JP7317541B2 - Radar device and target detection method - Google Patents

Description

The present invention relates to a radar device and a target detection method.

2. Description of the Related Art In recent years, the use of radar devices for detecting surrounding objects (targets) has been expanding, for example, for vehicle surroundings monitoring and ADAS (Advanced Driving Assistance Systems). In particular, automotive radar devices are required to detect nearby targets while realizing detection of distant targets. Automotive radar systems are required to accurately detect the position of pedestrians, etc., to prevent collisions, and to accurately detect the placement of surrounding obstacles when parking. be done. While it is required to be able to accurately detect the presence or absence of a long-distance target, it is necessary to specify the position of a short-distance target more accurately, especially the nearest point.

Regarding a radar device that can be used for automobiles, Patent Document 1 discloses that a pulse signal with a small pulse width is transmitted, and equivalent sampling of this pulse waveform is performed on the receiving side to obtain data of a plurality of distance positions (distance bins). A technique for confirming by disassembling is disclosed. Further, Patent Literature 2 discloses a technique in which a transmitting side forms a pulse signal with fast rise and fall times, and a receiving side detects a target using a differential value of the received waveform. Further, in Patent Document 3, while keeping the pulse width of the transmission side sufficiently wide, the reception side performs extremely narrow amplitude modulation of the order of 1/10 of the pulse width of the transmission side, and shifts the timing of the reception side. A technique for allowing the

Japanese Patent Application Laid-Open No. 2010-216980 Japanese Patent Application Laid-Open No. 2002-365362 JP 2016-516995 A

When multiple targets are present, it is difficult to separate them, especially when the difference in distance of multiple targets from the radar system is less than the resolution of the radar system. For example, when the radio wave reflection intensity of a distant target is large, the reflected waves of the closer target are buried in the reflected waves of the far target, making it impossible to separate and detect the closer target. there is a possibility. In particular, in the detection of nearby targets by radar equipment for automobiles, it is possible to reliably detect the nearest target without being affected by the surroundings, such as when detecting obstacles when parking, and to estimate the distance to the target. Accurate detection is often required.

The radar devices described in Patent Literatures 1 to 3 are based on single pulse pattern shaping, and a problem is assumed regarding compatibility between avoidance of saturation of nearby objects and detection of distant weak objects.

It is also possible to detect a weak target by making the rise of the transmission pulse steeper, but this is not preferable because the frequency band of the transmission pulse is widened and there is concern about the influence on peripheral devices.

Further, in Patent Documents 2 and 3, the transmission pulse width is set relatively wide with respect to the rise time, and when a plurality of targets are present in the vicinity of the vehicle, separation of these targets, particularly Detection of distant targets can be difficult.

Moreover, when the receiving side operates at high speed as disclosed in Patent Document 1 and the like, it is not preferable because of the influence of noise generation.

In view of such circumstances, it is an object of the present invention to provide a radar apparatus and a target detection method that achieve both long-range and short-range detection and improve short-range resolution.

A radar device according to the present invention is a radar device that detects a target using radio waves, and includes a transmission unit that transmits a first pulse and a second pulse having an amplitude and a pulse width larger than those of the first pulse; a receiving unit for receiving reflected waves of the first pulse and the second pulse transmitted by the transmitting unit by a target; and detecting the target based on a reflected wave signal of the reflected waves received by the receiving unit. a detection unit, wherein the transmission unit forms waveforms of the first pulse and the second pulse such that the rise time of the first pulse is shorter than the rise and fall times of the second pulse. .

A target detection method according to the present invention is a method for detecting a target using radio waves, comprising the step of transmitting a first pulse and a second pulse having an amplitude and a pulse width larger than those of the first pulse; a step of receiving reflected waves of the first pulse and the second pulse transmitted in the transmitting step by a target; and detecting the target based on a reflected wave signal of the reflected waves received in the receiving step. and forming the waveforms of the first pulse and the second pulse such that the rising time of the first pulse is shorter than the rising and falling times of the second pulse in the transmitting step. , a target detection method.

Advantageous Effects of Invention According to the present invention, it is possible to provide a radar device and a target detection method that achieve both long-range and short-range detection and improve short-range resolution.

1 is a block diagram showing the configuration of a radar device according to one embodiment of the present invention; FIG. FIG. 2 is a diagram showing a pulse waveform transmitted by a transmission unit of the radar device of FIG. 1; 3 is a diagram illustrating a waveform of a reflected wave of a first pulse received by a receiver of the radar device of FIG. 2; FIG. 2 is a diagram showing a process of forming a waveform signal of a first pulse in a transmission section of the radar device of FIG. 1; FIG. FIG. 4 is a diagram showing a change in inclination of the reflected wave signal of FIG. 3; FIG. 4 is a diagram illustrating a waveform of a reflected wave of a first pulse different from that in FIG. 3; FIG. 8 is a diagram showing a change in slope of the reflected wave signal of FIG. 7; 2 is a diagram showing equivalent time sampling in the radar system of FIG. 1; FIG. 2 is a flow chart showing a procedure of a target object detection method according to an embodiment of the present invention performed by the radar device of FIG. 1; It is a block diagram which shows the structure of the radar apparatus of 2nd embodiment of this invention. FIG. 11 is a diagram illustrating an intensity distribution for each angle and distance of a reflected wave signal in the radar device of FIG. 10; FIG. 12 shows angular peaks in the intensity distribution of FIG. 11; 12. It is a figure which illustrates the intensity distribution for every angle and distance in the case where angular resolution is lower than FIG.11 and FIG.12 in the radar apparatus of FIG. FIG. 14 is a diagram showing the waveform of the reflected wave of the first pulse at the angular peak for each distance in the intensity distribution of FIG. 13; 15 is a diagram showing changes in intensity and determination index values for each reflected wave signal distance in FIG. 14; FIG. FIG. 14 is a diagram showing angular difference values at angular peaks for each distance in the intensity distribution of FIG. 13;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a radar device 1 according to the first embodiment of the invention.

The radar device 1 of this embodiment is a device that detects a target using radio waves. The radar apparatus 1 repeatedly transmits a first pulse P1 as shown in FIG. 2 and a second pulse P2 having an amplitude and a pulse width larger than those of the first pulse P1 at a first timing having a first interval. a receiving unit 3 for receiving reflected waves of the first pulse and the second pulse transmitted by the transmitting unit 2 from the target; and a detecting unit for detecting the target based on the reflected wave signals received by the receiving unit 3. 4, and a control unit 5 that controls the transmission unit 2, the reception unit 3, and the detection unit 4.

In the radar device 1, the first pulse P1 is used to detect a target existing at a relatively short distance, and the second pulse P2 is used to detect a target existing at a relatively long distance. Used. The first pulse P1 has a resolution (when the distances of a plurality of targets from the radar device 1 are approximate, typically when a plurality of targets exist close to each other, they are detected as separate targets). The pulse has a relatively small pulse width so as to improve the ability to receive the signal, and has a relatively small amplitude so as not to saturate the receiving system due to an increase in the reception intensity of the reflected wave from the target. On the other hand, the second pulse P2 has a relatively large amplitude and a relatively large pulse width in order to detect the presence of a distant target with high sensitivity while the distance attenuation is large and the reception intensity is small as the distance increases. pulsed.

The transmission unit 2 includes an oscillation unit 21 that generates a local oscillation signal of a predetermined carrier frequency, a waveform formation unit 22 that forms waveform signals of the first pulse P1 and the second pulse P2, and a local oscillation generated by the oscillation unit 21. A gain control unit 23 multiplies the signal by a waveform signal formed by the waveform forming unit 22 and amplifies it, and a transmission antenna 24 converts the signal output from the gain control unit 23 into a radio wave and transmits the radio wave.

The oscillator 21 can be configured to have a well-known oscillator. Also, the oscillator 21 can generate a local oscillator signal under the control of the controller 5 .

The waveform forming section 22 forms a waveform signal that defines the waveforms of the first pulse P1 and the second pulse P2 such that the rise time of the first pulse P1 is shorter than the rise time and fall time of the second pulse P2. Further, the waveform forming section 22 generates a waveform signal that determines the waveforms of the first pulse P1 and the second pulse P2 so that the rising slope of the first pulse P1 is larger than the rising and falling slopes of the second pulse P2. preferably formed. The terms "rise time" and "fall time" mean the time during which the value increases from 10% to 90% of the peak value and the time during which the value decreases from 90% to 10% of the peak value. In addition, the rising (falling) slope is defined by dividing the value of 80% (90%-10%) of the peak value by the time it takes to increase from 10% to 90% (decrease from 90% to 10%) of the peak value. (absolute value).

As described above, since the pulse width of the first pulse P1 is relatively narrow, even if there are a plurality of targets existing in the vicinity of the radar apparatus 1 and having a small difference in distance to each other, the first pulse P1 can reach each target. The radio waves reflected by the target can be received by the radar device and separated into electric signals as a plurality of targets. Furthermore, by shortening the rise time of the first pulse P1, it is possible to prevent a closer target from being buried in a distant target and becoming unidentifiable.

In addition, when the rise time and fall time of the waveform of the transmission radio wave are reduced, the frequency band of the radio wave transmitted from the oscillator 21 tends to widen. However, for the purpose of accurate detection of the position (closest point) of the target at the closest distance from the radar device, only the first pulse P1 with a relatively small output and only the rise time are made small. Since the expansion of the frequency band can be suppressed, the influence on peripheral devices can be suppressed.

As shown in FIG. 4, the waveform forming section 22 is configured to form two original waveform signals having different rising times (a first original waveform signal U1 having a longer rising time and a second original waveform signal V1 having a shorter rising time). can be The waveform forming section 22 can form a waveform signal W1 that determines the waveform of the first pulse P1 by multiplying two original waveform signals U1 and V1 with different rise times while shifting them. By shifting and multiplying the first original waveform signal U1 and the second original waveform signal V1 so that the rising edge of the pulse of the second waveform signal is not superimposed on the pulse of the first original waveform signal U1, , the waveform signal W1 for generating the first pulse P1 having a relatively short rise time and a long fall time can be formed relatively easily.

When forming the waveform signal W1 of the first pulse P1 by shifting and multiplying the first original waveform signal U1 and the second original waveform signal V1, the first pulse is generated at the peak of the first original waveform signal U1 with a long rise time. It is preferable to multiply the two original waveform signals U1 and V1 so that the waveform signal W1 of P1 has a value (the second original waveform signal V1 has a value). More preferably, the two original waveform signals U1 and V1 are multiplied so that the waveform signal W1 of the first pulse P1 has the maximum value at the peak of the first original waveform signal U1 having a long rising time. As a result, the asymmetrical mountain-shaped waveform signal W1 whose rising time is shorter than its falling time can be formed relatively accurately and efficiently.

Further, the waveform forming section 22 generates a first original waveform signal U2 with a long rise time and a second original waveform signal V2 with a short rise time, which has a maximum value at least while the first original waveform signal U2 is valid. By multiplying, it is possible to form the waveform signal W2 of the second pulse P2 having relatively long rising and falling times.

The two original waveform signals U1/V1 and U2/V2 with different rise times can be formed by circuits with different time constants. That is, the first original waveform signals U1 and U2 with short rise times can be chevron-shaped or sinusoidal pulse signals output from a circuit with a large time constant, and the second original waveform signals V1 and V2 with short rise times can be used. can be a trapezoidal pulse signal output from a circuit with a small time constant. As a result, by adjusting the time control, a waveform signal W1 having a small amplitude and a small pulse width for the vicinity, where resolution is most required, and the first waveform signal W1 for transmission generated based thereon, are used. A steep rising edge can be selectively formed in the pulse P1 relatively easily and accurately.

The gain controller 23 amplifies the local oscillator signal generated by the oscillator 21 with an amplification factor proportional to the waveform signal generated by the waveform generator 22 to form a power signal to be supplied to the transmission antenna 24 . A well-known amplifier circuit can be used as the gain control unit 23 .

The transmission antenna 24 transmits the power signals of the first pulse P1 and the second pulse P2 supplied from the gain control section 23 as electromagnetic waves. A well-known antenna can be used as the transmitting antenna 24 .

The receiving unit 3 includes a receiving antenna 31 that receives electromagnetic waves, a mask unit 32 that can pass or block received electrical signals, a mixer unit 33 that down-converts the electrical signals that have passed through the mask unit 32, and signals that pass through the mask unit 32. and an AD converter 34 for converting the intensity signal extracted by the mixer 33 into a digital signal.

The receiving antenna 31 receives the reflected waves from the target of the first pulse P1 and the second pulse P2 transmitted by the transmitting antenna 24 and converts them into electrical signals (reflected wave signals). A well-known antenna can be used as the receiving antenna 31 .

The masking unit 32 passes the reflected wave signal of the first pulse P1 at fixed time intervals for a limited time (synchronizing part of the reflected wave signal of the first pulse P1 with a second timing having a second interval). Let On the other hand, the mask section 32 allows the entire reflected wave signal of the second pulse P2 to pass. That is, the masking unit 32 substantially receives the first pulse P1 from when the transmitting unit 2 starts transmitting the first pulse P1 until it starts transmitting the second pulse P2, as shown by the gain setting signal in FIG. During the period, the electrical signal is passed through for a limited time at regular time intervals (with a mask width equal to or less than the pulse width of the first pulse P1), and after the transmission of the second pulse P2 is started, the electrical signal is continuously transmitted. pass (pass the reflected wave signal of the second pulse P2). Such a mask part 32 is configured to be able to select whether to pass or block the electrical signal of the reflected wave received by the receiving antenna 31 . As a result, the sensitivity is ensured by not losing the second pulse P2 at a long distance where distance attenuation is large, while the resolution is reduced as will be described later by blocking the first pulse P1 and the mask section 32 at a short distance where the SN is abundant. security can be realized.

Specifically, the mask unit 32 forms a gain control unit 321 that amplifies or attenuates the electrical signal output from the receiving antenna 31, and a rectangular wave or trapezoidal gain setting signal that sets the gain of the gain control unit 321. It can be configured to have a gain setting unit 322 for The gain setting section 322 is controlled by the control section 5 to form a gain setting signal at an appropriate timing for transmission of the first pulse P1 and the second pulse P2 from the transmission section 2 . It is also preferable to directly control the gain control section 321 by a high-speed rectangular wave or trapezoidal control signal directly from the control section.

The AD converter 34, which will be described later, does not operate at a sufficiently high speed compared to the change speed of the intensity of the first pulse P1. Moreover, there is a case where a low-pass filter is loaded in one of the stages preceding the AD conversion section 34 (for example, between the AD conversion section 34 and the mixer section 33). Therefore, if the reflected wave signal of the first pulse P1 is allowed to pass through as it is, the band is limited by the action of the low-pass filter or the like and the AD conversion unit 34, and digital conversion is performed with the waveform in a state where the rising signal is dull. . In other words, even a signal that has been separated by a fast rising edge may have a dull waveform due to the band limitation, and may become difficult to separate due to the averaging of the peripheral time signal. Therefore, at least in the stage prior to the band limitation, the signal separated by the masking section 32 can be selected by selectively clipping the electric signal with respect to time by the masking section 32 . As a result, the reflected wave signal of the first pulse P1 at a specific time (that is, a specific distance) is reduced from the influence of the reflected wave signal that exists at a surrounding time (that is, a reflected wave signal caused by a target that exists in the vicinity). can be converted into digital data by the AD converter 34 . In this way, the time resolution and the distance resolution can be maintained by performing the limited time cut operation in the mask section 32 . Note that there may be a delay in signal transmission from the mask unit 32 to the AD conversion unit 34 due to the intervention of a circuit such as a low-pass filter. The unit 34 does not synchronize in absolute time, but synchronizes with the gain setting signal of the mask unit 32 offset so that the detection value in the AD conversion unit is sufficiently large, more preferably maximized, in consideration of the delay. is preferred. As a result, SN can be increased even when there is a circuit delay.

The mask unit 32 controls to shift the signal passage timing relative to the plurality of first pulses P1 in synchronization with the AD conversion unit 34 . In such a case, it is preferable to relatively shift the repeatedly transmitted transmission pulse with respect to the basic clock of the AD converter. As a result, the waveforms of the reflected wave signals of the first pulse P1 are relatively shifted, the signals at different timings are converted into digital data by the AD conversion section 34, and the detection section 4 combines these digital data to obtain the first pulse P1. Equivalent time sampling can be performed in which a sampling signal slower than the AD conversion speed of the pulse P1 is used as a more detailed time waveform, that is, a detailed distance waveform.

The rise time of the gain of the mask portion 32 is preferably equal to or less than the rise time of the first pulse P1, and the limited pass gain width of the mask portion is preferably equal to or less than the pulse width of the first pulse P1. . More preferably, the waveform of the gain is rectangular or trapezoidal. By doing so, it is possible to reduce the error in the intensity of the sampled reflected wave signal. Either the pulse operation on the transmission side or the mask operation on the reception side, whichever is slower and has a wider time width, may cause a decrease in resolution. The rise/fall time and gain width of , can be increased in speed and resolution while reducing the influence on peripheral devices. That is, in order to obtain the same degree of resolution, the rise time or pulse width of the first pulse P1 is made equal to or relatively large with respect to the gain rise/fall time or gain width of the mask section 32, thereby emitting as an electromagnetic wave. Since it is possible to suppress the spread of the frequency band of the first pulse P1 to be transmitted, it is possible to suppress the influence on the surrounding equipment.

The mixer unit 33 uses the local oscillator signal generated by the oscillation unit 21 to remove the frequency component of the carrier wave from the signal that has passed through the mask unit 32, thereby obtaining an analog signal representing the strength change of the reflected wave signal, that is, the envelope signal. Extract the waves.

The AD conversion section 34 converts the analog signal output from the mixer section 33 into a digital signal and provides the detection section 4 with the digital signal. This AD converter 34 can be configured by a well-known AD converter.

The detection unit 4 accumulates the digital data input from the AD conversion unit 34 and analyzes changes over time in the reflected wave signal, thereby reflecting the first pulse P1 and the second pulse P2 transmitted by the transmission unit 2. Identify the position of the target (target detection processing). The detection unit 4 can be configured by an arithmetic device having a CPU, FPGA, memory, and the like. A calculation procedure for the detector 4 to analyze the change over time of the reflected wave signal is described in a program and stored.

A specific example of the phenomenon obtained by the configuration described above, the result of detection, and the content of the calculation will be shown. FIG. 3 shows the receiver 3 when there is only one target in the vicinity area and when there are two targets in the vicinity area and the target on the far side is larger (easily reflects radio waves). shows an example of actual measurement of the intensity (amplitude) of the reflected wave signal received by . As shown in the figure, since the rising time of the first pulse P1 is short, the strength of the reflected wave signal of the first pulse P1 from the far target among the two targets existing in the vicinity area of the radar device 1 is high. Even in this case, an area where the slope near the peak of the waveform of the reflected wave from the nearby target is small (area near the peak) is less likely to be covered by the reflected wave from the distant target. As a result, the radar device 1 can detect a plurality of targets separately, so that the resolution at short distances can be particularly high.

3, the intensity of the reflected wave signal of the first pulse P1 is equal to or greater than a predetermined intensity threshold value Sa, and the intensity change of the received wave signal in FIG. ), it can be determined that a target exists when the slope of the reflected wave signal of the first pulse P1 is greater than 0 and equal to or less than a predetermined first slope threshold value Sg1. In FIG. 5, the distance position where the slope of the received wave signal is equal to or less than the first slope threshold value Sg1 (distance bin: after the transmitter 2 transmits the first pulse P1, the receiver 3 receives the reflected wave of the first pulse P1 The time until reception is converted into the distance from the radar device 1 to the target) corresponds to the front part of the near-peak region of the waveform due to the closer target in the reflected wave signal in FIG.

By setting the first slope threshold Sg1 to a value greater than 0 in this way, it is possible to detect the presence of a target at a point where the reflected wave signal does not reach its peak before it reaches its peak. The near side of the reflected wave signal is based on a steep rising waveform. Also, this steepness, that is, the loss of a large inclination is used as a judgment for detecting the existence of a target. As a result, even if the peak of the waveform of the closer target in the reflected wave signal is covered by the waveform of the farther target, the part just before the peak of the waveform of the closer target is If it is not covered with waves, it can detect the presence of a closer target. Therefore, the radar apparatus 1 can separate the closest target from the farther target and detect it more reliably.

6 and 7 show changes in intensity of reflected wave signals when two targets exist in FIGS. 3 and 5 and when the distance between the two targets is smaller than in FIGS. Shows a change in slope. In this case, there is a possibility that the closer target cannot be reliably detected due to the relationship between the slope of the reflected wave signal and the first slope threshold value Sg1. Therefore, the detection unit 4 determines that a target exists when the slope of the reflected wave signal of the first pulse P1 is equal to or less than a predetermined second slope threshold value Sg2 that is greater than 0 and continues for a predetermined reference time Ts or more. You may Here, the reference time Ts is equal to or longer than the time interval in equivalent sampling. In other words, the detection unit 4 determines that the target exists when the slope of the reflected wave signal of the first pulse P1 becomes equal to or smaller than the predetermined second slope threshold value Sg2 consecutively two or more times (twice in FIG. 7). Then, it may be determined (determined that this distance position is the point X0 where the target exists). In this case, the second tilt threshold Sg2 is set to a value larger than the first tilt threshold Sg1 at which it is determined that the target exists when the second tilt threshold Sg2 is equal to or less than the value even once.

In this way, by continuously confirming the slope of the reflected wave signal, the target can be detected from the area where the steep rise, that is, the loss of the large slope, continues with respect to the waveform that basically rises steeply. be able to. Therefore, even if the waveform of the closer target in the reflected wave signal is covered with the waveform of the distant target, the existence of the peak of the waveform of the closer target can be more reliably estimated. .

As described above, the detection unit 4 detects the point at which it is determined that the target exists in comparison with the first slope threshold value Sg1 or the second slope threshold value Sg2 of the slope of the reflected wave signal of the first pulse P1 (FIGS. 3 and 4). 6 and FIG. 7), the distance to the target may be calculated (distance calculation processing). Even if the distance to the target is calculated based on the complementary point (distance position X1 in FIGS. 3 and 6) on the closer side, which has a value smaller than the intensity at (point X0) by a predetermined value ΔR, good. At the point X0, since the change in the intensity of the reflected wave signal with respect to the distance is small, there is a possibility that the error between the point X0 at which it is determined that the target exists and the actual distance position becomes large. For this reason, the complementary point X1 having a value smaller than the intensity at the point X0 by a predetermined value ΔR is calculated, and the distance to the target is calculated more accurately by performing the distance calculation processing based on this. be able to.

The control unit 5 synchronizes the operation timings of the transmission unit 2, the reception unit 3, and the detection unit 4 so that the detection unit 4 can appropriately detect the target. The control unit 5 can be configured by, for example, an arithmetic device having a CPU, an FPGA, a memory, etc., and its operation procedure is described in a program and stored. The control unit 5 is normally configured integrally with the detection unit 4 . In other words, the detection unit 4 and the control unit 5 are functionally distinguished, and may not be clearly distinguished in terms of physical configuration and program configuration.

The control unit 5 controls the transmission unit 2 and the reception unit 3 so that the reception unit 3 appropriately performs equivalent time sampling of the reflected wave signal. That is, the control unit 5 causes the transmitting unit 2 to repeatedly transmit the first pulse P1 and the second pulse P2, and the receiving unit 3 receives the reflected wave signals of the first pulse P1 and the second pulse P2 relatively differently depending on the repetition. A/D conversion (sampling) is performed at the timing. In this way, by sampling the reflected wave signals of the first pulse P1 and the second pulse P2 in a plurality of different fields and combining the digital data of each field, even in low-speed A/D conversion, equivalently faster speeds can be obtained. The reflected wave signals of the first pulse P1 and the second pulse P2 can be sampled, and more detailed time waveform information, that is, detailed distance waveform information can be obtained.

When performing such equivalent time sampling, in the relative timing shift for that purpose, by making the interval of the timing shift of the first pulse finer than that of the timing shift of the second pulse, as shown in FIG. The first pulse is set so that the distance interval acquired by one pulse is set smaller than the distance interval acquired by the second pulse, and the number of signal acquisition times at the same distance is increased with the second pulse as compared with the first pulse. and the second pulse can be relatively shifted. As a result, in the pulse repeatedly transmitted in each field, the distance interval obtained by the detector 4 from the reflected wave of the first pulse P1 is narrowed, and the waveform is confirmed in detail, improving the resolution of the target existing at a short distance. In addition, by making the distance interval acquired by the reflected wave of the second pulse P2 relatively rough and confirming the signal at the same distance more times, for example, integration of a plurality of signals or FFT processing of a relatively large number of points can be performed. By doing so, even when the intensity of the reflected wave of the second pulse P2 is small, it becomes easy to distinguish it from noise. The first pulse P1 and the second pulse P2 by the transmission unit 2 are repeatedly transmitted while shifting the transmission interval, that is, by relatively shifting the first timing, the distance resolution and distance accuracy at a short distance are improved, It is possible to achieve both improvement in long-distance detection sensitivity.

The control unit 5 causes the transmission unit 2 to transmit two or more types of first pulses having different carrier frequencies, and the detection unit 4 detects the difference or phase difference between the complex amplitude vectors of the reflected wave signals of the two or more types of first pulses. A target may be detected based on The phase of the reflected wave signal that is transmitted from the transmitter 2, reflected by the target, and received by the receiver 3 changes according to the distance of the target and the carrier frequency. On the other hand, the phase of the received signal, which is transmitted from the transmitter 2 and reaches the receiver 3 directly and whose propagation distance is almost zero, hardly changes depending on the carrier frequency. For this reason, when receiving two or more types of first pulses with different carrier frequencies, it is possible to remove the component that has directly reached the receiving section 3 from the transmitting section 2 by calculating the difference or phase difference between the complex amplitude vectors of the signals. can. Further, by calculating such a difference, in addition to the radar interference signal not derived from the target, the interference signal in the installation environment where it is mounted, the noise component that goes around from the transmission unit 2 to the reception unit 3, high-speed control of the transmission pulse, Additional noise caused by fast mask control in the receiver can also be removed. Therefore, by using two or more types of first pulses with different carrier frequencies, it is possible to reduce noise and improve target detection accuracy. Note that the number of types of the first pulse with different carrier frequencies is at least two, and three or more types of carrier frequencies may be used stepwise. Alternatively, the difference value may be acquired after slightly phase-rotating the complex amplitude vector of the reflected wave signal at one carrier frequency by a predetermined propagation distance instead of setting the propagation distance to zero.

As described above, the radar apparatus 1 according to the present embodiment uses the first pulse P1 with a short rising time and the mask section 32 that passes through for a limited time, so that a plurality of targets existing at a short distance are relatively It can be separated with high precision and separately detected. For example, when the radar device 1 having a high short-range resolution is installed in a vehicle and the obstacles around the vehicle are checked when the vehicle is parked, the nearest target can be reliably detected. Allows for safe parking without contact with obstacles.

The target detection method performed by the radar device 1 of FIG. 1 described above is itself a target detection method according to an embodiment of the present invention. The target detection method performed by the radar device 1 of FIG. 1 includes, as shown in FIG. 9, a step of transmitting a first pulse P1 and a second pulse having a larger amplitude and pulse width than the first pulse (step S1: transmission step), a step of receiving reflected waves from the target of the first pulse and the second pulse transmitted in the transmission step (step S2: reception step), and a reflected wave signal of the reflected waves received in the reception step and a step of detecting the target (step S3: detection step).

In the target detection method of this embodiment, in the step of transmitting, the waveforms of the first pulse P1 and the second pulse P2 are adjusted so that the rising time of the first pulse P1 is longer than the rising and falling times of the second pulse P2. to form In this way, by using the first pulse P1 with a short rise time, it is possible to separate and separately detect a plurality of targets present at a short distance with relatively high accuracy. Also, the waveform forming method and the reflected wave signal processing method described for the radar apparatus 1 of FIG. 1 are configurations that can be employed in the target object detection method of the present embodiment.

Next, a radar device according to a second embodiment of the invention will be described. FIG. 10 is a block diagram showing the configuration of a radar device 1A according to the second embodiment of the invention. The radar device 1A of this embodiment includes a transmitter 2A that transmits a first pulse P1 and a second pulse P2, and a receiver that receives reflected waves of the first and second pulses transmitted by the transmitter 2A from a target. 3A, a detection unit 4A that detects a target based on the reflected wave signal received by the reception unit 3A, and a control unit 5A that controls the transmission unit 2, the reception unit A3, and the detection unit 4A. In the description of the radar device 1A of FIG. 10, the same components as those of the radar device 1 of FIG.

The transmission unit 2A includes an oscillation unit 21 that generates a local oscillation signal having a carrier frequency, a waveform formation unit 22 that forms waveform signals of the first pulse P1 and the second pulse P2, and a local oscillation signal generated by the oscillation unit 21. Any one of a gain control unit 23 that multiplies the waveform signal formed by the waveform forming unit 22, a plurality of transmission antennas 24 that transmit the signals output from the gain control unit 23 as radio waves, and a plurality of transmission antennas 24 is selected. and a transmission selection unit 25 for selection. That is, the transmitter 2A has a plurality of transmission channels.

The transmission selection unit 25 can be configured by a known selector that switches electric paths so that the signal output from the gain control unit 23 is transmitted to only one of the transmission antennas 24 according to the control unit 5A.

The receiving unit 3 includes a plurality of receiving antennas 31 that receive electromagnetic waves and convert them into electrical signals, a reception selection unit 35 that selects one of the plurality of reception antennas, and a reception antenna selected by the reception selection unit 35. 31, a mixer section 33 that extracts an amplitude component from the electrical signal that has passed through the mask section 32, and an AD conversion section 34 that converts the signal extracted by the mixer section 33 into a digital signal. and have That is, the receiver 3A has a plurality of reception channels.

The reception selection unit 35 can be configured by a known selector that switches electric paths so that only the signal of one of the reception antennas 31 is supplied to the mixer unit 33 via the mask unit 32 according to the control unit 5A.

The detection unit 4A calculates intensity information at angles (angle bins) and distances (distance bins) by performing angle arithmetic processing for each distance on the reflected wave signals of the first pulse P1 in the plurality of channels. (angle measurement processing). FIG. 11 shows an example of the intensity information data mapped with the angular position and the distance position as the horizontal axis and the vertical axis. Here, by synthesizing the signals of multiple channels by angle calculation processing, the noise of each of the multiple channel signals is random, whereas the reflected wave signal is coherent with respect to the direction in which the target exists. An integral effect is obtained in the angular peak direction. For this combined signal itself, it is possible to detect the target on the basis of the intensity change with respect to the distance for each angle as indicated by the arrows in FIG. 11, similar to the above-described FIGS. As a result, the target has azimuth information, and the position of the target can be detected with high resolution in terms of distance as described above.

Further, instead of the distance axis processing for all angle bins as in FIG. 11, the distance axis processing as described above may be performed only for the angle peaks obtained by the angle calculation processing. Specifically, as shown in FIG. 12, as a result of performing peak detection on the angle axis, the angle peak amplitude on each distance axis is then spliced together and used as distance amplitude information. 11 and 12, in the case where a plurality of targets exist, if the targets can be separated as a plurality of peaks, it is assumed that the reflected wave signals from the same target are relatively close to each other. are connected to form a plurality of distance amplitude information. As a result, the target has direction information, it is possible to separate a plurality of targets based on the direction information, and to achieve detection with high resolution in terms of distance as described above. In FIG. 11, it is possible to have abundant information, while in FIG. 12, the calculation load can be reduced by handling only the angle peaks.

Next, FIG. 13 shows a case in which the number of antenna channels is smaller than that in FIG. 11 and the angular resolution is lower. In this case, even if a plurality of targets exist, it may be difficult to separate them into two peaks on the angular axis as shown in FIG. Even in such a situation, detection with high resolution in distance can be achieved by obtaining amplitude distance information at the angle peak.

Specifically, as shown in addition to FIG. 13, the detection unit 4A identifies the angle at which the intensity of the reflected wave signal is maximized for each distance (extracts the maximum intensity for each distance position). FIG. 15 shows the variation of the extracted maximum intensity with distance. As shown in FIG. 14, the maximum intensity may be extracted only when the intensity of the reflected wave signal at the angular peak for each distance is equal to or greater than the intensity threshold value Sa. FIG. 15 shows intensity changes in the reflected wave signal of FIG. 14 in the same manner as FIGS. In other words, simply calculating the intensity change (slope) between distance bins does not reach the detection threshold value (intensity change before correction), making detection difficult. Here, the angle information obtained based on the angle calculation process is used. FIG. 16 shows the absolute value of the difference between the angle values that become the angle peak for each distance. It is confirmed that the angle values change sharply in the map of FIG. 13 and also in FIG. 16 at a specific distance, and in particular, the angle difference (the inclination of the angle) as shown in FIG. 16 can be extracted as a quantitative value. In addition, in the normal angle calculation process, there is a case where the existence angle of the target is calculated in stages including various calibrations. In this case, the angle value used here may not be the final detected angle, but may be the difference between the index values relating to the angle, which is intermediate information in the angle calculation result.

Then, as shown in FIG. 15, the detection unit 4A calculates a value obtained by multiplying the amount of change (inclination) between the distance bins of the angle (peak angle) at which the maximum intensity is obtained as shown in FIG. , a determination index value (change in intensity after correction) subtracted from the slope of the maximum intensity is calculated. The detection unit 4A can determine that a target exists when the determination index value becomes equal to or less than a predetermined third tilt threshold value Sg3. Also, as in FIG. 7, it may be determined that a target exists (this time position is determined to be the point X0) when the determination index value is equal to or less than a predetermined threshold continuously in a plurality of distance bins. . By using the amount of change in angle, it is possible to more reliably detect targets that have been difficult to detect in the past. It should be noted that the method of applying the amount of change in the angle is not limited to the above means.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various changes and modifications are possible. For example, in the present invention, the first pulse may have at least a short rising time, and may have a waveform with a short falling time as well as the rising time. Specifically, the first pulse may have a rectangular or trapezoidal waveform. Also, the second pulse may have a relatively large pulse width, for example, a frequency-modulated continuous wave whose pulse width is on the order of 10 times or more that of the first pulse and whose carrier frequency changes continuously.

In the radar apparatus according to the present invention, the transmitter may have a configuration different from that of the above-described embodiments, as long as it can transmit the first pulse and the second pulse as described above. As a specific example, a local oscillator signal may be amplified to form a symmetrical power signal, and this power signal may be amplified by an amplifier whose gain changes with time to form a power signal with a first pulse having a short rising time. . Further, even in the case of forming a waveform signal with a short rising time in the above-described embodiment, the method of forming the waveform signal is arbitrary.

In the radar apparatus according to the present invention, in FIG. 8, the transmission interval between the first pulse P1 and the second pulse P2 is shifted once by the shift amount of the signal passage timing of the mask section, and then returned to the original transmission interval. Although the reflected wave of the second pulse is AD-converted twice each at the same timing, the transmission interval may be shifted so that the reflected wave of the second pulse is AD-converted three times or more at the same timing. .

In the radar device according to the present invention, target detection processing may be performed based on the slope of each peak amplitude in the distance direction for one or more angle peaks obtained by performing angle measurement processing. Target detection processing may be performed based on the slope of each peak amplitude and the slope of each peak angle in the distance direction.

1, 1A radar device 2, 2A transmission unit 3, 3A reception unit 4, 4A detection unit 5, 5A control unit 21 oscillation unit 22 waveform formation unit 23 gain control unit 24 transmission antenna 25 transmission selection unit 31 reception antenna 32 mask unit 33 Mixer section 34 AD conversion section 35 reception selection section 321 gain control section 322 gain setting section

Claims (8)

A radar device that detects a target using radio waves,
a transmitter that transmits a first pulse and a second pulse having an amplitude and a pulse width greater than those of the first pulse;
a receiver that receives reflected waves from a target of the first pulse and the second pulse that are transmitted by the transmitter;
a detection unit that detects the target based on a reflected wave signal of the reflected wave received by the receiving unit;
with
The transmitting unit forms waveforms of the first pulse and the second pulse such that the rising time of the first pulse is shorter than the rising and falling times of the second pulse,
The first pulse and the second pulse are repeatedly transmitted at a first timing having a first interval,
The reception unit has a mask unit and an AD conversion unit that repeatedly samples a signal that has passed through the mask unit at a second timing having a second interval and converts the signal into a digital signal,
The mask unit passes a part of the reflected wave signal of the first pulse for a certain period of time in synchronization with the second timing, and passes the reflected wave signal of the second pulse,
A radar apparatus that performs equivalent time sampling of the reflected wave signals of the first and second pulses by relatively shifting the first timing and the second timing. The detection unit is
detecting the target existing at a relatively short distance based on the reflected wave signal of the first pulse;
2. The radar device according to claim 1, wherein the target existing at a relatively long distance is detected based on the reflected wave signal of the second pulse. The transmission unit makes the distance interval acquired by the first pulse smaller than the distance interval acquired by the second pulse, and makes the number of times of signal acquisition at the same distance greater with the second pulse than with the first pulse. 3. The radar device according to claim 1, wherein said first timing is relatively shifted. 4. The radar apparatus according to claim 1, wherein the rise time of the gain of said mask section is equal to or shorter than the rise time of said first pulse, or the mask width is equal to or shorter than the pulse width of said first pulse. A radar device that detects a target using radio waves,
a transmitter that transmits a first pulse and a second pulse having an amplitude and a pulse width greater than those of the first pulse;
a receiver that receives reflected waves from a target of the first pulse and the second pulse that are transmitted by the transmitter;
a detection unit that detects the target based on a reflected wave signal of the reflected wave received by the receiving unit;
with
The transmitting unit forms waveforms of the first pulse and the second pulse such that the rising time of the first pulse is shorter than the rising and falling times of the second pulse,
The detecting unit determines that the intensity of the reflected wave signal of the first pulse is equal to or greater than a predetermined intensity threshold and the slope of the reflected wave signal of the first pulse in the distance direction is greater than 0 and is equal to or less than a predetermined first slope threshold. radar device, which determines that the target exists when the target becomes A radar device that detects a target using radio waves,
a transmitter that transmits a first pulse and a second pulse having an amplitude and a pulse width greater than those of the first pulse;
a receiver that receives reflected waves from a target of the first pulse and the second pulse that are transmitted by the transmitter;
a detection unit that detects the target based on a reflected wave signal of the reflected wave received by the receiving unit;
with
The transmitting unit forms waveforms of the first pulse and the second pulse such that the rising time of the first pulse is shorter than the rising and falling times of the second pulse,
The detection unit determines that the target exists when the inclination of the reflected wave signal of the first pulse in the distance direction is equal to or less than a predetermined second inclination threshold larger than 0 continuously for a predetermined reference time or longer. Do, radar equipment. The detecting unit detects the target by using the complementary point on the closer side, which has a value smaller by a predetermined value than the intensity of the reflected wave signal at the point where it is determined that the target is present, based on the first pulse. 7. The radar device according to claim 5, wherein the distance to is calculated. A method of detecting a target using a radar device comprising a transmitting unit that transmits radio waves, a receiving unit that receives radio waves, and a detecting unit that analyzes the radio waves received by the receiving unit,
a step of transmitting a first pulse and a second pulse having an amplitude and a pulse width larger than those of the first pulse by the transmitting unit;
a step of receiving reflected waves from a target of the first pulse and the second pulse transmitted in the transmitting step by the receiving unit;
a step of detecting the target based on a reflected wave signal of the reflected wave received in the receiving step by the detection unit;
with
forming waveforms of the first pulse and the second pulse so that the rise time of the first pulse is shorter than the rise and fall times of the second pulse,
the transmitting unit repeatedly transmits the first pulse and the second pulse at a first timing having a first interval;
The receiving unit has a mask unit and an AD conversion unit that repeatedly samples a signal that has passed through the mask unit at a second timing having a second interval and converts the signal into a digital signal,
The mask unit allows a part of the reflected wave signal of the first pulse to pass for a certain period of time in synchronization with the second timing, and allows the reflected wave signal of the second pulse to pass through,
A target detection method, wherein equivalent time sampling is performed on the reflected wave signals of the first and second pulses by relatively shifting the first timing and the second timing.

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