JP2008224321A - Radar apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an improved radar apparatus for solving the problem that a plurality of radar apparatuses employing an FMCW modulation system and the like generate interferences when approaching another. <P>SOLUTION: In the radar apparatus employing the FMCW modulation system, respective amplitudes of a transmission signal and a reception signal are varied smoothly, such that they are small at the beginning and the termination, and large at the middle in a sweep period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radar device of an FMCW (Frequency Modulated Continuous Wave) modulation system or an FMICW (Frequency Modulated Integrated Wave) modulation system.

  Conventionally, in the FMCW modulation method, amplitude modulation is performed in which only the amplitude of the received signal is reduced at the beginning and end of the sweep period and smoothly increased at the middle period. On the other hand, in the FMICW modulation type radar apparatus, a method has been proposed in which the transmission signal is not suddenly changed between when there is an amplitude and when there is no amplitude (see, for example, Patent Document 1). This relates to a method of forming a transmission modulation signal, and forms a repetitive signal that is smooth in time and a transmission / reception switching signal that switches between a transmission period and a reception period in an arbitrary period of the repetitive signal that is smooth in time. Synchronously formed, rising and falling edge portions of the switching signal that are within the transmission period and that change from the lowest value to the highest value of the repetitive signal that is temporally smooth, or from the highest value to the lowest value This is a method of replacing the period that changes into the period from the lowest value to the highest value and the period from the highest value to the lowest value of the repetitive signal that is smooth in time.

That is, the rising and falling edges of each transmission pulse are smoothed to reduce the spread of the spectrum of the transmission signal, but the initial, middle and final amplitudes of the sweep cycle are substantially constant.
Japanese Patent No. 2560222

  In the radar apparatus according to the above-described prior art, when a plurality of radars of the same FMCM modulation method or the like approach, an interference problem occurs, and when the clutter power of a reflected wave from an unnecessary reflector is large and transmission / reception isolation is If it is insufficient, there is a problem that it is likely to malfunction.

  Also, in the FMICW modulation type radar apparatus, an interference problem occurs as in the FMCW modulation type radar apparatus.

  Therefore, an object of the present invention is to provide a radar apparatus that solves the interference problem that has occurred when a plurality of radar apparatuses of the same FMCM modulation method or the like approach each other.

According to one aspect of the present invention, an FMCW modulation method for measuring at least one of a distance and a relative speed with a baseband frequency obtained by mixing a transmission signal with a swept frequency and a reception signal reflected from the target. A radar device,
There is provided a radar apparatus characterized in that the amplitudes of the transmission signal and the reception signal are reduced at the initial and final periods of the sweep cycle and smoothly increased at the middle period.

  In the radar apparatus of the present invention, the transmission signal and the reception signal have substantially the same amplitude modulation waveform.

  In the radar apparatus according to the present invention, the transmission signal and the reception signal have different amplitude modulation waveforms.

  In the radar apparatus of the present invention, a low-pass filter is provided in the baseband frequency band.

  According to the present invention, even when a plurality of radar devices of the same modulation method approach, the distance to the target and the relative speed can be accurately grasped without interference.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same portions are denoted by the same reference numerals, and redundant description is omitted.

  First, an embodiment of the present invention will be described.

  FIG. 1 is a block diagram illustrating a configuration example of a radar apparatus according to an embodiment of the present invention. In FIG. 1, a radar apparatus 1 includes a sweep signal generator 10, a transmission amplifier 11, an amplitude modulator 12, a transmission / reception switching / amplitude modulation signal generator 13, a receiver 14, a transmission / reception switch 15, a transmission / reception antenna 16, and an amplitude modulator. 17 etc.

  A part of the output of the sweep signal generator 10 is sent to the receiver 14 as a local signal. The rest is sent to the amplitude modulator 12 where it is amplitude modulated. The output signal of the amplitude modulator 12 is sent to the transmission amplifier 11 and amplified. The amplified transmission signal is output from the transmission / reception antenna 16 via the transmission / reception switch 15. The reception signal reflected from the target is received by the transmission / reception antenna 16. The reception signal is sent to the receiver 14 via the transmission / reception switch 15. The transmission amplifier 11, the amplitude modulator 12, the transmission / reception switch 15, the receiver 14, and the amplitude modulator 17 are controlled by a transmission / reception switching / amplitude modulation signal generator 13.

  The radar apparatus of FIG. 1 measures at least one of the target distance and the relative velocity at the baseband frequency obtained by mixing the transmission signal whose frequency is swept and the reception signal reflected from the target with the above-described configuration.

  Next, the operation principle of the FMCW modulation method will be described. In FIG. 2, assuming that the distance to the target is R and the speed of light is c, the delay time τ until the transmission signal is reflected by the target and returned is calculated by the following equation (1).

τ = 2 · R / c (1)
In FIG. 2, when the sweep time is T and the sweep bandwidth is B, the baseband frequency due to the delay time is
Baseband frequency = τ · B / T = 2 · R · B / (c · T) (2)
Is calculated by

Further, when the relative speed with respect to the target is v and the wavelength of the transmission signal is λ, the trap frequency is
Trap frequency = 2 · v / λ (3)
Is calculated by

Further, since the trap frequency is 2 · v / λ as described above, the baseband frequency fdown of the down sweep is
fdown = 2 · B · R / (c · T) −2 · v / λ (4)
Is calculated by

On the other hand, the baseband frequency fup of the up sweep is
fup = −2 · B · R / (c · T) −2 · v / λ (5)
Is calculated by

From these, the distance R to the target is
R = -c.T. (Fup-fdown) / (4.B) (6)
Is calculated by

The relative speed v with the target is
v = −λ (fup + fdown) / 4 (7)
Is calculated by

Next, FIG. 3 explains the operation principle of the FMICW modulation method in which transmission waves are pulsed to switch transmission / reception intermittently. When the reception sampling interval of the FMCW modulation method is T / N, the transmission pulse interval in FIG. 3 is T / N, and the reception sampling interval Tk is
Tk = T / (N · K) (8)
Is calculated by

  The transmission pulse width Tp is the same as the reception sampling interval Tk, and the duty factor of the transmission pulse is 1 / K. Also, a delay time tb is set from the end of the transmission pulse to the first reception pulse k = 1. As a result, countermeasures against insufficient transmission and reception isolation and reflected waves from unnecessary reflectors in the vicinity of the antenna are dealt with.

    Here, the influence when a vehicle equipped with the same FMCW modulation vehicle-mounted radar is running in parallel will be considered. FIG. 4 is an explanatory diagram of a case where a vehicle equipped with the same in-vehicle radar is running side by side, an oncoming vehicle is nearby, and a person is far away. When the car a and the car b are running in parallel as shown in FIG. 4, the probability that the transmission frequency and the sweep start timing are the same is low even though the sweep bandwidth B and the sweep time T are almost the same. For example, in car a and car b, sweep time T = 2 ms, sweep bandwidth B = 300 MHz, FFT (Fast Fourier Transform) sample number 1024, antenna directivity gain 22 dB, antenna circuit loss 3 dB, Assume that the transmission power 8 dBm at the antenna feeding point and the noise figure 13 dB of the reception system are the same. When the center frequency of the transmission signal is 76.5 GHz for the vehicle a and 76.35 GHz for the vehicle b, and the sweep start of the vehicle b is delayed by 1 ms from the vehicle a, the transmission frequency is as shown in FIG. In the up sweep, it changes as shown in FIG. FIG. 5 illustrates the state of change in the transmission frequency down sweep, and FIG. 6 illustrates the state of change in the transmission frequency up sweep. Here, the transmission frequency of the car a is ftxa, and the transmission frequency of the car b is ftxb.

  For example, in FIG. 4, the car a is running 2m ahead of the car b (= Rab), the car 1 is on the opposite lane 15m (= Rla) ahead of the car a, and the cross-sectional area is 10 dBsm. There is a person 2 (assuming a cross-sectional area of −5 dBsm) at R21 = 55 m ahead. At this time, the speed of the car a is va = 100 km / h, the speed of the car b is vb = 120 km / h, and the speed of the car 1 is v1 = 100 km / h. In such a situation, the reception baseband frequency of the car a changes as shown in FIG. 7 in a down sweep. In FIG. 7, frxa1a represents the baseband frequency at which the vehicle a received the reflected wave from the vehicle 1 of the transmission signal of the vehicle a, and the baseband frequency at which the vehicle a received the reflected wave from the person 2 of the transmission signal from the vehicle a. frxa2a, the baseband frequency at which the vehicle a received the reflected wave from the vehicle 1 of the transmission signal of the vehicle b is frxa1b, and the baseband frequency at which the vehicle a received the reflected wave from the person 2 of the transmission signal of the vehicle b is frxa2b. Yes.

  FIG. 8 is an enlarged view of the frequency on the vertical axis in FIG. As shown in FIG. 8, it can be seen that frxa1b = 47 kHz and frxa2b = 88 kHz suddenly become constant at t = 1 ms in the center of the down sweep, and are close to frxa1a = 43 kHz and frxa2a = 84 kHz.

  On the other hand, the change in the up sweep of the reception baseband frequency of the car a will be considered. FIG. 9 is a diagram illustrating how the reception baseband frequency changes in an up sweep. FIG. 10 is an enlarged view of the frequency on the vertical axis of FIG. In the up sweep, as shown in FIGS. 9 and 10, frxa1b = −299985 kHz and frxa2b = −300054 kHz are constant at t = 1 ms in the center, but frxa1a = 13 kHz is far from frxa2a = −56 kHz. I understand that.

    Here, consider a case where amplitude modulation is applied to the voltage of the received baseband signal. Here, as shown in FIG. 11, only the amplitude of the received signal is reduced at the beginning and end of the sweep period T and smoothly increased at the center. In such a case, the power spectrum of the down sweep corresponding to the baseband frequency is as shown in FIG. FIG. 12 is a diagram showing a change in the reception power spectrum of the received baseband signal in a down sweep (no low pass filter, amplitude modulation for reception only). As can be seen from FIG. 12, frxa1a and frxa1b can be identified, but frxa2a and frxa2b are difficult to identify. Further, FIG. 13 shows changes in the reception power spectrum of the reception baseband signal in an up sweep (no low-pass filter, amplitude modulation for reception only). As can be seen from FIG. 13, frxa1a can be identified, but frxa2a is difficult to identify.

  In FIG. 13, the spectrum of about 47 kHz is due to the aliasing of higher frequency components than the Nyquist frequency 256 kHz (= N / (2 · T)) of the sampling theorem. Therefore, if a low-pass filter that attenuates high-frequency components exceeding 256 kHz is inserted before FFT, it can be eliminated. For example, when a low-pass filter having a 3 dB bandwidth of 2.56 MHz and -12 dB / octave at a higher frequency is inserted, the power spectrum is as shown in FIGS. That is, it can be seen that the up sweep of about 47 kHz does not disappear but the noise floor is also lowered.

  As shown in FIG. 11, the voltage amplitude Va1b received by the vehicle a of the reflected wave from the vehicle 1 of the transmission signal of the vehicle b becomes large at t = 1 ms (frxa1b = 47 kHz constant starting point) at the center of the down sweep. ing. Therefore, as shown in FIG. 14, it can be seen that frxa2a is buried in the spread of the power spectrum of frxa1b. On the other hand, in the up sweep in which the transmission frequencies of the cars a and b approach only at one point at t = 0 ms, the frxa1a that becomes constant after t = 1 ms is separated from the frxa2a. In addition, since it is attenuated by the low-pass filter, as shown in FIG. 15, frxa2a is not buried in the spread of the power spectrum.

  Next, consider a case where only the transmission signal is reduced at the beginning and end of the sweep period T and is smoothly increased at the center. FIG. 16 is a diagram illustrating a change in voltage amplitude (amplitude modulation only for transmission) of a transmission signal. FIG. 17 is a diagram showing a change in voltage amplitude (amplitude modulation only for transmission) of the received baseband signal. As shown in FIG. 17, the voltage amplitude Va1b at which the vehicle a receives the reflected wave from the vehicle 1 of the transmission signal of the vehicle b becomes large at t = 2 ms (frxa1b = 47 kHz constant end point) at the end of the down sweep. I can see that

  FIG. 18 is a diagram showing a change in the received power spectrum of the down sweep of the received baseband signal (with a low-pass filter, amplitude modulation only for transmission). Therefore, it can be seen that frxa2a is buried in the spread of the power spectrum of frxa1b as shown in the power spectrum of the down sweep in FIG.

  On the other hand, in the up sweep in which the transmission frequencies of the cars a and b approach only at one point at t = 0 ms, frxa1a that is constant until t = 1 ms is separated from frxa2a. FIG. 19 is a diagram showing a change in the reception power spectrum of an up sweep of a reception baseband signal (with a low-pass filter, amplitude modulation only for transmission). As can be seen from FIG. 19, frxa2a is not buried in the spread of the power spectrum of frxa1a.

  As described above, when only the reception signal or only the transmission signal is reduced at the beginning and end of the sweep cycle T and is smoothly increased at the center, the interference problem that frxa2a is buried in the spread of the power spectrum of frxa1b in the down sweep occurs. .

  Further, in FIG. 3 showing an example of the FMICW modulation method, if K = 4 and tb = 20 ns, the round trip distance received at the received sample k = 1 is 6 m to 152 m (if k is 2 or more, the distance is 152 m). more than). Since all of frxa1a, frxa2a, frxa1b, and frxa2b are received at k = 1, an interference problem that frxa2a is buried in the spread of the power spectrum of frxa1b occurs as in the FMCW modulation method.

  Therefore, in this embodiment, not only the reception signal is amplitude-modulated, but also the transmission signal is amplitude-modulated as shown in FIG. That is, the amplitudes of the transmission signal and the reception signal are reduced at the beginning and end of the sweep period and smoothly increased at the middle period. FIG. 21 is an explanatory diagram showing the voltage amplitude of the received baseband signal. As shown in FIG. 21, the voltage amplitude Va1b at which the vehicle a received the reflected wave from the vehicle 1 of the transmission signal of the vehicle b becomes smaller at the center t = 1 ms and at the end t = 2 ms. FIG. 22 is a diagram illustrating a change in the reception power spectrum of the down sweep of the reception baseband signal. As shown in FIG. 22, even when frxa1b becomes constant near frxa2a from the center t = 1 ms to the end t = 2ms of the down sweep, frxa2a is not buried in the spread of the power spectrum of frxa1b. In an up sweep in which the transmission frequencies of the cars a and b approach only at one point at t = 0 ms, frxa1b, which is constant from t = 1 ms, is away from frxa2a. FIG. 23 is a diagram illustrating a change in the reception power spectrum of the up sweep of the reception baseband signal. In the up sweep, since it is attenuated by a low-pass filter, frxa2a is not buried in the spread of the power spectrum of frxa1a. In this way, by amplitude modulating not only the reception signal but also the transmission signal, the car a can measure the distance and relative speed of the person 2 without causing interference problems.

    In the embodiment described above, the amplitude modulation waveforms of the transmission signal and the reception signal are the same. As another embodiment, a case where the amplitude modulation waveforms of the transmission signal and the reception signal are changed will be described. FIG. 24 shows the voltage amplitude of the reception baseband signal when the amplitude modulation waveforms of the transmission signal and the reception signal are changed. FIG. 25 shows changes in the reception power spectrum of the down sweep of the reception baseband signal when the amplitude modulation waveforms of the transmission signal and the reception signal are changed.

  FIG. 26 shows a change in the received power spectrum of the down sweep of the received baseband signal. FIG. 27 shows a change in the received power spectrum of the up sweep of the received baseband signal. As shown in FIGS. 26 and 27, the power spectra of the down sweep frxa1b and frxa2b can be relatively lower than those of FIGS. 22 and 23, and the spectrum separation of the frxa1a and frxa2a can be improved.

  Further, in FIG. 3 showing an example of the FMICW modulation method, when K = 4 and tb = 20 ns, the round trip distance received at the received sample k = 1 is 6 m to 152 m (if k is 2 or more, the distance is 152 m or more). , Frxa1a, frxa2a, frxa1b, frxa2b are all received at k = 1. However, according to the present invention, the vehicle a can measure the distance and relative speed of the person 2 without causing interference problems as in the FMCW modulation scheme.

  Note that an analog circuit can be realized more simply to perform amplitude modulation of a transmission signal or a reception signal in the RF band. However, baseband amplitude modulation can be realized with a simple configuration by signal processing using a digital circuit as well as an analog circuit.

  As described above, according to the embodiment of the present invention, even when a plurality of radar devices of the same modulation method approach each other, the distance to the target and the relative speed can be accurately grasped without interference.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

It is a block diagram which shows the structural example of the radar apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the principle of operation of a FMCW modulation system. It is explanatory drawing which shows the principle of operation of a FMICW modulation system. It is explanatory drawing in case the car and person carrying the same vehicle-mounted radar are running in parallel and facing each other. It is a figure explaining the mode of a change in the down sweep of a transmission frequency. It is a figure explaining the mode of a change by the up sweep of a transmission frequency. It is a figure showing the mode of change in the down sweep of the reception baseband frequency. It is an enlarged view of the frequency of the vertical axis | shaft of FIG. It is a figure showing the mode of change in the up sweep of the reception baseband frequency. It is an enlarged view of the frequency of the vertical axis | shaft of FIG. It is a figure showing the change by the voltage amplitude (only reception amplitude modulation) of a reception baseband signal. It is a figure showing the change of the reception power spectrum of the reception baseband signal of the down sweep (no low-pass filter, amplitude modulation only for reception). It is a figure showing the change of the reception power spectrum of the reception baseband signal up sweep (no low-pass filter, amplitude modulation for reception only). It is a figure showing the case where a low pass filter is inserted in FIG. It is a figure showing the case where a low pass filter is inserted in FIG. It is a figure showing the change by the voltage amplitude (amplitude modulation only for transmission) of a transmission signal. It is a figure showing the change by the voltage amplitude (only transmission amplitude modulation) of a reception baseband signal. It is a figure showing the change (with a low-pass filter, only transmission amplitude modulation) of the reception power spectrum of the down sweep of a reception baseband signal. It is a figure showing the change (with a low-pass filter, only transmission amplitude modulation) of the reception power spectrum of the reception baseband signal of the up sweep. It is explanatory drawing which shows the voltage amplitude of a transmission signal. It is explanatory drawing which shows the voltage amplitude of a reception baseband signal. It is a figure showing the change of the reception power spectrum of the down sweep of a reception baseband signal. It is a figure showing the change of the reception power spectrum of the up sweep of a reception baseband signal. It is explanatory drawing which shows the voltage amplitude of a transmission signal. It is explanatory drawing which shows the voltage amplitude of a reception baseband signal. It is a figure showing the change of the reception power spectrum of the down sweep of a reception baseband signal. It is a figure showing the change of the reception power spectrum of the up sweep of a reception baseband signal.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 1 ... Radar device, 10 ... Sweep signal generator, 11 ... Transmission amplifier, 12 ... Amplitude modulator, 13 ... Transmission / reception switching / amplitude modulation signal generator, 14 ... Receiver , 15 ... transmission / reception switch, 16 ... transmission / reception antenna, 17 ... amplitude modulator.

Claims (12)

A FMCW modulation type radar apparatus that measures at least one of a distance and a relative velocity with respect to a target at a baseband frequency obtained by mixing a transmission signal with a swept frequency and a reception signal reflected from the target,
A radar apparatus, wherein the amplitudes of the transmission signal and the reception signal are reduced at the initial and final stages of the sweep cycle and smoothly increased at the middle period.   The radar apparatus according to claim 1, wherein the transmission signal and the reception signal have substantially the same amplitude modulation waveform.   The radar apparatus according to claim 1, wherein the transmission signal and the reception signal have different amplitude modulation waveforms.   4. The radar apparatus according to claim 1, further comprising a low-pass filter in the baseband frequency band.   The radar apparatus according to claim 4, wherein the low-pass filter attenuates a high-frequency component set at a maximum detection distance and a maximum relative speed and exceeding a maximum baseband frequency. A signal whose frequency is swept is converted into a transmission signal, and transmission and reception are switched intermittently. An FMICW modulation radar device that measures at least one of velocities,
A radar apparatus, wherein the amplitudes of the transmission signal and the reception signal are reduced at the initial and final stages of the sweep cycle and smoothly increased at the middle period.   The radar apparatus according to claim 6, wherein the transmission signal and the reception signal have substantially the same amplitude modulation waveform.   The radar apparatus according to claim 6, wherein the transmission signal and the reception signal have different amplitude modulation waveforms.   9. The radar apparatus according to claim 6, further comprising a low-pass filter in the baseband frequency band.   The radar apparatus according to claim 9, wherein the low-pass filter attenuates a high frequency component exceeding a maximum baseband frequency set by a maximum detection distance and a maximum relative speed.   7. The radar apparatus according to claim 6, wherein in the FMICW modulation method, the transmission pulse width is set to the same width as the reception sample interval.   8. The radar apparatus according to claim 6, wherein the FMICW modulation method provides a delay time from the end of the transmission pulse to the first reception sample.

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