Bidirectional radar beam pattern steering

Abstract

A method of sensing an environment using a radar system includes applying a progressive phase shift between a plurality of antenna elements of the radar system, recording a signal return level of a bi-directional radiation pattern while applying the progressive phase shift, where the progressive phase shift moves a main lobe to a position outside an optical axis and increases a signal return level of at least one side lobe, and the signal return level of the at least one side lobe. And detecting at least one object at a position off-axis offset from the visual axis based on the increased signal return level of the at least one sidelobe.

Description

Technical Field

[0001] This disclosure relates to a two-way radar beam pattern steering, and more particularly to detecting objects using sidelobes of a two-way radar beam pattern. Background Art

[0002] In a radar system, the far-field radiation pattern of an antenna array typically includes multiple local maxima and minima in 3D space. The highest maximum is called the main lobe or main beam and can be fixed or scanned using hardware or digital signal processing techniques. Other maxima are called sidelobes. Targets detected by a radar are typically assumed to arrive from the angular direction corresponding to the main beam. However, at the angles corresponding to the sidelobes, the level of the transmitted (or received) signal is relatively high compared to other regions and cannot be ignored compared to the region focused by the main beam. Therefore, when the sidelobes are high, ambiguity occurs, and since target reflections may appear in the angular directions of the main beam or sidelobes and are accompanied by clutter (or unwanted echoes), the position and number of detected objects will be in doubt.

[0003] To solve this problem, many sidelobe cancellation (SLC) methods have been reported. In an SLC system, the basic principle used is to subtract the interference signal (caused by the sidelobes) from the antenna output, in a manner similar to many adaptive cancellation techniques used in today's communication systems to remove interference and multipath signals. Even for a radar with inherently low sidelobe levels, this problem may occur due to electronic attacks or 'jamming' rather than clutter caused by signals picked up by the sidelobes in the radar signal. Therefore, when a radar is jammed, the detected clutter is caused by external signals rather than by the inherent characteristics of the radar.

[0004] Figure 1 Shows a basic interference canceller, where the top antenna represents the'main' radar antenna (V MAIN (t)), and the bottom antenna is the auxiliary antenna (V AUX (t)) for collecting information on the interference signal caused by the jamming signal or the signal return from the sidelobes. The inverting gain block (K) is adjusted according to the error voltage V ERR (t), which is formed by subtracting a weighted version of the auxiliary channel signal V MAIN (t) from the main channel signal V AUX (t).

[0005] V ERR (t) = V MAIN (t) - KV AUX (t).......................... (1)

[0006] When the value of K is set correctly, it can be seen that the error signal V ERR (t) contains only the target signal or the desired signal. Of course, Figure 1 assuming that the auxiliary channel signal consists only of interference signals, which is unlikely in practice.

[0007] Sidelobe cancellation (SLC) can be regarded as an extension of space-time adaptive processing (STAP), which is a signal processing technique that uses multi-dimensional signal processing techniques to filter in the spatio-temporal domain of multiple dimensions with the aim of removing interference. In this regard, STAP has been used in MIMO radars, specifically to improve the spatial resolution of a large amount of clutter generated by the virtual array of MIMO radars.

[0008] Figure 2 The radar equivalent circuit signal path is shown. From this, the well-known radar equation is derived:

[0009]

[0010] where P r is the received power, P t is the transmitted power, is the transmit antenna gain (varying with angles θ and in spherical coordinate geometry), similarly is the receive antenna gain, λ is the wavelength of the transmit frequency, R is the distance to the target object, and σ is the radar cross section (RCS) of the target object.

[0011] The combined term (hereinafter referred to as G t G r ) is called the two-way antenna gain and is usually plotted as a two-way radiation pattern, which can be in the form of a 3D plot in spherical coordinate geometry or plotted as a 2D 'cut' where θ or is set to a constant value. Thus, the bi-directional radiation pattern is an important design component in a radar as its design and modification have a direct impact on the 3D spatial regions that may generate interference or clutter and thus appear in radar detections. In this regard, the sidelobe level of the bi-directional pattern is typically kept below 1 / 1000 of the main beam power to minimize the probability of clutter detection due to the radar's antenna pattern. In an antenna array, and more specifically in a MIMO radar, there are many ways to do this, such as'scaling / tapering / weighting' to form the beam pattern where the signal strengths arriving at different antenna elements (or individual radiators within the whole antenna), or from different antenna elements, are amplified or attenuated to manipulate the overall shape of the combined beam. Another method involves 'placement' where the spacing between the antenna elements within the array can be changed, thus changing the way their radiation fields combine and in this way changing the overall beam shape.

[0012] By considering the G t G r terms more carefully, it can be inferred that by aligning the angular regions where the transmitter radiation pattern G t is at a minimum with the points where the receiver radiation pattern G r is at a maximum, or vice versa, the resulting bi-directional pattern will have lower sidelobes or no regions prone to generating interference or signal clutter. Figure 3 shows a bi-directional pattern with lower sidelobes or no regions prone to generating interference or signal clutter. However, this method is typically difficult to implement and requires a more complex antenna feed structure, a larger number of antenna elements in the array, and a larger antenna aperture (or area).

[0013] Furthermore, in a MIMO radar, multiple transmitters and receivers work together, with the antennas placed close to each other and acting together to form a 'virtual' beamforming array. However, the ability to shape this virtual array in the manner described previously is limited because the transmit and receive antenna elements typically have radiation patterns with very wide main lobes (usually >80°), and the angular processing is done digitally, for example using the digital sampled mixer outputs of the transmit signals and the received signals from each receive antenna. In other embodiments, where the beamforming network is fixed or uses a network that is difficult to beamform (such as a lens-type structure, which has the advantage that by changing the shape of the lens or its geometry relative to the antenna elements, a multi-beam radar with various FOVs (fields of view) can be designed), such structures tend to have a larger sidelobe level that must be accounted for or removed when decoding the radar signal returns.

[0014] US 2021 / 083395 discloses a radar system for object detection using a metamaterial device. In the radar system of the said document, the material of the antenna can be bent to change the phase between elements. Moreover, the said system discloses performing raster scanning and adjusting the antenna to locate an object within the sidelobe region of the antenna. Further, the said system is limited to detecting only objects at the main lobe or sidelobe. In addition, the said document mentions scanning the receiving antenna to a given angle. However, adding a phase shifter on the receiving side to do this will introduce a large amount of signal noise to the system, thereby reducing the range of the system, unless additional costs such as an LNA are added.

[0015] JP H02 12082 discloses improving the accuracy of the BITE (Built-In Test Equipment) function by generating a test target as an angle off the line of sight. In view of the above, there is a need for an antenna configuration that helps remove signal clutter in radar signal detection and also helps simplify the radar antenna design and radar signal processing algorithms. Summary of the Invention

[0016] The present invention relates to an electronically beam-steering antenna.

[0017] In one aspect, there is provided a method of sensing an environment using a radar system, the method comprising: setting a two-way signal return level of a main lobe at the line of sight as a reference level; applying a progressive phase shift between a plurality of antenna elements of the radar system for moving the main lobe to a position off the line of sight to increase the two-way signal return level of at least one sidelobe; while applying the progressive phase shift, recording the signal return level of the two-way radiation pattern relative to the reference level; detecting at least one object at the line of sight or at a position off the line of sight based on comparing the applied progressive phase shift and the recorded signal return level with a look-up table, wherein the look-up table includes a set of phase shift conditions, and each phase shift condition includes a progressive phase shift to be applied between the plurality of antenna elements and a corresponding plurality of recorded signal return levels for detecting at least one object on or off the line of sight.

[0018] In an embodiment of the present invention, the plurality of antenna elements include a plurality of simultaneously excited transmit antenna elements of a MIMO radar.

[0019] In an embodiment of the present invention, the look-up table includes: a first phase shift condition, which includes a first progressive phase shift for moving the main lobe away from the optical axis by a first steering angle, and corresponding signal levels for detecting objects at the optical axis, at a first position off the optical axis, and at a second position off the optical axis when applying the first progressive phase shift; and a second phase shift condition, which includes a second progressive phase shift for moving the main lobe away from the optical axis by a second steering angle, and corresponding signal levels for detecting objects at the optical axis, at a third position off the optical axis, and at a fourth position off the optical axis when applying the second progressive shift.

[0020] In an embodiment of the present invention, the look-up table further includes: a third phase shift condition, which is applicable when an object is identified at the second position off the optical axis under the first phase shift condition, wherein the third phase shift condition includes: a third progressive phase shift for moving the main lobe away from the optical axis by a third steering angle; a corresponding signal return level for concluding that a single object exists at the second position off the optical axis when applying the third progressive phase shift; and a corresponding signal return level for concluding that one object exists at the optical axis and another object exists at the second position off the optical axis when applying the third progressive phase shift.

[0021] In an embodiment of the present invention, the look-up table further includes: a fourth phase shift condition, which is applicable when an object is identified at the fourth position off the optical axis under the second phase shift condition, wherein the fourth progressive phase shift condition includes: applying a fourth progressive phase shift for moving the main lobe away from the optical axis by a fourth steering angle; a corresponding signal return level for concluding that a single object exists at the fourth position off the optical axis when applying the fourth progressive phase shift; and a corresponding signal return level for concluding that one object exists at the optical axis and another object exists at the fourth position off the optical axis when applying the fourth progressive phase shift.

[0022] In an embodiment of the present invention, the second progressive phase shift is the negative value of the first progressive phase shift, the fourth progressive phase shift is the negative value of the third progressive phase shift, the second steering angle is the negative value of the first steering angle, and the fourth steering angle is the negative value of the third steering angle.

[0023] In an embodiment of the present invention, the method further includes determining the size of the detected object based on the value of the signal return level, the detection range, and the actual number of return signals from a given area.

[0024] In another aspect of the present invention, a method for sensing an environment using a radar system is provided. The method includes: applying a progressive phase shift between a plurality of antenna elements of the radar system for detecting an object at the boresight of the bidirectional radiation pattern of the radar system; recording the signal return level of the bidirectional radiation pattern when applying the progressive phase shift, wherein the progressive phase shift moves the main lobe to a position outside the boresight and increases the signal return level of at least one sidelobe; and detecting at least one object at a position offset from the boresight based on the increased signal return level of the at least one sidelobe.

[0025] In an embodiment of the present invention, the plurality of antenna elements include a plurality of simultaneously excited transmit antenna elements of a MIMO radar.

[0026] In an embodiment of the present invention, the method includes applying a first negative progressive phase shift between the plurality of antenna elements, wherein the first negative progressive phase shift is the negative value of a first progressive phase shift, moves the main lobe to a position outside the boresight, and increases the level of at least one sidelobe on the other side of the main lobe to detect at least one object at a position offset from the boresight on the other side.

[0027] In an embodiment of the present invention, the at least one object is detected based on a predefined look-up table, which includes a column of predefined progressive phase shifts and, for each predefined progressive phase shift, the signal return levels for detecting objects at the boresight and on either side offset from the boresight.

[0028] In an embodiment of the present invention, the method further includes: generating the look-up table by setting the bidirectional signal return level at the boresight to a reference level when applying a conventional phase shift; applying a first progressive phase shift between the plurality of antenna elements; and determining, for the first progressive phase shift, a first signal level for detecting an object at the boresight, a second signal level for detecting an object at a predefined position offset from the boresight on one side, and a third signal level for detecting an object at a predefined position offset from the boresight on the other side, wherein each of the first signal level, the second signal level, and the third signal level is determined relative to the reference level; applying a first negative progressive phase shift; and determining, for the first negative progressive phase shift, a first signal level for detecting an object at the boresight, a third signal level for detecting an object at a predefined position offset from the boresight on one side, and a second signal level for detecting an object at a predefined position offset from the boresight on the other side.

[0029] In an embodiment of the present invention, the method includes: generating a look-up table by applying a second progressive phase shift when an object is detected at a position on one side of the off-axis direction while applying a first progressive phase shift at a third signal level; concluding that a single object exists at a position on one side of the off-axis direction when the signal return level is smaller than the third signal level by a first value while applying the second progressive phase shift; and concluding that one object exists on the optical axis and another object exists at a position on one side of the off-axis direction when the signal return level is smaller than the third signal level by a second value while applying the second progressive phase shift.

[0030] In an embodiment of the present invention, the method includes: generating a look-up table by applying a second negative progressive phase shift when an object at a position on the other side of the off-axis direction is detected at a third signal level while applying a first negative progressive phase shift; concluding that a single object exists at a position on the other side of the off-axis direction when the signal return level is smaller than the third signal level by a first value while applying the second negative progressive phase shift; and concluding that one object exists on the optical axis and another object exists at a position on the other side of the off-axis direction when the signal return level is smaller than the third signal level by a second value while applying the second negative progressive phase shift.

[0031] In an embodiment of the present invention, the plurality of antenna elements includes a plurality of transmit antenna elements, a plurality of receive antenna elements, or a combination of both.

[0032] In an embodiment of the present invention, the progressive phase shift is independently applied to the plurality of transmit antenna elements and receive antenna elements.

[0033] In an embodiment of the present invention, each receive antenna element is configured with a fixed or switched beam pattern.

[0034] In an embodiment of the present invention, the method further includes applying one or more subsequent progressive phase shifts between the plurality of antenna elements to introduce further attenuation in the side lobe or main lobe of the bi-directional radiation pattern.

[0035] In an embodiment of the present invention, the plurality of antenna elements are configured using a beamforming network.

[0036] In an embodiment of the present invention, the method further includes recording and analyzing the signal return level of at least one side lobe of the bi-directional radiation pattern when applying the progressive phase shift when the signal return level of at least one side lobe exceeds a predefined threshold.

[0037] In an embodiment of the present invention, the spacing between the plurality of antenna elements is not equal.

[0038] In an embodiment of the present invention, the plurality of antenna elements are continuous antenna elements.

[0039] In an embodiment of the present invention, a radar system is provided. The radar system includes: at least one transmitter; a plurality of transmitting antenna elements; and a plurality of variable phase shifter components connected between the at least one transmitter and the plurality of transmitting antenna elements; at least one receiver; a plurality of receiving antenna elements; and a plurality of variable phase shifter components connected between the at least one receiver and the plurality of receiving antenna elements; and a radar control system.

[0040] A computer program is also provided. The computer program includes program instructions for causing a computer program to execute the above method, and the computer program can be implemented on a recording medium, a carrier signal or a read-only memory.

[0041] Various embodiments of the present invention disclose a two-way radar beam pattern steering method for collecting relevant information from the inherent side lobes of the antenna radiation pattern, rather than removing or mitigating these side lobes by methods such as filtering, to establish a more detailed view of the environment. This method eliminates signal clutter in radar signal detection, broadens the field of view, improves the discrimination between targets in analog and digital automotive radars, helps identify whether the identified object is real or miscomputed, and enables simplification of the radar antenna design and radar signal processing algorithms. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Referring to the accompanying drawings, the present invention will be more clearly understood from the description of its embodiments given below by way of example only, in which: -

[0043] Figure 1 The prior art configuration of a conventional interference canceller is shown;

[0044] Figure 2 The radar equivalent circuit signal path is shown;

[0045] Figure 3 The change in the shape of the two-way radiation pattern compared to the single antenna radiation pattern is shown;

[0046] Figure 4 The conventional 8-receiving-element antenna uniform linear array configuration and the equivalent MIMO configuration using 2 transmitting elements and 4 receiving elements are shown;

[0047] Figure 5 The normalized 'boresight' radiation pattern of a 10-element linear array is shown, and the spacing of these elements is half a wavelength;

[0048] Figure 6 Shows the use of Figure 5 The three cases where the radar returns of the objects detected by the array are exactly the same;

[0049] Figure 7Shows the effect of a 40-degree progressive phase shift on a three-element phased array;

[0050] Figure 8 Shows the effect on the bidirectional polarization radiation pattern of a three-element transmitting antenna and a ten-element receiving antenna when the receiving antenna is scanned to 0 degrees while applying a 40-degree progressive phase shift to the transmitting antenna;

[0051] Figure 9 Shows a millimeter-wave automotive radar system according to an embodiment of the present invention;

[0052] Figure 10 Is a flowchart showing a method of scanning the environment around a vehicle according to an embodiment of the present invention;

[0053] Figure 11 Is a flowchart showing a method of scanning the environment around a vehicle by a Figure 9 Millimeter-wave automotive radar system according to another embodiment of the present invention;

[0054] Figure 12 shows detecting a single object using the sidelobe of the bidirectional radiation pattern of a phased array radar according to an embodiment of the present invention;

[0055] Figure 13 Shows detecting two objects using the sidelobe of the bidirectional radiation pattern of a phased array radar according to an embodiment of the present invention;

[0056] Figure 14 Shows detecting two objects according to an embodiment of the present invention, where one object appears on the line of sight of the bidirectional radiation pattern of the phased array radar;

[0057] Figure 15 Shows the normalized array gain of a 12-element virtual array generated in a MIMO system with three transmitting elements and four receiving elements, and the array is digitally scanned to 0 degrees;

[0058] Figure 16 Shows when Figure 15 When all three transmitting elements are simultaneously excited in the shown transmitting array, the effect of a 40-degree progressive phase shift on the transmitted radiation pattern; and

[0059] Figure 17 Shows an implementation of the present invention in a MIMO array. Detailed Description of the Invention

[0060] Figure 4Shows a conventional 8-receiver-element antenna configuration and its equivalent MIMO configuration. Conventional digital beamforming architectures incorporate receivers dedicated to each antenna element. However, as the antenna array size grows larger, for applications such as automotive radar, the number of required receivers becomes prohibitively expensive. When low angular accuracy is required, a wide beam is sufficient and obtained with a small number of antenna elements. This means that the minimum number of receivers can be employed. However, when high angular accuracy is required, a narrower beam is needed, and a larger antenna array with additional elements must be utilized.

[0061] In the case of multiple-input multiple-output (MIMO) radar, it is known to those skilled in the art that measuring the amplitude and phase of the signals received at N receivers (multiple outputs) for each of M transmitters (multiple inputs) can be used to form a 'virtual' receive array larger than the physical receive array. There are various modulation schemes for MIMO, which aim to achieve orthogonality between the signals transmitted by each individual transmitter so that these signals can be separated at the receiver side. These schemes include, but are not limited to, time-division multiplexing (TDM), frequency-division multiplexing (FDM), and binary phase multiplexing (BPM). For TDM MIMO, the transmitters transmit one signal at a time in sequence. Then, the receive elements receive the signals from each transmitter in chronological order, and thus these signals can be separated according to which transmitter the signal originated from. When the spacing between the transmit elements and the receive elements is set accordingly, the signals at each receiver can be rearranged corresponding to the transmitter from which the signal originated, and the phase differences on each received radiation wave result in a larger number of equivalent receive elements than the actual number of receive elements present, and thus 'virtual' elements are produced. A virtual array is formed, which consists of (M×N) elements, but only (M + N) physical antenna elements are utilized, thus far exceeding the physical number of required transmitters and receivers. Therefore, MIMO technology is effective in improving the angular resolution of the radar for a given number of transceivers or reducing the number of transceivers required for a given angular resolution. It is well known that the digital signal processing (DSP) technology for TDM MIMO systems is to perform multiple fast Fourier transforms (FFT) and Constant False Alarm Rate (CFAR) threshold processing and other techniques on each virtual element after ADC sampling to determine the direction angle and velocity of each detection.

[0062] In the case of MIMO radar, the focusing effect produced by such a virtual array can be mathematically represented as an array factor, which is the complex-valued far-field radiation pattern of an isotropic radiator array (i.e., a theoretical antenna without directivity and radiating equal energy in all directions). At each discrete angle θ, the one-dimensional array factor of a linear array is calculated using the following formula:

[0063]

[0064] where w n is the complex weight (with magnitude and phase) of the nth element in the array, and d is the element spacing. The array factor is converted to decibels based on the following formula:

[0065] AF dB (θ) = 20 log 10 [AF(θ)]...................... (4)

[0066] When the array factor is calculated using the element positions of the array and multiplied by the radiation pattern of a single physical antenna element in the array (i.e., a real antenna, with its own complex radiation pattern), the resulting radiation pattern provides a good approximation of the radiation pattern of the array (excluding effects such as mutual coupling that may distort the pattern between the elements in the physical array). In decibel form, the gain of the array is given by:

[0067] G A (θ) = AF dB (θ) + G E (θ)...................... (5)

[0068] where G E is the gain of a single element (in dB).

[0069] By combining the array gains of each of the transmit and receive antennas, a two-way pattern is formed, and this two-way pattern is equivalent to the pattern formed using all the elements in the virtual array of a MIMO radar, where:

[0070] G dB双向 (θ) = G dB TX (θ) + G dB RX (θ)...................... (6)

[0071] These are the functions used to calculate the positions where sidelobes may occur (excluding external influencing factors such as interfering signals), and these sidelobes are caused by the number of elements within the array and their positions relative to each other.

[0072] Referring again to Figure 4Obviously, when a MIMO system is used in the TDM mode, not all virtual elements in the MIMO system can be measured simultaneously. When the number of transmitters used is M, the measurements must be repeated M times for each 'true' receiving element.

[0073] It has been previously stated that when the positions of the antenna elements are fixed, one way to control the sidelobes is by scaling / tapering, achieved by adjusting the magnitude of the weighting term w n and applying post - processing using DSP techniques (e.g., MIMO) or as part of the feed network (e.g., phased array). However, this generally has the adverse effect of reducing the array gain, unless amplification is applied at some elements (thus increasing the cost of the system). Figure 5 The effects and problems of the sidelobes without applying scaling are shown in [reference]. The normalized radiation pattern of a 10 - element array is shown, where the spacing between the elements is set to half the wavelength of the operating frequency and scanning is performed at the boresight. Here, the first sidelobe appears at 18 degrees off the boresight and is approximately 13 dB lower than the main beam. This means that a vehicle at a distance of 50 m, 15 m to the left or right of the radar, could be interpreted as being directly in front of the vehicle. Additionally, it is intuitively obvious that the amount of radar signal'reflected' by a detected object depends on the size of the object. Thus, a large vehicle on the side may be mistaken for a small vehicle directly in front. The amount of radar reflection provided by an object is called the radar cross - section (RCS) of the object and varies depending on the size, shape, and material of the object. Alternatively, the size of the detected object can be determined based on the value of the signal return level, the detection range, and the actual number of return signals from a given area. Typical RCS values for motor vehicles indicate that the radar reflection of a truck or lorry is on average 10 to 100 times that of a car, and the radar reflection of a car is in turn 10 times that of a motorcycle. This means that if the radar detects a truck in its sidelobe pattern at a specific distance / speed, the received signal strength at the boresight may be the same as that of a car at the same distance / speed at the boresight; or similarly, if the radar detects a car in its sidelobe pattern at a specific distance / speed, the received signal strength at the boresight may be the same as that of a motorcycle at the same distance / speed at the boresight. Therefore, Figure 6 Three examples are shown where the same radar readings will be given for single - vehicle detection and the conditions previously described using an omnidirectional transmitting antenna. The problem of single - vehicle detection can be solved using known sidelobe removal or mitigation techniques, but for Figure 6 the cases shown in [reference], if two or all of these scenarios are combined, the radar detections will merge to show a single object.

[0074] Figure 7Shows the effect of a 40-degree progressive phase shift on a 3-element transmitting antenna array. In a phased array, a progressive phase delay can be added across the linear array, i.e., at the nth element, (n - 1)Φ is added, where Φ is the added phase delay. Thus, to point the beam to each angle θ in 3D space, there is a specific value of Φ, where:

[0075]

[0076] where d is the spacing between elements, and λ is the wavelength of the operating frequency.

[0077] When these conditions are applied, the direction of the peak radiation pattern or main beam is shifted without mechanically or physically moving the individual antennas, and for the case described, the direction of the peak radiation pattern or main beam will be shifted by θ degrees off the boresight. Thus, the steering angle of the array will simply be controlled by changing the phases of the individual elements. In Figure 7 it shows the effect on a 3-element transmitting antenna array, where the radiation pattern of a normal 3-element array with no phase change is compared to the radiation pattern of an array with a 40-degree progressive phase delay, which shifts the main beam 12.8 degrees off the boresight in the negative direction. In this case, the phase delay was specifically chosen for its effect on the two-way radiation using a 10-element receiving array.

[0078] Figure 8 Compares two two-way radiation patterns on a polar plot (with and without progressive phase delay on the transmitting antenna), which is a more typical visualization of real-world conditions. The plot also shows how, by rotating the angle of the main beam, the effect of sidelobes, especially the significant sidelobe at 18 degrees, is further reduced by 10 dB. Here, it is worth noting that another sidelobe at -18 degrees rises slightly (3.5 dB), while the two-way boresight level also drops by <1.4 dB. When the progressive phase delay on the transmitting antenna is set to the negative of its value, the beam can be steered in the opposite direction, and the effect on the sidelobes is also reversed.

[0079] Figure 9Shows a millimeter-wave automotive radar system 900 according to an embodiment of the present invention. The millimeter-wave automotive radar system 900 can be used in any radar system, such as for defense or warfare, but is more specifically applicable to automotive radar safety systems (ADAS). The millimeter-wave automotive radar system 900 includes: at least one transmitter 902; a plurality of transmit antenna elements 904; and a plurality of variable phase shifters or time delay components 906, the number of which is equal to the number of transmit antenna elements 904 and are connected between the at least one transmitter 902 and the transmit antenna elements 904. The millimeter-wave automotive radar system 900 further includes at least one receiver 908 and a plurality of receive antenna elements 910. The number of transmit antenna elements 904 and receive antenna elements 910 can be the same or different, depending on the required angular resolution and radar detection range.

[0080] In one embodiment of the present invention, each receive antenna element 910 can be configured with a fixed or switched beam pattern. In another embodiment of the present invention, the receive antenna elements of the radar system 900 can be configured using a beamforming network (such as a lens structure) that can move the main beam to a specific angle off the line of sight in 3D space. It is known that there are significant challenges in maintaining a low sidelobe level with such a design, but by applying the present invention at these points, the sidelobes can be utilized.

[0081] Alternatively, a lens-based beamforming network can be used at both the transmit and receive antenna elements, where the time delay component 906 is in the form of a lens that has a plurality of excited input ports and modifies the beam pattern through amplitude tapering. This can make the lens design simpler and / or cheaper and / or easier to construct, and can achieve high angular resolution using fewer transceivers within a narrower field of view. Additionally, it can result in a greater number of antenna elements than receivers / transmitters, thereby reducing FFT processing and facilitating implementation over a larger RF bandwidth.

[0082] In another embodiment of the present invention, a plurality of variable phase shifters or time delay components (not shown), the number of which is equal to the number of receive antenna elements 910, can be connected between the at least one receiver 908 and the receive antenna elements 910. Thus, the 'phased array' (or an alternative steering method) can be moved from the transmit side to the receive side or the baseband. This increases the flexibility of the PCB layout, potentially reducing the overall size and cost.

[0083] In yet another embodiment of the present invention, the number of the plurality of variable phase shifters or time delay components 906 is equal to the total number of the transmit antenna elements 904 and the receive antenna elements 910.

[0084] In an embodiment of the present invention, the phase shift between the transmitting antenna element and the receiving antenna element can be implemented using a switched delay line.

[0085] In yet another embodiment of the present invention, the millimeter-wave transmitter 902 and the receiver 908 are replaced by a millimeter-wave transceiver unit.

[0086] Further, in one example, elements 902 to 910 form a phased array radar.

[0087] The millimeter-wave automotive radar system 900 further includes a radar control system 912, which is communicatively coupled to elements 902 to 910 to control their operations. The radar control system 912 includes, but is not limited to, a microprocessor, a microcontroller, a complex instruction set computing (CISC) microprocessor, a reduced instruction set (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, or any other type of processing circuitry.

[0088] In an embodiment of the present invention, the millimeter-wave automotive radar system 900 is configured to electronically sense the surrounding environment of the vehicle using electromagnetic signals to determine object positions, remove false object detections, and distinguish objects.

[0089] Further, it should be noted that the millimeter-wave automotive radar system 900 uses FMCW (frequency-modulated continuous wave) modulation for signal transmission / reception. The FMCW waveform, also known as a chirp, is a complex sinusoidal waveform whose frequency increases linearly with time. The FMCW radar emits chirps periodically at a period called the pulse repetition interval (PRI), and most commonly in a sawtooth configuration, although other chirp types are also available. The resulting target echo from the scene will contain a delayed and attenuated copy of the transmitted chirp. Mixing the received signal with the transmitted chirp produces a complex sinusoidal waveform. This waveform is called the beat signal, and its frequency is proportional to the distance to the detected object. Multiple chirps are collected within a single 'frame', allowing determination of the Doppler frequency change in the'slow time' dimension.

[0090] After digital sampling of the beat signal, the estimation of the beat frequency is typically carried out in the digital domain. Since the beat frequency is much less than the radar bandwidth, a low-speed analog-to-digital converter (ADC) can be used. By sampling the beat signal and placing the samples of each chirp in a separate column in a matrix, the row index of the matrix will correspond to the 'fast' time spent on a single chirp, and the column index will correspond to the'slow' time spent on multiple chirps. By applying a fast Fourier transform (FFT) to each column of the matrix, the range of the object is determined by detecting the beat frequency, and by applying a further FFT along the rows of the matrix, the velocity of the object can be determined by detecting the Doppler frequency. The use of these two FFTs is commonly referred to as 2D FFT and allows the determination of the object in both range and velocity. An incidental benefit of performing the 2D FFT is that it reduces the background noise by matched filtering of the beat frequency and Doppler frequency of the object. Obviously, depending on the range resolution and velocity resolution of the radar, the number of objects falling into the same range-velocity bin is usually small.

[0091] Although the range-velocity map gives a lot of useful information, it lacks details about the angular position of the object. This is overcome by plotting the instantaneous range-velocity map of each receiving port, rearranging the data to form a virtual array, and performing a third 'angle' FFT or 3D FFT. This is followed by a constant false alarm rate (CFAR), and this constant false alarm rate is a thresholding step where only the bins with a signal-to-noise ratio exceeding a specific threshold are retained. It is these levels that are directly related to the bidirectional radiation pattern. In other words, when there is an object, the signal return will be higher and thus exceed the CFAR threshold where the bidirectional radiation pattern level (or virtual array pattern) is higher.

[0092] Figure 10 is a flowchart showing a method of scanning the environment around a vehicle according to an embodiment of the present invention.

[0093] At step 1002, the bidirectional signal return level of the main lobe at the boresight is set as a reference level. At step 1004, a progressive phase shift is applied between a plurality of antenna elements of the radar system for moving the main lobe to a position off the boresight to increase the bidirectional signal return level of at least one sidelobe. At step 1006, when applying the progressive phase shift, the signal return level of the bidirectional radiation pattern relative to the reference level is recorded. At step 1008, based on comparing the progressive shift to be applied and the recorded signal return levels with a look-up table, at least one object at the boresight or at an off-boresight position is detected. The look-up table includes a set of phase shift conditions, and each phase shift condition includes a progressive phase shift to be applied between a plurality of antenna elements and a corresponding plurality of recorded signal return levels for detecting at least one object on or off the boresight.

[0094] Figure 11FIG. 0 is a flowchart showing a method of scanning the environment around a vehicle by a millimeter automotive phased array radar system 900 in another embodiment of the present invention. It will be apparent to those of ordinary skill in the art that the method can be applied to phased array radars as well as MIMO systems, in which measurements are made while multiple transmitter elements are active.

[0095] At Figure 11 step 1101, the radar control system 912 is configured to record the signal return level at the receiving element of the two-way radiation pattern of the system 900 to obtain distance, angle, and velocity, and analyze the data and record object detection under a basic reference signal. The two-way signal level at the main lobe along the line of sight can be referred to as the basic reference signal hereinafter, and the corresponding two-way beam pattern can be referred to as the basic reference pattern hereinafter.

[0096] At step 1104, the radar control system 912 is configured to apply a progressive phase shift or time delay between consecutive antenna elements 904. The antenna elements can be transmit antenna elements or receive antenna elements, or a combination of both. It will be apparent to those of ordinary skill in the art that the progressive phase shift can be applied independently to the transmit antenna elements and the receive antenna elements, where the phase shift or time delay can be changed to examine different regions of the 2D space. In an embodiment of the present invention, the progressive phase shift moves the main beam to a position on either side of the line of sight and increases the level of at least one sidelobe on the other side of the main beam in order to detect at least one object at an off-axis position on the other side. In the context of the present invention, a progressive phase shift with amplitude weighting can be introduced between multiple excited transmit antenna elements to introduce an attenuation different from that on the main lobe in the sidelobe region.

[0097] Reference Figure 8 explains in detail the application of the progressive phase shift. Figure 8 FIG. 15 shows the basic reference beam pattern 802 and the two-way pattern 804 obtained by applying a 40° progressive phase shift in addition to the conventional phase shift. When applying the 40° progressive phase shift, the signal level of the main beam decreases, but not significantly (<2 dB). The magnitude of the two-way sidelobe (due to reciprocity) appearing on the other side of the main beam will increase (~5 dB). When the progressive phase shift becomes negative, these effects are reversed. The change in the signal return indicates whether an object appears at the sidelobe position and which sidelobe position, or at the main beam position. By adding a further progressive phase shift and moving the main beam of the TX array to a further off-axis position where one sidelobe level remains the same but the main beam is significantly attenuated, additional changes in the two-way signal level can be measured (and used to identify whether there are more objects within the beam).

[0098] Return reference Figure 11, at step 1106, the radar control system 912 records the signal return level detected by the normal operation of the phased array radar / MIMO radar. In an embodiment of the present invention, the radar control system 912 is configured to record its signal return level when the signal return levels of at least two additional measurements exceed a predefined threshold, and compare the recorded signal levels with a reference level. At step 1106, the radar control system 912 is configured to analyze the signal return level and record object detection.

[0099] At step 1108, the radar control system 912 is configured to check whether a subsequent progressive phase shift needs to be applied. When a subsequent phase shift or additional measurement is required, the process returns to step 1104. The subsequent progressive phase shift can be introduced between multiple excited transmit antenna elements to introduce further different attenuation in the sidelobe region or on the main lobe. In addition, a similar progressive phase shift, i.e., the negative value of the subsequent progressive phase shift, can be introduced between the excited transmit antenna elements.

[0100] When no subsequent phase shift needs to be applied, then at step 1110, the radar control system 912 is configured to compare the signal return levels and identify the object. When the signal return levels of those measurements made with the subsequent phase shift are compared with the basic reference level measurements on at least one sidelobe, the radar control system 912 determines whether there is an object on the sidelobe. At step 1112, the radar control system 912 is configured to display the output.

[0101] In an embodiment of the present invention, the radar control system 912 is configured to use a predefined look-up table to detect at least one object, the look-up table including a column of predefined progressive phase shifts and the corresponding signal return levels for identifying objects on the line of sight and on the sidelobes on either side of the line of sight. The look-up table can be generated by setting the two-way signal return level at the line of sight as the reference level, and then measuring the signal return levels of the sidelobes relative to the reference level for various progressive phase shifts.

[0102] An exemplary look-up table is shown in Table I below,

[0103]

[0104]

[0105] Table I

[0106] Table I shows a first phase condition that includes a first progressive phase shift for moving the main beam away from the line of sight by a first steering angle between all 3 consecutive transmit antenna elements 904. The first steering angle corresponds to the main beam being offset 12.8 degrees in the counterclockwise direction. Any detected signal level caused by this condition is compared with a basic reference level. For this case, the signal comparison can be divided into three levels, where the first signal level corresponds to a detection occurring at 1.4 dB below the reference level (indicating that the object is indeed located on the line of sight), the second signal level corresponds to a detection occurring at 10 dB below the reference level (indicating that the object is located at a first position, i.e., on the first sidelobe at a given detection angle of +18 degrees in the clockwise direction), and the third signal level corresponds to a detection occurring at 3.5 dB above the reference level (indicating that the object is located at a second position, i.e., on the first sidelobe at -18 degrees (negative value of the detection angle) in the counterclockwise direction).

[0107] Table I further shows a second phase condition that includes a second progressive phase shift for moving the main beam away from the line of sight by a second steering angle. The second steering angle corresponds to the main beam being offset 12.8 degrees in the clockwise direction. In an embodiment, the second progressive phase shift is the negative of the first progressive phase shift and is also referred to hereinafter as the first negative progressive phase shift. For the first negative progressive phase shift, when a detection occurs at a third position (i.e., 10 dB below the reference level), the object is on the first sidelobe at -18 degrees (negative value of the detection angle) in the counterclockwise direction, and when a detection occurs at a fourth position (i.e., 3.5 dB above the reference level), the object is on the first sidelobe at the detection angle in the clockwise direction (i.e., +18 degrees).

[0108] Figure 12A and Figure 12B shows the detection of objects 1202 and 1204 based on the sidelobes of the bidirectional radiation pattern of the millimeter-wave automotive radar system 900 using Table I according to an embodiment of the present invention. Examples of object 1202 include cars, and examples of object 1204 include trucks.

[0109] It has been previously stated that the RCS value of the truck / vessel 1204 is approximately 10 dB higher than that of the car 1202, and the sidelobe level is approximately 13 dB lower than that of the main beam. However, by applying the first progressive phase shift, it is possible to determine whether the detected small vehicle 1202 is directly in front (i.e., on the line of sight), or the large vehicle 1204 is on the side (i.e., off the line of sight). This detection depends on at least three array conditions, although those skilled in the art will understand that many chirps or frames will be used under these conditions. Under the reference condition, the main beam of the phased transmitting array is positioned on the line of sight, the first phase shift condition positions the main beam at -12.8 degrees, and the second phase shift condition positions the beam at 12.8 degrees.

[0110] Therefore, based on Table I, it can be determined that the object 1202 is detected by the main lobe 1203, and the object 1204 is detected by the first sidelobe 1205. It should be understood that although Figure 12A and Figure 12B show the conditions for two different vehicle types, the present invention is not limited thereto, and vehicles of similar nature can also be detected.

[0111] Figure 13 FIG. shows the detection of two objects 1302 and 1304 using the sidelobes of the bidirectional radiation pattern of the millimeter-wave automotive radar system 900 based on Table I according to an embodiment of the present invention. Here, the two objects are two vehicles 1302 and 1304 that appear side by side with each other. The two vehicles have similar types. It should be understood that if the vehicles appear side by side as Figure 13 shown, both phase shift conditions 1 and 2 of Table I will record an increase in the signal return, i.e., the objects 1302 and 1304 will appear at +18 degrees and -18 degrees respectively, and are detected by the corresponding first sidelobes 1303 and 1305.

[0112] Therefore, if a single object appears off the line of sight, a reading of +3.5 dB will occur for only one of condition 1 or condition 2, but a reading of +3.5 dB for both condition 1 and condition 2 means that the objects 1302 and 1304 appear at +18 degrees and -18 degrees simultaneously respectively, and are detected by the corresponding two sidelobes 1303 and 1305.

[0113] Figure 14It shows that two objects 1402 and 1404 are detected from the bidirectional radiation pattern of the radar system 900, where object 1402 appears on the line of sight (detectable by the main lobe 1403), and object 1404 appears off the line of sight (detectable by the first side lobe 1405). In this case, Table I is not sufficient to enable the radar control system 912 to determine the two objects because one object 1402 is on the line of sight while the other object 1404 is off the line of sight. For this case, the radar control system 912 configures a second look-up table as shown below, which includes a third phase shift condition and a fourth phase shift condition, as well as the corresponding signal return levels relative to the third signal level of Table I.

[0114]

[0115] Table II

[0116] Table II shows the third phase shift condition (3), where when an object has been identified at the second position (i.e., -18 degrees in the counterclockwise direction) when applying the first progressive phase shift, a third progressive phase shift is added between all 3 consecutive transmit antenna elements 904 to move the main beam by a third steering angle, i.e., 35 degrees in the counterclockwise direction. When applying the third progressive phase shift, when the signal return level is 3.5 dB less than the third signal level, a single object is present at the second position (i.e., -18 degrees in the counterclockwise direction) (Table I - phase shift condition (1)). Further, when applying the third progressive phase shift, when the signal return level is 10 dB less than the third signal level (Table I), it can be concluded that one object is present on the line of sight and another object is present at the second position (i.e., -18 degrees in the counterclockwise direction).

[0117] Table II further shows the fourth phase shift condition (4), where when applying the first negative progressive phase shift condition, and an object has been identified at the fourth position (+18 degrees in the clockwise direction) under the second phase shift condition, a fourth progressive phase shift is added between all 3 consecutive transmit antenna elements 904 to move the main beam by a fourth steering angle, i.e., 35 degrees in the clockwise direction. The fourth progressive phase shift is the negative value of the third progressive phase shift and is also referred to as the third negative progressive phase shift hereinafter. When applying the third negative progressive phase shift, when the signal return level is 3.5 dB less than the third signal level, a single object is present at the fourth position (i.e., +18 degrees in the clockwise direction) (Table I - phase shift condition (2)). Further, when applying the third negative progressive phase shift, when the signal return level is 10 dB less than the third signal level (Table I), it can be concluded that one object is present on the line of sight and another object is present at +18 degrees in the clockwise direction.

[0118] Accordingly, various embodiments of the present invention facilitate the measurement of an observed scene using predefined and adjusted two-way antenna radiation patterns (as defined in Tables I and II). It will be apparent to those of ordinary skill in the art that the present invention is not limited to the predefined and adjusted two-way antenna radiation patterns as defined in Tables I and II, and subsequent adjusted two-way antenna radiation patterns using additional additional phase shift values can be observed and recorded at the transmitting element, receiving element, or both the transmitting and receiving elements of the antenna in the system. Thus, the present invention differs from traditional phased array methods in that the present invention actively uses sidelobes to extend the field of view into several additional regions where detection can be performed.

[0119] In the example, the angle and beam squint conditions as described in Tables I and II are specific cases for 3-element and 10-element two-way conditions. However, it will be recognized that the present invention can be extended to any number of elements, sidelobes, or even objects by changing the squint angle and is not limited in any way thereby.

[0120] Although the above examples of Tables I and II have been described for phased array radars, it is equally valid in MIMO systems, where measurements are made with multiple transmitter elements active and progressive phase shifts are applied between the elements in addition to the phase shifts typically employed in MIMO radars. In this regard, MIMO calculations are first performed using the described prior art MIMO radar method, and the measurements are repeated using the method Figure 10 explained. More than one of the M transmitters are simultaneously excited and progressive phase shifts are applied between these transmitters according to the spacing between the transmitter elements and the equivalent settings that will be defined for the system in Tables I and II. When comparing these calculations, the present invention can be used to remove the ambiguity of the detected targets derived from traditional MIMO calculations.

[0121] In addition, predefined and adjusted antenna radiation patterns, as explained in Tables I and II, have been described for the case of an ideal antenna array, where a constant spacing is maintained between each element in the array. However, if the array size is increased (to reduce the beamwidth), some elements can be removed while maintaining the total aperture size, without adversely affecting the array performance. In such a case, as more elements are removed, the sidelobe level becomes higher and may reappear significantly, thus affecting detection in the manner previously described. Such an array is called a sparse array and is advantageous because it reduces the number of receivers required in a radar and thus lowers the cost. However, the number of receivers required in such an array is ultimately limited by the minimum number of elements needed to maintain the array performance while reducing the'regeneration' of these sidelobe levels to an acceptable level. However, the present invention as described can be applied to such an array to turn its limitations into advantages.

[0122] Figure 15 The virtual array radiation pattern 1500 is shown, which is numerically formed for the case of a MIMO radar having three transmit antennas 1502 and four receive antennas 1504, designed such that the spacing between the elements of the 12 - element virtual array 1506 is half - wavelength. In this case, all transmit elements transmit individually, although it has been shown in the present invention that if all transmit antennas transmit simultaneously (using DDMA, BPM or other types of modulation), the virtual (or two - way) radiation pattern 1500 remains unchanged.

[0123] Figure 16 Shows the effect of a 40 - degree progressive phase shift on Figure 15 the radiation pattern of the transmit array 1502 when all three transmit elements are simultaneously excited. In the context of the present invention, the progressive phase shift can be added between the simultaneously excited transmit elements of a MIMO radar in a manner similar to Figure 7 as shown. It should be noted that although Figure 7 and Figure 16 both radiation patterns contain diagrams of 3 - element arrays, their shapes are different due to the spacing between the elements. However, Figure 17The virtual or bi-directional radiation patterns therein illustrate the same effect, where the detections found by the sidelobes are determined in a manner similar to that previously described. Those skilled in the art will also understand that a progressive phase shift can be added between the receiving elements that are simultaneously excited without affecting the performance of the present invention. In MIMO radars, it is a well-known technique to mitigate sidelobes by using sub-arrays to remove the influence of sidelobes from the radar analysis. Such techniques include removing portions of the virtual array from the DSP analysis, or analyzing different portions of the virtual array prior to comparison with a full virtual array analysis. However, such techniques reduce the range over which detections can be made and are distinguishable from the present invention.

[0124] In the specification, the terms “comprise, comprises, comprised and comprising” or any variation thereof and the terms “include, includes, included and including” or any variation thereof are considered to be interchangeable and they should all be given the broadest possible interpretation and vice versa.

[0125] The present invention is not limited to the embodiments described above, but may vary both in construction and detail.

Claims

1. A method for sensing an environment using a radar system, comprising: Setting a two-way signal return level of a main lobe at an optical axis as a reference level; Applying a progressive phase shift among a plurality of antenna elements of the radar system for moving the main lobe to a position outside the optical axis to increase a two-way signal return level of at least one side lobe; When applying the progressive phase shift, recording a signal return level of the two-way radiation pattern relative to the reference level; And Detecting at least one object at or off the optical axis based on comparing the applied progressive phase shift and the recorded signal return levels with a look-up table including a set of phase shift conditions, wherein each phase shift condition includes a progressive phase shift applied among the plurality of antenna elements and corresponding multiple recorded signal return levels for detecting at least one object on or off the optical axis.

2. The method according to claim 1, wherein The plurality of antenna elements include a plurality of simultaneously excited transmit antenna elements of a MIMO radar.

3. The method according to any one of the preceding claims, wherein The look-up table includes: A first phase shift condition, the first phase shift condition including a first progressive phase shift for moving the main lobe away from the optical axis by a first steering angle, and corresponding signal levels for detecting objects at the optical axis, at a first off-axis position, and at a second off-axis position when applying the first progressive phase shift; and A second phase shift condition, the second phase shift condition including a second progressive phase shift for moving the main lobe away from the optical axis by a second steering angle, and corresponding signal levels for detecting objects at the optical axis, at a third off-axis position, and at a fourth off-axis position when applying the second progressive phase shift.

4. The method according to claim 3, wherein The look-up table further includes: A third phase shift condition, the third phase shift condition being applicable when an object is identified at the second off-axis position under the first phase shift condition, wherein the third phase shift condition includes a third progressive phase shift for moving the main lobe away from the optical axis by a third steering angle, Corresponding signal return levels for concluding that a single object exists at the second off-axis position when applying the third progressive phase shift, and Corresponding signal return levels for concluding that one object exists at the optical axis and another object exists at the second off-axis position when applying the third progressive phase shift.

5. The method according to claim 4, wherein The look-up table further includes: A fourth phase shift condition, the fourth phase shift condition being applicable when an object is identified at the fourth off-axis position under the second phase shift condition, wherein the fourth progressive phase shift condition includes applying a fourth progressive phase shift for moving the main lobe away from the optical axis by a fourth steering angle, Corresponding signal return levels for concluding that a single object exists at the fourth off-axis position when applying the fourth progressive phase shift, and Corresponding signal return levels for concluding that one object exists at the optical axis and another object exists at the fourth off-axis position when applying the fourth progressive phase shift.

6. The method according to any one of the preceding claims, wherein, The second progressive phase shift is a negative value of the first progressive phase shift, the fourth progressive phase shift is a negative value of the third progressive phase shift, the second steering angle is a negative value of the first steering angle, and the fourth steering angle is a negative value of the third steering angle.

7. The method according to any one of the preceding claims, further comprising determining the size of the detected object based on the value of the signal return level, the detection range, and the actual number of return signals from a given area.

8. The method according to claim 1, wherein, The plurality of antenna elements includes a plurality of transmit antenna elements, a plurality of receive antenna elements, or a combination of both.

9. The method according to any one of the preceding claims, wherein, The progressive phase shifts are independently applied to the plurality of transmit antenna elements and receive antenna elements.

10. The method according to any one of the preceding claims, wherein, Each receive antenna element is configured with a fixed or switched beam pattern, and preferably, wherein the plurality of antenna elements are configured using a beamforming network.

11. The method according to any one of the preceding claims, further comprising applying one or more subsequent progressive phase shifts between the plurality of antenna elements to introduce further attenuation on the sidelobes or the main lobe of the bidirectional radiation pattern.

12. The method according to any one of the preceding claims, further comprising recording and analyzing the signal return level of the bidirectional radiation pattern when the signal return level of at least one sidelobe exceeds a predefined threshold while applying the progressive phase shift.

13. The method according to any one of the preceding claims, wherein, The spacing between the plurality of antenna elements is unequal.

14. The method according to any one of the preceding claims, wherein, The plurality of antenna elements are consecutive antenna elements.

15. A radar system (900) comprising: at least one transmitter (902), a plurality of transmit antenna elements (904), and a plurality of variable phase shifter components (906) connected between the at least one transmitter (902) and the plurality of transmit antenna elements (904); at least one receiver (908), a plurality of receive antenna elements (910), and a plurality of variable phase shifter components connected between the at least one receiver (908) and the plurality of receive antenna elements; and a radar control system (912) for implementing the method according to any one of claims 1 to 14.

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