 facing wave fronts shown in this figure by horizontal lines. The waves form a wave train moving at the speed Vwave and having a spacing Lwave between them. In the figure, the macro-cell C is of size (AR, RAAz) where the values ​​AR and RAAz correspond to processing resolutions in range and azimuth, respectively. The extraction processing for this macro-cell has a duration of NxTraf where Traf corresponds to the refresh time assumed to be constant between two measurements and N corresponds to the number of measurements, i.e., the number of times step 110 is implemented in the same pointing position.

[0071] A maritime target is considered to be detected when, following the analysis of macro-cell C, the radar 10 concludes that such a target is present in the macro-cell.

[0072] A maritime 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 macro-cell 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 a subsequent step 130, implemented at least once per radar cycle 10, the radar 10 determines the level of false alarms generated in each geographic sector. In particular, a "false alarm" is understood to mean any plot resulting from the detection and extraction processes that does not originate from a target useful from the radar operator's point of view (e.g., noise spikes, clutter spikes, etc.).

[0074] For this purpose, the radar 10 verifies, using additional processing other than that implemented during step 120, that each extracted detection does indeed correspond to a target of interest present in the corresponding sector.

[0075] This additional processing may include the implementation of a target density criterion per area (distance, azimuth) or a comparison of a number of maritime vessels on site declared by an automatic identification system of the "AIS" type (from the English Automatic Identification System) with regard to the density of radar plots.

[0076] A detection is confirmed when this additional processing confirms the presence of a target of interest and is considered a false alarm otherwise.

[0077] During a subsequent step 140 implemented at least once per turn, the radar 10 compares for each sector the number of false alarms with a predetermined threshold.

[0078] When this number is less than the threshold for all sectors, the next recurrence of steps 110 and 120 in relation to the next sector is implemented with the same parameters as before.

[0079] Otherwise, if for at least one of the sectors the threshold is exceeded, the parameters are readjusted on at least one of the points to be made to complete a full tour.

[0080] This readjustment is primarily aimed at reducing the Traf refresh time.

[0081] Indeed, as previously indicated, a series of false alarms can be mainly due to the stroboscopic phenomenon of the waves during the extraction processing implemented during step 120.

[0082] To avoid such a phenomenon, a wave front must not replace the next one in the same macrocell. This is true when the following two conditions are met:

[0083] 1) There is at most only one wave front per macro-cell: AT? < L wave

[0084] 2) The displacement of a wave front does not exceed the distance between two fronts: V wave XNT raf < E vague

[0085] Condition 2) is to be reproduced for the different viewing angles a; it is to be considered in terms of radial velocity with respect to the radar 10, i.e., replace Vwave with its projection Vwave cos(a) < Vwave

[0086] A solution consisting of reducing AR satisfies the first condition but not the second. Furthermore, this reduction in AR also decreases the maximum observable velocity of the targets. In addition, in practice, Lwave and Vwave are unknown and exhibit atypical clutter for high wave speeds and short wavelengths. Thus, to verify the second condition, the Traf refresh time must be reduced.

[0087] Thus, according to a first embodiment, during step 140, the radar 10 reduces the observation times for all the pointings in at least one sector. This reduces the Traffic refresh time for the complete circuit.

[0088] This is possible for example by accelerating the electronic scanning implemented by the radar 10, i.e. by decreasing the number of recurrences emitted in a direction.

[0089] The choice of the sector in which observation times should be reduced can be made according to different embodiment examples.

[0090] According to a first example, the sector chosen is the one in which the number of false alarms has exceeded the threshold.

[0091] According to a second example, on the contrary, such a sector is chosen at least initially, for example randomly and according to a predetermined rule, from among all the sectors whose number of false alarms has not exceeded the threshold.

[0092] Then, the "trial and error" principle can be applied during subsequent iterations of the process to confirm or modify this choice.

[0093] For example, when this choice has made it possible to reduce the number of false alarms in the corresponding sector, the choice of the same sector can be kept for a subsequent iteration of the steps of the process.

[0094] When, on the contrary, this choice has not made it possible to reduce the number of false alarms, another sector is chosen during a subsequent iteration of the steps of the process.

[0095] Alternatively or optionally, the radar adjusts the target extraction threshold for at least one given sector to reduce the number of false alarms. In this case, it could be the sector where the number of false alarms has exceeded the threshold.

[0096] According to a second embodiment, combinable with the first embodiment, the radar 10 adapts the type of signals emitted / received during step 110.

[0097] In particular, it is initially considered that the signals emitted / received during step 110 are of the so-called simple wave type.

[0098] In such a case, this step 110 includes a substep 111 of generating a pulse, a substep 112 of emitting this pulse in a predetermined frequency band, a substep 113 of receiving an echo of this pulse in a time window of predetermined duration and a substep 114 of preprocessing the received echoes including for example suitable filtering and suitable detection processing (for example in power or in contrast).

[0099] When the false alarm level is too high in a sector, the radar 10 changes the type of signals emitted / received during step 110 to the so-called communalized wave type in at least one sector. The selection of such a sector can be carried out according to the same principle as described above. In particular, this chosen sector may correspond to the sector with the false alarm level exceeding the threshold or, conversely, to a sector chosen randomly or according to a predetermined rule from among all the sectors whose number of false alarms has not exceeded the threshold. The "trial and error" principle can also be applied for subsequent iterations.

[0100] Each communalized wave comprises at least two consecutive pulses associated with different emission directions and / or different frequencies, and emitted in different frequency bands. Advantageously, the communalized wave allows for faster electronic scanning without changing the number of repetitions transmitted in a direction.

[0101] In such a case, during substep 111, the transmission unit 22 of the radar 10 generates two consecutive pulses associated with different frequencies or different emission directions.

[0102] In particular, during this substep, the emission unit 22 generates a first pulse h and a second pulse I2, illustrated in [Fig.4].

[0103] Each pulse is associated with a particular frequency or 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 Eh and Azi. 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.

[0104] 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.

[0105] 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.

[0106] The frequency bands Bi and B2 of the first pulse L 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.

[0107] During substep 112, the transmitting unit 22 emits the pulses generated during the previous substep in the corresponding frequency bands.

[0108] 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 a recurrence, as defined previously) minus the duration of the transmission window Te. Upon reception, the echoes corresponding to the different pulses are distinguished by their different frequency bands, using, for example, bandpass filters. Spatial filtering of the FFC type can also be applied in the direction associated with said band.

[0109] Of course, the number of pulses emitted during substep 111 can be greater than 2 and can also have a setting parameter during step 140 for the corresponding geographic sector. This then allows the refresh time to be reduced further. Advantageously, in one embodiment, the communalized wave uses the same number of recurrences transmitted in one direction by the simple waveform. This implies the use of the same number of post-integration, or even the same number of recurrences for the Doppler processing. Since at least two directions are played simultaneously, this allows the refresh time to be reduced.

[0110] Furthermore, when, for example, it is no longer necessary to track targets in a given geographical area, the radar 10 can readjust the parameters used in steps 110 and 120 for the corresponding area(s), by increasing the refresh rate. For this purpose, simple wave signals can then be used in this / these area(s).

[0111] 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).

[0112] The results of such pretreatment are used as inputs to step 120.

[0113] It is therefore understood that the method according to the invention makes it possible to improve the quality of maritime target detection even under atypical clutter conditions, in particular by reducing the level of false alarms. This is achieved by adapting, among other things, the observation times in at least one geographical sector (and consequently the overall refresh time) and possibly other parameters used for signal processing. The emission of communalized wave-type signals is particularly advantageous insofar as it makes it possible to cover several frequencies and / or directions simultaneously.

[0114] In certain embodiments, the operating method as explained above further includes the implementation of at least one technique for separating, during the transmission / reception of the communalized waves, the echoes of the pulses corresponding to different frequencies / directions and / or for rejecting from consideration certain echoes which are not necessary or are ambiguous in distance to reconstruct a complete image of the environment.

[0115] According to a first technique applicable to a Doppler mode, 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 to that pulse. Advantageously, the emission unit 22 adds a different random phase to each of the pulses. The pulse or pulses having an added random phase are hereafter referred to as a phase-shifted pulse.

[0116] 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.

[0117] 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 in the band corresponding to index i.

[0118] Thus, during the subsequent processing, only echoes corresponding to a specific direction / frequency can be processed coherently. The phase shift of the other echoes cannot be performed correctly, so they are considered white noise.

[0119] Other techniques for obtaining better isolation of echoes corresponding to different frequencies / directions during their reception are also possible.

[0120] Thus, according to a second technique applicable to Doppler and non-Doppler modes, 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 different frequencies / directions. 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 frequency / direction associated with each pulse. The same slope is then used for all pulses of this type in all iterations of step 110.

[0121] For example, for all recurrences, an upward slope is chosen for pulses associated with a particular frequency / direction and a downward slope is chosen for pulses associated with another particular frequency / direction.

[0122] Then, during the reception substep 113, the reception unit 23 receives echoes having different frequency slopes. This reception unit 23 therefore determines the received slopes (using in particular suitable filters) in order to isolate the echoes corresponding to the different frequencies / directions.

[0123] According to a third technique usable for Doppler and non-Doppler modes, and which also provides better isolation of echoes corresponding to different frequencies / directions upon reception, during the implementation of the nth recurrence of step 110, and in particular during the transmission sub-step 112, the transmission unit 22 implements different polarizations of the waves used to emit the pulses associated with the different frequencies / directions. In other words, during this sub-step 112, the transmission unit 22 emits the wave carrying each pulse with a polarization chosen according to the frequency / direction associated with that pulse. This same polarization is chosen for this type of pulse for all recurrences of step 110.

[0124] 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.

[0125] 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 frequencies / directions.

[0126] The principle just described can be refined by using several polarizations in the same pulse.

[0127] In such a case, each pulse has a specific polarization signature. Such a signature corresponds to a polarization code.

[0128] This technique thus makes it possible to color the different impulses in space and to obtain an additional rejection of 20 to 30 dB.

[0129] 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.

Claims

Demands

1. Method of operating a target detection radar (10) in maritime surveillance mode, the detection radar (10) implementing a scan in a plurality of geographical sectors; the method comprising a step (140) of determining a false alarm level in each geographical sector; the method further comprising, for each geographical sector, the implementation of several recurrences of a step (110) of transmitting / receiving signals of a type selected from simple waves and communalized waves, according to the false alarm level determined for at least one of the geographical sectors; each communalized wave comprising at least two consecutive pulses associated with different emission directions and / or different frequencies, and emitted in different frequency bands; each simple wave comprising a single pulse.

2. A method according to claim 1, wherein the communalized waves are chosen in a geographical sector when the level of false alarms in at least one of the geographical sectors is greater than a predetermined threshold.

3. A method according to claim 1 or 2, further comprising a step (130) of adapting according to the level of false alarms in at least one of the geographical sectors of at least one of the parameters chosen from the group comprising: - an observation time of each pointing position included in this geographical sector or in another geographical sector; - a target extraction threshold in this geographical sector; - a number of pulses emitted in each communalized wave in this geographical sector or in another geographical sector.

4. A method according to claim 2 or 3, wherein the geographical area in which the communalized waves are chosen is chosen randomly or according to a predetermined rule, from among all the geographical areas whose number of false alarms has not exceeded the threshold.

5. A method according to any one of the preceding claims, wherein each geographical sector corresponds to a dial describing the sea clutter as a function of the wind.

6. Method according to claim 5, wherein each dial corresponds to a domain of the type "downwind", "upwind" and "crosswind".

7. A method according to any one of the preceding claims, wherein a false alarm is determined by applying a target density criterion per zone and / or by analyzing the number of targets in a zone according to external data.

8. A method according to any one of the preceding claims, further comprising a step (120) of analyzing the echoes of received signals comprising a turn-by-turn extraction process.

9. 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 emission directions and / or different frequencies; + transmission (112) of the pulses in different frequency bands; + reception (113) in a common time window of the pulse echoes.

10. A method according to claim 9, 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.

11. A method according to any one of claims 9 to 10, 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 emission directions and / or frequencies are distinguished by determining the slopes of the corresponding chirps.

12. A method according to any one of claims 9 to 11, wherein: - during the emission substep (112), the corresponding pulses are emitted using different polarizations; - during the reception substep (113), echoes associated with different emission directions and / or frequencies are distinguished by determining their polarizations.

13. A method according to claim 12, wherein a polarization is emitted for each pulse or a set of polarizations forming a signature is emitted for each pulse.

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