JP4330634B2 - FM-CW radar equipment - Google Patents

Description

  The present invention relates to an FM-CW radar apparatus. In particular, in order to prevent erroneous detection of noise or a long-distance target as a target object, a signal from the target object is identified or noise or a long-distance target is suppressed. The present invention relates to an apparatus provided with means.

  FM-CW radar is used as a radar system for measuring relative speed and distance with a target object. This type of radar is used as an anti-collision radar for automobiles because it can measure the relative speed and distance from the preceding vehicle with a simple signal processing circuit, and can easily configure a transceiver.

  The principle of FM-CW radar is as follows. The oscillator is FM-modulated with, for example, a triangular wave of several hundred Hz and the FM-modulated wave is transmitted, the reflected signal from the target object is received, and the received signal is FM-detected using the FM-modulated wave as a local. The reflected wave from the target object causes a deviation (beat) from the transmission signal according to the distance between the radar and the target object and according to the Doppler shift due to the relative speed. Therefore, it is possible to measure the distance to the target object and the relative speed from this frequency shift.

  In an FM-CW radar apparatus, a triangular wave is often used as a modulation signal, and in the following description, a case where a triangular wave is used as a modulation wave signal will be described. Modulated waves other than triangular waves can be used.

FIG. 1 is a diagram for explaining the principle of a conventional FM-CW radar when the relative speed with respect to a target object is zero. The transmission wave is a triangular wave, and its frequency changes as shown by the solid line in FIG. The transmission center frequency of the transmission wave is f ₀ , the FM modulation width is Δf, and the repetition period is Tm. This transmission wave is reflected by the target object and received by the antenna, and becomes a reception wave indicated by a broken line in FIG. The round-trip time T of the radio wave with the target object is T = 2r / C where r is the distance to the target object and C is the propagation speed of the radio wave.
This received wave causes a frequency shift (beat) with the transmission signal according to the distance between the radar and the target object.
This beat frequency component fb can be expressed by the following equation.
fb = fr = (4 · Δf / C · Tm) r (1)

On the other hand, FIG. 2 is a diagram for explaining the principle of the conventional FM-CW radar when the relative velocity with respect to the target object is v. The frequency of the transmission wave changes as shown by the solid line in FIG. This transmission wave is reflected by the target and received by the antenna, and becomes a reception wave indicated by a broken line in FIG. This received wave causes a frequency shift (beat) with the transmission signal according to the distance between the radar and the target object. In this case, since there is a relative speed v between the target object and the target object, a Doppler shift occurs, and the beat frequency component fb can be expressed by the following equation.
fb = fr ± fd
= (4 · Δf / C · Tm) r ± (2 · f _o / C) v (2)
In the above formulas (1) and (2), each symbol means the following.

fb: transmission / reception beat frequency
fr: Distance frequency
fd: speed frequency
f _o : center frequency of transmission wave
Δf: FM modulation width
Tm: Modulation wave period
C: Light speed (Radio wave speed)
T: Round trip time of radio wave to the target object
r: Distance to the target object
v: Relative speed with respect to target object FIG. 3 is a diagram showing a configuration of a conventional FM-CW radar of the two antenna system. As shown in the figure, a modulation signal is added to the voltage controlled oscillator 2 from the modulation signal generator 1 to perform FM modulation, and the FM modulated wave is transmitted to the outside via the transmission antenna AT, and a part of the transmission signal is branched. And added to the frequency converter 3 such as a mixer. On the other hand, the reflected signal reflected by the target object such as the preceding vehicle is received via the receiving antenna AR, and the frequency converter 3 mixes with the output signal of the voltage controlled oscillator 2 to generate a beat signal. This beat signal is A / D converted by the A / D converter 5 through the baseband filter 4 and is subjected to signal processing by the fast Fourier transform or the like by the CPU 6 to obtain the distance and relative velocity.

  FIG. 4 is a diagram showing a configuration of a conventional FM-CW radar of the one antenna time division ON / OFF control method. As shown in the figure, the antenna is a transmission / reception antenna ATR, and a transmission / reception switch 7 comprising switching means is provided, and transmission / reception is switched by time-division ON-OFF control. A first frequency converter 3-1 and a second frequency converter 3-2 are provided on the receiving side.

  The transmission / reception antenna ATR efficiently emits the signal output from the transmission / reception switch 7 to the space. A modulation signal generator 8 generates a modulation signal having a frequency fsw for switching the transmission / reception switch 7. The signal reflected from the target object is received by the transmission / reception antenna ATR, and the received signal is mixed with the output of the voltage controlled oscillator 2 by the first frequency converter 3-1, generating an IF signal. The second frequency converter 3-2 mixes the signal output from the first frequency converter 3-1 with the signal of the frequency fsw generated from the modulation signal generator 8, down-converts it, and distances from the target object And a signal containing relative velocity information.

There has been proposed an FM-CW radar that changes a modulation gradient, a modulation width, and a modulation period to accurately identify a target object (Cited document 1).
In FM-CW radar, it has been proposed to switch and transmit a plurality of frequency modulation waves having different modulation repetition periods (Cited document 2).
JP-A-8-5733 Japanese Patent Laid-Open No. 10-20025

FIG. 5 is a diagram showing the spectrum of the BB signal that has passed through the baseband filter 4 of the FM-CW radar shown in FIG.
However, as shown in FIG. 5, in addition to the signal fb from the target object, noise may appear as fn, which may be erroneously determined as a signal from the target object.

  FIG. 6 shows the spectrum of the IF signal that is the output signal of the first frequency converter 3-1 and the BB signal that has passed through the baseband filter 4 in the case of the FM-CW radar of the time-division ON-OFF control method of FIG. FIG. As shown in FIG. 6A, the output signal of the first frequency converter 3-1 in FIG. 4 is a signal of the frequency fsw and its sideband frequencies fsw−fr and fsw + fr. Here, fsw is a switching frequency of the transmission / reception switch 7, and fr is a distance frequency to the target object whose relative speed is zero. As the distance from the target object increases, the frequency of the sideband increases from fsw. This output signal is mixed with the signal of the frequency fsw in the second frequency converter 3-2, down-converted to the frequency of the difference between fsw and fsw ± fr, fb is taken out, passes through the BB filter and is converted to A as a BB signal. / D converter 5 to output. However, at this time, as shown in FIG. 6A, the noise signal fn may appear in the vicinity of the switching frequency fsw in the frequency band of the IF signal. This signal enters the BB band as it is and appears as fn1 or is down-converted and appears as fn2 in the BB band.

  FIG. 7 shows the spectrum of the IF signal that is the output signal of the first frequency converter 3-1 and the BB signal that has passed through the baseband filter in the case of the FM-CW radar of the time-division ON-OFF control method as in FIG. 6. FIG. As shown in FIG. 7A, the homodyne component of the medium-distance target signal that is not the target object in the IF signal frequency band reaches the IF frequency band and appears as a signal fh, and the signals fh1 and fh2 appear in the beat signal band. Appears as In this case, since the frequency is higher than the BB band, it is removed by the BB filter.

  FIG. 8 shows the spectrum of the IF signal that is the output signal of the first frequency converter 3-1 and the BB signal that has passed through the baseband filter in the case of the FM-CW radar of the time division ON-OFF control method as in FIG. FIG. As shown in FIG. 8A, when a long-distance target exists, its homodyne component reaches the IF frequency band and appears as a signal fh. As shown in FIG. 8A, this signal appears as a signal fh1 in the beat signal band or as a signal fh2 in the BB band. In this case, since the frequency of the signal fh1 is higher than that of the BB band, it is removed by the BB filter. However, since the signal fh2 is not removed by the BB filter, it is detected despite the noise, and it may be erroneously detected by determining that the target object exists at a distance closer to the actual distance.

  The present invention discriminates whether the signal appearing on the radar is a signal from the target object or other noise even when such a noise or a signal of a target existing at a mid-range distance is generated, and the distance of the target object is correct. An object of the present invention is to provide a radar apparatus that can identify whether or not measurement is possible.

  In the FM-CW radar apparatus of the present invention, the modulation signal output from the modulation signal generator has a gradient with respect to the time axis (hereinafter referred to as “modulation gradient”) like a triangular wave, for example. Means for changing the slope of the modulation is provided. For example, the slope of the modulation is changed by changing the amplitude or the period. Then, by utilizing the fact that the modulation slope is changed and the frequency of the signal from the target object changes in accordance with this change, means for identifying the signal component that changes in accordance with the change in the modulation inclination is provided, and the target object is provided. Can be distinguished from other signals.

  Further, in the case of an FM-CW radar apparatus that performs transmission, reception, or transmission / reception by time-division ON-OFF control, the frequency of the signal from the target object changes according to this change when the frequency for ON-OFF control is changed. Thus, a means for identifying a signal that changes in accordance with the change in frequency is provided so that a signal from the target object can be identified from other signals.

  Further, in the heterodyne type FM-CW radar apparatus, when the frequency of the IF signal that is a down-conversion signal is changed, a means for identifying a signal that changes in accordance with the change in the frequency is provided, and the signal from the target object is provided. It can be distinguished from other signals.

  Then, the modulation signal is a triangular wave signal, and for each set or a plurality of sets in which the upward and downward gradients of the triangular wave are combined, or for each upward and downward gradient of the triangular wave, the modulation slope, The frequency for switching between transmission and reception or the frequency of the IF signal is changed.

  Further, the FM-CW radar apparatus performs transmission / reception by time-division ON-OFF control, and is provided with means for changing a pattern including a duty ratio of the time-division ON-OFF control so that a signal by a target other than the target object is transmitted. Generation is suppressed.

  Further, the linearity of the frequency modulation change is a non-linear shape, for example, an arc shape, and the target object is identified from the frequency distribution of the signal from the received target.

  As described above, according to the present invention, the modulation signal is controlled to change the modulation gradient, for example, the amplitude and the period, and the signal of the target object can be easily identified by identifying the signal component that changes in accordance with this change. Whether it can be identified.

  Also, in the case of FM-CW radar that performs time-division ON-OFF control of transmission and reception, it is possible to easily determine whether the signal is a target object signal by changing the ON-OFF frequency and identifying the signal component that changes according to this change. Can be identified.

  Further, in the case of a heterodyne type FM-CW radar, it is possible to easily identify whether the signal is a target object signal by changing the frequency of the IF signal and identifying a signal component that changes in accordance with this change.

  Further, the FM-CW radar apparatus performs transmission / reception by time-division ON-OFF control. By changing the pattern of the time-division ON-OFF control, generation of a signal by a target other than the target object can be suppressed.

  Further, it is possible to identify whether the signal is a target object from the frequency distribution of the signal from the received target by making the frequency modulation change non-linear.

  As described above, according to the present invention, signals from the target object can be identified and unnecessary signals can be suppressed with a simple configuration.

  FIG. 9 is a diagram showing an embodiment of the FM-CW radar apparatus of the present invention. The configuration is the same as that shown in FIG. 3 except that the modulation signal generator controller 10 is provided. In this figure, the control unit 10 variably controls the inclination, for example, the amplitude and the period, of the modulation signal output from the modulation signal generator 1 based on the control of the CPU 6.

The present invention will be described first in the case where the amplitude of the modulation signal is variably controlled. As described above with reference to FIG. 1, when the relative velocity with respect to the target object is 0, the frequency of the transmission wave changes as shown by the solid line in FIG. This transmission wave is reflected by the target object and received by the antenna, and becomes a reception wave indicated by a broken line in FIG. This received wave causes a frequency shift (beat) with the transmission signal according to the distance between the radar and the target object. This beat frequency component fb can be expressed by equation (1) as described above.
fb = fr = (4 · Δf / C · Tm) r (1)

  Focusing on Δf in equation (1), this represents the FM modulation width, and Δf can be changed by changing the amplitude of the modulation signal. For example, if the amplitude of the modulation signal is doubled, Δf is doubled, and fb is also doubled from the equation (1). FIG. 10 is a diagram showing a triangular wave when the amplitude is changed when a triangular wave is used as the modulation signal. (A) is a triangular wave having a normal amplitude (corresponding to Δf), and (b) is a triangular wave having a double amplitude (corresponding to 2Δf).

  In the FM-CW radar apparatus of FIG. 9, when the control unit 10 controls the modulation signal generator 1 to change the amplitude of the modulation signal to increase n times, the value of the beat frequency component fb becomes n times as described above. Become. As shown in FIG. 5, a signal fb and a noise signal fn from the target object appear in the received signal. Therefore, the control unit 10 controls the modulation signal generator 1 to change the frequency width of the triangular wave, and Δf is changed n times. Then, the frequency fb of the signal from the target object changes n times according to the change of Δf. However, since the frequency fn of the noise signal does not change, it is possible to identify which is the signal from the target object. The identification is performed by the CPU 6 of the FM-CW radar. The CPU 6 also performs the identification described below.

  Next, a case where the period of the modulation signal is variably controlled will be described. Focusing on Tm in equation (1), this represents the period of the modulation signal. Therefore, when the period Tm of the modulation signal is increased by, for example, n times, the beat frequency component fb becomes 1 / n. FIG. 10C shows a triangular wave when the period is changed when a triangular wave is used as the modulation signal. (A) is a triangular wave having a normal period Tm, and (c) is a triangular wave having an n-fold period nTm.

  In the FM-CW radar apparatus of FIG. 9, when the modulation signal generator 1 is controlled by the control unit 10 to change the period of the modulation signal and the period nTm is n times the normal period Tm, the beat frequency component fb The value is 1 / n times. Therefore, the control unit 10 controls the modulation signal generator 1 to change the period of the triangular wave and change Tm n times. Then, the frequency fb of the signal from the target object changes to 1 / n times according to the change of Tm. However, since the frequency fn of the noise signal does not change, it is possible to identify which is the signal from the target object.

As shown in FIG. 2, when the relative velocity with respect to the target is v, the frequency of the transmission wave changes as shown by the solid line in FIG. This transmission wave is reflected by the target object and received by the antenna, and becomes a reception wave indicated by a broken line in FIG. This received wave depends on the distance between the radar and the target object. This causes a frequency shift (beat) with the transmission signal. In this case, the beat frequency component fb can be expressed by equation (2) as described above.
fb = fr ± fd
= (4 · Δf / C · Tm) r ± (2 · f _o / C) v (2)

Also in this case, paying attention to Δf or Tm, if the controller 10 changes the amplitude or period Tm of the modulation signal, the beat frequency component fb changes, so that it can be identified whether the signal is from the target object. The frequency component fb consists of a distance frequency component fr and a velocity frequency component fd. In this case, only the distance frequency component fr changes. However, since the frequency component fb as a whole changes, it is possible to identify whether the signal is from the target object.
In the above embodiment, the case where the present invention is applied to a two-antenna FM-CW radar has been described. However, the present invention can also be applied to a one-antenna FM-CW radar.

  FIG. 11 is a diagram showing an embodiment of the FM-CW radar apparatus of the present invention. The figure at the time of applying this invention to FM-CW radar of a 1 antenna time division ON-OFF control system is shown. 11 is the same as that shown in FIG. 4 except that the modulation signal generator controller 11 is provided in the modulation signal generator 8. In this figure, the control unit 11 variably controls the frequency (cycle) of the modulation signal output from the modulation signal generator 8 based on the control of the CPU 6. As a result, the ON / OFF frequency (cycle) of the transmission / reception switch 7 changes, and the frequency applied to the second frequency converter 3-2 also changes. Then, since the switching frequency fsw changes, the frequencies fsw−fr and fsw + fr of the sideband signals shown in FIGS. 6 to 8 change, so that it is possible to identify whether the signal is from the target object.

  The frequency (period) of the modulation signal output from the modulation signal generator 8 is changed, for example, as shown in FIG. In this case, the frequency is changed in synchronization with the triangular wave output from another modulation signal generator 1. In Example 1 of FIG. 12, the frequency is sequentially changed to fsw1, fsw2, and fsw3 every time the triangular wave is up and down. Then, the ON-OFF switching frequency fsw also changes, and fsw-fr and fsw + fr also change. On the other hand, since the frequency of noise or the like does not change, it is possible to distinguish between a signal from the target object and a signal that is not.

  In FIG. 12, Example 2 changes the frequency of the modulation signal output from the modulation signal generator 8 every time the triangular wave rises and falls. In this case, the frequency of the signal from the target object changes every time the triangular wave rises and falls.

FIG. 13 is a diagram showing a two-antenna heterodyne FM-CW radar apparatus. Here, a two-antenna type radar apparatus will be described, but a one-antenna type may be used. The apparatus shown in FIG. 11 is different from the configuration shown in FIG. 11 in that it is a two-antenna system and includes a transmission antenna AT and a reception antenna AR and does not have a transmission / reception switch. Further, an up-converter 9 is provided between the voltage-controlled oscillator 2 and the first frequency converter 3-1, and the frequency of the signal from the modulation signal generator 8 input thereto is variably controlled by the modulation signal generator control unit 11. I can do it. The up-converter 9 receives a signal having a frequency f ₀ from the voltage controlled oscillator 2 and a modulation signal having a frequency If 1 from the modulation signal generator 8, and the first frequency converter 3-1 has a frequency f ₀ + If ₁ . Is output as a local signal. Also in this case, if the frequency If1 of the signal from the modulation signal generator 8 is changed, the frequencies fsw (If1) −fr and fsw (If2) + fr of the signals shown in FIGS. 6 to 8 are changed. Since the beat frequency component fb changes, the signal from the target object can be identified.

  The frequency (period) of the modulation signal output from the modulation signal generator 8 is changed, for example, as shown in FIG. In this case, the frequency is changed in synchronization with the triangular wave output from another modulation signal generator 1. In Example 1 of FIG. 14, the frequency is sequentially changed as If1, If2, and If3 every time the triangular wave rises and falls. Then, at the output terminal of the first frequency converter 3-1, the signals of Ifn + fr and Ifn−fr change. On the other hand, the noise frequency does not change. Can be identified.

  In FIG. 14, Example 2 is obtained by changing the frequency of the modulation signal output from the modulation signal generator 8 every time the triangular wave is up and down. In this case, the frequency of the signal from the target object changes every time the triangular wave rises and falls.

  FIG. 15 and FIG. 16 are diagrams for explaining an embodiment when the present invention is applied to a time-division ON-OFF control type FM-CW radar. Description will be made with reference to the time-division ON-OFF control type FM-CW radar apparatus shown in FIG.

  FIG. 15 shows a signal processing waveform of a conventional time-division ON-OFF control type FM-CW radar. In the figure, (a) is a waveform showing the switching timing of the transmission / reception switch 7, and this signal Ssw is output from the modulation signal generator 8. (B) is a waveform Ton showing the timing when transmission is turned on based on Ssw, and (c) is a waveform Ron showing the timing when receiving is turned on based on Ssw. (D) is a waveform SA showing the timing at which the transmitted signal is reflected and returned, and (e) is a waveform SB showing the timing at which the reflected signal is received by the radar when reception is ON. It is.

Here, the timing of the waveform SA is delayed from the waveform Ton by the reciprocation of the distance between the radar and the target object. For example, the time interval T between the hatched pulse of the waveform Ton and the hatched pulse of the waveform SA is 2r / C. Here, r is the distance between the radar and the target object, and C is the speed of light. When the object is far away, for example, a horizontal line pulse of the waveform SA is returned with respect to the pulse of the diagonal line of the waveform Ton. In this case, the pulse time interval T ′ is 2r ′ / C.

FIG. 16 is a diagram for explaining an embodiment of the present invention. In the present invention the gates of the reception timing of the reflected wave from the object of intermediate- or long-distance non-target object is returned to the OFF, is obtained so as not to receive it. Therefore, in the present invention, as shown in FIG. 16A, a period Toff during which no signal is transmitted / received is provided for the signal Ssw. Thus, Ton and Ron are provided with periods Ton-off and Ron-off during which no transmission or reception is performed, respectively. Therefore, for example, when the transmission signal at the timing of the Ton diagonal line is reflected and returned by a distant object , a pulse appears in the waveform SA shown in (d) at the timing indicated by the dotted line, but the Ron gate is closed. Therefore, unnecessary signals from distant objects can be removed. By thus changing the pattern of transmission and reception, it is possible to suppress the generation of a signal from an object other than the target object existing in the middle distance.

  FIG. 17 is a diagram for explaining an embodiment of the present invention. FIG. 17A shows the waveform of the transmission wave of the FM-CW radar. Conventionally, this waveform is a triangular wave as shown in FIG. On the other hand, as shown in the figure, the transmission wave of the present invention deteriorates the linearity of the conventional waveform to have a non-linear shape, in this case, an arc shape, and the frequency deviation of the triangular wave is non-linear.

  FIG. 18B shows the waveforms of a conventional transmission wave and reception wave. This waveform is the same as that shown in FIG. In this case, the frequency difference fr between the transmitted wave and the received wave is always the same at any time.

  On the other hand, in the case of the transmission wave of the present invention, as shown in FIG. 17C, the reception wave has a shape in which the linearity is similarly deteriorated. Therefore, the frequency difference fr between the transmitted wave and the received wave varies with time. For example, as shown in the figure, the frequency difference fr1 in the first half of the up waveform and the frequency difference fr2 in the second half are different, and fr1> fr2. The difference between fr1 and fr2 increases as the target is further away. Therefore, this can be used to distinguish signals from distant targets and exclude them from the target object.

FIG. 18 shows the distribution of the detected frequency spectrum. As shown in the figure, when the target is near, the distribution is a, and when the target is far, the distribution is b. Accordingly, when a distribution such as b is detected, it can be excluded as a far target.
In the case of the above embodiment, for example, the configuration shown in FIG. 9 can be used as the FM-CW radar. Further, the shape of the triangular wave is not limited to the circular arc as shown in the figure, but may be any shape that causes a difference between fr1 and fr2.

It is a figure for demonstrating the principle of the conventional FM-CW radar in case the relative speed with respect to a target object is zero. It is a figure for demonstrating the principle of the conventional FM-CW radar in case the relative speed with respect to a target object is v. It is the figure which showed the structure of the conventional FM-CW radar of 2 antenna systems. It is the figure which showed the structure of the conventional FM-CW radar of 1 antenna time division ON-OFF control system. It is the figure which showed the frequency spectrum of the baseband signal of the conventional FM-CW radar. It is the figure which showed the frequency spectrum of IF signal and baseband signal of the conventional FM-CW radar of a time division ON-OFF control system. It is the figure which showed the frequency spectrum of IF signal and baseband signal of the conventional FM-CW radar of a time division ON-OFF control system. It is the figure which showed the frequency spectrum of IF signal and baseband signal of the conventional FM-CW radar of a time division ON-OFF control system. It is a figure which shows embodiment of FM-CW radar of this invention. It is the figure which showed the triangular wave at the time of changing the frequency width and period of the triangular wave of FM-CW radar by this invention. It is a figure which shows embodiment of this invention FM-CW radar. FIG. 6 is a diagram showing how the frequency from the modulation signal generator is changed according to the present invention. It is a figure which shows embodiment of the heterodyne type FM-CW radar by this invention. FIG. 6 is a diagram showing how the frequency from the modulation signal generator is changed according to the present invention. It is the figure which showed the waveform of the conventional signal processing of the time division ON-OFF control system FM-CW radar. It is the figure which showed the waveform of the signal processing of this invention of the time division ON-OFF control system FM-CW radar. FIG. 6 is a diagram illustrating transmission and reception waveforms according to an embodiment of the present invention. It is the figure which showed distribution of the frequency spectrum by embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Modulation signal generator 2 Voltage control oscillator 3 Frequency converter 3-1 1st frequency converter 3-2 2nd frequency converter 4 Baseband filter 5 A / D converter 6 CPU
7 Transmission / Reception Switcher 8 Modulation Signal Generator 9 Upconverter 10 Modulation Signal Generator Control Unit 11 Modulation Signal Generator Control Unit AT Transmission Antenna AR Reception Antenna ATR Transmission / Reception Antenna

Claims (1)

A voltage-controlled oscillator that is FM-modulated by applying a modulation signal from a modulation signal generator, and a transmission / reception switcher that switches a single antenna between transmission and reception by time-division ON-OFF control, the FM-modulated FM modulation An FM-CW radar device that transmits a wave by time-division ON-OFF control and receives a reflected wave by time-division ON-OFF control,
The transmission / reception switch changes the time-division ON-OFF control pattern so as to have a first reception OFF period and a second reception OFF period (Ron-off) longer than the first reception OFF period. , thereby suppressing generation of a signal by an object other than the target object by not receiving the reflected wave between the second reception OFF period (Ron-off), FM- CW radar apparatus.

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