Bidirectional radar beam pattern steering

Abstract

A method for sensing an environment using a radar system includes applying a gradual phase shift between multiple antenna elements of the radar system and recording a signal return level of a bidirectional radiation pattern upon application of the gradual phase shift, wherein the gradual phase shift moves a main lobe to a position off-boresight and increases a signal return level of at least one side lobe, and at least one object is detected at an off-boresight position based on the increased signal return level of the at least one side lobe.

Description

[Technical Field]

[0001] The present disclosure relates to steering bidirectional radar beam patterns, and more particularly to detecting objects using sidelobes of bidirectional radar beam patterns. [Background technology]

[0002] In radar systems, the far-field radiation pattern of an antenna array typically consists of numerous local maxima and minima in three-dimensional space. The highest maxima, known as the main lobe or main beam, may be fixed or scannable using hardware or digital signal processing techniques. Other maxima are known as side lobes. Objects detected by radar are typically assumed to arrive from the angular direction corresponding to the main beam. However, at angles corresponding to the side lobes, the transmitted (or received) signal level is high compared to other areas and is significant compared to the area focused by the main beam. Therefore, high side lobes can cause object reflections from both the angular direction of the main beam and the angular direction of the side lobes, generating clutter (or unwanted echoes) that can cast doubt on the location and number of detected objects, leading to ambiguity.

[0003] Many sidelobe cancellation (SLC) methods have been reported to solve this problem. SLC systems use the basic principle of subtracting interfering signals (due to sidelobes) from the antenna output, a method similar to many adaptive cancellation techniques used to remove interference and multipath signals in today's communications systems. Even radars with inherently low sidelobe levels can exhibit problems as a result of electronic attacks or "jamming," rather than due to clutter caused by signals picked up by the sidelobes within the radar signal. In this way, when a radar is jammed, the detected clutter is caused by external signals, not an inherent characteristic of the radar.

[0004] Figure 1 shows a basic interference canceller, with the top antenna being the "main" radar antenna (V MAIN (t)), and the bottom antenna is an auxiliary antenna (V AUX (t)). The inverting gain block (K) converts the main channel signal V MAIN (t) to the auxiliary channel signal V AUX The error voltage V is formed by subtracting a weighted version of (t) ERR (t) is adjusted accordingly.

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[0005] If the value of K is set correctly, the error signal V ERR We can see that (t) contains only the target, or desired, signal. Of course, Figure 1 assumes that the auxiliary channel signal consists solely of interfering signals, which is unlikely in practice.

[0006] Sidelobe cancellation (SLC) can be considered an extension of Space-Time Adaptive Processing (STAP), a signal processing technique that uses multidimensional signal processing techniques to filter in the space-time domain across multiple dimensions with the goal of eliminating interference. In this regard, STAP has been used in MIMO radar, specifically to improve spatial resolution against large amounts of clutter caused by the virtual array of MIMO radars.

[0007] Figure 2 shows the radar equivalent circuit signal path, from which the well-known radar equations are derived.

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[0008] compound term G t (θ,φ)G r (θ,φ)(hereinafter G t G r The bidirectional antenna gain is often plotted as a bidirectional radiation pattern, which may take the form of a three-dimensional plot on a spherical coordinate geometry or a two-dimensional "cut" where either θ or φ are set to a constant value. The bidirectional radiation pattern is therefore a key design element for radar, as its design and modification directly impacts the three-dimensional spatial region where interference and clutter can occur and appear in radar detection. In this regard, the sidelobe levels of the bidirectional pattern are typically kept to less than one thousandth of the power of the main beam to minimize the probability of clutter being detected due to the radar's antenna pattern. There are many methods used to do this for antenna arrays, and more specifically for MIMO radars. These include "scaling / tapering / weighting" to form beam patterns in which the signal strength is amplified or attenuated for various antenna elements (or individual radiators within the entire antenna) to manipulate the overall shape of the combined beam. Another method involves "placement," which changes the spacing between antenna elements in the array, thereby changing how their radiation fields combine and altering the overall beam shape.

[0009] G t G r By examining the term in more detail, the radiation pattern of the transmitter G t The angular region where is the smallest is called the receiver radiation pattern G rBy aligning with the point where is maximum, or vice versa, it can be inferred that the resulting two-way pattern will have low sidelobes or no areas prone to interference or signal clutter. Figure 3 shows a two-way pattern with low sidelobes or no areas prone to interference or signal clutter. However, such methods are often difficult to achieve, requiring more complex antenna feed structures, more antenna elements in the array, and larger antenna apertures (or areas).

[0010] Furthermore, in MIMO radar, multiple transceivers are coordinated, with antennas placed close to each other and working together to form a "virtual" beamforming array. However, the ability to form this virtual array in this manner is limited because the transmit and receive antenna elements typically have radiation patterns with very wide main lobes (typically greater than 80°) and angular processing is performed digitally, for example, using digitally sampled mixer outputs of the receive and transmit signals from each receive antenna. In other embodiments, if the beamforming network is fixed or uses a network that is difficult to beamform (such as in lens-type structures, which have the advantage of being able to design multi-beam radars with various fields of view (FOV) by varying the shape of the lenses or their geometry relative to the antenna elements), such structures tend to have large sidelobe levels that must be considered or removed when decoding the radar signal return.

[0011] US2021 / 083395 discloses a radar system for object detection using a metamaterial device. In this radar system, the antenna material can be bent to change the phase between elements. The system also describes performing a raster scan and adjusting the antenna to locate objects within the antenna's sidelobe region. Furthermore, the system is limited to detecting objects in the mainlobe or sidelobe. The document also describes scanning the receiving antenna at a predetermined angle. However, adding a phase shifter to achieve this on the receiving side adds significant signal noise to the system, reducing the system's range, unless additional costs are added, such as an LNA.

[0012] Japanese Patent Application Laid-Open No. 2-12082 discloses that the accuracy of built-in testing equipment (BITE) functions is improved by generating an object to be inspected at an off-boresight angle. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 083395 [Patent Document 2] Japanese Patent Application Publication No. 2-12082 Summary of the Invention [Problem to be solved by the invention]

[0014] In view of the above, there is a need for an antenna configuration that facilitates the removal of signal clutter from radar signal detection and simplifies radar antenna design and radar signal processing algorithms. [Means for solving the problem]

[0015] The present invention relates to an electronic beam steering antenna.

[0016] In one aspect, a method of sensing an environment using a radar system is provided, the method including: setting a two-way signal return level of a main lobe at a boresight as a reference level; applying incremental phase shifts between a plurality of antenna elements of the radar system to move the main lobe to a position other than the boresight to increase a two-way signal return level of at least one side lobe; recording the signal return level of the two-way radiation pattern relative to the reference level upon application of the incremental phase shifts; and detecting at least one object at a boresight or off-boresight location based on comparing the applied incremental phase shifts and the recorded signal return levels to a lookup table, the lookup table including a set of phase shift conditions, each phase shift condition including an incremental phase shift to apply between the plurality of antenna elements and a corresponding plurality of recorded signal return levels for detecting at least one object on or off-boresight.

[0017] In one embodiment of the present invention, the plurality of antenna elements includes multiple simultaneously excited transmit antenna elements of a MIMO radar.

[0018] In one embodiment of the present invention, the lookup table includes a first phase shift condition including a first gradual phase shift for moving the main lobe away from the boresight by a first steering angle and corresponding signal levels for detecting objects at the boresight, a first off-boresight position, and a second off-boresight position when the first gradual phase shift is applied; and a second phase shift condition including a second gradual phase shift for moving the main lobe away from the boresight by a second steering angle and corresponding signal levels for detecting objects at the boresight, a third off-boresight position, and a fourth off-boresight position when the second gradual phase shift is applied.

[0019] In one embodiment of the present invention, the lookup table includes a third phase shift condition that is applied when an object is identified as being at a second off-boresite location under the first phase shift condition, the third phase shift condition including a third incremental phase shift for moving the main lobe away from the boresite by a third steering angle, corresponding signal return levels for concluding that a single object is present at the second off-boresite location upon application of the third incremental phase shift, and corresponding signal return levels for concluding that one object is present at the boresite and another object is present at the second off-boresite location upon application of the third incremental phase shift.

[0020] In one embodiment of the present invention, the lookup table includes a fourth phase shift condition that is applied when an object is identified at a fourth off-boresite location under the second phase shift condition, the fourth phase shift condition including applying a fourth incremental phase shift to move the main lobe away from the boresite by a fourth steering angle; corresponding signal return levels for concluding that a single object is present at the fourth off-boresite location upon application of the fourth incremental phase shift; and corresponding signal return levels for concluding that one object is present at the boresite and another object is present at the fourth off-boresite location upon application of the fourth incremental phase shift.

[0021] In one embodiment of the present invention, the second gradual phase shift is the negative of the first gradual phase shift, the fourth gradual phase shift is the negative of the third gradual phase shift, the second steering angle is the negative of the first steering angle, and the fourth steering angle is the negative of the third steering angle.

[0022] In one embodiment of the present invention, the method further includes determining the size of the detected object from the signal return level values, the detected range, and the actual number of returned signals from a given area.

[0023] In another aspect of the invention, a method of sensing an environment using a radar system is provided, the method including applying incremental phase shifts between multiple antenna elements of the radar system to detect an object at a boresight of a two-way radiation pattern of the radar system, recording signal return levels of the two-way radiation pattern upon application of the incremental phase shifts, the incremental phase shifts moving a main lobe to an off-boresight location and increasing the signal return level of at least one side lobe, and detecting at least one object at the off-boresight location based on the increased signal return level of the at least one side lobe.

[0024] In one embodiment of the present invention, the plurality of antenna elements includes multiple simultaneously excited transmit antenna elements of a MIMO radar.

[0025] In one embodiment of the present invention, the method includes applying a first negative progressive phase shift between a plurality of antenna elements, the first negative progressive phase shift being a negative of the first progressive phase shift, to move a main lobe to an off-boresight position and increase a level of at least one side lobe on another side of the main lobe to detect at least one object at an off-boresight position on the other side.

[0026] In one embodiment of the present invention, the at least one object is detected based on a predefined lookup table, which includes a list of predefined incremental phase shifts and, for each predefined incremental phase shift, signal return levels for detecting an object on either side of the boresight and off-boresight.

[0027] In one embodiment of the present invention, the method further includes generating the lookup table by setting the two-way signal return level at the boresight as a reference level when conventional phase shifts are applied; applying a first incremental phase shift between the plurality of antenna elements to determine, for the first incremental phase shift, a first signal level for detecting an object at the boresight, a second signal level for detecting an object at a predetermined position off-boresight on one side, and a third signal level for detecting an object at a predetermined position off-boresight on the other side, each of the first, second, and third signal levels being determined relative to the reference level; and applying a first negative incremental phase shift to determine, for the first negative incremental phase shift, a first signal level for detecting an object at the boresight, a third signal level for detecting an object at a predetermined position off-boresight on one side, and a second signal level for detecting an object at a predetermined position off-boresight on the other side.

[0028] In one embodiment of the present invention, the method includes generating a lookup table by applying a second incremental phase shift when an object is detected at a third signal level at an off-boresight location on one side when applying the first incremental phase shift, concluding that a single object is present at the off-boresight location on one side if the signal return level is less than the third signal level by a first value when applying the second incremental phase shift, and concluding that one object is present at the boresight and another object is present at the off-boresight location on one side when applying the second incremental phase shift,

[0029] In one embodiment of the present invention, the method includes generating the lookup table by applying a second negative progressive phase shift when an object is detected at an off-boresight location on the other side at a third signal level upon application of the first negative progressive phase shift, concluding that a single object is present at the off-boresight location on the other side if, upon application of the second negative progressive phase shift, the signal return level is less than the third signal level by a first value, and concluding that one object is present at the boresight and another object is present at the off-boresight location on the other side if, upon application of the second negative progressive phase shift, the signal return level is less than the third signal level by a second value.

[0030] In one embodiment of the present invention, the plurality of antenna elements includes a plurality of transmitting antenna elements, a plurality of receiving antenna elements, or a combination of both.

[0031] In one embodiment of the present invention, the gradual phase shifts are applied independently to multiple transmit and receive antenna elements.

[0032] In one embodiment of the present invention, each receive antenna element is configured in a fixed beam shape or a switched beam shape.

[0033] In one embodiment of the present invention, the method further includes applying one or more subsequent incremental phase shifts between the plurality of antenna elements to introduce further attenuation on the side lobes or on the main lobe of the bidirectional radiation pattern.

[0034] In one embodiment of the present invention, the multiple antenna elements are configured using a beamforming network.

[0035] In one embodiment of the present invention, the method further comprises recording and analyzing the signal return level of at least one side of the bidirectional radiation pattern upon application of the gradual phase shift when the signal return level of the lobe of at least one side exceeds a predefined threshold.

[0036] In one embodiment of the present invention, the spacing between the antenna elements is non-uniform.

[0037] In one embodiment of the present invention, the plurality of antenna elements are contiguous antenna elements.

[0038] In one embodiment of the present invention, a radar system is provided that includes at least one transmitter, a plurality of transmit antenna elements, a plurality of variable phase shifter components connected between the at least one transmitter and the plurality of transmit antenna elements, at least one receiver, a plurality of receive antenna elements, a plurality of variable phase shifter components connected between the at least one receiver and the plurality of receive antenna elements, and a radar control system.

[0039] Also provided is a computer program comprising program instructions for causing a computer program to carry out the above method, which may be embodied on a record medium, a carrier signal or a read-only memory.

[0040] Various embodiments of the present invention disclose a bidirectional radar beam pattern steering method that gleans relevant information from the inherent side lobes of the antenna radiation pattern, rather than removing or mitigating them by methods such as filtering, to build a more detailed view of the environment. Such a method can help remove signal clutter from radar signal detection, increase the moving field of view, improve discrimination between targets in analog and digital automotive radar, and distinguish between real and miscalculated identified objects, simplifying radar antenna design and radar signal processing algorithms. [Brief explanation of the drawings]

[0041] The invention will be more clearly understood from the following description of embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which: [Figure 1] 1 shows a prior art configuration of a conventional interference canceller. [Figure 2] The signal path of the radar equivalent circuit is shown. [Figure 3] Shows how the two-way radiation pattern shape changes compared to the individual antenna radiation patterns. [Figure 4] A conventional uniform linear array configuration of eight receiving element antennas and an equivalent MIMO configuration using two transmitting elements and four receiving elements are shown. [Figure 5] The normalized "boresight" radiation pattern for a 10-element linear array with elements spaced half a wavelength apart is shown. [Figure 6] Three situations are shown that give identical radar returns for objects detected using the array of FIG. [Figure 7] The effect of a 40 degree gradual phase shift in a three-element phased array is shown. [Figure 8] The effect on the bi-polarized radiation pattern of a 3-element transmit antenna and a 10-element receive antenna is shown, along with a 40-degree incremental phase shift to the transmit antenna with the receive antenna scanned at 0 degrees. [Figure 9] 1 illustrates a millimeter automotive radar system according to an embodiment of the present invention. [Figure 10] 3 is a flowchart illustrating a method for scanning an environment around a vehicle, according to one embodiment of the present invention. [Figure 11] 10 is a flowchart illustrating a method for scanning an environment around a vehicle with the millimeter automotive radar system of FIG. 9 in accordance with another embodiment of the present invention. [Figure 12A] FIG. 1 illustrates the detection of a single object using side lobes of a phased array radar bidirectional radiation pattern in accordance with an embodiment of the present invention. [Figure 12B] FIG. 1 illustrates the detection of a single object using side lobes of a phased array radar bidirectional radiation pattern in accordance with an embodiment of the present invention. [Figure 13] FIG. 1 illustrates the detection of two objects using side lobes of a phased array radar's bidirectional radiation pattern, according to an embodiment of the present invention. [Figure 14]1 illustrates the detection of two objects, one occurring in the boresight, from a bidirectional radiation pattern of a phased array radar, according to an embodiment of the present invention. [Figure 15] Normalized array gain is shown for a virtual 12-element array generated by a MIMO system with three transmit and four receive elements, digitally scanned at 0 degrees. [Figure 16] 15 shows the effect of a 40 degree incremental phase shift on the transmit radiation pattern when all three transmit elements are excited simultaneously in the transmit array shown in FIG. [Figure 17] 1 illustrates an implementation of the present invention in a MIMO array. DETAILED DESCRIPTION OF THE INVENTION

[0042] Figure 4 shows a traditional eight-receive element antenna configuration and an equivalent MIMO configuration. Traditional digital beamforming architectures incorporate a dedicated receiver for each antenna element. However, as the size of the antenna array increases, the number of required receivers becomes prohibitive for applications such as automotive radar. When low angular accuracy is required, a wide beam is sufficient, which can be achieved when a small number of antenna elements are used, thereby minimizing the number of receivers used. However, when high angular accuracy is required, a narrower beam is required, and a larger antenna array with additional elements must be utilized.

[0043] Those skilled in the art know that in a multiple-input multiple-output (MIMO) radar, measuring the magnitude and phase of signals received by N receivers (multiple outputs) for each of M transmitters (multiple inputs) can be used to create a "virtual" receive array larger than the physical receive array. There are various modulation schemes for MIMO that aim to orthogonalize the signals transmitted by individual transmitters so that they can be separated at the receiver. These schemes include, but are not limited to, time division multiplexing (TDM), frequency division multiplexing (FDM), and binary phase multiplexing (BPM). In TDM MIMO, transmitters transmit signals one at a time sequentially. The receiving elements then receive the signals from each transmitter sequentially in time, allowing them to be separated according to which transmitter they originated from. When the spacing between the transmit and receive elements is appropriately set, the signals at each receiver can be rearranged to correspond to the transmitter from which they originated, and the phase difference between each received radiation wave makes it appear as if there are equivalently more receive elements than actually exist, resulting in the creation of "virtual" elements. The virtual array consists of (M × N) elements, but uses only (M + N) physical antenna elements, far exceeding the physical number of transmitters and receivers required. Therefore, MIMO technology is effective in improving the angular resolution of a radar for a given number of transceivers or reducing the number of transceivers required for a given angular resolution. Digital signal processing (DSP) techniques for TDM MIMO systems are well known, and after ADC sampling, multiple fast Fourier transforms (FFTs) and constant false alarm rate (CFAR) thresholding are performed on each virtual element to determine the direction and velocity of each detection.

[0044] The focusing effect caused by such a virtual array can be mathematically expressed in terms of the array factor, which, for MIMO radar, is a complex representation of the far-field radiation pattern of an isotropic radiator (i.e., a theoretical antenna that has no directionality and radiates equal energy in all directions). The one-dimensional array factor of a linear array is calculated at each discrete angle θ using the following equation:

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[0045] If the array factor is calculated using the element positions in the array and multiplied by the radiation pattern of a single physical antenna element in the array (i.e., a real element with its own complex radiation pattern), the resulting radiation pattern will be a good approximation of the radiation pattern of the array (not including effects such as mutual coupling between elements in the physical array that can modify the pattern). In decibel form, the gain of the array is given by:

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[0046] The combined gain of the arrays of the transmit and receive antennas forms a two-way pattern that is equivalent to the pattern formed using all elements in the virtual array of the MIMO radar.

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[0047] These functions are used to calculate where possible sidelobes will occur (excluding external influences such as jamming signals), and are generated by the number of elements in the array and their positions relative to each other.

[0048] Referring again to Figure 4, it becomes clear that when a MIMO system is used in TDM mode, it is not possible to measure all virtual elements in the MIMO system simultaneously, and the measurement must be repeated M times at each "real" receiving element, where M is the number of transmitters used.

[0049] If the antenna element positions are fixed, one way to control the sidelobes is scaling / tapering, which is done by the weighting term w nThis is achieved by adjusting the size of the element, applied either through post-processing using DSP techniques (e.g., MIMO) or as part of the feed network (e.g., phased array). However, this typically has the adverse effect of reducing the gain of the array unless amplification at specific elements (thus adding cost to the system) is applied. The impact and problem of side lobes when no scaling is applied is illustrated in Figure 5, which shows the normalized radiation pattern of a 10-element array scanned at boresight with inter-element spacing set to half the wavelength of the operating frequency. Here, the first side lobe appears 18 degrees off boresight and is approximately 13 dB lower than the main beam. This means that at a distance of 50 m, a vehicle 15 m to the left or right of the radar could be interpreted as being directly in front of the host vehicle. Furthermore, it is intuitively clear that the amount of radar signal "reflected" by a detected object depends on the size of the object, so a large vehicle to the side could be mistaken for a smaller vehicle directly in front. The amount of radar return an object provides, known as the object's radar cross section (RCS), varies depending on the object's size, shape, and material. Alternatively, the size of a detected object can be determined from the signal return level, the detected range, and the actual number of return signals from a given area. Typical RCS values ​​for moving vehicles indicate that, on average, a truck or lorry provides a radar return 10 to 100 times stronger than a passenger car, which in turn provides a radar return 10 times stronger than a motorcycle. This means that if a radar detects a truck on its sidelobe pattern at a specific distance / speed, it is likely to appear at the boresight with the same received signal strength as a passenger car at the same distance / speed. Similarly, if a radar detects a passenger car on its sidelobe pattern at a specific distance / speed, it is likely to appear at the boresight with the same received signal strength as a motorcycle at the same distance / speed. Figure 6 therefore shows three examples giving the same radar measurements for the detection of a single vehicle and the conditions mentioned above, using an omnidirectional transmitting antenna.This problem can be solved for single vehicle detections using known side lobe removal or mitigation techniques, but for the case shown in Figure 6, when two or all of these scenarios are combined, the radar detections will be combined to indicate a single object.

[0050] Figure 7 shows the effect of a 40-degree incremental phase shift on a three-element transmit antenna array. In a phased array, at the nth element, an incremental phase delay of (n-1)Φ may be added across the linear array, where Φ is the additional phase delay. Thus, to steer the beam to each angle θ in three-dimensional space, there exists a specific value of Φ in the following equation:

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[0051] When these conditions are applied, the peak radiation pattern or main beam direction is shifted, in the described case by θ degrees off-boresight, without mechanically or physically moving any individual antenna. Thus, the steering angle of the array is easily controlled by varying the phase of the individual elements. Figure 7 shows the effect on a three-element transmit antenna array, comparing the radiation pattern of a typical three-element array with no phase variation to the radiation pattern with a 40-degree incremental phase delay that shifts the main beam -12.8 degrees off-boresight. The phase delay in this case was specifically chosen to account for its effect on bidirectional radiation using a 10-element receive array.

[0052] Figure 8 compares two two-way radiation patterns (with and without incremental phase delay on the transmit antenna) in polar plots, providing a more representative visualization of real-world conditions. It also shows the effect on sidelobes of rotating the main beam by angle, specifically, the significant sidelobe at 18 degrees, which is reduced by an additional 10 dB. Importantly, the other sidelobe occurring at -18 degrees increases by a small amount (3.5 dB), while the two-way boresight level also decreases by <1.4 dB. When the incremental phase delay on the transmit antenna is reversed, the beam is steered in the opposite direction, and the effect on the sidelobes is reversed.

[0053] FIG. 9 illustrates 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 for any radar system, such as defense or combat systems, but more specifically, can be applied to automotive radar safety systems (ADAS). The millimeter-wave automotive radar system 900 includes at least one transmitter 902, a plurality of transmitting antenna elements 904, and a plurality of variable phase shifters or time delay elements 906, the number of which is equal to the number of transmitting antenna elements 904, connected between the at least one transmitter 902 and the transmitting antenna elements 904. The millimeter-wave automotive radar system 900 further includes at least one receiver 908 and a plurality of receiving antenna elements 910. The number of transmitting antenna elements 904 and the number of receiving antenna elements 910 may be the same or different depending on the required angular resolution and radar detection range.

[0054] In one embodiment of the present invention, each receive antenna element 910 may be configured with a fixed or switched beam shape. In another embodiment of the present invention, the receive antenna elements of the radar system 900 may be configured with a beamforming network (e.g., a lens structure) that can shift the main beam to a specific angle off-boresight in three-dimensional space. Such designs are known to present significant challenges in maintaining low sidelobe levels, but the present invention can be applied in these respects to take advantage of the sidelobes.

[0055] Alternatively, lens-based beamforming networks may be used on both the transmit and receive antenna elements, with the time delay component 906 taking the form of a lens with multiple input ports excited and with amplitude tapering to modify the beam shape. This allows for a simpler and / or cheaper and / or easier to build lens design, allowing for fewer transceivers to be used with a narrower field of view to achieve high angular resolution. It also allows for a larger number of antenna elements than the number of receivers / transmitters, reducing FFT processing and facilitating implementation with larger RF bandwidths.

[0056] In another embodiment of the present invention, multiple variable phase shifters or time delay components (not shown), in a number equal to the number of receive antenna elements 910, may be connected between at least one receiver 908 and the receive antenna elements 910. Thus, the "phased array" (or alternative methods of steering) may be moved from the transmit side to the receive side or to baseband, thereby providing greater flexibility in PCB layout and potentially reducing overall size and cost.

[0057] In yet another embodiment of the present invention, the number of variable phase shifters or time delay elements 906 is equal to the total number of transmit antenna elements 904 and receive antenna elements 910 .

[0058] In one embodiment of the present invention, the phase shift between the transmit and receive antenna elements may be incorporated using switched delay lines.

[0059] In yet another embodiment of the present invention, mm-wave transmitter 902 and mm-wave receiver 908 are replaced with a mm-wave transceiver unit.

[0060] Furthermore, in one example, elements 902-910 form a phased array radar.

[0061] The millimeter-wave automotive radar system 900 further includes a radar control system 912 communicatively coupled to the elements 902-910 to control the operation of the elements 902-910. 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.

[0062] In one embodiment of the present invention, the millimeter wave automotive radar system 900 is configured to electronically sense the vehicle's surrounding environment using electromagnetic signals to determine object location, eliminate false object detections, and discriminate between objects.

[0063] Furthermore, it should be noted that the millimeter-wave automotive radar system 900 uses frequency-modulated continuous wave (FMCW) modulation for signal transmission and reception. An FMCW waveform, also known as a chirp, is a complex sine wave whose frequency increases linearly with time. FMCW radar transmits chirps at a period called the pulse repetition interval (PRI), most often in a sawtooth configuration, although other chirp types exist. 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 results in a complex sine wave. This waveform is called a beat signal, and its frequency is proportional to the distance to the detected object. By collecting multiple chirps within a single "frame," Doppler frequency changes in the "slow time" dimension can be determined.

[0064] Beat frequency estimation is typically performed in the digital domain after digitally sampling the beat signal. Because the beat frequency is much smaller than the radar bandwidth, a slow analog-to-digital converter (ADC) can be used. By sampling the beat signal and placing each chirp sample in a separate column of a matrix, the row index of the matrix corresponds to the "fast" time span of a single chirp, while the column index corresponds to the "slow" time span of multiple chirps. Applying a Fast Fourier Transform (FFT) to each column of the matrix determines the object's range through the detection of its beat frequency, and applying an additional FFT along the rows of the matrix determines the object's velocity through the detection of its Doppler frequency. This use of two FFTs, commonly referred to as a 2D FFT, allows for the determination of both range and velocity of the object. Performing a 2D FFT has the advantage of reducing the noise level through matched filtering of the object's beat frequency and Doppler frequency. Obviously, the number of objects in the same range-velocity range is usually small, depending on the range and velocity resolution of the radar.

[0065] While range-velocity plots provide a lot of useful information, they lack detail about the angular position of objects. This is overcome by taking instantaneous range-velocity plots at each receive port, rearranging the data to form a virtual array, and performing a third "angular" or 3D FFT. A Constant False Alarm Rate (CFAR) thresholding step follows, whereby only bins with a signal-to-noise ratio above a certain threshold are retained. It is these levels that directly relate to the two-way radiation pattern. In other words, where an object is present, the signal return will be high, thus exceeding the CFAR threshold, where the two-way radiation pattern level (or virtual array pattern) will be high.

[0066] FIG. 10 is a flow chart illustrating a method for scanning an environment around a vehicle, according to one embodiment of the present invention.

[0067] In step 1002, a two-way signal return level of the main lobe at the boresight is set as a reference level. In step 1004, incremental phase shifts are applied between multiple antenna elements of the radar system to move the main lobe to a position other than the boresight to increase the two-way signal return level of at least one side lobe. In step 1006, the signal return level of the two-way radiation pattern is recorded relative to the reference level upon application of the incremental phase shifts. In step 1008, at least one object is detected at a boresight or off-boresight location based on comparing the applied incremental shifts and the recorded signal return levels to a lookup table. The lookup table includes a set of phase shift conditions, each phase shift condition including an incremental phase shift to apply between multiple antenna elements and a corresponding plurality of recorded signal return levels for detecting at least one object on or off the boresight.

[0068] 11 is a flow chart illustrating a method for scanning the environment around a vehicle with a millimeter vehicle-mounted phased array radar system 900 in accordance with another embodiment of the present invention. Those skilled in the art will appreciate that the method may be applied to phased array radars as well as MIMO systems where measurements are taken with multiple transmitter elements active.

[0069] 11, the radar control system 912 is configured to record signal return levels of the two-way radiation pattern of the system 900 at the receiving elements with respect to range, angle, and velocity, analyze the data, and record object detections in the base reference signal. Hereinafter, the main lobe two-way signal level at the boresight may be referred to as the base reference signal, and the corresponding two-way beam pattern may be referred to as the base reference pattern.

[0070] In step 1104, the radar control system 912 is configured to apply a gradual phase shift or time delay between successive antenna elements 904. The antenna elements may be either transmitting or receiving antenna elements, or a combination of both. It will be apparent to those skilled in the art that the gradual phase shift may be applied independently to the transmitting and receiving antenna elements, and that the phase shift or time delay may be varied to interrogate different regions of two-dimensional space. In one embodiment of the present invention, the gradual phase shift moves the main beam to either side of the boresight and increases the level of at least one side lobe on the other side of the main beam to detect at least one object at an off-boresight location on the other side. In the context of the present invention, gradual phase shifts with amplitude weighting may be introduced between multiple excited transmitting antenna elements to introduce different attenuation in the side lobe region than in the main lobe region.

[0071] The application of gradual phase shifts is described in more detail with reference to FIG. 8. FIG. 8 shows a base reference beam pattern 802 and a two-way pattern 804 obtained by applying a 40° gradual phase shift in addition to a conventional phase shift. When a 40° gradual phase shift is applied, the signal level of the main beam decreases, but not significantly (<2 dB). Two-way sidelobes that appear on the other side of the main beam (due to interactions) increase in size (~5 dB). Making the gradual phase shift negative reverses these effects. The change in signal return indicates the location of the sidelobes and whether an object appears at the main beam location. By adding more gradual phase shifts and moving the TX array's main beam to a further off-boresite position, which keeps one sidelobe level the same but significantly attenuates the main beam, additional changes in the two-way signal level can be measured (and used to identify whether more objects are present in the beam).

[0072] 11 , in step 1106, the radar control system 912 records signal return levels detected by normal operation of the phased array radar / MIMO radar. In one embodiment of the present invention, the radar control system 912 is configured to record the signal return levels of at least two additional measurements when the signal return levels exceed a predefined threshold and compare the recorded signal levels to a reference level. In step 1106, the radar control system 912 is configured to analyze the signal return levels and record an object detection.

[0073] In step 1108, the radar control system 912 is configured to check whether a subsequent incremental phase shift needs to be applied. If a subsequent phase shift or additional measurements are required, the process returns to step 1104. Subsequent incremental phase shifts may be introduced between multiple excited transmit antenna elements to introduce further differential attenuation in the sidelobe regions or on the mainlobe. Similar incremental phase shifts may also be introduced between excited transmit antenna elements that are negative relative to the subsequent incremental phase shift.

[0074] If no subsequent phase shifts need to be applied, then in step 1110, radar control system 912 is configured to compare signal return levels and identify an object. When the signal return levels of those measurements made with the subsequent phase shifts are compared to the base reference level measurements of at least one side lobe, radar control system 912 determines whether an object is present on the side lobe. In step 1112, radar control system 912 is configured to display the output.

[0075] In one embodiment of the present invention, the radar control system 912 is configured to detect at least one object using a predefined lookup table that includes a list of predefined incremental phase shifts and corresponding signal return levels for identifying objects on the boresight and side lobes on either side of the boresight. The lookup table may be generated by setting the two-way signal return level at the boresight as a reference level and then measuring the signal return level of the side lobes relative to the reference level for various incremental phase shifts.

[0076] An exemplary lookup table is shown in Table 1. [Table 1]

[0077] Table 1 shows a first phase condition involving a first incremental phase shift to move the main beam away from the boresight by a first steering angle, equivalent to shifting the main beam counterclockwise by 12.8 degrees, between three consecutive transmit antenna elements 904. The signal level of the detection resulting from this condition is compared to a base reference level. In this scenario, the signal comparison can be divided into three levels: the first signal level is equivalent to a detection appearing 1.4 dB below the reference level (indicating that the object is indeed in the boresight); the second signal level is equivalent to a detection appearing 10 dB below the reference level (indicating that the object is in a first position, i.e., on the first sidelobe clockwise at a given detection angle of +18 degrees); and the third signal level is equivalent to a detection appearing 3.5 dB above the reference level (indicating that the object is in a second position, i.e., on the first sidelobe counterclockwise at the negative of the detection angle, −18 degrees).

[0078] Table 1 further shows a second phase condition, which includes a second incremental phase shift to move the main beam away from the boresight by a second steering angle, equivalent to shifting the main beam 12.8 degrees clockwise. In one embodiment, the second incremental phase shift is the negative of the first incremental phase shift, hereinafter also referred to as the first negative incremental phase shift. For the first negative incremental phase shift, when detection appears at the third position, i.e., 10 dB below the reference level, the object is on the first sidelobe at −18 degrees (the negative of the detection angle) in the counterclockwise direction, and when detection appears at the fourth position, i.e., 3.5 dB above the reference level, the object is on the first sidelobe at the detection angle, i.e., +18 degrees in the clockwise direction.

[0079] 12A and 12B illustrate the detection of objects 1202 and 1204, respectively, using side lobes of the bidirectional radiation pattern of the millimeter-wave automotive radar system 900 according to the beamforming configuration of an embodiment of the present invention based on Table 1. An example of object 1202 includes a car, and an example of object 1204 includes a truck.

[0080] As previously noted, the RCS value of the truck / lorry 1204 is approximately 10 dB higher than the RCS value of the car 1202, and the sidelobe level is approximately 13 dB lower than the main beam. However, by applying a first incremental phase shift, it is possible to determine whether the detection is for a small vehicle 1202 directly ahead, i.e., at boresight, or a large vehicle 1204 to the side, i.e., off-boresight. At a minimum, this detection depends on three array conditions, but those skilled in the art will understand that many chirps or frames are used in these conditions. In the reference condition, the main beam of the phased transmit array is located at the boresight; in the first phase shift condition, the main beam is located at -12.8 degrees; and in the second phase shift condition, the beam is located at 12.8 degrees.

[0081] Therefore, based on Table 1, it may be possible to determine that object 1202 is detected by main lobe 1203 and object 1204 is detected by first side lobe 1205. While Figures 12A and 12B illustrate conditions for two different types of vehicles, it will be understood that the present invention is not so limited and vehicles of a similar nature may also be detected.

[0082] 13 is a diagram illustrating the detection of two objects 1302 and 1304 using side lobes of the bidirectional radiation pattern of the millimeter-wave automotive radar system 900 based on Table 1, in accordance with an embodiment of the present invention. Here, the two objects are two vehicles 1302 and 1304 displayed alongside each other. The two vehicles are of similar type. As shown in FIG. 13, it can be seen that when the vehicles appear alongside each other, phase shift conditions 1 and 2 in Table 1 both record an increase in signal return, i.e., objects 1302 and 1304 appear at +18 degrees and −18 degrees, respectively, and are detected by first side lobes 1303 and 1305, respectively.

[0083] Thus, if a single object appears off-boresight, a +3.5 dB reading will only appear for either condition 1 or condition 2, but a +3.5 dB reading in both condition 1 and condition 2 means that objects 1302 and 1304 appear simultaneously at +18 degrees and -18 degrees, respectively, and are detected by two side lobes 1303 and 1305, respectively.

[0084] 14 illustrates the detection of two objects 1402 and 1404 from the bidirectional radiation pattern of radar system 900, with object 1402 occurring at the boresight (detectable by main lobe 1403) and object 1404 occurring off-boresight (detectable by first side lobe 1405). In such a scenario, Table 1 is insufficient to allow radar control system 912 to determine the two objects, in that one object 1402 is at the boresight and another object 1404 is off-boresight. For such a scenario, radar control system 912 configures a second lookup table that includes a third phase shift condition and a fourth phase shift condition and corresponding signal return levels for the third signal level of Table 1, as shown below.

[0085] [Table 2]

[0086] Table 2 shows a third phase shift condition (3), in which, when an object is already identified at the second position, i.e., -18 degrees counterclockwise, upon application of the first incremental phase shift, a third incremental phase shift is added between all three consecutive transmit antenna elements 904 to move the main beam by a third steering angle, i.e., 35 degrees counterclockwise. When the third incremental phase shift is applied, if the signal return level is 3.5 dB lower than the third signal level, a single object is present at the second position, i.e., -18 degrees counterclockwise (Table 1 - Phase Shift Condition (1)). Furthermore, when the third incremental phase shift is applied, if the signal return level is 10 dB lower than the third signal level (Table 1), it can be concluded that one object is present in the boresight and another object is present at the second position, i.e., -18 degrees counterclockwise.

[0087] Table 2 further illustrates a fourth phase shift condition (4), in which, when applying the first negative gradual phase shift, an object is already identified at the fourth position, +18 degrees clockwise, in the second phase shift condition, and a fourth gradual phase shift is added between all three consecutive transmit antenna elements 904 to move the main beam by a fourth steering angle, i.e., 35 degrees clockwise. The fourth gradual phase shift is the negative of the third gradual phase shift and is hereinafter also referred to as the third negative gradual phase shift. When applying the third negative gradual phase shift, a single object is present at the fourth position, i.e., +18 degrees clockwise, when the signal return level is 3.5 dB lower than the third signal level (Table 1 - Phase Shift Condition (2)). Furthermore, when applying the third negative incremental phase shift, when the signal return level is 10 dB less than the third signal level (Table 1), it can be concluded that one object is present at the boresight and another object is present at +18 degrees clockwise.

[0088] Various embodiments of the present invention thus facilitate measuring an observed scene using predefined, adjusted bidirectional antenna radiation patterns (as defined in Tables 1 and 2). Those skilled in the art will appreciate that the present invention is not limited to predefined, adjusted bidirectional antenna radiation patterns as defined in Tables 1 and 2, but may observe and record subsequent adjusted bidirectional antenna radiation patterns that use additional phase shift values ​​in either the transmit elements, the receive elements, or both the transmit and receive elements of the antennas in the system. Thus, the present invention distinguishes itself from traditional phased array approaches by actively utilizing side lobes to extend the moving field of view to several additional detectable zones.

[0089] As an example, the angles and beam squint conditions listed in Tables 1 and 2 are for the specific cases of 3-element and 10-element bidirectional conditions, however, it will be recognized that the invention can be extended to any number of elements, sidelobes, or objects by varying the squint angle and is not limited thereby.

[0090] While the examples in Tables 1 and 2 above were described for a phased array radar, they are equally valid for MIMO systems where multiple transmitter elements are activated and incremental phase shifts are applied between them in accordance with the described invention to perform measurements in addition to those typically performed in MIMO radar. In this regard, the MIMO calculations are first performed using the described prior art MIMO radar method, and the measurements are repeated using the method described with reference to FIG. 10. More than one of the M transmitters is excited simultaneously, and incremental phase shifts are applied between the transmitter elements according to the spacing between the transmitter elements and the equivalent settings in Tables 1 and 2 defined for the system. This comparison demonstrates that the present invention can eliminate the ambiguity of targets resulting from traditional MIMO calculations.

[0091] Furthermore, as described in Tables 1 and 2, the predefined and tuned antenna radiation patterns are described for an ideal antenna array in which the spacing between each element of the array is maintained constant. However, increasing the array size (to reduce the beamwidth) may allow the removal of some elements without adversely affecting array performance while maintaining the overall aperture size. In such cases, as more elements are removed, sidelobe levels may increase and become more pronounced again, potentially affecting detection as described above. Such arrays are called sparse arrays and have the advantage of reducing the number of receivers, and therefore the cost, required for a radar. However, the number of receivers required for such an array is ultimately limited by the minimum number of elements required to mitigate the "regrowth" of sidelobe levels to an acceptable level while maintaining array performance. However, applying the described invention to such arrays can turn that limitation into an advantage.

[0092] 15 shows a digitally generated virtual array radiation pattern 1500 for a MIMO radar with three transmit antennas 1502 and four receive antennas 1504, where a 12-element virtual array 1506 is designed with half-wavelength spacing between elements. In this case, all transmit elements transmit separately, but the present invention shows that the virtual (or two-way) radiation pattern 1500 does not change if all transmit antennas transmit simultaneously (using DDMA, BPM, or other types of modulation).

[0093] FIG. 16 illustrates the effect of a 40-degree incremental phase shift on the radiation pattern of the transmit array 1502 of FIG. 15 when all three transmit elements are simultaneously excited. In the context of the present invention, incremental phase shifts may be added between simultaneously excited transmit elements of a MIMO radar in a manner similar to that shown in FIG. 7. Note that while the radiation patterns in both FIG. 7 and FIG. 16 include plots for a three-element array, the shapes differ due to the spacing between the elements. However, the virtual or two-way radiation pattern plot of FIG. 17 illustrates the same effect, and the determination of detections found by sidelobes is made in a manner similar to that described above. Those skilled in the art will also appreciate that incremental phase shifts can be added between simultaneously excited receive elements without affecting the performance of the present invention. In MIMO radar, the use of subarrays to mitigate sidelobes is a known technique for removing their effects from radar analysis. Such techniques include removing portions of the virtual array from the DSP analysis or analyzing different portions of the virtual array before comparing with the full virtual array analysis. However, such techniques reduce the detectable range and are distinct from the present invention.

[0094] In this specification, the terms "comprise", "comprises", "comprised", "comprising" or variations thereof and "include", "includes", "included", "including" or variations thereof are considered interchangeable and all are to be given the broadest possible interpretation and vice versa.

[0095] The invention is not limited to the embodiments described herein, which may vary both in structure and detail.

Claims

1. 1. A method of sensing an environment using a radar system, comprising: setting a two-way signal return level of the main lobe at the boresight as a reference level; applying a progressive phase shift between a plurality of antenna elements of the radar system to move the main lobe to a location other than the boresight to increase a two-way signal return level of at least one side lobe; recording a signal return level of the two-way radiation pattern relative to the reference level upon application of the incremental phase shifts; detecting at least one object at a boresight or off-boresight location based on comparing the applied incremental phase shift and recorded signal return level to a look-up table containing a set of phase shift conditions; wherein each phase shift condition includes a progressive phase shift to apply between the plurality of antenna elements and a corresponding plurality of recorded signal return levels for detecting at least one object on or off boresight.

2. The method of claim 1 , wherein the plurality of antenna elements comprises a plurality of simultaneously excited transmit antenna elements of a MIMO radar.

3. The lookup table is a first phase shift condition including a first gradual phase shift for moving the main lobe away from the boresight by a first steering angle and corresponding signal levels for detecting an object at the boresight, a first off-boresight location, and a second off-boresight location when applying the first gradual phase shift; and a second phase shift condition comprising a second gradual phase shift for moving the main lobe away from the boresight by a second steering angle and corresponding signal levels for detecting objects at the boresight, a third off-boresight position, and a fourth off-boresight position when applying the second gradual phase shift.

4. The lookup table is a third phase shift condition that is applied when an object is identified as being at the second off-boresight position under the first phase shift condition, the third phase shift condition including a third incremental phase shift for moving the main lobe away from the boresight by a third steering angle; a corresponding signal return level for concluding that a single object is present at the second off-boresight location upon application of the third incremental phase shift; and and a corresponding signal return level upon application of the third gradual phase shift to conclude that one object is present at the boresight and another object is present at the second off-boresight location.

5. The lookup table is a fourth phase shift condition that is applied when an object is identified at the fourth off-boresight location under the second phase shift condition, the fourth phase shift condition including applying a fourth incremental phase shift to move the main lobe away from the boresight by a fourth steering angle; a corresponding signal return level for concluding that a single object is present at the fourth off-boresight location upon application of the fourth incremental phase shift; and and a corresponding signal return level upon application of the fourth incremental phase shift to conclude that one object is present at the boresight and another object is present at the fourth off-boresight location.

6. 6. The method of claim 1, wherein the second gradual phase shift is a negative of the first gradual phase shift, the fourth gradual phase shift is a negative of the third gradual phase shift, the second steering angle is a negative of the first steering angle, and the fourth steering angle is a negative of the third steering angle.

7. 7. The method of claim 1, further comprising determining a size of a detected object from the signal return level value, the detected range, and the actual number of returned signals from a given area.

8. The method of claim 1 , wherein the plurality of antenna elements comprises a plurality of transmit antenna elements, a plurality of receive antenna elements, or a combination of both.

9. The method of claim 1 , wherein the gradual phase shifts are applied independently to the plurality of transmit and receive antenna elements.

10. 10. The method according to any one of claims 1 to 9, wherein each receive antenna element is configured with a fixed beam shape or a switched beam shape, preferably wherein the plurality of antenna elements are configured using a beamforming network.

11. 11. The method of claim 1, further comprising applying one or more subsequent incremental phase shifts between the plurality of antenna elements to introduce further attenuation onto the side lobes or onto the main lobe of the bidirectional radiation pattern.

12. 12. The method of claim 1, further comprising recording and analyzing signal return levels of the bidirectional radiation pattern upon application of gradual phase shifts when the signal return level of at least one side lobe exceeds a predefined threshold.

13. The method of claim 1 , wherein the spacing between the antenna elements is non-uniform.

14. The method according to any one of claims 1 to 13, wherein the plurality of antenna elements are the consecutive antenna elements.

15. 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 (910); and a radar control system (912) for implementing the method according to any one of claims 1 to 14.

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