Method of operating a detection radar according to several detection configurations in a weather and associated radar detection mode

Abstract

Method of operating a detection radar in multiple detection configurations in a weather and associated radar detection mode. The present invention relates to a method of operating a target detection radar in clutter analysis mode in multiple detection configurations, each detection configuration corresponding to a different detection range. The method comprises implementing multiple repetitions of a signal transmission / reception step (110), each Nth repetition of said step (110) comprising the following substeps: + generation (111) of a sequence of consecutive pulses, each pulse of the sequence being associated with a respective detection configuration; + 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 2

Description

Title of the invention: Method of operating a detection radar according to several detection configurations in a weather and associated radar detection mode

[0001] The present invention relates to a method for 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 or non-Doppler operating mode throughout the mission. This is the case, for example, with a maritime surveillance Doppler 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 preserving system performance.

[0012] To this end, the invention relates to a method of operating a target detection radar in clutter analysis mode according to several detection configurations, each detection configuration corresponding to a different detection distance, 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 a sequence of consecutive pulses, each pulse of the sequence being associated with a respective detection configuration;

[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 method comprises a or several of the following characteristics, taken individually or in all technically possible combinations:

[0017] - the method further comprises a preliminary step of selecting a number M corresponding to a level of ambiguity to be addressed in a beam of emitted / received signals by radar, the number M varying between 0 and a maximum number of ambiguity ranks in the beam;

[0018] 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;

[0019] during the sub-step of receiving each Nth recurrence, the phase shift of the received echoes being compensated for the frequency band of the phase-shifted pulse, by the random phase associated with the number NM.

[0020] - each pulse is emitted with a random phase associated with the band corresponding frequency.

[0021] - the reception substep includes compensation for the phase shift of the echoes received in each frequency band, by the random phase associated with the NM number and that frequency band.

[0022] - the pulses of each recurrence share the same frequency support and are emitted with a frequency difference greater than each of the said frequency bands.

[0023] - the frequency gap is chosen to be able to distinguish the frequency bands different upon receiving the echoes.

[0024] - the sequence comprises a number greater than or equal to 2 pulses.

[0025] - the different detection configurations correspond to directions different transmission and reception methods.

[0026] - the different emission and reception directions correspond to angles different, the angles being chosen from site angles defined with respect to a pointing direction or azimuth angles defined with respect to a pointing direction.

[0027] - the method comprises, after receiving the pulses of the sequence, a step implementation of an emission and reception of an additional pulse, the implementation step being repeated so that the number of additional pulses is equal to the number of pulses in the sequence.

[0028] - the emission direction of each additional pulse is the same as that of an impulse from the sequence.

[0029] - during the emission substep, the pulses associated with the configurations of Different detections are emitted using different slopes of chirps used to emit them.

[0030] - during the reception substep, echoes associated with the configurations Different detection methods are distinguished by determining the slopes of the corresponding chirps.

[0031] - during the emission substep, the pulses associated with the configurations of Different detection signals are emitted using different polarizations.

[0032] - a polarization is emitted for each pulse.

[0033] - a set of polarizations forming a signature is emitted for each pulse.

[0034] - during the reception substep, echoes associated with the configurations of Different detection methods are distinguished by determining their polarizations.

[0035] The invention also relates to a target detection radar comprising technical means configured to implement the method as defined above.

[0036] 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:

[0037] - [Fig. 1] [Fig. 1] is a schematic view of a detection radar according to the invention;

[0038] - [Fig.2] [Fig.2] is a flowchart of a method for operating the radar of the [Fig.l];

[0039] - [Fig.3] [Fig.4] [Fig.5] [Fig.6] Figures 3 to 5 are different views illustrating the implementation of the process of [Fig.2];

[0040] - [Fig.7] [Fig.7] illustrates another example of a pulse sequence that can be used in the operating process of [Fig.2], and

[0041] - [Fig.8] [Fig.9] [Fig.10] Figures 8 to 10 illustrate how to best exploit the sequence of [Fig.7] in a particular case.

[0042] 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 fixedly mounted.

[0043] The radar 10 allows the detection of targets according to at least several detection configurations.

[0044] A detection configuration may correspond to a completely different radar mode or to the same radar mode but with a different observation (for example, a different emission direction or a different observation distance).

[0045] A radar mode allows the detection of targets of a particular type located or moving in a particular medium relative to the radar. For example, when the radar 10 is mounted on a carrier moving through the air, each radar mode allows the detection of targets moving with a particular relative speed in the air or on a land or sea surface.

[0046] Advantageously, the radar 10 allows the detection of targets following at least two different radar modes.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The operating method of radar 10 will now be explained with reference to [Fig.2] showing a flowchart of its steps.

[0051] 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.

[0052] This method includes in particular the implementation of several recurrences of a step 110 of signal transmission / reception.

[0053] The repetition frequency of these recurrences is chosen based on the repetition frequencies associated with the different detection configurations. The repetition frequency of each detection configuration is chosen according to the application selected for the radar 10.

[0054] Each Nth recurrence of step 110 includes the implementation of substeps 111 to 113 explained in detail below.

[0055] During substep 111, the emission unit 22 generates a sequence of at least two consecutive pulses associated with a respective detection configuration.

[0056] In particular, during this substep, the emission unit 22 generates a first pulse h associated with a first detection configuration and a second pulse I2 associated with a second detection configuration.

[0057] 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 El; and Az;. In all that follows, the subscript i=1 denotes the first radar mode and i=2 denotes the second radar mode.

[0058] 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.

[0059] 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 all that follows, a frequency band is defined by a center frequency and a bandwidth.

[0060] Advantageously, in the following, all frequency bands have the same width.

[0061] The frequency band Bi of the first pulse L, that is to say of the pulse associated with the first detection configuration, is chosen to be the same for each recurrence.

[0062] Advantageously, this choice is independent of the application of radar 10.

[0063] This is schematically illustrated in Figures 3 and 4, which show several consecutive recurrences corresponding to two distinct applications of the radar 10. Thus, the same center frequency Fei is chosen for the first pulse in each recurrence in each application.

[0064] The frequency band of the second pulse I2, i.e. of the pulse associated with the second detection configuration, is chosen according to the application of the radar 10.

[0065] 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.

[0066] In the example of [Fig.3], when k=2, two frequency bands B2 and B3 (i.e. two center frequencies) are then chosen alternately for each second pulse I2.

[0067] For the second application, the same frequency band B2 for the second pulse I2 is chosen in each recurrence, as illustrated in [Fig.4].

[0068] During substep 112, the transmission unit 22 emits the pulses generated during the previous substep in the corresponding frequency bands.

[0069] During substep 113, the receiving unit 23 receives echoes corresponding to the pulses emitted within a common reception time window. The duration 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.

[0070] During reception, the echoes corresponding to the different pulses are distinguished by their different frequency bands, for example by using bandpass filters. Spatial filtering of the FFC type can also be applied in the direction associated with said band.

[0071] 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 detection configuration and the pulses associated with the second detection configuration. Such coherent processing consists of applying filtering adapted to the waveform of the desired configuration, for example, pulse compression on the short time axis (within a recurrence).

[0072] 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.

[0073] Such non-coherent processing performs the power average of the signals received on each frequency band in the same direction (after coherent processing).

[0074] 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.

[0075] 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.

[0076] 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.

[0077] In certain embodiments, the operating method as explained above further includes the implementation of at least one technique enabling the separation of the echoes of the two modes, or even the rejection from consideration of 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.

[0078] Figure 5 illustrates an example of such a case according to the GMTI radar mode. According to this example, the radar beam emitted by the radar 10 from the carrier 12 covers several portions of the Earth's surface, the echoes of which overlap as the carrier moves along direction D. To avoid processing all the echoes from the ground beam footprint, a first technique consisting of choosing and processing only a single rank of ambiguity within the beam is implemented.

[0079] 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 opening of the radar beam. As illustrated in [Fig. 5], the ambiguity rank M can correspond to the central part of the radar beam.

[0080] In certain 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.

[0081] 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 (pjN) to each of the pulses. The pulse or pulses having an added random phase are hereafter referred to as a phase-shifted pulse.

[0082] 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.

[0083] It should also be noted that the value of the random phase for the or each pulse is then stored for at least M subsequent recurrences of step 110.

[0084] 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 the band corresponding to the index i.

[0085] Thus, during the subsequent processing, only the echoes corresponding to ambiguity rank M can be processed coherently. The phase shift of the others Echoes cannot be made properly, so they are considered white noise.

[0086] This principle is illustrated schematically in Figure 6. 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 2 is used to compensate for the phase shift in the corresponding frequency band.

[0087] 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.

[0088] Furthermore, it is also possible to obtain better isolation of the echoes corresponding to the different radar modes during their reception.

[0089] Thus, according to a second technique, during the implementation of the Nth recurrence of step 110 and in particular during the sub-step of emission 112, the emission unit 22 implements different slopes of the chirps used to emit the pulses associated with the different detection configurations.

[0090] In other words, during this substep 112, the transmitting unit 22 emits the pulses using either an ascending or a descending slope depending on the configuration associated with each pulse. The same slope is then used for all pulses of this type in all recurrences of step 110.

[0091] For example, for all recurrences, an upward slope is chosen for the impulses associated with the first configuration and a downward slope is chosen for the impulses associated with the second configuration.

[0092] 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 in order to isolate the echoes corresponding to the different detection configurations.

[0093] For this purpose, the receiving unit 23 uses filters adapted to the corresponding chirp slopes.

[0094] According to a third technique allowing also to obtain better isolation of the echoes corresponding to the different radar modes during their reception, during the implementation of the Nth recurrence of step 110 and in particular during the sub-step of the emission 112, the emission unit 22 implements different polarizations of the waves used to emit the pulses associated with the different radar modes.

[0095] In other words, during this substep 112, the transmitting 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 recurrences of step 110.

[0096] For example, two polarizations, namely a vertical polarization and a horizontal polarization, can be chosen for the pulses emitted during substep 112.

[0097] According to other examples, 45° or circular polarization can be used. For example, left-hand circular polarization can be associated with the first configuration and right-hand circular polarization can be associated with the second configuration.

[0098] Then, during the reception substep 113, the receiving unit 23 receives echoes having different polarizations. This receiving unit 23 therefore determines the received slopes in order to isolate the echoes corresponding to the different configurations.

[0099] For this purpose, the receiving unit 23 uses filters adapted to the corresponding polarization slopes.

[0100] The principle just described can be refined by using several polarizations in the same pulse.

[0101] In such a case, each pulse has a specific polarization signature. Such a signature corresponds to a polarization code.

[0102] This technique thus makes it possible to color the different impulses in space and to obtain an additional rejection of 20 to 30 dB.

[0103] 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.

[0104] It is therefore understood that the present invention has a number of advantages.

[0105] First, the invention allows the two detection configurations to be processed simultaneously, enabling operation with a common refresh rate in each radar application. This offers a clear advantage for target tracking applications.

[0106] In addition, a modern radar architecture makes it possible to implement a particular configuration (frequency, direction) of each pulse in the emission window Te.

[0107] Simultaneous processing of both modes also presents an advantage in terms of detection and management of false alarms.

[0108] 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 additional strong isolation between the signals of each detection configuration.

[0109] 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.

[0110] Furthermore, the waveforms shown in Figures 3 and 4 are not limiting.

[0111] Any waveform can be considered, presenting a sequence of pulses where each pulse corresponds to a specific detection configuration and a common reception phase.

[0112] Another example of such a waveform is shown in [Fig.7].

[0113] The [Fig.7] corresponds to the particular case of 4 pulses, it being understood that the number of pulses can be arbitrary.

[0114] In particular, the number of pulses can be greater than or equal to 3 and greater than or equal to 4.

[0115] The case of [Fig. 7] corresponds to 4 pulses L; having an identical pulse width and frequency bandwidth. The pulses allow the initial bandwidth to be divided into 4.

[0116] Furthermore, as can be seen in the lower right part of [Fig.7], the pointing directions associated with each pulse show an increasing azimuth, the azimuth extension of one pulse partially overlapping the azimuth extension of the next pulse.

[0117] Figure 8 schematically illustrates an example of the use of such a waveform for a weather mode.

[0118] A weather mode is an operating mode of the radar 10 in which the radar 10 seeks to determine one or more meteorological information.

[0119] This makes it possible to obtain a weather mode corresponding to the same clutter-to-noise ratio (often noted RFB) but with a distance resolution multiplied by a factor of 4 and a much reduced refresh time.

[0120] The minimum distance of observation of a target by the radar varies depending on the positioning of each pulse in the sequence.

[0121] To better visualize this effect, [Fig.8] schematically illustrates the observation range of each pulse (each observation range is identified by a number corresponding to the position of the pulse in the sequence), this range extending between the minimum observation distance and the maximum observation distance.

[0122] More specifically, it represents a panoramic view at a constant elevation angle of the space observed by each pulse.

[0123] Such a view is more often called a PPL view. The abbreviation PPI refers to the corresponding English name "Plan Position Indicator", which literally means "plan position indicator".

[0124] Analysis of the observation ranges shows that each range has the same extent but shifts towards radar 10, i.e., the minimum observation distance decreases with the position of the pulse in the sequence. The earlier the pulse is in the sequence, the greater the minimum distance.

[0125] The associated distance gain is clearly shown when comparing the PPI view of [Fig.8] with the PPI view of [Fig.9].

[0126] In [Fig.9], the PPI view on the right obtained after using a waveform visible on the left is shown.

[0127] The waveform of [Fig.9] corresponds to the successive sending and receiving of four pulses, respectively labeled A, B, C and D. These pulses are increasingly closer together.

[0128] Each observation range is identified by the letter of the impulse to which it belongs.

[0129] It appears that the observation ranges A to D are much more restricted than the observation ranges 1 to 4 of [Fig.8].

[0130] Furthermore, it can be observed that the maximum distance decreases with the position of the pulses A to D but the minimum distance remains the same.

[0131] Thus, advantageously, as is the case in [Fig.10], by simultaneously using the waveforms of [Fig.8] and [Fig.9], the same minimum distance and an extended observation range are obtained.

[0132] In such a case, the method includes, after receiving the pulses of the sequence, a step of implementing an emission and a reception of an additional pulse (here pulses A to D, the implementation state being repeated so that the number of additional pulses is equal to the number of pulses of the sequence).

[0133] The pointing direction of each additional pulse is, moreover, the same as that of a pulse in the sequence.

[0134] With regard to the refresh time, the reduction obtained using the waveform of [Fig. 10] can be better understood through the following reasoning.

[0135] The refresh time reduction factor depends on the TGAP time gap and the recurrence period ratios.

[0136] By way of example, for the waveform of [Fig.8], assuming that the extension of the TR sequence is 1.4 ms and a proportion of time range allocated to emission with respect to the recurrence period of 20% (i.e. a form factor FF of 20%).

[0137] An emission window comprises 4 time intervals TGap and the 4 pulses 1 to 4, each having the same width. It follows that the following relationship:

[0138] 57(^+4.1^ = FF.Tr = 0.2x1.4 ms = 280 fis

[0139] For a TGAP time gap of 10 ps, ​​the width of a pulse 1 to 4 is 57.5 ps.

[0140] Such a value corresponds to a pulse form factor of approximately 4%.

[0141] Furthermore, with regard to the waveform of [Fig.9], taking a pulse width of 6 ps and pulse spacing values ​​of 286 ps, 218.5 ps, 151 ps and 83.5 ps respectively, there is an associated time budget of 739 ps.

[0142] This results in a total budget for the waveform of [Fig. 10] equal to the sum of 1.4 ms and 739 ps or 2.14 ms.

[0143] Since each pulse corresponds in the case of [Fig.8] to a different azimuth angle, a time budget of 4x1.4 or 6.4 ms is involved with the waveform of [Fig.9],

[0144] The gain is therefore 66% if we want to have the same level of information, which implies that the use of the specific waveform allows us to gain a factor of 3.

[0145] This significant gain on the time budget allocated to a weather mode can be used by a radar scheduler to devote more time to other radar functions such as air surveillance or maritime surveillance.

[0146] It could also be considered to use the best distance resolution only for the necessary observation directions, such as a direction in which precipitation is observed.

[0147] This specific waveform can also be used to analyze clutter of other types than the volumetric type of weather, and in particular surface clutter present during sea or land observation.

[0148] Indeed, the methods of clutter analysis, surface (land, sea) or volumetric (weather) each aim to estimate the radar equivalent area of ​​the observed clutter and to deduce characteristic environmental information useful to the radar operator: sea state, wind speed, presence of clouds, precipitation such as rain or hail.

[0149] In each of the different cases just described in this description, a specific waveform is used to obtain several distinct detection configurations.

Claims

Demands

1. Method of operating a target detection radar (10) in clutter analysis mode according to several detection configurations, each detection configuration corresponding to a different detection distance, the method comprising the implementation of several recurrences of a signal emission / reception step (110), each Nth recurrence of said step (110) comprising the following substeps: + generation (111) of a sequence of consecutive pulses, each pulse of the sequence being associated with a respective detection configuration; + emission (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 for 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 impulses of each recurrence share the same medium frequency and are emitted with a frequency difference greater than 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 the sequence comprises a number greater than or equal to 2 pulses.

8. A method according to any one of claims 1 to 7, wherein the different detection configurations correspond to different emission and reception directions.

9. A method according to claim 8, wherein the different emission and reception directions correspond to different angles, the angles being chosen from site angles defined with respect to a pointing direction or azimuth angles defined with respect to a pointing direction.

10. A method according to claim 9, wherein the method comprises, after receiving the pulses of the sequence, a step of implementing an emission and reception of an additional pulse, the implementation step being repeated so that the number of additional pulses is equal to the number of pulses of the sequence.

11. A method according to claim 10, wherein the emission direction of each additional pulse is the same as that of a pulse in the sequence.

12. A method according to any one of claims 1 to 11, wherein, during the emission substep (112), the pulses associated with the different detection configurations are emitted using different slopes of the chirps used to emit them.

13. A method according to claim 12 wherein, during the reception substep (113), echoes associated with different detection configurations are distinguished by determining the slopes of the corresponding chirps.

14. A method according to any one of claims 1 to 13, wherein during the emission substep (112), the pulses associated with the different detection configurations are emitted using different polarizations.

15. A method according to claim 14, wherein a polarization is emitted for each pulse.

16. A method according to claim 14, wherein a set of polarizations forming a signature is emitted for each pulse.

17. A method according to any one of claims 14 to 16, wherein, during the reception substep (113), echoes associated with different detection configurations are distinguished by determining their polarizations.

18. Target detection radar (10) comprising technical means (21, 22, 23) configured to implement the method according to any one of claims 1 to 17.

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