Radar device and vehicle equipped with same

Abstract

Provided are a radar device capable of distinguishing between a plurality of stationary target objects existing in similar positions, and precisely measuring the azimuth of each target object, without being affected by cross-correlation components between each received signal, and a vehicle provided with said radar device. An FMCW radar device 1 includes a radar module 11 and a vibrating body 13. An actuator 13a that initiates vibrations having a magnitude less than a distance resolution of the radar device 1 is used as an example of the vibrating body 13. A shielding case 10 is supported by a bracket 9, by way of fixing portions 14. The fixing portions 14 comprise a resilient material, the shielding case 10 vibrates irregularly in conjunction with the vibration of the actuator 13a, and the vibrations of the shielding case 10 are transmitted to a circuit board 11a. A pattern constituting an array antenna 3 is formed on a top surface of the circuit board 11a, and an electronic component 11b constituting the radar module 11 is mounted on a rear surface thereof.

Description

[Technical field]

[0001] The present invention relates to a radar device having a radar module that calculates the direction of arrival of signals from a plurality of stationary targets, and to a vehicle equipped with the same. [Background technology]

[0002] Conventionally, an example of this type of radar device is the radar device disclosed in Patent Document 1.

[0003] This radar device includes an extended calculation unit and an azimuth calculation unit in a signal processing device. The extended calculation unit acquires a signal for each antenna based on a received signal received by the array antenna, and generates a correlation matrix based on the acquired signal for each antenna. Then, using this correlation matrix, an extended correlation matrix is ​​generated by a Khatri-Rao product, and a spatial average extended correlation matrix is ​​generated by performing spatial averaging on this extended correlation matrix. The azimuth calculation unit calculates the arrival direction of a signal from a target included in the received signal, based on the spatial average extended correlation matrix generated by the extended calculation unit.

[0004] In this radar system, the number of receiving antennas is virtually increased by generating an extended correlation matrix using the Khatri-Rao product, thereby expanding the array. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-90229 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the conventional radar device disclosed in Patent Document 1, although the cross-correlation components between received signals can be reduced by spatial averaging processing by generating a spatial average extended correlation matrix, they cannot be fully removed. Therefore, when multiple stationary targets are present at similar distances, it is difficult for the conventional radar device to estimate the azimuth of each target with high accuracy. [Means for solving the problem]

[0007] The present invention has been made to solve such problems, By expanding the array using the extended correlation matrix, the number of receiving antennas is virtually increased to detect multiple stationary targets. The received signal is measured multiple times for each of the virtually increased receiving antennas, and multiple extended signals obtained in each measurement are time-averaged to be equivalent to the received signal of each receiving antenna. a radar module for calculating a direction of arrival of a signal; A vibration applying structure that applies vibrations to the radar module randomly, the vibrations being less than the distance resolution of the radar. A radar device having the above structure was constructed.

[0008] In a radar system using array expansion, the expanded signals of the virtual antenna elements that constitute the elements of the expanded correlation matrix using the Khatri-Rao product have cross-correlation components between the received signals, expressed as an exponential function with e as the base and the absolute phases of multiple targets as the exponent. When multiple targets to be positioned are stationary, the absolute phase of each target does not change and the cross-correlation components between the received signals maintain the same value, making it difficult to identify each target and their orientation.

[0009] However, according to this configuration, the vibration imparting structure irregularly imparts vibrations of a magnitude less than the radar's distance resolution to the radar module, causing the distances between the radar device and a number of stationary targets to fluctuate irregularly. Meanwhile, the absolute phase of each target is proportional to the distance between the radar device and the target. Therefore, by transmitting and receiving positioning signals multiple times using the radar device in a state in which vibrations of a magnitude less than the radar's distance resolution are irregularly imparted to the radar module by the vibration imparting structure, the absolute phase of each target obtained for each measurement changes randomly. Therefore, the cross-correlation components expressed by exponential functions contained in the extended signals obtained in each measurement have different values ​​for each extended signal, and can be cancelled out by averaging the extended signals obtained multiple times.

[0010] Further, the present invention provides a vehicle including the above-mentioned radar device. Effect of the Invention

[0011] Therefore, according to the present invention, it is possible to provide a radar device that can identify multiple stationary targets that are located in similar positions and measure the direction of each target with high accuracy without being affected by cross-correlation components between received signals, and a vehicle equipped with the same. [Brief description of the drawings]

[0012] [Figure 1] 1 is a block diagram showing a schematic configuration of a radar module constituting a radar device according to an embodiment of the present invention; [Diagram 2] 1 is a perspective view of a vehicle equipped with a radar device according to an embodiment. [Diagram 3] 1 is a diagram illustrating a vibration applying structure constituting a radar device according to an embodiment. [Figure 4] 4 is a flowchart illustrating an operation of a radar device according to an embodiment. [Diagram 5] 5 is a graph illustrating signals transmitted and received and signals calculated by a radar device according to an embodiment. [Figure 6]FIG. 2 is a diagram illustrating a receiving antenna that is expanded into an array in a radar device according to an embodiment. [Figure 7] FIG. 11 is a diagram for explaining a simulation performed to confirm the effect of the radar device according to the embodiment. [Figure 8] 8 is a graph showing the results of the simulation shown in FIG. 7 performed without applying vibration to the radar module constituting the radar device according to the embodiment. [Figure 9] 8 is a graph showing the results of the simulation shown in FIG. 7, which was performed by applying vibration to the radar module constituting the radar device according to the embodiment. [Figure 10] 10A and 10B are diagrams illustrating a modified example of a vibration applying structure constituting the radar device according to the embodiment. [Figure 11] 13A and 13B are diagrams illustrating a vibration applying structure constituting a radar device according to another embodiment of the present invention. [Figure 12] 11 is a graph showing the results of a simulation of an error in target angle estimation by a radar module constituting a radar device according to one embodiment or another embodiment. [Figure 13] 13 is a graph showing the change over time in vibration in the x-axis direction of a parked vehicle. [Figure 14] 1 is a graph showing changes over time in vibration in the y-axis and z-axis directions of a parked vehicle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Next, a radar device and a vehicle including the same according to an embodiment of the present invention will be described.

[0014] FIG. 1 is a block diagram showing a schematic configuration of a radar module 11 that constitutes an FMCW (Frequency Modulated Continuous Wave) radar device 1 according to an embodiment of the present invention.

[0015] The radar module 11 includes an RF (Radio Frequency) signal generator 2, an array antenna 3, a mixer 4, an ADC (Analog to Digital Converter) 5, and a computing unit 6.

[0016] FIG. 2 is a perspective view of a vehicle 7 equipped with an FMCW radar device 1. The FMCW radar device 1 is provided inside a door 7a on the side of the vehicle 7, behind an emblem 7b, inside a door handle, behind or inside a bumper, on the chassis, behind a grill, inside a back door of the vehicle 7, etc., and is concealed by the exterior surface of the vehicle body.

[0017] In this embodiment, the FMCW radar device 1 is configured such that the radar module 11, together with the vibrating body 13, is mounted on the bracket 9 on the rear side of the exterior surface 8 of the vehicle body in the shield case 10, as conceptually shown in Fig. 3(a) and (b). The FMCW radar device 1 has the radar module 11 and the vibrating body 13, and the radar module 11 transmits a transmission wave 12 from the rear side of the exterior surface 8. Fig. 3(a) shows a vibration imparting structure of the FMCW radar device 1 in which the radar module 11 is provided on the front side of the shield case 10 alongside the vibrating body 13. Fig. 3(b) shows a vibration imparting structure of the FMCW radar device 1 in which the radar module 11 is provided on the front side of the shield case 10 and the vibrating body 13 is provided on the rear side of the shield case 10. Each of these vibration imparting structures is structured to impart vibrations caused by the vibrating body 13 to the radar module 11 irregularly, and the vibrating body 13 causes vibrations of a magnitude less than the distance resolution of the FMCW radar device 1.

[0018] FIG. 1C is a diagram showing a specific example of the vibration imparting structure of the FMCW radar device 1. In this specific example, a power-saving, thin linear resonant actuator 13a is used as the vibrating body 13. The shielding case 10 is supported by the bracket 9 via a fixed part 14. The fixed part 14 is made of a material having elasticity, such as a movable part or an elastic body, and is structured so that the shielding case 10 vibrates in accordance with the vibration of the linear resonant actuator 13a, and the vibration of the shielding case 10 is transmitted to the circuit board 11a constituting the radar module 11. A pattern constituting the array antenna 3 is formed on the surface of the circuit board 11a facing the exterior surface 8, and various electronic components 11b constituting the radar module 11 are mounted on the surface opposite the exterior surface 8. The linear resonant actuator 13a provided in the shielding case 10 is electrically connected to the electronic components 11b via a cable 11c.

[0019] FIG. 1D shows a drive circuit for the linear resonant actuator 13a. The linear resonant actuator 13a is connected to a driver IC 15 that operates by receiving a power supply of a predetermined voltage, and the driver IC 15 is connected to an MCU (Micro Controller Unit) 16 that controls the radar module 11. The driver IC 15 is PWM (Pulse Width Modulation) controlled by the MCU 16, whereby the resonant frequency of the vibration caused by the linear resonant actuator 13a is controlled, and vibrations of various magnitudes are generated irregularly. Here, the linear resonant actuator 13a is used as an example of the vibrating body 13, but the vibrating body 13 is not limited to this, and for example, an eccentric rotating mass (ERM) motor, a piezoelectric element, or the like can also be used.

[0020] FIG. 4 is a flowchart showing the operation of the radar module 11 executed by the MCU 16.

[0021] Under the control of the MCU 16, the radar module 11 first transmits a transmission signal (see step 101 in FIG. 4). The RF signal generator 2 shown in FIG. 1 is a signal generator capable of changing the signal frequency over time, and generates a chirp signal as a transmission signal. The array antenna 3 is composed of a transmission antenna Tx and receiving antennas Rx(1), ..., Rx(M-1), Rx(M). Here, M is a natural number, and so on. The transmission antenna Tx transmits a transmission signal wave corresponding to the transmission signal generated by the RF signal generator 2. The radar module 11 then receives a reception signal (see step 102 in FIG. 4). The receiving antennas Rx(1), ..., Rx(M-1), Rx(M) receive, as a reception signal wave, a reflected wave that is the transmission signal wave transmitted from the transmission antenna Tx and reflected by a target and returns.

[0022] Fig. 5(a) is a graph showing the waveforms of the chirp signal Ca of the transmitted wave sent from the transmitting antenna Tx, and the chirp signal Cb of the reflected wave received by the receiving antenna Rx. The horizontal axis of the graph is time [t], and the vertical axis is frequency [GHz]. The chirp signal Ca of the transmitted wave is shown by a solid line, and the chirp signal Cb of the reflected wave is shown by a dashed line. Each chirp signal Ca, Cb has a bandwidth BW, which is the frequency difference between the maximum frequency fmax and the minimum frequency fmin, and a duration Tm.

[0023] The radar module 11 then generates a beat signal (see FIG. 4, step 103). The mixer 4 multiplies the transmission signal and the reception signal for each reception antenna Rx of the array antenna 3, converts them into intermediate frequency (IF) signals (IF signals) IF(1), ..., IF(M-1), IF(M), and generates the IF signal as a beat signal from the frequency difference between the transmission signal and the reception signal. FIG. 5(b) is a graph showing this IF signal, where the horizontal axis is time [t] and the vertical axis is IF frequency [GHz].

[0024] The above transmission signal and reception signal are expressed as Vtx and Vrx in the following equations (1) and (2), respectively: where Atx and Arx are the amplitudes of the transmission signal Vtx and reception signal Vrx, ωtx is the angular frequency of the chirp signal Ca, R is the distance to the target, c is the speed of light, and φ1 is the initial phase.

number

[0025] Moreover, the chirp signal Ca is expressed as ftx in the following equation (3) using the bandwidth BW, duration Tm, and minimum frequency fmin.

number

[0026] The IF signal is expressed as VIF in the following equation (4) based on equations (1) to (3): The ADC 5 converts this input IF signal from an analog signal to a digital signal, and outputs it to the calculator 6.

number

[0027] In equation (4), the coefficient of time t represents the IF frequency fif, and the constant represents the absolute phase α of the target. From this IF frequency fif, the distance R to the target is calculated by the following equation (5). The radar module 11 performs processing in the calculator 6 to estimate the distance R to the target using this equation (5) (see FIG. 4, step 104).

number

[0028] The radar module 11 then performs an array expansion calculation process in the calculator 6 (see FIG. 4, step 105). The calculator 6 performs a discrete Fourier transform on the IF signal shown in equation (4), and assumes that a target exists at a distance corresponding to a frequency where the power of the IF signal after the discrete Fourier transform is strong, and acquires phase information and amplitude information of the frequency component at that distance for each receiving antenna Rx. The calculator 6 then sets signals x1, x2, ..., xM-1, xM having phase information and amplitude information of the distance where the target is likely to exist as vector X expressed in the following equation (6).

number

[0029] Next, the calculator 6 calculates the transposed vector X of the vector X expressed by the following equation (7): T Then, the transposed vector X T The complex conjugate of is the Hermitian transpose vector X H Here, x * is the complex conjugate of the received signal x.

number

[0030] Next, the calculator 6 calculates the Hermitian transpose vector X expressed by the formula (6) and the Hermitian transpose vector X expressed by the formula (8). H From the correlation matrix XX based on the received signal obtained H Then, the generated correlation matrix XX H Using this, we generate the extended correlation matrix Rxx by the Khatri-Rao product shown in the following equation (9). Here, E[XX H ] is the correlation matrix XX H means the expected value of

number

[0031] Each element Rij=xixj of the extended correlation matrix Rxx shown in equation (9) His an extended signal equivalent to the received signal of a virtual antenna located at the difference between the i-th receiving antenna Rx and the j-th receiving antenna Rx. Therefore, taking the linear array antenna 3 as an example, as shown in Fig. 6, when array extension is applied to signals x1, x2, ..., xM-1, xM of frequency components corresponding to targets extracted from the IF signal, extended signals R11, R21, R31, ..., R(M-1)1, RM1 of the receiving antenna elements shown by solid lines in a linear arrangement are generated at the same positions as the signals x1, x2, ..., xM-1, xM, and extended signals R12, R13, ..., R1(M-1), R1M of the virtual antenna elements are generated at the positions shown by dashed lines with the phase reference as a reference. As a result, the number of receiving antenna elements increases from M to 2M-1.

[0032] As an example, when the number of arriving reflected waves is two, the expansion signal R21 that generates the expansion signal R12 of the virtual antenna element that appears at the difference position between the first and second antenna elements is expanded as shown in the following formula (10): Here, A1 is the amplitude of the reflected wave from the target a at the first antenna element, A2 is the amplitude of the reflected wave from the target b at the first antenna element, α1 is the absolute phase of the reflected wave from the target a at the first antenna element, α2 is the absolute phase of the reflected wave from the target b at the first antenna element, w1 is the amount of phase rotation of the reflected wave from the target a at the second antenna element, and w2 is the amount of phase rotation of the reflected wave from the target b at the second antenna element.

number

[0033] Next, the calculator 6 calculates the directions of arrival of signals from multiple stationary targets based on the receiving antennas whose number has been virtually increased by array expansion using the above-mentioned extended correlation matrix, and estimates the azimuth of each target (see FIG. 4, step 106).

[0034] As described above, in the FMCW radar device 1 using array extension, the extended signals of the virtual antenna elements constituting the element Rij of the extended correlation matrix Rxx by the Khatri-Rao product have cross-correlation components between the received signals enclosed in a frame in equation (10), which are expressed as an exponential function with e as the base and the absolute phases α1, α2 of the multiple targets a, b as the exponents, as in the extended signal R21 shown in equation (10). Generally, when multiple targets a, b to be positioned are stationary, the absolute phases α1, α2 of the targets a, b do not change and the cross-correlation components between the received signals maintain the same values, making it difficult to identify the targets a, b and their orientations.

[0035] However, according to the FMCW radar device 1 of this embodiment, the vibration imparting structure as shown in FIG. 3 imparts vibrations of a magnitude less than the distance resolution of the radar device 1 to the radar module 11, causing the distances R between the radar device 1 and a plurality of stationary targets a, b to vary irregularly. The vibration of the radar module 11 is equivalent to the vibration of the targets a, b as seen from the radar device 1, that is, the change in the distance R. Meanwhile, the absolute phases α1, α2 of the targets a, b are proportional to the distance R between the radar device 1 and the targets a, b, as shown in the absolute phase α term of Equation (4). Therefore, by transmitting and receiving positioning signals multiple times by the radar device 1 in a state in which the vibration imparting structure imparts vibrations of a magnitude less than the distance resolution of the radar device 1 to the radar module 11 irregularly, the absolute phases α1, α2 of the targets a, b obtained for each measurement change randomly.

[0036] Therefore, the cross-correlation components expressed as an exponential function in equation (10) contained in the extended signal R21 obtained in each measurement have different values ​​for each extended signal R21, so that they can be cancelled out by averaging the multiple extended signals R21 obtained. Therefore, it becomes possible to identify multiple stationary targets a and b that exist in similar positions by the FMCW radar device 1 without being affected by the cross-correlation components between the received signals, and to measure the azimuth of each target a and b with high accuracy.

[0037] In particular, in this embodiment, the vibrations generated by the vibrating body 13 are actively and irregularly applied to the radar module 11, so that the distances R between the radar device 1 and the multiple stationary targets a, b fluctuate irregularly and the absolute phases α1, α2 of the targets a, b obtained in each measurement change randomly. This makes it possible to provide an FMCW radar device 1 that can reliably identify two stationary targets a, b or three or more targets (not shown) that are in similar positions and reliably measure the azimuth of each target with high accuracy without being affected by cross-correlation components between received signals.

[0038] Furthermore, by configuring the vehicle 7 with the FMCW radar device 1 as in this embodiment, it is possible to provide a vehicle 7 that can identify multiple stationary targets that are in similar positions, such as stationary car stops 17, ground 18, and people 19 that are all located at the same distance R to the vehicle 7, R0 as shown in FIG. 2, using the FMCW radar device 1 without being affected by cross-correlation components between received signals, and can measure their orientations with high accuracy.

[0039] Furthermore, limiting the vibration applied to the radar module 11 to a magnitude less than the distance resolution of the radar device 1 prevents the frequency of the IF signal from appearing to change due to the vibration displacement applied to the radar module 11 being too large. In the case of a millimeter wave radar, a displacement of several centimeters or less is usually less than the distance resolution of the radar, and in order to obtain a sufficient effect, a vibration of about half the wavelength λ of the radar transmission wave (approximately 0.5λ) applied to the radar module 11 is sufficient.

[0040] In order to confirm the above-mentioned effects of the FMCW radar device 1 according to this embodiment, a simulation was performed to compare the angle estimation error when vibration was applied to the radar module 11 by the vibrating body 13 and when vibration was not applied to the radar module 11.

[0041] This simulation was performed under the simulation parameters shown in Table 1 below, using the root mean square error (RMSE) as an evaluation index for the angle estimation error in the azimuth direction (i.e., the angle direction on the xy plane with the x-axis direction being 0 degree) when one of two stationary targets a and b shown in FIG. 7, a target a, was fixed in front of the radar device 1 and the angular difference θaz between the other target b and the target a was changed. [Table 1]

[0042] That is, in the case of x, y, and z coordinates as shown in Fig. 7, the coordinates in the y direction of the transmitting antenna TX in the radar module 11 are set to 0.5λ, 1.5λ, and 2.5λ when the wavelength of the transmitting wave is λ, and the coordinates in the y direction of the receiving antenna RX are set to 3.5λ and 4.0λ. In addition, the transmitting center frequency of the transmitting wave is 79 [GHz], the bandwidth BW is 4 [GHz], the sampling frequency of the IF signal in the ADC5 is 2.75 [MHz], the number of sampling points is 128 points, the number of transmitting chirps of the chirp signal Ca is 4, 8, and 16, the ratio SNR of the signal to thermal noise is 20 [dB], and the AF (Annihilating Filter) method is used as the angle estimation method.

[0043] The vibration applied to the radar module 11 is expressed by adding random numbers generated with a specific magnitude in each direction of the x, y, and z coordinates shown in FIG. 7. This is equivalent to applying irregular vibration to the radar module 11. In this specification, the irregular vibration applied to the radar module 11 by the vibration applying structure may vary the position of the radar module 11 on the x-axis, y-axis, z-axis, xy plane, xz plane, yz plane, or in the xyz space shown in FIG. In addition, the irregular variation in the distance between the FMCW radar device 1 and a plurality of stationary targets caused by the vibration being applied irregularly to the radar module 11 does not have to be always different for each positioning of the targets.

[0044] 8 is a graph showing the results of the angle estimation error for the angle difference θaz obtained by performing the above simulation without applying vibration to the radar module 11, for transmission chirp numbers 4 and 16. The horizontal axis of the graph represents the angle difference θaz [deg] between target b and target a, and the vertical axis represents the RMSE [deg]. Furthermore, characteristic line 21 shown by a long dashed line represents the angle estimation error for transmission chirp number 4, and characteristic line 22 shown by a short dashed line represents the angle estimation error for transmission chirp number 16. In the graph, characteristic lines 21 and 22 overlap, and characteristic line 22 is below characteristic line 21 and is almost invisible.

[0045] From this graph, we can see that depending on the array expansion installation angle, the RMSE can reach a large value of about 10[deg], resulting in a large error. Also, according to the array expansion principle, there is no difference in error between the transmission chirp numbers of 4 and 16, and it can be seen that increasing the number of transmissions and receptions of the chirp signal Ca does not improve the angle estimation accuracy.

[0046] 9 is a graph showing the results of the above simulation performed while applying irregular vibrations to the radar module 11 in each of the x, y, and z coordinate directions to obtain angle estimation errors for the angle difference θaz, for each transmission chirp number of 4, 8, and 16, along with a characteristic line 22 for a transmission chirp number of 16 without vibration shown in FIG. 8. The horizontal and vertical axes of the graph are the same as those of the graph shown in FIG. 8. Furthermore, characteristic line 23, which is a solid line with x marks plotted, represents the angle estimation error for a transmission chirp number of 4, characteristic line 24, which is a solid line only, represents the angle estimation error for a transmission chirp number of 8, and characteristic line 25, which is a solid line with ◇ marks plotted, represents the angle estimation error for a transmission chirp number of 16.

[0047] From the graph, it can be seen that by applying irregular vibrations to the radar module 11, the RSME value is lower over a wide range of angle differences, and the fluctuation of the angle estimation error is suppressed, compared to when vibrations are not applied. This is thought to be because when the positions of the targets a and b change slightly, their absolute phases α change randomly, and the correlation components between the received signals as shown in equation (10) are cancelled out. In addition, since the RSME value decreases in proportion to an increase in the number of transmitted chirps, and the accuracy of the angle estimation improves, it can be seen that the correlation components between the received signals are cancelled out better when the absolute phases α of the targets a and b change more randomly.

[0048] In the above embodiment, the case has been described in which the radar module 11, together with the vibrating body 13, is mounted on the shield case 10 on the bracket 9 on the rear side of the exterior surface 8 of the vehicle body to form a vibrating body applying structure, as shown in Fig. 3. However, as shown in Fig. 10, the radar module 11, together with the vibrating body 13, may be mounted on the shield case 10 and installed on the rear side of the exterior surface 8 of the vehicle body to form a vibrating body applying structure. In Fig. 10, parts that are the same as or correspond to those in Fig. 3 are given the same reference numerals, and their description will be omitted.

[0049] 11 is a conceptual diagram showing a vibration applying structure constituting an FMCW radar device 31 according to another embodiment of the present invention. In this figure, parts that are the same as or correspond to those in FIG. 3 are given the same reference numerals and their explanation will be omitted.

[0050] An FMCW radar device 31 according to this other embodiment differs from the FMCW radar device 1 according to the embodiment only in that the vibration imparting structure is different from the vibration imparting structure of the FMCW radar device 1 according to the above-described embodiment shown in Figures 3 and 10. The other configurations are similar to those of the FMCW radar device 1 according to the embodiment.

[0051] The vibration applying structure of the FMCW radar device 31 shown in Fig. 11(a) is a structure in which the shield case 10 is mounted on a bracket 9, and a suspension 32 supporting the radar module 11 on the shield case 10 amplifies vibrations occurring in the body of the vehicle 7 when the engine is idling and transmits them irregularly to the radar module 11. The vibration applying structure of the FMCW radar device 31 shown in Fig. 11(b) is a structure in which the shield case 10 is mounted on a bracket 9, and a cushion 33 supporting the radar module 11 on the shield case 10 amplifies vibrations occurring in the body of the vehicle 7 when the engine is idling and transmits them irregularly to the radar module 11.

[0052] 11(c) is a structure in which the shield case 10 is installed on the back side of the exterior surface 8 of the vehicle body, and a suspension 32 supporting the radar module 11 on the shield case 10 amplifies vibrations generated in the vehicle body of the vehicle 7 when the engine is idling and transmits them irregularly to the radar module 11. Also, the vibration-applying structure of the FMCW radar device 31 shown in Fig. 11(d) is a structure in which the shield case 10 is installed on the back side of the exterior surface 8 of the vehicle body surrounding the radar module 11, and a cushion 33 supporting the radar module 11 on the back side of the exterior surface 8 of the vehicle body amplifies vibrations generated in the vehicle body of the vehicle 7 when the engine is idling and transmits them irregularly to the radar module 11.

[0053] The suspension 32 and cushion 33 (e.g., shock absorbing material, rubber, gel material, etc.) constituting the elastic body in each of these vibration applying structures have an elastic constant that amplifies vibrations occurring in the vehicle body when the engine of the vehicle 7 on which the radar device 31 is mounted is idling, and has a spring constant that prevents resonance at a specific frequency. Also, each vibration applying structure shown in Fig. 11 is illustrated as using either the suspension 32 or the cushion 33 as the elastic body, but may be configured to include both the suspension 32 and the cushion 33.

[0054] According to the FMCW radar device 31 of this embodiment, vibrations occurring in the body of the vehicle 7 during engine idling are amplified by the elastic constants of the suspensions 32 and cushions 33, and are passively and irregularly applied to the radar module 11 supported by the suspensions 32 and cushions 33. Due to these vibrations, the distances R between the radar device 31 and a plurality of stationary targets fluctuate irregularly, and the absolute phase α of each target obtained for each measurement changes randomly.

[0055] Therefore, as with the FMCW radar device 1 according to the embodiment, it is possible to provide an inexpensive FMCW radar device 31 capable of identifying multiple stationary targets located in similar positions and measuring the azimuth of each target with high accuracy without being affected by cross-correlation components between received signals. Also, it is possible to provide a vehicle 7 capable of identifying multiple stationary targets located in similar positions with the FMCW radar device 31 and measuring the azimuth of each target with high accuracy without being affected by cross-correlation components between received signals.

[0056] In each of the above embodiments, the array antenna 3 has one transmitting antenna Tx and multiple receiving antennas Rx. However, the array antenna 3 may have one or more transmitting antennas Tx and multiple receiving antennas Rx. In this case, the same effects as those of the above embodiments can be achieved.

[0057] In each of the above embodiments, the vibration applying structure is preferably a structure that applies vibration in the direction of arrival of a received signal that is transmitted from the radar module 11 and reflected off a target.

[0058] 2, when a target is present on the side of the vehicle 7 and a received signal arrives at the radar module 11 from the side of the vehicle 7, it is preferable that the vibration imparting structure including the vibrator 13, the suspension 32, the cushion 33, etc. is provided inside the door 7a on the side of the vehicle 7, inside the door knob, etc., and is a structure that generates vibrations in the lateral direction of the vehicle 7. When a target is present in front of or behind the vehicle 7 and a received signal arrives at the radar module 11 from the front or rear of the vehicle 7, it is preferable that the vibration imparting structure is provided on the back side of the emblem 7b, the back side of the grill, inside the back door, inside the door knob, etc., and is a structure that generates vibrations in the front or rear direction of the vehicle 7.

[0059] Furthermore, in the case where there is a target in front of, behind, to the left, or to the right of the vehicle 7 and a received signal arrives at the radar module 11 from the front, rear, left, or right directions of the vehicle 7, the vibration imparting structure may be a structure provided on the back side or inside of a bumper attached to the front, rear, left, or right of the vehicle 7. In this case, the vibration imparting structure is configured to impart vibration in the front-rear direction of the vehicle 7, which is a direction perpendicular to the bumpers attached to the front and rear of the vehicle 7 in a plan view of the vehicle 7, or in the left-right direction of the vehicle 7, which is a direction perpendicular to the bumpers attached to the left and right of the vehicle 7 in a plan view of the vehicle 7.

[0060] By vibrating the vehicle 7 in each direction in this manner, the change in the distance R between the radar module 11 and the target becomes greater, making it possible to measure the azimuth of each target with greater accuracy, as described below.

[0061] The graph shown in FIG. 12 is a graph showing the results of simulating the error in estimating the angle of a target by the radar module 11 in a situation where the distance between the radar module 11 and the target is fluctuating slightly.

[0062] This simulation was performed with one target a of two stationary targets a and b fixed in front of the radar device 1, and the angular difference θaz between the other target b and the target a was set to 5[deg], as shown in Fig. 7. The vibrations given to the radar module 11 in each direction of the x, y, and z coordinates were assumed to follow a uniform distribution, as in the previous simulation. Here, the amount between the lower limit value and the upper limit value of the vibration amount is defined as the vibration amount.

[0063] The horizontal axis of the graph represents the vibration amount due to the vibration applying structure, and the vertical axis represents RMSE [deg]. The vibration amount on the horizontal axis is expressed as a ratio to a half wavelength (0.5λ) of the transmission wave wavelength λ of the radar module 11. If the magnitude of the vibration amount of the radar module 11 is D, this ratio is expressed as D / (0.5λ).

[0064] It can be seen from the graph that the RMSE (root mean square error of estimation accuracy) monotonically decreases as the magnitude of the vibration applied to the radar module 11 increases. Since the vibration applied to the radar module 11 corresponds to a change in the distance R between the radar module 11 and the target, it can be seen from the graph that the RMSE, i.e., the error in the angle estimation, decreases as the change in the distance R between the radar module 11 and the target increases. In other words, if the vibration applying structure is a structure that generates large vibrations in the direction of arrival of the received signal reflected off the target, it can be said that the azimuth of each target can be measured with higher accuracy.

[0065] The graphs shown in Fig. 13 and Figs. 14(a) and (b) show the change over time in vibration of a parked vehicle. The horizontal axis of the graph is time, and the vertical axis is the displacement of the vehicle body due to vibration. The vehicle is a hybrid vehicle, but the engine is running, and minute vibrations are occurring in the vehicle body. The vibration was measured by a six-axis acceleration sensor fixedly installed in the vehicle cabin, and the displacement was calculated in each of the x, y, and z coordinate directions by integrating the measured acceleration information twice. The x, y, and z coordinates are the same as those shown in Fig. 7, and the angular direction on the xy plane with the x-axis direction being 0 degrees is the azimuth direction (azimuth direction), and the direction perpendicular to the xy plane is the z direction.

[0066] The graph shown in Fig. 13 shows the displacement of the vehicle body in the x-axis direction, i.e., the front-rear direction of the vehicle, calculated by the above measurements. The graph shown in Fig. 14(a) shows the displacement of the vehicle body in the y-axis direction, i.e., the left-right direction of the vehicle, calculated by the above measurements. The graph shown in Fig. 14(b) shows the displacement of the vehicle body in the z-axis direction, i.e., the vertical direction of the vehicle, calculated by the above measurements. The vibration of the vehicle body swings in the + and - directions in each direction over time, centered on a displacement of 0.

[0067] For example, in the 77 [GHz] to 81 [GHz] band, the vibration of the car body in the x-axis direction shown in Figure 13 is only a displacement width (= vibration amount) D 0 is about 1 [mm]. On the other hand, for example, in the 77 [GHz] to 81 [GHz] band, the FMCW radar device has the finest distance resolution Δd of 3.75 [cm]. In other words, if the speed of light is c [m / s] and the bandwidth is BW [Hz], the distance resolution Δd can be expressed as c / (2BW). Also, in the 77 [GHz] to 81 [GHz] band, the bandwidth BW is 4 [GHz], so the distance resolution Δd is 3.75 [cm] as shown in the following equation (11). Δd = c / (2BW) = (3 × 10 8 ) / (2×4×10 9 )=3.75 …(11)

[0068] That is, the vehicle body vibration amount D of a stopped vehicle 0 = 1 [mm] is a very small value compared to the distance resolution Δd of 3.75 [cm]. Also, the vehicle body vibration amount D 0 It can be seen that λ = 1 [mm] is a smaller value than 0.5λ. Therefore, the cross-correlation components expressed as an exponential function in equation (10) contained in the extended signal R21 obtained in each measurement by using the body vibration of a parked vehicle cannot be canceled. On the other hand, by using the vibration applying structure of each of the above embodiments, D 0By applying vibrations to the radar module 11 having a magnitude greater than or equal to / (0.5λ) and less than the distance resolution Δd of the radar module 11, the cross-correlation components expressed as an exponential function as in equation (10) can be cancelled out, and the effects of each of the above embodiments can be reliably achieved.

[0069] The vibration applying structure of each of the above embodiments is D 0 By applying vibrations to the radar module 11 that are greater than or equal to / (0.5λ) and less than the distance resolution Δd of the radar module 11, it is possible to selectively apply larger random vibrations compared to a case in which only the vibrations of the vehicle itself are present, thereby ensuring the effect of improving the accuracy of angle estimation. [Industrial Applicability]

[0070] In the above embodiments, the FMCW radar devices 1, 31 are described as being applied to a vehicle, but they can also be applied to a parked aircraft, a moored ship, etc. In that case, the same advantageous effects are achieved. [Explanation of symbols]

[0071] 1,31...FMCW radar equipment 2. RF signal generator 3…Array antenna Tx: Transmitting antenna Rx(1),…,Rx(M-1),Rx(M)…Receiving antennas 4. Mixer 5…ADC 6...Arithmetic unit 7…Vehicle 8…Exterior surface of vehicle 7 9…Bracket 10…Shield case 11…Radar module 11a...Circuit board 11b...Electronic components 11c…Cable 12...Transmission wave 13...Vibration body 13a...Linear resonant actuator (vibration body) 14...Fixed part 32...Suspension (elastic body) 33...Cushion (elastic body)

Claims

1. a high frequency signal generator that generates, as a transmission signal, a chirp signal whose signal frequency changes over time; an array antenna including one or more transmitting antennas for transmitting the transmission signal and a plurality of receiving antennas for receiving a reception signal of the transmission signal reflected by a target; a mixer that multiplies the transmission signal transmitted from the transmission antenna by the reception signal received by the reception antenna to convert the signal into an intermediate frequency signal; an analog-to-digital converter for converting the intermediate frequency signal from an analog signal to a digital signal; a computing unit that virtually increases the number of the receiving antennas by array expansion using an extended correlation matrix based on the intermediate frequency signal, measures the received signals for a plurality of stationary targets a plurality of times, and calculates the direction of arrival of the received signals by time-averaging a plurality of extended signals obtained in each measurement for each of the virtually increased receiving antennas equivalent to the received signals of each receiving antenna; A radar module comprising: a vibration applying structure that applies vibrations to the radar module irregularly, the vibrations being less than the distance resolution of the radar module; A radar device having the above structure.

2. 2. The radar device according to claim 1, wherein the calculator generates a correlation matrix based on the intermediate frequency signals acquired for each of the receiving antennas, and generates the extended correlation matrix by a Khatri-Rao product using the generated correlation matrix.

3. 3. The radar device according to claim 1, wherein the vibration applying structure is a structure that applies vibrations generated by a vibrating body to the radar module irregularly.

4. 4. The radar device according to claim 3, wherein the vibrator is a linear resonant actuator.

5. 3. The radar device according to claim 1, wherein the vibration-imparting structure is a structure in which an elastic body supporting the radar module has an elastic constant that amplifies vibrations occurring in a vehicle body when an engine of a vehicle on which the radar device is mounted is idling, and the elastic body amplifies the vibrations occurring in the vehicle body and transmits them to the radar module in an irregular manner.

6. 6. The radar device according to claim 5, wherein the elastic body is a suspension.

7. 6. The radar device according to claim 5, wherein the elastic body is made of rubber.

8. A vehicle comprising the radar device according to claim 1 or 2.

9. 9. The vehicle according to claim 8, wherein the radar device is provided inside a door.

10. 9. The vehicle according to claim 8, wherein the radar device is provided on the rear side of an emblem.

11. 9. The vehicle according to claim 8, wherein the radar device is provided inside a door handle.

12. 9. The vehicle according to claim 8, wherein the radar device is provided behind or inside a bumper.

13. 9. The vehicle according to claim 8, wherein the radar device is provided behind a grill.

14. The vehicle according to claim 9 , wherein the vibration applying structure applies vibration in a lateral direction of the vehicle.

15. The vehicle according to claim 9 , wherein the vibration applying structure applies vibration in a front-rear direction of the vehicle.

16. The vehicle according to claim 12, wherein the vibration applying structure applies vibration in a direction perpendicular to the bumper in a plan view of the vehicle.

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