radar system

Abstract

To provide a radar system capable of increasing the aperture length without overlapping the positions of virtual antennas. The system includes a local oscillator (30) that supplies radars (10, 20) with a reference signal for generating a radar signal, and a processor (15) that estimates the azimuth of a target based on the signal generated by the radars (10, 20). The radars (10, 20) include RF circuits (13, 23) that process signals in the same frequency band as the radar signal to generate an IF signal with a lower frequency than the radar signal, and BB circuits (14, 24) that process the IF signal. The processor (15) calculates a delay time Δt of the RF circuit between the radars (10, 20). RF , and the delay time of the BB circuit Δt BB a delay time calculation unit 155 that calculates the delay time Δt based on the measurement results of the target; RF , Δt BB and a direction estimation unit 157 that estimates the direction of the target based on the corrected IF signal.

Description

[Technical Field]

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

[0002] In a radar system that estimates the azimuth of a target using transmitted and received signals from multiple radars, the frequencies and phases of the transmitted and received signals must be synchronized between the radars to improve the accuracy of azimuth estimation. For example, a known configuration achieves frequency and phase synchronization by distributing a common reference signal generated by a local oscillator to multiple radars and multiplying the reference signal at each radar to generate a transmission signal.

[0003] However, differences in delay time occur between radars due to variations in wiring and circuit manufacturing, and a phase error proportional to the difference in delay time occurs in the phase of the reflected signal from the target observed by the receiving antenna.

[0004] For example, Patent Document 1 proposes a method of arranging some of the virtual antennas formed by each radar at overlapping positions and correcting the phase error so that the phases of the virtual antennas at the overlapping positions become equal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 157007 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the method described in Patent Document 1, it is necessary to overlap the positions of some of the virtual antennas, which places restrictions on the placement of the antennas and reduces the aperture length.

[0007] In view of the above, an object of the present disclosure is to provide a radar system that can increase the aperture length without overlapping the positions of virtual antennas. [Means for solving the problem]

[0008] To achieve the above object, according to one aspect of the present disclosure, a radar system includes a plurality of radars (10, 20) arranged in a spatially separated state, each having a transmitting antenna (11, 21) for transmitting a radar signal and a receiving antenna (12, 22) for receiving a radar signal reflected by a target, a local oscillator (30) for supplying a reference signal for generating the radar signal to the plurality of radars, and a processor (15, 71) for estimating the azimuth of the target based on the signals generated by the plurality of radars, wherein the plurality of radars each include an RF circuit (13, 23) for processing a signal in the same frequency band as the radar signal to generate an IF signal having a frequency lower than that of the radar signal, and a BB circuit (14, 24) for processing the IF signal, and the processor controls a delay time Δt of the RF circuit between the plurality of radars. RF , and the delay time of the BB circuit Δt BB a delay time calculation unit (155, 712) that calculates the delay time Δt based on the measurement results of the target; RF , Δt BB and a direction estimation unit (157, 714) that estimates the direction of a target based on the corrected IF signal.

[0009] According to this method, the delay times of the RF circuit and BB circuit are calculated based on the measurement results of the target, and the phase of the IF signal is corrected based on the calculated delay time, so there is no need to overlap the positions of the virtual antennas, and the aperture length can be increased.

[0010] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a radar system according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating a detailed configuration of a radar system. [Figure 3] FIG. 2 illustrates the amplitude of a reference signal and a radar signal. [Figure 4] FIG. 10 is a diagram showing the frequencies of radar signals in two measurements. [Figure 5] 3A and 3B are diagrams illustrating transmitted and received signals in each radar. [Figure 6] 10A and 10B are diagrams illustrating beat signals in each radar. [Figure 7] FIG. 10 is a diagram for explaining a phase correction method. [Figure 8] FIG. 10 is a diagram illustrating the relationship between the position of a virtual antenna and a delay time. [Figure 9] FIG. 10 is a diagram illustrating the relationship between the position and phase of a virtual antenna. [Figure 10] 10 is a flowchart of a direction estimation process. [Figure 11] 10 is a flowchart of a phase acquisition process. [Figure 12] FIG. 10 is a diagram showing the result of azimuth estimation when the phase is not corrected. [Figure 13] FIG. 4 is a diagram showing a direction estimation result in the first embodiment. [Figure 14] FIG. 10 is a diagram for explaining a method for estimating a phase error in Comparative Example 1. [Figure 15] FIG. 10 is a diagram for explaining a method for estimating a phase error in Comparative Example 2. [Figure 16] FIG. 10 is a diagram illustrating the frequency of a radar signal in the second embodiment. [Figure 17] FIG. 10 is a diagram for explaining a method for measuring a target in a third embodiment. [Figure 18] FIG. 10 is a diagram illustrating a configuration of a radar system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the following embodiments, identical or equivalent parts will be denoted by the same reference numerals.

[0013] (First embodiment) A first embodiment will be described. A radar system 1 of this embodiment shown in Fig. 1 is mounted on a vehicle, for example, and performs azimuth estimation of targets such as other vehicles. The radar system 1 has a transmitting antenna that transmits radar signals and a receiving antenna that receives radar signals reflected by targets, and is equipped with multiple radars that are spatially separated from one another. In this embodiment, a case will be described in which the radar system 1 is equipped with two radars.

[0014] 1 and 2, the radar system 1 includes a radar 10, a radar 20, a local oscillator 30, and a modulation control unit 40. The radar 10 corresponds to a first radar, and the radar 20 corresponds to a second radar. The local oscillator 30 supplies the radars 10 and 20 with a reference signal for generating a radar signal. The modulation control unit 40 controls modulation of the reference signal generated by the local oscillator 30, and the frequency of the reference signal is set by the signal input from the modulation control unit 40 to the local oscillator 30.

[0015] The radar system 1 is configured such that a reference signal generated by a local oscillator 30 is supplied to the radars 10 and 20, and the radars 10 and 20 transmit and receive radar signals generated from this reference signal.

[0016] In this embodiment, linear frequency modulation is used as the modulation method for the radar signal. Specifically, the modulation control unit 40 controls the frequency of the reference signal so that the radar signal contains a chirp signal whose frequency changes linearly at a predetermined chirp rate. In this embodiment, the modulation control unit 40 modulates the frequency of the reference signal so that the radar signal and the reference signal contain an up-chirp signal as shown in FIG. 3 . However, the modulation control unit 40 may also modulate the frequency of the reference signal so that the radar signal and the reference signal contain a down-chirp signal. An up-chirp signal is a signal whose frequency increases over time, and a down-chirp signal is a signal whose frequency decreases over time.

[0017] 2, in this embodiment, the local oscillator 30 and the modulation control unit 40 are arranged inside the radar 10, but the local oscillator 30 and the modulation control unit 40 may also be arranged inside the radar 20. The reference signal generated by the local oscillator 30 is input via a wiring 51 to RF circuits 13 and 23, which will be described later.

[0018] 1 and 2, the radar 10 includes a plurality of transmitting antennas 11 and a plurality of receiving antennas 12. The plurality of transmitting antennas 11 and the plurality of receiving antennas 12 are arranged in a row on a substrate (not shown). Note that only a portion of the transmitting antennas 11 and the receiving antennas 12 is shown in FIG.

[0019] The radar 10 detects targets using MIMO, which combines multiple transmitting antennas 11 and multiple receiving antennas 12 to form a virtual antenna. Any modulation method such as TDM, DDM, RDM, FDM, or CDM can be used for multiplexing multiple transmission signals. MIMO stands for Multiple Input Multiple Output. TDM stands for Time Division Multiplexing. DDM stands for Doppler Division Multiplexing. RDM stands for Range Division Multiplexing. FDM stands for Frequency Division Multiplexing. CDM stands for Code Division Multiplexing.

[0020] In this embodiment, a case will be described in which the radar 10 includes two transmitting antennas 11 and four receiving antennas 12. As shown in Fig. 2, the radar 10 includes an RF (Radio Frequency) circuit 13, a BB (Base Band) circuit 14, a processor 15, and a communication IF (Interface) 16.

[0021] The RF circuit 13 processes the reference signal supplied from the local oscillator 30 to generate a radar signal, and processes a signal in the same frequency band as the radar signal to generate an IF (Intermediate Frequency) signal with a lower frequency than the radar signal. The IF signal is a signal in a frequency band between the signal processed by the RF circuit 13 and the signal generated by the BB circuit 14.

[0022] In this embodiment, as an example, the reference signal and radar signal have carrier frequencies in the GHz band, specifically the millimeter wave band, the BB circuit 14 generates a signal in the MHz band, for example, several tens of MHz, and the IF signal is a beat signal generated by multiplying the radar signal. The carrier frequency is preferably 24.05 GHz to 24.25 GHz, or 76 GHz to 81 GHz, or 136 GHz to 148.5 GHz, but may be other frequencies. The RF circuit 13 includes a multiplier 131, a PA (power amplifier) ​​132, and a mixer 133. The RF circuit 13 also includes a phase shifter, an LNA (low noise amplifier), and the like, not shown.

[0023] The multiplier 131 multiplies the frequency of the reference signal supplied from the local oscillator 30 by an integer and outputs the result. The output signal of the multiplier 131 is input to the PA 132 and the mixer 133.

[0024] The PA 132 amplifies the signal input from the multiplier 131 to generate a radar signal. The radar signal generated by the PA 132 is transmitted to the outside of the radar system 1 by the transmitting antenna 11, reflected by a target, and then received by the receiving antenna 12.

[0025] The mixer 133 multiplies the signal input from the multiplier 131 by the radar signal received by the receiving antenna 12 to generate a beat signal, which is an IF signal. The beat signal generated by the mixer 133 is input to the BB circuit 14.

[0026] The BB circuit 14 processes the beat signal input from the RF circuit 13 to generate a signal with a lower frequency than the beat signal. The BB circuit 14 includes an LPF (low pass filter) 141 and an ADC (analog-to-digital converter) 142, and the output signal of the mixer 133 is input to the LPF 141. The beat signal generated by the mixer 133 has high frequency components removed by the LPF 141 and low frequency components extracted, and then the beat signal is converted into a digital signal by the ADC 142 and input to the processor 15.

[0027] The processor 15 estimates the distance, speed, and direction of a target based on the signals generated by the radars 10 and 20. The processor 15 includes a distance / speed estimation unit 151, a peak extraction unit 152, a phase calculation unit 153, a phase error calculation unit 154, a delay time calculation unit 155, a phase error correction unit 156, and a direction estimation unit 157, and the output signal of the BB circuit 14 is input to the distance / speed estimation unit 151. Note that the radar 20 may also include configurations similar to those of the phase error calculation unit 154 to the direction estimation unit 157, and may perform processes of phase error calculation, delay time calculation, phase error correction, and direction estimation, which will be described later.

[0028] The distance and speed estimation unit 151 estimates the distance between the radar 10 and a target, and the speed of the target. The distance and speed estimation results by the distance and speed estimation unit 151 are input to the peak extraction unit 152.

[0029] The peak extraction unit 152 extracts peaks of the signal input from the distance / speed estimation unit 151. The peak extraction result by the peak extraction unit 152 is input to the phase calculation unit 153.

[0030] The phase calculation section 153 calculates the phase of the peak extracted by the peak extraction section 152. The phase calculation result by the phase calculation section 153 is input to the phase error calculation section 154 and the phase error correction section 156.

[0031] Like the radar 10, the radar 20 has two transmitting antennas 21 and four receiving antennas 22. Only a portion of the transmitting antennas 21 and receiving antennas 22 is shown in FIGS. 1 and 2 . The radar 20 also has an RF circuit 23 and a BB circuit 24 that have the same configurations as the RF circuit 13 and the BB circuit 14 of the radar 10. The radar 20 also has a processor 25, which has a distance / speed estimation unit 251, a peak extraction unit 252, and a phase calculation unit 253 that have the same configurations as the distance / speed estimation unit 151, the peak extraction unit 152, and the phase calculation unit 153. The phase calculation result by the phase calculation unit 253 is input to the phase error calculation unit 154 via the communication IF 26, the wiring 52, and the communication IF 16.

[0032] The phase error calculation unit 154 calculates the phase error between the beat signal generated by the BB circuit 14 and the beat signal generated by the BB circuit 24, based on the phase calculation results by the phase calculation units 153 and 253. The phase error calculation result by the phase error calculation unit 154 is input to the delay time calculation unit 155.

[0033] The delay time calculation unit 155 calculates the delay time of the RF circuits 13 and 23 and the delay time of the BB circuits 14 and 24 based on the target measurement result and the phase error calculated by the phase error calculation unit 154. The target measurement result is the result of transmitting and receiving a radar signal to the target, specifically the frequency of the radar signal and the frequency of the beat signal. The delay time calculation unit 155 then calculates the delay time Δt RF The delay time calculation unit 155 calculates the delay time Δt BB The delay time Δt calculated by the delay time calculation unit 155 RF , Δt BB The calculation result is input to the phase error correction unit 156.

[0034] The phase error correction unit 156 calculates the phase error by comparing the phase calculation result by the phase calculation unit 153 with the delay time Δt RF , ΔtBB The phase error correction result by the phase error correction unit 156 is input to the direction estimation unit 157.

[0035] The direction estimation unit 157 estimates the direction of the target based on the beat signal whose phase has been corrected by the phase error correction unit 156. When the radar system 1 is mounted on a vehicle, the direction estimation result by the direction estimation unit 157 is transmitted to, for example, an ECU (Electronic Control Unit) not shown, and is used to perform collision avoidance operations, etc.

[0036] The details of the processing executed by the processor 15 will be described. First, the method of calculating the phase of the beat signal by the distance / speed estimation unit 151 and the peak extraction unit 152 will be described. The beat signals generated by the BB circuits 14 and 24 are respectively S b1 , S b2 Let's say.

[0037] The distance / speed estimation unit 151 receives the beat signal S input from the BB circuit 14. b1 By performing frequency analysis on the signal, a spectrum having frequency components corresponding to the distance and speed of the target is acquired, and the distance and speed are estimated from this spectrum. For example, FFT (Fast Fourier Transform), DFT (Discrete Fourier Transform), etc. can be used as a frequency analysis method. The distance and speed estimation unit 151 transmits the estimated results of the distance and speed and the acquired spectrum to the peak extraction unit 152.

[0038] The peak extraction unit 152 extracts, as peaks, the maximum values ​​of the spectrum corresponding to the distance and speed of the target by performing threshold processing on the signal input from the distance and speed estimation unit 151. For example, CA-CFAR (Cell Averaging Constant False Alarm Rate), OS-CFAR (Order Statistic Constant False Alarm Rate), etc. can be used as the threshold processing.

[0039] The distance and speed estimation unit 151 estimates the distance and speed, and the peak extraction unit 152 extracts the peaks for each of the virtual antennas 171 to 178, which will be described later. b2 The distance and velocity are estimated and peaks are extracted using the beat signal S b1 , S b2 The phases of the peaks extracted from are defined as X1 and X2, respectively.

[0040] Next, a method for calculating the phase error by the phase error calculation unit 154 and a method for calculating the delay time by the delay time calculation unit 155 will be described. b1 , S b2 The phase error, i.e., the difference between the phase X1 and the phase X2, is defined as Y. The phase error Y can be formulated as a linear sum of the phase error caused by the difference in delay time between the RF circuits 13 and 23 and the difference in delay time between the BB circuits 14 and 24. That is, the phase error Y is the difference between the delay time Δt RF , Δt BB Using the above, it is expressed as Equation 1.

[0041]

number

[0042] π is the ratio of the circumference of a circle to its diameter. f0 is the frequency of the signal passing through the RF circuits 13 and 23, i.e., the carrier frequency of the radar signal. f b is the frequency of the signal passing through the BB circuits 14 and 24, i.e., the frequency of the beat signal.

[0043] In Equation 1, the unknown is Δt RF and Δt BB Since there are two independent equations, Δt RF and Δt BB For example, it is possible to estimate the delay time Δt based on the measurement results of a target using radar signals having multiple different carrier frequencies f0. RF , Δt BB can be calculated.

[0044] In this embodiment, as shown in FIG. 4, two different carrier frequencies f 01 , f 02 By measuring the target using the radar signal of the carrier frequency f 01 and the transmission and reception of radar signals at carrier frequency f 02 The radar signal is transmitted and received by the phase calculation units 153 and 253, and the beat signal S b1 , S b2 The chirp rate of the radar signal is assumed to be the same in both measurements. Therefore, the frequency of the beat signal, f b is the same value in two measurements.

[0045] The radar 10 transmits the carrier frequency f 01 , f 02 Beat signal S when transmitting and receiving radar signals b1 The phase of each 11 , X 12 The radar 20 transmits a carrier frequency f 01 , f 02 Beat signal S when transmitting and receiving radar signals b2 The phase of each 21 , X 22 Let's say.

[0046] The phase error calculation unit 154 calculates the phase X 11 and phase X 21 The error between the phase error and the phase error is Y1, and Y1=X 21 -X 11 Furthermore, the phase error calculation unit 154 calculates the phase X 12 and phase X 22 The error between this and the phase error Y2 is expressed as phase error Y2=X 22 -X 12 By performing these two measurements, Equation 2 and Equation 3 are obtained.

[0047]

number

[0048]

number

[0049] Then, by subtracting Equation 3 from Equation 2, Equation 4 is obtained, and the delay time Δt is calculated as shown in Equation 5. RF Also, the delay time Δt BB can be calculated from the equations 2 and 3. In this way, the delay time calculation unit 155 calculates the phase errors Y1 and Y2 and the carrier frequency f 01 , f 02 and based on the delay time Δt RF , Δt BB Calculate.

[0050]

number

[0051]

number

[0052] When the radar system 1 is mounted on a vehicle, the delay time Δt RF , Δt BB The delay time Δt may be estimated either before the vehicle is shipped or while the vehicle is running. RF , Δt BB When estimating the delay time Δt before shipping a vehicle, two measurements are taken using a corner reflector as a target. RF , Δt BB When estimating the vehicle speed while driving, two measurements are taken using other vehicles, roadside objects, etc. as targets.

[0053] Delay time Δt RF , Δt BB The details of the calculation method of the signal S are as follows. t1 , S r1 The transmitted signal and the received signal of the radar 20 are respectively S t2 , S r2The signal S from the radar 10 t1 From the start of transmission of signal S r1 The time until reception starts is τ 11 and the signal S t2 From the start of transmission of signal S r2 The time until reception starts is τ 22 Let's say.

[0054] signal S t1 , S r1 , S t2 , S r2 is as shown in Figure 5. That is, the signal S t1 From the start of transmission to the time τ 11 After the time has elapsed, the signal S r1 is received and the signal S r1 Delay time Δt from reception of RF After the time has elapsed, the signal S t2 is transmitted, and the signal S t2 From the start of transmission to the time τ 22 After the time has elapsed, the signal S r2 is received.

[0055] Also, the beat signal S b1 , S b2 is as shown in Figure 6. That is, the beat signal S b2 is the beat signal S b1 Delay time Δt BB The signal S is delayed by t. t1 , S r1 , S t2 , S r2 Phase φ of io 1 (t), φ rx 1→1 (t), φ io 2 (2), φ rx 2→2 (t) are expressed by Formulas 6 to 9, respectively.

[0056]

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[0057]

number

[0058]

number

[0059]

number

[0060] μ is the chirp rate of the radar signal, and μ=df / dt where f is the frequency of the radar signal. Φ is the phase noise of the radar signal. δ is the initial phase of the radar signal. From Equations 6 to 9, the beat signal S b1 , S b2 The phases X1 and X2 are expressed as in Equations 10 and 11.

[0061]

number

[0062]

number

[0063] Considering the difference in delay time between the BB circuits 14 and 24, t = t + Δt BB Then, the phase X2 is expressed as in Equation 12.

[0064]

number

[0065] τ 11 ≒τ 22 , and Φ(t)-Φ(t-τ 11 )≒Φ(t+Δt BB )-Φ(t+Δt BB -(τ 22 +Δt RF )), the phase error Y is given by Equation 13.

[0066]

number

[0067] φ mix 1→1 (t), φ mix 2→2 (t) is the beat signal S b1 , S b2 is the phase of, and X1=φ mix 1→1 (t), X2=φ mix 2→2 (t). In Equation 13, the carrier frequency f0 is 01 , f 02 By doing so, the following equations 14 and 15 are obtained for the phase errors Y1 and Y2.

[0068]

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[0069]

number

[0070] By subtracting Equation 15 from Equation 14, Equation 4 is obtained, and Δt is calculated as Equation 5. RF And, this Δt RF Using Equation 14 or Equation 15, Δt BB is required.

[0071] The number of virtual antennas formed by the transmitting antennas 11 and the receiving antennas 12 of the radar 10 is defined as K. In this embodiment, the numbers of transmitting antennas 11 and 21 are the same, and the numbers of receiving antennas 12 and 22 are the same, so the number of virtual antennas formed by the transmitting antennas 21 and the receiving antennas 22 of the radar 20 is also K. In this embodiment, K=8. Let i be an integer between 1 and K. Of the virtual antennas formed by the radar 10, the i-th virtual antenna is defined as virtual antenna 17i. Of the virtual antennas formed by the radar 20, the i-th virtual antenna is defined as virtual antenna 27i.

[0072] The phase error correction unit 156 corrects the delay time Δt RF , Δt BB 7, the phase error of the radars 10 and 20 is corrected based on the phase error Y calculated from the phase error Y. That is, as shown in Fig. 7, the phase X2 of the beat signal generated from the transmission and reception signals of the virtual antennas 271 to 278 is corrected from the value indicated by the dashed line to the value indicated by the solid line, as indicated by the white arrow, so that the phases X1 and X2 become equal. As a result, the phase X2 of the beat signal generated from the transmission and reception signals of the virtual antennas 271 to 278 becomes equal to the phase X1 of the beat signal generated from the transmission and reception signals of the virtual antennas 171 to 178.

[0073] The direction estimation method will be described. The direction estimation unit 157 estimates the direction of the target using beamforming. The transmit signal and receive signal of the virtual antenna 17i are multiplied by the mixer 133, and the beat signal obtained by processing by the LPF 141 is then input to the S b1、i The beat signal obtained by processing the transmission signal and the reception signal of the virtual antenna 27i in the RF circuit 23 and the BB circuit 24 in the same manner as the mixer 133 and the LPF 141 is expressed as S b2、i The beat signal S b1、1 is the difference frequency between the transmission signal and the reception signal of the virtual antenna 171, and is expressed by Equation 16, where j is the imaginary unit.

[0074]

number

[0075] The phase calculation unit 153 performs FFT processing on the input beat signal. Since the beat signal is a sine wave of the difference frequency, when FFT processing is performed, a peak appears at the difference frequency. b1、1 The signal generated by FFT processing is expressed by Equation 17.

[0076]

number

[0077] The phase of the maximum peak of this signal is x 11 Then, the phase x 11 is expressed by Equation 18.

[0078]

number

[0079] Beat signal S b1、2 ~S b1、K Similarly, FFT processing and peak phase x 12 ~x 1K is extracted to obtain a vector of phase X1 as shown in Equation 19.

[0080]

number

[0081] In Equation 19, and Equations 20 and 22 described later, "T" represents a transpose. Similarly, in the radar 20, a vector with phase X2 is obtained.

[0082]

number

[0083] When an incoming wave from a target is received by the virtual antennas 171 to 17K, the delay time of the beat signal is proportional to the antenna position, and the phase is proportional to the delay time. In other words, the phase is proportional to the antenna position. Specifically, as shown in FIG. 8, the azimuth of the target is θ, and the distance between the virtual antenna 171 and the virtual antenna 17i is d. i It should be noted that d1=0. When a reflected signal from a target reaches the virtual antenna 171, the distance between the wavefront of the arriving wave and the virtual antenna 17i is d i Since it is sinθ, the delay time of the signal received by virtual antenna 17i relative to the signal received by virtual antenna 171 is (2π / λ)d i sinθ. And the phase x 1i is the delay time (2π / λ)d i Since it is proportional to sinθ, as shown in Figure 9, the phase x 1i is the distance d i From these facts, the steering vector of the direction θ, that is, the reference signal a(θ) for correlating with the phase of the beat signal, is expressed as in Equation 21.

[0084]

number

[0085] The phases X1 and X2 of the radars 10 and 20 are concatenated to obtain the phase X of the entire radar system 1.

[0086]

number

[0087] By correlating the phase X with the steering vector a(θ), the azimuth spectrum P BF (θ) is obtained.

[0088]

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[0089] In Equation 23, "H" is the Hermitian transpose. At the azimuth θ where the correlation with the phase X is high, the azimuth spectrum P BF The direction estimating unit 157 estimates this direction θ as the direction of the target.

[0090] The target azimuth estimation process flow will be described. In the azimuth estimation process, the radar system 1 sequentially executes steps S101 to S109 shown in Fig. 10. The order in which steps S101 to S106 are executed is not particularly limited as long as there is no technical contradiction. For example, step S101 may be executed simultaneously with step S102 or after step S102. Furthermore, step S104 may be executed simultaneously with step S105 or after step S105. Furthermore, steps S101 to S103 may be executed simultaneously with steps S104 to S106 or after steps S104 to S106.

[0091] In step S101, the radar system 1 detects a phase X 11 Specifically, the radar system 1 sequentially executes steps S201 to S203 shown in FIG.

[0092] In step S201, the radar 10 processes the reference signal generated by the local oscillator 30 with the multiplier 131 and the PA 132 to generate a carrier frequency f 01 The radar signal is generated and transmitted from the transmitting antenna 11.

[0093] In step S202, the radar 10 receives the radar signal reflected by the target with the receiving antenna 12, and processes the received radar signal with an LNA or the like (not shown).

[0094] In step S203, the radar 10 multiplies the transmission signal by the reception signal by the mixer 133, and processes the signal thus generated by the LPF 141 to generate a beat signal S b1 Then, the radar 10 generates a beat signal S b1is converted into a digital signal by the ADC 142, and processed by the distance / speed estimation unit 151 and the peak extraction unit 152, and then the phase X 11 Calculate.

[0095] In step S102, the radar system 1 detects the phase X 21 Specifically, the radar system 1 acquires the carrier frequency f 01 In other words, the radar 20 performs the same process as in step S101 by setting the carrier frequency f 01 The radar signal is transmitted and received, and a beat signal S is generated from the transmitted signal and the received signal. b2 Generates phase X 21 Calculate.

[0096] In step S103, the radar system 1 acquires the phase error Y1. Specifically, the phase error calculation unit 154 calculates the phase X calculated in step S101. 11 , and the phase X calculated in step S102 21 Therefore, Y1=X 21 -X 11 Calculate.

[0097] In step S104, the radar system 1 detects the phase X 12 Specifically, the radar system 1 acquires the carrier frequency f 02 In other words, the radar 10 performs the same process as in step S101 by setting the carrier frequency f 02 The radar signal is transmitted and received, and a beat signal S is generated from the transmitted and received signals. b1 Generates phase X 12 Calculate.

[0098] In step S105, the radar system 1 detects the phase X 22 Specifically, the radar system 1 acquires the carrier frequency f 02 In other words, the radar 20 performs the same process as in step S101 by setting the carrier frequency f 02 The radar signal is transmitted and received, and a beat signal S is generated from the transmitted and received signals.b2 Generates phase X 22 Calculate.

[0099] In step S106, the radar system 1 acquires the phase error Y2. Specifically, the phase error calculation unit 154 calculates the phase X2 calculated in step S104. 12 , and the phase X calculated in step S105 22 Therefore, Y2=X 22 -X 12 Calculate.

[0100] In step S107, the radar system 1 calculates the delay time Δt RF , Δt BB Specifically, the delay time calculation unit 155 calculates the delay time Δt RF , Δt BB Calculate.

[0101] In step S108, the radar system 1 corrects the phase error between the radar 10 and the radar 20. Specifically, the phase error corrector 156 corrects the delay time Δt RF , Δt BB Based on this phase error Y, the beat signal S is calculated by the above-mentioned method. b1 , S b2 Correct the phase of

[0102] In step S109, the radar system 1 acquires the azimuth of the target. Specifically, the azimuth estimation unit 157 calculates the phase of the beat signal S b1 , S b2 Based on this, the target's azimuth is estimated by the method described above.

[0103] The effect of this embodiment will be described below. In the radar system 1, a difference in the length of the wiring 51 between the part connecting the local oscillator 30 and the radar 10 and the part connecting the local oscillator 30 and the radar 20 causes a difference in delay time, and the beat signal S b1 , Sb2 Furthermore, a phase error occurs between the beat signal S due to the difference in delay time between the RF circuit 13 and the RF circuit 23 and the difference in delay time between the BB circuit 14 and the BB circuit 24. b1 , S b2 A phase error occurs between the two. The phase error increases in proportion to the total delay time.

[0104] If the phase error is not corrected, the true azimuth of the target and the azimuth spectrum P BF The difference between the direction θ at which (θ) reaches its peak becomes large, and the direction estimation error becomes large.

[0105] In contrast, by correcting the phase error as in this embodiment, the true azimuth of the target and the azimuth spectrum P BF The difference between the direction θ at which (θ) reaches its peak can be reduced, thereby reducing the direction estimation error.

[0106] Also, as shown in Fig. 14, for example, a method can be considered in which some of the virtual antennas 171 to 178 are configured at positions overlapping with some of the virtual antennas 271 to 278, and the phase error is estimated so that the phases of the overlapping virtual antennas become equal. Fig. 14 illustrates the portion surrounded by the dashed line, i.e., the case where the positions of the virtual antennas 178 and 271 overlap. In this case, the beat signal S generated from the transmission and reception signals of the virtual antennas 178 and 271 is b18 , S b21 The beat signal S b21 ~S b28 From the phase of the beat signal S b18 , S b21 However, this method places restrictions on the placement of the virtual antennas 171 to 178 and 271 to 278, reducing the degree of freedom in design. Also, the aperture lengths of the virtual antennas 171 to 178 and 271 to 278 become smaller.

[0107] In contrast to this, in this embodiment, there is no need to overlap the positions of the virtual antennas 171-178 and 271-278, which improves the degree of freedom in design and allows the aperture lengths of the virtual antennas 171-178 and 271-278 to be increased.

[0108] Another possible method is to transmit reference signals from the radars 10 and 20 to the processor 15 as return signals, and estimate the phase error based on the difference between the reference and return signals in the processor 15. Specifically, as shown in Fig. 15, wirings 61 and 62 of equal length are formed so that the reference signals are transmitted from the radars 10 and 20 to the processor 15 as return signals. Also, a reference signal is transmitted from the local oscillator 30 to the processor 15 in addition to the RF circuits 13 and 23. The processor 15 then mixes the reference signal and the return signal, and estimates the phase error based on the difference signal obtained thereby.

[0109] However, although this method can estimate the phase error due to the difference in wiring length, it cannot estimate the phase error due to the difference in delay time of the RF circuits 13, 23 and the BB circuits 14, 24, because the reference signal before passing through the RF circuits 13, 23 is used as the return signal. In addition, since wiring 61, 62 is required to transmit the return signal and the reference signal to the processor 15, the manufacturing cost of the radar system 1 increases.

[0110] In contrast to this, in this embodiment, it is possible to estimate the phase error due to the difference in delay time between the RF circuits 13 and 23 and the BB circuits 14 and 24, thereby improving the accuracy of azimuth estimation compared to the comparative example shown in Fig. 15. Furthermore, since the wiring 61 and 62 are not required, it is possible to suppress an increase in the manufacturing cost of the radar system 1.

[0111] As described above, in this embodiment, the delay time Δt RF and the delay time Δt which is the difference between the delay times of the BB circuits 14 and 24 BB Then, the calculated delay time Δt RF , ΔtBB The beat signal S is an IF signal based on b1 , S b2 Therefore, it is not necessary to overlap the positions of the virtual antennas 171 to 178 and 271 to 278, and the aperture length can be increased.

[0112] (Second embodiment) The second embodiment will be described. In this embodiment, the delay time Δt RF , Δt BB The method of calculating the value of is changed, and the rest is the same as in the first embodiment, so only the parts that are different from the first embodiment will be explained.

[0113] In this embodiment, two different beat frequencies f b By measuring the target using the radar signal of the beat frequency f, two equations for the phase error Y are obtained. Specifically, as shown in Figure 16, the first measurement transmits a radar signal with a chirp rate μ1, and the second measurement transmits a radar signal with a chirp rate μ2. b Since is proportional to the chirp rate μ, two different beat frequencies can be obtained by changing the chirp rate μ in this way. The beat frequencies corresponding to the radar signals with chirp rates μ1 and μ2 are respectively b1 , f b2 Note that the frequencies at the start and end of the radar signal sweep are the same in both measurements. Therefore, the carrier frequency f0 is the same in both measurements.

[0114] In this embodiment, the phases of the beat signals when the radar 10 transmits and receives radar signals with chirp rates μ1 and μ2 are respectively expressed as X 11 , X 12 In addition, the phases of the beat signals when the radar 20 transmits and receives radar signals with chirp rates μ1 and μ2 are respectively expressed as X 21 , X 22 Let's say.

[0115] The phase error calculation unit 154 calculates the phase X 11 and phase X 21The error between the phase error and the phase error is Y1, and Y1=X 21 -X 11 Furthermore, the phase error calculation unit 154 calculates the phase X 12 and phase X 22 The error between this and the phase error Y2 is expressed as phase error Y2=X 22 -X 12 By performing two measurements in this way, Equation 24 and Equation 25 are obtained.

[0116]

number

[0117]

number

[0118] Then, by subtracting Equation 25 from Equation 24, Equation 26 is obtained, and the delay time Δt BB Also, the delay time Δt RF The delay time calculation unit 155 calculates the delay time Δt based on the phase errors Y1 and Y2 and the chirp rates μ1 and μ2. RF , Δt BB Calculate.

[0119]

number

[0120]

number

[0121] This embodiment has the same configuration and operation as the first embodiment, and can therefore obtain the same effects as the first embodiment.

[0122] (Third embodiment) The third embodiment will be described. In this embodiment, the beat frequency f b1, f b 2 is obtained in a different way, and the rest of the method is the same as in the second embodiment, so only the differences from the second embodiment will be explained.

[0123] In this embodiment, as shown in Fig. 17, in the first measurement, the radar system 1 transmits a radar signal to a target at a distance R1, and in the second measurement, the radar signal is transmitted to a target at a distance R2. b is proportional to the distance to the target, so by measuring targets at two different distances in this way, two different beat frequencies are obtained.

[0124] In this embodiment, the phases of the beat signals when the radar 10 transmits and receives radar signals to targets at distances R1 and R2 are respectively expressed as X 11 , X 12 In addition, the phases of the beat signals when the radar 20 transmits and receives radar signals to targets at distances R1 and R2 are respectively expressed as X 21 , X 22 The beat frequencies corresponding to distances R1 and R2 are f b1 , f b2 Let's say.

[0125] This embodiment has the same configuration and operation as the first and second embodiments, and can therefore obtain the same effects as the first and second embodiments.

[0126] (Fourth embodiment) The fourth embodiment will be described. This embodiment is different from the first embodiment in that the local oscillator 30, the modulation control unit 40, and the locations of some of the processors are changed, but the rest is the same as the first embodiment, so only the parts that are different from the first embodiment will be described.

[0127] In this embodiment, the local oscillator 30 and the modulation control unit 40 are arranged in a radar bridge 70 connected to the radars 10 and 20. The radar bridge 70 also includes a processor 71 and a communication IF 72. The processor 71 includes a phase error calculation unit 711, a delay time calculation unit 712, a phase error correction unit 713, and an azimuth estimation unit 714. The processor 15 does not include the phase error calculation unit 154 to the azimuth estimation unit 157, and the phase error calculation unit 711 to the azimuth estimation unit 714 have the same configuration as the phase error calculation unit 154 to the azimuth estimation unit 157 in the first embodiment.

[0128] The phase calculation result by the phase calculation unit 153 is transmitted to the phase error calculation unit 711 and the phase error correction unit 713 via the communication IF 16, the wiring 53, and the communication IF 72. The phase calculation result by the phase calculation unit 253 is transmitted to the phase error calculation unit 711 and the phase error correction unit 713 via the communication IF 26, the wiring 54, and the communication IF 72.

[0129] Based on the transmitted phase calculation results, the radar bridge 70 performs processes such as phase error calculation, delay time calculation, phase error correction, and azimuth estimation, similar to the radar 10 of the first embodiment.

[0130] This embodiment has the same configuration and operation as the first embodiment, and can therefore obtain the same effects as the first embodiment.

[0131] Furthermore, according to the above embodiment, the following effects can be obtained.

[0132] (1) The local oscillator 30, and the phase error calculation unit 711 to the direction estimation unit 714 are arranged in the radar bridge 70. This allows the configuration of the processor, which has high manufacturing costs, to be concentrated in the radar bridge 70, and also allows the radars 10 and 20 to have similar configurations, thereby reducing the manufacturing cost of the radar system 1.

[0133] (Other embodiments) The present disclosure is not limited to the above-described embodiments and can be modified as appropriate. Furthermore, the above-described embodiments are not unrelated to each other and can be combined as appropriate unless the combination is clearly impossible. It goes without saying that, in each of the above-described embodiments, the elements constituting the embodiments are not necessarily essential unless they are specifically stated as essential or are considered to be clearly essential in principle. Furthermore, in each of the above-described embodiments, when numerical values ​​such as the number, numerical value, amount, and range of the components of the embodiments are mentioned, they are not limited to the specific number unless they are specifically stated as essential or are clearly limited to a specific number in principle.

[0134] For example, in the second and third embodiments, the radar system 1 may include a radar bridge 70 as in the fourth embodiment, and the local oscillator 30 and the phase error calculation unit 711 to the direction estimation unit 714 may be arranged in the radar bridge 70.

[0135] Furthermore, although linear frequency modulation is used as the modulation method for the radar signal in the first to fourth embodiments, other modulation methods may be used, such as OFDM (Orthogonal Frequency Division Multiplexing) and PMCW (Phase Modulated Continuous Wave). [Explanation of symbols]

[0136] 10. Radar 13 RF circuit 14 BB Circuit 15 processors 20 Radar 23 RF circuit 24 BB Circuit 30 Local Oscillator 71 processors

Claims

1. 1. A radar system comprising: a plurality of radars (10, 20) arranged in a spatially separated state, each having a transmitting antenna (11, 21) for transmitting a radar signal and a receiving antenna (12, 22) for receiving the radar signal reflected by a target; a local oscillator (30) for supplying a reference signal to the plurality of radars for generating the radar signals; a processor (15, 71) for estimating the azimuth of a target based on signals generated by the plurality of radars; Each of the plurality of radars includes: an RF circuit (13, 23) that processes a signal in the same frequency band as the radar signal to generate an IF signal having a frequency lower than that of the radar signal; a BB circuit (14, 24) for processing the IF signal; The processor: The delay time Δt of the RF circuit between the plurality of radars ＲＦ , and the delay time Δt of the BB circuit ＢＢ a delay time calculation unit (155, 712) that calculates the delay time based on the measurement results of the target; The calculated delay time Δt ＲＦ , Δt ＢＢ a phase error correction unit (156, 713) that corrects the phase of the IF signal based on and an azimuth estimation unit (157, 714) that estimates the azimuth of a target based on the corrected IF signal.

2. The delay time calculation unit calculates the delay time Δt based on the measurement result of the target using the radar signal having a plurality of different carrier frequencies. ＲＦ , Δt ＢＢ 2. The radar system of claim 1, wherein:

3. Two radars included in the plurality of radars are designated as a first radar (10) and a second radar (20), The two different carrier frequencies are respectively f ０１ , f ０２ year, The first radar transmits the carrier frequency f ０１ The phase of the IF signal when transmitting and receiving the radar signal is X １１ year, The first radar transmits the carrier frequency f ０２ The phase of the IF signal when transmitting and receiving the radar signal is X １２ year, The second radar transmits the carrier frequency f ０１ The phase of the IF signal when transmitting and receiving the radar signal is X ２１ year, The second radar transmits the carrier frequency f ０２ The phase of the IF signal when transmitting and receiving the radar signal is X ２２ year, The phase X １１ and the phase X ２１ The error between １ year, The phase X １２ and the phase X ２２ The error between ２ As, The delay time calculation unit calculates the phase error Y １ , Y ２ and the carrier frequency f ０１ , f ０２ Based on this, the delay time Δt ＲＦ , Δt ＢＢ 3. The radar system of claim 2, wherein:

4. the radar signal includes a chirp signal whose frequency changes at a predetermined chirp rate; The delay time calculation unit The delay time Δt is calculated based on the measurement results of the target using the radar signals having different chirp rates. ＲＦ , Δt ＢＢ 2. The radar system of claim 1, wherein:

5. Two radars included in the plurality of radars are designated as a first radar (10) and a second radar (20), The two different chirp rates are respectively μ １ , μ ２ year, The first radar detects the chirp rate μ １ The phase of the IF signal when transmitting and receiving the radar signal is X １１ year, The first radar detects the chirp rate μ ２ The phase of the IF signal when transmitting and receiving the radar signal is X １２ year, The second radar detects the chirp rate μ １ The phase of the IF signal when transmitting and receiving the radar signal is X ２１ year, The second radar detects the chirp rate μ ２ The phase of the IF signal when transmitting and receiving the radar signal is X ２２ year, The phase X １１ and the phase X ２１ The error between １ year, The phase X １２ and the phase X ２２ The error between ２ year, The chirp rate μ １ , μ ２ The frequencies of the IF signals corresponding to ｂ 1. f ｂ 2. As The delay time calculation unit calculates the phase error Y １ , Y ２ and the frequency f ｂ 1. f ｂ 2 and the delay time Δt ＲＦ , Δt ＢＢ 5. The radar system of claim 4, wherein the radar system calculates:

6. The delay time calculation unit The delay time Δt is calculated based on the measurement results of targets at a plurality of different distances. ＲＦ , Δt ＢＢ 2. The radar system of claim 1, wherein:

7. Two radars included in the plurality of radars are designated as a first radar (10) and a second radar (20), The two different distances are respectively R １ , R ２ year, The first radar detects the distance R １ The phase of the IF signal when the radar signal is transmitted and received to the target is X １１ year, The first radar detects the distance R ２ The phase of the IF signal when the radar signal is transmitted and received to the target is X １２ year, The second radar detects the distance R １ The phase of the IF signal when the radar signal is transmitted and received to the target is X ２１ year, The second radar detects the distance R ２ The phase of the IF signal when the radar signal is transmitted and received to the target is X ２２ year, The phase X １１ and the phase X ２１ The error between １ year, The phase X １２ and the phase X ２２ The error between ２ year, The distance R １ , R ２ The frequencies of the IF signals corresponding to ｂ 1. f ｂ 2. As The delay time calculation unit calculates the phase error Y １ , Y ２ and the frequency f ｂ 1. f ｂ 2 and the delay time Δt ＲＦ , Δt ＢＢ 7. The radar system of claim 6, wherein:

8. 8. The radar system according to claim 1, wherein the local oscillator is disposed in one of the plurality of radars.

9. 8. A radar system according to claim 1, wherein the local oscillator is located in a radar bridge (70) connected to the plurality of radars.

10. 8. The radar system according to claim 1, wherein the processor is disposed in one of the plurality of radars.

11. 8. The radar system of claim 1, wherein the processor is located in a radar bridge (70) connected to the plurality of radars.

12. 8. The radar system according to claim 1, wherein the modulation method of the radar signal is linear frequency modulation, OFDM, or PMCW.

13. 8. The radar system according to claim 1, which is mounted on a vehicle.

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