JP2010185720A - Radio wave reflecting device and method of adjusting optical axis - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a work space for adjusting the optical axis of a radar device. <P>SOLUTION: A radio wave reflecting device 2 includes: a reception antenna 21 that is arranged opposite to the radar device 1, reflects radio wave signals transmitted from the radar device 1, and receives radio wave signals transmitted from the radar device 1; a delay circuit 22 for delaying the radio wave signals received by the reception antenna 21 by preset delay time ΔT, and generates delayed signals; and a transmission antenna 23 for transmitting the delay signals generated by the delay circuit toward the radar device 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radio wave reflection device that is disposed to face a radar device and reflects a radio wave signal transmitted from the radar device, for example, when adjusting the optical axis of a radar device mounted on a vehicle. The present invention also relates to an optical axis adjustment method for adjusting the optical axis of a radar device mounted on a vehicle, for example.

  Conventionally, since the relative position and relative speed detected via the radar device are used for determining a collision with an object such as an oncoming vehicle, a predetermined optical axis (or radio wave axis) of the radar device is set in advance. It is necessary to arrange it in the correct direction. On the other hand, in order to adjust the optical axis of the radar apparatus, the distance between the radar apparatus and the reference reflector needs to be sufficiently large (for example, 5 m or more) from the detection principle (for details, see FIG. 4). Etc. will be described later). Further, it is required that no other object exists around the reference reflector.

  Therefore, in order to adjust the optical axis of the radar apparatus, a large work space is required, but there are cases where a large work space cannot be secured. Therefore, various methods, devices, and the like for reducing the work space necessary for adjusting the optical axis of the radar apparatus have been disclosed (see, for example, Patent Document 1).

  In the detection axis adjustment method described in Patent Document 1, a plurality of tires T as electromagnetic wave absorbers are stacked further in front of the reference reflector R, and electromagnetic waves are radiated from the radar device to cause the reference reflector R to detect the detection area of the radar device. The object detection axis Ar of the radar apparatus is adjusted so as to be the reference position. Therefore, it is not necessary to secure a large work space in front of the reference reflector R without an object that reflects electromagnetic waves, and accurate adjustment work can be performed even when a sufficiently large work space cannot be secured. Become.

JP 2003-240837 A

  However, in the detection axis adjustment method described in Patent Document 1, the influence of other objects existing around the reference reflector is reduced by disposing the electromagnetic wave absorber, but it still remains between the radar device and the reference reflector. The distance needs to be sufficiently separated.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a radio wave reflection device capable of reducing a work space for adjusting an optical axis of a radar device, and an optical axis. It is to provide an adjustment method.

  In order to achieve the above object, the present invention has the following features. A first aspect of the invention is a radio wave reflection device that is disposed to face a radar device and reflects a radio wave signal transmitted from the radar device when adjusting the optical axis of the radar device mounted on the vehicle. A receiving antenna that receives a radio signal transmitted from the radar device, a delay unit that generates a delayed signal by delaying the radio signal received by the receiving antenna by a preset delay time, and A transmission antenna that transmits the delayed signal generated by the delay means toward the radar device.

  In a second aspect based on the first aspect, the delay means includes a delay line having a length corresponding to the delay time.

  According to a third aspect, in the second aspect, the delay unit is interposed between the reception antenna and the delay wire, and reduces a frequency of a radio signal received by the reception antenna. A low-frequency signal that is interposed between the first frequency converter that generates a signal, the delay wire, and the transmission antenna and is delayed by the delay wire corresponds to a radio signal received by the reception antenna. And a second frequency converter for converting into a high frequency signal.

  According to a fourth invention, in the third invention, the delay means includes an oscillator that generates a sine wave having a preset frequency based on a frequency of a radio wave signal transmitted from the radar device, and the first frequency A converter generates the low frequency signal by superimposing a radio wave signal received by the receiving antenna with a sine wave generated by the oscillator, and the second frequency converter is delayed by the delay wire. The low-frequency signal thus generated is superposed on the sine wave generated by the oscillator to convert it to the high-frequency signal.

  In a fifth aspect based on the first aspect, the delay time is set based on a shortest distance from an object that can be detected by the radar device.

  In a sixth aspect based on the first aspect, the delay means includes a waveguide having a length corresponding to the delay time.

  In a seventh aspect based on the first aspect, the delay means comprises a first amplifier that amplifies the radio signal received by the receiving antenna.

  In an eighth aspect based on the first aspect, the delay means includes a second amplifier that amplifies the delayed signal.

  In a ninth aspect based on the first aspect, the delay means passes a signal having a frequency corresponding to the radio signal transmitted from the radar apparatus and corresponds to the radio signal transmitted from the radar apparatus. A filter that cuts off a signal having a frequency separated from the frequency is provided.

  In a tenth aspect based on the first aspect, the radar apparatus is a FMCW (Frequency Modulation Continuous Wave) type radar apparatus.

  An eleventh aspect of the invention is an optical axis adjustment method for adjusting an optical axis of a radar device mounted on a vehicle, and is directed to the radar device according to any one of claims 1 to 9. A radio signal is transmitted, and the radar apparatus receives a signal transmitted from the radio wave reflection apparatus as a reflection signal, and adjusts the optical axis of the radar apparatus based on the reflection signal.

  According to the first aspect, the radio signal transmitted from the radar device is received by the receiving antenna. Then, the received radio wave signal is delayed by a preset delay time by the delay means, and a delay signal is generated. Further, the generated delay signal is transmitted to the radar apparatus by the transmission antenna. Therefore, the radio signal received from the radar device is delayed by a preset delay time to generate a delay signal, and the generated delay signal is sent to the radar device. The work space for adjusting the optical axis can be reduced.

  That is, by setting the delay time to an appropriate value, the reflected wave received by the radar device is substantially the same as the reflected wave from a reflector separated from the radar device by an appropriate distance (for example, 5 m). Since the reflected waves having the same characteristics (for example, frequency characteristics) can be obtained, it is not necessary to separate the radio wave reflecting apparatus from the radar apparatus.

  For example, when the radar apparatus is an FMCW (Frequency Modulation Continuous Wave) radar apparatus, the beat signals of the transmission wave and the reception wave are not buried in noise (DC noise or the like) (= accurate detection) The beat signal needs to be equal to or higher than a predetermined frequency. Therefore, by setting the delay time to an appropriate value, the frequency of the beat signal of the transmission wave and the reception wave can be set to an appropriate value (see FIG. 7). It is no longer necessary to move away from it.

  According to the second aspect of the invention, since the radio wave signal received from the radar apparatus is delayed by the delay time by the delay wire having a length corresponding to the delay time, the delay signal can be configured with a simple configuration. Can be generated.

  According to the third aspect of the present invention, the frequency of the radio signal received by the receiving antenna is reduced by the first frequency converter interposed between the receiving antenna and the delay wire, and the low frequency signal Is generated. Further, a low frequency signal delayed by the delay wire by a second frequency converter interposed between the delay wire and the transmission antenna is a high frequency signal corresponding to a radio signal received by the reception antenna. Is converted to Therefore, since the frequency of the signal delayed by the delay wire can be reduced, it is possible to suppress the attenuation of the signal accompanying the delay of the radio wave signal received from the radar apparatus. Therefore, the optical axis of the radar apparatus can be adjusted accurately.

  That is, when a high-frequency signal is delayed by the delay wire, the signal attenuation due to propagation through the delay wire is large due to the skin effect. Therefore, by reducing the frequency of the signal delayed by the delay wire, it is possible to suppress signal attenuation accompanying propagation through the delay wire.

  According to the fourth aspect of the invention, the oscillator generates a sine wave having a preset frequency based on the frequency of the radio signal transmitted from the radar device. The first frequency converter superimposes the radio signal received by the receiving antenna with the sine wave generated by the oscillator, thereby generating the low frequency signal. Further, the low-frequency signal delayed by the delay wire is superimposed on the sine wave generated by the oscillator and converted into the high-frequency signal by the second frequency converter. Therefore, the frequency can be converted with a simple configuration.

  According to the fifth aspect, since the delay time is set based on the shortest distance from the object that can be detected by the radar apparatus, the delay time can be set to an appropriate value. Therefore, the optical axis of the radar apparatus can be accurately adjusted in a narrow work space.

  That is, for example, when the radar apparatus is a FMCW (Frequency Modulation Continuous Wave) radar apparatus, the beat signals of the transmission wave and the reception wave are not buried in noise (DC noise or the like) (= accurate). The beat signal needs to be equal to or higher than a predetermined frequency. Therefore, by setting the delay time based on the shortest distance from the object that can be detected by the radar apparatus, the frequency of the beat signal of the transmission wave and the reception wave can be set to an appropriate value (see FIG. 7). ).

  According to the sixth aspect of the invention, the radio wave signal received from the radar apparatus is delayed by the delay time by the waveguide having a length corresponding to the delay time. Signal attenuation associated with delaying the radio signal can be suppressed. Therefore, the optical axis of the radar apparatus can be adjusted more accurately.

  According to the seventh aspect, since the radio signal received from the radar apparatus is amplified by the first amplifier, the attenuation of the signal accompanying the delay of the radio signal received from the radar apparatus is supplemented. be able to. Therefore, the optical axis of the radar apparatus can be adjusted accurately.

  According to the eighth aspect of the invention, since the delayed signal is amplified by the second amplifier, it is possible to compensate for the signal attenuation caused by delaying the radio wave signal received from the radar apparatus. Therefore, the optical axis of the radar apparatus can be adjusted more accurately in a narrow work space.

  According to the ninth aspect of the invention, the filter passes a signal having a frequency corresponding to the radio signal transmitted from the radar apparatus, and a frequency separated from the frequency corresponding to the radio signal transmitted from the radar apparatus. Is interrupted. Therefore, when the delay signal is generated, noise mixed in the delay signal can be removed, so that the optical axis of the radar apparatus can be adjusted more accurately in a narrow work space.

  According to the tenth aspect of the invention, since the radar apparatus is an FMCW type radar apparatus, the optical apparatus can adjust the optical axis of the radar apparatus that can detect the relative position and relative velocity of the object with a simple configuration. Can be performed more accurately in a narrow work space.

  According to the eleventh aspect of the invention, the radar device transmits a radio signal to the radio wave reflecting device according to any one of claims 1 to 9. The radar device receives a signal transmitted from the radio wave reflection device as a reflection signal. Further, the optical axis of the radar apparatus is adjusted based on the reflected signal. Therefore, the work space for adjusting the optical axis of the radar apparatus can be reduced.

  That is, in the radio wave reflection device, the radio signal received from the radar device is delayed by a preset delay time to generate a delay signal, and the generated delay signal is sent to the radar device. Therefore, the work space for adjusting the optical axis of the radar apparatus can be reduced.

Plan view showing an example of relative position and relative velocity detected by the radar device A graph for explaining an example of a method in which the radar apparatus detects the distance R0 and the relative velocity Vd0. The top view which shows an example of the optical-axis adjustment method which adjusts the optical axis of a radar apparatus A graph showing an example of a detection signal detected by the radar device when a reflector is provided instead of the radio wave reflection device Block diagram showing an example of the configuration of the radio wave reflection device FIG. 5 is a block diagram showing an example of the delay circuit shown in FIG. A graph showing an example of a detection signal detected by the radar apparatus shown in FIG. Conceptual diagram showing an example of a method of detecting an angle θ that defines the relative position of the oncoming vehicle VR2 in the radar device.

  Embodiments of a radio wave reflection device according to the present invention will be described below with reference to the drawings. The radio wave reflection device according to the present invention is disposed so as to face the radar device when adjusting the optical axis of the radar device mounted on the vehicle, and reflects the radio wave signal transmitted from the radar device. Device. First, an example of a method for detecting a radar device mounted on a vehicle will be described with reference to FIGS.

  FIG. 1 is a plan view illustrating an example of a relative position and a relative velocity detected by the radar apparatus. The radar apparatus 1 is mounted on the host vehicle VR1 traveling upward in the figure, and an oncoming vehicle VR2 exists within the detection range. The oncoming vehicle VR2 travels in the direction of the vector V (downward in the drawing) at a position on the right side by an angle θ with respect to the traveling direction of the host vehicle VR1 (upward in the drawing).

  The radio wave signal transmitted from the radar device 1 propagates in the air along the straight line WL and is reflected at the capture point DP of the oncoming vehicle VR2. Then, the reflected wave propagates again in the air along the straight line WL and is detected by the radar device 1. In this case, the distance R0 that defines the relative position of the oncoming vehicle VR2 (capture point DP) detected by the radar apparatus 1 is a distance between the radar apparatus 1 and the capture point DP, as shown in the figure. . The angle θ that defines the relative position of the oncoming vehicle VR2 (capture point DP) detected by the radar apparatus 1 is detected by a method described later with reference to FIG.

The relative speed Vd0 of the oncoming vehicle VR2 (capture point DP) detected by the radar apparatus 1 is defined by the following equation (1).
Vd0 = V × cosφ (1)
Here, the speed V is a relative speed of the oncoming vehicle VR2 with respect to the host vehicle VR1, and the angle φ is an angle formed by the traveling direction of the oncoming vehicle VR2 (direction of the speed vector V) and the straight line WL.

  FIG. 2 is a graph for explaining an example of a method in which the radar apparatus 1 detects the distance R0 and the relative speed Vd0. In the present embodiment, a case will be described in which the radar apparatus 1 is an FMCW (Frequency Modulation Continuous Wave) radar apparatus. FIG. 2A is a graph showing an example of the frequency of a signal transmitted and received by the radar apparatus 1, the horizontal axis is time T, and the vertical axis is frequency F. FIG. 2B is a graph G20 showing an example of the frequency of the beat signal generated by the reception signal and the transmission signal, the horizontal axis is time T, and the vertical axis is the frequency FB of the beat signal.

  A graph G0 indicated by a solid line in FIG. 2A is a graph showing an example of a transmission wave transmitted from the radar apparatus 1. As shown in the figure, the transmission wave transmitted from the radar apparatus 1 is a modulation wave in which the frequency F repeats increasing and decreasing linearly. A graph G10 indicated by a broken line in FIG. 2A is a graph showing an example of a reflected wave reflected by an object (here, oncoming vehicle VR2: see FIG. 1). As shown in the figure, when a reflected wave (= received wave) is reflected from an object (here, oncoming vehicle VR2: see FIG. 1) that is separated by a distance R0, Since it is delayed by 2R0 / c (here, speed of light c), when both are mixed, a beat wave is generated. The beat wave frequency Fr is obtained by the following equation (2).

Fr0 = 2R0 / c × a (2)
However, the modulation degree a is an absolute value of the frequency modulation degree that is a change amount of the frequency per unit time, and is a frequency difference Fm that is modulated up and down by a triangular wave, and a time Tm that is required to sweep by the frequency difference. Is given by the following equation (3).

a = Fm / Tm (3)
On the other hand, when the object (here, the oncoming vehicle VR2: see FIG. 1) is moving relative to the radar device 1 (the host vehicle VR1), the frequency according to the distance R0 shown in the above equation (2). In addition to the deviation, a frequency shift Fv occurs due to the Doppler effect, and the frequency shift Fv is given by the following equation (4).

Fv0 = 2Vd0 / c × Fc (4)
However, Vd0: relative speed, Fc: center frequency of transmission wave. Therefore, by mixing the transmission wave and the reception wave that are frequency-modulated with the triangular wave, beat waves having the distance R0 and the relative velocity Vd0 represented by the expressions (2) and (4) are generated.

For example, the beat frequency Fu0 at the time of the upward gradient of the triangular wave (period T2 to time T3 in FIG. 2) is given by the following equation (5).
Fu0 = Fr0−Fv0 (5)
On the other hand, the beat frequency Fd0 when the triangular wave has a downward slope (period T0 to time T1 in FIG. 2) is given by the following equation (6).
Fd0 = Fr0 + Fv0 (6)

The following formulas (7) and (8) are obtained by solving the above formulas (2) to (6) for the distance R0 and the relative speed Vd0.
R0 = (Fd0 + Fu0) / 4 / a × c (7)
Vd0 = (Fd0−Fu0) / 4 / Fc × c (8)
Therefore, the radar apparatus 1 detects the beat wave frequencies Fu0 and Fd0 of the upward and downward gradients of the frequency modulation by the triangular wave, respectively, and uses the equations (7) and (8), respectively. The distance R0 and the relative speed Vd0 can be obtained.

  Further, the frequencies Fu0 and Fd0 of the beat wave generated by the reception signal and the transmission signal are obtained by frequency analysis of the beat wave using a DFT (Discrete Fourier Transform) method or the like. FIG. 2C is a graph G30 showing an example of the frequency characteristic of the beat signal generated by the reception signal and the transmission signal. The horizontal axis is the beat signal frequency FB, and the vertical axis is the signal intensity.

  As shown in FIG. 2C, the beat frequencies Fu0 and Fd0 are detected as the frequencies of the peaks Pu0 and Pd0 in the frequency characteristics of the beat signal, respectively. As shown in FIG. 2C, the beat signal includes a low-frequency noise signal D0 called so-called DC (direct current) noise.

  Thus, since the radar apparatus 1 is an FMCW radar, the distance R0 to the object (here, the oncoming vehicle VR2) and the relative speed Vd0 can be detected with a simple configuration. In the present embodiment, the case where the radar apparatus 1 is an FMCW radar apparatus will be described. However, the radar apparatus 1 may be a radar apparatus of another system (for example, a pulse system).

  FIG. 3 is a plan view showing an example of an optical axis adjustment method for adjusting the optical axis of the radar apparatus 1. FIG. 3A is a side view, and FIG. 3B is a plan view. As shown in the drawing, the radar apparatus 1 emits a radio signal having a vertical spread angle θ1 and a horizontal spread angle θ2 forward (right side in the figure). That is, the detection range DA of the radar apparatus 1 is an elliptical cone-shaped area having the vertex at the radar apparatus 1 defined by the vertical angle θ1 and the horizontal angle θ2. The optical axis of the radar apparatus 1 indicated by the one-dot chain line in the figure is the central axis of the spread angles θ1 and θ2.

  As shown in the figure, when the optical axis adjustment method according to the present invention is performed, the radio wave reflection device 2 according to the present invention is disposed in front of the radar device 1 at a position facing the radar device 1. The The radio wave reflection device 2 is a device that reflects a radio wave signal transmitted from the radar device 1. Here, the radio wave reflection device 2 is disposed at a distance R 1 from the radar device 1. Further, the position in the height direction and the position in the left-right direction of the radio wave reflection device 2 are adjusted and arranged in advance so as to coincide with the reference position of the optical axis of the radar device 1. In other words, the radio wave reflection device 2 is disposed on the optical axis of the radar device 1 indicated by a one-dot chain line in the drawing.

  Then, the radar apparatus 1 is caused to transmit a radio signal toward the radio wave reflection apparatus 2, and the radar apparatus 1 is caused to receive a signal transmitted from the radio wave reflection apparatus 2 as a reflection signal, and the radar apparatus 1 is based on the reflection signal. Adjust the optical axis. That is, the radio wave signal transmitted from the radar apparatus 1 is transmitted so that the reflected signal from the radio wave reflecting device 2 disposed at the reference position of the optical axis is maximized or the center of the phase characteristic coincides with the optical axis direction. The direction is adjusted.

  FIG. 4 shows a radar apparatus when a reflector fixed to the radar apparatus 1 (own vehicle VR1) is provided in place of the radio wave reflection apparatus 2 at the position of the radio wave reflection apparatus 2 shown in FIG. 2 is a graph showing an example of a detection signal detected by 1. FIG. 4A is a graph showing an example of the frequency of a signal transmitted and received by the radar apparatus 1, where the horizontal axis is time T and the vertical axis is frequency F. FIG. 4B is a graph G21 showing an example of the frequency of the beat signal generated by the reception signal and the transmission signal, the horizontal axis is time T, and the vertical axis is the frequency FB of the beat signal.

  A graph G0 indicated by a solid line in FIG. 4A is a graph illustrating an example of a transmission wave transmitted from the radar apparatus 1. A graph G11 indicated by a broken line in FIG. 4A is a graph illustrating an example of a reflected wave reflected by the reflecting plate. As shown in the figure, when a reflected wave (= received wave) is reflected by a reflector (see FIG. 3) located at a distance R1 from the radar apparatus 1, it is 2R1 / Since it is delayed by c (here, the speed of light c), when both are mixed, a beat wave is generated. The beat wave frequency Fr1 is obtained by the following equation (9).

Fr1 = 2R1 / c × a (9)
However, the modulation degree a is an absolute value of the frequency modulation degree that is a change amount of the frequency per unit time, and is a frequency difference Fm that is modulated up and down by a triangular wave, and a time Tm that is required to sweep by the frequency difference. Is given by the following equation (10) (for convenience, the above equation (3) is reprinted).

a = Fm / Tm (10)
On the other hand, since the reflecting plate is fixed with respect to the radar apparatus 1 (the host vehicle VR1), a frequency shift due to the Doppler effect does not occur. Therefore, by mixing a transmission wave and a reception wave that are frequency-modulated with a triangular wave, a beat wave having a distance R1 expressed by the above equation (9) is generated.

Further, the beat frequency Fu1 when the triangular wave has an upward slope and the beat frequency Fd1 when the triangular wave has a downward slope are given by the following equation (11).
Fu1 = Fd1 = Fr1 (11)
Therefore, the radar apparatus 1 can obtain the distance R1 by detecting the frequencies Fu1 and Fd1 of the respective beat waves of the ascending gradient and the descending gradient of the frequency modulation by the triangular wave.

  FIG. 4C is a graph G31 showing an example of the frequency characteristic of the beat signal generated by the reception signal and the transmission signal, the horizontal axis is the frequency FB of the beat signal, and the vertical axis is the signal intensity. As shown in FIG. 4C, the beat frequencies Fu1 and Fd1 correspond to peaks Pu1 and Pd1 in the frequency characteristics of the beat signal, respectively. However, as shown in FIG. 4C, the beat signal includes a low-frequency noise signal D0 called so-called DC (direct current) noise, and peaks Pu1 and Pd1 are affected by the noise signal D0. Cannot be detected.

  That is, since the distance R1 is smaller than the shortest detectable distance (for example, 5 m) (for example, 2 m), the beat frequencies Fu1 and Fd1 are small (= low frequency), and the noise signal D0 exists. Due to this, the peaks Pu1 and Pd1 cannot be detected. For this reason, conventionally, in order to adjust the optical axis of the radar apparatus 1, a vast work space has been required. That is, conventionally, the distance between the radar apparatus 1 and the reflector has to be sufficiently large (for example, 5 m or more).

  Next, an example of the configuration of the radio wave reflection device 2 according to the present invention will be described with reference to FIGS. FIG. 5 is a block diagram illustrating an example of the configuration of the radio wave reflection device 2. As shown in the figure, the radio wave reflection device 2 includes a reception antenna 21, a delay circuit 22, and a transmission antenna 23. The receiving antenna 21 is an antenna that receives a radio signal transmitted from the radar apparatus 1, and outputs the received radio signal to the delay circuit 22.

  The delay circuit 22 (corresponding to a delay means) is a circuit that generates a delay signal by delaying a radio wave signal received by the reception antenna 23 by a preset delay time ΔT. The delayed signal generated by the delay circuit 22 is output to the transmission antenna 23. The transmission antenna 23 is an antenna that transmits the delay signal generated by the delay circuit 22 toward the radar apparatus 1. The delay time ΔT is set based on the shortest distance (for example, 5 m) from an object that can be detected by the radar apparatus 1 as will be described later with reference to FIG.

  FIG. 6 is a block diagram showing an example of the delay circuit 22 shown in FIG. The delay circuit 22 includes an oscillation circuit 221, a first frequency converter 222, a delay wire 223, and a second frequency converter 224. The oscillation circuit 221 (corresponding to an oscillator) is a sine of a frequency (for example, 75 GHz) set in advance based on the frequency of the radio signal transmitted from the radar apparatus 1 (for example, the center frequency Fc = 76 GHz: see FIG. 4). It is a circuit that generates waves. The generated sine wave is output to the first frequency converter 222 and the second frequency converter 224.

  The first frequency converter 222 is interposed between the receiving antenna 21 and the delay wire 223, and reduces the frequency of the radio signal received by the receiving antenna 21 to generate a low frequency signal. Specifically, the first frequency converter 222 generates a low frequency signal by superimposing a radio wave signal received by the receiving antenna 21 with a sine wave generated by the oscillation circuit 221. Here, since the center frequency Fc of the radio wave signal received by the receiving antenna 21 is 76 GHz and the frequency of the sine wave generated by the oscillation circuit 221 is 75 GHz, the first frequency converter 222 causes 1 GHz (= 76 GHz). A low frequency signal of -75 GHz) is generated.

  The delay wire 223 is a wire made of a coaxial cable or the like, and generates a delay signal by delaying the low-frequency signal output from the first frequency converter 222 by a preset delay time ΔT. . Here, the delay wire 223 has a length corresponding to the delay time ΔT. The delay signal generated by the delay wire 223 is output to the second frequency converter 224.

  The second frequency converter 224 is interposed between the delay wire 223 and the transmission antenna 23, and converts the low frequency signal delayed by the delay wire 223 into a high frequency signal corresponding to the radio signal received by the reception antenna 21. Convert. Specifically, the second frequency converter 224 converts the low frequency signal delayed by the delay wire 223 into a high frequency signal by superimposing it on the sine wave generated by the oscillation circuit 221. Here, since the frequency of the low-frequency signal delayed by the delay wire 223 is 1 GHz and the frequency of the sine wave generated by the oscillation circuit 221 is 75 GHz, the second frequency converter 224 causes 76 GHz (= 1 GHz + 75 GHz). Are generated.

  In this way, since the radio wave signal received from the radar apparatus 1 is delayed by the delay time ΔT by the delay wire 223 having a length corresponding to the delay time ΔT, the delay signal can be generated with a simple configuration. Can do.

  Further, when a high-frequency signal is delayed by the delay wire 223, the signal attenuation due to propagation through the delay wire 223 due to the skin effect is large. Therefore, since the frequency of the signal delayed in the delay wire 223 can be reduced by the first frequency converter 222, signal attenuation accompanying propagation through the delay wire 223 can be suppressed.

  Further, the first frequency converter 222 superimposes the radio wave signal received by the receiving antenna 21 with the sine wave generated by the oscillation circuit 221 to generate a low frequency signal, and the second frequency converter 224 Since the low-frequency signal delayed by the delay wire 223 is superimposed on the sine wave generated by the oscillation circuit 221 and converted to a high-frequency signal, the frequency can be converted with a simple configuration.

  In the present embodiment, the case where the radio wave reflection device 2 (delay circuit 22) includes a delay wire 223 that delays the radio wave signal received from the radar device 1 by the delay time ΔT will be described. Instead of the electric wire 223, a form provided with a waveguide that delays the radio wave signal received from the radar apparatus 1 by the delay time ΔT may be used. In this case, since it is possible to suppress signal attenuation associated with delaying the radio wave signal received from the radar apparatus 1, the oscillation circuit 221, the first frequency converter 222, and the second frequency converter 224 are suppressed. This arrangement can be omitted.

  In the present embodiment, the case where the low frequency signal from the first frequency converter 222 is output to the delay wire 223 has been described. However, an amplifier (corresponding to the first amplifier) that amplifies the low frequency signal is The form interposed between the 1 frequency converter 222 and the delay wire 223 may be sufficient. In this case, since the attenuation of the signal accompanying the delay of the signal in the delay wire 223 (= the signal propagates through the delay wire 223) can be complemented, the optical axis of the radar device 1 is adjusted more accurately. be able to. Instead of (or in addition to) the amplifier interposed between the first frequency converter 222 and the delay line 223, an amplifier (second amplifier) is provided between the delay line 223 and the second frequency converter 224. May be provided.

  Further, in the present embodiment, the case where the low frequency signal from the first frequency converter 222 is output to the delay wire 223 has been described, but a low pass filter (LPF: Low) that passes the low frequency signal and blocks the high frequency signal. -Pass Filter (BPF: Band-Pass Filter) (equivalent to a filter) may be provided between the first frequency converter 222 and the delay wire 223. In this case, when the delay signal is generated, noise mixed in the delay signal can be removed, so that the optical axis of the radar apparatus 1 can be adjusted more accurately. In addition, instead of (or in addition to) the low-pass filter (or band-pass filter) interposed between the first frequency converter 222 and the delay line 223, the delay line 223 and the second frequency converter 224 A low-pass filter (or band-pass filter) may be interposed between the two.

  FIG. 7 is a graph showing an example of a detection signal detected by the radar apparatus 1 shown in FIG. FIG. 7A is a graph showing an example of the frequency of a signal transmitted and received by the radar apparatus 1, where the horizontal axis is time T and the vertical axis is frequency F. FIG. 7B is a graph G22 showing an example of the frequency of the beat signal generated by the reception signal and the transmission signal, the horizontal axis is time T, and the vertical axis is the frequency FB of the beat signal.

  A graph G0 indicated by a solid line in FIG. 7A is a graph illustrating an example of a transmission wave transmitted from the radar apparatus 1. A graph G12 indicated by a thick broken line in FIG. 7A is a graph showing an example of a reflected wave reflected by the radio wave reflection device 2 shown in FIGS. A graph G11 indicated by a thin broken line in FIG. 7A is a graph showing an example of a reflected wave reflected by the reflecting plate shown in FIG. As shown in the figure, when the reflected wave (= received wave) is reflected by the radio wave reflecting device 2 (see FIG. 3) that is separated from the radar device 1 by the distance R1, Since it is delayed by (2R1 / c + ΔT) (here, the speed of light c), when both are mixed, a beat wave is generated. The beat wave frequency Fr2 is obtained by the following equation (12).

Fr2 = (2R1 / c + ΔT) × a (12)
However, the modulation degree a is an absolute value of the frequency modulation degree that is a change amount of the frequency per unit time, and is a frequency difference Fm that is modulated up and down by a triangular wave, and a time Tm that is required to sweep by the frequency difference. Is given by the following equation (13) (for the sake of convenience, the above equation (3) is repeated).

a = Fm / Tm (13)
On the other hand, since the radio wave reflection device 2 is fixed with respect to the radar device 1 (the host vehicle VR1), a frequency shift due to the Doppler effect does not occur. Therefore, by mixing the transmission wave and the reception wave that are frequency-modulated with the triangular wave, a beat wave having the distance R1 and the delay time ΔT expressed by the above equation (12) is generated.

Further, the beat frequency Fu2 when the triangular wave has an upward slope and the beat frequency Fd2 when the triangular wave has a downward slope are given by the following equation (14).
Fu2 = Fd2 = Fr2 (14)
Therefore, the radar apparatus 1 can obtain the distance R1 by detecting the frequencies Fu2 and Fd2 of the respective beat waves of the upward gradient and the downward gradient of the frequency modulation by the triangular wave.

  FIG. 7C is a graph G32 showing an example of the frequency characteristic of the beat signal generated by the reception signal and the transmission signal, the horizontal axis is the beat signal frequency FB, and the vertical axis is the signal intensity. As shown in FIG. 7C, the beat frequencies Fu2 and Fd2 correspond to peaks Pu2 and Pd2 in the frequency characteristics of the beat signal, respectively. In addition, unlike the case shown in FIG. 4, the frequencies Fu2 and Fd2 of the peaks Pu1 and Pd1 are sufficiently high, so that the detection thereof is not hindered by the noise signal D0.

  That is, even if the distance R1 is smaller than the shortest detectable distance (for example, 5 m) (for example, 2 m), the signal is delayed by the delay time ΔT by the radio wave reflection device 2, and therefore the beat frequency Fu1. And Fd1 are sufficiently large, and detection of the peaks Pu1 and Pd1 is not hindered by the noise signal D0. Therefore, the work space required for adjusting the optical axis of the radar apparatus 1 can be reduced by using the radio wave reflection apparatus 2 instead of the reflection plate.

Here, the delay time ΔT is set based on the shortest distance RM (for example, 5 m) from an object that can be detected by the radar apparatus 1. For example, when the frequency Fr2 of the beat wave detected by the radar device 1 during the optical axis adjustment (see the above equation (12)) detects an object separated by the shortest distance RM, the beat wave detected by the radar device 1 What is necessary is just to set so that it may become more than the frequency Fr. That is, the delay time ΔT may be set so as to satisfy the following equation (15).
(2R1 / c + ΔT) ≧ 2RM / c (15)
For example, when the distance R1 between the radar apparatus 1 and the radio wave reflection apparatus 2 at the time of optical axis adjustment is 2 m and the shortest distance RM to the object detectable by the radar apparatus 1 is 5 m, the following (16) In order to satisfy the equation, the delay time ΔT may be set.
ΔT ≧ 2 × (RM−R1) /c=0.02 μsec (16)

  As described above, the delay time ΔT can be set to an appropriate value by setting the delay time ΔT based on the shortest distance RM (for example, 5 m) from the object that can be detected by the radar apparatus 1. That is, by setting the delay time ΔT based on the shortest distance RM from the object that can be detected by the radar apparatus 1, as shown in FIG. 7, the frequency of the beat signal of the transmission wave and the reception wave (beat frequency Fu2 and Fd2) can be set to an appropriate value.

  FIG. 8 is a conceptual diagram showing an example of a method of detecting an angle θ (see FIG. 1) that defines the relative position of the oncoming vehicle VR2 in the radar apparatus 1. As shown in the figure, in the radar apparatus 1, receiving antennas 111 and 112 having substantially the same characteristics are arranged side by side with a distance Δd 1 apart in a direction orthogonal to the optical axis shown in FIG. That is, the receiving antennas 111 and 112 are arranged side by side in a substantially vertical direction (or a substantially horizontal direction). Here, in order to describe a case where the angle θ shown in FIG. 1 is detected, the receiving antennas 111 and 112 are arranged in a substantially horizontal direction.

Reflected waves from the oncoming vehicle VR2 are incident on the receiving antennas 111 and 112 from the upper left side forming an angle θ from the optical axis indicated by the alternate long and short dash line in the figure. In this case, the reflected wave incident on the receiving antenna 112 is incident with a delay of the distance Δd2 with respect to the reflected wave incident on the receiving antenna 111. Here, the distance Δd2 is expressed by the following equation (17) using the interval Δd1 between the receiving antennas 111 and 112.
Δd2 = Δd1 × sin θ (17)

The reflected wave incident on the receiving antenna 112 is compared with the reflected wave incident on the receiving antenna 111 by using the distance Δd2 and the wavelength λ of the reflected wave. Incident is delayed by a phase difference Δψ.
Δψ = 2π × Δd2 / λ (18)

By substituting the above equation (17) into the equation (18), the following equation (19) is obtained.
Δψ = 2π × Δd1 × sin θ / λ (19)
Therefore, by detecting the phase difference Δψ of the reflected wave incident on the receiving antenna 112 with respect to the reflected wave incident on the receiving antenna 111, the angle θ can be obtained using the above equation (19). This method is called a phase comparison monopulse method.

Note that the optical axis adjustment method of the radio wave reflection device 2 and the radar device 1 according to the present invention is not limited to the above embodiment, and may be the following embodiment.
(A) In the present embodiment, the case where the delay unit is configured by the delay circuit 22 has been described. However, the delay unit may be realized by a mode other than the circuit. For example, the delay unit may be a waveguide or the like. Further, the delay means may be functionally realized by an arithmetic processing unit such as a microcomputer or a CPU (Central Processing Unit) executing software.

  (B) In the present embodiment, the case where the radar apparatus 1 detects an object in front of the vehicle VR1 (here, the oncoming vehicle VR2) has been described. However, the radar apparatus 1 is an object around the vehicle VR1. Any form may be used if it is detected. For example, the radar apparatus 1 may be configured to detect an object behind the vehicle VR1, or the radar apparatus 1 may be configured to detect an object located on the side of the vehicle VR1.

  (C) Although the case where the radar apparatus 1 is an FMCW radar apparatus has been described in the present embodiment, the radar apparatus 1 may be a radar apparatus of another system (for example, a pulse system).

  The present invention is applied, for example, to a radio wave reflection device that is arranged to face a radar device and reflects a radio signal transmitted from the radar device when adjusting the optical axis of a radar device mounted on a vehicle. can do. Further, the present invention can be applied to an optical axis adjustment method for adjusting the optical axis of a radar device mounted on a vehicle, for example.

DESCRIPTION OF SYMBOLS 1 Radar apparatus 111,112 Reception antenna 2 Radio wave reflection apparatus 21 Reception antenna 22 Delay circuit (delay means)
221 Oscillator circuit (oscillator)
222 first frequency converter 223 delay wire 224 second frequency converter 23 transmitting antenna

Claims (11)

When adjusting the optical axis of a radar device mounted on a vehicle, the radio wave reflection device is disposed to face the radar device and reflects a radio wave signal transmitted from the radar device,
A receiving antenna for receiving a radio wave signal transmitted from the radar device;
Delay means for delaying the radio signal received by the receiving antenna by a preset delay time to generate a delayed signal;
A radio wave reflection apparatus comprising: a transmission antenna that transmits a delay signal generated by the delay means toward the radar apparatus.   The radio wave reflection device according to claim 1, wherein the delay unit includes a delay wire having a length corresponding to the delay time. The delay means is
A first frequency converter that is interposed between the receiving antenna and the delay wire, reduces a frequency of a radio signal received by the receiving antenna, and generates a low-frequency signal;
A second frequency converter interposed between the delay wire and the transmission antenna and converting a low frequency signal delayed by the delay wire into a high frequency signal corresponding to a radio wave signal received by the reception antenna; The radio wave reflection device according to claim 2, further comprising: The delay means is
An oscillator that generates a sine wave having a preset frequency based on the frequency of the radio signal transmitted from the radar device;
The first frequency converter generates the low frequency signal by superimposing a radio wave signal received by the receiving antenna with a sine wave generated by the oscillator,
4. The radio wave reflection according to claim 3, wherein the second frequency converter converts the low-frequency signal delayed by the delay wire into the high-frequency signal by superimposing the low-frequency signal on a sine wave generated by the oscillator. apparatus.   The radio wave reflection device according to claim 1, wherein the delay time is set based on a shortest distance from an object detectable by the radar device.   The radio wave reflection device according to claim 1, wherein the delay unit includes a waveguide having a length corresponding to the delay time.   The radio wave reflection device according to claim 1, wherein the delay unit includes a first amplifier that amplifies the radio wave signal received by the reception antenna.   The radio wave reflection device according to claim 1, wherein the delay unit includes a second amplifier that amplifies the delay signal.   The delay means includes a filter that allows a signal having a frequency corresponding to a radio wave signal transmitted from the radar apparatus to pass, and blocks a signal having a frequency separated from a frequency corresponding to the radio wave signal transmitted from the radar apparatus. The radio wave reflecting device according to claim 1.   The radio wave reflection device according to claim 1, wherein the radar device is an FMCW (Frequency Modulation Continuous Wave) radar device. An optical axis adjustment method for adjusting an optical axis of a radar device mounted on a vehicle,
The radar device transmits a radio signal toward the radio wave reflection device according to any one of claims 1 to 9,
The radar device receives a signal transmitted from the radio wave reflection device as a reflection signal,
An optical axis adjustment method for adjusting an optical axis of the radar apparatus based on the reflected signal.

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