JP2008145425A - Radar device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely discriminate a plurality of targets by a radar device. <P>SOLUTION: Transmission signals having three or more kinds of frequencies are outputted from an oscillator 10, and transmission waves are radiated from a transmitting antenna 14 toward a target 100. Reflected waves are received by a receiving antenna 16, and the transmission signal is mixed with a receiving signal by a mixer to generate a beat signal. A signal processing device 24 detects a Doppler frequency signal from the beat signal by FFT and detects a distance to the target 100 by Fourier analysis, by using a complex signal component of the Doppler frequency signal in each channel as a progression. The maximum detection distance is increased by differentiating a frequency difference between the three or more kinds of transmission signals. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radar device, and more particularly to a CW radar device using a continuous wave.

  When the vicinity of a vehicle is monitored with a radar, the target may not be detected due to the influence of a reflected wave from a stationary object such as a utility pole or guardrail. Since there are a large number of stationary objects on a general road, the detection performance of the target may deteriorate as the viewing angle of the radar is increased. In such a situation, the CW radar as described in Non-Patent Document 1 can separate the target due to the difference in relative speed, and thus can easily detect the target without the influence of a stationary object. However, a CW radar only detects a signal with a single Doppler frequency even when there are a plurality of targets having the same speed and different distances.

  FIG. 20 shows a configuration of a conventional two-frequency CW radar apparatus, and FIG. 21 shows a transmission wave. As shown in FIG. 21, the oscillator 10 outputs transmission signals of two types of frequencies, f0 and f0 + Δf, and transmits them from the transmission antenna 14. The reflected wave from the object is received by the receiving antenna 16 and mixed with the transmission signal by the mixer 18 to generate a beat signal. A beat signal is extracted by the BPF 20 via the changeover switch 19, converted to a digital signal by the A / D 22, and supplied to the signal processing device 24. The signal processing device 24 performs FFT processing on the beat signal to obtain the spectrum shown in FIG. 22, and the relative velocity with the object is detected from the Doppler frequency. When there are a plurality of targets having the same relative velocity, a signal having the same Doppler frequency is received as described above although a signal having a different signal amplitude and phase is received from each target. One signal. For this reason, in the CW radar that calculates the distance from the phase information of the signal of the Doppler frequency, it is difficult to correctly detect each distance by separating a plurality of targets having the same relative velocity.

  In situations where the vehicle moves and approaches a stationary target, it is expected that there will be multiple other stationary objects in the vicinity.In this case, the distance to the approaching target can be detected correctly for the above reason. It becomes difficult.

  On the other hand, in Patent Document 1, a transmission signal is modulated with a signal generated by a sawtooth frequency generator and input to a mixer so that a frequency difference corresponding to the propagation delay time of radio waves can be detected. Can distinguish and detect targets with different distances.

MERRILL I.SKOLNIK, "RADAR SYSTEM", McGRAW-HILL BOOK COMPANY, INC, p106-p111 Japanese Patent Laid-Open No. 2003-167048 Japanese Patent No. 3746235

  However, the radar apparatus of Patent Document 1 requires a sawtooth frequency generator and a modulator for modulating a transmission signal using a sawtooth frequency signal, and the circuit configuration is complicated.

  An object of the present invention is to provide a radar apparatus which can detect a distance and a speed of each target equally by separating a plurality of targets having different distances at the same speed with a simple configuration.

  The present invention includes an oscillator having a variable oscillation frequency, a transmission antenna that transmits a signal generated from the oscillator, a reception antenna that receives a reflected wave of the transmission wave from an object, a reception signal from the reception antenna, and the A mixer that mixes transmission signals, and a signal processing circuit that detects a distance to the object and a velocity of the object based on a beat signal generated by the mixer, and the oscillator is a continuous wave Three or more types of transmission signals of different frequencies are output, and the signal processing circuit detects the speed by detecting the Doppler frequency by frequency analysis of the beat signals obtained from the transmission signals of the respective frequencies, The distance is detected by detecting the propagation delay time using the amplitude and phase information of the signal of the Doppler frequency obtained by frequency analysis, and the transmission signal of the different frequency is detected. Unlike wavenumber intervals, and at least one of the frequency intervals being different and successive integral multiples of the frequency difference Δf of the reference. Here, different frequency intervals of transmission signals of different frequencies means that at least one of the frequency intervals is different, if only any one frequency interval is different, if any one of a plurality of frequency intervals is different, Any case where all frequency intervals are different is included. Also, if any frequency interval is different from the continuous integer multiple of the reference frequency difference Δf, the frequency interval is 1 time, 2 times, 3 times, 4 times, 5 times, 6 times,... If the frequency interval is not an integral multiple of Δf, for example, 0.5 times, for example, 1 time, 2 times, 4 times, 5 times, 6 times,. Any of the following cases are included. When the frequency interval is 1 time, 2 times, 2.5 times, 3 times, 4 times, 5 times, 6 times, etc., respectively, or when the frequency interval is 1 time, 2 times, 3 times, 4.7 times, 5.5 times, 6.2 times, etc.

  In the present invention, when three or more types of transmission waves having different frequencies are transmitted toward an object, a reflected wave from the object is received, and a beat signal obtained by mixing the transmission signal and the reception signal is frequency-analyzed, The amplitude spectrum of each channel is theoretically the same, and is detected as a signal of Doppler frequency generated in the object. In the spectrum of each channel, the spectrum obtained by arranging complex signal components of Doppler frequency in ascending order of frequency and further analyzing the frequency by a method such as Fourier analysis is the dimension of propagation delay time, and there are multiple objects of the same speed In addition, they are detected separately according to the propagation delay time. For example, when two objects having different distances exist in a signal of a certain Doppler frequency, they are detected as two signals according to the propagation delay time (that is, the distance). And the maximum detection distance is lengthened by making the frequency interval of the transmission wave of a different frequency different.

  According to the present invention, it is possible to correctly detect the distance and speed of each target by separating a plurality of targets having different distances at the same speed with a simple configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a case where the frequency of a transmission signal is set at a constant interval will be described as a reference example. By taking these reference examples into consideration, the effectiveness of the present embodiment will become more apparent.

<First Reference Example>
FIG. 1 is a block diagram showing the configuration of a radar apparatus according to this reference example. The radar apparatus includes an oscillator 10 having a variable oscillation frequency, a directional coupler 12 that branches an output signal of the oscillator 10, that is, a transmission signal, and a transmission that radiates a transmission wave corresponding to a transmission signal from the directional coupler 12. The antenna 14, the reception antenna 16 that receives the radio wave reflected by the target 100, the mixer 18 that mixes the reception signal from the reception antenna 16 and the transmission signal branched by the directional coupler 12, and the transmission signal from the mixer 18 A band pass filter (BPF) 20 that extracts a beat signal having a frequency difference between the frequency and the frequency of the received signal is provided. If there is a relative speed between the target 100 and the radar apparatus, a frequency shift occurs due to the Doppler effect, and a difference occurs between the frequencies of the transmission signal and the reception signal. A signal having the difference frequency is extracted as a beat signal by the mixer 18 and the BPF 20. The extracted beat signal is sampled as a digital signal by the A / D converter 22 and supplied to the signal processing device 24. The signal processing device 24 processes the input digital signal to obtain information on the target 100. In the present embodiment, the A / D converter 22 digitizes the beat signal, but the beat signal may be processed as an analog signal.

  FIG. 2 shows the frequency of the transmission signal that is the output signal of the oscillator 10 in FIG. 1, that is, the frequency of the transmission wave. In the figure, the horizontal axis represents time and the vertical axis represents frequency. The fundamental frequency is f0, and f is transmitted by changing n types (where n is 3 or more) at a frequency interval Δf from f0 to f0 + (n−1) Δf, and the reflected wave from the target 100 is received by the receiving antenna 16. In the case of n = 3, transmission waves having frequencies of f0, f0 + Δf, and f0 + 2Δf are transmitted. A plurality of targets 100 may exist. However, it is assumed that the position and speed of the target 100 hardly change during the entire observation time. The frequency of the reflected wave is shifted from the frequency of the transmitted wave by the Doppler frequency according to the relative speed between the radar apparatus and the target 100. For this reason, when the beat signal having the difference frequency is extracted by the BPF 20 from the output of the mixer 18 that mixes the transmission signal and the reception signal, the beat signal having the same frequency as the Doppler frequency can be detected. In the target 100 having no relative speed with the radar apparatus, the output of the mixer 18 becomes DC and is removed by the BPF 20. The Doppler frequency changes in proportion to not only the relative speed but also the frequency of the transmission wave. For example, in the 76 GHz millimeter wave band, the Doppler frequency changes only 1.3% even if the frequency changes by 1 GHz. The frequency difference has little effect on the Doppler frequency.

  FIG. 3 shows an amplitude spectrum obtained as a result of frequency analysis of each beat signal acquired during transmission of the transmission signal of each frequency. Frequency f0 is channel 1 (CH1), frequency f0 + Δf is channel 2 (CH2), and frequency f0 + (n−1) Δf is channel n (CHn). As shown in the figure, the amplitude spectrum of each channel is theoretically the same and is detected as a signal of the Doppler frequency generated in the target 100. At this time, since the Doppler frequency is different among the plurality of targets 100 having different speeds, a signal of the Doppler frequency for each speed appears. In the figure, there are two types of movement speed targets, and two types of Doppler frequency signals fd1 and fd2 are obtained.

  In the spectrum of ch1 to chn, the peak complex signal components of the frequency fd1 are represented as X1fd1,..., Xnfd1. At this time, since the signals X1fd1,..., Xnfd1, or X1fd2,. When analyzed, a spectrum as shown in FIG. 4 is obtained. The spectrum obtained by this analysis becomes the dimension of the propagation delay time and represents the distance to the target 100. Further, when there are a plurality of targets having the same speed as the target 100, they can be detected separately according to the distance. For example, when there are two targets 100 and 101 having different distances in the signal of the Doppler frequency of fd1. As shown in the figure, two signals corresponding to the distance can be detected. As described above, in this example, the three targets 100, 101, and 102 are separately detected and can be detected as (distance, speed) = (R1, v1), (R2, v1), (R3, v2).

  In this reference example, FFT is used as a Fourier analysis method in order to obtain a propagation delay time, but other Fourier transform methods and high resolution analysis methods such as MUSIC may be used. Also, in order to set the distance resolution more finely, it is necessary to increase the maximum frequency change (n−1) Δf. When FFT is used, the distance resolution is c / 2nΔf. Where c is the radio wave velocity.

  In this reference example, a plurality of transmission antennas 14 or reception antennas 16 may be provided at a predetermined interval, and the direction may be detected in addition to the distance and speed of the target 100.

<Second Reference Example>
FIG. 5 shows a configuration block diagram of this reference example. In this configuration, RF switches 13 and 17 for turning ON / OFF the transmission antenna 14 and the reception antenna 16 are added to the configuration of FIG. FIG. 6 shows the transmission / reception timing obtained by controlling the RF switches 13 and 17. The RF switches 13 and 17 are turned on for a predetermined time T1, and then turned off. The cycle of the ON timing is a predetermined time T2. Here, T1 = 2Rmax / c, T2 = 2R ′ / c, Rmax is the maximum detection distance, and R ′ is not affected by the received signal of the target 100 because the reflected wave is attenuated even if an object is present. The estimated minimum distance. As described above, the radio waves reflected from the target located farther away are received by controlling the RF switches 13 and 17 so as to transmit and receive radio waves only for the time (T1) corresponding to the maximum detection distance Rmax. Only the desired target 100 can be accurately detected without any problem. Then, it is desirable to provide a time (T2) during which no radio wave is received for a time when it is expected that the reflected wave having an effect will not be received.

<Third reference example>
FIG. 7 shows a transmission signal in another reference example. This is a case where the frequency of the transmission wave is switched in a shorter time and transmitted. If it is the same as the transmission time of the transmission signal shown in FIG. 2, the time for acquiring the beat signal of each channel can be made longer than in the case of FIG. 2, and a beat signal with a lower frequency can be extracted. Therefore, the target 100 having a slower relative speed can also be detected.

  FIG. 8 is a block diagram showing the configuration of the radar apparatus according to this reference example. In addition to the configuration of FIG. 1, a selector switch 19 is provided at the subsequent stage of the mixer 18 to switch and output a signal for each channel, and a BPF and an A / D converter are provided for each channel. That is, CH1 is provided with a BPF 20-1 and an A / D converter 22-1 to extract a beat signal for the transmission frequency f0 and supply it to the signal processing device 24. Further, BPF 20-n and A / D converter 22-n are provided in CHn, and a beat signal for the transmission frequency f 0 + (n−1) Δf is extracted and supplied to the signal processing device 24. Since the transmission frequency changes every Δt, the changeover switch 19 is also controlled to switch every Δt.

<Fourth Reference Example>
FIG. 9 shows a transmission signal in this reference example. The multi-frequency modulation and FM-CW shown in FIG. 2 are transmitted in a time division manner. That is, multi-frequency modulation is performed from time 0 to nT, and FM-CW is performed from nT to nT + 2T ′. In multi-frequency modulation, the frequency changes from f0 to f0 + (n−1) Δf, and in FM-CW, the frequency continuously changes from f0 to f0 + (n−1) Δf. In FM-CW, the resolution increases as the frequency change width increases. In multi-frequency modulation, the frequency is changed from f0 to f0 + (n−1) Δf as described above, and therefore the frequency change width increases. Therefore, by combining multi-frequency modulation and FM-CW and combining the frequency change width of FM-CW with the frequency change width of multi-frequency modulation, the oscillator can be shared and the frequency change width of FM-CW can be increased. It is easy to ensure and improve the resolution. That is, an FM-CW radar can be realized with the same hardware configuration, and a target with a relative speed of 0 that cannot be detected by a multi-frequency CW radar can be detected simultaneously.

  FIG. 10 shows an example of optimizing the detection range by switching antennas when multi-frequency CW and FM-CW are transmitted in time division. Multi-frequency CW radar has a relatively short maximum detection distance depending on the frequency interval of the transmission signal. At this time, if a reflected wave from a farther target is received, there is a risk of erroneously detecting the distance of a nearby target. Therefore, when operating with a multi-frequency CW radar, the region 200 is measured using an antenna with a wide angle and low maximum sensitivity, and when operating with an FM-CW radar, the region 300 is measured using an antenna with a narrow angle and high maximum sensitivity. . At the same time, a two-frequency CW radar can be easily realized. At this time, by measuring the region 400 using a wide-angle and relatively high-sensitivity antenna, it is possible to easily detect a target approaching at a high speed from a distance. Become. This is because in the CW radar, even if the detection range is widened, the influence of a stationary object around is small and it is easy to detect a moving target.

The summary of switching between CW and FM-CW is as follows.
(1) When the vehicle travels and there is no object at a short distance Monitor the surroundings with CW + wide-angle antenna (moving object)
Monitor the direction of travel with FM-CW + narrow-angle antenna (moving object + stationary object)
(2) When the vehicle travels and there is an object at a short distance Monitor the wide angle with CW + wide-angle antenna (moving object)
Monitor the direction of travel with CW + narrow-angle antenna (moving object + stationary object)
(3) When the vehicle stops and there is no object at a short distance Monitor the surroundings with CW + wide-angle antenna (moving object)
Use FM-CW + narrow-angle antenna to monitor high-risk directions (moving object + stationary object)
(4) When the vehicle stops and there is an object at a short distance Monitor the wide angle with CW + wide-angle antenna (moving object)
Highly dangerous direction is monitored with CW + narrow-angle antenna (moving object)
In addition, short distance means below the shortest detection distance of FM-CW. The stationary object includes an extremely low speed moving body that cannot be detected by the CW.

  In each of the above reference examples, as described above, the frequencies (three or more types) of transmission signals are set at regular intervals. Therefore, for example, when n types of set frequencies are set, Δf is the frequency difference, and (n−1) Δf is the maximum frequency transition, the maximum detection distance is c / 2Δf and the distance resolution is c / nΔf. In order to increase the maximum detection distance while making the resolution of the distance as fine as possible, it is necessary to increase Δ by decreasing Δf, and the type of frequency to be set may increase, and it may take time for measurement. Therefore, based on the above reference example, a method for increasing the maximum detection distance without greatly increasing the type of frequency to be set will be described.

<First Embodiment>
FIG. 11 shows a transmission signal in the present embodiment. In FIG. 2, the frequency changes from f0 to f0 + (n−1) Δf and the frequency changes at intervals of Δf. In this embodiment, the frequency interval ranges from f0 to f0 + Δf _n − ₁ and from f1 to f _n−1. n types change. Such a multi-frequency CW is transmitted toward the target 100, a reflected wave from the target 100 is received, and the transmission signal and the reception signal are mixed by the mixer 18 to generate a beat signal.

  FIG. 12 shows an amplitude spectrum obtained as a result of frequency analysis of the beat signal. The amplitude spectrum of each channel is theoretically the same, and is detected as a Doppler frequency signal generated at the target 100. In the figure, a case where an fd Doppler frequency signal is obtained is shown. In the spectrum of ch1 to chn, the complex signal components at the peak of the frequency fd are X1fd, X2fd,... Xnfd. FIG. 13 shows an example of a change in the phase difference of X2fd,..., Xnfd with respect to the distance to the target 100 with X1fd as a phase reference. The distance to the target 100 can be uniquely determined by comparing the change in the phase difference and the observation result. In the figure, the phase is changed by 2π at the maximum detection distance in X2fd having the smallest phase change, but the maximum detection distance can be made longer depending on the frequency setting method.

In the present embodiment, the frequency intervals of the transmission signals are set to f1 to f _n−1 , but the frequency intervals need not be all different, and there may be transmission waves having frequencies set at the same interval.

  Also in this embodiment, the multi-frequency CW and FM-CW may be combined and the multi-frequency CW and FM-CW may be transmitted in a time division manner.

<Second Embodiment>
FIG. 14 shows a transmission signal of this embodiment. The frequency interval reference is Δf. For example, the fourth frequency is not f0 + 3Δf but f0 + 4Δf, and the frequency is n−1. That is, the frequencies are f0, f0 + Δf, f0 + 2Δf, f0 + 4Δf, f0 + 5Δf,..., F0 + (n−1) Δf. F0 + 3Δf does not exist as the frequency interval, and the frequency interval is not a continuous integer multiple of Δf. Such a multi-frequency CW is transmitted toward the target 100, a reflected wave from the target 100 is received, and the transmission signal and the reception signal are mixed by the mixer 18 to generate a beat signal.

15, in the spectrum of ch1 to chn, the complex signal components of the peak of the frequency fd are X1fd, X2fd,... Xnfd, and X2fd,..., X (n−1) Fd The change of the phase difference with respect to the distance to the target 100 is shown. These are arranged in ascending order of the frequency of the transmission signal, and the complex signal component obtained by the missing transmission signal is interpolated with 0 so that the set frequency becomes a constant interval, and Fourier analysis is performed by FFT or the like. That is,
X1fd, X2fd, X3fd, 0, X4fd, ... Xn-1fd
Is subjected to Fourier analysis. The fourth “0” is the interpolated signal. As a result, a spectrum having a dimension of propagation delay time is obtained, and the distance to the target 100 can be detected. Similar to the first embodiment, a plurality of targets having different distances at the same speed can also be detected separately.

  In the present embodiment, the types of set frequencies can be reduced without changing the maximum frequency and frequency interval, and the signal acquisition time can be reduced and the circuit can be simplified.

In the present embodiment, only the frequency of the fourth type of transmission wave from the lowest frequency is set to be 2Δf instead of the fixed interval Δf, but can be set to an arbitrary order and in a plurality of orders. Instead of the constant interval Δf, 2Δf may be used. For example, focus on the second and fifth,
The frequencies may be f0, f0 + 2Δ, f0 + 3Δf, f0 + 4Δf, f0 + 6Δf,. Further, the frequency interval is not limited to 2Δf and may be 3Δf or the like.

  Also in the present embodiment, the multi-frequency CW and the FM-CW may be transmitted in a time division manner.

<Third Embodiment>
In each of the above embodiments, the maximum frequency transition needs to be increased in order to make the distance resolution finer. For example, in the first embodiment, it is necessary to increase the maximum frequency transition (n−1) Δf. When FFT is used, the distance resolution is c / 2nΔf. However, there is a limit to the maximum frequency transition due to the Radio Law and other reasons. For example, when the two targets 100 and 101 having the same speed are so close that the difference in propagation delay time is less than the resolution of the distance, FIG. A spectrum with respect to such propagation delay time is obtained. That is, the spectrum of the target 100 and the spectrum of the target 101 overlap each other and appear as one spectrum. In the figure, it is shown as a spectrum on a square. In this case, the two targets 100 and 101 cannot be separated and their respective peaks cannot be detected, and the number and distance of a plurality of targets cannot be detected correctly.

  Therefore, in the present embodiment, a plurality of targets are detected by detecting the rise of the spectrum.

  FIG. 17 shows the distance detection method of this embodiment. A detection threshold is provided, and the distance when the detection threshold is reached with respect to the observed spectrum, that is, the distance at the rising edge of the spectrum is detected, and this is used as the distance R to the target. As a result, although the plurality of targets 100 and 101 cannot be identified, even when the plurality of close targets 100 and 101 are moving at the same speed, the distance to at least the nearest target among the targets 100 and 101 is set. Detection can be performed while suppressing errors in detection results.

  Since the true propagation delay time is detected from the peak, in order to detect it by the rise of the spectrum as in the present embodiment, the deviation between the true value and the detected value needs to be always constant. However, in practice, as shown in FIG. 18, the amount of deviation from the peak differs depending on the signal intensity and is not constant. In the figure, the signal intensity of the target 101 is larger than the signal intensity of the target 100, and the deviation of the target 101 is large. Thus, if the deviation is not constant, the deviation cannot be easily corrected, and a detection error occurs. Therefore, the waveform of the spectrum is detected in more detail by a method such as extrapolating 0 at the time of analysis such as FFT for obtaining a spectrum of propagation delay time, and two kinds of preset detection threshold values (detection threshold value 1 and detection threshold value 2). Thus, the true propagation delay time is detected by estimating the amount of deviation from the difference (A and B) in the detection results. Specifically, a deviation amount corresponding to a detection result (A or B) using two types of detection thresholds is determined in advance and stored in a memory as a map, and the deviation amount is obtained according to the detection result to obtain a true value. Detect propagation delay time. Alternatively, the true propagation delay time can be detected by estimating the shift amount from the maximum value (A ′ or B ′) of the spectrum. In any case, in short, the true propagation delay time can be detected by estimating the shift amount according to the value of the peak intensity of the spectrum.

<Fourth embodiment>
In the third embodiment, the detection of the distance when two spectra overlap to form one spectrum has been described, but in this embodiment, whether or not the spectra of a plurality of targets overlap is detected from the spectrum waveform. Processing to be performed will be described.

  FIG. 19 shows the processing of this embodiment. Two types of detection threshold values (detection threshold value 1 and detection threshold value 2) are used for the FFT result having a complex signal component obtained at frequency fd of each spectrum of ch1 to chn as a sequence. The rise and fall of the spectrum are detected for the two types of detection thresholds 1 and 2, respectively. For the observed spectrum 500, the rising edge of the detection threshold 1 is a distance R11, the falling edge is R14, the rising edge of the detection threshold 2 is a distance R12, and the falling edge is R13. At this time, the difference R11−R12 in the rising detection result and the difference R13−R14 in the falling detection result are compared with each other to determine whether or not R11−R12 = R13−R14 holds. If the target is a single target, the spectrum is symmetric about the peak, so R11−R12 = R13−R14. On the other hand, when there are a plurality of targets, they are asymmetric and R11-R12 ≠ R13-R14. Therefore, if R11−R12 ≠ R13−R14, the observed spectrum 500 can be identified as being due to a plurality of targets. Similarly, if R21−R22 ≠ R23−R24 with respect to the observed spectrum 600, the observed spectrum 600 can be identified as having a plurality of targets.

<Fifth Embodiment>
In the first embodiment, the case where n kinds of frequency intervals of the transmission signal are changed is shown, but the case where the frequency interval is changed is also shown in this embodiment. As shown in FIG. 23, the frequency of the transmission signal is set to f0, f1, f2,..., Fn-1, for example, n-1 = 9, and 10 types of frequencies f0 to f9 are set as shown in FIG. . Nine frequencies of f0 to f8 are equally spaced at 10 MHz intervals, and are varied by changing f9. That is, f9 = 76500 MHz + fm, and if fm = 90 MHz, the intervals are equal, but otherwise, the intervals are unequal. The amplitude spectrum of the beat signal is theoretically the same regardless of the frequency of f9, and the signal of the Doppler frequency generated at the target is detected.

  FIG. 25 shows the result of detecting the target distance. The horizontal axis represents distance (m) and the vertical axis represents the strength (dB) of the evaluation function. Here, the evaluation function indicates the high possibility that the target exists at that distance. The Capon method (J. Capon: “High resolution frequency-wavenumber spectrum analysis”, Proc. IEEE, Vol. 57, pp .1408-1418 (1969)). The figure shows the results when fm = 92 MHz, 94 MHz, 96 MHz, and 98 MHz. When the solid line is 92 MHz, the one-dot chain line is 94 MHz, the two-dot chain line is 96 MHz, and the broken line is 98 MHz. Ghost peaks also occur at distances that do not exist with respect to the distance peaks that actually exist. However, by changing fm to have unequal intervals, the target setting position and the ghost can be distinguished from each other by the size of the evaluation function. become. For example, the strength of the evaluation function can be determined with -20 dB as a threshold value. The strength of the evaluation function is greater than or equal to the threshold value, and there is actually a peak that does not change with fm (peaks with distances of 5 m and 8 m). Can be removed. Thus, the maximum detection distance can be extended without narrowing the frequency interval. If fm = 90 MHz, the interval is equal as described above, and a ghost peak (turnback caused by the sampling frequency of the frequency analysis) occurs at a period of Rc = c / 10 MHz / 2 = 15 m to specify the true value. I can't (I don't know 5m, 20m or 35m).

  FIG. 26 shows the phase difference between the component of f0 and the components of f1 to f9 with respect to the distance R to the target for the complex signal component obtained by frequency analysis of the transmission frequencies f0 to f9 when there is one target. An example of change will be shown. The phase difference of f9 with respect to f0 is not 0 (= 2π) at Rc, and no aliasing occurs. Therefore, the distance to the target can be accurately detected. It should be noted that at fm = 90 Mhz, the intervals are equal, and at distances 0 and Rc, all phases are 0 (= 2π) and cannot be distinguished. In this embodiment, the method of setting fm is arbitrary, and it is possible to increase the maximum detection distance depending on the method of setting the frequency, or to improve the separation judgment ability with the evaluation function.

<Sixth Embodiment>
In the fifth embodiment, the case where the targets exist at 5 m and 8 m is shown, but in this embodiment, the case where the targets exist at 15 m and 18 m is shown in FIG. The transmission frequency is the same as that shown in FIG. 24, and is changed to fm = 92 MHz, 94 MHz, 96 MHz, and 98 MHz. The intensity of the evaluation function is greater than or equal to the threshold value, and there is actually a peak that does not change with fm (peaks with distances of 15 m and 18 m). Can be removed.

<Seventh embodiment>
The case of changing the transmission frequency as shown in FIG. 28 in the configuration of the fifth embodiment will be described. That is, when fm = 90 MHz and f0 to f9 are equally spaced, nine types of f0 to f8 are unevenly spaced, and eight types of f0 to f7 are unevenly spaced. FIG. 29 shows the detection result. The solid lines are equally spaced, the alternate long and short dashed lines are f0 to f8, and the dashed lines are f0 to f7. By setting the frequency more finely than in the fifth embodiment, the distance and the extent of overlapping with each other in the phase difference change as shown in FIG. Also, the ghost periodicity is reduced. Furthermore, even if the number of frequency settings is reduced as unequal intervals, the same resolution can be obtained with a small number of frequency settings without reducing the distance resolution by making the apertures (90 MHz in this example) the same.

It is a block diagram of a configuration of a reference example. It is a timing chart of a transmission wave. It is a spectrum figure which shows the FFT result of the received signal of FIG. It is a spectrum figure which shows the FFT result which made the complex signal component of the Doppler frequency signal of FIG. 3 the number sequence. It is a block diagram of a configuration of another reference example. It is a timing chart which shows transmission / reception timing. It is a timing chart of the transmission wave in other reference examples. It is a block diagram of a configuration of another reference example. It is a timing chart of the transmission wave in other reference examples. It is switching explanatory drawing of multifrequency CW mode and FM-CW mode. It is a timing chart of the transmission wave in an embodiment. It is a spectrum figure which shows the FFT result of the received signal of the transmission wave shown in FIG. It is a figure which shows the phase difference of the complex signal component of the Doppler frequency signal shown in FIG. It is a timing chart of the transmission wave in other embodiments. It is a figure which shows the phase difference of the complex signal component of the Doppler frequency signal of the transmission wave shown in FIG. It is a spectrum figure in case the spectrum of a some target overlaps. It is an explanatory view of the rise of the spectrum. It is explanatory drawing which shows the deviation | shift amount of the rise of a spectrum and a peak. It is identification explanatory drawing of the several target using the rise and fall of a spectrum. It is a block diagram of the configuration of a dual-frequency CW radar apparatus. It is a timing chart of a transmission wave. It is a spectrum figure which shows the FFT result of the received signal of the transmission wave shown in FIG. It is a timing chart of the transmission wave in other embodiments. It is setting explanatory drawing of frequency f0-f9. It is a detection spectrum figure at the time of changing fm of FIG. FIG. 25 is an explanatory diagram of a phase difference when there is one target in FIG. 24. It is a detection spectrum figure in case the distance of a target differs in FIG. It is frequency setting explanatory drawing in other embodiment. It is a detection spectrum figure in the case of the setting of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Oscillator, 12 Directional coupler, 14 Transmitting antenna, 16 Receiving antenna, 18 Mixer, 20 BPF, 22 A / D converter, 24 Signal processing apparatus.

Claims (14)

An oscillator with a variable oscillation frequency;
A transmitting antenna for transmitting a signal generated from the oscillator;
A receiving antenna for receiving a reflected wave of the transmitted wave from an object;
A mixer for mixing the reception signal from the reception antenna and the transmission signal;
A signal processing circuit for detecting a distance to the object and a speed of the object based on a beat signal generated by the mixer;
Have
The oscillator is a continuous wave and outputs transmission signals of three or more different frequencies,
The signal processing circuit detects the speed by frequency analysis of the beat signal obtained from the transmission signal of each frequency and detects the Doppler frequency, and the amplitude of the signal of the Doppler frequency obtained by frequency analysis. And detecting the distance by detecting the propagation delay time using the phase information,
The radar apparatus according to claim 1, wherein the frequency intervals of the transmission signals having different frequencies are different, and at least one of the frequency intervals is different from a continuous integer multiple of the reference frequency difference Δf. The apparatus of claim 1.
The radar apparatus according to claim 1, wherein at least one of the frequency intervals of the transmission signals having different frequencies is not an integral multiple of a reference frequency difference Δf. The apparatus according to claim 1,
The signal processing circuit detects the propagation delay time by performing a Fourier analysis on the Doppler frequency signal obtained by the frequency analysis. Interpolation is performed by regarding the Doppler frequency signal as 0 at different frequency intervals. A radar apparatus characterized in that the frequency interval is fixed by processing and Fourier analysis is performed. The apparatus according to claim 1,
The radar apparatus, wherein the signal processing circuit detects a propagation delay time by analyzing a Doppler frequency signal obtained by the frequency analysis by a Capon method. In the apparatus in any one of Claims 1-4,
A radar apparatus, wherein a difference between a maximum frequency and a minimum frequency among the three or more different frequencies is set according to a resolution of a desired distance. In the apparatus in any one of Claims 1-5,
A switch that switches ON / OFF transmission of the transmission antenna and ON / OFF reception of the reception antenna;
A radar apparatus that performs transmission and reception only for a time set according to a desired maximum detection distance by switching the switch. In the apparatus in any one of Claims 1-5,
The radar apparatus according to claim 1, wherein the signal processing circuit determines a propagation delay time based on a spectrum peak obtained by analyzing a sequence of complex signal components of a Doppler frequency signal obtained by the frequency analysis. In the apparatus in any one of Claims 1-5,
The signal processing circuit determines a propagation delay time based on a spectrum rise obtained by analyzing a sequence of complex signal components of a Doppler frequency signal obtained by the frequency analysis, and the rise is at least one threshold value. A radar apparatus characterized by being determined using The apparatus of claim 8.
The radar apparatus according to claim 1, wherein the signal processing circuit determines the propagation delay time by correcting the rising edge based on a peak intensity value of the spectrum. The apparatus of claim 8.
2. The radar apparatus according to claim 1, wherein the signal processing circuit determines the propagation delay time by using two types of the threshold values and correcting the difference based on a difference between rising edges of the spectrum with respect to the first threshold value and the second threshold value. In the apparatus in any one of Claims 1-5,
The signal processing circuit uses two types of thresholds for a spectrum obtained by analyzing a sequence of complex signal components of a signal of Doppler frequency obtained by the frequency analysis, and the first threshold and the second threshold are compared with each other. A radar apparatus, wherein a plurality of objects are detected based on a comparison between a difference between rising edges of a spectrum and a difference between falling edges of the spectrum with respect to a first threshold value and a second threshold value. The device according to any one of claims 1 to 11,
A radar apparatus, wherein a frequency-modulated continuous wave whose frequency monotonously changes with a certain time gradient in addition to the transmission signals of three or more different frequencies is transmitted from the transmission antenna as a transmission signal. The apparatus of claim 12.
The radar apparatus according to claim 1, wherein a minimum frequency and a maximum frequency of the transmission signals of three or more different frequencies are equal to a minimum frequency and a maximum frequency of the frequency modulation continuous wave, respectively. The device according to any one of claims 12 and 13,
A plurality of at least one of the transmitting antenna and the receiving antenna,
When transmitting and receiving three or more types of transmission waves having different frequencies, a relatively wide-angle and low-sensitivity antenna is used. When transmitting and receiving the frequency-modulated continuous wave, a relatively narrow-angle and high-sensitivity antenna is used. A radar apparatus characterized by being used.

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