Multiple-input multiple-output imaging radar system

Abstract

This invention relates to a MIMO imaging radar system, comprising: - a transmit channel (Ve1, VeM); - a receive channel (Vr1, VrN); - a co-located radiating element (ER) forming a two-dimensional antenna array. e1 ER eM ER r1 ER rN ), each radiating element (ER) e1 ER eM ER r1 ER rN The radar has a predetermined instantaneous coverage area; each radiating element is formed by p more radiating sub-elements (SeElt1, SsEltp) distributed in at least one of the two dimensions of the antenna array, and the radar includes multiple electronic steering modules (MD). e1 , ..., MD rN Each electronic steering module is connected to a radiating element, and each steering module is configured to apply steering commands (Cmd) between all radiating sub-elements (SeElt1, SsEltp) of a given radiating element. The steering commands (Cmd) are the same from one radiating element to the next, so as to move the coverage area of ​​each radiating element in the same direction.

Description

Technical Field

[0001] This invention relates to MIMO imaging radar systems, to aircraft including such systems, and to methods for controlling MIMO imaging radar systems, where MIMO is an acronym for Multiple Input Multiple Output. Background Technology

[0002] Millimeter-wave imaging radar (frequency between 30 GHz and 300 GHz) now allows the generation of images of the aircraft’s external environment under any external visibility conditions (such as severe weather conditions like snow, rain, fog, or even at night) with an angular resolution better than 1 degree.

[0003] Specifically, during the landing phase, it is crucial for the pilot to obtain as much real-time information as possible on the runway (sizes, boundaries, and the presence of obstacles).

[0004] A system that allows runway images to be displayed while still visible on a screen is called an Enhanced Flight Vision System (EFVS).

[0005] This information is displayed on the aircraft's screens or directly to the pilot through their helmet.

[0006] These systems require an angular resolution much better than 1 degree, and their range must be greater than 1 kilometer. In addition, to compensate for sudden changes in aircraft attitude, especially yaw (deviation of the aircraft's longitudinal axis) in the presence of strong crosswinds, it is necessary to cover a large angular range of tens of degrees.

[0007] Two main types of antennas are used in EFVS: mechanically scanned antennas and electronically scanned antennas.

[0008] In mechanically scanned antennas, a radar beam (sometimes called a "pencil beam") is generated relative to the antenna and then mechanically oriented to scan the desired domain. (See the literature "REVS") TM The paper "A Radar-Based Enhanced Vision System for Degraded Visual Environments" (Alex Brailovsky et al., SPIE, 2014) proposes an EFVS that includes a mechanically scanned antenna operating in the millimeter-wave band (94 GHz).

[0009] The system proposed in this literature meets the requirements of EFVS: the maximum range is 3 kilometers, and the angular resolution is 0.5 degrees for azimuth and 1 degree for elevation (see Table 1 of the cited literature).

[0010] However, the system is based on moving mechanical components, which frequently cause reliability issues. Furthermore, the radar's repetition cycle (scanning cycle) imposes constraints on the refresh rate of the radar image.

[0011] More generally, the current general trend among aircraft manufacturers is to avoid mechanically moving components.

[0012] Electronically scanned antennas allow for the resolution of issues related to reliability and refresh rate.

[0013] Phased array antennas are the first type of electronically scanned antennas. They are constructed with radiating elements fed by radio frequency signals (with relative phase shifts controlled). The wavefront is located based on the phase gradient within the antenna array.

[0014] These antennas can generate rapid scans, but they require a considerable number of controlled phase radiating elements to achieve good resolution and wide angular coverage. Furthermore, these phase shifts must be precisely controlled to achieve all desired pointing directions.

[0015] This requires a high-resolution phase shifter, as well as a calibration table that allows for compensation of technique dispersion and temperature behavior (and appropriate frequency behavior). Furthermore, these phase shift commands must be very fast to quickly cover the scan space.

[0016] These solutions are very expensive and not suitable for mid-cost systems such as EFVS, which are designed to be installed in any type of commercial jet or passenger aircraft.

[0017] The most common alternative for achieving electronic scanning with good angular resolution and large coverage at a lower cost is known as MIMO arrays (MIMO is an acronym for Multiple Input Multiple Output).

[0018] Figure 1 An example of a two-dimensional MIMO antenna array is shown schematically (by convention, the azimuth corresponds to the horizontal dimension and the elevation corresponds to the vertical dimension).

[0019] exist Figure 1 The diagram shows a total of j x k radiating elements (or antennas). In continuous wave mode, each of the j x k radiating elements is associated with either a transmit channel or a receive channel. In pulse mode, each of the j x k radiating elements is associated with both a transmit channel and a receive channel. Of the j x k radiating elements, M are associated with a transmit channel and N are associated with a receive channel.

[0020] Each element has a dimension DA along the azimuth axis and a dimension DE along the elevation axis. The complete antenna array has a dimension LA along the azimuth axis and a dimension LE along the elevation axis.

[0021] Then, the virtual MIMO array consisting of M x N elements is reconstructed in the digital domain.

[0022] To explain the concepts of coverage area and angular resolution, please refer to [reference needed]. Figure 2 , Figure 2 The antenna gain of the beam formed by the antenna array is shown as a function of the azimuth sine (the same principle applies to the elevation axis).

[0023] The beam of the antenna array (solid line) has a width corresponding to the angular resolution (λ / LA or λ / LE, depending on the axis under discussion, where λ corresponds to the wavelength used). The beam can be moved within the coverage area shown by the dashed line.

[0024] The coverage area is limited relative to λ / DA or λ / DE, depending on whether the azimuth or pitch axis is considered.

[0025] By carefully selecting the geometry of the transmitting and receiving arrays, the angular resolution of an imaging radar system can be improved without adding additional radiating elements to the array. For information on virtual networks, those skilled in the art can refer, for example, to the document https: / / www.mathworks.com / help / phased / ug / increasing-angular-resolution-with-mimo-radars.html.

[0026] Therefore, it is possible to obtain low-cost radar based on easily integrated on-chip components.

[0027] However, the main limitation of this type of system is caused by the fact that antenna arrays are often highly sparse: the intentional creation of “gap” in the antenna layout (the spacing between transmitting radiating elements is different from the spacing between receiving radiating elements, and the spacing between individual radiating elements may be irregular and greater than the wavelength) produces uncertainty in the radiation pattern, but these uncertainties will be removed in the digital part.

[0028] Using sparse antennas simplifies the computation in the digital synthesis of channels in a virtual array by limiting the number of channels that will be processed.

[0029] However, due to the limited number of emitting elements, the sparse nature of MIMO arrays implies a lower overall gain. Therefore, typically, acquiring a range of approximately 100 meters for an object with a radar cross-section (RCS) of a few square meters is insufficient for EFVS applications.

[0030] Using a full MIMO antenna to increase power would result in a large number of channels being modulated during transmission and digitized during reception. Digital synthesis of the virtual array's channels would then become extremely computationally expensive, making it impractical for airborne applications.

[0031] Therefore, the present invention aims to provide an imaging radar with moderate complexity and cost, comprising non-moving components, having good angular resolution and long range, and being able to handle large angular coverage. Summary of the Invention

[0032] Therefore, one subject of the present invention is a multiple-input multiple-output imaging radar system, comprising:

[0033] - Multiple transmission channels;

[0034] - Multiple receive channels;

[0035] - Multiple co-located radiating elements forming a two-dimensional antenna array, each radiating element being able to be fed through one of the transmit channels and / or being able to feed one of the receive channels, each radiating element having a predetermined instantaneous coverage area;

[0036] Each radiating element is formed by p more radiating sub-elements distributed in at least one of the two dimensions of the antenna array.

[0037] The radar includes multiple electronic steering modules, each of which is connected to a radiating element. Each steering module is configured to apply steering commands between all radiating sub-elements of a given radiating element. The steering commands are the same from one radiating element to the next, so as to move the coverage area of ​​each radiating element in the same direction.

[0038] Advantageously, each electronic steering module includes:

[0039] - A distributor or combiner, connected to the transmit channel or the receive channel respectively, and

[0040] - Multiple phase shifters, each connected to one of the radiating sub-elements of the radiating element.

[0041] Advantageously, each electronic steering module includes multiple amplification devices, each of which is connected to a radiating sub-element.

[0042] Advantageously, the steering command includes a phase gradient applied between the individual radiating sub-elements.

[0043] Advantageously, the phase gradient corresponds to a constant angular difference selected from the following values: 0; ±π / 4, ±π / 2, ±3π / 4; ±π.

[0044] Advantageously, the radiating element is located on the antenna panel, and the radiating element occupies at least 50% of the area of ​​the antenna panel.

[0045] Advantageously, the radiating sub-elements are placed in the azimuth and elevation dimensions of the 2D array.

[0046] Favorably, p = 2 or 4.

[0047] Advantageously, the system includes a calibration table configured to compensate for steering errors between transmit channels and / or receive channels generated by the electronic steering module for each steering command.

[0048] Advantageously, the system is configured to operate in the millimeter-wave band.

[0049] Another subject of the invention is an aircraft including a system as described above, wherein the system includes a computer configured to change steering commands based on the difference between the aircraft’s heading and route.

[0050] Advantageously, the steering command is recalculated at a frequency between 10Hz and 15Hz.

[0051] Another subject of the present invention is a method for controlling a multiple-input multiple-output imaging radar system, the method comprising the following steps:

[0052] - Transmit radio signals on multiple transmission channels;

[0053] - Receive radar signals on multiple receiving channels after reflection or backscattering from the target;

[0054] By forming a co-located set of radiating elements in a two-dimensional antenna array, the transmit and receive channels are fed and / or are fed separately to obtain a predetermined instantaneous coverage area for each radiating element.

[0055] Each radiating element is formed by p more radiating sub-elements distributed in at least one of the two dimensions of the antenna array, and the method further includes the following steps:

[0056] - Apply a steering command between all radiating sub-elements of a given radiating element, the steering command being the same from one radiating element to the next, so as to move the instantaneous coverage area of ​​each radiating element in the same direction.

[0057] Advantageously, the method includes a calibration step, in which the following sub-steps are performed:

[0058] - For a given steering command, measure the phase error and / or amplitude error between the coverage areas of the radiating elements relative to the center of the theoretical shifted scan domain of each radiating element;

[0059] - Determine the calibration coefficients based on the measured phase error and / or amplitude error;

[0060] - The calibration coefficients are stored in a table called the calibration table, which is specific to the steering command.

[0061] Advantageously, calibration steps are performed for all possible steering commands and for multiple operating temperature ranges. Attached Figure Description

[0062] Other features, details, and advantages of the invention will become apparent upon reading the description given with reference to the accompanying drawings, which are provided by way of example and illustrate the invention in detail below:

[0063] Figure 1 (Already described) shows a 2D antenna array used in a MIMO radar according to the prior art;

[0064] Figure 2 (Already described) shows the coverage area of ​​the radiating elements of a radar system according to the prior art and the fine beam formed by the complete antenna;

[0065] Figure 3 The architecture of a radar system in continuous wave mode according to the present invention is shown;

[0066] Figure 4 The coverage area of ​​the radiating element of the radar system according to the invention and the fine beam formed by the complete antenna are shown.

[0067] Figure 5 A detailed view of the steering module according to the present invention is shown;

[0068] Figure 6 The coverage area of ​​the radiating element according to the steering command is shown;

[0069] Figure 7A The field of view and energy field of view are shown in the absence of crosswinds;

[0070] Figure 7B The field of view and energy field of view of the system implemented according to the present invention are shown in the presence of crosswinds;

[0071] Figure 8 This illustrates the architecture of a radar system in pulse mode according to the present invention;

[0072] Figure 9 The coverage area of ​​multiple radiating elements is shown after the calibration step. Detailed Implementation

[0073] Figure 3The architecture of a radar system in continuous wave mode according to the present invention is shown. It should be recalled that in continuous wave mode, each radiating element is specifically associated with either a transmit channel or a receive channel.

[0074] The radar system according to the present invention includes a MIMO-level EtMIMO, which includes multiple transmit channels (Ve1, ..., VeM) and multiple receive channels (Vr1, ..., VrN).

[0075] The radar system according to the present invention includes a plurality of radiating elements (ERe1, EReM, ERr1, ERrN), each radiating element (ERe1, EReM, ERr1, ERrN) being associated with a transmit channel (Ve1, ..., VeM) or a receive channel (Vr1, ..., VrN).

[0076] Each transmit channel has the characteristic of being able to apply a unique signature to the transmitted radar signal. There are many ways to obtain such a signature, such as Barker codes, DDMA coding (DDMA stands for Doppler Frequency Division Multiple Access), OFMD coding (OFMD stands for Orthogonal Frequency Division Multiplexing, which allows the use of orthogonal frequencies in the form of multiple different subcarriers), amplitude coding, or even polarization coding.

[0077] In the context of this invention, phase coding is particularly likely to be used, which allows orthogonality to be achieved between transmit channels in a burst pulse. This coding is performed via box DephMIMO.

[0078] The phase coding of the transmit channel is controlled by the COD (Cycles of Diagram) component, which controls the phase coding of the transmit channel. The COD component can be placed in the radar system's computer, CALC.

[0079] Because each receive channel contains a frame NUM, the receive channel (Vr1, ..., VrN) itself has the characteristic of digitizing the signal received through its associated radiating element. Digital phase shifting is then applied. Next, a frame FFC dedicated to calculating beamforming allows for the formation of the receive pattern after digital processing of the received signal.

[0080] In this way, the acquired array is a MIMO array, which allows for the reconstruction of radar images by benefiting from the angular resolution associated with the antenna array size (λ / LA or λ / LE along the azimuth or elevation axis) and the instantaneous coverage area (λ / DA or λ / DE along the azimuth or elevation axis) given by the radiation pattern of a single radiating element.

[0081] Each radiating element is further divided into p smaller sub-elements. Electronic steering modules (MDe1, MDeM, MTr1, MTrN) are inserted between each channel and radiating element.

[0082] This module allows a signal to be divided into p paths, each of which undergoes a controlled phase shift and optionally a power amplification. Each of these signals then feeds a sub-element (SeElt1, SsEltp).

[0083] As in Figure 4 As can be seen, by further dividing the radiating element into movable phase sub-elements, the instantaneous domain of MIMO coverage can be adjusted according to the region to be observed without increasing the number of MIMO channels and the associated computational complexity.

[0084] The size of the accessible global domain is given by the reciprocal of the size of a radiating sub-element.

[0085] Figure 5 The connection between the electronic steering module and the corresponding radiating element is shown in detail. To simplify the representation, the radiating element is subdivided in only one dimension.

[0086] By further dividing the radiating element into p sub-elements, the total domain that can be accessed is p times the instantaneous domain covered by MIMO.

[0087] exist Figure 5 In the example, the radiating element is further divided into four sub-elements (SsElt1, SsElt2, SsElt3, SsElt4) in the azimuth dimension. Therefore, the accessible global domain is four times the instantaneous domain covered by MIMO.

[0088] In order to make all the radiating elements of the antenna array move their coverage areas simultaneously in the same direction, each steering module (MD) e1 MD eM MD r1 MD rN It is necessary to apply a steering command Cmd between all radiating sub-elements of a given radiating element, and the steering command Cmd is the same from one radiating element to the next. The steering command Cmd can be transmitted by engaging the steering control block (BLC) to the data bus of the individual phase shifters.

[0089] Through the radar system's computer CALC (see also...) Figure 3 This generates the steering command Cmd. The steering command Cmd addresses each steering module (e.g., ...). Figure 5 MDe1 in (the middle).

[0090] The steering module MDe1 includes as many phase shifters (φ1, φ2, φ3, φ4) as the existing sub-elements (SsElt1, SsElt2, SsElt3, SsElt4).

[0091] Each steering module coupled to the transmit channel includes a distributor, and each steering module coupled to the receive channel includes a combiner, in order to distribute / combine signals to p paths. These components can be readily integrated into the MMIC chip (MMIC stands for Monolithic Microwave Integrated Circuit) targeted in the context of this invention.

[0092] Unlike AESA-type active phased array antennas, which require very fine adjustments to the phase shifters one by one with a resolution of approximately 6 to 8 bits per phase shifter, the phase shifters (φ1, φ2, φ3, φ4) do not need to have high resolution. In the example, a resolution of, for example, three bits may be sufficient, where the step size is + / -π / 4 or more (depending on the command, it is + / -π / 2 or + / -π).

[0093] By applying the commands in the table below, a single radiation pattern can be moved in eight different directions contained within the aperture of the radiating sub-element. These commands utilize very simple logic and a minimal number of phase states, making this solution easy to integrate.

[0094] Advantageously, a phase gradient is applied between the constituent radiating sub-elements of each radiating element.

[0095] Phase shifter The phase shift value (where i is between 1 and 4) is represented as Δψi:

[0096] Order Δψ1 Δψ2 Δψ3 Δψ4 1 0 0 0 0 2 0 π / 4 π / 2 3π / 4 3 0 π / 2 π 3π / 2 4 0 3π / 4 -π / 2 π / 4 5 0 π 0 π 6 0 -3π / 4 π / 2 -π / 4 7 0 -π / 2 -π -3π / 2 8 0 -π / 4 -π / 2 -3π / 4

[0097] This table corresponds to a scheme using four phase shifters. Those skilled in the art will be able to apply this scheme to different numbers of phase shifters without difficulty.

[0098] Figure 6 This shows the orientation of the radiation pattern of the radiating element according to the commands of the application. The coverage area of ​​the antenna is shown as a function of the sine of the azimuth angle θ.

[0099] The lobe corresponding to command 5 is not shown. In the phase shifter configuration given by example, this command produces the "right" half-lobe of command 4 and the "left" half-lobe of command 6, thus forming a bridge between the two radiation patterns.

[0100] Therefore, this invention allows the field of view of a millimeter-wave MIMO radar system to be redirected at any given time.

[0101] like Figure 7A and7B As illustrated in the figure, this invention allows for a wider field of view (FoR) of the radar system. Figure 7A and 7B The examples show the cases with and without crosswinds.

[0102] exist Figure 7A In the absence of wind, the aircraft's velocity vector... It is correctly positioned within the radar's field of view (FoV). Through electronic steering, the field of view (FoR) corresponding to the total area that can be obtained by the sensor is widened.

[0103] exist Figure 7B In the middle, crosswinds cause crab approach, that is, the aircraft approaches the runway like a crab (i.e., laterally). Since the FoV is centered on the aircraft's axis, the radar system can no longer cover the runway.

[0104] Conversely, the radar system according to the invention allows the FoV to move relative to the aircraft's fuselage axis (its heading) so that it remains aligned with the aircraft's velocity vector despite crosswinds. (Their routes) are the same.

[0105] To compensate for the aircraft's crabbing, it is conceivable to refresh the turning commands at a frequency between 10Hz and 15Hz.

[0106] This frequency allows for the acquisition of a high-quality video stream based on visual persistence, perceived by the pilot, without degrading the real-time performance of the radar system.

[0107] Advantageously, the steering command can also be varied periodically at a predetermined frequency—thus expanding the FoR of the radar system.

[0108] Using two or four sub-elements of each radiating element (in one of the two dimensions) is particularly advantageous.

[0109] More specifically, as will be reviewed, the coverage area of ​​the radiating element, i.e., the aperture of the lobe, is given by λ / D, where D is the range of the radiating element in the dimension under discussion. In the millimeter-wave band, based on the space typically available on the antenna panel, the aperture of the lobe (i.e., the field of view) for MIMO radar is typically between approximately 10 degrees and approximately 20 degrees.

[0110] By multiplying this value by 2 or 4, a sufficiently large field of view (FoR) can be obtained for EFVS applications.

[0111] It will be noted that it began Figure 6The example shown in the middle figure illustrates how a row of radiating sub-elements associated with a phase shifter can be added to achieve pitch steering. Various steering operations can then be performed along both axes while preserving the same resolution used for the phase shifter.

[0112] The pitch command then causes an additional phase shift between lines, which again produces commands accessible using the resolution of the phase shifter.

[0113] Specifically, in Figure 3 In the diagram, the sub-units that make up each radiating element are shown in a 2D array, in which rows and columns are arranged to align with the azimuth and elevation axes.

[0114] The fact that radiating sub-elements are placed in the azimuth and pitch dimensions of the 2D array allows the coverage area of ​​each radiating element to be moved in the azimuth and pitch directions.

[0115] However, the steering command Cmd is the same as the case where the radiating sub-elements are arranged in only one direction. Therefore, the low-resolution characteristics of the phase shifter are preserved (e.g., three bits for eight phase states).

[0116] Besides the fact that the field of view must be large enough (where p=2 or p=4), limiting each radiating element to four sub-elements in the azimuth direction and four sub-elements in the pitch direction also introduces implementation constraints. More specifically, in chips used in the millimeter-wave band, designs for distributors or combiners with up to 16 paths (sub-elements in a 4x4 array) can be envisioned based on the chip's etchable feature thickness and size. Furthermore, signal routing also presents challenges.

[0117] Advantageously, amplification devices (PA1, PA2, PA3, PA4) can be provided in each electronic steering module MDe1. Each amplification device (PA1, PA2, PA3, PA4) is associated with a radiating sub-element (SSeElt1, SsElt2, SSeElt3, SsElt4).

[0118] The electronic steering module associated with the transmit channel includes an amplification device consisting of power amplifiers (PA1, PAp), while the electronic steering module associated with the receive channel includes an amplification device consisting of low-noise amplifiers (LNA1, LNAp).

[0119] If the number of amplification devices used in a radar system is multiplied by p, the amplification devices can be directly integrated into the chip of the steering module in a distributed manner without experiencing heat dissipation problems (which would occur if a single centralized amplification device for each radiating element were integrated into the chip).

[0120] Chips commonly used in millimeter-wave amplification devices typically consist of active components and substrates made of silicon-germanium. Due to physical limitations related to current density, these substrates cannot withstand the heat dissipated by such large integrated amplifiers, whose size limits radar range to approximately one kilometer or more. Gallium arsenide-based or even gallium nitride-based technologies could handle the required power, but they are expensive, and incorporating digitally controlled phase shifters into such technologies is even more difficult.

[0121] This is one of the reasons why existing MIMO radar systems have a range of approximately 100 meters.

[0122] By multiplying the amplification devices, the power of the amplification devices is combined into the electromagnetic field, not into the chip. Therefore, a greater range can be obtained.

[0123] Furthermore, on-chip integration of the amplification device allows for the avoidance of the drawbacks associated with the size and high power consumption of non-integrated technologies such as resonant cavities.

[0124] It will be noted that the effect at the receiver is similar, and the combination of multiple low-noise amplifiers (LNAs) in the close proximity of small-sized radiating sub-elements allows for minimization of upstream losses and thus reduces the noise figure, which has the effect of improving radar sensitivity.

[0125] The presence of a magnification device is not necessary for obtaining the effect of turning the coverage area in a given direction. This is, for example, in the case of detection at close range.

[0126] In the context of this invention, the array of radiating elements does not need to be full-pitch or regularly pitched, but it will have full-pitch characteristics as much as possible. For example, the radiating elements occupying the antenna panel may represent at least 50% of the antenna panel area. This constraint arises, particularly in the air transport sector, from the need to achieve a long radar range with a low volume.

[0127] This invention can also be implemented in pulse wave MIMO radar systems, such as... Figure 8 As illustrated, the radiating sub-element is connected to both the transmit channel and the receive channel.

[0128] exist Figure 8 The radiating elements ER1 to ERi have been shown. Each radiating element (ER1, ERi) can be fed by one of the transmit channels (Ve1, Vei) and can also be fed by one of the receive channels (Vr1, Vri).

[0129] For example, this connection between the sub-element and the transmission channel can be achieved by a circulator or by a device used to protect the receiving channel when the transmission channel is active.

[0130] The present invention also relates to a method for controlling the aforementioned MIMO imaging radar system.

[0131] This method advantageously includes the step of calibrating the transmit and receive channels. This step occurs prior to the operational imaging step.

[0132] To select the phase shift coefficient, the computer uses the calibration table TAB (in... Figure 3 and 8 (As shown in the diagram), the calibration table TAB allows phase shifts present in each of the transmit and receive channels to correctly form beams and obtain an accurate estimate of the absolute direction of each formed beam.

[0133] More specifically, applying phase shift coefficients (which are intended to steer the MIMO coverage area) in the electronic steering module can impair the calibration of individual channels. If these coefficients are not precise in each radiating sub-element, this will result in phase and / or amplitude errors in each channel. Consequently, MIMO beamforming in the steering domain will be disrupted.

[0134] To avoid this defect, the calibration procedure implements the following sub-steps.

[0135] like Figure 9 As illustrated in the diagram, in the first sub-step, for each steering command (e.g., one of the eight commands in the aforementioned table), the error between the radiation patterns of each moved radiation element is measured. This measurement corresponds to the error of each radiation element relative to the center of the theoretical shifted scan domain.

[0136] In the second sub-step, the radiation pattern of the radiating element is re-aligned by compensating for the phase and / or amplitude errors measured in the previous sub-step, which allows for the acquisition of calibration coefficients.

[0137] These calibration coefficients are then stored in the calibration table TAB specific to the steering command Cmd in question. Figure 3 and 8 To simplify the accompanying drawings, a single table is shown in the computer CALC.

[0138] This calibration step must be performed in particular to compensate for the fact that the phase shifter integrated into the chip does not include an integrated calibration device.

[0139] Repeat the calibration process for all possible steering commands and multiple operating temperature ranges.

[0140] Computer-aided error compensation ensures a correctly focused antenna. From a radiation pattern perspective, this means the envelope of the radiating element's steering pattern can tolerate small distortions and variations. It is the phase adjustment of the MIMO channel that makes precise and refocused beamforming possible. It's important to note that since the electronic steering modules are identical and the phase shift command is the same at any given time, the expected error for all modules is essentially the same.

[0141] Phase adjustment of a MIMO channel occurs in any architecture of the MIMO type; therefore, there is no need to modify the computer.

[0142] In addition to a temperature calibration table (which is conventionally present in MIMO radar systems to compensate for temperature drift), the radar system according to the invention therefore also includes a calibration table to correct steering.

[0143] The radar system according to the invention can be advantageously located on an aircraft. It is conceivable to use radar chips manufactured for motor vehicle applications at low cost and to associate them with electronic steering modules produced using ASICs in advanced integration technology, the cost of which is also limited by the simplicity of the integrated functions (amplification, low-resolution phase shift).

Claims

1. A multiple-input multiple-output imaging radar system, comprising: - Multiple transmission channels (Ve1, VeM, Vei); - Multiple receive channels (Vr1, VrN, Vri); - Multiple co-located radiating elements (ER) forming a two-dimensional antenna array e1 ER eM ER r1 ER rN ER1, ERi), ​​each radiating element (ER e1 ER eM ER r1 ER rN Each radiating element (ER1, ERi) can be fed through one of the transmit channels (Ve1, VeM, Vei) and / or can be fed to one of the receive channels (Vr1, VrN, Vri). e1 ER eM ER r1 ER rN ER1, ERi) have a predetermined instantaneous coverage area; The characteristic feature is that each radiating element (ER) is formed by p more radiating sub-elements (SeElt1, SsEltp) distributed in at least one of the two dimensions of the antenna array. e1 ER eM ER r1 ER rN ,ER1,ERi), The radar includes multiple electronic steering modules (MDs). e1 , ..., MD rN MD ei MD ri ), each electronic steering module (MD e1 , ..., MD rN MD ei MD ri It is connected to a radiating element (ER) e1 ER eM ER r1 ER rN ER1, ERi), ​​each steering module (MD) e1 MD eM MD r1 MD rN MD ei MD ri ) is configured to radiate a given radiating element (ER) e1 ER eM ER r1 ER rN A steering command (Cmd) is applied between all radiating sub-elements (SeElt1, SsEltp) of ER1, ERi, and Eri, wherein the steering command (Cmd) is initiated from one radiating element (ER1, Eri). e1 ER eM ER r1 ER rN The radiating elements (ER1, ERi) are identical to the next radiating element so that each radiating element (ER1, ERi) can be moved in the same direction. e1 ER eM ER r1 ER rN The coverage area of ​​ER1, ERi).

2. The system according to claim 1, wherein, Each electronic steering module (MD) e1 MD eM MD r1 MD rN MD ei MD ri )include: - A distributor or combiner, respectively connected to the transmit channel (Ve1, VeM, Vei) or the receive channel (Vr1, VrN, Vri), and - Multiple phase shifters (φ1, φp), each phase shifter (φ1, φp) is connected to the radiating element (ER). e1 ER eM ER r1 ER rN One of the radiating sub-elements (SeElt1, SsEltp) of ER1, ERi, and ERi.

3. The system according to claim 1, wherein, Each electronic steering module includes multiple amplification devices (PA1, PAp, LNA1, LNAp), and each amplification device (PA1, PAp, LNA1, LNAp) is connected to a radiating sub-element (SeElt1, SsEltp).

4. The system according to any one of claims 1 to 3, wherein, The steering command (Cmd) includes the phase gradient applied between the individual radiating sub-elements (SeElt1, SsEltp).

5. The system according to claim 4, wherein, The phase gradient corresponds to a constant angle difference selected from the following values: 0; ±π / 4, ±π / 2, ±3π / 4; ±π.

6. The system according to any one of claims 1 to 3, wherein, The radiating element (ER) e1 ER eM ER r1 ER rN ER1, ERi) are located on the antenna panel, and the radiating element (ER) e1 ER eM ER r1 ER rN ER1, ERi) occupy at least 50% of the area of ​​the antenna panel.

7. The system according to any one of claims 1 to 3, wherein, The radiating sub-elements (SeElt1, SsEltp) are positioned according to the azimuth and elevation dimensions of the two-dimensional antenna array.

8. The system according to any one of claims 1 to 3, wherein, p equals 2 or 4.

9. The system according to any one of claims 1 to 3, comprising a calibration table (TAB) configured to compensate for each steering command (Cmd) via the electronic steering module (MD). e1 MD eM MD r1 MD rN MD ei MD ri The turning error between the transmit channels (Ve1, VeM, Vei) and / or between the receive channels (Vr1, VrN, Vri) caused by the ).

10. The system according to any one of claims 1 to 3, configured to operate in the millimeter-wave band.

11. An aircraft comprising the system according to any one of the prior claims, wherein, The system includes a computer (CALC) configured to change the steering command based on the difference between the aircraft's heading and route.

12. The aircraft according to claim 11, wherein, The steering command is recalculated at a frequency between 10 Hz and 15 Hz.

13. A method for controlling a multiple-input multiple-output imaging radar system, the method comprising the following steps: - Transmit radar signals on multiple transmission channels (Ve1, VeM, Vei); - The radar signal is received on multiple receiving channels (Vr1, VrN, Vri) after reflection or backscattering from the target; By forming a co-located set of radiating elements (ER) in a two-dimensional antenna array e1 ER eM ER r1 ER rN The transmit channels (Ve1, VeM, Vei) and receive channels (Vr1, VrN, Vri) are respectively fed and / or fed to obtain the signal for each of the radiating elements (ER1, ERi). e1 ER eM ER r1 ER rN The predetermined instantaneous coverage area of ​​ER1, ERi, etc. The characteristic feature is that each radiating element (ER) is formed by p more radiating sub-elements (SeElt1, SsEltp) distributed in at least one of the two dimensions of the antenna array. e1 ER eM ER r1 ER rN The method further includes the following steps: ER1, ERi). In a given radiating element (ER) e1 ER eM ER r1 ER rN A steering command (Cmd) is applied between all radiating sub-elements (SeElt1, SsEltp) of a radiating element (ER). e1 ER eM ER r1 ER rN The radiating elements (ER1, ERi) are identical to the next radiating element so that each radiating element (ER1, ERi) can be moved in the same direction. e1 ER eM ER r1 ER rN The instantaneous coverage area of ​​ER1, ERi).

14. The method of claim 13, further comprising a calibration step, wherein the calibration step includes the following sub-steps: - For a given steering command (Cmd), the measuring radiation element (ER) e1 ER eM ER r1 ER rN The coverage areas of ER1, ERi) are relative to each radiating element (ER1, ERi). e1 ER eM ER r1 ER rN The phase error and / or amplitude error at the center of the theoretical shifted scan domain of ER1, ERi; - Determine the calibration coefficients based on the measured phase error and / or amplitude error; - The calibration coefficients are stored in a table called the Calibration Table (TAB) that is specific to the steering command (Cmd).

15. The method according to claim 14, wherein, The calibration steps are performed for all available steering commands (Cmd) and for multiple operating temperature ranges.

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