Radar device

Abstract

To provide a radar device capable of appropriately identifying whether a signal corresponding to a target is a real image or a false image.SOLUTION: A radar device 1 comprises: a transmitting antenna group 3 including a plurality of first antenna elements Tx; a receiving antenna group 4 including a plurality of second antenna elements Rx; and a control portion 6. The control portion 6 has a first signal detection portion 61 that detects a signal corresponding to a target using a first array antenna including first antenna elements Tx of the predetermined number that becomes two or more, and the plurality of second antenna elements Rx. The control portion 6 has a second signal detection portion 62 that detects a signal corresponding to the target using a second array antenna including first antenna elements Tx of the number larger than the predetermined number, and the plurality of second antenna elements Rx. The control portion 6 includes an identification portion 63 that compares a detection result of the first signal detection portion 61 and a detection result of the second signal detection portion 62 and identifies whether the signal corresponding to the target is a real image or a false image on the basis of a comparison result.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a radar device. [Background technology]

[0002] In this type of radar device, a technique is known for identifying whether a signal corresponding to a target detected based on radio waves received by an antenna is a real image or a virtual image (see, for example, Patent Document 1). Patent Document 1 discloses a technique for comparing a target detection result based on radio waves transmitted from one antenna and received by multiple antennas with a target detection result based on radio waves transmitted from multiple antennas and received by multiple antennas to identify whether the image is real or virtual. In the following, a configuration in which radio waves transmitted from multiple antennas are received by multiple antennas may be referred to as "MIMO", and a configuration in which radio waves transmitted from one antenna are received by multiple antennas may be referred to as "SIMO". Note that MIMO is an abbreviation for Multi Input Multi Output. SIMO is an abbreviation for Single Input Multi Output. MISO is an abbreviation for Multi Input Single Output. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-136232 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a SIMO antenna configuration, when the spacing between antenna elements is increased, grating lobes are generated at a certain distance from the target position. If the location where the grating lobes are generated overlaps with the target position, the corresponding signals may interfere with each other in a destructive manner. In this case, the peak level of the signal detected by the SIMO antenna configuration becomes extremely smaller than the peak level of the signal detected by the MIMO antenna configuration, making it impossible to properly identify whether the signal corresponding to the target is a real image or a false image.

[0005] An object of the present disclosure is to provide a radar device capable of appropriately identifying whether a signal corresponding to a target is a real image or a false image. The purpose of this document is to: [Means for solving the problem]

[0006] The invention described in claim 1 is A radar device that detects targets using radio waves, A transmitting antenna group (3) including a plurality of actual first antenna elements (Tx); A receiving antenna group (4) including a plurality of actual second antenna elements (Rx); a first signal detection unit (61) that detects a signal corresponding to a target using a first array antenna including a predetermined number (two or more) of first antenna elements and a plurality of second antenna elements; a second signal detection unit (62) that detects a signal corresponding to a target using a second array antenna including a number of first antenna elements greater than a predetermined number and a plurality of second antenna elements; and a discrimination section (63) that compares the detection result of the first signal detection section with the detection result of the second signal detection section and discriminates whether the signal corresponding to the target is a real image or a false image based on the comparison result.

[0007] In a MIMO antenna configuration, the distance between adjacent antenna elements is smaller than in a SIMO antenna configuration, making it less likely that grating lobes will occur. Therefore, if a configuration is adopted in which the detection results of a signal corresponding to a target are compared using MIMO with different antenna configurations and whether or not the signal corresponding to the target is a real image is identified based on the comparison results, it is possible to appropriately identify whether the signal corresponding to the target is a real image or a false image compared to conventional technology.

[0008] Note that the reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of a radar device according to a first embodiment. [Diagram 2] 1 is a schematic diagram showing a transmitting antenna group including a plurality of actually existing transmitting antenna elements in a radar device according to a first embodiment. [Diagram 3] 1 is a schematic diagram showing a receiving antenna group including a plurality of actual receiving antenna elements in a radar device according to a first embodiment. [Figure 4] FIG. 2 is an explanatory diagram for explaining a first array antenna for MIMO and a second array antenna for MIMO in the radar device according to the first embodiment. [Diagram 5] FIG. 13 is an explanatory diagram for explaining a covariance matrix of an extension array antenna in a radar device according to a fourth embodiment. [Figure 6] FIG. 11 is an explanatory diagram for explaining a window function. [Figure 7] 4 is a flowchart showing a flow of a target detection process executed by a control unit of the radar device. [Figure 8] FIG. 2 is a schematic diagram showing an example of an arrangement of antenna elements in a radar device. [Figure 9] FIG. 2 is an explanatory diagram for explaining a power spectrum of a signal corresponding to a target in SIMO. [Figure 10]FIG. 2 is an explanatory diagram for explaining a power spectrum of a signal corresponding to a target in MIMO. [Figure 11] FIG. 9 is a spectrum diagram showing a simulation result when the azimuth of one target is estimated with the antenna configuration of FIG. 8. [Figure 12] FIG. 2 is an explanatory diagram for explaining a power spectrum in SIMO when there are two targets. [Figure 13] 1A and 1B are explanatory diagrams for explaining a case where the outgoing path and the return path of the radio wave coincide with each other and a case where the outgoing path and the return path of the radio wave do not coincide with each other. [Figure 14] FIG. 1 is an explanatory diagram for explaining a power spectrum in MIMO when there are two targets and the outgoing path and the return path of radio waves coincide with each other. [Figure 15] FIG. 11 is a spectrum diagram showing a simulation result when the azimuths of two targets are estimated in a case where the outgoing path and the return path of the radio wave coincide with each other. [Figure 16] FIG. 11 is an explanatory diagram for explaining a power spectrum in MIMO when there are two targets and the outgoing path and the return path of radio waves do not match. [Figure 17] FIG. 11 is a spectrum diagram showing a simulation result when estimating the azimuths of two targets in an example where the outgoing path and the return path of radio waves do not match. [Figure 18] FIG. 11 is a spectrum diagram showing a simulation result when estimating the azimuths of two targets in another example in which the outbound and return paths of radio waves do not match. [Figure 19] FIG. 11 is a spectrum diagram showing a simulation result when estimating the azimuths of two targets in a case where the outbound and inbound paths of radio waves do not match. [Figure 20] FIG. 11 is an explanatory diagram for explaining a simulation result of a bearing in SIMO when the position of a signal corresponding to a target and the position where a grating lobe occurs overlap. [Figure 21] 5 is a flowchart showing the flow of a signal determination process executed by a control unit of the radar device according to the first embodiment. [Figure 22]FIG. 11 is a spectrum diagram showing a simulation result when directional estimation is performed using two types of MIMO in an example where the outgoing path and the return path of radio waves coincide with each other. [Diagram 23] FIG. 11 is a spectrum diagram showing a simulation result in which direction estimation is performed using two types of MIMO only for reflected waves when the outgoing path and the return path of radio waves do not match. [Figure 24] FIG. 11 is a spectrum diagram showing a simulation result in which direction estimation is performed using two types of MIMO only for reflected waves when the outgoing path and the return path of radio waves do not match. [Diagram 25] FIG. 11 is a schematic configuration diagram of a radar device according to a second embodiment. [Figure 26] FIG. 11 is a spectrum diagram showing a simulation result in which direction estimation is performed using two types of MIMO and SIMO only for reflected waves when the outgoing path and the return path of radio waves do not match. [Figure 27] 10 is a flowchart showing the flow of a target detection process executed by a control unit of a radar device according to a second embodiment. [Figure 28] 10 is a flowchart showing the flow of a signal determination process executed by a control unit of a radar device according to a second embodiment. [Figure 29] FIG. 11 is a spectrum diagram showing a simulation result of the azimuth according to the second embodiment when the position of a signal corresponding to a target and the position where a grating lobe occurs overlap. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, the same reference numerals are used for parts that are the same as or equivalent to those described in the preceding embodiments, and the description thereof may be omitted. In addition, in the embodiments, when only a part of the components is described, the components described in the preceding embodiments can be applied to the other parts of the components. In the following embodiments, each embodiment can be partially combined with each other, even if not specifically stated, as long as it does not cause any trouble in combination.

[0011] (First embodiment) The present embodiment will be described with reference to Fig. 1 to Fig. 24. In the present embodiment, an example will be described in which a radar device 1 of the present disclosure is applied to a target detection device that is mounted on a vehicle and detects various targets existing around the vehicle.

[0012] The radar device 1 emits radio waves ahead of the vehicle and receives radio waves reflected by a target ahead of the vehicle to determine the distance to the target, the relative speed with respect to the vehicle, the direction with respect to the vehicle, etc.

[0013] The radar device 1 employs the FMCW method as a signal modulation method. The radar device 1 operates at a radio frequency in a frequency band corresponding to millimeter waves (e.g., 76.5 GHz). Note that the operating frequency of the radio waves transmitted and received by the radar device 1 is not limited to a frequency corresponding to millimeter waves, and may be a frequency other than millimeter waves.

[0014] As shown in FIG. 1, the radar device 1 includes a transmitter 2, a transmitting antenna group 3 including a plurality of actual first antenna elements Tx, a receiving antenna group 4 including a plurality of actual second antenna elements Rx, a receiver 5, and a control unit 6.

[0015] The transmitter 2 generates a signal to be transmitted from the transmitting antenna group 3 and transmits it to the transmitting antenna group 3. Specifically, the transmitter 2 generates a local signal and transmits the generated local signal to the receiver 5. In addition, the transmitter 2 generates a chirp signal whose frequency changes continuously and provides the generated chirp signal to the transmitting antenna group 3.

[0016] The transmitting antenna group 3 transmits radio waves corresponding to the chirp signal provided by the transmitter 2 toward the front of the vehicle. In this example, the transmitting antenna group 3 is composed of four actual first antenna elements Tx. The first antenna elements Tx are arranged in a row along the arrangement direction in a predetermined direction at a predetermined interval.

[0017] The first antenna elements Tx of this embodiment are arranged in the width direction of the vehicle. As shown in Fig. 2, the first antenna elements Tx are arranged at a position spaced apart from the one located at the end by "2d", which is twice the reference distance d, a position spaced apart by "10d", which is ten times the reference distance d, and a position spaced apart by "12d", which is twelve times the reference distance d. The spacing between the first antenna elements Tx may be strictly a multiple of the reference distance d, or may include an error that is generally permitted in the technical field to which the technology of the present disclosure belongs and does not contradict the spirit of the technology of the present disclosure.

[0018] Here, the reference distance d is set so as to satisfy the following formula F1 when the detection range of the radar device 1 is "±1 / 2·θfov". In this embodiment, θfov is set to "180°" and the reference distance d is set to "1 / 2·λ", where λ is the wavelength of the radio wave.

[0019] 1 / sin(θfov / 180 π) 2 <d ···(F1) The receiving antenna group 4 receives radio waves and the like transmitted from the transmitting antenna group 3 and reflected by a target. The receiving antenna group 4 is composed of four actual second antenna elements Rx. In this example, the second antenna elements Rx are arranged in a row along the arrangement direction in a predetermined direction at a predetermined interval.

[0020] The second antenna elements Rx of this embodiment are arranged at equal intervals in the width direction of the vehicle. As shown in Fig. 3, the second antenna elements Rx are arranged at intervals of "3d" which is three times the reference distance d.

[0021] The interval between the second antenna elements Rx may be strictly a multiple of the reference distance d, or may include an error that is generally acceptable in the technical field to which the technology of the present disclosure belongs and does not violate the spirit of the technology of the present disclosure. Moreover, "equally spaced" does not only mean a state in which the intervals are exactly the same, but also includes an error that is generally acceptable in the technical field to which the technology of the present disclosure belongs and does not violate the spirit of the technology of the present disclosure.

[0022] The receiving unit 5 generates a beat signal based on the reception signals received by the receiving antenna group 4 and the local signal transmitted from the transmitting unit 2, samples the beat signal, and provides it to the control unit 6. Although not shown, the receiving unit 5 is configured to include a mixer, an amplifier, an AD converter, etc.

[0023] The control unit 6 is an electronic control device mainly composed of a microcomputer equipped with a processor and a memory. The memory is, for example, a ROM, a RAM, etc. Various functions of the microcomputer are realized by the processor executing a program stored in a non-transient physical storage medium.

[0024] The control unit 6 detects a signal corresponding to a target based on radio waves received when radio waves are transmitted and received using a first array antenna for MIMO including a predetermined number (2 or more) of first antenna elements Tx and a plurality of second antenna elements Rx. The first array antenna of this embodiment has an antenna configuration including two first antenna elements Tx and four second antenna elements Rx. In this embodiment, the software and hardware of the control unit 6 that detects a signal corresponding to a target based on radio waves received when radio waves are transmitted and received using the first array antenna constitutes a "first signal detection unit 61."

[0025] The first array antenna of this embodiment is a virtual array including four second antenna elements Rx and four virtual antenna elements Vx, as shown on the left side of FIG. 4. Such a virtual array is obtained by receiving radio waves transmitted from two first antenna elements Tx at four second antenna elements Rx and performing signal processing. The first array antenna of this embodiment is configured such that the antenna elements are arranged at unequal intervals. In other words, the first array antenna has an antenna configuration including a portion where the interval between antenna elements is larger than in other portions.

[0026] In such an antenna configuration, it may be possible to supplement signals at missing parts of the antenna by expansion processing using a differential signal corresponding to the phase difference between the multiple antenna elements caused by radio waves arriving from a direction intersecting the arrangement direction of the multiple antenna elements. In this expansion processing, among the multiple antenna elements constituting the second array antenna, the signal of a virtual antenna element positioned between antenna elements with a larger gap compared to the others is interpolated using a differential signal corresponding to the phase difference between the multiple antenna elements.

[0027] An example of the expansion process is Khatri-Rao product expansion array processing, in which the signals of virtual antenna elements positioned between antenna elements with larger spacing compared to the others are interpolated using a differential signal corresponding to the phase difference between the multiple antenna elements.

[0028] The matrix shown on the left side of FIG. 5 is the dispersion matrix e between the received signal at the antenna element and the complex conjugate of the received signal for the antenna configuration shown on the left side of FIG. iω The matrix shown in the center of Figure 5 is the variance matrix e iω This matrix shows only the exponent parts of the independent components in the matrix. This matrix is ​​equivalent to an arrangement in which the numerical values ​​corresponding to the arrangement positions of the antenna elements of the second array antenna are arranged in the top row, and the numerical values ​​corresponding to the arrangement positions of the antenna elements are arranged with their signs inverted in the leftmost column, and these numerical values ​​are added vertically and horizontally. The numerical values ​​(exponents) arranged in the matrix shown in the center of Figure 5 correspond to each arrangement position in the extended array antenna. The number of tables shown on the right side of Figure 5 corresponds to the number of signals corresponding to each antenna element.

[0029] The expanded array antenna obtained by such an expansion process has a large aperture antenna configuration with an antenna aperture length of "22d." The radar device 1 of this embodiment performs the expansion process on the virtual array shown in the middle left part of Fig. 4, and detects signals corresponding to targets by using the expanded array antenna obtained by the expansion process as the first array antenna.

[0030] In the extended array antenna, the antenna elements are arranged so that they are spaced at equal intervals near the center. Specifically, the extended array antenna has 21 antenna elements, and the antenna elements at both ends are arranged at an interval of "2d", and the central antenna elements excluding both ends are arranged at an interval of "1d". In this way, in the extended array antenna of this example, the indexes of the independent components are not consecutive on both ends. For example, the index of the independent components is "-11" after "-9", and there is no "-10". This is a factor that leads to an increase in the side lobe SL, and is likely to occur when the first antenna element Tx or the second antenna element Rx are arranged at equal intervals.

[0031] Considering this, in the extension process, the control unit 6 of this embodiment performs weighting by window function processing on signals corresponding to antenna elements constituting the extension array antenna. In this window function processing, for example, the Hann window or Blackman window shown in Fig. 6 can be used. The Hann window has a narrow dynamic range but a high frequency resolution. On the other hand, the Blackman window has a low frequency resolution but a wide dynamic range.

[0032] In addition, in the extended array antenna of this embodiment, the antenna elements are arranged so that the number of signals (number of overlaps) detected at a position close to the median value of the index of the independent components arranged in a matrix is ​​greater than the number of signals detected at a position farthest from the median value. Specifically, in the extended array antenna, as shown on the right side of FIG. 5, multiple signals are obtained at positions where the index of the independent components is "-9", "-8", "-6" to "0" to "6", "8", and "9". In the extended array antenna of this example, when the position where the index of the independent component is "0" is taken as the reference position, the number of signals does not decrease as it moves away from the reference position, but increases and decreases. For example, the number of signals is 8 at the reference position, but decreases to 3 at "-1", increases to 4 at "-2", increases to 6 at "-3", and decreases to 2 at "-4".

[0033] Considering this, when multiple signals corresponding to the antenna elements constituting the extended array antenna are obtained in the extension process, the control unit 6 adds and averages the multiple signals. In other words, when there are multiple numbers corresponding to the arrangement positions in the extended array antenna, the control unit 6 averages the multiple difference signals obtained at the arrangement positions. This suppresses interference between adjacent targets.

[0034] The control unit 6 detects a signal corresponding to a target based on radio waves received when radio waves are transmitted and received using a second array antenna for MIMO corresponding to an antenna configuration including a number of first antenna elements Tx and a plurality of second antenna elements Rx that is greater than a predetermined number. The second array antenna of this embodiment has an antenna configuration including four first antenna elements Tx and four second antenna elements Rx. In this embodiment, the software and hardware of the control unit 6 that detects a signal corresponding to a target based on radio waves received when radio waves are transmitted and received using the second array antenna constitutes a "second signal detection unit 62."

[0035] The second array antenna of this embodiment is a virtual array in which four second antenna elements Rx are added to eight virtual antenna elements Vx, as shown in the middle right side of Fig. 4. Such a virtual array is obtained by receiving radio waves transmitted from four first antenna elements Tx at four second antenna elements Rx and performing signal processing. The second array antenna of this embodiment is configured such that the antenna elements are arranged at unequal intervals.

[0036] The radar device 1 of this embodiment performs the above-mentioned expansion process on the virtual array shown in the middle right part of FIG. 4, and detects signals corresponding to targets using the expanded array antenna obtained by the expansion process as a second array antenna.

[0037] Furthermore, the control unit 6 compares the detection result of the signal corresponding to the target when the first array antenna is used with the detection result of the signal corresponding to the target when the second array antenna is used, and identifies whether the signal corresponding to the target is a real image or a false image based on the comparison result. In this embodiment, the control unit 6 includes an "identification unit 63" that compares the detection result of the signal corresponding to the target by the first signal detection unit 61 with the detection result of the signal corresponding to the target by the second signal detection unit 62, and identifies whether the signal corresponding to the target is a real image or a false image based on the comparison result.

[0038] Next, the target detection process executed by the control unit 6 of the radar device 1 will be described with reference to Fig. 7. The process shown in Fig. 7 is executed by the control unit 6 periodically or irregularly when chirp signals are transmitted from the transmitting antenna group 3 at a predetermined transmission period.

[0039] 7, in step S100, the control unit 6 receives a reflected wave from a target at the receiving antenna group 4. This received signal is mixed with a local signal by the mixer of the receiving unit 5. After that, a desired frequency component is extracted by a low-pass filter, and the frequency component is provided from the receiving unit 5 to the control unit 6 as a beat signal.

[0040] Next, the control unit 6 performs distance FFT processing in step S110. The control unit 6 obtains the distance to the target by performing frequency analysis of the beat signal using FFT. Note that FFT is an abbreviation for Fast Fourier Transform.

[0041] Next, the control unit 6 performs a velocity FFT process in step S120. The control unit 6 performs an FFT for each beat frequency component to obtain a Doppler frequency, and obtains the relative velocity of the target based on the Doppler frequency.

[0042] Next, in step S130, the control unit 6 performs a first azimuth estimation process to detect the azimuth of the target relative to the radar device 1 using the first array antenna for MIMO. The control unit 6 detects the azimuth of the target based on the fact that the phase of the received signal received by the antenna elements constituting the first array antenna differs depending on the arrival angle of the reflected wave.

[0043] Next, in step S140, the control unit 6 performs a second azimuth estimation process to detect the azimuth of the target by the second array antenna for MIMO. The control unit 6 detects the azimuth of the target based on the fact that the phase of the received signal received by the antenna elements constituting the second array antenna differs depending on the arrival angle of the reflected wave.

[0044] Next, in step S150, the control unit 6 performs a signal determination process to determine whether the signal corresponding to the target is a real image or a false image. In this signal determination process, the detection result of the signal corresponding to the target in the first array antenna for MIMO is compared with the detection result of the signal corresponding to the target in the second array antenna for MIMO, and identifies whether the signal corresponding to the target is a real image or a false image based on the comparison result. Specifically, the control unit 6 compares the power spectrum of the signal corresponding to the target in the first array antenna with the power spectrum of the signal corresponding to the target in the second array antenna, and identifies whether the signal corresponding to the target is a real image or a false image.

[0045] Here, the power spectrum of a signal corresponding to a target will be described with reference to Figs. 9 to 20, taking the arrangement of antenna elements xlm shown in Fig. 8 as an example. In the following, the SIMO antenna configuration may be called "SIMO" and the MIMO antenna configuration may be called "MIMO". In xlm, "l" is an index corresponding to a transmitting antenna, and "m" is an index corresponding to a receiving antenna.

[0046] When the received signal at each antenna element xlm is represented by vector X as shown in Fig. 9 (1.1), and the direction U is represented by array vector A as shown in Fig. 9 (1.2), the spectrum signal Sp in the direction U as shown in Fig. 9 (1.3) can be obtained by multiplying the two. In Fig. 9, "n" indicates the number of antennas, "m" indicates the antenna position of the second antenna element Rx, "l" indicates the antenna position of the first antenna element Tx, and "U" indicates the sine of the azimuth angle θ (sin θ). In MIMO, it is a combination of "l" and "m."

[0047] In the case of SIMO, the received signal when there are k targets is shown in (1.4) of Fig. 9, and when there is one target, it is shown in (1.5) of Fig. 9. For example, when k=1 and the target position is "U=0 (θ1=0°)", the vector X is (1, 1) T Therefore, the spectrum signal Sp is as shown in (1.6) of Fig. 9. In the case of SIMO, since there is one first antenna element Tx, dm = 0.

[0048] According to (1.6) in Fig. 9, when U = 0 indicating the target, the spectral signal Sp becomes 2s1 and is at its maximum. Furthermore, when U = 2 / 3, 3π sinθ = 2π, and the terms in (1.6) in Fig. 9 are in phase and reinforce each other, so that the spectral signal Sp becomes 2s1. In other words, the spectral signal Sp reaches its maximum peak even at positions other than the target position (U = 0). This is the grating lobe GL.

[0049] Here, when the number of equally spaced antenna elements is increased, the spectrum signal Sp becomes "Sp=s1+s1e^(-j3πU)+s1e^(-j2*3πU)+s1e^(-j3*3πU)+···". For this reason, under the same conditions, the phase of each term will be an integer multiple of 2π and will be the same, resulting in the generation of grating lobes GL. In other words, grating lobes GL may occur depending on the arrangement of equally spaced antenna elements. Note that if the reference distance d of the antenna elements is 1 / 2λ, this does not satisfy -1<(2π / λ)·3dsinθ<1, and so no grating lobes GL will occur.

[0050] On the other hand, in the case of MIMO, the received signal when there are k targets is as shown in (2.1) of Figure 10. For example, when k=1 and the target position is "U=0", the vector X is (1, 1, 1, 1). T Therefore, the spectrum signal Sp is as shown in (2.2) of FIG.

[0051] According to (2.2) in FIG. 10, when U=0, the spectral signal Sp becomes 4s1 and is at its maximum. However, there is no case where the terms are in phase except when U=0. In other words, grating lobes GL do not occur in MIMO. However, for terms smaller than 4s1, the terms reinforce each other and the absolute value of the spectral signal Sp may have a peak. This is the side lobe SL. It is difficult to determine this side lobe SL using a theoretical formula, so it is necessary to calculate it through simulation.

[0052] In MIMO, when the positions of the antenna elements "dl+dm" are arranged at intervals of "1 / 2 λ", the spectrum signal Sp is "Sp=s1+s1e^(-jπU)+s1e^(-j2πU)+s1e^(-j3πU)+···". Since the phase terms of the factorials of e of each term are arranged with natural number multiples of πU, it is difficult for an azimuth angle that reinforces the phase to exist, and the spectrum signal Sp becomes a sum of complex numbers of the same amplitude with a rotating phase, so the spectrum signal Sp approaches zero except for U=0. For this reason, for example, the side lobe SL can be reduced by increasing the number of antenna elements arranged at intervals of 1 / 2 λ using a differential signal based on the phase difference of each antenna element. Note that in the case of equal intervals of 1 / 2 λ or more, a grating lobe GL is formed under the condition that each term of the spectrum signal Sp has the same phase, but the side lobe SL is minimized because it is not a sum of each term with various phase components as in the case of arrangement at 1 / 2 λ intervals.

[0053] Fig. 11 shows the simulation results of the power spectrum when the target is in the center (U1 = 0) and the reflected power s1 = 1. As shown in Fig. 11, the SIMO spectrum signal Sp has grating lobes GL other than at the target position. On the other hand, the MIMO spectrum signal Sp does not have grating lobes GL other than at the target position. Therefore, by comparing the SIMO spectrum signal Sp and the MIMO spectrum signal Sp, it is possible to identify whether the signal indicating the target is a real image or a false image.

[0054] Next, we will explain the case where there are two targets due to the addition of reflection from a mirror, as shown on the left side of Fig. 13. Under this premise, the received signal at each antenna element xij in SIMO is shown in Fig. 12 (3.1), the vector X is shown in Fig. 12 (3.2), and the spectrum signal Sp is shown in Fig. 12 (3.3). Note that examples of mirrors include guardrails and walls placed on the side of the road.

[0055] On the other hand, in MIMO, when the outbound and return paths of radio waves coincide and reflection by a mirror is added, the received signal at each antenna element xlm is as shown in (4.1) of FIG. 14, the vector X is as shown in (4.2) of FIG. 14, and the spectrum signal Sp is as shown in (4.3) of FIG. 12.

[0056] In (4.1) and (4.2) of Figure 14, terms showing reflection by a mirror are added. As a result, in (4.3) showing the spectrum signal Sp, the direction U that reinforces the phase of the factorial of e of each term shifts from "0", and its absolute value also differs from that shown in (2.2) of Figure 10.

[0057] In addition to this, “θ 2 "The term that indicates reflection by the mirror is constructive, so "θ 2 The absolute value of the spectral signal Sp becomes large even near ". Note that the equations for (3.3) in Figure 12 showing the SIMO spectral signal Sp and (4.3) in Figure 14 showing the MIMO spectral signal Sp are different, so the peak positions and absolute values ​​are different.

[0058] Fig. 15 shows the simulation results of the power spectrum when there are two targets (U1 = 0, U2 = 0.643) and the reflected power is s1 = s2 = 1. As shown in Fig. 15, the peak position and peak level (i.e., amplitude) of the SIMO spectrum signal Sp at the target position are different from the peak position and peak level of the MIMO spectrum signal Sp.

[0059] In this way, when there are multiple targets, even if the paths are the same, the peak positions and peak levels of the spectrum signals Sp may differ between SIMO and MIMO.

[0060] Next, a case will be described where the outgoing and return paths of radio waves do not match, as shown in the center and right side of Fig. 13. In MIMO, when the outgoing and return paths of radio waves do not match and there is one target, the received signal at each antenna element xlm is as shown in Fig. 16 (5.1). When the outgoing path of radio waves is θ t =θ 2 , and the return path is θ r =θ 1 When =0, the vector X is as shown in (5.2) of FIG. 16, and the spectral signal Sp is as shown in (5.3) of FIG.

[0061] The spectrum signal Sp shown in (5.3) of Fig. 16 has more terms than the spectrum signal Sp shown in (1.6) of Fig. 9, each of which has a phase corresponding to the position of the antenna element xlm, and is the sum of these terms. For this reason, the absolute value of the spectrum is not maximum at U=0, but is maximum at a different position, and the value is different from SIMO.

[0062] In addition, the spectrum signal Sp shown in (5.3) of FIG. 16 has a different shape from that shown in (4.3) of FIG. 14, which shows the spectrum signal Sp when the paths are coincident in MIMO and reflection by a mirror is added. r =0° or θ tThe peak may be at a different position from the peak at the time of the signal. This is a false image caused by path mismatch in MIMO. When this received signal is digitally beamformed (i.e., DBF) using SIMO, the spectrum signal Sp is as shown in (5.4) of Figure 16.

[0063] Fig. 17 shows the comparison result between the spectrum signal Sp shown in (5.3) of Fig. 16 and the spectrum signal Sp shown in (5.4) of Fig. 16. As shown in Fig. 17, the peak position and peak level of the SIMO spectrum signal Sp are different from the peak position and peak level of the MIMO spectrum signal Sp.

[0064] In addition, the outgoing path of the radio wave θ t =θ 1 =0, the return path is θ r =θ 2 In this case, the vector X is as shown in (5.5) of Fig. 16, and the spectrum signal Sp is as shown in (5.6) of Fig. 16. When this received signal is digitally beamformed using SIMO, the spectrum signal Sp is as shown in (5.7) of Fig. 16.

[0065] Figure 18 shows the comparison result between the spectrum signal Sp shown in (5.6) of Figure 16 and the spectrum signal Sp shown in (5.7) of Figure 16. As shown in Figure 18, the peak position and peak level of the SIMO spectrum signal Sp are different from the peak position and peak level of the MIMO spectrum signal Sp.

[0066] There may also be cases where radio waves with mismatching paths overlap. In this case, the received signal is the sum of (5.3) and (5.5) in Fig. 16. In this case, the peak position and peak level of the spectrum signal Sp change, for example, as shown in Fig. 19. Such changes also occur when radio waves with matching paths and radio waves with mismatching paths overlap.

[0067] Furthermore, in a SIMO antenna configuration, if the spacing between antenna elements is wide, grating lobes GL will occur at a certain interval from the target position. For example, as shown in Fig. 20, if the target position U2 overlaps with the location where the grating lobes GL occur (e.g., U = ±2 / 3), the corresponding signals may interfere with each other destructively. This can cause the signal corresponding to the target to be unable to be properly identified as a real image or a false image.

[0068] In this way, the peak positions and peak levels of the spectrum signal Sp obtained with the SIMO antenna configuration and the MIMO antenna configuration may change even in the directions U1 and U2 indicating the target position.

[0069] In consideration of this, the control unit 6 of this embodiment is configured to perform a signal determination process for determining whether or not the peak position and peak level of the spectrum signal Sp obtained by the first array antenna for MIMO and the second array antenna for MIMO are within a predetermined determination region JA. The signal determination process performed by the control unit 6 will be described below with reference to Fig. 21. Note that, hereinafter, the first array antenna for MIMO may be referred to as "MIMO1" and the second array antenna for MIMO may be referred to as "MIMO2".

[0070] As shown in Fig. 21, in step S151, the control unit 6 selects a spectral signal Sp to be determined. For example, the control unit 6 selects a spectral signal Sp having a peak level exceeding a predetermined selection threshold as a determination target from among the spectral signals Sp in MIMO2. The selection threshold is set by experiment or simulation. For example, the selection threshold is set to the minimum value of the peak of the spectral signal Sp when a signal corresponding to a target is a real image. Note that the control unit 6 may select the spectral signal Sp to be determined based on the spectral signals Sp in MIMO1.

[0071] Next, in step S152, the control unit 6 determines whether or not the difference between the peak position of the spectrum signal Sp in MIMO1 and the peak position of the spectrum signal Sp in MIMO2 is within a predetermined range. Specifically, it determines whether or not the peak position of the spectrum signal Sp in MIMO1 is within a predetermined range including the peak position of the spectrum signal Sp to be determined.

[0072] The predetermined range is set by experiments or simulations. For example, the predetermined range is set to the maximum value between the peak position of the spectrum signal Sp in MIMO1 and the peak position of the spectrum signal Sp in MIMO2 when the signal corresponding to the target is a real image. According to the study by the inventors, there is a tendency that the peak position of the spectrum signal Sp in MIMO1 or MIMO2 is often present within the range of the half-width of the peak of the spectrum signal Sp in MIMO1 or MIMO2 when the signal corresponding to the target is a real image. For this reason, the predetermined range may be set to the half-width of the peak of the spectrum signal Sp in MIMO1 or MIMO2.

[0073] If the difference between the peak position of the spectrum signal Sp in MIMO1 and the peak position of the spectrum signal Sp in MIMO2 is outside a predetermined range, the control unit 6 determines in step S153 that the signal corresponding to the target to be determined is a “false image.”

[0074] On the other hand, if the difference between the peak position of the spectrum signal Sp in MIMO1 and the peak position of the spectrum signal Sp in MIMO2 is within the predetermined range, the control unit 6 proceeds to step S154. In step S154, the control unit 6 determines whether the difference between the peak level of the spectrum signal Sp in MIMO1 and the peak level of the spectrum signal Sp in MIMO2 is equal to or less than a predetermined threshold. Specifically, it is determined whether the difference in peak levels of the spectrum signals Sp whose peak positions are within the predetermined range is equal to or less than a predetermined threshold.

[0075] The predetermined threshold is set by experiments or simulations. The predetermined range is set to the maximum value of the difference between the peak level of the spectrum signal Sp in MIMO1 and the peak level of the spectrum signal Sp in MIMO2 when the signal corresponding to the target is a real image, for example.

[0076] If the difference between the peak level of the spectral signal Sp in MIMO1 and the peak level of the spectral signal Sp in MIMO2 is equal to or less than a predetermined threshold, the control unit 6 identifies in step S155 that the signal corresponding to the target to be determined is a “real image”.

[0077] Furthermore, if the difference between the peak level of the spectrum signal Sp in MIMO1 and the peak level of the spectrum signal Sp in MIMO2 exceeds a predetermined threshold, the control unit 6 determines in step S153 that the signal corresponding to the target to be judged is a “false image.”

[0078] When there are multiple signals to be determined, such signal determination processing is performed for each of the signals to be determined. When the signal determination processing is completed, the control unit 6 proceeds to step S160 in Fig. 7 and detects targets based on the signals identified as real images in the signal determination processing.

[0079] The radar device 1 described above detects signals corresponding to targets using both MIMO1 and MIMO2 in the target detection process, and identifies whether the signal corresponding to the target is a real image or a false image based on the detection result.

[0080] As mentioned above, in a SIMO antenna configuration, if the spacing between antenna elements is large, grating lobes will occur at a certain distance from the target position. If the location where these grating lobes occur overlaps with the target position, the corresponding signals may interfere with each other in a destructive manner.

[0081] On the other hand, in a MIMO antenna configuration, the spacing between adjacent antenna elements is smaller than in a SIMO antenna configuration, which suppresses the occurrence of grating lobes compared to a SIMO antenna configuration. Therefore, even if the location where the grating lobe occurs overlaps with the location of the target, the above-mentioned interference is less likely to occur.

[0082] Figure 22 shows the simulation results of power spectra for two types of MIMO (i.e., MIMO1 and MIMO2) when there are two targets (U1=0, U2=-2 / 3) and the reflected power is 1 (0 dB). As shown in Figure 22, in both MIMO1 and MIMO2, it is possible to detect a signal peak corresponding to the target that overlaps with the position where the grating lobe occurs, and therefore it is possible to determine that the image at the target position is a real image.

[0083] Therefore, if a configuration is adopted in which the detection results of a signal corresponding to a target are compared using MIMO with different antenna configurations, and whether or not the signal corresponding to the target is a real image is identified based on the comparison results, it is possible to appropriately identify whether the signal corresponding to the target is a real image or a false image, compared to conventional technology.

[0084] Moreover, the radar device 1 of this embodiment has the following features.

[0085] (1) In the radar device 1, the second antenna elements Rx are arranged at equal intervals at a reference interval that is multiple times a predetermined reference distance d. The first antenna elements Tx include elements arranged at an interval (in this example, "2d") that is smaller than the reference interval by the reference distance d. In this way, by arranging the first antenna elements Tx and the second antenna elements Rx at equal intervals at the reference interval for one of them and including an interval smaller than the reference interval for the other, the spacing between the antenna elements in MIMO can be reduced. In this case, the side lobes SL in MIMO tend to be small, and erroneous detection of the side lobes SL as real images is suppressed.

[0086] (2) The first antenna elements Tx include those arranged at intervals of a value ("12d" in this example) obtained by adding the antenna aperture length ("9d" in this example) of the four second antenna elements Rx to a reference interval ("3d" in this example). This makes it easier to arrange virtual antenna elements between real antenna elements in MIMO. This contributes to suppressing the occurrence of side lobes SL in MIMO1 and MIMO2.

[0087] Here, it is preferable that the first antenna elements Tx are arranged at intervals (in this example, "2d") smaller than the reference interval by the reference distance d with respect to the first antenna element Tx at one end and the first antenna element Tx at the other end. This contributes to suppressing the occurrence of side lobes SL in MIMO2.

[0088] (3) MIMO1 and MIMO2 are configured as extended array antennas including virtual antenna elements that are complemented using differential signals corresponding to the phase difference between each antenna element caused by radio waves arriving from a direction intersecting the arrangement direction of each antenna element. This makes it possible to adequately suppress the occurrence of side lobes SL, which are a cause of false images, and therefore makes it possible to more appropriately distinguish between real and false images.

[0089] (4) When two targets are targeted, interference between the targets can cause a signal with a large peak to appear between the two main lobes corresponding to the real image. Such a signal can affect the results of identifying whether the image is real or false.

[0090] Considering these points, in the radar device 1 of this embodiment, when multiple signals corresponding to the antenna elements constituting the extended array antenna are obtained in the extension process, the multiple signals are averaged. This makes it possible to reduce the influence of interference between targets, so that even when two targets are targeted, it is possible to properly distinguish whether the image is real or false.

[0091] (5) In addition, the radar device 1 weights the signals corresponding to the antenna elements constituting the extended array antenna by window function processing. This reduces the side lobes SL that cause false images, so that even when two targets are targeted, it is possible to properly distinguish whether the image is real or false.

[0092] 13, the radar device 1 receives three types of reflected waves, namely, a direct wave, a specular reflected wave, and a reflected wave with a mismatched path. The signals of the three types of reflected waves have random phases because they follow different paths.

[0093] Figures 23 and 24 show the simulation results of the power spectrum when there is a target (U1=0, s1=1) in the center, with a mirror reflection position (U2=0.174) nearby. In this example, the reflectivity of the mirror reflection signal amplitude is set to "0.316". In this case, the power of the specular reflected wave is 0.01 (≒0.316^4). Also, the power of the reflected wave when the outbound and return paths of the radio wave do not match is 0.1 (≒0.316^2). Note that Figures 23 and 24 show the results when the phase of the target signal source is the same.

[0094] Specifically, Fig. 23 shows the simulation results of the power spectrum when the signals of three types of reflected waves, i.e., direct waves, specular reflected waves, and reflected waves with mismatched paths, cannot be separated based on the difference in path distance. As shown in Fig. 23, in MIMO1, a peak corresponding to the reflected waves with mismatched paths occurs, but in MIMO2, the peak is small enough that it can be determined to be a false image.

[0095] In addition, although not shown in the figure, when simulating the power spectrum of the direct wave and the specular reflected wave in the case where the three types of reflected wave signals can be separated based on the difference in path distance, it is possible to determine that the image at the target position is a real image because no reflected waves with mismatched paths are included.

[0096] Figure 24 shows the simulation results of the power spectrum of reflected waves with mismatched paths when the three types of reflected wave signals can be separated based on the difference in path distance. As shown in Figure 24, when the outbound and inbound paths of the radio waves do not match, the peak level of the spectrum signal Sp in SIMO and MIMO at the target position falls outside the judgment area JA. In this case, the image at the target position will be judged to be a false image, but this does not pose a problem because the image at the target position can be judged to be a real image based on the direct wave and specular reflected wave.

[0097] (6) Specifically, the control unit 6 classifies an image as a real image when the peak positions of the signals corresponding to the targets detected by MIMO1 and MIMO2 are within a predetermined range and the difference in peak levels of the signals corresponding to the targets is equal to or less than a predetermined threshold. Also, the control unit 6 classifies an image as a virtual image when the peak positions of the signals corresponding to the targets detected by MIMO1 and MIMO2 are outside the predetermined range or the difference in peak levels of the signals corresponding to the targets exceeds a predetermined threshold.

[0098] According to this, when the outbound and inbound radio waves coincide with each other, even if the peak positions of the signals detected by MIMO1 and MIMO2 are shifted due to differences in the antenna configurations, it is possible to determine the signals as real images.

[0099] (7) The predetermined range is set based on the result of simulating the power spectrum of the signal corresponding to the target, with reference to the fluctuation range of the peak position of the signal that becomes the real image. Also, the predetermined threshold is set based on the result of simulating the power spectrum of the signal corresponding to the target, with reference to the fluctuation range of the peak level of the signal that becomes the real image. In this way, by setting the predetermined range and the predetermined threshold based on the simulation result, it is possible to appropriately identify whether the signal corresponding to the target is a real image or a false image.

[0100] Here, various signals of different sizes are detected in MIMO1 and MIMO2, but since the radar device 1 only needs to be able to detect targets, it is not necessary to distinguish whether all signals are real or false. For this reason, it is desirable for the control unit 6 to determine signals whose peak levels detected in one of MIMO1 and MIMO2 exceed a predetermined selection threshold, and to compare the signals to be determined with the signals detected in the other of MIMO1 and MIMO2.

[0101] (Modification of the first embodiment) As in the above embodiment, the second antenna elements Rx are preferably arranged at equal intervals at a reference interval that is a multiple of the predetermined reference distance d, but are not limited thereto. The second antenna elements Rx may be arranged such that at least some of them are unevenly spaced.

[0102] As in the above embodiment, it is preferable that the first antenna elements Tx include those arranged at intervals smaller than the reference interval by the reference distance d, but this is not necessary. Also, it is preferable that the first antenna elements Tx are arranged at intervals smaller than the reference interval by the reference distance d with respect to the first antenna elements Tx at both ends, but this is not necessary. The first antenna elements Tx may be arranged in a configuration different from that of the above embodiment as long as they are arranged so as to suppress the generation of side lobes SL in each of MIMO1 and MIMO2.

[0103] As in the above embodiment, it is preferable that MIMO1 and MIMO2 are configured as extended array antennas, but this is not necessary. Note that the signal averaging and weighting by window function processing in the Khatri-Rao product extension processing are not essential and may be omitted.

[0104] The control unit 6 in the above embodiment is configured to distinguish a signal corresponding to a target detected by each of MIMO1 and MIMO2 from a real image when the peak positions of the signals corresponding to the target are within a predetermined range and the difference in peak levels of the signals corresponding to the target is equal to or less than a predetermined threshold. This predetermined range is preferably set based on the result of simulating the power spectrum of the signal corresponding to the target, with reference to the fluctuation width of the peak position of the signal that becomes a real image, but is not limited thereto. The predetermined range may be set to, for example, an empirically obtained range (e.g., half-width).

[0105] The predetermined threshold is preferably set based on the result of simulating the power spectrum of the signal corresponding to the target, with reference to the fluctuation range of the peak level of the signal that is a real image, but is not limited to this. For example, the predetermined threshold may be set to the average or maximum value of the difference between the peak level of the spectrum signal Sp in MIMO1 and the peak level of the spectrum signal Sp in MIMO2 when the signal corresponding to the target is a real image.

[0106] Second embodiment Next, a second embodiment will be described with reference to Figures 25 to 29. In this embodiment, differences from the first embodiment will be mainly described.

[0107] The control unit 6 of this embodiment detects a signal corresponding to a target based on radio waves received when radio waves are transmitted and received using a third array antenna for SIMO corresponding to an antenna configuration of one first antenna element Tx and multiple second antenna elements Rx. The third array antenna of this embodiment has an antenna configuration of one first antenna element Tx and four second antenna elements Rx. As shown in FIG. 25, in this embodiment, the software and hardware of the control unit 6 that detects a signal corresponding to a target based on radio waves received when radio waves are transmitted and received using the first array antenna constitutes a "third signal detection unit 64."

[0108] In the actual environment in which the vehicle is used, the target object vibrates and moves, and the target position changes in units of mm each time a signal is detected. Therefore, the phase of the signal changes according to the target position fluctuation. In other words, the signals detected by the signal detection units 61 and 62 of the control unit 6 change each time a target object is detected.

[0109] FIG. 26 shows the results of simulating the power spectrum under the same conditions as FIG. 24 described in the first embodiment, where there is a target (U1=0, s1=1) in the center and a mirror reflection position (U2=0.174) is located nearby. In this example, the reflectance in the signal amplitude of the mirror reflection is set to "0.316". In this case, the power of the mirror reflected wave is 0.01 (≒0.316^4). Also, the power of the reflected wave when the outward and return paths of the radio wave do not match is 0.1 (≒0.316^2). However, the signal phase is changed randomly. As shown in FIG. 26, the position of the peak may vary due to the influence of the vibration or movement of the target, and images at similar positions may be judged to be real images or false images.

[0110] Considering this, the control unit 6 of this embodiment is configured to compare the signals detected by the signal detection units 61, 62, and 64 in the signal determination process to determine whether the signal to be determined is a real image or a false image.

[0111] The target detection process executed by the control unit 6 will be described below with reference to Fig. 27. Note that the process from steps S200 to S240 in the target detection process is the same as the process from steps S100 to S140 in the target detection process described in the first embodiment, and therefore the description thereof will be omitted.

[0112] 27, after performing a second direction estimation process to detect the direction of a target by the second array antenna for MIMO in step S240, the control unit 6 proceeds to step S250. In step S250, the control unit 6 performs a third direction estimation process to detect the direction of a target by the third array antenna for SIMO.

[0113] Next, in step S260, the control unit 6 performs a signal determination process to determine whether the signal corresponding to the target is a real image or a false image. In this signal determination process, the detection results of the signal corresponding to the target at the first to third array antennas are compared, and based on the comparison result, it is determined whether the signal corresponding to the target is a real image or a false image.

[0114] Hereinafter, the signal determination process executed by the control unit 6 will be described with reference to Fig. 28. Note that the process from steps S261 to S264 in the signal detection process is the same as the process from steps S151 to S154 in the target detection process described in the first embodiment, and therefore the description thereof will be omitted.

[0115] As shown in FIG. 28, when it is determined in step S264 that the difference between the peak level of the spectrum signal Sp in MIMO1 and the peak level of the spectrum signal Sp in MIMO2 is equal to or smaller than the predetermined threshold, the control unit 6 proceeds to step S265.

[0116] In step S265, the control unit 6 determines whether or not the difference between the peak level of the spectrum signal Sp in SIMO and the peak level of the spectrum signal Sp in one of the MIMOs, MIMO1 and MIMO2, is equal to or smaller than a predetermined value. The predetermined value is set to, for example, a peak level expected when a grating lobe and a signal corresponding to a target interfere with each other in a destructive manner.

[0117] If the result of the determination in step S265 is that the difference between the peak level of the spectrum signal Sp in SIMO and the peak level of the spectrum signal Sp in MIMO is equal to or less than a predetermined value, it is considered that interference between the grating lobe and the signal corresponding to the target does not occur. Therefore, in step S266, the control unit 6 determines whether or not the peak position of the spectrum signal Sp in SIMO and the peak position of the spectrum signal Sp in MIMO are within a predetermined range. In this determination, for example, it is determined whether or not the peak position of the spectrum signal Sp in SIMO is within a predetermined range including the peak position of the spectrum signal Sp in MIMO2. Note that the predetermined range may be the same as or different from that used in the determination in step S262.

[0118] If the peak positions are outside the predetermined range, the control unit 6 identifies the signal corresponding to the target being judged as a “false image” in step S263, and if the peak positions are within the predetermined range, the control unit 6 proceeds to step S267.

[0119] In step S267, the control unit 6 determines whether or not the difference in peak level between the spectrum signal Sp in SIMO and the spectrum signal Sp in MIMO is equal to or less than a predetermined threshold. In this determination, for example, it determines whether or not the difference in peak level between the spectrum signal Sp in MIMO2 and the spectrum signal Sp in SIMO is equal to or less than a predetermined threshold. Note that the predetermined threshold may be the same value as that used in the determination in step S264, or may be a different value.

[0120] If the difference between the peak levels exceeds a predetermined threshold, the control unit 6 determines in step S263 that the signal corresponding to the target being determined is a "false image." If the peak positions are within a predetermined range, the control unit 6 determines in step S268 that the signal corresponding to the target being determined is a "real image." In this way, by using SIMO that is not affected by path mismatch, it is possible to properly remove false images due to path mismatch. As a result, it is possible to properly detect the signal corresponding to the target.

[0121] On the other hand, if the result of the determination in step S265 is that the difference between the peak level of the spectrum signal Sp in SIMO and the peak level of the spectrum signal Sp in MIMO is greater than the predetermined value, there is a possibility that interference between the grating lobe and the signal corresponding to the target occurs. Therefore, if the difference between the peak level of the spectrum signal Sp in SIMO and the peak level of the spectrum signal Sp in MIMO exceeds the predetermined value, the control unit 6 does not perform the determination process using SIMO and proceeds to step S268. In step S268, the control unit 6 identifies the signal corresponding to the target to be determined as a "real image."

[0122] Fig. 29 shows a simulation result of the power spectrum of a signal corresponding to a reflected wave resulting in a path mismatch when there are two targets (U1=0, U2=-2 / 3) and the reflected power is 1 (0 dB), similar to Fig. 20. As shown in Fig. 29, in each of MIMO1 and MIMO2, a signal peak corresponding to a target overlapping with the occurrence position of a grating lobe can be detected, and therefore an image at the target position can be determined as a real image. Note that the radar device 1 of this embodiment does not perform a determination process using SIMO, because the difference between the peak level of the spectrum signal Sp in SIMO and the peak level of the spectrum signal Sp in MIMO becomes larger than a predetermined value, as shown in Fig. 20.

[0123] When there are multiple signals to be determined, such signal determination processing is performed for each of the signals to be determined. When the signal determination processing is completed, the control unit 6 proceeds to step S270 in Fig. 27 and detects targets based on the signals identified as real images in the signal determination processing.

[0124] The rest is the same as in the first embodiment. The radar device 1 of this embodiment can obtain the same effects as in the first embodiment, which are achieved by a configuration common to the first embodiment or an equivalent configuration.

[0125] Moreover, the radar device 1 of this embodiment has the following features.

[0126] (1) When the difference between the peak levels of the signals detected by SIMO and MIMO is small, it is assumed that there is no signal interference due to the overlap of the grating lobe generation position and the target position.

[0127] Considering this, the radar device 1 of this embodiment includes a third signal detection unit 64 that detects a signal corresponding to a target using a third array antenna for SIMO. Then, the discrimination unit 63 of the control unit 6 judges whether or not the difference between the peak level of the signal corresponding to the target detected by the third signal detection unit 64 and the peak level of the signal corresponding to the target detected by at least one of the first signal detection unit 61 and the second signal detection unit 62 is within a predetermined value. If the result of this judgment is that the difference between the peak levels is within the predetermined value, the discrimination unit 63 compares the detection result of the first signal detection unit 61, the detection result of the second signal detection unit 62, and the detection result of the third signal detection unit 64, and discriminates whether the signal corresponding to the target is a real image or a false image based on the comparison result. In this way, by also using the detection result of the signal corresponding to the target in SIMO, it is possible to appropriately discriminate whether the signal corresponding to the target is a real image or a false image.

[0128] (Modification of the second embodiment) The radar device 1 of the above embodiment detects a signal corresponding to a target by the third array antenna for SIMO and identifies whether the signal corresponding to the target is a real image or a false image based on the detection result, but is not limited to this. For example, the radar device 1 may detect a signal corresponding to a target by an array antenna for MISO and identify whether the signal corresponding to the target is a real image or a false image based on the detection result.

[0129] (Other embodiments) Representative embodiments of the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments and can be modified in various ways, for example, as described below.

[0130] In the above-described embodiment, a specific example of the antenna configuration of the radar device 1 is given, but the antenna configuration of the radar device 1 is not limited to the above-described one, and the antenna configuration may be different from the above-described one.

[0131] In the above embodiment, an example has been described in which the radar device 1 of the present disclosure is applied to a target detection device that is mounted on a vehicle and detects various targets present around the vehicle, but the application of the radar device 1 is not limited to this. The radar device 1 can also be applied to, for example, moving objects other than vehicles and stationary devices.

[0132] In the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except in cases where it is particularly expressly stated that they are essential or where they are clearly considered to be essential in principle.

[0133] In the above-described embodiments, when numerical values ​​such as the number, values, amounts, ranges, etc. of components of the embodiments are mentioned, they are not limited to the specific numbers unless expressly stated as required or clearly limited to a specific number in principle.

[0134] In the above-described embodiments, when referring to the shapes, positional relationships, etc. of components, etc., there is no limitation to those shapes, positional relationships, etc., unless specifically stated or in principle limited to a specific shape, positional relationship, etc.

[0135] The control unit and the method of the present disclosure may be implemented in a special-purpose computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. The control unit and the method of the present disclosure may be implemented in a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. The control unit and the method of the present disclosure may be implemented in one or more special-purpose computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. The computer program may also be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer. [Explanation of symbols]

[0136] 1. Radar equipment 3 Transmitting antennas 4 Receiving antennas 61 First signal detection unit 62 Second signal detection unit 63 Identification section Tx 1st antenna element Rx 2nd antenna element

Claims

1. A radar device that detects targets using radio waves, A transmitting antenna group (3) including a plurality of actual first antenna elements (Tx); A receiving antenna group (4) including a plurality of actual second antenna elements (Rx); a first signal detection unit (61) that detects a signal corresponding to the target using a first array antenna including a predetermined number (two or more) of the first antenna elements and a plurality of the second antenna elements; a second signal detection unit (62) that detects a signal corresponding to the target using a second array antenna including a number of the first antenna elements greater than the predetermined number and a plurality of the second antenna elements; and an identification unit (63) that compares the detection result of the first signal detection unit with the detection result of the second signal detection unit and identifies whether the signal corresponding to the target is a real image or a false image based on the comparison result.

2. Among the plurality of first antenna elements and the plurality of second antenna elements, one antenna element is arranged at equal intervals at a reference interval that is a multiple of a predetermined reference distance, 2. The radar device according to claim 1, wherein the other of the plurality of first antenna elements and the plurality of second antenna elements includes an antenna element that is arranged at an interval that is smaller than the reference interval by an amount equal to the reference distance.

3. 3. The radar device according to claim 2, wherein the other antenna element includes a plurality of antenna elements arranged at intervals equal to an antenna aperture length of the one antenna element plus the reference interval.

4. 4. The radar device according to claim 1, wherein the first array antenna and the second array antenna are configured as extended array antennas including virtual antenna elements complemented by a differential signal corresponding to a phase difference between a plurality of antenna elements caused by radio waves arriving from a direction intersecting an arrangement direction of the plurality of antenna elements.

5. 5. The radar device according to claim 4, wherein when a plurality of signals corresponding to antenna elements constituting the extended array antenna are obtained, the first signal detection unit and the second signal detection unit average the plurality of signals.

6. 5. The radar device according to claim 4, wherein the first signal detection unit and the second signal detection unit weight signals corresponding to antenna elements constituting the extended array antenna by window function processing.

7. a third signal detection unit (64) that detects a signal corresponding to the target using a third array antenna including one antenna element included in one of the transmitting antenna group and the receiving antenna group and two or more antenna elements included in the other antenna group, 4. The radar device according to claim 1, wherein the identification unit compares the detection result of the first signal detection unit, the detection result of the second signal detection unit, and the detection result of the third signal detection unit, when a difference between a peak level of the signal corresponding to the target detected by the third signal detection unit and a peak level of the signal corresponding to the target detected by at least one of the first signal detection unit and the second signal detection unit is within a predetermined value, and identifies whether the signal corresponding to the target is a real image or a false image based on a comparison result.

Images