JP2024050945A - Radar device and target detection method - Google Patents

Abstract

To provide a radar device that achieves both the detection of a long distance and the detection of a short distance, and improves resolution in the short distance.SOLUTION: A radar device 1 includes: a transmission unit 2 for transmitting a first pulse, and a second pulse having larger amplitude and pulse width than the first pulse; a reception unit 3 for receiving reflection waves of the first pulse and the second pulse by a target; and a detection unit 4 for detecting the target on the basis of reflection wave signals of reflection waves received by the reception unit 3. The transmission unit 2 forms waveforms of the first pulse and the second pulse such that a rising time of the first pulse becomes smaller than a rising time and a falling time of the second pulse, at least one of the transmission unit 2 and the reception unit 3 has multiple channels, and the detection unit 4 executes target detection processing to at least one angle peak acquired by performing angle measurement processing from a reflection wave signal of the first pulse on the basis of an inclination of each peak amplitude in a distance direction, and executes distance calculation processing to each peak amplitude.SELECTED DRAWING: Figure 10

Description

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

In recent years, the use of radar devices that detect surrounding objects (targets), such as for automobile perimeter monitoring and ADAS (Advanced Driver Assistance Systems), has expanded. In particular, radar devices for automobiles are required to detect distant targets while also detecting nearby targets. When detecting nearby targets, radar devices for automobiles are required to accurately detect the positions of pedestrians, etc., for example, to prevent collisions, and to accurately detect the placement of surrounding obstacles when parking. While there is a demand to accurately detect the presence or absence of distant targets, there is a need to identify the exact position of close-by targets, particularly the closest point.

Regarding radar devices that can be used for automobiles, Patent Document 1 discloses a technology in which a pulse signal with a small pulse width is transmitted, and the receiving side performs equivalent sampling of this pulse waveform to break it down into data for multiple distance positions (distance bins) for confirmation. Patent Document 2 discloses a technology in which the transmitting side forms a pulse signal with a fast rise and fall, and the receiving side detects targets using the differential value of the received waveform. Furthermore, Patent Document 3 discloses a technology in which the receiving side performs amplitude modulation that is extremely narrow, on the order of 1/10 of the transmitting side pulse width, while keeping the transmitting side pulse width sufficiently wide, and shifts the receiving side timing.

JP 2010-216980 A JP 2002-365362 A JP 2016-516995 A

When there are multiple targets, it is difficult to separate them, especially when the difference in distance between the targets and the radar device is smaller than the resolution of the radar device. For example, when the radio wave reflection strength of a more distant target is high, the reflected wave from the closer target may be buried in the reflected wave from the more distant target, making it impossible to separate and detect the closer target. In particular, when detecting nearby targets using radar devices for automobiles, it is often required to reliably detect the nearest target without being affected by the surroundings, and to accurately detect the distance to the target, for example when detecting obstacles while parking.

The radar devices described in Patent Documents 1 to 3 are based on single pulse pattern shaping, and issues are anticipated regarding compatibility between avoiding saturation of nearby objects and detecting weak distant objects.

It is also possible to detect weak objects by making the rise of the transmission pulse steeper, but this is not desirable because it broadens the frequency band of the transmission pulse and raises concerns about the effects on surrounding devices.

In addition, in Patent Documents 2 and 3, the transmission pulse width is set relatively wide relative to the rise time, and when multiple targets are close to the vehicle, it can be difficult to separate these targets, especially to detect targets that are farther away.

In addition, as disclosed in Patent Document 1 and other documents, when performing high-speed operations on the receiving side, this is not preferable due to concerns about the effects of noise generation.

In view of this situation, the present invention aims to provide a radar device and a target detection method that can detect targets at both long and short distances and has improved resolution at short distances.

The radar device according to the present invention is a radar device that detects a target using radio waves, and includes a transmitter that transmits a first pulse and a second pulse having a larger amplitude and pulse width than the first pulse, a receiver that receives the reflected waves of the first pulse and the second pulse transmitted by the transmitter, and a detector that detects the target based on the reflected wave signal of the reflected wave received by the receiver, the transmitter forms the 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, at least one of the transmitter and the receiver has multiple channels, and the detector performs target detection processing based on the slope of each peak amplitude in the distance direction for one or more angle peaks obtained by performing angle measurement processing from the reflected wave signal of the first pulse, and performs distance calculation processing for each peak amplitude.

The present invention provides a radar device and a target detection method that can detect both long and short distances and improves the resolution at short distances.

1 is a block diagram showing a configuration of a radar device according to an embodiment of the present invention; 2 is a diagram showing a pulse waveform transmitted by a transmitter of the radar device of FIG. 1; 3 is a diagram illustrating an example of a waveform of a reflected wave of a first pulse received by a receiving unit of the radar device of FIG. 2 . 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. 4 is a diagram showing a change in the slope of the reflected wave signal in FIG. 3 . 4 is a diagram illustrating an example of a waveform of a reflected wave of a first pulse different from that shown in FIG. 3 . FIG. 8 is a diagram showing a change in the slope of the reflected wave signal in FIG. 7 . FIG. 2 is a diagram showing equivalent time sampling in the radar device of FIG. 1; 2 is a flowchart showing the procedure of a target detection method according to an embodiment of the present invention, which is performed by the radar device of FIG. 1 . FIG. 11 is a block diagram showing a configuration of a radar device according to a second embodiment of the present invention. 11 is a diagram illustrating an example of the 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 . 13 is a diagram illustrating an example of intensity distribution for each angle and distance in a case where the angular resolution in the radar device of FIG. 10 is lower than that in FIGS. 11 and 12 . FIG. 14 is a diagram showing the waveform of a reflected wave of a first pulse at an angle peak for each distance in the intensity distribution of FIG. 13 . 15 is a diagram showing a change in intensity and a judgment index value for each distance of the reflected wave signal in FIG. 14 . FIG. 14 is a diagram showing angle difference values at angle peaks for each distance in the intensity distribution of FIG. 13 .

Hereinafter, an embodiment 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 a first embodiment of the present invention.

The radar device 1 of this embodiment is a device that detects targets using radio waves. The radar device 1 includes a transmitter 2 that repeatedly transmits a first pulse P1 and a second pulse P2 having a larger amplitude and pulse width than the first pulse P1 at a first timing having a first interval as shown in FIG. 2, a receiver 3 that receives the reflected waves of the first pulse and the second pulse transmitted by the transmitter 2 from the target, a detector 4 that detects the target based on the reflected wave signal received by the receiver 3, and a controller 5 that controls the transmitter 2, the receiver 3, and the detector 4.

In the radar device 1, the first pulse P1 is used to detect targets that are relatively close, and the second pulse P2 is used to detect targets that are relatively far away. The first pulse P1 is a pulse with a relatively small pulse width to improve resolution (the ability to detect multiple targets as separate targets when the distances from the radar device 1 of the multiple targets are similar, typically when multiple targets are close to each other), and is a pulse with a relatively small amplitude to prevent the reception strength of the target's reflected wave from becoming too strong and saturating the receiving system. On the other hand, the second pulse P2 is a pulse with a relatively large amplitude and a relatively large pulse width to detect the presence of distant targets with high sensitivity, even though the reception strength becomes small due to large distance attenuation.

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

The oscillator 21 may be configured to have a known oscillator. The oscillator 21 may generate a local oscillator signal in response to control by the controller 5.

The waveform forming unit 22 forms a waveform signal that determines the waveforms of the first pulse P1 and the second pulse P2 so that the rise time of the first pulse P1 is smaller than the rise time and fall time of the second pulse P2. It is also preferable that the waveform forming unit 22 forms a waveform signal that determines the waveforms of the first pulse P1 and the second pulse P2 so that the slope of the rise of the first pulse P1 is larger than the slope of the rise and fall of the second pulse P2. Note that the "rise time" and "fall time" refer to the time for a value to increase from 10% to 90% of the peak value and the time for a value to decrease from 90% to 10% of the peak value. In addition, the slope of the rise (fall) refers to the value (absolute value) obtained by dividing 80% (90%-10%) of the peak value by the time for a value to increase from 10% to 90% of the peak value (decrease from 90% to 10%).

In this way, because the pulse width of the first pulse P1 is relatively narrow, even if there are multiple targets located near the radar device 1 and the difference in distance between them is small, the radar device can receive the radio waves reflected by each of the targets from the first pulse P1 and separate them into electrical signals representing multiple targets. Furthermore, by shortening the rise time of the first pulse P1, it is possible to prevent closer targets from being buried by more distant targets and becoming unable to be identified.

In addition, when the rise time or fall time of the waveform of the transmitted radio wave is shortened, the frequency band of the radio wave transmitted from the oscillator 21 tends to widen. However, for the purpose of accurately detecting the position of the target closest to the radar device (closest point), shortening only the rise time of the first pulse P1, which has a relatively small output, can relatively suppress the widening of the frequency band, thereby suppressing the impact on surrounding devices.

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

When forming the waveform signal W1 of the first pulse P1 by multiplying the first original waveform signal U1 and the second original waveform signal V1 with a shift, it is preferable to multiply the two original waveform signals U1 and V1 so that the waveform signal W1 of the first pulse P1 has a value (the second original waveform signal V1 has a value) at the peak of the first original waveform signal U1, which has a long rise time. More preferably, it is preferable to multiply the two original waveform signals U1 and V1 so that the waveform signal W1 of the first pulse P1 has a maximum value at the peak of the first original waveform signal U1, which has a long rise time. This makes it possible to relatively accurately and efficiently form an asymmetrical mountain-shaped waveform signal W1 whose rise time is shorter than its fall time.

In addition, the waveform forming unit 22 can form a waveform signal W2 of the second pulse P2 with a relatively long rise time and fall time by multiplying the first original waveform signal U2, which has a long rise time, with the second original waveform signal V2, which has a short rise time and is at a maximum value at least while the first original waveform signal U2 has a value.

Two original waveform signals U1/V1 and U2/V2 with different rise times can be formed by circuits with different time constants. In other words, the first original waveform signals U1 and U2 with a short rise time can be a mountain-shaped or sine-wave pulse signal output from a circuit with a large time constant, and the second original waveform signals V1 and V2 with a short rise time can be a trapezoidal pulse signal output from a circuit with a small time constant. This allows a steep rise to be selectively and relatively easily and accurately formed by adjusting the time control in the area where ensuring resolution is most required, in this case the waveform signal W1 with a small amplitude and pulse width for the vicinity, and the first pulse P1 for transmission generated based on this.

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

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

The receiver 3 has a receiving antenna 31 that receives electromagnetic waves, a masking section 32 that can pass or block the received electrical signal, a mixer section 33 that down-converts the electrical signal that has passed through the masking section 32, and an AD converter 34 that converts the intensity signal that has passed through the masking section 32 and been extracted by the mixer section 33 into a digital signal.

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

The mask unit 32 passes the reflected wave signal of the first pulse P1 for a limited time at a fixed time interval (a part of the reflected wave signal of the first pulse P1 is synchronized with the second timing having the second interval). On the other hand, the mask unit 32 passes the reflected wave signal of the second pulse P2 as a whole. That is, the mask unit 32 passes the electrical signal at a fixed time interval for a limited time (with a mask width equal to or less than the pulse width of the first pulse P1) during the substantial reception period of the first pulse P1 from when the transmitter 2 starts transmitting the first pulse P1 to when it starts transmitting the second pulse P2, as shown in the gain setting signal in FIG. 8, and passes the electrical signal continuously (passes the reflected wave signal of the second pulse P2) after starting to transmit the second pulse P2. Such a mask unit 32 is configured to be able to select whether to pass or block the electrical signal due to the reflected wave received by the receiving antenna 31. This ensures sensitivity by preventing loss of the second pulse P2 at long distances where distance attenuation is large, while ensuring resolution by blocking the first pulse P1 and the mask section 32 at short distances where the signal-to-noise ratio is abundant, as described below.

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

The AD conversion unit 34 described later does not operate at a sufficiently high speed compared to the change speed of the intensity of the first pulse P1. In addition, a low-pass filter may be installed at any stage before the AD conversion unit 34 (for example, between the AD conversion unit 34 and the mixer unit 33). For this reason, if the reflected wave signal of the first pulse P1 is passed as is, the band is limited by the action of the low-pass filter or the AD conversion unit 34, and the digital conversion is performed with a waveform in which the rising signal is blunted. In other words, even if the signal is separated by a fast rising edge, the waveform may be blunted by these band limitations, and the signals in the surrounding time may be averaged, making it difficult to separate. Therefore, at least at the stage before these band limitations, the mask unit 32 cuts out the electrical signal in a limited manner in time, so that the signal separated by the mask unit 32 can be selected. As a result, the reflected wave signal of the first pulse P1 at a specific time (i.e., a specific distance) can be converted into digital data by the AD conversion unit 34 while reducing the influence of the reflected wave signal present in the surrounding time (i.e., the reflected wave signal due to the target present in the vicinity). In this way, by performing a limited cut-off operation on the time in the masking unit 32, it is possible to maintain the time resolution and distance resolution. Note that there may be a delay in the signal transmission from the masking unit 32 to the AD conversion unit 34 due to the presence of a circuit such as a low-pass filter. In such a case, it is preferable to synchronize the gain setting signal of the masking unit 32 shown in FIG. 8 with the AD conversion unit 34 in absolute time, but to offset the gain setting signal of the masking unit 32 so that the detection value in the AD conversion unit is sufficiently large, more preferably maximum, taking into account the delay. This makes it possible to increase the SN ratio even when there is a circuit delay.

The masking unit 32 synchronizes with the AD conversion unit 34 and controls the signal passing timing to be shifted relatively for the multiple first pulses P1. In such a case, it is preferable to relatively shift the repeatedly transmitted transmission pulse with respect to the basic clock of the AD conversion unit. This allows the waveforms of the reflected wave signals of the first pulses P1 to be shifted relatively, and the signals at different timings to be converted into digital data by the AD conversion unit 34, and the detection unit 4 combines these digital data, thereby enabling equivalent time sampling to be performed in which a sampling signal slower than the AD conversion speed of the first pulses P1 is converted into a more detailed time waveform, i.e., a detailed distance waveform.

The rise time of the gain of the masking section 32 is preferably equal to or less than the rise time of the first pulse P1, and the limited pass gain width of the masking section is preferably equal to or less than the pulse width of the first pulse P1. It is more preferable that the gain waveform is rectangular or trapezoidal. In this way, the error in the intensity of the sampled reflected wave signal can be reduced. The slower and wider the time width of either the pulse operation on the transmitting side or the masking operation on the receiving side, the lower the resolution may be, but since at least the operation of the masking section 32 is not related to the emission of electromagnetic waves, the rise and fall time and gain width of the gain can be increased in speed and resolution while reducing the impact on the surrounding equipment. In other words, when obtaining the same level of resolution, the rise time and pulse width of the first pulse P1 can be made equal to or relatively larger than the rise and fall time and gain width of the gain of the masking section 32 to suppress the spread of the frequency band of the first pulse P1 emitted as electromagnetic waves, thereby suppressing the impact on the surrounding equipment.

The mixer unit 33 uses the local oscillator signal generated by the oscillator unit 21 to remove the frequency components of the carrier wave from the signal that has passed through the mask unit 32, thereby extracting an analog signal that represents the change in intensity of the reflected wave signal, i.e., the envelope wave.

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

The detection unit 4 accumulates the digital data input from the AD conversion unit 34 and identifies the position of the target that reflected the first pulse P1 and the second pulse P2 transmitted by the transmission unit 2 by analyzing the change over time of the reflected wave signal (target detection process). This detection unit 4 can be configured by a calculation device having a CPU, FPGA, memory, etc. The calculation procedure by which the detection unit 4 analyzes the change over time of the reflected wave signal is described in a program and stored.

Specific examples of phenomena, detected results, and calculation contents obtained by the above configuration are shown below. Figure 3 shows actual measurement examples of the strength (amplitude) of the reflected wave signal received by the receiver 3 when there is only one target in the vicinity area and when there are two targets in the vicinity area, with the farther target being larger (easier to reflect radio waves). As shown in the figure, since the rise time of the first pulse P1 is short, even if the strength of the reflected wave signal of the first pulse P1 by the farther target of the two targets present in the vicinity area of the radar device 1 is large, the region with a small slope near the peak of the waveform of the reflected wave by the nearby target (peak vicinity region) is less likely to be obscured by the reflected wave from the farther target. As a result, the radar device 1 can detect multiple targets separately, thereby making it possible to particularly increase the resolution at close ranges.

The detection unit 4 can determine that a target is present when the intensity of the reflected wave signal of the first pulse P1 is equal to or greater than a predetermined intensity threshold Sa, as illustrated in FIG. 3, and the slope of the reflected wave signal of the first pulse P1 is equal to or less than a predetermined first slope threshold Sg1 greater than 0, as illustrated in FIG. 5 (a diagram showing the intensity change of the received wave signal in FIG. 3, i.e., the slope in the distance direction). In FIG. 5, the distance position where the slope of the received wave signal is equal to or less than the first slope threshold Sg1 (distance bin: the time from when the transmitter 2 transmits the first pulse P1 to when the receiver 3 receives the reflected wave of the first pulse P1, converted into the distance from the radar device 1 to the target) corresponds to the front of the peak vicinity region of the waveform of the closer target in the reflected wave signal in FIG. 3.

In this way, by setting the first slope threshold Sg1 to a value greater than 0, the presence of a target can be detected at a point before the reflected wave signal reaches a peak, but not at the peak. The near side of the reflected wave signal is based on a steep rising waveform. The steepness, i.e., the loss of a large slope, is used to determine whether or not a target is present. As a result, even if the peak of the waveform of a closer target in the reflected wave signal is covered by the waveform of a more distant target, the presence of the closer target can be detected as long as the portion immediately before the peak of the waveform of the closer target is not covered by the waveform of the more distant target. Therefore, the radar device 1 can separate the closest target from targets that are further away, and detect them more reliably.

6 and 7 show the change in the intensity and the change in the slope of the reflected wave signal when two targets are present as in FIG. 3 and FIG. 5 and when the distance between the two targets is even shorter than that in FIG. 3 and FIG. 5. In this case, the relationship between the slope of the reflected wave signal and the first slope threshold Sg1 may not allow the closer target to be detected reliably. Therefore, the detection unit 4 may determine that a target is present when the slope of the reflected wave signal of the first pulse P1 is equal to or less than a predetermined second slope threshold Sg2 that is greater than 0 for a predetermined reference time Ts or more. Here, the reference time Ts is set to be equal to or more than the time interval in equivalent sampling. In other words, the detection unit 4 may determine that a target is present (this distance position is determined to be the point X0 where the target is present) when the slope of the reflected wave signal of the first pulse P1 is equal to or less than the predetermined second slope threshold Sg2 for two or more consecutive times (two times in FIG. 7). In this case, the second slope threshold Sg2 is set to a value greater than the first slope threshold Sg1, which is determined to be equal to or less than that value even once.

In this way, by continuously checking the slope of the reflected wave signal, it is possible to detect a target from an area where the steepness, i.e., the loss of a large slope, continues in a waveform that is based on a steep rise. Therefore, even if the waveform of a closer target in the reflected wave signal is covered by the waveform of a more distant target, it is possible to more reliably estimate the presence of a peak in the waveform of the closer target.

As described above, the detection unit 4 may calculate the distance to the target (distance calculation process) based on the point (distance position X0 in Figures 3, 6, and 7) at which it is determined that the target exists in comparison with the first slope threshold Sg1 or the second slope threshold Sg2 of the slope of the reflected wave signal of the first pulse P1, but may also calculate the distance to the target based on a closer complementary point (distance position X1 in Figures 3 and 6) at which the intensity of the reflected wave signal of the first pulse P1 is smaller by a predetermined value ΔR than the intensity at the point (point X0) at which it is determined that the target exists. At point X0, the change in intensity of the reflected wave signal with respect to the distance is small, so there is a risk of a large error between point X0 at which it is determined that the target exists and the actual distance position. For this reason, the complementary point X1, which is smaller by a predetermined value ΔR than the intensity at point X0, is calculated, and the distance calculation process is performed based on this, so that the distance to the target can be calculated more accurately.

The control unit 5 synchronizes the operation of the transmission unit 2, reception unit 3, and detection unit 4, allowing the detection unit 4 to properly detect targets. The control unit 5 can be configured, for example, by a calculation device having a CPU, FPGA, memory, etc., and its operation procedures are described in a program and stored. The control unit 5 is usually configured integrally with the detection unit 4. In other words, the detection unit 4 and the control unit 5 are functionally distinct, and do not need to be clearly distinguishable in terms of physical configuration and program configuration.

The control unit 5 controls the transmission unit 2 and the reception unit 3 to allow the reception unit 3 to appropriately perform equivalent time sampling of the reflected wave signal. In other words, the control unit 5 causes the transmission unit 2 to repeatedly send out the first pulse P1 and the second pulse P2, and causes the reception unit 3 to AD convert (sample) the reflected wave signals of the first pulse P1 and the second pulse P2 at relatively different timings depending on the repetition. In this way, by sampling the reflected wave signals of the first pulse P1 and the second pulse P2 in multiple different fields and combining the digital data of each field, it is possible to sample the reflected wave signals of the first pulse P1 and the second pulse P2 at an equivalently faster speed even with slow AD conversion, and more detailed time waveform information, i.e., detailed distance waveform information, can be obtained.

When performing such equivalent time sampling, the timing of the first pulse is shifted more finely than that of the second pulse in the relative timing shift for that purpose, so that the distance interval acquired by the first pulse is smaller than that acquired by the second pulse, and the number of times the second pulse acquires a signal at the same distance is greater than that of the first pulse, as shown in FIG. 8. The timing of the transmission interval between the first pulse and the second pulse can be shifted relatively. As a result, in the pulses repeatedly transmitted in each field, the detection unit 4 can improve the resolution of targets located in close range by making the distance interval acquired by the reflected wave of the first pulse P1 fine and checking the waveform in detail, while at the same distance, by checking the signal more times while making the distance interval acquired by the reflected wave of the second pulse P2 relatively coarse, it becomes easy to distinguish from noise even when the intensity of the reflected wave of the second pulse P2 is low, for example, by integrating multiple signals or performing FFT processing at relatively many points. By repeatedly transmitting the first pulse P1 and the second pulse P2 from the transmitter 2 while shifting the transmission interval, i.e., by relatively shifting the first timing, it is possible to improve the distance resolution and distance accuracy in close range, while improving the detection sensitivity in long range.

The control unit 5 may cause the transmission unit 2 to transmit two or more types of first pulses having different carrier frequencies, and cause the detection unit 4 to detect the target based on the difference or phase difference of the complex amplitude vectors of the reflected wave signals of the two or more types of first pulses. The phase of the reflected wave signal transmitted from the transmission unit 2, reflected at the target, and received by the reception unit 3 changes depending on the distance of the target and the carrier frequency. On the other hand, the phase of the received signal, which is transmitted from the transmission unit 2 and reaches the reception unit 3 directly with a propagation distance of almost zero, does not change depending on the carrier frequency. Therefore, the reception of two or more types of first pulses having different carrier frequencies can remove the components that reach the reception unit 3 directly from the transmission unit 2 by calculating the difference or phase difference of the complex amplitude vectors of the signals. In addition, by calculating such a difference, in addition to the radar's wraparound signal that is not derived from the target, the wraparound signal in the installation environment, and the noise components that wrap around from the transmission unit 2 to the reception unit 3, additional noise generated by high-speed control of the transmission pulse and high-speed mask control in the reception unit can also be removed. Therefore, by using two or more types of first pulses having different carrier frequencies, the noise can be reduced and the detection accuracy of the target can be improved. The number of types of first pulses with different carrier frequencies is at least two, and three or more types of carrier frequencies may be used in stages. Also, the propagation distance need not be strictly zero, and the complex amplitude vector of the reflected wave signal at one of the carrier frequencies may be slightly phase-rotated by a predetermined propagation distance to obtain the above difference value.

As described above, the radar device 1 according to this embodiment can separate and separately detect multiple targets that are close to each other with relatively high accuracy by using the first pulse P1, which has a short rise time, and the mask portion 32, which passes for a limited time. The radar device 1, which has such high short-distance resolution, can reliably detect the closest target when mounted on an automobile to check for surrounding obstacles while parking, for example, and can therefore safely park the automobile without contacting any obstacles.

The target detection method performed by the radar device 1 of FIG. 1 described above is itself a target detection method according to one embodiment of the present invention. As shown in FIG. 9, the target detection method performed by the radar device 1 of FIG. 1 includes 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 of the first pulse and the second pulse transmitted in the transmission step by a target (step S2: reception step), and a step of detecting a target based on a reflected wave signal of the reflected wave received in the reception step (step S3: detection step).

In the target detection method of this embodiment, in the transmission process, the waveforms of the first pulse P1 and the second pulse P2 are formed so that the rise time of the first pulse P1 is greater than the rise and fall times of the second pulse P2. In this way, by using the first pulse P1 with a short rise time, multiple targets that exist in close range can be separated and detected separately with relatively high accuracy. In addition, the method of forming the waveform and the method of processing the reflected wave signal described for the radar device 1 in Figure 1 are both configurations that can be adopted in the target detection method of this embodiment.

Next, a radar device according to a second embodiment of the present invention will be described. FIG. 10 is a block diagram showing the configuration of a radar device 1A according to a second embodiment of the present invention. The radar device 1A according to this embodiment includes a transmitter 2A that transmits a first pulse P1 and a second pulse P2, a receiver 3A that receives the reflected waves of the first and second pulses transmitted by the transmitter 2A from a target, a detector 4A that detects a target based on the reflected wave signal received by the receiver 3A, and a controller 5A that controls the transmitter 2, the receiver A3, and the detector 4A. In the description of the radar device 1A in FIG. 10, the same components as those in the radar device 1 in FIG. 1 are designated by the same reference numerals, and duplicate descriptions will be omitted.

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

The transmission selection unit 25 can be configured with a well-known selector that switches the electrical path so that the signal output from the gain control unit 23 is transmitted to only one of the transmission antennas 24 in accordance with the control unit 5A.

The receiving unit 3 has a plurality of receiving antennas 31 that receive electromagnetic waves and convert them into electrical signals, a receiving selection unit 35 that selects one of the plurality of receiving antennas, a masking unit 32 that can pass or block the electrical signal of the receiving antenna 31 selected by the receiving selection unit 35, a mixer unit 33 that extracts amplitude components from the electrical signal that has passed through the masking unit 32, and an AD conversion unit 34 that converts the signal extracted by the mixer unit 33 into a digital signal. In other words, the receiving unit 3A has a plurality of receiving channels.

The reception selection unit 35 can be configured as a well-known selector that switches the electrical path so that only the signal from one of the reception antennas 31 is supplied to the mixer unit 33 via the mask unit 32 in accordance with the control unit 5A.

The detection unit 4A can calculate the intensity information at the angle (angle bin) and distance (distance bin) by performing angle calculation processing on the reflected wave signals of the first pulse P1 in the above-mentioned multiple channels for each distance (angle measurement processing). Figure 11 shows an example of this intensity information data mapped with the angle position and distance position as the horizontal and vertical axes. Here, by combining the signals of multiple channels using angle calculation processing, the noise of each of the multiple channel signals is random, while the reflected wave signal is coherent in the direction in which the target exists, so an integration effect is obtained in the angle peak direction. For this combined signal itself, it is possible to detect the target based on the intensity change with respect to the distance similar to the above-mentioned Figures 5 and 7 for each angle, as shown by the arrows in Figure 11. This makes it possible to detect the target's position with azimuth information and high resolution in distance as described above.

In addition, instead of performing distance axis processing on all angle bins as in FIG. 11, distance axis processing as described above may be performed only on the angle peaks obtained by the angle calculation processing. Specifically, as shown in FIG. 12, after peak detection on the angle axis, the angle peak amplitudes on each distance axis are connected to obtain distance amplitude information. In addition, in the case where multiple targets are present as in FIGS. 11 and 12, if the targets can be separated as multiple peaks, the amplitudes for each distance with relatively close angle peaks that are assumed to be reflected wave signals from the same target are connected to obtain multiple distance amplitude information. This makes it possible to have azimuth information for the target, realize separation of multiple targets in the azimuth information, and realize detection with high resolution in distance as described above. While it is possible to have abundant information in FIG. 11, the calculation load can be reduced by handling only angle peaks in FIG. 12.

Next, Figure 13 shows a case where the number of antenna channels is smaller and the angular resolution is lower than in Figure 11. In this case, even if multiple targets are present, it may be difficult to separate them into two peaks on the angle axis as in Figure 12. Even in such a situation, detection with high resolution in distance can be achieved by obtaining amplitude distance information at the angle peaks.

Specifically, as shown in FIG. 13, the detection unit 4A identifies the angle at which the intensity of the reflected wave signal is maximum for each distance (extracts the maximum intensity for each distance position). FIG. 15 shows the change in the extracted maximum intensity with respect to distance. As shown in FIG. 14, the extraction of the maximum intensity may be performed by extracting only those where the intensity of the reflected wave signal at the angle peak for each distance is equal to or greater than the intensity threshold Sa. FIG. 15 shows the intensity change in the reflected wave signal in FIG. 14 in the same way as FIG. 5 and FIG. 7, but in this case, the distance between the two targets is even smaller than in FIG. 6, and the value (intensity change before correction) does not reach the detection threshold by simply calculating the intensity change (slope) between the distance bins alone, 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 in the angle value that is the angle peak for each distance. It was confirmed that the angle value changes sharply at a specific distance in the maps of FIG. 13 and FIG. 16, and in particular, the angle difference (angle slope) as shown in FIG. 16 can be extracted as a quantitative value. In addition, in the normal angle calculation process, the target's existence angle may be calculated in stages, including various calibrations. In such cases, the angle value used here does not have to be the final detected angle, but may be the difference between the angle-related index values, which are intermediate information in the angle calculation results.

Then, as shown in FIG. 15, the detection unit 4A calculates a judgment index value (corrected intensity change) by multiplying the change (slope) between distance bins of the angle (peak angle) at which the intensity becomes maximum as shown in FIG. 16 described above by a certain coefficient and subtracting the resultant value from the slope of the maximum intensity. The detection unit 4A can determine that a target exists when this judgment index value is equal to or less than a predetermined third slope threshold Sg3. Also, as in FIG. 7, the detection unit 4A may determine that a target exists (this time position is determined to be point X0) when the judgment index value is equal to or less than a predetermined threshold consecutively between multiple distance bins. By using the change in angle, targets that were previously difficult to detect can be detected more reliably. Note that the method of using the change in angle here is not limited to the above-mentioned means.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and various changes and modifications are possible. For example, in the present invention, the first pulse may have a waveform in which at least the rise time is short, and the fall time is also short like the rise time. Specifically, the first pulse may have a rectangular or trapezoidal waveform. In addition, the second pulse may have a relatively large pulse width, for example, a frequency modulated continuous wave in which the pulse width is on the order of 10 times or more that of the first pulse and the carrier frequency changes continuously.

In the radar device according to the present invention, the transmitting unit may have a configuration different from that of the above-mentioned embodiment, so long as it is capable of transmitting the first and second pulses 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 over time to form a power signal of a first pulse with a short rise time. Also, even when forming a waveform signal with a short rise time as in the above-mentioned embodiment, the method of forming the waveform signal is arbitrary.

In the radar device 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 passing timing of the mask section, and then returned to the original transmission interval, and the reflected wave of the second pulse is AD converted twice at the same timing, but the transmission interval may be shifted so that the reflected wave of the second pulse is AD converted a fixed number of times, three or more times, 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, or target detection processing may be performed based on the slope of each peak amplitude in the distance direction and the slope of each peak angle.

REFERENCE SIGNS LIST 1, 1A radar device 2, 2A transmitter 3, 3A receiver 4, 4A detector 5, 5A controller 21 oscillator 22 waveform generator 23 gain controller 24 transmitter antenna 25 transmitter selection unit 31 receiver antenna 32 masker 33 mixer 34 AD converter 35 receiver selection unit 321 gain controller 322 gain setting unit

Claims (2)

A radar device that detects targets using radio waves,
a transmitter 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 that receives reflected waves of the first pulse and the second pulse transmitted by the transmitting unit from a target;
a detection unit that detects the target based on a reflected wave signal of the reflected wave received by the receiving unit;
Equipped with
the transmitting unit forms waveforms of the first pulse and the second pulse such that a rise time of the first pulse is shorter than rise and fall times of the second pulse;
At least one of the transmitting unit and the receiving unit has a plurality of channels,
The detection unit performs a target detection process on one or more angle peaks acquired by performing an angle measurement process on the reflected wave signal of the first pulse, based on a slope of each peak amplitude in a distance direction, and performs a distance calculation process on each peak amplitude. The radar device according to claim 1, wherein the detection unit further performs target detection processing based on the slope of the peak angle and performs distance calculation processing for each peak amplitude.

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