Detection system comprising a phased array antenna and associated detection method
By employing a network control antenna with phase control to interlace the imaging of multiple target zones, the detection process enhances the efficiency of radar imaging by reducing unnecessary listening times and optimizing the use of electronic scanning agility.
Patent Information
- Application Number
- FR2023004250
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-04-27
- Publication Date
- 2025-05-09
- Estimated Expiration
- 2043-04-27
AI Technical Summary
Traditional radar imaging processes with opening synthesis (RSO) and reverse opening synthesis (RSOI) suffer from inefficiencies due to the alternation of emission and listening phases, where only a small portion of the listening time produces useful signals, leading to wasted time and reduced imaging effectiveness.
A detection process utilizing a network control antenna with phase control, allowing for simultaneous or interlaced imaging of multiple target zones by applying different phase laws to the antenna's radiating elements, thereby optimizing the use of listening time and reducing unnecessary delays.
This approach significantly reduces the total acquisition time required for imaging multiple target zones by exploiting dead time during the imaging process and leveraging the agility of electronic scanning, resulting in more efficient and effective radar imaging.
Smart Images
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Abstract
Description
Title of the invention: Detection system comprising a phased array antenna and associated detection method Technical field
[0001] The invention lies in the field of imaging resulting from the analysis of reflections (echoes), of emitted signals, on obstacles encountered by the emitted signals and using an electronic scanning antenna, making it possible to apply selective phase shifts of the electrical signals supplying the radiating elements according to linear phase laws and to modify them dynamically, which has the effect of pointing the beam in different successive directions.
[0002] The basics of synthetic aperture radar imaging are given in particular in L. FERRO-FAMIL, Principles of Synthetic Aperture Radar (SAR) imaging, Engineering Techniques, 2013. Prior art
[0003] Traditional Synthetic Aperture Radar (SAR) or Inverse Synthetic Aperture Radar (ISAR) imaging methods emit pulses of waveforms sized to construct a very high distance resolution and very high angular resolution image of the portion of ground of interest. Usually, only a fraction of the time used for the reception of each pulse (generally the end) produces the signal actually used by the imaging method.
[0004] They consist of the alternation of a phase of emission of one or more pulses, followed by a listening phase during which the Radar system (same for a Sonar Radar) digitizes and processes the echoes received. This alternation of emission / listening phase is repeated a large number of times (depending on the transverse resolution desired for the final image), the digitized signals then undergoing a sequence of processing (migration compensation, Fourier transform, focusing, conformity, etc.). In many cases, only a small portion of the listening phase produces a useful signal, so most of the listening time is wasted.
[0005] There is therefore a need to improve the efficiency of these imaging methods. Summary of the invention
[0006] To this end, according to a first aspect, the present invention describes a detection method in a detection system comprising a phased array antenna comprising unit radiating elements, said system being adapted to, via said array antenna, transmit waves and receive echoes of said transmitted waves and to analyze the received echoes; said detection method comprising the following steps in each of several consecutive treatment cycles: - controlling the application of a first determined phase law to electrical feed signals of the unit radiating elements of the network antenna to direct the antenna radiation towards a first target zone; - the first controlled phase law being applied to said radiating elements in response to said command: at least a first wave emission is carried out, echoes from said first wave emission are received; then - an initial analysis of said echoes received is carried out; - an image of the first target area is determined based on at least said first analysis;
[0007] said method being characterized in that it further comprises the following steps during each of said cycles: - controlling the application of at least one second determined phase law to electrical feed signals of said unit radiating elements of the array antenna to direct the antenna radiation towards a second target zone; the second phase law being different from the first law controlled during said same cycle and the second target zone being separate from the first target zone; - the second controlled phase law being applied to said radiating elements in response to said command: at least one second wave emission is carried out, echoes from said second wave emission are received; then - a second analysis of said echoes received is carried out; - an image of the second target area is determined based on at least said second analysis.
[0008] The method according to the invention aims to exploit the agility of electronic scanning in order to fill the unnecessary listening times mentioned above, by executing, in parallel with the imaging of a target zone, one or more additional aperture synthesis imaging processes, on another target zone and using the same unit radiating elements (or at least some of them).
[0009] In embodiments, such a method will further comprise at least one of the following features: - for at least one of the said cycles: - the elevation angle of the array antenna during the application of the second phase law is different from the elevation angle of the array antenna during the application of the first phase law; and / or - the azimuth angle of the array antenna during the application of the second phase law is different from the azimuth angle of the array antenna during the application of the first phase law; and / or - the resolution of the image of the first target area is distinct from the resolution of the image of the second target area; and / or - the size of the image of the first target area is distinct from the size of the image of the second target area; - a first waveform is selectively used for the first wave transmission towards the first target area and a second waveform distinct from the first is selectively used for the second wave transmission towards the second target area according to one or more of the following arrangements: - the first waveform is transmitted on a first carrier frequency Fl and the second waveform is transmitted on a second carrier frequency distinct from the first carrier frequency; - when the first target zone and the second target zone are located at different distances from the antenna, during the first, respectively second, transmission, the pulse duration and the repetition period during the first, respectively second transmission, are distinct and are a function of the distance of the first, respectively second target, from the antenna; - the polarization of the first waveform is distinct from the polarization of the second waveform, each defined according to the observation geometry and the type of target area, so as to maximize the target-to-clutter ratio of the image;
[0010] the first target zone remains the same over several consecutive cycles and the second target zone remains the same over several consecutive cycles;
[0011] during each of said cycles: - the first wave emission towards the first target zone is carried out, the first controlled phase law being applied to said radiating elements; then - the second wave emission towards the second target zone is carried out, the second controlled phase law being applied to said radiating elements; then - the echoes from the first, respectively second wave emission, are received, the first, respectively second controlled phase law then being applied to said radiating elements.
[0012] According to another aspect, the invention describes a detection system comprising a phased array antenna comprising unit radiating elements, said system being adapted to, via said array antenna, transmit waves and receive echoes of said transmitted waves and to analyze the received echoes; the detection system being adapted to, at each of several consecutive processing cycles, control the application of a first determined phase law to electrical feed signals of the unit radiating elements of the array antenna to direct the antenna radiation towards a first target zone; and the first controlled phase law being applied to said radiating elements in response to said control: to carry out at least a first wave transmission and receive echoes from said first wave emission are received; then to carry out a first analysis of said received echoes and to determine an image of the first target area based on at least said first analysis;
[0013] said detection system being characterized in that it is further adapted, during each of said cycles, to control the application of at least one second determined phase law to electrical feed signals of said unit radiating elements of the array antenna to direct the antenna radiation towards a second target zone, the second phase law being different from the first law controlled during said same cycle and the second target zone being disjoint from the first target zone then, the second controlled phase law being applied to said radiating elements in response to said control, to carry out at least one second wave emission and receive echoes from said second wave emission, then to carry out a second analysis of said received echoes and determine an image of the second target zone as a function of at least said second analysis.
[0014] In embodiments, such a system will further comprise at least one of the following features: - for at least one of said cycles: the elevation angle of the array antenna during the application of the second phase law is different from the elevation angle of the array antenna during the application of the first phase law; and / or the azimuth angle of the array antenna during the application of the second phase law is different from the azimuth angle of the array antenna during the application of the first phase law; and / or the resolution of the image of the first target area is distinct from the resolution of the image of the second target area; and / or the size of the image of the first target area is distinct from the size of the image of the second target area; - the detection system is adapted to selectively use a first waveform for the first wave emission towards the first target zone and to selectively use a second waveform distinct from the first for a second wave emission towards the second target zone according to one or more of the following arrangements: - the first waveform is transmitted on a first carrier frequency Fl and the second waveform is transmitted on a second carrier frequency distinct from the first carrier frequency; - when the first target zone and the second target zone are located at different distances from the antenna, during the first, respectively second, transmission, the pulse duration and the repetition period during the first, respectively second transmission, are distinct and are a function of the distance of the first, respectively second target, from the antenna;
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[0023] - the polarization of the first waveform is distinct from the polarization of the second waveform, each defined according to the observation geometry and the type of target area, so as to maximize the target-to-clutter ratio of the image; - the first target zone remains the same over several consecutive cycles and the second target zone remains the same over several consecutive cycles; - the detection system is adapted for, during each of the said cycles: - carry out the first wave emission towards the first target zone (Zl), the first controlled phase law being applied to said radiating elements; then - carry out the second wave emission towards the second target zone (Z2), the second controlled phase law being applied to said radiating elements; then - receive the echoes from the first, respectively second wave emission, the first, respectively second controlled phase law then being applied to said radiating elements. Brief description of the drawings The invention will be better understood and other characteristics, details and advantages will appear more clearly on reading the following description, given without limitation, and thanks to the appended figures, given by way of example. [Fig.l] [Fig.l] is an illustration of different target areas to be imaged by a wearer; [Fig.2] [Fig.2] illustrates cycles for imaging a first target area in the prior art; [Fig.3] [Fig.3] illustrates cycles for imaging a second target area in the prior art; [Fig.4] [Fig.4] illustrates cycles for interlacingly imaging a first target area and a second target area in one embodiment of the invention; [Fig.5] [Fig.5] schematically represents a multi-panel antenna system in one embodiment of the invention; [Fig.6] [Fig.6] schematically represents a detection system in one embodiment of the invention; [Fig.7] [Fig.7] schematically represents the steps of a detection method in one embodiment of the invention. Identical references may be used in different figures when they designate the same or comparable elements. Description of the embodiments
[0024] [Fig.6] represents a detection system 1 in one embodiment of the invention.
[0025] The detection system 1 comprises in particular a control block 10, a radar transmission and reception block 11 and an antenna system 12 as shown in [Fig.6]. This detection system 1 is electronically scanned, i.e. the antenna system 12 comprises one or more phased array antennas. An array antenna comprises unit radiating elements distributed over a panel.
[0026] In the example considered, the detection system 1 is of the RSO or RSOI RADAR type.
[0027] The detection system 1 is adapted to, in at least one acquisition direction considered, pointing at a target, which will be called hereinafter target zone, emit radar pulses, receive then analyze the echoes of these pulses.
[0028] The control block 10 is adapted to transmit commands to the radar transmission and reception block 11. These commands define the phases of the respective electrical signals to be generated by the radar transmission and reception block 11 and then supplied to the respective unit radiating elements. These commands define when to trigger the phase changes of the electrical signals.
[0029] In a known manner, the control block 11 is adapted to adjust the phase value of each electrical signal intended to feed a unitary radiating element (and thus adjust the phase shifts between the signals feeding separate radiating elements) so as to modify the transmission pattern of the array antenna (“electronic depointing”, used to concentrate the antenna gain in the desired observation direction). In reception, similarly, the depointing is carried out by the selective phase adjustment of the electrical signals delivered by each elementary radiating element. In one embodiment, in the reception phase, the same phase law as during the transmission phase is applied: an antenna is thus produced which “looks” in the same direction as during transmission.At the electrical level in the reception phase, this effectively ensures that all the antenna's reception modules produce "in-phase" signals for the observation direction, which can then be summed coherently, thus producing the desired antenna gain.
[0030] The radar transmission and reception block 11 is adapted to, in accordance with the commands received from the control block 10, generate electrical signals intended for the antenna system 12 and to process electrical signals received from the antenna system 12.
[0031] The detection system 1 in [Fig.l] is embedded in a carrier 50, for example a fixed vehicle or a mobile vehicle of the aircraft type (airplane, helicopter, drone, glider, etc.), a satellite, a marine or submarine vessel, a rolling vehicle, etc.
[0032] [Fig.l] schematically represents in top view, a carrier 50, here an airplane, represented by a black arrow and carrying the detection system 1, as well as two distinct zones of interest, ZI and Z2, corresponding to distinct angular domains and which we wish to image, on which it is therefore appropriate to sequentially focus the radiation pattern of the antenna 12.
[0033] A first, respectively second, cone (filled in dotted lines) represents the main lobe of the antenna diagram 12 when electronically depointed on the first zone Z1, respectively the second zone Z2 (by the application of a phase gradient to the antenna defined by a first, respectively second phase law). The intersection of this main lobe with the surface (land or sea here in the case of a radar, seabed in the case of a sonar) gives approximately a conical section, represented here in denser dotted lines.
[0034] In the pointing direction focused on the zone Zi, i = 1, 2, a waveform is emitted by the detection system 1 for the duration L;, then follows a listening period, for the duration Tr - during which any echoes are digitized. We thus obtain the minimum and maximum instrumented distances according to the generic formulas:
[0035]
[0036] £> . . = —c — '-'minmst 2 niaxrn.vr 2
[0037] with c the propagation speed of the emitted waves.
[0038] These generic formulas can potentially be adapted according to the nature of the treatments subsequently applied, but these treatments are not the subject of the invention.
[0039] The distances and F>maxin <st depuis le porteur 50 sont représentées en [Fig. 1] par des arcs de cercles noirs pour chacun des 2 pointages (le procédé est également utilisable pour plus de 2 pointages), référencés par 60_l et 70_l pour le pointage vers la zone Zl et par 60_2 et 70_2 pour le pointage vers la zone ZL
[0040] Generally speaking (material limit), we have:
[0041] pp. < pp. 1 1 mm “ Tr ~ 1 1 max
[0042] where FF is the acronym for Form Factor. In particular, for certain acquisition geometries, the footprint of the main antenna lobe (symbolized by the dense dotted lines in [Fig.l]) does not allow the entire illustrated domain to be covered, which is the case for the example in [Fig.l]. Generally, this limited footprint or the computational load of the imaging processing leads to using only a portion (called 'useful domain') of the distance domain instrumented by the waveform to construct the image by Aperture Synthesis. The limits of this useful portion are shown in [Fig.l] by the lines 80_l concerning the pointing direction towards the zone Zl and by the lines 80_2 concerning the pointing direction towards the zone Z2. The zone ZI is positioned between the two lines 80_l and zone Z2 is positioned between the two lines 80_2. Each of these useful distance domains corresponds to a useful listening period.
[0043] In the radar imaging systems of the prior art, the execution of the imaging processing by Aperture Synthesis on the 2 (or more) zones Z1, Z2 of Figure 1 is carried out sequentially. These state-of-the-art systems are therefore subject to the constraint (1): the total acquisition time TeJot is the sum of the unit acquisition times T( / e {1,2} in the example of Figure 1, z G {1, ..., jV] in general).
[0044] Figure 2 shows 2 transmission / reception cycles of duration Tr of a radar system of the prior art, used to image the zone Zl alone during the cycles. During each cycle, the radar therefore enters once into the transmission phase (transmitted wave Eml'), and once into the listening phase. The portion of the useful listening time (Ecl') corresponding to the useful distance domain (section between the lines 80_l of [Fig.l]) is delimited by vertical dashes.
[0045] Similarly, Figure 3 shows 2 transmission / reception cycles of a prior art system, used to image the zone Z2 alone during the cycles. During each cycle of duration Tr, the radar system therefore enters once into the transmission phase (transmitted wave Em2'), and once into the listening phase. The portion of the useful listening time (Ec2'), corresponding to the useful distance domain (section between the lines 80_2 of [Fig.l]) is delimited by vertical dashes.
[0046] The method according to the invention aims to reduce this time required to image distinct zones by temporally interleaving the formation of the images of the different zones. A system according to the invention is therefore subject to the constraint: the total acquisition time is the maximum of the different unit acquisition times T ei. This significant reduction in the total processing time is obtained by joint exploitation of the dead times (listening phases outside useful listening) during the imaging process and the agility of the electronic scanning.
[0047] A detection method according to the invention comprises the following steps in a consecutive processing cycle, of duration Tr; - the control block 10 controls the application of a first determined phase law (that so that the zone Zl is in the sector delimited by the lines 80_l) to the electrical feed signals of the unit radiating elements of the network antenna 12 to direct the antenna radiation towards Zl; - the first controlled phase law being applied to said radiating elements in response to said command: at least a first wave emission is carried out, echoes from said first wave emission are received; then - an initial analysis of said echoes received during the useful listening time is performed ; - an image of the first target area is determined based on at least said first analysis.
[0048] According to the method, during the same cycle, an acquisition on the zone Z2 (transmission, useful listening) is carried out, during the time of the cycle not occupied either by the transmission on the zone Z1, nor by the useful listening of the echoes of this transmission.
[0049] Thus: - the control block 10 controls the application of at least one second determined phase law, distinct from the first phase law (that so that the zone Z2 is in the sector delimited by the lines 80_2) to the electrical feed signals of said unitary radiating elements of the network antenna to direct the antenna radiation towards the zone Z2; - the second controlled phase law being applied to said radiating elements in response to said command: at least one second wave emission is carried out, echoes from said second wave emission are received; then - a second analysis of said echoes received is carried out; - an image of the second target area is determined based on at least said second analysis.
[0050] The second wave emission is positioned temporally in the cycle considered so that this second wave emission as well as the useful listening time of the echoes of this second wave emission are outside on the one hand the time of the first wave emission and on the other hand the useful listening time of the echoes of the first wave emission.
[0051] During the next cycle, these steps are repeated. In one embodiment, in the next cycle, the same zones Z1, Z2 (and the corresponding phase laws) as in the previous cycle are considered. In another embodiment, zone Z1 and / or zone Z2 is modified.
[0052] In a particular embodiment, the detection system 1 is adapted to implement the steps of the detection method 100 described below with reference to [Fig.7].
[0053] In the cycle considered, in a step 101, the control block 10 commands that - an emission (Eml) of a first waveform is carried out at Tl, for a duration pointing to the zone Zl (associated with the first phase law); - an emission (Em2) of a second waveform is carried out at T2, for a duration L2, pointing at the zone Z2 (associated with the second phase law); - reception of the echoes of the second waveform is carried out at T3, during a useful listening duration Ec2 (associated with the second phase law); - reception of the echoes of the first waveform is carried out at T4, during a useful listening duration Ecl (associated with the first phase law).
[0054] Following step 101, in step 102, the radar transmission and reception block 11 generates the electrical signals in accordance with this ordering and transmits them in due time to the network antenna 12, which will thus switch successively, in terms of pointing, at T1 to Z1, at T2 to Z2, at T4 to Z1, at T1+T2 to Z2 etc. The radar transmissions and receptions are then carried out in accordance with the ordered ordering.
[0055] Then the cycle of steps 101 and 102 is repeated.
[0056] At the end of each cycle of steps 101-102, in a step 103, the electrical signals supplied by the antenna 12 in reception of the echoes during the useful listening Ec2 starting at T3 (and not of the echoes received during the useful listening Ecl starting at T4) are then processed (digitization, filtering, migration compensation, Fourier transform, focusing, conforming) and an image of the zone Z2 is determined by the radar block 11 as a function of these processed signals. Similarly, the electrical signals supplied by the antenna 12 as a function of the echoes received during the useful listening Ecl starting at T4 (and not of the echoes received during the useful listening Ec2 starting at T3) are processed and an image of the zone Zl is determined by the radar block 11 as a function of these processed signals.
[0057] A radar system (same as a sonar system) can only emit a certain quantity of energy in a cycle time Tr. It may therefore happen that the construction of the interleaving involves reducing the pulse lengths of the different interleaved waveforms so as not to exceed this limit (this is the case in 4, the value of each L; is divided by 2 relative to the graphs in figures 2 and 3).
[0058] Furthermore, the movement, if applicable, of the carrier 50 (in particular, its approach to or distance from the imaged area) must be taken into account when developing the interlacing. Over time, it is indeed necessary to temporally shift the useful listening domains, and it is therefore necessary to ensure in advance that the interlaced listening domains cannot overlap temporally (i.e., sufficient spacing must be left between these domains).
[0059] In one embodiment, at least one or more of the following provisions will be taken into account: - if the cycle time value Tr for the different acquisitions to be interlaced is not the same, the different Tr have a harmonic relationship between them (let Zi, i = 1 to N the zones whose radar imagery is interlaced, the value of Tr for any zone Zi is equal to a factor n or 1 / n near, to the value of Tr for any zone Zj,, n being an integer); - interleaving does not cause collision between listening domains of useful ones; - the sum of the n does not exceed the maximum form factor (i.e. generally , with 2 the carrier wavelength, the distance from k - that radar 1 does not emit more energy than it can in a given time); - the Lj resulting from interlacing (i.e. potentially reduced) lead to a sufficient signal-to-noise ratio (i.e. greater than a predefined threshold) for each final image.
[0060] As an example, the phase laws used in the example above are of the type kSm(e) ) ith radiating element of the antenna at the center of the antenna, and G the desired electronic misalignment angle.
[0061] The interleaving case described above and illustrated in [Fig.4] is only an example: the ordering between the transmission to zone Z1, the transmission to zone Z2, the useful listening relative to Z1 and the useful listening relative to Z2 can be different, depending in particular on the location of the zones. For example: transmission to zone Z1 then transmission to zone Z2, then useful listening relative to Z1, then useful listening relative to Z2.
[0062] In embodiments, one and / or the other of the following arrangements is implemented during at least one cycle: - the elevation angle during the application of the second phase law is different from the elevation angle during the application of the first phase law; - the azimuth angle of the array antenna 12 during the application of the second phase law is different from the azimuth angle of the array antenna during the application of the first phase law; and / or - the resolution of the image of the first target area is distinct from the resolution of the image of the second target area; and / or - the image size of the first target area is distinct from the image size of the second target area.
[0063] We recall that: - the elevation angle is the angle between the plane tangent to the surface of the earth and the direction of observation of the antenna 12; - the azimuth angle is the angle between the sighting direction and North.
[0064] The invention, in a period Tr which was necessary, in the prior art to produce a single image, makes it possible to produce several images of sectors which are not necessarily contiguous, in particular non-contiguous in azimuth and / or non-contiguous in elevation (each sector corresponding for example to the intersection of the main radiation lobe with the surface of interest: surface of the ground or of the sea or of the seabed).
[0065] In one embodiment, during each cycle, the waveform Eml is transmitted on a carrier frequency Fl distinct from the carrier frequency F2 on which the waveform Em2 is transmitted. Reception during useful listening Ecl is centered on Fl and it is centered on F2 during useful listening Ec2. This frequency separation prevents the different imaging processes from polluting each other; and / or
[0066] a suitable waveform is selectively defined for each target area in terms of one and / or the other of these other parameters: - during each transmission phase towards a target area, the pulse duration and the repetition period depending on the distance of the target from the antenna, the distance between the antenna and some of the different target areas being for example at different distances from the antenna; - polarization of the emitted wave defined as a function of the observation geometry (for example, for large elevation angles, and under normal conditions, the calculation shows that it is more advantageous to vertically polarize the emitted waveform; conversely, horizontal polarization becomes preferable for small elevation angles) and the type of target, so as to maximize the contrast (target to clutter ratio (sea or ground clutter depending on the applications)) of the image.
[0067] By reducing the Signal to Noise Ratio of each image, the solution presented above, by exploiting the scanning agility offered by electronic scanning RADAR systems in order to angularly interleave the construction of multiple SAR images, thus makes it possible, in the same acquisition time as was required to produce a single image, to produce several angularly spaced images, and without reducing the distance / frequency resolutions of the images obtained.
[0068] The interlacing has been described above with reference to two zones. The invention is of course applicable to a number N of zones greater than or equal to 3, then interlacing in the same cycle the construction of N images.
[0069] In an embodiment illustrated in [Fig.5], the antenna system 12 of the detection system on board the carrier represented by the arrow 50, comprises three distinct network antennas (i.e. 3 panels) 12_1, 12_2 and 12_3 shown diagrammatically by bars on either side of the carrier, which allows the detection system to cover a bearing domain of 330° (see gray area), with a blind sector at the tail of the device.
[0070] The invention has been described above with reference to a RADAR. It is of course applicable to any detection system equipped with a phased array antenna and adapted to emit waves and analyze the reflections of these waves on obstacles, such as SONAR-based devices (SSO for "Synthetic Aperture Sonar" or "SAS" in English terminology; SSOI for "Inverse Synthetic Aperture Sonar" or "ISAS" in English terminology), LIDAR...
[0071] For example, the invention is implemented in one embodiment in a submarine carrying a sonar to produce SSO (synthetic aperture sonar) images and image the seabed for observation and navigation purposes by recognizing the observed seabed.
[0072] In one embodiment, the invention is used in ISAR mode so as to simultaneously image several maritime targets disjointed in bearing and elevation, by exploiting the Doppler effect generated by their own movements and indicated by the echoes received: pitch / roll due to the swell.
Claims
1. Claims A method of detection in a detection system (1) comprising a phased array antenna (12) comprising unit radiating elements, said system being adapted to, via said array antenna (12), transmit waves and receive echoes of said transmitted waves and to analyze the received echoes; said detection method comprising the following steps implemented by the detection system (1) at each of several consecutive processing cycles: - controlling the application of a first determined phase law to electrical feed signals of the unit radiating elements of the network antenna to direct the antenna radiation towards a first target zone (Zl); - the first controlled phase law being applied to said radiating elements in response to said command: at least a first wave emission is carried out, echoes from said first wave emission are received; then - an initial analysis of said echoes received is carried out; - an image of the first target area (Zl) is determined in function of at least said first analysis; said method being characterized in that it further comprises the following steps implemented by the detection system (1) during each of said cycles: - controlling the application of at least one second determined phase law to electrical feed signals of said unitary radiating elements of the array antenna to direct the antenna radiation towards a second target zone (Z2); the second phase law being different from the first law controlled during said same cycle, the second target zone (Z2) being disjoint from the first target zone (Zl) and the distance between the first target zone (Zl) and the array antenna (12) being distinct from the distance between the second target zone (Z2) and the array antenna (12); - the second controlled phase law being applied to said radiating elements in response to said command: at least a second wave emission is carried out, echoes from of said second wave emission are received; then - a second analysis of said received echoes is carried out; - an image of the second target area (Z2) is determined based on at least said second analysis.
2. Detection method according to claim 1, according to which for at least one of said cycles: - the elevation angle of the array antenna (12) during the application of the second phase law is different from the elevation angle of the array antenna during the application of the first phase law; and / or - the azimuth angle of the array antenna (12) during the application of the second phase law is different from the azimuth angle of the array antenna (12) during the application of the first phase law; and / or - the resolution of the image of the first target area (Z1) is distinct from the resolution of the image of the second target area (Z2); and / or - the size of the image of the first target area (Zl) is distinct from the size of the image of the second target area (Z2).
3. A detection method according to claim 1 or 2, wherein a first waveform is selectively used for the first wave emission towards the first target area (Z1) and a second waveform distinct from the first is selectively used for the second wave emission towards the second target area (Z2) according to one or more of the following arrangements: - the first waveform is transmitted on a first carrier frequency Fl and the second waveform is transmitted on a second carrier frequency distinct from the first carrier frequency; - when the first target zone (Z1) and the second target zone (Z2) are located at different distances from the antenna (12), during the first, respectively second, transmission, the pulse duration and the repetition period during the first, respectively second transmission, are distinct and are a function of the distance of the first, respectively second target, from the antenna; - the polarization of the first waveform is distinct from the polarization of the second waveform, each defined as a function of the observation geometry and the type of target area, so as to maximize the target-to-clutter ratio of the image.
4. A detection method according to any preceding claim, wherein the first target area (Z1) remains the same over several consecutive cycles and the second target area (Z2) remains the same over several consecutive cycles.
5. Detection method according to one of the preceding claims, according to which during each of said cycles: - the first wave emission towards the first target zone (Z1) is carried out, the first controlled phase law being applied to said radiating elements; then - the second wave emission towards the second target zone (Z2) is carried out, the second controlled phase law being applied to said radiating elements; then - the echoes from the first, respectively second wave emission, are received, the first, respectively second controlled phase law then being applied to said radiating elements.
6. A detection system (1) comprising a phased array antenna (12) comprising unit radiating elements, said system being adapted to, via said array antenna (12), transmit waves and receive echoes of said transmitted waves and to analyze the received echoes; the detection system (1) being adapted to, at each of several consecutive processing cycles, control the application of a first determined phase law to electrical feed signals of the unit radiating elements of the array antenna to direct the antenna radiation towards a first target zone (Zl); and the first controlled phase law being applied to said radiating elements in response to said control: to perform at least a first wave transmission and receive echoes from said first wave transmission are received; then to perform a first analysis of said received echoes and to determine an image of the first target area (Zl) based on at least said first analysis; said detection system (1) being characterized in that it is further adapted, during each of said cycles, to control the application of at least one second determined phase law to electrical feed signals of said unit radiating elements of the array antenna to direct the antenna radiation towards a second target zone (Z2), the second phase law being different from the first law controlled during said same cycle and the second target zone (Z2) being disjoint from the first target zone (Zl) and the distance between the first target zone (Zl) and the array antenna (12) being distinct from the distance between the second target zone (Z2) and the array antenna (12);then, the second controlled phase law being applied to said radiating elements in response to said command, to carry out at least a second wave emission and receive echoes from said second wave emission, then to carry out a second analysis of said received echoes and determine an image of the second target zone (Z2) as a function of at least said second analysis.;
7. Detection system (1) according to claim 6, wherein for at least one of said cycles: - the elevation angle of the array antenna (12) during the application of the second phase law is different from the elevation angle of the array antenna during the application of the first phase law; and / or - the azimuth angle of the array antenna (12) during the application of the second phase law is different from the azimuth angle of the array antenna (12) during the application of the first phase law; and / or - the resolution of the image of the first target area (Z1) is distinct from the resolution of the image of the second target area (Z2); and / or - the size of the image of the first target area (Zl) is distinct from the size of the image of the second target area (Z2).
8. A detection system (1) according to claim 6 or 7, adapted to selectively use a first waveform for the first wave emission towards the first target area (Zl) and to selectively use tively a second waveform distinct from the first for second wave emission towards the second target zone (Z2) according to one or more of the following arrangements: - the first waveform is emitted on a first carrier frequency Fl and the second waveform is emitted on a second carrier frequency distinct from the first carrier frequency; - when the first target zone (Zl) and the second target zone (Z2) are located at different distances from the antenna (12), during the first, respectively second, emission, the pulse duration and the repetition period during the first, respectively second emission, are distinct and are a function of the distance of the first, respectively second target, relative to the antenna;- the polarization of the first waveform is distinct from the polarization of the second waveform, each defined according to the observation geometry and the type of target area, so as to maximize the target-to-clutter ratio of the image.;
9. A detection system (1) according to any one of claims 6 to 8, wherein the first target area (Z1) remains the same over several consecutive cycles and the second target area (Z2) remains the same over several consecutive cycles.
10. Detection system (1) according to any one of claims 6 to 9, adapted for, during each of said cycles: carrying out the first wave emission towards the first target zone (Z1), the first controlled phase law being applied to said radiating elements; then - carrying out the second wave emission towards the second target zone (Z2), the second controlled phase law being applied to said radiating elements; then - receiving the echoes from the first, respectively second wave emission, the first, respectively second controlled phase law then being applied to said radiating elements.