JP2014224794A - Radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately perform a grouping of a peak for each target when there is a plurality of reflection points of a target.SOLUTION: A frequency spectrum (thereafter referred to as a first frequency spectrum) of a beat signal is calculated by subjecting the beat signal to FFT by use of the beat signal of a frequency increase segment or for T/2 of a frequency reduction segment. Further, out of the beat signal of the frequency increase segment or for the T/2 of the frequency reduction segment, only a part of a predetermined segment T' smaller than the T/2 is extracted, the extracted beat signal is used to be subjected to the FFT, and a second frequency spectrum is calculated. Respective peaks of the first frequency spectrum and the second frequency spectrum are detected and compared. Then, as to each peak of the second frequency spectrum, a grouping of a peak group of the first frequency spectrum included in the peak as one group is performed.

Description

  The present invention relates to a radar apparatus capable of grouping detected peaks from the same target into one group.

  A radar device is known as a device for detecting a target. The radar device irradiates a target with radio waves, receives a reflected wave reflected by the target, and detects a distance, speed, and direction to the target. As a method for measuring distance and speed, an FM-CW method, a multi-frequency CW method, a pulse method, and the like are known. Further, as a method for measuring the azimuth, a digital beam forming method, a phase monopulse method, and the like are known. In recent years, radar devices are also mounted on automobiles and the like, which are used for vehicle interval control and collision avoidance.

  When measuring the distance with a radar device, the target is a three-dimensional shape with a normal size, so there are multiple reflection points for one target, and as a result, multiple peaks are detected. There is. That is, although there is only one target, there is a risk of erroneous detection as if there were a plurality of targets. Therefore, it is necessary to group a plurality of detected peaks for each target (grouping) so that the number of groups matches the number of targets so that the target can be detected correctly.

  As a grouping method, there is a method described in Patent Document 1. Patent Document 1 describes that a group of peaks having the same or approximately the same distance at a plurality of azimuth angles and forming a maximum value are grouped as one group. Then, it is described that the azimuth angle of the target is detected by image recognition using a camera or the like and the grouping is corrected. For example, when two adjacent targets are detected as one group, division into two groups is performed by correction by image recognition.

JP 2010-151621

  In-vehicle radars aimed at preventing collisions have recently been required to have high resolution for detecting pedestrians. As the resolution of the radar increases, the number of peaks detected from one target increases. Therefore, the importance of a technique for grouping a plurality of detected peaks for each target is also increasing.

  However, when detecting a pedestrian with a radar, the number of detection peaks and the like vary depending on the orientation of the pedestrian. For example, when the pedestrian is sideways with respect to the radar, the azimuth width is small, and a plurality of peaks are likely to be detected in the depth direction. Therefore, accurate grouping was difficult.

  In the method of Patent Document 1, it is difficult to group pedestrians and vehicles when the vehicle and the pedestrian are adjacent to each other and the pedestrian is located in front of the vehicle. The amplitude may be smaller than the vehicle peak, and it is difficult to separate the vehicle peak from the pedestrian peak.

  In addition, unlike a target such as a vehicle, a pedestrian changes its reflection point of radio waves greatly due to movement caused by breathing, and the amplitude of a detected peak changes greatly with time. For this reason, the position of the maximum value of the pedestrian's peak group frequently changes, and accurate grouping is difficult with the method of Patent Document 1.

  Therefore, an object of the present invention is to provide a radar apparatus that can group a plurality of detection peaks with high accuracy for each target.

  In a radar apparatus that transmits a transmission wave to a target and receives a reception wave reflected by the target, a first spectrum that is a function of a physical quantity used for distance measurement is calculated using the reception wave. A first spectrum calculating means; a second spectrum calculating means for calculating a second spectrum as a function of a physical quantity used for distance measurement using a part of the frequency band of the received wave used in the first spectrum calculating means; A radar apparatus comprising: a grouping unit that groups, in each peak of two spectra, a group of first spectrum peaks at positions included in each peak from the same target .

  The physical quantity used for the distance measurement depends on the distance measuring method of the radar apparatus of the present invention. For example, the frequency is used in the FM-CW system, the phase is used in the multi-frequency CW system, and the time is used in the pulse system.

  The part of the frequency band of the received wave at the time of calculating the second spectrum may be not only a part of the received wave itself but also a part of the signal after being converted into a beat signal or a baseband signal. Further, not only the frequency band but also a section (for example, time) of a parameter directly or indirectly related to the frequency is meant.

  When the radar apparatus of the present invention is an FM-CW system, the first spectrum calculation means is a means for generating a beat signal having a difference frequency between a transmission wave and a reception wave and calculating a frequency spectrum of the beat signal. The second spectrum calculation means generates a beat signal having a difference frequency between the transmission wave and the reception wave, extracts a predetermined continuous section of the time waveform of the beat signal, and calculates a frequency spectrum of the extracted beat signal. It can be a means to do.

  When the radar apparatus of the present invention is a multi-frequency CW system, the first spectrum calculation means generates a beat signal having a difference frequency between the transmission wave and the reception wave, and calculates the frequency spectrum of the beat signal for each step. The second spectrum calculation means generates a beat signal having a difference frequency between the transmission wave and the reception wave, and calculates a phase difference spectrum between the transmission wave and the reception wave from the frequency spectrum. The frequency spectrum of the beat signal can be calculated for each of some steps among all the steps, and the spectrum of the phase difference between the transmission wave and the reception wave can be calculated from the frequency spectrum. Various methods known in the art can be used for calculating the phase difference spectrum.

  When the radar apparatus of the present invention is a pulse system, the first spectrum calculating means is means for detecting the time waveform of the received wave, and the second spectrum calculating means passes the received wave through a filter of a predetermined frequency band, It can be a means for detecting the time waveform of the transmitted reception wave. Further, a pulse compression method can be used in the present invention.

  In the radar apparatus of the present invention, the azimuth measurement result may be used for grouping. For example, peaks within a predetermined azimuth angle can be grouped into one group, and the grouping of the present invention can be further used within the group to further subdivide the group. According to this method, the load of the grouping process of the present invention can be reduced. As the azimuth measurement method, a digital beam forming (DBF) method, a phase monopulse method, or the like can be used.

  In the present invention, the first spectrum is calculated using the received signal, and the second spectrum is calculated using a part of the frequency band of the received signal, and the distance resolution is lower than that of the first spectrum. Therefore, the peak of the second spectrum is wider than the peak of the first spectrum. By using this widened peak to group the peaks of the first spectrum, it is possible to group a plurality of detected peaks with high accuracy for each target. The radar apparatus of the present invention is particularly suitable as a radar for detecting a pedestrian such as an in-vehicle radar.

1 is a diagram illustrating a configuration of a radar apparatus according to Embodiment 1. FIG. The graph which showed the time change of the frequency of a signal. The graph which showed one example of the 1st and 2nd frequency spectrum. FIG. 5 is a diagram illustrating a configuration of a radar apparatus according to a second embodiment. The graph which showed the time change of the frequency of a signal. The graph which showed the frequency spectrum in each step. FIG. 6 is a diagram illustrating a configuration of a radar apparatus according to a third embodiment. The graph which showed the time waveform of the transmission signal. The graph which showed one example of the 1st and 2nd time waveform. FIG. 6 is a diagram illustrating a configuration of a radar apparatus according to a fourth embodiment. The graph which showed the waveform of the transmission signal.

  Specific examples of the present invention will be described below, but the present invention is not limited to the examples.

  FIG. 1 is a diagram illustrating a configuration of a radar apparatus according to the first embodiment. The radar apparatus according to the first embodiment is an apparatus that uses the FM-CW method for measuring distance and speed and uses the phase monopulse method for measuring azimuth. As shown in FIG. 1, the radar apparatus according to the first embodiment includes an oscillator 10, a directional coupler 11, a transmission antenna 12, K reception antennas 13-1 to 13 -K, a switch 14, and a mixer 15. And a band pass filter 16, an AD converter 17, and a signal processing unit 18.

  Hereinafter, each configuration of the radar apparatus according to the first embodiment will be described, and the operation thereof will be described.

The oscillator 10 oscillates a frequency-modulated signal (transmission signal) as shown in FIG. Specifically, the transmission signal is a triangular wave having a period T, a frequency displacement width ΔF, and a center frequency f _0, and the frequency increases ΔF linearly with respect to time in the interval ₀ to T / 2. In the interval from 2 to T, the frequency decreases by ΔF linearly with respect to time. The oscillator 10 is connected to the input port of the directional coupler 11.

  The transmission signal may be a sawtooth wave in which the frequency increases or decreases ΔF linearly with respect to time in the interval from 0 to T.

  A transmission signal from the oscillator 10 is input to the directional coupler 11. The directional coupler 11 has an output port connected to the transmission antenna 12 and a coupling port connected to the mixer 15. The transmission signal from the oscillator 10 is branched and output to the transmission antenna 12 and the mixer 15.

  A transmission signal is input to the transmission antenna 12 from the oscillator 10 via the directional coupler 11, and a transmission wave is radiated as an electromagnetic wave from the transmission antenna 12. The receiving antennas 13-1 to 13-K receive the received waves reflected by the target, respectively. A microstrip antenna or the like can be used for the transmission antenna 12 and the reception antennas 13-1 to 13 -K.

  The switch 14 is connected to the K receiving antennas 13-1 to 13 -K on the input side, and is connected to the mixer 15 on the output side. One of the reception antennas 13-1 to 13 -K is selected by the switch 14, and a reception signal from the selected reception antenna 13 is input to the mixer 15.

  The mixer 15 has two input terminals respectively connected to the coupling port of the directional coupler 11 and the output terminal of the switch 14, and mixes the transmission signal from the directional coupler 11 and the reception signal from the switch 14. Output. Then, the output signal is passed through the band pass filter 16 to extract a beat signal. The beat signal is a signal having a frequency that is the difference between the frequency of the transmission signal and the frequency of the reception signal. The beat signal is sampled as a digital signal by the AD converter 17 and input to the signal processing unit 18.

  As shown in FIG. 1, the signal processing unit 18 includes a first spectrum calculating unit 18a, a second spectrum calculating unit 18b, and a grouping unit 18c. The beat signal is input to the first spectrum calculating unit 18a and the second spectrum calculating unit 18b, respectively, and the frequency spectrum is calculated. And a target is detected based on the frequency spectrum. The operation in the signal processing unit 18 will be described in detail later. The signal processing unit 18 can be a computer equipped with a CPU, memory, storage, input / output device, and the like, and various signals in the first spectrum calculation unit 18a, the second spectrum calculation unit 18b, and the grouping unit 18c are programmed. Processing can be performed. Note that the processing equivalent to that of the bandpass filter 16 may be realized as digital processing in the signal processing unit 18 without providing the bandpass filter 16.

  Next, the operation of the radar apparatus according to the first embodiment will be described.

In the radar apparatus according to the first embodiment, the signal processing unit 18 calculates the frequency spectrum by performing FTT (Fast Fourier Transform) on the beat signal input to the signal processing unit 18, and calculates the target spectrum from the peak position of the frequency spectrum. The distance L and speed V are measured. Specifically, the frequency spectrum of the beat signal in the frequency increase interval (0 to T / 2 interval in FIG. 2) is calculated, the beat frequency fu is obtained from the peak position, and the frequency decrease interval (T / T in FIG. 2) is calculated. 2 to T), the beat frequency fd is calculated from the peak position, and L = cT (fu + fd) / (8ΔF), where c is the speed of light and the distance L is The speed V can be calculated by V = c (fd−fu) / (4f ₀ ).

  Further, the orientation of the target can be measured by a DBF, a phase monopulse method, or the like by receiving a reception signal from each reception antenna 13 by switching the switch 14.

  Here, the target is a three-dimensional shape having a normal size. Therefore, if the distance resolution is high, there may be a plurality of reflection points of the target. If ΔF is sufficiently large, that is, if the distance resolution is sufficiently high, there will be a plurality of peaks corresponding to each reflection point in the frequency spectrum of the beat signal. For example, in an in-vehicle radar, a vehicle or a pedestrian is a target, but when the target is a pedestrian, peaks 1 to 5 exist. In order to detect the target correctly, it is necessary to group these peaks for each target.

  Therefore, in the radar apparatus of the first embodiment, the signal processing unit 18 performs grouping by performing signal processing as follows.

  The beat signal input to the signal processing unit 18 is processed as follows in each of the first spectrum calculating unit 18a and the second spectrum calculating unit 18b.

  The first spectrum calculation means 18a performs FFT (Fast Fourier Transform) using the beat signal of T / 2 in the frequency increasing section or the frequency decreasing section to perform the frequency spectrum of the beat signal (hereinafter referred to as the first frequency spectrum). Is calculated.

  Further, the second spectrum calculating means 18b extracts only the portion of the predetermined section T ′ smaller than T / 2 from the beat signal for T / 2 in the frequency increasing section or the frequency decreasing section, and the extracted beat The second frequency spectrum is calculated by performing FFT using the signal. The section T ′ is set to an appropriate value depending on the radar device configuration, measurement environment, target type, and the like.

  A method other than FFT may be used for frequency analysis in the first spectrum calculation unit 18a and the second spectrum calculation unit 18b.

  The grouping unit 18c detects and compares the respective peaks of the first frequency spectrum and the second frequency spectrum. Then, for each peak of the second frequency spectrum, grouping is performed with the peak group of the first frequency spectrum included in the peak as one group.

  Here, the beat signal in the section T ′ used to calculate the second frequency spectrum corresponds to a beat signal when the frequency displacement width of the transmission signal is ΔF · 2T ′ / T (FIG. 2). reference). Since the frequency displacement width is smaller than when the frequency displacement width is ΔF, the frequency resolution is low, and the peak that can be separated in the first frequency spectrum cannot be separated in the second frequency spectrum. That is, in the first frequency spectrum, a plurality of reflection points existed in one target, and thus a plurality of peaks existed. In the second frequency spectrum with low resolution, a plurality of reflection points of the target were present. Cannot be distinguished from each other, and there is one peak for one target. From this, when the first frequency spectrum and the second frequency spectrum are superimposed, the peak group of the first frequency spectrum included in one peak of the second frequency spectrum is derived from one target. I can say things. Therefore, grouping can be performed by dividing the peak of the first frequency spectrum for each such peak group.

  Whether or not the peak of the first frequency spectrum is included in the peak of a certain second frequency spectrum is determined as follows, for example. First, two local minimum values existing immediately before and after a certain second frequency spectrum peak are extracted. If there is no minimum value, a point that is equal to or less than a predetermined threshold is extracted. The peak of the first frequency spectrum existing between the two minimum values is included in the peak of the second frequency spectrum. In addition, the inclusion of the peak may be determined based on the half width of the peak.

  FIG. 3 is a diagram illustrating an example of the first frequency spectrum and the second frequency spectrum. The grouping method will be specifically described with reference to FIG. In the first frequency spectrum shown in FIG. 3, there are eight peaks a to h in order from the low frequency side. Note that the peak existing in the vicinity of the frequency of 0 is due to the influence of the sneak of the transmission wave, and is ignored here. On the other hand, the second frequency spectrum has two peaks A and B in order from the low frequency side. Among these two peaks, four peaks a to d of the first frequency spectrum exist between the minimum values of the peak A on the low frequency side. Therefore, these four peaks a to d are set as one group. Also, four peaks e to h of the first frequency spectrum exist between the minimum values of the peak B on the high frequency side among the peaks of the second frequency spectrum. These four peaks e to h are set as one group. As described above, the eight peaks of the first frequency spectrum are grouped into two peak groups.

  In the above grouping, it is also possible to use a grouping using a direction detection result. The grouping using the detection result of the azimuth can be performed, for example, by grouping peaks existing within a predetermined azimuth angle range as one group. By the grouping using the azimuth detection result, the grouping result can be corrected, or the group can be subdivided. Further, by performing grouping using the orientation detection result first and then performing the grouping later, the load of the grouping process can be reduced.

  As described above, according to the radar apparatus of the first embodiment, it is possible to perform grouping with high accuracy for each target when there are a plurality of peaks for spectrum peaks used for distance measurement.

  Further, when measuring the speed, it is necessary to associate the peak of the frequency spectrum in the frequency increasing section with the peak of the frequency spectrum in the frequency decreasing section (referred to as pairing). If grouping is performed, a pairing combination may be searched in the same group, and the load of the pairing process can be reduced.

  FIG. 4 is a diagram illustrating a configuration of the radar apparatus according to the second embodiment. The radar apparatus according to the second embodiment measures distance and speed by a multi-frequency CW method. As shown in FIG. 4, the radar apparatus according to the second embodiment is obtained by replacing the oscillator 10 and the signal processing unit 18 of the radar apparatus according to the first embodiment with an oscillator 20 and a signal processing unit 28, respectively. This is the same as the radar apparatus of the first embodiment.

The oscillator 20 oscillates a transmission signal whose frequency changes as shown in FIG. This transmission signal repeats the frequency increasing stepwise with respect to time and returning. As shown in FIG. 5, with f ₀ as an initial value, the frequency increases step by step at time intervals t by f ₀ , f ₀ + Δf, f ₀ + 2Δf,. The above natural number) returns to the original frequency f ₀ . Contrary to the above, a signal whose frequency decreases stepwise with respect to time can be used as the transmission signal, or a signal that repeatedly increases and decreases stepwise can be used.

  The signal processing unit 28 includes a first spectrum calculation unit 28a that will be described below with respect to the first spectrum calculation unit 18a, the second spectrum calculation unit 18b, and the grouping unit 18c in the signal processing unit 18 in the radar apparatus according to the first embodiment. The second spectrum calculating unit 28b and the grouping unit 28c are used.

In the radar apparatus according to the second embodiment, frequency analysis is performed on the beat signal in each step to calculate a frequency spectrum, and a phase difference is obtained from the frequency spectrum to calculate a distance. The specific method is as follows (see FIG. 6). A total of n corresponding peak values are extracted from each frequency spectrum. The peak value is a complex value including the phase value that is the phase difference between the transmitted wave and the received wave, and the phase θ _k in k steps is θ _k = 2π · (2R / c) · (f ₀ + kΔf), where Where R is the distance to the reflection point of the target and c is the speed of light. The extracted peak values are arranged in ascending order of the number of steps to form the array S. Then, the array S is Fourier transformed in the frequency step direction to obtain a 2R / c spectrum, and the peak of the spectrum is extracted to calculate the distance R of the target. Note that the frequency spectrum obtained by frequency analysis of the beat signal indicates the Doppler frequency, and the difference in peak position indicates the difference in speed. Therefore, it is possible to separately detect targets having different speeds at the same distance. In the case of FIG. 6, by forming the array S with the peak value of the Doppler frequency f1 and the peak value of f2, the distance can be detected separately.

  Also in the radar apparatus of the second embodiment, if Δf or the number of steps is large, the target may have a plurality of reflection points. In such a case, the spectrum obtained by Fourier transforming the array S has a plurality of spectra. Has a peak. Therefore, the radar apparatus according to the second embodiment performs grouping as follows.

  First, the first spectrum calculation means 28a of the signal processing unit 28 performs FFT on the beat signal for each step to calculate a frequency spectrum. Then, a total of n peak values having the same Doppler frequency are extracted from each frequency spectrum. The array S is configured by arranging those peak values in ascending order of the number of steps. The array S is configured for each speed when there are a plurality of targets having different speeds. The array S is subjected to FFT to calculate a spectrum (hereinafter referred to as a first spectrum).

  Next, a part of the array S is extracted by the second spectrum calculation means 28 b of the signal processing unit 28. That is, out of n elements of the array S, a predetermined number n 'elements smaller than n are extracted and set as the array S'. Using this array S ', a spectrum (hereinafter referred to as a second spectrum) is calculated in the same manner as described above. The number of elements n ′ of the array S ′ is set to an appropriate value depending on the radar apparatus configuration, measurement environment, target type, and the like.

  Next, the grouping unit 28c of the signal processing unit 28 performs grouping in the same manner as the grouping unit 18c in the radar apparatus of the first embodiment. That is, the respective peaks of the first spectrum and the second spectrum are detected and compared. Then, for each peak of the second spectrum, the peak group of the first spectrum included in the peak is grouped as one group. The determination of whether or not the peak is included is the same as in the first embodiment.

  The reason why grouping is possible by the above method is the same as in the first embodiment. In the distance measurement by the multi-frequency CW method, the frequency modulation width of the transmission signal, that is, Δf · n determines the distance resolution. Since the array S ′ uses a part of the elements of the array S extracted, this corresponds to setting the frequency modulation width of the transmission signal to Δf · n ′. Therefore, when the array S ′ is used, the distance resolution is lower than when the array S is used. As a result, in the second spectrum, a plurality of reflection points of the target cannot be distinguished, and one peak exists for one target. From this, it can be said that the peak group of the first spectrum included in the peak of the second spectrum is derived from a plurality of reflection points of a certain target, and grouping can be performed by the above method.

  As described above, according to the radar apparatus of the second embodiment, it is possible to perform grouping with high accuracy as in the radar apparatus of the first embodiment.

  FIG. 7 is a diagram illustrating the configuration of the radar apparatus according to the third embodiment. The radar apparatus according to the third embodiment measures distance by a pulse method. That is, the target distance is measured from the time delay of the pulse. As shown in FIG. 7, the radar apparatus according to the third embodiment is the same as the radar apparatus according to the first embodiment, except that the oscillator 10 is replaced with the oscillator 30 and a switch 39 is provided between the directional coupler 11 and the transmission antenna 12. 15 is replaced with band-pass filters 36a and 36b, AD converters 37a and 37b, and a signal processing unit 38. Other configurations are the same as those of the radar apparatus of the first embodiment. Hereinafter, components different from those in the first embodiment will be described.

  The oscillator 30 oscillates a signal that is a continuous wave having a predetermined frequency. The switch 39 conducts / cuts off the signal from the directional coupler 11 at a predetermined interval. The switch 39 adjusts the signal from the oscillator 30 into a pulse shape having a pulse width τ (see FIG. 8). Then, a pulsed transmission wave is transmitted from the transmission antenna 12.

  The output side of the mixer 15 is connected to the bandpass filters 36a and 36b, respectively, and the signals output from the mixer 15 are input to the bandpass filters 36a and 36b, respectively. The bandpass filter 36a is the same as the bandpass filter 16a, whereby a signal in a predetermined band is transmitted and a signal is extracted. Further, a band pass filter having a narrower frequency pass band than the band pass filter a is used as the band pass filter b. The output sides of the bandpass filters 36a and 36b are connected to the signal processing unit 38 via AD converters 37a and 37b, respectively. Note that the passband of the bandpass filter 36b is set to an appropriate value depending on the configuration of the radar apparatus, the measurement environment, the type of the target, and the like.

  As shown in FIG. 7, the signal processing unit 38 includes a first spectrum calculation unit 38a, a second spectrum calculation unit 38b, and a grouping unit 38c. Signals from the bandpass filters 36a and 36b are input to the first spectrum calculating unit 38a and the second spectrum calculating unit 38b, respectively.

  Also in the radar apparatus according to the third embodiment, if the pulse width τ is small, the target may have a plurality of reflection points. In such a case, the first time waveform detected by the first spectrum calculation unit 38a. Has multiple peaks. Therefore, the radar apparatus according to the third embodiment performs grouping as follows.

  First, the first spectrum calculation means 38a detects the time waveform of the signal from the bandpass filter 36a (hereinafter referred to as the first time waveform). Similarly, the second spectrum calculation means 38b detects the time waveform of the signal from the bandpass filter 36b (hereinafter referred to as the second time waveform).

  Next, the grouping unit 38c of the signal processing unit 38 extracts the peaks of the first time waveform and the second time waveform, respectively. The peak positions of the first time waveform and the second time waveform are compared, and the peaks of the first time waveform included in the peaks are grouped for each peak of the second time waveform. The method for determining whether or not the peak is included is the same as in the first and second embodiments.

  The grouping will be specifically described with reference to an example of the first and second time waveforms shown in FIG. In the example shown in FIG. 9, two peaks A and B exist in the second time waveform. There are seven peaks a to g in the first time waveform. The peak A of the second time waveform includes the peaks a to c of the first time waveform, and the peak B of the second time waveform includes the peaks d to g of the first time waveform. Therefore, among the seven peaks of the first time waveform, the peaks a to c are grouped into one group, and the peaks d to g are grouped into one group.

  The reason why accurate grouping can be performed by the above method is the same as in the first embodiment. In the distance measurement by the pulse method, the distance resolution is determined by the pulse width, and the distance resolution decreases as the pulse width increases.

  Here, the pulse width of the pulse and the frequency band are in an inversely proportional relationship. The pass band of the band pass filter 36b is narrower than the pass band of the band pass filter 36a. Therefore, the signal output from the bandpass filter 36b has a wider pulse width than the signal output from the bandpass filter 36a.

  Therefore, the time waveform of the signal output from the bandpass filter 36b has a lower distance resolution (time resolution) than the signal output from the bandpass filter 36a. As a result, in the second time waveform, a plurality of reflection points of the target cannot be distinguished, and one peak exists for one target. From this, it can be said that the peak group of the first time waveform included in the peak of the second time waveform is derived from a plurality of reflection points of a certain target, and grouping can be performed by the above method.

  As described above, the radar apparatus according to the third embodiment can perform grouping with high accuracy in the same manner as the radar apparatuses according to the first and second embodiments.

  FIG. 10 is a diagram illustrating the configuration of the radar apparatus according to the fourth embodiment. The radar apparatus according to the fourth embodiment measures distance by a pulse compression method. As shown in FIG. 10, the radar apparatus according to the fourth embodiment includes oscillators 40a and 40b, switches 14 and 49, an expander 41, a directional coupler 11, mixers 45a and 45b, a transmission antenna 12, and a reception. Antennas 13-1 to 13 -K, band pass filters 46 a and 46 b, compressors 42 a and 42 b, AD converters 37 a and 37 b, and a signal processing unit 48 are included. In addition, the same code | symbol is used about the part with the same structure as the radar apparatus of Example 3. FIG.

  Each configuration and operation of the radar apparatus according to the fourth embodiment will be described more specifically.

  A signal from the oscillator 40 b is input to the switch 49. The switch 49 conducts / cuts off a signal from the oscillator 40b at a predetermined interval. The switch 49 adjusts the signal from the oscillator 40b into a pulse shape having a pulse width τ.

  The decompressor 41 performs FM modulation on the pulse signal from the switch 49 so that the frequency of the signal linearly increases by ΔF as the time τ increases (see FIG. 11).

  A signal from the oscillator 40 a is input to the mixers 45 a and 45 b by the directional coupler 11. In the mixer 45b, the signal from the oscillator 40a and the signal from the expander 41 are mixed, frequency-converted, and output. The output side of the mixer 45 b is connected to the transmission antenna 12.

  Since the transmission antenna 12, the reception antennas 13-1 to 13-K, and the switch 14 are the same as those in the third embodiment, description thereof is omitted.

  The received signal from the switch 14 and the signal from the oscillator 40a are input to the mixer 45a. The mixer 45a mixes the two signals and passes them through band-pass filters 46a and 46b to convert them into baseband signals. A band pass filter 46b having a narrower pass band than the band pass filter 46a is used.

The signals that have passed through the bandpass filters 46a and 46b are input to the compressors 42a and 42b, respectively. The compressors 42a and 42b are filters whose frequency characteristics with respect to the delay time are inverted from those of the expander 41. By the compressors 42a and 42b, the pulse width of the input signal is compressed from τ to 1 / ΔF, and the amplitude is increased to (τ.ΔF) ^1/2 .

  As described above, in the radar apparatus according to the fourth embodiment, the expander 41 and the compressors 42a and 42b ensure the detection distance by increasing the average power by increasing the pulse width τ when transmitting a signal and increasing the average power. The distance resolution can be increased by compressing the pulse width during reception.

  As shown in FIG. 10, the signal processing unit 48 includes a first spectrum calculating unit 48a, a second spectrum calculating unit 48b, and a grouping unit 48c. The signals output from the compressors 42a and 42b are input to the first spectrum calculation unit 48a and the second spectrum calculation unit 48b, respectively.

  The radar apparatus according to the fourth embodiment performs grouping in the same manner as the radar apparatus according to the third embodiment. That is, the first spectrum calculation means 48a obtains the time waveform of the input signal (referred to as the first time waveform), and the signal input to the second spectrum calculation means 48b (referred to as the second time waveform). And the grouping unit 48c extracts the peaks of the first time waveform and the second time waveform, respectively. Then, the peak positions of the first time waveform and the second time waveform are compared, and the peaks of the first time waveform included in the peaks are grouped for each peak of the second time waveform.

  Thereby, the reason why accurate grouping can be performed is the same as in the third embodiment. Since the pass band of the band pass filter 46b is narrower than the pass band of the band pass filter 46a, the signal input to the second spectrum calculating unit 48b is more distance-resolving than the signal input to the first spectrum calculating unit 48a. This is because of a low.

  As described above, the radar apparatus according to the fourth embodiment can also perform grouping with high accuracy in the same manner as the radar apparatuses according to the first to third embodiments.

[Modification]
The radar apparatus of the present invention is not limited to the distance and speed measurement methods shown in the embodiments. For example, the present invention can be applied to various conventionally known measurement methods such as a method combining the FMCW method and the multi-frequency CW method. In any method, in addition to the first spectrum used for the original distance measurement, the second spectrum is calculated using a part of the frequency band of the received wave used for the distance measurement, and at each peak of the second spectrum, If the peak group of the first spectrum included in the peak is grouped as one group, the grouping for each target can be performed with high accuracy.

  In addition, as a direction measurement method, the radar apparatus shown in the embodiment provides a plurality of reception antennas and measures the direction by DBF or phase monopulse method. However, the present invention is not limited to this. The orientation may be measured by scanning automatically.

  Moreover, although the radar apparatus of Examples 1-4 measured the distance, speed, and direction of a target, the radar apparatus of this invention should just measure at least distance, and a speed and direction This measurement is not always necessary.

  Also, in the second to fourth embodiments, as described in the first embodiment, it is possible to use a grouping that uses the direction detection result in combination.

  The radar apparatus of the present invention can be used as, for example, an on-vehicle radar to detect a pedestrian.

10, 20, 30, 40a, b: oscillator 11: directional coupler 12: transmitting antenna 13-1 to 13-K: receiving antenna 14, 49: switch 15, 45a, b: mixer 16, 36a, b, 46a , B: band pass filter 17, 37a, b: AD converter 18, 28, 38, 48: signal processing unit 18a, 28a, 38a, 48a: first spectrum calculating means 18b, 28b, 38b, 48b: second spectrum Calculation means 18c, 18c, 38c, 48c: Grouping unit 41: Expander 42a, b: Compressor

Claims (7)

In a radar apparatus that transmits a transmission wave to a target and receives a reception wave reflected by the target,
First spectrum calculation means for calculating a first spectrum that is a function of a physical quantity used for distance measurement using the received wave;
Second spectrum calculating means for calculating a second spectrum that is a function of a physical quantity used for distance measurement using a part of the frequency band of the received wave used in the first spectrum calculating means;
In each peak of the second spectrum, a grouping unit that groups the peak group of the first spectrum at a position included in each peak as from the same target,
A radar apparatus comprising: The radar apparatus is an FM-CW system,
The first spectrum calculation means is a means for generating a beat signal having a difference frequency between the transmission wave and the reception wave, and calculating a frequency spectrum of the beat signal as a first spectrum,
The second spectrum calculation unit generates a beat signal having a difference frequency between the transmission wave and the reception wave, extracts a predetermined continuous section of the time waveform of the beat signal, and extracts the frequency spectrum of the extracted beat signal. Is a means for calculating as a second spectrum,
The radar apparatus according to claim 1. The radar apparatus is a multi-frequency CW system,
The first spectrum calculation means generates a beat signal having a difference frequency between the transmission wave and the reception wave, calculates a frequency spectrum of the beat signal for each step, and uses the transmission wave from the frequency spectrum. And a means for calculating a spectrum of a phase difference between the received wave and the received wave as a first spectrum,
The second spectrum calculation means generates a beat signal having a difference frequency between the transmission wave and the reception wave, and calculates a frequency spectrum of the beat signal for each step with respect to some steps among all steps. , Means for calculating a spectrum of a phase difference between the transmission wave and the reception wave as a second spectrum from the frequency spectrum,
The radar apparatus according to claim 1. The radar device is a pulse system,
The first spectrum calculating means is means for detecting a time waveform of the received wave as a first spectrum,
The second spectrum calculating means is means for passing the received wave through a filter of a predetermined frequency band and detecting a time waveform of the transmitted received wave as a second spectrum.
The radar apparatus according to claim 1.   The radar apparatus according to claim 4, wherein the radar apparatus is a pulse compression method. It further has an orientation detection means,
Grouping based on the detected orientation, and then grouping each group by the grouping unit,
The radar apparatus according to any one of claims 1 to 5, wherein the radar apparatus is characterized in that:   The grouping unit extracts, in each peak of the second frequency spectrum, two local minimum values that exist immediately before and after the peak, and the same peak group of the first frequency spectrum that exists between the local minimum values. The radar device according to claim 1, wherein the radar device is grouped as a target from the target.

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