Radar device

Abstract

A radar device (1) is provided with a transmission antenna (130), a plurality of array antennas, and an angle estimation unit (332), the plurality of array antennas including a first antenna set, which is a set of two array antennas disposed at a first distance (D1), and a second antenna set, which is a set of two array antennas disposed at a second distance (D2). The first distance is set such that the estimated accuracy characteristic of the angle becomes a first estimated accuracy characteristic, the second distance is set such that the estimated accuracy characteristic becomes a second estimated accuracy characteristic different from the first estimated accuracy characteristic, and the angle estimation unit estimates the angle using the first estimation result and the second estimation result. The first estimation result is estimated using a received signal received by the first antenna set, and the second estimation result is estimated using a received signal received by the second antenna set.

Description

Technical Field

[0001] The present disclosure relates to a radar apparatus. Background Art

[0002] There is known a technique for estimating the angle indicating the arrival direction of the reflected wave using reception signals obtained by receiving reflected waves from a reflecting target using two array antennas (Non-Patent Document 1).

[0003] Prior art literature

[0004] Non-patent literature

[0005] Non-patent document 1: Yan Ma et al. "A Novel ESPRIT-Based Algorithm for DOAEstimation with Distributed Subarray Antenna", Circuits Syst Signal Process34, p.2951-2972, 2015 Summary of the Invention

[0006] In angle estimation using two array antennas, the inventors discovered a problem in which estimation accuracy decreases at specific angles.

[0007] The present disclosure can be implemented as the following technical solutions.

[0008] According to a technical solution disclosed herein, a radar device is provided. The radar device comprises: a transmitting antenna for transmitting a transmission wave as an electromagnetic wave; a plurality of array antennas, each having a plurality of antenna elements arranged at equal intervals in a straight line along a predetermined arrangement direction, arranged relative to each other in the arrangement direction, and receiving a reflected wave generated by a reflector reflecting the electromagnetic wave as a received signal; and an angle estimating unit for estimating an angle representing an arrival direction of the reflected wave using the received signal received by the plurality of array antennas; the plurality of array antennas comprising a first antenna set, which is a set of two array antennas arranged at a first distance, and a second antenna set, which is a set of two array antennas arranged at a second distance. The angle estimation unit estimates the angle using a first estimation result and a second estimation result, wherein the first estimation result is estimated using the received signal received by the first antenna set, and the second estimation result is estimated using the received signal received by the second antenna set.

[0009] According to the radar device of this technical solution, the multiple array antennas include a first antenna set configured to achieve a first estimation accuracy characteristic and a second antenna set configured to achieve a second estimation accuracy characteristic different from the first estimation accuracy characteristic. The angle estimating unit estimates the angle using the first estimation result and the second estimation result. Therefore, by selectively using the first estimation result and the second estimation result having different estimation accuracy characteristics, a decrease in the estimation accuracy of the angle can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a diagram showing the positional relationship between a vehicle equipped with a radar device and other vehicles.

[0011] Figure 2 This is a block diagram showing a schematic configuration of a radar device.

[0012] Figure 3 It is an explanatory diagram showing the schematic structure of an array antenna.

[0013] Figure 4 It is an explanatory diagram showing the estimation accuracy characteristics of the first estimation result.

[0014] Figure 5 It is an explanatory diagram showing the estimation accuracy characteristics of the second estimation result.

[0015] Figure 6 : is a flowchart showing the steps of the angle estimation process. DETAILED DESCRIPTION

[0016] A. Implementation method:

[0017] A-1. Device structure:

[0018] like Figure 1 As shown, the radar device 1 of the embodiment is mounted on the vehicle M1. The radar device 1 is, for example, set in the front grille of the vehicle M1. The radar device 1 detects a reflective marker existing in the front direction of the vehicle M1. In the present embodiment, the reflective marker is another vehicle M2. More specifically, the radar device 1 radiates electromagnetic waves as a transmission wave IL. The transmission wave IL is reflected by a reflective marker outside the vehicle M1 and becomes a reflected wave RL. The radar device 1 detects the direction in which the reflective marker exists relative to the vehicle M1 based on the angle indicating the arrival direction of the reflected wave RL. In addition, the radar device 1 is not limited to the front direction of the vehicle M1, and can also detect reflective markers existing in any direction around the vehicle M1.

[0019] like Figure 2As shown, the radar device 1 includes a transmitter 100, a receiver 200, and a processor 300. The radar device 1 is a millimeter wave radar. In the embodiment, the radar device 1 is an FMCW (Frequency Modulated Continuous Wave) radar.

[0020] Transmitter 100 includes an oscillator 110, a distributor 120, and a transmitting antenna 130. Oscillator 110 is, for example, a voltage-controlled oscillator (VCO). Oscillator 110, upon receiving a triangular wave voltage signal from transmission / reception control unit 320 of processing unit 300, outputs a frequency-modulated high-frequency signal as a transmission signal. The transmission signal output by oscillator 110 includes a rising interval, in which the frequency increases over time, and a falling interval, in which the frequency decreases over time.

[0021] The distributor 120 distributes the transmission signal supplied from the oscillator 110 to the transmission antenna 130 and the first, second, and third mixers 220, 250, and 280 of the reception unit 200. The transmission antenna 130 radiates the transmission signal supplied from the oscillator 110 via the distributor 120 as electromagnetic waves to the outside of the vehicle M1.

[0022] The receiving unit 200 includes a first array antenna 210, a first mixer 220, a first A / D (Analog Digital) converter 230, a second array antenna 240, a second mixer 250, a second A / D converter 260, a third array antenna 270, a third mixer 280, and a third A / D converter 290. Thus, the radar apparatus 1 of this embodiment includes a plurality of array antennas.

[0023] The first array antenna 210 is as follows Figure 3 As shown, this is an equally spaced linear array antenna composed of K antenna elements 211 spaced apart from each other by a distance d and arranged at equal intervals in a straight line along a predetermined arrangement direction. K is an integer greater than or equal to 2. The K antenna elements 211 correspond to each channel from the 1st channel to the Kth channel.

[0024] In this embodiment, the distance d is equal to half the wavelength of the transmission wave IL. However, the distance d may not be strictly equal to half the wavelength of the transmission wave IL, as long as it can be considered equal to half the wavelength of the transmission wave IL after taking into account design errors and variations.

[0025] The first array antenna 210 receives the reflected wave RL reflected by the reflector as a received signal, and outputs the received signal to the first mixer 220 .

[0026] Figure 1 The first mixer 220 shown mixes the transmission signal distributed by the distributor 120 with the received signals input from each antenna element 211, and outputs a beat signal. Since a triangular wave is used as a carrier wave in the radar device 1, the first mixer 220 generates and outputs a beat signal in both the rising and falling intervals. The beat signal output by the first mixer 220 is supplied to the first A / D converter 230.

[0027] The first A / D converter 230 samples and quantizes the beat signal at a sampling frequency to convert it into a digital signal. The converted digital signal is supplied to the processor 300 .

[0028] The second array antenna 240 is as follows Figure 3 As shown, similar to first array antenna 210, this is an equally spaced linear array antenna consisting of K antenna elements 241 spaced apart from each other by a distance d and arranged at equal intervals in a straight line along a predetermined arrangement direction. K is an integer greater than or equal to 2. The K antenna elements 241 correspond to each channel from the 1st channel to the Kth channel.

[0029] The first array antenna 210 and the second array antenna 240 are arranged with a distance D1 between them along the arrangement direction of the antenna elements 211 and 241. More specifically, the first array antenna 210 and the second array antenna 240 are arranged so that the distance between the antenna element 211 closest to the second array antenna 240 among the multiple antenna elements 211 constituting the first array antenna 210 and the antenna element 241 closest to the first array antenna 210 among the multiple antenna elements 241 constituting the second array antenna 240 is distance D1. In this embodiment, distance D1 is set to 400 times half the wavelength of the transmission wave IL. Distance D1 corresponds to the "first distance" in this disclosure. In the following description, the set of the first array antenna 210 and the second array antenna 240 will also be referred to as the "first antenna set."

[0030] The second array antenna 240 receives the reflected wave RL reflected by the reflector as a reception signal, and outputs the reception signal to the second mixer 250 .

[0031] Figure 2 The structure of the second mixer 250 is the same as that of the first mixer 220, so its description is omitted. The structure of the second A / D converter 260 is the same as that of the first A / D converter 230, so its description is omitted.

[0032] The third array antenna 270 is as follows Figure 3As shown, similar to first array antenna 210, this is an equally spaced linear array antenna consisting of K antenna elements 271 spaced apart from each other by a distance d and arranged at equal intervals in a straight line along a predetermined arrangement direction. K is an integer greater than or equal to 2. The K antenna elements 271 correspond to each channel from the 1st channel to the Kth channel.

[0033] The first array antenna 210 and the third array antenna 270 are arranged with a distance D2 between them along the arrangement direction of the antenna elements 211 and 271. More specifically, the first array antenna 210 and the third array antenna 270 are arranged so that the distance between the antenna element 211 closest to the third array antenna 270 among the multiple antenna elements 211 constituting the first array antenna 210 and the antenna element 271 closest to the first array antenna 210 among the multiple antenna elements 271 constituting the third array antenna 270 is D2. In this embodiment, the distance D2 is set to 300 times half the wavelength of the transmission wave IL. The distance D2 corresponds to the "second distance" in this disclosure. In the following description, the set of the first array antenna 210 and the third array antenna 270 will also be referred to as the "second antenna set."

[0034] In this embodiment, distance D2 is set so that the ratio of distance D1 to distance D2 falls within the range of "1.3 + n to 1.5 + n (n is an integer greater than or equal to 0)." As described above, in this embodiment, distance D1 is set to 400 times half the wavelength of transmission wave IL, and distance D2 is set to 300 times half the wavelength of transmission wave IL. That is, in this embodiment, the ratio of distance D1 to distance D2 is approximately "1.33," falling within the range of "1.3 to 1.5." By setting distance D2 in this way, the estimation accuracy characteristics of the first estimation result and the second estimation result, described later, can be appropriately differentiated. By using the first and second estimation results separately, a decrease in estimation accuracy can be suppressed. In addition, in this embodiment, through preliminary experiments and simulations, it was determined that when the ratio of distance D1 to distance D2 is in the range of "from 1.3+n to 1.5+n (n is an integer greater than 0)", the estimation accuracy characteristics of the first estimation result can be appropriately made different from the estimation accuracy characteristics of the second estimation result.

[0035] The third array antenna 270 receives the reflected wave RL reflected by the reflector as a reception signal, and outputs the reception signal to the third mixer 280 .

[0036] Figure 2 The structure of the third mixer 280 is the same as that of the first mixer 220, so its description is omitted. The structure of the third A / D converter 290 is the same as that of the first A / D converter 230, so its description is omitted.

[0037] The processing unit 300 includes a storage unit 310, a transmission and reception control unit 320, and a signal processing unit 330. The processing unit 300 is composed of a computer including a CPU (Central Processing Unit), memory, and other components. The storage unit 310 stores various programs and data executed by the radar device 1. The transmission and reception control unit 320 controls the transmitter 100 and receiver 200.

[0038] The signal processing unit 330 periodically performs a series of signal processing operations. It functions as a frequency processing unit 331 and an angle estimation unit 332. The frequency processing unit 331 performs frequency conversion on the digital signals input from the first A / D converter 230, the second A / D converter 260, and the third A / D converter 290, for example, using an FFT (Fast Fourier Transform) to calculate the beat frequency. The frequency processing unit 331 outputs the calculated beat frequency to the angle estimation unit 332.

[0039] The angle estimating unit 332 estimates the angle indicating the arrival direction of the reflected wave RL based on the beat frequency. In this embodiment, the angle estimating unit 332 uses ESPRIT (Estimation of Signal Parameter via Rotational Invariance Technique) as a calculation algorithm to estimate the angle indicating the arrival direction of the reflected wave RL. In this embodiment, the angle estimating unit 332 performs a first estimation process based on the beat frequency of the received signal received by the first antenna set, and a second estimation process based on the beat frequency of the received signal received by the second antenna set.

[0040] Reference Figure 4 The estimation accuracy characteristics of the first estimation process will be described. In the following description, the estimation accuracy characteristics of the first estimation process will also be referred to as "first estimation accuracy characteristics." Figure 4 In the figure, the vertical axis represents the detection rate and the horizontal axis represents the target angle. Figure 4, the estimation accuracy characteristics in the angle range of 0° to 1° for the target angle are shown. "Target angle" refers to the angle formed by the arrival direction of the reflection wave RL of the first reflection mark and the arrival direction of the reflection wave RL of the second reflection mark in the reflection mark detection with two reflection marks as the object. "Detection rate" refers to the ratio of the number of times the angle estimation is properly performed in the angle estimation with a pre-set number of attempts for each target angle. In this embodiment, when the angle estimation result is included in the angle range of the same size as the target angle centered on the target angle, for example, in the angle estimation with the target angle set to 0.4°, when the angle estimation result is included in the angle range of 0.4°±0.2°, it is judged that the angle estimation is properly performed.

[0041] exist Figure 4 In FIG, the angle range of the target angle with a detection rate of 0.8 or more is hatched. Figure 4 As shown, the angle range with a detection rate of 0.8 or more and the angle range with a detection rate of less than 0.8 appear alternately in the angle range of the target angle of 0° to 1°. The inventors have discovered that the angle range with a detection rate of 0.8 or more and the angle range with a detection rate of less than 0.8 vary depending on the beam pattern of each array antenna and the positional relationship between the two array antennas. According to the first estimation accuracy characteristic of this embodiment, the detection rate is less than 0.8 in the angle ranges below 0.1°, 0.2° to 0.3°, around 0.5°, and around 0.8°.

[0042] Next, refer to Figure 5 The estimation accuracy characteristics of the second estimation process will be described. In the following description, the estimation accuracy characteristics of the second estimation process will also be referred to as "second estimation accuracy characteristics." Figure 5 In , the vertical axis represents the detection rate and the horizontal axis represents the target angle. Figure 5 In, with Figure 4 Similarly, the estimation accuracy characteristics in the target angle range of 0° to 1° are shown. Figure 5 In FIG, the angle range of the target angle with a detection rate of 0.8 or more is hatched. Figure 5 As shown, according to the second estimation accuracy characteristic, the detection rate is less than 0.8 in the angle ranges below 0.1°, 0.3° to 0.4°, and around 0.7°. Thus, the angle ranges in which the detection rate is less than 0.8 in the first estimation process and the angle ranges in which the detection rate is less than 0.8 in the second estimation process are different.

[0043] A-2. Angle estimation processing:

[0044] The angle estimation unit 332 executes the Figure 6In step S2, the angle estimating unit 332 performs a first estimation process based on the beat frequency of the received signal received by the first radar set, and obtains a first estimation result on the target angle.

[0045] In step S4, the angle estimating unit 332 determines whether high resolution is required. In this embodiment, the angle estimating unit 332 determines that high resolution is required when the first estimation result is less than 1°.

[0046] If it is determined that high resolution is required (step S4 : Yes), in step S6 , the angle estimating unit 332 performs a second estimation process using the beat frequency based on the received signal received by the second radar set to obtain a second estimation result regarding the target angle.

[0047] In step S8, the angle estimating unit 332 adopts an appropriate estimation result based on the respective estimation accuracy characteristics of the first estimation result and the second estimation result. For example, if the first estimation result is "0.5°" included in the angle range with a low detection rate in the first estimation accuracy characteristic, the angle estimating unit 332 adopts the second estimation result. That is, generally speaking, the angle estimating unit 332 estimates the angle representing the arrival direction of the reflected wave RL by referring to the first estimation result and the second estimation result, which have different angle ranges with a detection rate of less than 0.8 as described above, and the estimation result with a detection rate of 0.8 or more with respect to the target angle. In this way, in this embodiment, angle estimation is performed by selectively referring to one of the first estimation result and the second estimation result. Therefore, it is possible to adopt an appropriate estimation result based on the estimation accuracy characteristic, and it is possible to suppress a decrease in the estimation accuracy of the arrival direction. Furthermore, when the detection rates for the target angle in both the first estimation result and the second estimation result are 0.8 or higher, the angle estimation unit 332 may perform angle estimation with reference to one of the preset estimation results.

[0048] If it is determined in step S4 that high resolution is not required (step S4: No), the angle estimation unit 332 adopts the first estimation result and terminates the angle estimation process. Since the first estimation result is adopted when high resolution is not required, there is no need to further perform angle estimation based on the received signal received by the second radar set, which can reduce the time required for angle estimation.

[0049] According to the radar device 1 of the embodiment described above, a first antenna assembly is configured to achieve a first estimation accuracy characteristic; and a second antenna assembly is configured to achieve a second estimation accuracy characteristic different from the first estimation accuracy characteristic. The angle estimating unit 332 estimates the angle using the first and second estimation results. Therefore, by selectively using the first and second estimation results, each having a different estimation accuracy characteristic, a decrease in the estimation accuracy of the angle can be suppressed.

[0050] Furthermore, since the angle is estimated by referring to the estimation result whose angle estimation accuracy is greater than or equal to a preset threshold value among the first and second estimation results, an appropriate estimation result can be adopted according to the estimation accuracy characteristics, and a decrease in the estimation accuracy of the arrival direction can be further suppressed.

[0051] In addition, by regulating the relationship between distance D1 and distance D2 so that the ratio of the first distance to the second distance is in the range of 1.3+n to 1.5+n (n is an integer greater than 0), the first accuracy estimation characteristic and the second estimation accuracy characteristic can be appropriately made different, and the decrease in estimation accuracy can be suppressed by distinguishing between the first estimation result and the second estimation result.

[0052] Furthermore, in angle estimation using ESPRIT, a decrease in estimation accuracy can be suppressed.

[0053] B. Other Implementation Methods

[0054] (B1) In the above embodiment, the radar device 1 includes three array antennas: the first array antenna 210, the second array antenna 240, and the third array antenna 270. However, the present disclosure is not limited to this. Furthermore, the first array antenna 210 is included in both the first radar set and the second radar set, but the present disclosure is not limited to this. For example, the radar device 1 may further include a fourth array antenna, and utilize the set of the third array antenna 270 and the fourth array antenna as the second radar set. Such an embodiment also achieves the same effects as the above embodiment.

[0055] Furthermore, the radar device 1 includes two radar sets: a first radar set and a second radar set, but the present disclosure is not limited thereto. The radar device 1 may also include three or more radar sets with different estimation accuracy characteristics. Such an embodiment also achieves the same effects as the above embodiment. Furthermore, since the number of options for estimation accuracy characteristics can be increased, the possibility of estimation results being included in areas with low detection rates can be reduced, further suppressing a decrease in the estimation accuracy of angle estimation.

[0056] (B2) In the above embodiment, distance D2 is set so that the ratio of distance D1 to distance D2 falls within the range of "1.3 + n to 1.5 + n (n is an integer greater than or equal to 0)", but the present disclosure is not limited to this. The relationship between distance D1 and distance D2 may also be such that one of distance D1 and distance D2 is not an integer multiple of the other. In such an embodiment, as in the above embodiment, the estimation accuracy characteristics of the first estimation result and the second estimation accuracy characteristics can be made different. By using the first estimation result and the second estimation result separately, a decrease in estimation accuracy can be suppressed.

[0057] (B3) In the above embodiment, the angle estimating unit 332 uses ESPRIT as the calculation algorithm to estimate the angle indicating the arrival direction of the reflected wave RL. However, the present disclosure is not limited to this. The angle estimating unit 332 may also use another calculation algorithm, such as MUSIC (Multiple Signal Classification), to estimate the angle indicating the arrival direction of the reflected wave RL. Such an embodiment also achieves the same effects as the above embodiment.

[0058] (B4) In the above embodiment, in step S4 of the angle estimation process, the angle estimating unit 332 determines that high resolution is required when the first estimation result is within 1°. However, the present disclosure is not limited to this. For example, the angle estimating unit 332 may determine that high resolution is required when the distance to the reflective mark estimated using the beat frequency is greater than a predetermined threshold. Such an embodiment also achieves the same effects as the above embodiment. Furthermore, the angle estimating unit 332 may always use the first and second estimation results to perform angle estimation, regardless of whether high resolution is required.

[0059] (B5) In the above embodiment, in step S4 of the angle estimation process, the angle estimating unit 332 estimates the angle indicating the arrival direction of the reflected wave RL by referring to the estimation result with a detection rate of 0.8 or greater among the first and second estimation results. However, the present disclosure is not limited to this. The angle estimating unit 332 may also estimate the angle indicating the arrival direction of the reflected wave RL by referring to the estimation result with a detection rate of 0.8 or greater, which is not limited to 0.8. The threshold value can be arbitrarily set according to the estimation accuracy required for the angle estimation. Such an embodiment also achieves the same effects as the above embodiment.

[0060] (B6) In the above embodiment, the angle estimating unit 332 selectively refers to either the first estimation result or the second estimation result to perform angle estimation, but the present disclosure is not limited to this. For example, when the detection rates for the target angle in both the first estimation result and the second estimation result are 0.8 or greater, the angle estimating unit 332 may perform angle estimation using the result obtained by averaging the first estimation result and the second estimation result.

[0061] The processing unit 300 and the method thereof described in the present disclosure may also be implemented by a special-purpose computer provided by a processor and a memory programmed to perform one or more functions embodied by a computer program. Alternatively, the processing unit 300 and the method thereof described in the present disclosure may also be implemented by a special-purpose computer provided by a processor composed of one or more special-purpose hardware logic circuits. Alternatively, the processing unit 300 and the method thereof described in the present disclosure may also be implemented by one or more special-purpose computers composed of a combination of a processor and a memory programmed to perform one or more functions and a processor composed of one or more hardware logic circuits. In addition, the computer program may also be stored in a computer-readable non-removable tangible recording medium as instructions executed by a computer.

[0062] The present disclosure is not limited to the above-mentioned embodiments and can be implemented by various structures within the scope of its main purpose. For example, the technical features in each embodiment corresponding to the technical features in the embodiment described in the Summary of the Invention can be appropriately replaced or combined in order to solve part or all of the above-mentioned problems or to achieve part or all of the above-mentioned effects. In addition, as long as the technical features are not described as essential in this specification, they can be appropriately deleted.

Claims

1. A radar device, characterized in that: have: a transmitting antenna that transmits the transmission wave as an electromagnetic wave; A plurality of array antennas each having a plurality of antenna elements arranged linearly and at equal intervals along a predetermined arrangement direction, the antennas being arranged in parallel with each other in the arrangement direction and receiving reflected waves generated by the electromagnetic waves reflected by the reflective marker as received signals; as well as an angle estimating unit for estimating an angle indicating an arrival direction of the reflected wave using the reception signals received by the plurality of array antennas; The plurality of array antennas include a first antenna set consisting of two array antennas arranged at a first distance apart, and a second antenna set consisting of two array antennas arranged at a second distance apart, the first distance being set so that the angle estimation accuracy characteristic becomes a first estimation accuracy characteristic, and the second distance being set so that the estimation accuracy characteristic becomes a second estimation accuracy characteristic different from the first estimation accuracy characteristic. The angle estimating unit estimates the angle using a first estimation result and a second estimation result, wherein the first estimation result is estimated using the received signal received by the first antenna set, and the second estimation result is estimated using the received signal received by the second antenna set.

2. The radar device according to claim 1, wherein The angle estimating unit estimates the angle by referring to an estimation result, of the first estimation result and the second estimation result, in which the estimation accuracy of the angle with respect to the target angle is equal to or greater than a preset threshold value.

3. The radar device according to claim 1 or 2, characterized in that The first distance and the second distance have a relationship in which one of them is not an integral multiple of the other.

4. The radar device according to claim 3, wherein The ratio of the first distance to the second distance is within a range of 1.3+n to 1.5+n, where n is an integer greater than or equal to 0.

5. The radar device according to claim 1 or 2, characterized in that The angle estimating unit estimates the angle using ESPRIT.

Images