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 identifies whether a signal is a real image or a false image on the basis of a detection result of a signal corresponding to a target using one first antenna element Tx and the plurality of second antenna elements Rx and a detection result of a signal corresponding to the target using the plurality of first antenna elements Tx and the plurality of second antenna elements Rx. The control portion 6 identifies the signal as a real image when a peak position of the signal corresponding to the target detected by each signal detection portion 61, 62 is within a predetermined range and a difference of peak levels of the signals corresponding to the target is equal to or less than a predetermined threshold. The control portion 6 also identifies the signal as a false image when the peak position is outside the predetermined range or the difference of the peak levels exceeds the predetermined threshold.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a radar device for detecting a target. [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 Patent Document 1, when the outbound and return paths of radio waves do not match, the peak position of the signal detected by MIMO is considered to be shifted, and whether the signal corresponding to the target is a real image or a false image is identified based on the peak positions of the signals detected by MIMO and SIMO. Specifically, when the peak positions of the signals detected by MIMO and SIMO are different, the signal is determined to be a false image, and when the peak positions of the signals detected by MIMO and SIMO match, the signal is determined to be a real image.

[0005] However, even when the outgoing and return paths of radio waves are the same, the peak positions of the signals detected by MIMO and SIMO may differ depending on the antenna configuration. In other words, the antenna arrangement configuration shown in Patent Document 1 may not be able to properly distinguish whether a signal corresponding to a target is a real image or a false image. The same is true when comparing the target detection results in a MIMO configuration with the target detection results in a configuration (MISO) in which radio waves transmitted from multiple antennas are received by one antenna.

[0006] 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. [Means for solving the problem]

[0007] 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 based on radio waves received when radio waves are transmitted and received using one antenna element included in one of the transmitting antenna group and two or more antenna elements included in the other of the receiving antenna group; a second signal detection unit (62) that detects a signal corresponding to a target based on radio waves received when radio waves are transmitted and received between two or more antenna elements included in one antenna group and two or more antenna elements included in the other antenna group; a discrimination unit (63) that compares a detection result of a signal corresponding to the target by the first signal detection unit with a detection result of a signal corresponding to the target by the second signal detection unit, and discriminates whether the signal corresponding to the target is a real image or a false image based on a comparison result; The identification unit identifies an image as a real image when the peak positions of the signals corresponding to the target detected by the first signal detection unit and the second signal detection unit 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, and identifies an image as a virtual image when the peak positions are outside the predetermined range or the difference in peak levels exceeds the predetermined threshold.

[0008] According to this, when the outgoing and return paths of the radio waves are the same, even if the peak positions of the signals detected by the MIMO and SIMO are shifted due to differences in the antenna configuration, it is possible to determine the signal as a real image. Therefore, compared to the above-mentioned conventional technology, it is possible to appropriately identify whether the signal corresponding to the target is a real image or a false image.

[0009] 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]

[0010] [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 second array antenna for MIMO in the radar device according to the first embodiment. [Diagram 5] 4 is a flowchart showing a flow of a target detection process executed by a control unit of the radar device. [Figure 6] FIG. 2 is a schematic diagram showing an example of an arrangement of antenna elements in a radar device. [Figure 7] FIG. 2 is an explanatory diagram for explaining a power spectrum of a signal corresponding to a target in SIMO. [Figure 8] FIG. 2 is an explanatory diagram for explaining a power spectrum of a signal corresponding to a target in MIMO. [Figure 9] FIG. 7 is a spectrum diagram showing a simulation result when the azimuth of one target is estimated using the antenna configuration of FIG. 6. [Figure 10] 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 11] FIG. 2 is an explanatory diagram for explaining a power spectrum in SIMO when there are two targets. [Figure 12] 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 13] 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 14] 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 15] 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 16] 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 17]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 18] 5 is a flowchart showing a flow of a signal determination process executed by a control unit of the radar device. [Figure 19] FIG. 4 is an explanatory diagram for explaining an antenna configuration serving as a comparative example of the first embodiment. [Figure 20] FIG. 11 is a spectrum diagram showing the estimation result of the azimuth in an antenna configuration serving as a comparative example to the first embodiment. [Figure 21] FIG. 2 is an explanatory diagram for explaining an antenna configuration of the radar device according to the first embodiment. [Figure 22] FIG. 4 is a spectrum diagram showing a simulation result of the azimuth in the antenna configuration of the radar device according to the first embodiment. [Figure 23] FIG. 11 is an explanatory diagram for explaining an antenna configuration of a radar device according to a second embodiment. [Figure 24] FIG. 11 is a spectrum diagram showing a simulation result of the azimuth in the antenna configuration of the radar device according to the second embodiment. [Diagram 25] FIG. 11 is an explanatory diagram for explaining an antenna configuration of a radar device according to a third embodiment. [Figure 26] FIG. 11 is a spectrum diagram showing a simulation result of the azimuth in the antenna configuration of the radar device according to the third embodiment. [Figure 27] FIG. 13 is an explanatory diagram for explaining an extended array antenna in a radar device according to a fourth embodiment. [Figure 28] 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 29] FIG. 11 is an explanatory diagram for explaining a window function. [Diagram 30] FIG. 13 is a spectrum diagram showing the simulation results of the azimuth when an extended array antenna is used. [Diagram 31] FIG. 13 is a spectrum diagram showing the simulation results of the azimuth when the second array antenna is used. [Diagram 32] FIG. 13 is a spectrum diagram showing the simulation results of the azimuth when an extended array antenna is used. [Diagram 33] FIG. 11 is a spectrum diagram showing the results of a simulation of the azimuth direction in a situation where reflected waves are mixed, in which the outgoing path and the return path of the radio wave coincide and do not coincide. [Diagram 34] FIG. 13 is a spectrum diagram showing the simulation results of the azimuth in a situation where only reflection exists when the outgoing path and the return path of the radio wave do not match. [Diagram 35] This is a spectrum diagram showing the simulation results of the azimuth in a situation where the phase changes randomly, resulting in a phase condition different from that in Figure 34, and where only reflection exists when the outbound and return paths of the radio waves do not match. [Diagram 36] This is a spectrum diagram showing the simulation results of the azimuth in a situation where the phase changes randomly, resulting in phase conditions different from those in Figures 34 and 35, and where only reflection exists when the outbound and return paths of the radio waves do not match. [Figure 37] 13 is a flowchart showing the flow of a signal determination process executed by a control unit of a radar device according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 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.

[0012] (First embodiment) The present embodiment will be described with reference to Figures 1 to 22. 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] The transmitting antenna group 3 transmits radio waves corresponding to the chirp signal provided from the transmitter 2 toward the front of the vehicle. In this example, the transmitting antenna group 3 is composed of two actual first antenna elements Tx. The first antenna elements Tx are arranged in a row along the arrangement direction in a predetermined direction with a predetermined interval between them.

[0018] The first antenna elements Tx of this embodiment are arranged side by side in the width direction of the vehicle. As shown in Fig. 2, the first antenna elements Tx are arranged at an interval of "2d" which is twice the reference distance d. The interval between the first antenna elements Tx 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 contradict the spirit of the technology of the present disclosure.

[0019] 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.

[0020] 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. In this example, the receiving antenna group 4 is composed of four second antenna elements Rx that actually exist. The second antenna elements Rx are arranged in a row along the arrangement direction in a predetermined direction at a predetermined interval.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 SIMO corresponding to an antenna configuration of one first antenna element Tx and multiple second antenna elements Rx. The first array antenna of this embodiment has an antenna configuration of one first antenna element 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."

[0026] The control unit 6 detects a signal corresponding to the 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 of a plurality of first antenna elements Tx and a plurality of second antenna elements Rx. The second array antenna of this embodiment has an antenna configuration of 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 the target based on radio waves received when radio waves are transmitted and received using the second array antenna constitutes the "second signal detection unit 62". The second signal detection unit 62 executes an interpolation process to generate a virtual antenna by MIMO or the like, and detects a signal corresponding to the target based on the processing result of the interpolation process.

[0027] Here, an array antenna for MIMO will be described. The second array antenna of this embodiment is a virtual array in which four second antenna elements Rx are added to four virtual antenna elements Vx. 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 second array antenna of this embodiment is configured such that the antenna elements are arranged at unequal intervals.

[0028] Specifically, the radar device 1 of this embodiment has, as actual antenna elements, two first antenna elements Tx arranged at an interval of “2d” and four second antenna elements Rx arranged at an interval of “3d”, as shown in the upper part of FIG. 4.

[0029] When the angle of arrival of the radio wave with respect to the front direction of the second antenna element Rx is "θ", the path difference between adjacent second antenna elements Rx is "3dsinθ". In addition, when the wavelength of the radio wave is λ, the phase difference between adjacent second antenna elements Rx is "(2π / λ)·3dsinθ", which is the path difference multiplied by "2π / λ". In addition, when multiplexing from two first antenna elements Tx, the path difference corresponding to the distance between the two first antenna elements Tx is also added.

[0030] Therefore, the second array antenna of this embodiment is configured as a virtual array in which four second antenna elements Rx and four virtual antenna elements Vx are arranged as shown in the lower part of FIG.

[0031] However, this virtual array is premised on the assumption that the angles of the outgoing and return paths of the radio waves are approximately the same. If the angles of the outgoing and return paths of the radio waves differ due to multipath, the second array antenna detects not only the signal corresponding to the target, but also a signal corresponding to a direction different from that of the target as a false image. Examples of mirrors include guardrails and walls placed on the side of the road.

[0032] On the other hand, since the first array antenna is a SIMO array antenna composed of real antenna elements, the angles of the outgoing and return paths of the radio waves do not need to be approximately the same, and therefore the first array antenna is not affected by false images due to multipath.

[0033] In consideration of these, the radar device 1 detects signals corresponding to targets by both the first array antenna and the second array antenna in the target detection process, and identifies whether the signals corresponding to targets are real or false images based on the detection results. Specifically, the control unit 6 compares the detection results of signals corresponding to targets when the first array antenna is used with the detection results of signals corresponding to targets when the second array antenna is used, and identifies whether the signals corresponding to targets are real or false images based on the comparison results. In this embodiment, the control unit 6 includes an "identification unit 63" that compares the detection results of signals corresponding to targets by the first signal detection unit 61 with the detection results of signals corresponding to targets by the second signal detection unit 62, and identifies whether the signals corresponding to targets are real or false images based on the comparison results.

[0034] The target detection process executed by the control unit 6 of the radar device 1 will be described below with reference to Fig. 5. The process shown in Fig. 5 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.

[0035] 5, 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.

[0036] 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.

[0037] 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.

[0038] 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 SIMO. 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.

[0039] 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.

[0040] 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 SIMO 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.

[0041] Here, the power spectrum of a signal corresponding to a target will be described with reference to Figs. 7 to 17, taking the arrangement of antenna elements xlm shown in Fig. 6 as an example. In the following, the first array antenna for SIMO may be called "SIMO" and the second array antenna for MIMO 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.

[0042] When the received signal at each antenna element xlm is represented by vector X as shown in Fig. 7 (1.1), and the direction U is represented by array vector A as shown in Fig. 7 (1.2), the spectrum signal Sp in the direction U as shown in Fig. 7 (1.3) can be obtained by multiplying the two. In Fig. 7, "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 (sinθ) of the azimuth angle θ. In MIMO, it is a combination of "l" and "m."

[0043] In the case of SIMO, the received signal when there are k targets is shown in (1.4) of Fig. 7, and when there is one target, it is shown in (1.5) of Fig. 7. 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. 7. In the case of SIMO, since there is one first antenna element Tx, dm = 0.

[0044] According to (1.6) in Fig. 7, 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. 7 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.

[0045] 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.

[0046] 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 8. 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.

[0047] According to (2.2) in Figure 8, 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.

[0048] 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.

[0049] Fig. 9 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. 9, 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.

[0050] 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. 10. Under this premise, the received signal at each antenna element xij in SIMO is shown in Fig. 11(3.1), the vector X is shown in Fig. 11(3.2), and the spectrum signal Sp is shown in Fig. 11(3.3).

[0051] 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 FIG. 12(4.1), the vector X is as shown in FIG. 12(4.2), and the spectrum signal Sp is as shown in FIG. 12(4.3).

[0052] In (4.1) and (4.2) of Figure 12, 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 is also different from that shown in (2.2) of Figure 8.

[0053] In addition, the terms indicating reflection by the mirror at "θ2" are reinforced, so the absolute value of the spectrum signal Sp becomes large even near "θ2". Note that (3.3) in Figure 11 showing the SIMO spectrum signal Sp and (4.3) in Figure 12 showing the MIMO spectrum signal Sp have different formulas, so the peak positions and absolute values ​​are different.

[0054] Fig. 13 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. 13, 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.

[0055] 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.

[0056] Next, we will explain the case where the outgoing and return paths of the radio waves do not match, as shown in the center and right side of Figure 10. In MIMO, when the outgoing and return paths of the radio waves do not match and there is one target, the received signal at each antenna element xlm is as shown in (5.1) of Figure 14. When the outgoing path of the radio waves is θ t =θ2, return path is θ r When =θ1=0, the vector X is as shown in (5.2) of FIG. 14, and the spectral signal Sp is as shown in (5.3) of FIG.

[0057] The spectrum signal Sp shown in (5.3) of Fig. 14 has more terms than the spectrum signal Sp shown in (1.6) of Fig. 7, each of which has a phase corresponding to the position of the antenna element xm, and is the sum of these terms. Therefore, 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.

[0058] In addition, the spectrum signal Sp shown in (5.3) of FIG. 14 has a different shape from that shown in (4.3) of FIG. 12, 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 an artifact 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 14.

[0059] Fig. 15 shows a comparison result between the spectrum signal Sp shown in (5.3) of Fig. 14 and the spectrum signal Sp shown in (5.4) of Fig. 14. As shown in Fig. 15, 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.

[0060] In addition, the outgoing path of the radio wave θ t =θ1=0, the return path is θ r When = θ2, the vector X is as shown in (5.5) of Fig. 14, and the spectrum signal Sp is as shown in (5.6) of Fig. 14. When this received signal is digitally beamformed using SIMO, the spectrum signal Sp is as shown in (5.7) of Fig. 14.

[0061] Figure 16 shows the comparison result between the spectrum signal Sp shown in (5.6) of Figure 14 and the spectrum signal Sp shown in (5.7) of Figure 14. As shown in Figure 16, 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.

[0062] There may also be cases where radio waves with mismatched paths overlap. In this case, the received signal is the sum of (5.3) and (5.5) in Fig. 14. In this case, the peak position and peak level of the spectrum signal Sp change, for example, as shown in Fig. 17. Such changes also occur when radio waves with matching paths and radio waves with mismatched paths overlap.

[0063] In this way, the peak positions and peak levels of the SIMO and MIMO spectrum signals Sp may change even in the azimuths U1 and U2 indicating the target position. In consideration of this, the control unit 6 of this embodiment is configured to perform a signal determination process for determining whether the peak positions and peak levels of the SIMO and MIMO spectrum signals Sp are within a predetermined determination region JA. Hereinafter, the signal determination process performed by the control unit 6 will be described with reference to FIG. 18.

[0064] As shown in Fig. 18, in step S151, the control unit 6 selects a spectrum signal Sp to be determined. For example, the control unit 6 selects a spectrum signal Sp having a peak level exceeding a predetermined selection threshold as the determination target from among the MIMO spectrum signals Sp. 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 spectrum signal Sp when the signal corresponding to the target is a real image. Note that the control unit 6 may be configured to select the spectrum signal Sp to be determined based on the SIMO spectrum signal Sp.

[0065] Next, in step S152, the control unit 6 determines whether the difference between the peak position of the SIMO spectrum signal Sp and the peak position of the MIMO spectrum signal Sp is within a predetermined range. Specifically, it determines whether the peak position of the SIMO spectrum signal Sp is within a predetermined range including the peak position of the spectrum signal Sp to be determined.

[0066] 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 SIMO spectrum signal Sp when the signal corresponding to the target is a real image and the peak position of the MIMO spectrum signal Sp. According to the study by the inventors of the present invention, there is a tendency that the peak position of the SIMO spectrum signal Sp is present within the range of the half-width of the peak of the MIMO spectrum signal Sp 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 MIMO spectrum signal Sp.

[0067] If the difference between the peak position of the spectrum signal Sp in SIMO and the peak position of the spectrum signal Sp in MIMO 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.”

[0068] On the other hand, if the difference between the peak position of the spectrum signal Sp in SIMO and the peak position of the spectrum signal Sp in MIMO 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 SIMO and the peak level of the spectrum signal Sp in MIMO is equal to or less than a predetermined threshold. Specifically, it is determined whether the difference between the peak levels of the spectrum signals Sp whose peak positions are within the predetermined range is equal to or less than a predetermined threshold.

[0069] The predetermined threshold is set by experiments or simulations. The predetermined range is set to, for example, the maximum value of the difference between the peak level of the spectrum signal Sp in SIMO and the peak level of the spectrum signal Sp in MIMO when the signal corresponding to the target is a real image.

[0070] 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 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”.

[0071] Furthermore, 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 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.”

[0072] 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. 5 and detects targets based on the signals identified as real images in the signal determination processing.

[0073] In the above-described radar device 1, in the target detection process, signals corresponding to the target are detected by both the first array antenna and the second array antenna, and based on the detection result, the signal corresponding to the target is identified as a real image or a false image. This makes it possible to detect the target with high accuracy.

[0074] In particular, the control unit 6 classifies a real image when the peak positions of the signals corresponding to the target detected by the SIMO and MIMO 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 value. Also, the control unit 6 classifies a virtual image when the peak positions of the signals corresponding to the target detected by the SIMO and MIMO are outside the predetermined range or the difference in peak levels of the signals corresponding to the target exceeds a predetermined threshold value.

[0075] According to this, when the outgoing and return paths of radio waves are the same, even if the peak positions of the signals detected by MIMO and SIMO are shifted due to differences in antenna configuration, it is possible to determine the signal as a real image. Therefore, compared to conventional technology, it is possible to appropriately identify whether a signal corresponding to a target is a real image or a false image.

[0076] Moreover, the radar device 1 of this embodiment has the following features.

[0077] (1) The predetermined range is set based on the result of simulating the power spectrum of the signal corresponding to the target, with the fluctuation range of the peak position of the signal that becomes the real image as a reference. Also, the predetermined threshold is set based on the result of simulating the power spectrum of the signal corresponding to the target, with the fluctuation range of the peak level of the signal that becomes the real image as a reference. 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.

[0078] Here, while SIMO and MIMO detect various signals of different sizes, it is not necessary for the radar device 1 to distinguish whether all signals are real or false, as long as it can detect targets. For this reason, it is preferable that the control unit 6 is configured to determine, among the signals detected by either SIMO or MIMO, those whose peak levels exceed a predetermined selection threshold, and compare the signals to be determined with the signals detected by the other of SIMO and MIMO.

[0079] (2) The antenna configuration of the prior art is configured to have two first antenna elements Tx spaced apart by “4d” and four second antenna elements Rx spaced apart by “1d”, as shown in FIG.

[0080] In this antenna configuration, the antenna aperture length of the SIMO is "3d" and that of the MIMO is "7d". In other words, the antenna aperture length of the MIMO is more than twice that of the SIMO, and the resolution of the two is significantly different. This leads to a decrease in accuracy when determining whether a signal corresponding to a target is a real image or a false image.

[0081] Fig. 20 shows the simulation results of the power spectrum when there are two targets (U1 = 0, U2 = 0.259) and the reflected power is 1 (0 dB) in the antenna configuration of the conventional technology. As shown in Fig. 20, when two close targets are targets, the MIMO configuration can detect two signal peaks corresponding to the two targets, but the SIMO configuration cannot detect two signal peaks corresponding to the two targets. In this case, the peak positions of the spectrum signal Sp in the SIMO and MIMO are outside the judgment area JA, and there is a risk that the image at the target position will be judged as a false image.

[0082] In contrast, in the radar device 1 of this embodiment, the first antenna element Tx and the second antenna element Rx are arranged so that the antenna aperture length of SIMO is larger than half the antenna aperture length of MIMO. Such an antenna configuration is obtained by making the interval of the first antenna elements Tx smaller than the antenna aperture length of SIMO. In the radar device 1 of this embodiment, the second antenna elements Rx are arranged side by side at equal intervals with a reference interval that is multiple times the reference distance d, and the first antenna elements Tx are arranged at an interval smaller than the reference interval. Note that, when there are three or more first antenna elements Tx, an antenna configuration in which the antenna aperture length of SIMO is larger than half the antenna aperture length of MIMO can be obtained by making the maximum interval of the first antenna elements Tx smaller than the antenna aperture length of SIMO.

[0083] Specifically, as shown in Fig. 21, the radar device 1 includes two first antenna elements Tx spaced apart by "2d" and four second antenna elements Rx spaced apart by "3d". In this antenna arrangement, the SIMO antenna aperture length is "9d" and the MIMO antenna aperture length is "11d". In other words, the SIMO antenna aperture length is larger than half the MIMO antenna aperture length.

[0084] Fig. 22 shows the simulation results of the power spectrum when there are two targets (U1 = 0, U2 = 0.259) and the reflected power is 1 (0 dB) in the antenna configuration of this embodiment. As shown in Fig. 22, when two close targets are targets, two signal peaks corresponding to the two targets can be detected in both the MIMO configuration and the SIMO configuration. Then, both the peak positions and peak levels of the spectrum signal Sp in the SIMO and MIMO configurations are within the judgment region JA, and the image at the target position can be judged to be a real image.

[0085] In this way, the radar device 1 of this embodiment is less susceptible to a decrease in the accuracy of determining whether a real image or a false image is caused by the difference in resolution between SIMO and MIMO, and can appropriately identify whether a signal corresponding to a target is a real image or a false image, compared to the conventional technology described above.

[0086] (3) The second antenna elements Rx are arranged at equal intervals with a reference interval that is multiple times the predetermined reference distance d. The first antenna elements Tx include elements arranged at intervals smaller than the reference interval. In this way, if the first antenna elements Tx and the second antenna elements Rx are arranged at equal intervals with a reference interval for one of them and an interval smaller than the reference interval for the other, the interval between the antenna elements in MIMO can be reduced. In this case, the side lobe SL in MIMO tends to be small, and erroneous detection of the side lobe SL as a real image is suppressed.

[0087] (4) The first antenna elements Tx include those arranged at intervals that are smaller than the reference interval by the reference distance d. In this way, the interval between the actual antenna element and the virtual antenna element in MIMO is the reference distance d, so that the occurrence of side lobes SL in MIMO can be suppressed.

[0088] (Modification of the first embodiment) As in the above embodiment, it is preferable that the first antenna element Tx and the second antenna element Rx are arranged so that the antenna aperture length of SIMO is larger than half of the antenna aperture length of MIMO, but is not limited thereto. For example, the radar device 1 may arrange the first antenna element Tx and the second antenna element Rx so that the antenna aperture length of MISO is equal to or smaller than half of the antenna aperture length of MIMO.

[0089] 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.

[0090] As in the above embodiment, it is preferable that the first antenna elements Tx include those arranged at intervals that are smaller than the reference interval by the reference distance d, but this is not necessarily required.

[0091] The control unit 6 in the above embodiment is configured to distinguish a signal corresponding to a target detected by SIMO and MIMO 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 fluctuation width of the peak position of the signal that becomes a real image based on the simulation result of the power spectrum of the signal corresponding to the target, but is not limited to this. The predetermined range may be set to, for example, an empirically obtained range (e.g., half-width).

[0092] 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 thereto. 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 SIMO and the peak level of the spectrum signal Sp in MIMO when the signal corresponding to the target is a real image.

[0093] Second embodiment Next, a second embodiment will be described with reference to Figures 23 and 24. In this embodiment, differences from the first embodiment will be mainly described.

[0094] As shown in Fig. 23, the receiving antenna group 4 of this embodiment includes four second antenna elements Rx. The second antenna elements Rx of this embodiment are arranged at equal intervals at a reference interval that is multiple times the reference distance d. Specifically, the second antenna elements Rx are arranged at an interval of "6d" that is six times the reference distance d.

[0095] Moreover, the transmitting antenna group 3 of this embodiment includes three first antenna elements Tx. The first antenna elements Tx are arranged at intervals smaller than the reference interval. Specifically, when the first antenna element Tx located at one end side is defined as a reference element, the first antenna elements Tx are arranged at a position spaced apart by "2d", which is twice the reference distance d, from the reference element, and at a position spaced apart by "5d", which is five times the reference distance d. Note that the first antenna elements Tx of this example include those arranged at intervals smaller than the reference interval by the reference distance d.

[0096] In this antenna configuration, the SIMO antenna aperture length is "18d" and the MIMO antenna aperture length is "23d". In other words, the SIMO antenna aperture length is larger than half the MIMO antenna aperture length. In addition, the second array antenna that constitutes the MIMO is arranged so that the spacing between antenna elements is consecutive, such as "1d", "2d", "3d", "4d", "5d", and "6d".

[0097] Fig. 24 shows the simulation results of the power spectrum when there are two targets (U1 = 0, U2 = 0.174) and the reflected power is 1 (0 dB) in the antenna configuration of this embodiment. As shown in Fig. 24, when two close targets are targets, two signal peaks corresponding to the two targets can be detected in both the MIMO configuration and the SIMO configuration. Then, both the peak positions and peak levels of the spectrum signal Sp in the SIMO and MIMO configurations are within the judgment region JA, and the image at the target position can be judged to be a real image.

[0098] Here, the large spacing between the second antenna elements Rx in the SIMO generates a large amount of grating lobes GL. On the other hand, the spacing between the antenna elements in the MIMO is arranged in consecutive numbers such as "1d", "2d", "3d", "4d", "5d", and "6d", so the side lobes SL are small. Therefore, according to the radar device 1 of this embodiment, it is possible to determine that an image other than the target position is a false image.

[0099] As described above, the radar device 1 of this embodiment is less susceptible to a decrease in the accuracy of determining whether a real image or a false image is caused by the difference in resolution between SIMO and MIMO, and can appropriately identify whether a signal corresponding to a target is a real image or a false image.

[0100] 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.

[0101] Third embodiment Next, a third embodiment will be described with reference to Figures 25 and 26. In this embodiment, differences from the first embodiment will be mainly described.

[0102] As shown in Fig. 25, the receiving antenna group 4 of this embodiment includes four second antenna elements Rx. The second antenna elements Rx of this embodiment are arranged at equal intervals at a reference interval that is multiple times the reference distance d. Specifically, the second antenna elements Rx are arranged at an interval of "8d" that is eight times the reference distance d.

[0103] Moreover, the transmitting antenna group 3 of this embodiment includes three first antenna elements Tx. The first antenna elements Tx are arranged at intervals smaller than the reference interval. Specifically, when the first antenna element Tx located at one end side is defined as a reference element, the first antenna elements Tx are arranged at a position spaced apart by "2d", which is twice the reference distance d, from the reference element, and at a position spaced apart by "7d", which is seven times the reference distance d. Note that the first antenna elements Tx of this example include those arranged at intervals smaller than the reference interval by the reference distance d.

[0104] In this antenna configuration, the SIMO antenna aperture length is 24d, and the MIMO antenna aperture length is 31d. In other words, the SIMO antenna aperture length is larger than half the MIMO antenna aperture length. In addition, the second array antenna that constitutes the MIMO has antenna elements spaced at intervals of 1d, 2d, 3d, 5d, 6d, 7d, and 8d, with the exception of 4d, which is a consecutive arrangement.

[0105] Fig. 26 shows the simulation results of the power spectrum when there are two targets (U1 = 0, U2 = 0.122) and the reflected power is 1 (0 dB) in the antenna configuration of this embodiment. As shown in Fig. 26, when two close targets are targets, two signal peaks corresponding to the two targets can be detected in both the MIMO configuration and the SIMO configuration. Then, both the peak positions and peak levels of the spectrum signal Sp in the SIMO and MIMO configurations are within the judgment region JA, and the image at the target position can be judged to be a real image.

[0106] Here, the large spacing between the second antenna elements Rx in the SIMO generates a large amount of grating lobes GL. On the other hand, the side lobes SL are small because the spacing between the antenna elements in the MIMO includes consecutive numbers such as "1d", "2d", "3d" and "5d", "6d", "7d", and "8d". Therefore, the radar device 1 of this embodiment can determine that an image other than the target position is a false image.

[0107] As described above, the radar device 1 of this embodiment is less susceptible to a decrease in the accuracy of determining whether a real image or a false image is caused by the difference in resolution between SIMO and MIMO, and can appropriately identify whether a signal corresponding to a target is a real image or a false image.

[0108] 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.

[0109] (Fourth embodiment) Next, a fourth embodiment will be described with reference to Figures 27 to 34. In this embodiment, differences from the first embodiment will be mainly described.

[0110] The second array antenna for MIMO of this embodiment has the same antenna configuration as that of the first embodiment. As shown in Fig. 27, the second array antenna has an unevenly spaced array in which some of the antenna elements constituting the second array antenna are spaced at unequal intervals. In other words, the second array antenna has an antenna configuration including a portion where the spacing between antenna elements is larger than in other portions.

[0111] In such an antenna configuration, signals at missing parts of the antenna can be complemented by an expansion process using a differential signal corresponding to a 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 the expansion process, signals of virtual antenna elements positioned between antenna elements that are spaced apart more widely than the others among the multiple antenna elements constituting the second array antenna are interpolated using a differential signal corresponding to the phase difference between the multiple antenna elements. Then, the radar device 1 detects signals corresponding to targets using the expanded array antenna obtained by the expansion process instead of the second array antenna.

[0112] The extension process in this example is Khatri-Rao product extension array processing, in which the signals of virtual antenna elements positioned between antenna elements with larger spacing compared to the others are interpolated using differential signals corresponding to the phase differences between multiple antenna elements.

[0113] The matrix shown on the left side of FIG. 28 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 in FIG. iω The matrix shown in the center of FIG. 28 is the variance matrix e iω This matrix shows only the exponent parts of the independent components in the matrix. This matrix corresponds 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 with their signs inverted are arranged 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 Fig. 28 correspond to each arrangement position in the extended array antenna. The number of tables shown on the right side of Fig. 28 corresponds to the number of signals corresponding to each antenna element.

[0114] The expanded array antenna obtained by such expansion processing has a large aperture antenna configuration with an antenna aperture length of "22d", as shown in the lower part of FIG.

[0115] In the extended array antenna of this embodiment, the antenna elements are arranged so that they are arranged 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 component 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.

[0116] 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. 29 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.

[0117] 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. 28, 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 but increases and decreases as it moves away from the reference position. 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".

[0118] 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.

[0119] FIG. 30 shows the simulation results of the power spectrum when there are two targets (U1=0, U2=0.259) and the reflected power is 1 (0 dB) in the antenna configuration of this embodiment.

[0120] As shown in Fig. 30, when two close targets are used as targets, two signal peaks corresponding to the two targets can be detected in both the MIMO and SIMO configurations. Both the peak positions and peak levels of the spectrum signal Sp in the SIMO and MIMO configurations are within the judgment region JA, and the image at the target position can be judged as a real image.

[0121] Here, the reflectivity of the targets varies, and there may be a weak reflector such as a pedestrian next to a strong reflector such as a car. Figures 31 and 32 show the simulation results of the power spectrum when there is a target (U2 = 0.259) with a reflected power of 1 / 10 (s2 = 0.1) near the target in the center (U1 = 0). Note that in Figures 31 and 32, the phase of the target signal source is random, and the results are shown when there is a certain phase relationship.

[0122] Figure 31 shows the simulation results of estimating the azimuth of the target using the second array antenna. As shown in Figure 31, when using the second array antenna, the side lobe SL in MIMO is large, and an image that appears in a place where the target does not exist may be judged as a real image. This is because the side lobe SL in MIMO has a large power for a signal corresponding to a weak reflector.

[0123] Figure 32 shows the results of a simulation in which the azimuth of the target was estimated using an extended array antenna. In the simulation shown in Figure 32, the signals corresponding to the antenna elements constituting the extended array antenna are weighted by window function processing. As shown in Figure 32, when an extended array antenna is used, the side lobe SL in MIMO is small, and an image that appears in a place where no target exists can be determined to be a false image.

[0124] 10, the radar device 1 receives three types of reflected waves: 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.

[0125] Figures 33 and 34 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 in signal amplitude of the mirror reflection 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 33 and 34 show the results when the phase of the target signal source is the same.

[0126] Specifically, Fig. 33 shows the results of a simulation 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. 33, in MIMO, a peak corresponding to the reflected waves with mismatched paths occurs, but since it is sufficiently smaller than the peak in SIMO, it can be determined to be a false image.

[0127] In addition, although not shown in the figure, when the power spectra of the direct wave and the specular reflected wave are simulated 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.

[0128] Figure 34 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 34, 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.

[0129] 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.

[0130] Moreover, the radar device 1 of this embodiment has the following features.

[0131] (1) The second array antenna for MIMO is an unevenly spaced array in which some of the antenna elements constituting the second array antenna are unevenly spaced. The control unit 6 executes an extension process to interpolate signals of virtual antenna elements using a differential signal corresponding to a phase difference between the antenna elements caused by radio waves arriving from a direction intersecting the arrangement direction of the antenna elements constituting the second array antenna. The control unit 6 then detects a signal corresponding to a target using the extended array antenna obtained by the extension process. This sufficiently suppresses the occurrence of side lobes SL, which are a cause of false images, and allows for more appropriate identification of whether an image is real or false.

[0132] (2) 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.

[0133] 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.

[0134] (3) In the extension process, the radar device 1 performs weighting using window function processing on signals corresponding to antenna elements constituting the extension array antenna. This reduces 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.

[0135] (Modification of the fourth embodiment) When multiple signals corresponding to antenna elements constituting the extended array antenna are obtained in the extension process, the radar device 1 is preferably configured to average the multiple signals, but is not limited to this. For example, when multiple signals corresponding to antenna elements constituting the extended array antenna are obtained in the extension process, the radar device 1 may be configured to select the maximum or minimum signal from the multiple signals.

[0136] The radar device 1 is preferably configured to weight signals corresponding to antenna elements constituting the extended array antenna by window function processing in the extension processing, but is not limited to this. The radar device 1 may not weight signals corresponding to antenna elements constituting the extended array antenna by window function processing in the extension processing.

[0137] Fifth embodiment Next, a fifth embodiment will be described with reference to Figures 35 to 37. In this embodiment, differences from the first embodiment will be mainly described.

[0138] 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. Such a change can cause a false image to be erroneously determined to be a real image.

[0139] Here, Fig. 35 and Fig. 36 are simulation results of the power spectrum when there is a target (U1 = 0, s1 = 1) in the center and a mirror reflection position (U2 = 0.174) is located nearby under the same conditions as Fig. 33 and Fig. 34 described in the fourth embodiment. The reflectance in the signal amplitude of the mirror reflection is set to "0.316" as in the third embodiment. In this case, the power of the mirror reflected wave is 0.01 (≒ 0.316^4). 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 movement is changed randomly. As shown in Fig. 35 and Fig. 36, the position of the peak of the target object fluctuates due to the influence of vibration and movement, and images in the same position may be judged to be real images or false images.

[0140] In consideration of this, the control unit 6 of this embodiment is configured to compare the signals detected by each of the signal detection units 61 and 62 multiple times in the signal determination process to determine whether the signal to be determined is a real image or a false image. The signal determination process executed by the control unit 6 will be described below with reference to Fig. 37. Note that the processes in steps S151 to S154 in the signal determination process are the same as those described in the first embodiment, and therefore description thereof will be omitted.

[0141] As shown in FIG. 37, when it is determined in step S154 that the difference between the peak level of the SIMO spectrum signal Sp and the peak level of the MIMO spectrum signal Sp is equal to or smaller than the predetermined threshold, the control unit 6 proceeds to step S156.

[0142] In step S156, the control unit 6 determines whether or not a plurality of snapshots (samples) have been determined to be real images. Specifically, it 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 MIMO has been determined to be equal to or less than a predetermined threshold value in the most recent few snapshots.

[0143] As a result, if the image is determined to be a real image in multiple snapshots, the control unit 6 proceeds to step S157 and identifies the signal corresponding to the target to be determined as a “real image.” If the image is not determined to be a real image in multiple snapshots, the control unit 6 proceeds to step S153 and identifies the signal corresponding to the target to be determined as a “false image.”

[0144] 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.

[0145] Moreover, the radar device 1 of this embodiment has the following features.

[0146] (1) The control unit 6 selects, as a determination target, one of the signals detected by one of the first signal detection unit 61 and the second signal detection unit 62, whose peak level exceeds a predetermined selection threshold. Then, the control unit 6 compares the signals detected by the first signal detection unit 61 and the second signal detection unit 62 multiple times in a determination target range including the signal to be determined, to identify whether the signal to be determined is a real image or a false image. In this way, if the signals detected by the signal detection units 61 and 62 are compared multiple times to identify whether the signal to be determined is a real image or a false image, it is possible to reduce the effects of vibration and movement of the target object and appropriately identify whether the signal corresponding to the target is a real image or a false image.

[0147] (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.

[0148] 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.

[0149] The radar device 1 of the above embodiment detects a signal corresponding to a target by both the first array antenna for SIMO and 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 detection result, but is not limited thereto. The radar device 1 may detect a signal corresponding to a target by both the array antenna for MISO and 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 detection result. In this case, the first antenna element Tx and the second antenna element Rx may be arranged so that the antenna aperture length of MISO is larger than half the antenna aperture length of MIMO. Such an antenna configuration can be obtained by making the interval between the first antenna elements Tx smaller than the antenna aperture length of MISO. Note that the array antenna for MISO has an antenna configuration in which radio waves transmitted from multiple first antenna elements Tx are received by one second antenna element Rx.

[0150] In contrast, in the radar device 1 of this embodiment, the first antenna element Tx and the second antenna element Rx are arranged so that the antenna aperture length of MISO is larger than half the antenna aperture length of MIMO. Such an antenna configuration is obtained by making the interval between the first antenna elements Tx smaller than the antenna aperture length of SIMO.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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]

[0156] 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 based on radio waves received when radio waves are transmitted and received using one antenna element included in one of the transmitting antenna group and two or more antenna elements included in the other antenna group, out of the transmitting antenna group and the receiving antenna group; a second signal detection unit (62) that detects a signal corresponding to the target based on radio waves received when radio waves are transmitted and received between two or more antenna elements included in the one antenna group and two or more antenna elements included in the other antenna group; an identification unit (63) that compares a detection result of the signal corresponding to the target by the first signal detection unit with a detection result of the signal corresponding to the target by the second signal detection unit, and identifies whether the signal corresponding to the target is a real image or a false image based on a comparison result; the identification unit identifies an image as a real image when peak positions of signals corresponding to the target detected by each of the first signal detection unit and the second signal detection unit are within a predetermined range and a difference in peak levels of the signals corresponding to the target is equal to or smaller than a predetermined threshold, and identifies an image as a virtual image when the peak positions are outside the predetermined range or the difference in peak levels exceeds the predetermined threshold.

2. the predetermined range is set based on a fluctuation width of the peak position of a signal that is a real image, based on a simulation result of a power spectrum of a signal corresponding to the target; The radar device according to claim 1 , wherein the predetermined threshold is set based on a fluctuation range of the peak level of a signal that becomes a real image, based on a result of the simulation.

3. 2. The radar device according to claim 1, wherein the identification unit selects, as a determination target, from among the signals detected by one of the first signal detection unit and the second signal detection unit, a signal whose peak level exceeds a predetermined selection threshold, and compares the signals detected by the first signal detection unit and the second signal detection unit a plurality of times in a determination target range including the signal to be determined, to determine whether the signal to be determined is a real image or a false image.

4. 4. The radar device according to claim 1, wherein the plurality of first antenna elements and the plurality of second antenna elements are arranged such that an antenna aperture length of a first array antenna constituted by one antenna element included in the one antenna group and two or more antenna elements included in the other antenna group is larger than half an antenna aperture length of a second array antenna for MIMO constituted by two antenna elements included in the one antenna group and two or more antenna elements included in the other antenna group.

5. The second array antenna is an unequally spaced array in which some of the antenna elements constituting the second array antenna are unequally spaced, 5. The radar device according to claim 4, wherein the second signal detection unit performs an expansion process to interpolate signals of virtual antenna elements positioned between antenna elements that are spaced apart more widely than the others among the plurality of antenna elements that configure the second array antenna, by using a differential signal corresponding to a phase difference between the plurality of antenna elements that are generated by radio waves arriving from a direction intersecting an arrangement direction of the plurality of antenna elements that configure the second array antenna, and detects a signal corresponding to the target using an expanded array antenna obtained by the expansion process.

6. The radar device according to claim 5 , wherein when a plurality of signals corresponding to antenna elements constituting the extended array antenna are obtained in the extension process, the second signal detection unit averages the plurality of signals.

7. The radar device according to claim 5 , wherein the second signal detection unit performs weighting by window function processing on signals corresponding to antenna elements constituting the extended array antenna in the extension processing.

Images