Radar calibration method

Abstract

To perform accurate correction while suppressing the enlargement of a radar system.SOLUTION: A calibration method for a radar 1 includes the following steps of determining: a provisional correction value for correcting the phase from a received signal of a first antenna array 210 on the assumption that the direction of a target CT1 is a known direction; a corrected phase in the first antenna array 210 by correction with the provisional correction value; a corrected phase in a second antenna array 240 by correction with the provisional correction value; and a correction value by modifying the provisional correction value so as to set a difference between the corrected phase in the first antenna array 210 and the corrected phase in the second antenna array 240 to be a phase difference of received signals generated between the first antenna array and the second antenna array obtained from the distance in the depth direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for calibrating a radar. [Background technology]

[0002] Radars are used, for example, in automobile safety driving support systems, and are expected to estimate the direction of arrival of incoming waves with high accuracy. However, errors can occur in the estimated direction of arrival due to variations in the characteristics of each antenna element, variations in element placement, etc. For this reason, radars correct received signals using a correction value calculated in advance.

[0003] It has been known in the past to estimate the direction of arrival of a reflected wave from a calibration target placed in a known direction before operation, and then calculate a correction value so that the estimated direction matches the known direction. However, if there is a deviation in the position of the calibration target, the correction value will contain an error. As a result, the accuracy of the correction process will decrease. For this reason, various considerations have been made to improve the accuracy of the correction process. For example, Patent Document 1 describes providing a radar with an optical sensor used to correct the received signal. In the technology described in Patent Document 1, the received signal is corrected based on an image acquired by the optical sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2019 / 0265330 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology disclosed in Patent Document 1 requires the radar to be equipped with an optical sensor, which causes a problem of increasing the size of the radar. [Means for solving the problem]

[0006] The present disclosure can be realized in the following forms.

[0007] According to an embodiment of the present disclosure, there is provided a method for calibrating a radar, the radar (1) including a first antenna array (210) as a receiving antenna; The receiving characteristics are the same as those of the first antenna array. and a second antenna array (240). In the radar , The aforementioned First Antenna Array Configure a first antenna surface provided with a plurality of antennas (211, 212, 213, 214); The aforementioned Second Antenna Array Configure The second antenna surface on which the plurality of antennas (241, 242, 243, 244) are provided is arranged so as to face the same direction and at a distance (δz) in the depth direction, which is perpendicular to the vertical direction. .child The method for calibrating the radar is to assume that the direction of the target (CT1) is known, The aforementioned First Antenna Array The first target antenna (212, 213, 214) calculating provisional correction values ​​(T2, T3, T4) for correcting the phase from the received signal; the first target antenna The phase of the received signal at (A12, A13, A14) of The aforementioned By correcting with the provisional correction value, the first target antenna in Received signal Corrected phase The first phase is A step of finding (B12, B13, B14); The aforementioned Second Antenna Array The second target antenna (242, 243, 244) The phase of the received signal at (A42, A43, A44) of The aforementioned By correcting with the provisional correction value, the second target antenna in Received signal Corrected phase The second phase is A step of finding (B42, B43, B44); The first phase and the second phase The difference between the phases is The aforementioned In the depth direction The aforementioned Calculated from distance Received Phase difference of the received signal Ideal value of (Φi) TosuSo that, The aforementioned and a step of obtaining correction values ​​(C2, C3, C4) by modifying the provisional correction values.

[0008] According to this aspect, it is possible to perform correction with high accuracy while suppressing an increase in the size of the radar system. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram showing the positional relationship between a vehicle equipped with a radar and other vehicle's vehicles. [Figure 2] FIG. 1 is a block diagram showing a schematic configuration of a radar. [Figure 3] FIG. 1 is a diagram showing the arrangement of antennas. [Figure 4] FIG. 2 is a diagram showing the arrangement of the antenna array when the radar is viewed from the front. [Figure 5] FIG. 2 is a diagram showing the arrangement of an antenna array when the radar is viewed from the side. [Figure 6] FIG. 2 is a diagram for explaining a received wave at an antenna. [Figure 7] FIG. 2 is a diagram showing the positional relationship between an antenna and a target. [Figure 8] 10 is a flowchart of a correction value calculation process. [Figure 9] FIG. 2 is a diagram showing the positional relationship between a first antenna array and a second antenna array. [Figure 10] This is a graph of a sine function. [Figure 11] FIG. 10 is a side view of the antenna according to the first alternative embodiment. [Figure 12] FIG. 10 is a side view of an antenna according to another embodiment 2. [Figure 13] FIG. 10 is a diagram showing the arrangement of antennas according to another embodiment 4. DETAILED DESCRIPTION OF THE INVENTION

[0010] A. Embodiment As shown in FIG. 1, a radar 1 according to the embodiment is mounted on a host vehicle M1. The radar 1 is installed, for example, in the front grill of the host vehicle M1. The radar 1 detects an observation target, that is, another vehicle M2, present in the forward direction of the host vehicle M1. More specifically, the radar 1 emits radio waves as a transmission wave IL. The transmission wave IL is reflected by an observation target outside the host vehicle M1, such as the other vehicle M2, and becomes a reflected wave RL. Based on the reflected wave RL, the radar 1 detects the direction in which the observation target exists relative to the host vehicle M1.

[0011] 2, the radar 1 includes a transmitting unit 100, a receiving unit 200, and a processing unit 300. The radar 1 is a millimeter wave radar. In the embodiment, the radar 1 is an FMCW (Frequency Modulated Continuous Wave) radar.

[0012] The transmitter 100 includes an oscillator 110, a distributor 120, and a transmitting antenna 130. The oscillator 110 is, for example, a voltage-controlled oscillator (VCO). When a triangular wave voltage signal is input from the transmission / reception control unit 320 of the processing unit 300, the oscillator 110 outputs a frequency-modulated high-frequency signal as a transmission signal. Because the triangular wave voltage signal is used for modulation, the transmission signal output by the oscillator 110 includes an uplink section in which the frequency increases over time, and a downlink section in which the frequency decreases over time.

[0013] The distributor 120 distributes the transmission signal supplied from the oscillator 110 to the transmitting antenna 130 and the first mixer 220 and second mixer 250 of the receiving unit 200. The transmitting antenna 130 radiates the transmission signal supplied from the oscillator 110 via the distributor 120 as a radio wave to the outside of the vehicle M1.

[0014] The receiving section 200 includes a first antenna array 210, a first mixer 220, a first A / D (Analog to Digital) conversion section 230, a second antenna array 240, a second mixer 250, and a second A / D conversion section 260.

[0015] As shown in FIG. 3, the first antenna array 210 is a microstrip array antenna and includes antennas 211-214 and a feed line 219. The antennas 211-214 and the feed line 219 are formed on a substrate P. The substrate P has a dielectric layer L1 and conductor layers L2 and L3 that sandwich the dielectric layer L1. The feed line 219, which is a linear strip line, and the antennas 211-214, which are patch antennas, are formed on the conductor layer L2. The conductor layer L3 serves as the ground. The feed line 219 is wiring for feeding power to each of the antennas 211-214. The antennas 211-214 are connected to the respective feed lines 219. The antennas 211-214 are formed in a patch shape. All of the antennas 211-214 have the same area. The angle formed between the side having the feeding point of each of the antennas 211 to 214 and each of the feeding lines 219 is, for example, a right angle.

[0016] The antennas 211 to 214 are arranged at equal intervals in the direction along the feed line 219 so that the feed phases at the design frequency f0 are the same. Specifically, the antennas 211 and 212, the antennas 212 and 213, and the antennas 213 and 214 are arranged at intervals c in the direction along the feed line 219. In the embodiment, the interval c between the antennas is set to be 1 / 2 the wavelength λ of the design frequency f0. The length b from the connection point between each of the antennas 211 to 214 and the feed line 219 to the open end is set to be 1 / 2 the wavelength λ of the design frequency f0. The antennas 211 to 214 convert the received reflected waves into received signals and output the received signals to the corresponding first mixers 221 to 224, respectively.

[0017] As shown in Fig. 2, the first mixer 220 includes first mixers 221 to 224. The first mixer 221 mixes the transmission signal distributed by the distributor 120 with the reception signal input from the antenna 211, and outputs a beat signal. Since a triangular wave is used as the carrier wave in the radar 1, the first mixer 221 generates beat signals in each of the uplink and downlink sections. The first mixers 222 to 224 similarly generate beat signals. The first mixers 221 to 224 output beat signals to the corresponding first A / D conversion units 231 to 234.

[0018] The first A / D conversion unit 230 includes first A / D conversion units 231 to 234. The first A / D conversion unit 231 converts the beat signal input from the first mixer 221 into a digital signal. The first A / D conversion units 232 to 234 similarly generate the beat signals into digital signals. The first A / D conversion units 231 to 234 output the converted signals to the processing unit 300, respectively.

[0019] 3, the second antenna array 240 is a microstrip array antenna and includes antennas 241 to 244 and a feed line 249. The feed line 249 is a wiring for feeding power to each of the antennas 241 to 244. The antennas 241 to 244 and the feed line 249 are formed on the same substrate P as the first antenna array 210. The antennas 241 to 244 and the feed line 249 are formed on the substrate P in the same arrangement as the first antenna array 210. The antennas 241 to 244 convert the received reflected waves into received signals and output the received signals to the corresponding second mixers 251 to 254, respectively.

[0020] As shown in Fig. 4, the first antenna array 210 and the second antenna array 240 are arranged along the X-axis direction on the substrate P. In Fig. 4, an XYZ orthogonal coordinate system is set for ease of understanding.

[0021] As shown in Fig. 5, the antenna plane of the first antenna array 210 and the antenna plane of the second antenna array 240 are arranged to face the same direction. In addition, by tilting the substrate P with respect to the XY plane, the antenna plane of the first antenna array 210 and the antenna plane of the second antenna array 240 are arranged at a distance δz in the Z-axis direction. In the embodiment, the Z-axis direction is referred to as the depth direction. The depth direction is a direction perpendicular to the vertical direction. The distance δz is set to be equal to or less than ¼ (λ / 4) of the wavelength λ of the design frequency f0. The antenna plane of the first antenna array 210 is also referred to as the first antenna plane. The antenna plane of the second antenna array 240 is also referred to as the second antenna plane. The wavelength λ is also referred to as the wavelength of the transmission signal.

[0022] The first antenna array 210 and the second antenna array 240 have equivalent characteristics. This is because the resonant frequencies of the first antenna array 210 and the second antenna array 240 are aligned so that the first antenna array 210 and the second antenna array 240 receive signals under equivalent conditions. In the embodiment, first, the first antenna array 210 and the second antenna array 240 each have the same number of patch antennas. The area of ​​each patch antenna in the first antenna array 210 is equal to the area of ​​each patch antenna in the second antenna array 240. The distance between the patch antennas included in the first antenna array 210 is equal to the distance between the patch antennas included in the second antenna array 240. The wiring length of the feed line 219 included in the first antenna array 210 is equal to the wiring length of the feed line 249 included in the second antenna array 240. Specifically, as shown in FIG. 3, the wiring length of the feed line 219 between the patch antennas included in the first antenna array 210 is equal to the wiring length of the feed line 249 between the patch antennas included in the second antenna array 240. Furthermore, the wiring length does not refer to the physical length but to the electrical length. The wiring length of the feed line 219 is also referred to as the first wiring length. The wiring length of the feed line 249 is also referred to as the second wiring length. Since the first antenna array 210 and the second antenna array 240 are both formed on the substrate P, the distances between the patch antennas included in each of the first antenna array 210 and the second antenna array 240 and the ground are equal. Therefore, the first antenna array 210 and the second antenna array 240 have equal characteristics.

[0023] The second antenna array 240 is provided in the radar 1 for calculating correction values ​​used in the correction process. The calculation of the correction values ​​will be described in detail later.

[0024] As shown in Fig. 2, second mixer 250 includes second mixers 251 to 254. Second mixer 251 mixes the transmission signal distributed by distributor 120 with the reception signal input from antenna 241 to generate a beat signal. Second mixer 251 generates beat signals in each of the uplink section and the downlink section. Second mixers 252 to 254 similarly generate beat signals. Second mixers 251 to 254 output beat signals to corresponding second A / D conversion units 261 to 264.

[0025] The second A / D conversion unit 260 includes second A / D conversion units 261 to 264. The second A / D conversion unit 261 converts the beat signal input from the second mixer 251 into a digital signal. The second A / D conversion units 262 to 264 similarly convert the beat signals into digital signals. The second A / D conversion units 261 to 264 each output the converted signals to the processing unit 300.

[0026] The processing unit 300 includes a storage unit 310, a transmission / reception control unit 320, and a signal processing unit 330. The processing unit 300 is configured by a computer including a CPU (Central Processing Unit), a memory, and the like.

[0027] The storage unit 310 stores various programs and data executed in the radar 1. For example, the storage unit 310 stores correction values ​​used in correction processing. The transmission / reception control unit 320 controls the transmission unit 100 and the reception unit 200.

[0028] The signal processing unit 330 periodically executes a series of signal processing steps. The signal processing unit 330 includes a frequency processing unit 331, a correction unit 332, an arrival direction calculation unit 333, and a calculation unit 334.

[0029] The frequency processing unit 331 performs frequency conversion on each of the digital signals input from the first A / D conversion units 231 to 234 and the second A / D conversion units 261 to 264, for example, by FFT (Fast Fourier Transform). The frequency processing unit 331 performs frequency conversion on the uplink section signal and the downlink section signal for each channel. The converted data includes signal strength and phase for each frequency. The frequency processing unit 331 outputs the converted data to the correction unit 332. Furthermore, when calculating a correction value, the frequency processing unit 331 outputs the converted data to the calculation unit 323.

[0030] The correction unit 332 corrects the phase of the received signal included in the data input from the frequency processing unit 331. The radar 1 calculates the direction of arrival, which is the direction in which an observation target exists, based on the phase difference between the receiving antennas. It is known that in the radar 1, phase differences can occur due to specific variations in antenna elements, mutual coupling between elements occurring between each antenna channel, and the like. When such a phase difference is added to the phase difference between the receiving antennas, the direction of arrival cannot be accurately estimated. For this reason, when calculating the direction of the radar 1, a correction value is generally used to correct the direction. The correction value is calculated in advance prior to operation of the radar 1. For example, the correction value is calculated during calibration of the radar 1 in an inspection process before shipping the radar 1 from the factory and is stored in the memory unit 310 included in the radar 1. In this embodiment, the correction value calculated by the calculation unit 334 is stored in the memory unit 310.

[0031] The arrival direction calculation unit 333 estimates the arrival direction based on the corrected received signal using a calculation algorithm such as MUSIC (Multiple Signal Classification) or ESPRIT (Estimation of Signal Parameter via Rotational Invariance Techniques).

[0032] The calculation unit 334 calculates the correction value used by the correction unit 332. Before describing the method for calculating the correction value according to the embodiment, first, a description will be given of the difference in phase of the received signal that occurs depending on the difference in the propagation distance of the signal.

[0033] In the example shown in FIG. 6, the reflected wave is incident on antenna 211 and antenna 212 at an angle θ. The angle θ is the angle with respect to the direction perpendicular to the antenna surface. The direction perpendicular to the antenna surface is set to 0 degrees. When the first antenna array 210 is far away from the observation target, the reflected wave that reaches the first antenna array 210 can be approximated as a plane wave. A plane wave is a wave whose equiphase surface is flat. Here, being far away means that the distance between the first antenna array 210 and the observation target is sufficiently large compared to the wavelength of the reflected wave. Therefore, the reflected wave is incident on antenna 211 and antenna 212 at the same angle θ.

[0034] When antenna 211 is used as a reference, a difference occurs between the propagation distance of a signal to antenna 211 and the propagation distance of a signal to antenna 212. Due to the difference in the signal propagation distance, the signal arrives at antenna 212 later than at antenna 211. Therefore, when the phase of the signal received at antenna 211 is used as a reference, a shift occurs in the phase of the signal received at antenna 212. The difference in phase of the signal received at antenna 212 from the phase of the signal received at antenna 211 occurs according to distance L, which is the difference between the propagation distance of the signal to antenna 211 and the propagation distance of the signal to antenna 212. The phase difference can be expressed as Δφ=(2π / λ)·L. Furthermore, when the distance between the antennas is d, distance L, which is the difference in signal propagation distance, can be expressed as d·sinθ. In the example shown in the figure, the distance between antennas 211 and 212 is distance d1. Therefore, distance L, which is the difference between the propagation distance of the signal to antenna 211 and the propagation distance of the signal to antenna 212, is d1·sinθ.

[0035] Therefore, the phase difference Δφ of the received signal can be expressed as in equation (1), where λ is the wavelength of the received signal. Δφ=(2π / λ)·d1·sinθ …(1)

[0036] Next, an example of a conventional method for calculating a correction value will be described. The ideal value of the phase when a reflected wave reflected from a calibration target located in a known direction is received is calculated in advance using equation (1). Then, the reflected wave reflected from the calibration target located in the known direction is actually received, and the phase is obtained from the received signal. After that, the difference between the phase obtained from the actual received signal and the ideal phase value calculated in advance is obtained as the correction value.

[0037] The above conventional method is based on the premise that the calibration target is accurately positioned at a specified position, but in reality, the calibration target may be positioned at a position that is displaced from the specified position.

[0038] In the example shown in FIG. 7, the calibration target CT1 is positioned at a position offset from the specified direction. FIG. 7 shows the calibration target CT1, the first antenna array 210, and the second antenna array 240 viewed from above. The calibration target CT1 has a regular tetrahedron shape with equilateral triangular faces. The specified direction is assumed to be perpendicular to the antenna planes of the first antenna array 210 and each antenna included in the second antenna array, as indicated by dashed line S1. The calibration target CT1 is intended to be positioned at position E1, where one side of its bottom surface intersects perpendicularly with dashed line S1. However, in the illustrated example, the calibration target CT1 is positioned in the direction indicated by dashed line S2.

[0039] Even if the calibration target CT1 is positioned at a position deviated from the specified direction in this way, in the conventional method for calculating the correction value, the radar 1 calculates the correction value assuming that the calibration target CT1 is in the 0 degree direction. Therefore, the correction value contains an error, which reduces the accuracy of the correction process.

[0040] Therefore, in this embodiment, the calculation unit 334 calculates the correction value using the following method.

[0041] As shown in Fig. 8, in step S101, the calculation unit 334 first calculates a correction value using a conventional method. The calculated correction value is set as a provisional correction value. Any algorithm can be used to calculate the correction value. For example, the correction value is calculated by subtracting the ideal value of the phase when a reflected wave is received from a known direction from the phase when the reflected wave is actually received. The correction value for antenna 212 calculated using the conventional method is set as provisional correction value T2, the correction value for antenna 213 as provisional correction value T3, and the correction value for antenna 214 as provisional correction value T4.

[0042] In step S102, the calculation unit 334 corrects the phase for each antenna of the first antenna array 210 using the provisional correction value. The phase for each antenna of the first antenna array 210 is the difference between the phases of the antennas 212 to 214 when the antenna 211 is used as a reference. Specifically, the calculation unit 334 corrects phase A12, which is the difference between the phase of the signal actually received by antenna 211 and the phase of the signal actually received by antenna 212, using the provisional correction value T2 to obtain a corrected phase B12. The calculation unit 334 corrects phase A13 for antenna 213 using the provisional correction value T3 to obtain a corrected phase B13. The calculation unit 334 corrects phase A14 for antenna 214 using the provisional correction value T4 to obtain a corrected phase B14.

[0043] In step S103, the calculation unit 334 corrects the phase for each antenna of the second antenna array 240 with the provisional correction value. The phase for each antenna of the second antenna array 240 is the difference in phase between the antennas 242 to 244 when the antenna 241 is used as the reference. As described above, the characteristics of the first antenna array 210 and the second antenna array 240 are equivalent, so here, the phase for each antenna of the second antenna array 240 is corrected with the correction value found for each antenna of the first antenna array 210.

[0044] Specifically, the calculation unit 334 corrects phase A42, which is the difference between the phase of the signal actually received by antenna 241 and the phase of the signal actually received by antenna 242, using the provisional correction value T2 to obtain a corrected phase B42. The calculation unit 334 corrects phase A43 for antenna 243 using the provisional correction value T3 to obtain a corrected phase B43. The calculation unit 334 corrects phase A44 for antenna 244 using the provisional correction value T4 to obtain a corrected phase B44.

[0045] In step S104, the calculation unit 334 calculates an ideal value of the phase of the received signal between the first antenna array 210 and the second antenna array 240.

[0046] As shown in Fig. 9, when the calibration target is in the 0 degree direction, the difference between the propagation distance of signals to antennas 211 to 214 of first antenna array 210 and the propagation distance of signals to antennas 241 to 244 of second antenna array 240 is a distance δz. In Fig. 9, for ease of viewing the drawing, the positions of first antenna array 210 and second antenna array 240 are shifted left and right. The actual positions of first antenna array 210 and second antenna array 240 are as shown in Fig. 4.

[0047] As described above, the phase difference occurs depending on the difference in signal propagation distance. In the example shown in Fig. 9, the phase difference between the first antenna array 210 and the second antenna array 240 can be expressed by equation (2). Δφ=(2π / λ)·δz …(2)

[0048] The calculation unit 334 calculates the ideal value Φi of the phase difference between the received signals of the first antenna array 210 and the second antenna array 240 using the above equation (2).

[0049] The distance δz is set to be equal to or less than ¼ wavelength (λ / 4) of the transmission signal for the following reason. First, radio waves can be expressed by a sine function as shown in FIG. 10. In the illustrated example, the period is 2π. In this embodiment, in order to detect minute angular differences in the phase between the first antenna array 210 and the second antenna array 240, the radar 1 uses the degree of change in amplitude y that appears when θ is near 0 (0 degrees) in the sine function. Therefore, it is more preferable to set the reception phase difference between the first antenna array 210 and the second antenna array 240 to a value near 0 degrees. However, the reception phase difference is not set to 0 degrees.

[0050] Furthermore, when the angle θ exceeds +π / 2 (+90 degrees), the sine function may take the same value for the amplitude y even if the angle θ is different. When the angle θ is below -π / (-90 degrees), the sine function may take the same value even if the angle θ is different. Therefore, the distance δz is set to -¼ wavelength (-λ / 4) of the transmitted wave to +¼ wavelength (+λ / 4) of the transmitted wave. When the distance δz is set to -¼ wavelength (-λ / 4) of the transmitted wave, the positions of the first antenna array 210 and the second antenna array 240 on the Z axis shown in FIG. 5 can be swapped. In this case, the first antenna array 210 is positioned on the -Z side of the second antenna array 240.

[0051] For example, when the distance δz is +1 / 8 wavelength of the transmission wave, this means that the distance δz between the antenna surfaces is 1 / 8 wavelength, and that the first antenna array 210 is disposed on the +Z side of the second antenna array 240, as shown in Fig. 5. Furthermore, when the distance δz is -1 / 8 wavelength of the transmission wave, this means that the distance δz between the antenna surfaces is 1 / 8 wavelength, and that the first antenna array 210 is disposed on the -Z side of the second antenna array 240.

[0052] As shown in FIG. 8, in step S105, the calculation unit 334 calculates the difference between the corrected phase for the antenna of the first antenna array 210 and the corrected phase for the corresponding antenna of the second antenna array 240.

[0053] Specifically, the calculation unit 334 calculates, as the difference D12, the difference between the corrected phase B12 for antenna 212 and the corrected phase B42 for antenna 242. The calculation unit 334 calculates, as the difference D13, the difference between the corrected phase B13 for antenna 213 and the corrected phase B43 for antenna 243. The calculation unit 334 calculates, as the difference D14, the difference between the corrected phase B14 for antenna 214 and the corrected phase B44 for antenna 244.

[0054] In step S106, the calculation unit 334 modifies the provisional correction values ​​T2 to T4 using the ideal value Φi of the phase difference between the received signals between the first antenna array 210 and the second antenna array 240 calculated in step S104 and the differences D12 to D14.

[0055] Specifically, the calculation unit 334 calculates a correction value C2 for the antenna 212 by subtracting the absolute value of the value obtained by subtracting the ideal value Φi from the difference D12 from the provisional correction value T2. The calculation unit 334 calculates a correction value C3 for the antenna 213 by subtracting the absolute value of the value obtained by subtracting the ideal value Φi from the difference D13 from the provisional correction value T3. The calculation unit 334 calculates a correction value C4 for the antenna 214 by subtracting the absolute value of the value obtained by subtracting the ideal value Φi from the difference D14 from the provisional correction value T4. The correction values ​​C2 to C4 obtained in this way are correction values ​​in which errors caused by positional deviation of the calibration target CT1 have been corrected.

[0056] In step S107, the calculation unit 334 stores the correction values ​​C2 to C4 in the storage unit 310. The above is the method for calculating the correction values ​​in this embodiment.

[0057] The correction unit 332 corrects the phase of the received signal using the correction values ​​C2 to C4 obtained by the above method, so that the radar 1 can perform the correction with high accuracy.

[0058] As described above, in this embodiment, the provisional correction value calculated by the conventional method is corrected using the ideal value of the phase difference between the two antenna arrays calculated from the distance in the depth direction. Therefore, even if there is a deviation in the position where the calibration target CT1 is placed, the error in the provisional correction value can be corrected. Therefore, the accuracy of the correction process can be improved.

[0059] Furthermore, by simply adding an antenna array with characteristics equivalent to the receiving antenna array, it is possible to perform accurate correction while suppressing an increase in the size of the radar system.

[0060] B1. Other embodiment 1 In the embodiment, the substrate P on which the first antenna array 210 and the second antenna array 240 are provided is tilted so that the antenna plane of the first antenna array 210 and the antenna plane of the second antenna array 240 are arranged at a distance in the depth direction. The method of arranging the first antenna array 210 and the second antenna array 240 is not limited to this.

[0061] 11, an extension member B may be provided between the first antenna array 210 and the substrate P with the substrate P positioned without tilting relative to the XY plane. In this case, the first antenna array 210 and the second antenna array 240 can also be positioned with a distance δz between their respective antenna planes. In this case, the same effects as those of the embodiment can be achieved.

[0062] B2. Other embodiment 2 12, the first antenna array 210 and the second antenna array 240 may be disposed on a substrate P having a curved surface. In order to adjust the inclination of the antenna plane of the second antenna array, an extension member B is provided between the second antenna array and the substrate P. In this case, the same effects as those of the embodiment can be achieved.

[0063] B3. Other embodiment 3 5, 11, and 12 show examples in which first antenna array 210 is arranged on the +Y side and second antenna array 240 is arranged on the -Y side. Alternatively, first antenna array 210 may be arranged on the -Y side and second antenna array 240 may be arranged on the +Y side.

[0064] B4. Other embodiment 4 In the embodiment, an example has been described in which the first antenna array 210 and the second antenna array 240 have the same number of antennas. However, the number of antennas included in the second antenna array 240 may be less than the number of antennas included in the first antenna array 210. The following description will focus on differences from the embodiment.

[0065] 13, when the first antenna array 210 has four antennas 211 to 214, the second antenna array 240 may have two antennas 211 to 212. Furthermore, the antennas 211 and 241, and the antennas 212 and 242, are made to correspond to each other. In the example shown in the figure, the wiring length of the feed line 219 to the antenna 211 is equal to the wiring length of the feed line 249 to the antenna 241, and the wiring length of the feed line 219 between the antennas 211 and 212 is equal to the wiring length of the feed line 249 between the antennas 241 and 242. Alternatively, when the wiring length between the patch antennas included in the first antenna array 210 is different from the wiring length between the patch antennas included in the second antenna array 240, the difference may be set to be a positive integer multiple of the wavelength λ of the design frequency f0. This is because the resonant frequencies of the first antenna array 210 and the second antenna array 240 are aligned, and the first antenna array 210 and the second antenna array 240 receive signals under the same conditions.

[0066] 13, after a provisional correction value is calculated, the phase of antenna 212 is corrected using the calculated provisional correction value. Furthermore, the phase of antenna 242 is corrected using the provisional correction value. Then, the provisional correction value is modified so that the difference between the corrected phase in first antenna array 210 and the corrected phase in second antenna array 240 becomes the ideal value of the phase difference calculated from distance δz.

[0067] B5. Other Embodiment 5 3, the wiring length of the feed line 219 between the patch antennas included in the first antenna array 210 is the same as the wiring length of the feed line 249 between the patch antennas included in the second antenna array 240. However, the wiring length of the feed line 219 between the patch antennas included in the first antenna array 210 may be different from the wiring length of the feed line 249 between the patch antennas included in the second antenna array 240. In this case, the difference is set to be a positive integer multiple of the wavelength λ of the design frequency f0. A specific method is as follows. For example, suppose that the wiring length between antennas 211 and 212, the wiring length between antennas 212 and 213, and the wiring length between antennas 213 and 214 are each length N1. Suppose that the wiring length between antennas 241 and 242, the wiring length between antennas 242 and 243, and the wiring length between antennas 243 and 244 are each length N2. In this case, the difference between the length N1 and the length N2 is set to be a positive integer multiple of the wavelength λ of the design frequency f0, in order to align the resonant frequencies of the first antenna array 210 and the second antenna array 240 and enable the first antenna array 210 and the second antenna array 240 to receive signals under equivalent conditions.

[0068] The processing unit 300 of the radar 1 may also include a distance calculation unit that calculates the distance between the host vehicle M1 and the observation target. In this case, the distance calculation unit can calculate the distance to the observation target using the target frequency in the uplink section and the target frequency in the downlink section. The processing unit 300 of the radar 1 may also include a speed calculation unit that calculates the relative speed of the observation target with respect to the host vehicle M1.

[0069] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0070] A12, A13, A14, A42, A43, A44, B12, B13, B14, B42, B43, B44...phase, C2, C3, C4...correction value, CT1...calibration target, T2, T3, T4...provisional correction value, δz...distance, Φi...ideal value, 1...radar, 210...first antenna array, 211, 212, 213, 214...antenna, 240...second antenna array, 241, 242, 243, 244...antenna

Claims

1. 1. A method of calibrating a radar, comprising: The radar (1) The receiving antenna includes a first antenna array (210) and a second antenna array (240) having the same receiving characteristics as the first antenna array, a first antenna surface on which a plurality of antennas (211, 212, 213, 214) constituting the first antenna array is provided, and a second antenna surface on which a plurality of antennas (241, 242, 243, 244) constituting the second antenna array is provided, the first antenna surface and the second antenna surface are arranged to face in the same direction and to be spaced apart by a distance (δz) in a depth direction that is a direction perpendicular to a vertical direction, The method for calibrating the radar includes: Assuming that the direction of the target (CT1) is known, a step of obtaining provisional correction values ​​(T2, T3, T4) for correcting the phase from the received signal of the first target antenna (212, 213, 214) of the first antenna array; a step of correcting a phase (A12, A13, A14) of the received signal at the first target antenna using the provisional correction value to obtain a first phase (B12, B13, B14) which is a corrected phase of the received signal at the first target antenna; a step of correcting a phase (A42, A43, A44) of a received signal at a second target antenna (242, 243, 244) of the second antenna array using the provisional correction value, thereby obtaining a second phase (B42, B43, B44) which is a corrected phase of the received signal at the second target antenna; calculating correction values ​​(C2, C3, C4) by correcting the provisional correction value so that the difference between the first phase and the second phase becomes an ideal value (Φi) of the phase difference of the received signal calculated from the distance in the depth direction; 10. A method for calibrating a radar, comprising:

2. 2. A method for calibrating a radar according to claim 1, comprising: In the radar, the distance in the depth direction is set to be equal to or less than ¼ of the wavelength of a transmission signal transmitted by the radar. How to calibrate radar.

3. A method for calibrating a radar according to claim 1 or 2, comprising: In the radar, the wiring length of wiring for feeding power to each of the antennas constituting the first antenna array is the same as the wiring length of wiring for feeding power to each of the antennas constituting the second antenna array. How to calibrate radar.

4. A method for calibrating a radar according to claim 1 or 2, comprising: In the radar, a difference between a wiring length of wiring for feeding power to each of the antennas constituting the first antenna array and a wiring length of wiring for feeding power to each of the antennas constituting the second antenna array is set to be a positive integer multiple of a wavelength of a transmission signal transmitted by the radar. How to calibrate radar.

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