JP2011180030A - Radar system and azimuth calculation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology concerning a radar system capable of accurately calculating the azimuth of each target, even when the frequency spectra corresponding to different targets overlap. <P>SOLUTION: The radar system receives reflection signals, received via at least two receiving antennas as a receiving signal of each receiving antenna, calculates a phase difference between peak frequencies of the beat signals generated from a transmitting signal and the receiving signal; stores the calculated phase difference to a storing region; and calculates the azimuth of a target, on the basis of the calculated phase difference. In addition, the radar system predicts whether the peak frequencies of a plurality of the targets overlap; on the basis of prediction information predicting change of the peak frequency of the beat signal; including the azimuth information concerning the calculated azimuth, calculates the phase difference as prediction phase difference, when the peak frequencies overlap on the basis of the phase difference stored to the storing region, and calculates the azimuth of the target, on the basis of the prediction phase difference, when it is predicted that the peak frequencies overlap. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radar apparatus and a direction calculation method for detecting a target.

  A monopulse radar device is known as a radar device that detects a target (see, for example, Patent Document 1). In Patent Document 1, a radar wave composed of a frequency raising unit, a frequency lowering unit, and a constant frequency unit is transmitted, and the reflected wave of the radar wave is received by two antennas. A beat signal indicating a frequency difference between the transmission signal and the reception signal is generated for each frequency lowering unit and constant frequency unit. And if both peak frequencies cannot be matched based on the phase difference of the beat signal at the peak frequency of the frequency rising part beat signal and the peak frequency of the frequency falling part beat signal, it is considered that the peak frequencies by multiple objects overlap. Thus, the phase of the object is calculated from the phase difference at the peak frequency of the beat signal of the constant frequency portion.

JP 2004-340755 A

  A phase monopulse method is known as one of methods for measuring the orientation of a target with respect to a radar apparatus. FIG. 1 shows a principle diagram of a phase monopulse system. In the phase monopulse system, for example, two antennas A1 and A2 are arranged, and the direction of incoming radio waves is obtained based on the phase difference (Δφ) of signals received by the antennas A1 and A2. The phase difference is expressed by Formula 1 from the arrival angle θ, the antenna interval d, and the wavelength λ of the carrier wave (reflected wave).

[Equation 1]
Δφ = 2π · (d · sinθ / λ)

  In calculating the phase difference, a transmission wave modulated with a triangular wave is first output from the antenna, and the frequency of the beat signal is acquired by mixing a part of the transmission wave reflected from the target and received by the antenna. . Then, a Fourier transform process is performed on the beat signal to obtain frequency spectrum data, and the peak frequency of the frequency spectrum is detected from the frequency spectrum data. The frequency spectrum data is represented as a complex vector in the complex plane. The peak frequency of the detected frequency spectrum is a frequency according to the distance to the target and the relative speed. When the peak frequency of the frequency spectrum is specified, the phase of the beat signal at the peak frequency is calculated. Here, since the frequency spectrum data is represented as a complex vector in the complex plane, the phase of the beat signal can be calculated from, for example, an angle between the complex vector and the real axis in the complex plane. Then, the phase difference is calculated by obtaining the phase difference of the beat signal, and the azimuth of the target can be calculated from the calculated phase difference.

Here, in the above-described phase monopulse method, when there are a plurality of targets, the direction of each target may not be accurately calculated if the peak frequencies of the frequency spectrum corresponding to each target overlap. FIG. 2 shows an example of the positional relationship between the target and the radar apparatus. More specifically, FIG. 2 shows that an oncoming vehicle (moving target) is in progress from the front of a vehicle (own vehicle) on which a radar device is mounted, and a guardrail having a plurality of columns (on the side of the oncoming vehicle) This shows the state where a stationary target is installed.

  Here, FIG. 3A is an example of frequency spectrum data acquired by the conventional radar apparatus in the situation shown in FIG. 2, and FIG. 3B shows a diagram representing the frequency spectrum data in FIG. 3A as a complex vector. In FIG. 3A, the horizontal axis is frequency and the vertical axis is reflection level. The solid line in FIG. 3A represents the reflection level from the stationary target, ie the guardrail, and the four peaks in FIG. 3A correspond to the reflected waves from the guardrail struts. The dotted line in FIG. 3A represents the reflection level from the moving target, that is, the oncoming vehicle. In the example of FIG. 3A, the peak frequency of the moving target and the peak frequency of the stationary target overlap, and the peak values match. . When the peak frequencies of the frequency spectrum overlap in this way, the radar device cannot synthesize and separate the phases. In other words, although the frequency spectrum data inherently includes a complex vector corresponding to the guardrail support and a complex vector corresponding to the oncoming vehicle, only the combined vector of the two complex vectors can actually be acquired. become unable. Note that FIG. 3B shows a complex plane, where the X axis is a real axis and the Y axis is an imaginary axis. In FIG. 3B, the actually acquired composite vector and the stationary target that cannot be actually acquired A complex vector corresponding to a reflected wave from a moving object and a complex vector corresponding to a reflected wave from a moving target are shown.

  Thus, if the peak frequencies of the frequency spectrum corresponding to each target overlap, the orientation of each target cannot be calculated accurately. Moreover, in that case, there is a possibility of causing a malfunction of a PC-Sc (Pre-crash Safety System) and non-detection of a target.

  It is an object of the present invention to provide a technique related to a radar apparatus that can accurately calculate the direction of each target even when frequency spectra corresponding to different targets overlap.

  In the present invention, in order to solve the above-described problem, the phase difference of the target is stored in the storage area, and when it is assumed that the peak frequencies of the frequency spectrum corresponding to the reflected waves from different targets overlap. From the phase difference history stored in the storage area, the target phase difference when the peak frequencies of the frequency spectrum overlap is calculated as the predicted phase difference, and the target orientation is calculated using the calculated predicted phase difference.

  More specifically, the present invention relates to a transmission unit that transmits a frequency-modulated transmission signal as a transmission wave transmitted via a transmission antenna, and a reflected wave in which the transmission wave is reflected by a target, at least A receiving unit that receives a reflected wave received via two receiving antennas as a received signal of each receiving antenna, and a phase difference between peak frequencies of beat signals generated from the transmitted signal and the received signals of each receiving antenna A phase difference calculation unit that calculates the phase difference, a storage unit that stores the phase difference calculated by the phase difference calculation unit in a storage area, and calculates an orientation of the target based on the phase difference calculated by the phase difference calculation unit Based on prediction information for predicting a change in the peak frequency of the beat signal, which is prediction information including azimuth information relating to the azimuth calculated by the azimuth calculation unit A prediction unit that predicts whether or not the peak frequencies of a plurality of targets overlap, and a prediction phase difference that calculates a phase difference when the peak frequencies overlap as a prediction phase difference based on the phase difference stored in the storage area A calculation unit, and the direction calculation unit calculates the direction of the target based on the prediction phase difference calculated by the prediction phase difference calculation unit when the prediction unit predicts that the peak frequencies overlap. , A radar device.

One feature of the radar apparatus according to the present invention is that the phase difference itself calculated by the azimuth calculating unit is stored in a storage area. By storing not the azimuth and the relative velocity calculated based on the phase difference but the phase difference itself, it is possible to calculate a predicted value of the phase difference (predicted phase difference) based on the stored phase difference. Thereby, when it is predicted by the prediction unit that the peak frequencies of a plurality of targets overlap, the orientation of the target based on the calculated predicted phase difference can be calculated. Thereby, even if it is a case where the peak frequency of a some target overlaps, the azimuth | direction of each target can be calculated correctly. As a result, it is possible to avoid malfunction of PCS (Pre-crash Safety System) and non-detection of the target. Prediction of whether or not peak frequencies overlap is performed based on prediction information. The prediction information includes at least azimuth information related to the azimuth calculated by the azimuth calculation unit. The prediction information includes, for example, relative speed information related to the relative speed between the radar apparatus and the target and information related to the interval between the receiving antennas, in addition to the direction information. By storing the prediction information, it is possible to predict whether or not the peak frequencies of a plurality of targets overlap.

  The radar apparatus according to the present invention can calculate the orientation of a moving object (moving target) such as another traveling vehicle, or a stationary object (stationary target) such as a sign or a guardrail by being mounted on the vehicle, for example. The target in the present invention includes the moving target and the stationary target. The phase difference stored in the storage area includes the phase difference regarding the moving target and the stationary target.

  Here, in the radar apparatus according to the present invention, the target includes a moving target that moves relative to the radar apparatus and a stationary target that is stationary, and the storage unit is calculated by the azimuth calculating unit. Of the phase difference of the reflected wave from the moving target is stored in the storage area, and the prediction phase difference calculation unit, when the prediction unit predicts that the peak frequency overlaps, the storage area The phase difference when the peak frequencies overlap is calculated as the predicted phase difference based on the phase difference of the reflected wave from the moving target that is stored in the azimuth calculation unit. When it is predicted that they overlap, the direction of the target is calculated based on the predicted phase difference of the reflected wave from the moving target calculated by the predicted phase difference calculation unit. It may be.

  The predicted phase difference is used when it is predicted that the peak frequencies overlap. In the aspect where the peak frequencies overlap, the peak value of the reflection level of the peak frequency between different targets (hereinafter simply referred to as the peak value) is used. In the case of complete coincidence, the peak value of one peak frequency is higher than the peak value of the other peak frequency, or the peak value of one peak frequency is lower than the peak value of the other peak frequency. For example, when the peak value of the peak frequency related to the moving target is larger than the peak value of the peak frequency related to the stationary target, the peak frequency related to the moving target can be extracted. However, although the peak frequency relating to the moving target can be extracted, the phase difference calculated from the extracted peak frequency includes the phase difference of the moving target and the phase difference of the stationary target. That is, the extracted peak frequency is merely a combination of the phase difference of the moving target and the phase difference of the stationary target. Therefore, the radar apparatus according to the present invention is preferably used not only when the peak frequencies completely match, but also when the peak value of one peak frequency exceeds or falls below the peak value of the other peak frequency. it can. As a result, the orientation of the target can be calculated more accurately.

Here, in the radar apparatus according to the present invention, when the prediction unit predicts that the peak frequencies overlap, the prediction phase difference calculated by the prediction phase difference calculation unit and the phase difference calculated by the direction calculation unit The prediction phase difference calculating unit calculates an average phase difference obtained by averaging the phase differences stored in the storage area, and determining whether the average level difference is within the predetermined range. Correcting the phase difference calculated by the azimuth calculation unit based on the phase difference to calculate the predicted phase difference, and the azimuth calculation unit, when the determination unit determines that the difference is within a predetermined range, When the direction of the target is calculated based on the predicted phase difference calculated by being corrected based on the average phase difference, and the determination unit does not determine that the difference is within a predetermined range, Said prediction not based on average phase difference It may be calculated the azimuth of the target based on the phase difference.

  The average phase difference is a value obtained by averaging the phase differences stored in the storage area, in other words, a moving average of the phase differences. Smoothing out the phase difference as time-series data and correcting the phase difference calculated by the bearing calculation unit based on this smoothed average phase difference to calculate the predicted phase difference, thereby suppressing phase difference variation As a result, the orientation of the target can be calculated more accurately. The moving average includes a simple moving average that simply averages n phase differences stored in the storage area, for example, a weighted moving average that weights and averages the latest phase differences.

  Further, the present invention may be a method for realizing the processing executed by the above-described radar apparatus. Specifically, the present invention includes a transmission step of transmitting a frequency-modulated transmission signal as a transmission wave transmitted via a transmission antenna, and a reflected wave in which the transmission wave is reflected by a target, at least A reception step of receiving reflected waves received via two reception antennas as reception signals of the respective reception antennas, and a phase difference between peak frequencies of beat signals generated from the transmission signals and reception signals of the respective reception antennas Calculated in the azimuth calculation step, the azimuth calculation step for calculating the azimuth of the target based on the phase difference, the storage step for storing the phase difference calculated in the azimuth calculation step in a storage area, and the azimuth calculation step. Prediction information including azimuth information related to the azimuth, and based on prediction information for predicting a change in the peak frequency of the beat signal, A prediction step for predicting whether or not the peak frequencies of the get overlap, and a prediction phase difference calculation step for calculating a phase difference when the peak frequencies overlap based on the phase difference stored in the storage area as a prediction phase difference Is executed by the computer of the radar apparatus, and in the azimuth calculation step, when it is predicted that the peak frequencies overlap in the prediction step, the target is calculated based on the prediction phase difference calculated in the prediction phase difference calculation step. Is calculated.

  In the present invention, for example, even in an existing radar device, the target orientation can be calculated by causing the computer of the radar device to execute a predetermined step related to the above-described orientation calculation method. In other words, the bearing calculation accuracy can be improved without changing the hardware of the radar apparatus.

  Note that the present invention may be a program for realizing the processing executed by the radar apparatus described above. Furthermore, the present invention may be a computer-readable recording medium that records such a program. In this case, the function can be provided by causing the computer or the like to read and execute the program of the recording medium. Note that a computer-readable recording medium is a recording medium that accumulates information such as data and programs by electrical, magnetic, optical, mechanical, or chemical action and can be read from a computer or the like. Say.

  ADVANTAGE OF THE INVENTION According to this invention, even when the frequency spectrum corresponding to a different target overlaps, the technique regarding the radar apparatus which can calculate the azimuth | direction of each target correctly can be provided.

The principle diagram of a phase monopulse system is shown. An example of the positional relationship between a target and a radar apparatus is shown. An example of the frequency spectrum data acquired by the conventional radar apparatus in the situation shown in FIG. The figure which represented the frequency spectrum data in FIG. 3A as a complex vector is shown. 1 shows a schematic configuration of a radar apparatus according to a first embodiment. 2 shows an example of a storage area in a memory. An example of the frequency spectrum data acquired by the radar apparatus according to the first embodiment in the situation shown in FIG. The figure which represented the frequency spectrum data in FIG. 6A as a complex vector is shown. 6 shows a processing flow of azimuth detection executed by the radar apparatus according to the first embodiment. The principle figure of FM-CW system is shown. 6 shows a processing flow of azimuth detection executed by a radar apparatus according to a second embodiment.

Next, an embodiment of a radar apparatus of the present invention will be described based on the drawings. The radar apparatus 2 according to the present embodiment is mounted on the vehicle 1 and can be used to detect targets existing around the vehicle, such as other vehicles, signs, guardrails, and the like. The target detection result is output to a storage device of the vehicle 1, an ECU (Electrical Control Unit), etc.
It can be used for vehicle control such as CS (Pre-crash Safety System). However, the radar device 2 according to the present embodiment may be used for purposes other than the on-vehicle radar device.

<First embodiment>
In the radar apparatus 2 according to the first embodiment, a phase monopulse method is used as an angle measurement method for detecting the azimuth of the target, and FM-CW (Frequency Modulated Continuous Wave) is used as a distance measurement method for detecting the relative speed and distance from the target. Use the method. In the phase monopulse method, for example, two antennas A1 and A2 are arranged, and the direction of incoming radio waves is obtained based on the phase difference (Δφ) of signals received by the antennas A1 and A2 (see FIG. 1). The FM-CW system transmits a transmission wave modulated with a triangular wave, and the frequency of the reflected wave reflected by the target includes a time delay due to distance and a Doppler shift component due to a speed difference, and therefore the difference between the reflected wave and the transmission wave is obtained. To calculate distance and speed.

[Constitution]
FIG. 4 shows a schematic configuration of the radar apparatus 2 according to the first embodiment. The radar device 2 according to the first embodiment is mounted on the front portion of the vehicle 1 and includes an antenna 3 and a control unit 4. Although not shown in the drawing, the radar apparatus 2 according to the first embodiment includes a transmission circuit, a reception circuit, an AD converter, a DA converter, a Fourier, which are included in an existing radar apparatus as a hardware configuration controlled by the control unit 4. A conversion circuit and the like are provided. In this embodiment, a case where the radar apparatus 2 is mounted on the front portion of the vehicle 1 will be described as an example. However, the mounting position may be mounted on, for example, a side portion or a rear portion of the vehicle.

  The antenna 3 transmits a transmission wave in the millimeter wave band, and receives a reflected wave in which the transmission wave is reflected by the target. The antenna 3 according to the first embodiment has three ports 1, 2, and 3 arranged at equal intervals d. The functions of the ports 1, 2, and 3 (hereinafter simply referred to as ports when there is no need to distinguish between each port) can be appropriately switched by the control unit 4. In the first embodiment, the antenna 3 has three ports. However, the antenna 3 only needs to have at least two ports that function as reception antennas, and the number of ports is not particularly limited.

The control unit 4 controls each component included in the radar apparatus 2 and can be realized by a computer including a CPU (Central Processing Unit) 40, a memory 41, and the like and a program executed on the computer. The memory 41 includes a volatile RAM (Random Access Memory) and a nonvolatile ROM (Read Only Memory). ROM includes flash memory, E
It includes rewritable semiconductor memories such as PROM (Erasable Programmable Read-Only Memory) and EEPROM (Electrically Erasable Programmable Read-Only Memory). The CPU 40 expands various programs for controlling the radar apparatus 2 stored in the ROM in the work area of the RAM, and executes processing according to the various programs according to various data input to the control unit 4. To do. Each component included in the control unit 4 can be configured as a computer program executed on the CPU 40. Each configuration may be configured as a dedicated processor. Each configuration of the control unit 4 includes a transmission unit 42, a reception unit 43, an orientation calculation unit 44, a storage unit 45, a prediction unit 46, a predicted phase difference calculation unit 47, a determination unit 48, and a distance measurement unit 49.

  The transmitter 42 transmits the frequency-modulated transmission signal as a transmission wave transmitted via the antenna 3. In the radar apparatus 2 according to the first embodiment, the phase monopulse method is used as the angle measurement method, and the FM-CW method is used as the distance measurement method. Therefore, in the first embodiment, the transmission unit 42 transmits a transmission wave modulated with a triangular wave from the antenna 3.

  The receiving unit 43 receives a reflected wave obtained by reflecting the transmission wave at the target as a reception signal of each port of the antenna 3. In addition, although each port of the antenna 3 can switch a transmission function and a reception function suitably, this transmission can be performed by the transmission part 42 or the reception part 43. In addition, a switching unit may be provided separately for switching. Further, an antenna port dedicated for transmission or reception may be provided.

  The azimuth calculation unit 44 calculates the phase difference between the peak frequency of the beat signal generated from the transmission signal and the reception signal corresponding to each port for each of the upstream section (UP) and the downstream section (DOWN), and the calculated phase difference The orientation of the target is calculated based on The azimuth calculating unit 44 acquires the frequency of the beat signal by mixing a part of the received wave and the transmitted wave received by the antenna 3. The beat signal is calculated by obtaining a difference between the transmission signal and the reception signal. When the prediction unit 46 predicts that the peak frequencies overlap, the direction calculation unit 44 calculates the target direction based on the prediction phase difference calculated by the prediction phase difference calculation unit 47.

  The storage unit 45 stores the phase difference calculated by the phase difference calculation unit in a predetermined area in the RAM included in the memory 41. FIG. 5 shows an example of a storage area in the memory. FIG. 5 shows an example in which a plurality of phase differences (Δφ) between the upstream section (UP) and the downstream section (DOWN) are stored for each target.

  The prediction unit 46 predicts whether or not the peak frequencies of a plurality of targets overlap based on prediction information including azimuth information related to the azimuth calculated by the azimuth calculation unit 44, relative speed information, and information related to the receiving antenna. The relative speed information is information related to the relative speed between the radar apparatus 2 and the target, and is calculated by the distance measuring unit 49. The information related to the reception antenna is information related to the interval between the ports of the antenna 3 (in this embodiment, the interval d).

  The predicted phase difference calculation unit 47 calculates the phase difference when the peak frequencies overlap as a predicted phase difference based on the phase difference stored in the storage area in the RAM of the memory 41. Specifically, the phase difference in either the upstream section or the downstream section is appropriately selected, and the predicted phase difference when the peak frequencies overlap is calculated based on the selected phase difference. For example, the predicted phase difference calculation unit 47 calculates an average phase difference obtained by averaging the phase differences stored in the storage area of the memory 41, and corrects the phase difference calculated by the azimuth calculation unit 44 based on the average phase difference. And calculated as a predicted phase difference.

When the prediction unit 46 predicts that the peak frequencies overlap, the determination unit 48 determines that the difference between the prediction phase difference calculated by the prediction phase difference calculation unit 47 and the phase difference calculated by the direction calculation unit 44 is within a predetermined range. It is determined whether or not. The predetermined range can be set based on the distance between the ports of the antenna 3, the accuracy of the calculated azimuth, the detection range of the reflected wave, and the like.

  The distance measuring unit 49 calculates the relative speed and distance to the target by the FM-CW method. A specific calculation method will be described later.

[Processing flow]
Next, processing executed by the radar device 2 according to the first embodiment described above will be described. The order of processing shown below is merely an example, and the order of processing may be appropriately changed according to the embodiment. In the following description, the case where the direction of the moving target is detected in the situation shown in FIG. 2 will be described as an example. In FIG. 2, an oncoming vehicle (moving target) is in progress from the front of the vehicle 1 on which the radar device 2 is mounted, and a guard rail (stationary target) having a plurality of columns is installed on the side of the oncoming vehicle. Indicates the state. As described above, in the situation shown in FIG. 2, when the peak frequency of the moving target and the peak frequency of the stationary target overlap, the radar apparatus cannot synthesize and separate the phases (see FIGS. 3A and 3B). ).

  3A and 3B are examples in which the peak frequency of the moving target and the peak frequency of the stationary target overlap, and the reflection level peak value (hereinafter simply referred to as the peak value) coincides. Means that the peak value of one peak frequency is higher than the peak value of the other peak frequency, or the peak value of one peak frequency is higher than the peak value of the other peak frequency. The case where the peak value is lower than the peak value is included. For example, when the peak value of the peak frequency of the moving target is larger than the peak value of the peak frequency of the stationary target, the peak frequency of the moving target can be extracted. However, the phase difference calculated from the extracted peak frequency includes the phase difference of the moving target and the phase difference of the stationary target. That is, the extracted peak frequency is merely a phase difference obtained by combining the phase difference of the moving target and the phase difference of the stationary target.

  6A is an example of frequency spectrum data acquired by the radar apparatus according to the first embodiment in the situation shown in FIG. 2, and FIG. 6B is a diagram showing the frequency spectrum data in FIG. 6A as a complex vector. Indicates. In FIG. 6A, the horizontal axis is frequency and the vertical axis is reflection level. The solid line in FIG. 6A represents the reflection level from the guard rail, which is a stationary target, and the four peaks in FIG. 6A correspond to the reflected wave from the guard rail column. The dotted line in FIG. 6A represents the reflection level from the oncoming vehicle that is the moving target. In the example of FIG. 6A, the peak frequency of the moving target and the peak frequency of the stationary target overlap, and the peak value of the moving target is slightly higher than the peak value of the stationary target. In the example shown in FIGS. 6A and 6B, the peak value of the moving target exceeds the peak value of the stationary target, and it is possible to extract the peak frequency of the moving target. However, the complex vector of the moving target corresponding to the phase difference calculated from the extracted peak frequency is a composite vector of the complex vector of the moving target and the complex vector of the stationary target as long as the moving target and the stationary target overlap. It is. That is, if the combined vector shown in FIG. 6B is a complex vector of the moving target, an error occurs in the calculated direction. Therefore, in the first embodiment, the occurrence of this error is suppressed by performing processing described later. FIG. 6B shows a complex plane, where the X axis is a real axis and the Y axis is an imaginary axis. FIG. 6B shows a composite vector actually acquired, a complex vector corresponding to a stationary target and a complex vector corresponding to a moving target that cannot be actually acquired. FIG. 6B also shows the previous complex vector.

In the following description, the case where the peak value of the peak frequency of the moving target exceeds the peak value of the peak frequency of the stationary target as described above will be described as an example. However, according to the radar device 2 according to the first embodiment, it is possible to accurately calculate the azimuth even when the peak values completely match or when the peak frequency of the moving target is lower than the peak frequency of the stationary target. Can do.

  Here, FIG. 7 shows a processing flow of azimuth detection executed by the radar apparatus according to the first embodiment. Processing described below is executed by the control unit 4. First, in step S <b> 01, the reception unit 43 receives a reflected wave obtained by reflecting a transmission wave transmitted from the transmission unit 42 via the antenna 3 on the target as a reception signal of each port of the antenna 3. When the reception signal is received, the process proceeds to step S02.

  In step S <b> 02, the azimuth calculation unit 44 calculates the phase difference of the peak frequency of the beat signal, and the calculated phase difference is stored in the memory 41. The phase difference calculated in step S02 is a phase difference based on actual measurement and is different from a predicted phase difference described later. In addition, the phase difference when the frequency spectrum of the moving target and the frequency spectrum of the stationary target overlap is the sum of the phase difference calculated from the frequency spectrum of the moving target and the phase difference calculated from the frequency spectrum of the stationary target. It is a phase difference.

  The calculation of the phase difference is performed based on the phase monopulse method. Specifically, the azimuth calculation unit 44 acquires the frequency of the beat signal by mixing a part of the received wave and the transmitted wave received by the antenna 3. In the first embodiment, Fourier transform processing is performed on the acquired beat signal to obtain frequency spectrum data, and the peak value of the frequency spectrum is detected from this frequency spectrum data. Since the frequency spectrum data is expressed as a complex vector in the complex plane, the phase of the beat signal can be calculated from, for example, an angle formed between the complex vector and the real axis in the complex plane. Then, the phase difference is calculated by obtaining the phase difference of the beat signal, and the direction of the target is calculated based on the phase difference. Note that the beat signal phase difference is calculated for each of the up and down sections of the triangular wave. The calculated phase difference is stored in a predetermined storage area in the memory 41 by the storage unit 45. In FIG. 5, the phase difference is stored for each target, that is, the phase difference between the moving target and the stationary target is stored. However, in the first embodiment, only the phase difference of the moving target is stored. It may be. When the phase difference is stored, the process proceeds to step S03.

  In step S03, the bearing calculation unit 44 calculates the bearing of the target based on the calculated phase difference of the moving target. The distance measuring unit 49 calculates the relative speed and distance from the target. The relative speed and distance are calculated based on the FM-CW method.

  Here, FIG. 8 shows a principle diagram of the FM-CW system. The relationship between the distance frequency fr and the velocity frequency fv is shown in Equation 2, where fu is the frequency of the upward section of the triangular wave and fd is the frequency of the downstream section.

[Equation 2]
fu = fr−fv
fd = fr + fv (approaching speed +)

Here, the modulation frequency of the transmission wave is FM, the modulation width with f ₀ as the center frequency is Δf, and the speed of light is c
When the distance is R and the relative speed is V, it is expressed by Equation 3. As a result, the distance to the target and the relative speed can be obtained from the detected fu and fd.

[Equation 3]
fr = ((4 × Δf × FM) / c) × R
fv = (2 × f ₀ / c) × V

  When the azimuth of the target and the relative speed with the target are calculated, the process proceeds to step S04.

  In step S04, the prediction unit 46 predicts whether or not the peak frequencies of the stationary target and the moving target overlap. Specifically, the prediction unit 46 includes prediction information including azimuth information related to the azimuth calculated by the azimuth calculation unit 44, relative speed information related to the relative speed calculated by the distance measurement unit 49, and information related to the port interval of the receiving antenna. Based on this, it is predicted whether or not the peak frequencies of the stationary target and the moving target overlap. In other words, the frequency spectrum change is predicted from the target orientation, the relative speed with the target, and the displacement of the target distance, and the peak frequency is verified by collating the frequency spectrum change calculated for each moving target and stationary target. It can be determined whether or not. If it is not determined that the peak frequencies overlap, the process proceeds to step S05, and the direction calculated in step S03 is adopted. That is, the orientation calculated based on the actually measured phase difference is employed. The adopted direction is output to the ECU, for example, and used for vehicle control such as PCS. On the other hand, if it is determined that the peak frequencies overlap, the process proceeds to step S06.

  In step S06, the predicted phase difference calculation unit 47 accesses the storage area in the memory 41 shown in FIG. 5, for example, and based on the stored phase difference of the moving target, the phase difference of the moving target when the peak frequencies overlap. Is calculated as a predicted phase difference. For example, the predicted phase difference calculation unit 47 maps the phase difference history of the moving target, and calculates the predicted phase difference when the peak frequencies overlap from the phase difference history of the moving target. When the predicted phase difference of the moving target is calculated, the process proceeds to step S07.

  In step S07, the determination unit 48 determines that the difference between the predicted phase difference of the moving target calculated by the predicted phase difference calculation unit 47 and the phase difference calculated by the azimuth calculation unit 44 (phase difference measured by actual measurement) is within a predetermined range. It is determined whether or not. The predetermined range can be set based on the distance d between the ports of the antenna 3, the accuracy of the calculated azimuth, the detection range of the reflected wave, and the like. If the difference between the predicted phase difference and the phase difference of the moving target is within a predetermined range, the process proceeds to step S08. On the other hand, if the difference between the predicted phase difference and the phase difference of the moving target is not within the predetermined range, the process proceeds to step S10.

  In step S08, the predicted phase difference calculation unit 47 corrects the predicted phase difference of the moving target calculated in step S06. For example, the predicted phase difference calculation unit 47 calculates an average phase difference obtained by averaging the phase differences of the moving targets stored in the storage area of the memory 41, and the movement calculated by the azimuth calculation unit 44 based on the average phase difference. The phase difference of the target is corrected and calculated as the predicted phase difference of the moving target. The average phase difference can be obtained as a value obtained by averaging the phase differences stored in the storage area, in other words, a moving average of the phase differences. Smoothing out the phase difference as time-series data and correcting the phase difference calculated by the bearing calculation unit based on this smoothed average phase difference to calculate the predicted phase difference, thereby suppressing phase difference variation As a result, the orientation of the target can be calculated more accurately. The moving average can be calculated as a simple moving average by simply averaging the phase differences of n moving targets stored in the storage area. In addition, the moving average may be calculated as a weighted moving average by, for example, averaging the phase difference of the latest moving target with a weight. The weighting can be changed according to the relative speed between the radar device and the moving target. For example, a predetermined relative speed with little data variation is determined in advance, and the position within the range of the predetermined speed is determined. The phase difference can be weighted. When the predicted phase difference is corrected, the process proceeds to step S09.

In step S09, the azimuth calculation unit 44 calculates the azimuth of the target again based on the predicted phase difference of the moving target corrected in step S08. Step S1
In 0, the azimuth calculation unit 44 calculates the azimuth of the target based on the predicted phase difference of the moving target calculated in step S06.

[Effect]
According to the radar apparatus 2 according to the first embodiment described above, the direction of each target, particularly the direction of the moving target, can be accurately calculated even when the frequency spectra corresponding to different targets overlap. In the first embodiment, the peak frequency of the moving target exceeds the peak value of the peak frequency of the stationary target, and the peak frequency of the moving target can be acquired, but the peak frequency of the moving target acquired in this case is Including the peak frequency of the stationary target, an error occurs in the calculated direction. In the radar apparatus 2 according to the first embodiment, the phase difference itself is stored in the memory 41 instead of the azimuth and the relative speed calculated based on the phase difference, so that the predicted value of the phase difference based on the stored phase difference. (Predicted phase difference) can be calculated, and when the prediction unit 46 predicts that the peak frequencies of a plurality of targets overlap, the target phase based on the predicted phase difference calculated by the predicted phase difference calculating unit 47 can be calculated. The direction can be calculated. Therefore, even if the peak frequencies of a plurality of targets overlap, the orientation of each target can be calculated accurately. As a result, it is possible to avoid malfunction of PCS (Pre-crash Safety System) and non-detection of the target. In the radar apparatus 2 according to the first embodiment, the predicted phase difference calculation unit 47 also has a function of calculating the average phase difference and correcting the phase difference of the moving target. Can be increased. Further, the radar apparatus 2 according to the first embodiment can calculate the azimuth based on the above-described processing by incorporating the control unit 4 or a part of the configuration of the control unit 4 into the existing radar apparatus 2. In other words, the radar apparatus according to the first embodiment can improve the azimuth calculation accuracy without changing the hardware of the radar apparatus.

[Modification]
In the first embodiment described above, the aspect in which the predicted phase difference calculation unit 47 also has a function of calculating the average phase difference and correcting the phase difference has been described. However, the predicted phase difference calculation unit 47 may be configured not to have such a correcting function. Specifically, the radar apparatus 2 can be configured to not include steps S07 to S09. By doing in this way, it becomes possible to reduce the processing burden of the control part 4.

<Second embodiment>
The radar apparatus 2 according to the second embodiment predicts the phase difference of the stationary target, and if the peak frequency of the moving target and the peak frequency of the stationary target overlap, synthesizes the predicted phase difference of the stationary target predicted in advance. And a function of calculating the phase difference of the moving target by subtracting from the phase difference.

[Constitution]
The configuration of the radar apparatus according to the second embodiment is basically the same as that of the radar apparatus according to the first embodiment. However, a part of the configuration of the control unit 4 further has a function described below.

The predicted phase difference calculation unit 47 calculates the predicted phase difference of the stationary target in addition to the predicted phase difference of the moving target as the predicted phase difference. Further, the determination unit 48 determines whether the difference between the predicted phase difference of the moving target calculated by the predicted phase difference calculation unit 47 and the phase difference calculated by the azimuth calculation unit 44 is within a predetermined range. In addition, it is determined whether or not the difference between the predicted phase difference of the stationary target calculated by the predicted phase difference calculation unit 47 and the phase difference calculated by the azimuth calculation unit 44 is within a predetermined range. The predetermined range in the latter determination can be set based on the distance between the ports of the antenna 3, the accuracy of the calculated azimuth, the detection range of the reflected wave, and the like, similarly to the predetermined range in the former determination. When the difference between the predicted phase difference of the stationary target calculated by the predicted phase difference calculating unit 47 and the phase difference calculated by the azimuth calculating unit 44 is within a predetermined range, the azimuth calculating unit 44 The direction of the moving target is calculated based on the previously calculated phase difference (measured phase difference). When the difference between the predicted phase difference of the stationary target calculated by the predicted phase difference calculation unit 47 and the phase difference calculated by the azimuth calculation unit 44 is not within a predetermined range, the predicted phase difference calculation unit 47 calculates the azimuth calculation. The predicted phase difference of the moving target is calculated from the difference between the phase difference (phase difference obtained by actual measurement) previously calculated by the unit 44 and the predicted phase difference of the stationary target. Then, the azimuth calculating unit 44 calculates the azimuth of the moving target based on the predicted phase difference of the moving target based on the difference calculated by the predicted phase difference calculating unit 47.

[Processing flow]
FIG. 9 shows a processing flow of azimuth detection executed by the radar apparatus according to the second embodiment. The order of processing illustrated in FIG. 9 is merely an example, and the order of processing may be appropriately changed according to the embodiment. Further, the process shown in FIG. 9 can be incorporated into the process in the first embodiment. In the following description, it will be described as a process performed when it is not determined in step S07 that the difference between the predicted phase difference and the phase difference is within a predetermined range.

  First, in step S21, the predicted phase difference calculating unit 47 calculates the predicted phase difference of the stationary target as the predicted phase difference in addition to the predicted phase difference of the moving target. For example, the storage area in the memory 41 shown in FIG. 5 is accessed, and the phase difference of the stationary target when the peak frequencies overlap is calculated as the predicted phase difference of the stationary target based on the stored phase difference of the stationary target. For example, the predicted phase difference calculation unit 47 maps the phase difference history of the stationary target, and calculates the predicted phase difference of the stationary target when the peak frequencies overlap from the phase difference history of the stationary target. When the predicted phase difference of the stationary target is calculated, the process proceeds to step S22.

  In step S22, the determination unit 48 determines that the difference between the predicted phase difference of the stationary target calculated by the predicted phase difference calculation unit 47 and the phase difference calculated by the azimuth calculation unit 44 (phase difference measured by actual measurement) is within a predetermined range. It is determined whether or not. When the difference between the predicted phase difference of the stationary target and the actually measured phase difference is within a predetermined range, the process proceeds to step S10. In step S10, the azimuth calculation unit 44 calculates the azimuth of the target based on the predicted phase difference of the moving target calculated in step S06. On the other hand, if the difference between the predicted phase difference of the stationary target and the actually measured phase difference is not within the predetermined range, the process proceeds to step S23.

  In step S <b> 23, the predicted phase difference calculation unit 47 calculates the predicted phase difference of the moving target from the difference between the actually measured phase difference previously calculated by the azimuth calculation unit 44 and the predicted phase difference of the stationary target. As described above, since the frequency spectrum data is represented as a complex vector in the complex plane, the phase of the beat signal can be calculated from the angle formed between the complex vector and the real axis in the complex plane. Since the measured phase difference and the predicted phase difference of the stationary target are each expressed as a complex vector, the moving target is subtracted from the complex vector of the estimated target phase difference from the measured phase difference complex vector. Can be calculated (see FIG. 6B). When the predicted phase difference of the moving target based on the difference is calculated, the process proceeds to step S24.

  In step S24, the azimuth calculation unit 44 calculates the azimuth of the moving target based on the predicted phase difference of the moving target based on the difference.

[Effect]
According to the radar apparatus according to the second embodiment described above, the phase difference of the stationary target is predicted, and when the peak frequency of the moving target and the peak frequency of the stationary target overlap, The phase difference of the moving target can be calculated by subtracting the phase difference from the actually measured phase difference, that is, the synthesized phase difference. Thereby, the precision of a direction can be raised more. In the second embodiment, the direction of the moving target based on the predicted phase difference of the moving target and the direction of the moving target based on the predicted phase difference of the stationary target are detected. Therefore, a comparison control unit for comparing and controlling both positions is separately provided. When the difference between the two positions is not within the predetermined range, the direction is detected again, and the difference between both positions is within the predetermined range. In some cases, an average value of both positions may be adopted.

  The preferred embodiments of the present invention have been described above, but the radar apparatus according to the present invention is not limited to these, and can include combinations thereof as much as possible. In the description of the embodiment, the case where the phase monopulse method is used as the angle measurement method for detecting the azimuth of the target and the FM-CW method is used as the distance measurement method for detecting the relative speed and distance to the target has been described as an example. . However, the technique related to the radar apparatus according to the present invention can be applied to other side angle systems and ranging systems as long as it is a technique for calculating an azimuth or the like based on a phase difference.

DESCRIPTION OF SYMBOLS 1 ... Vehicle 2 ... Radar apparatus 3 ... Antenna 4 ... Control part 40 ... CPU
41 ... Memory 42 ... Transmitting unit 43 ... Receiving unit 44 ... Phase difference calculating unit 45 ... Storage unit 46 ... Predicting unit 47 ... Predicting phase difference calculating unit 48 ... Judgment part 49 ... Distance measurement part

Claims (4)

A transmission unit that transmits a frequency-modulated transmission signal as a transmission wave transmitted through a transmission antenna;
A receiving unit that receives the reflected wave received through at least two receiving antennas as a received signal of each receiving antenna, which is a reflected wave reflected by the target,
Calculating a phase difference between peak frequencies of beat signals generated from the transmission signals and reception signals of the reception antennas, and calculating an orientation of the target based on the calculated phase differences;
A storage unit that stores the phase difference calculated by the azimuth calculation unit in a storage area;
Prediction information including azimuth information about the azimuth calculated by the azimuth calculation unit, and predicting whether or not the peak frequencies of a plurality of targets overlap based on prediction information for predicting a change in the peak frequency of the beat signal A predictor to
A predicted phase difference calculation unit that calculates a phase difference when the peak frequencies overlap as a predicted phase difference based on the phase difference stored in the storage area;
When the prediction unit predicts that the peak frequencies overlap, the azimuth calculation unit calculates the azimuth of the target based on the predicted phase difference calculated by the predicted phase difference calculation unit. The target includes a moving target that moves relative to the radar device, and a stationary target that is stationary.
The storage unit stores the phase difference of the reflected wave from the moving target in the storage area among the phase differences calculated by the azimuth calculation unit,
The predicted phase difference calculation unit, when the prediction unit predicts that the peak frequencies overlap, based on the phase difference of the reflected wave from the moving target stored in the storage area, when the peak frequency overlaps Calculating a phase difference as the predicted phase difference;
The azimuth calculation unit calculates the azimuth of the target based on the predicted phase difference of the reflected wave from the moving target calculated by the prediction phase difference calculation unit when the prediction unit predicts that the peak frequencies overlap. The radar apparatus according to claim 1. If the prediction unit predicts that the peak frequencies overlap, whether the difference between the predicted phase difference calculated by the predicted phase difference calculation unit and the phase difference calculated by the azimuth calculation unit is within a predetermined range A determination unit for determining whether or not
The predicted phase difference calculation unit calculates an average phase difference obtained by averaging the phase differences stored in the storage area, and corrects the phase difference calculated by the azimuth calculation unit based on the average phase difference to calculate the prediction Calculated as phase difference,
When the determination unit determines that the difference is within a predetermined range, the azimuth calculation unit determines the azimuth of the target based on the predicted phase difference calculated by correcting the difference based on the average phase difference. The target is calculated based on the predicted phase difference that is not based on the average phase difference when the determination unit does not determine that the difference is within a predetermined range. The radar device described in 1. A transmission step of transmitting a frequency-modulated transmission signal as a transmission wave transmitted via a transmission antenna;
A reception step in which the transmission wave is a reflected wave reflected by a target and is received as a reception signal of each reception antenna;
An azimuth calculating step of calculating a phase difference between peak frequencies of beat signals generated from the transmission signal and a reception signal of each receiving antenna, and calculating an azimuth of the target based on the phase difference;
A storage step of storing the phase difference calculated in the azimuth calculation step in a storage area;
Prediction information including azimuth information related to the azimuth calculated in the azimuth calculation step, and predicting whether or not peak frequencies of a plurality of targets overlap based on prediction information for predicting a change in the peak frequency of the beat signal A prediction step to
Based on the phase difference stored in the storage area, the phase difference calculation step of calculating the phase difference when the peak frequencies overlap as a predicted phase difference is executed by the computer of the radar apparatus,
In the azimuth calculation step, when it is predicted that the peak frequencies overlap in the prediction step, the azimuth calculation method calculates the azimuth of the target based on the prediction phase difference calculated in the prediction phase difference calculation step.

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