JP2009133682A - Reflector for millimeter wave radar - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflector device for a millimeter wave radar with less fluctuation of reflectance due to rain or snow. <P>SOLUTION: The reflector 3 for a millimeter wave radar comprises, a pole 15 comprising a base part 16, a reflector 10, a support part 11 supporting the reflector 10 by means of a reflector fixing screw 12, a fixture 13 fixing the support part 11 onto the pole 15, and a fixing screw 14 for fixing the fixture 13 onto the pole. As material of the reflector, aluminum, stainless materials or the like is used. Adhesion of rain or snow is prevented by means of Teflon (R) coating, titanium oxide coating, urethane coating or the like. There is provided a gap by making the reflector 10 simple ring shape so that rain or snow hardly adheres onto it. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reflector for millimeter wave radar that reflects millimeter waves transmitted from a radar transmitter.

  Conventionally, as a technology for improving the safety of a vehicle, a radar device is provided on the front part of the vehicle, and a millimeter wave is radiated to the preceding vehicle and the reflected wave is received. There is known a rear-end collision prevention system for preventing rear-end collisions. For example, Patent Document 1 discloses a reflector device for a radar system used in such a rear-end collision prevention system.

  As such a reflector device, as shown in Patent Document 2, a corner cube-shaped device in which three right-angled isosceles triangular reflectors are combined is used. FIG. 8 shows a corner cube-shaped reflector device 20. The reflector device 20 includes three reflecting plates 22, 24, and 26 that can reflect an incident radio wave Sin, and each reflecting plate is formed into a right-angled isosceles triangle that is congruent with each other, and is a vertex thereof. Are joined in a corner cube shape by aligning the right-angled portions indicated by dotted lines and making them perpendicular to each other.

  As shown in FIG. 8, when an externally transmitted radio wave is incident on the reflector device 20 as an incident radio wave Sin, the incident radio wave Sin is reflected from the reflecting surface of the reflector 26 at a reflection angle equal to the incident angle of the incident radio wave Sin. Further, the reflected radio wave is incident on the reflection plate 22 and reflected from the reflection plate 22 in the incident direction of the incident radio wave Sin. In this way, the incident radio wave Sin is reflected a plurality of times on the reflecting surfaces of the reflectors 22, 24, and 26, and the reflected radio wave Sout is reflected in the incident direction of the incident radio wave Sin.

JP 2000-103283 A JP-A-8-125434

  When the reflector device of the radar system described above is used, there is a problem that the reflectance of the millimeter wave fluctuates due to rain or snow adhering to the reflector device. This is because in millimeter waves of several tens of GHz, water droplets and water films have the same radio wave reflectance as that of metal surfaces. In general, since the opening of a conventional reflector is oriented horizontally, water drops and water films tend to accumulate, and a means for detecting the weather condition is separately provided, and a means for correcting the reflectance of the reflector device according to the weather condition is required. Met.

  In particular, when a reflector device is used as a reference signal detection device in a radar system that detects the intrusion of a person or vehicle into a predetermined outdoor area, the reflecting surface of the reflector device becomes contaminated with exhaust gas or dirt, and rain or snow adheres. There is a problem that the reference reflection signal fluctuates due to fluctuations in reflectance due to rain or snow. Therefore, an object of the present invention is to provide a reflector device for millimeter wave radar in which the reflectance fluctuation due to rain or snow is small.

  In order to achieve the above object, a reflector for millimeter wave radar according to the present invention is a reflector for millimeter wave radar that reflects a millimeter wave transmitted from a radar transmitter so as to have a predetermined reflection distribution. And a supporting member that supports the reflecting plate at a predetermined angle, and by opening the non-reflecting part, the reflection performance is changed due to adhesion of rain or snow. It is characterized by being suppressed.

  In the reflector for millimeter wave radar according to the present invention, the reflecting plate is characterized in that the width of the reflecting portion and the width of the opening are set so as to have a convex reflection distribution.

  In the reflector for millimeter wave radar according to the present invention, the reflector has a convex reflection distribution at the center and the outer periphery thereof.

  In the reflector for millimeter wave radar according to the present invention, the reflecting plate has a convex reflection distribution in which the reflection characteristic at the outer periphery is reduced by a predetermined value with respect to the reflection characteristic at the center.

  Furthermore, in the reflector for millimeter wave radar according to the present invention, the reflecting plate is coated with a water-repellent paint in order to keep the surface of the reflecting portion uniform.

  By using the millimeter-wave radar reflector according to the present invention, it is possible to provide a millimeter-wave radar reflector with less variation in reflectance due to rain or snow. Also, it is desirable that the side lobe level is low in order to reduce the influence of multipath from the ground and other reflecting objects. The millimeter wave radar reflector according to the present invention is advantageous in that it is less susceptible to multipath by selecting an appropriate number of slots and can be further miniaturized at the same time.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings.

  FIG. 1 shows an appearance of the millimeter wave radar reflector 3. What is characteristic in the present embodiment is that the reflector 10 has a simple ring shape so as to prevent rain and snow from adhering, and a gap is positively provided.

  The millimeter wave radar reflector 3 includes a pole 15 having a base portion 16, a reflector 10, and a reflector fixing screw 12 that fixes the reflector 10 to a support portion 11. The support portion 11 supports the reflector 10, and the support portion 11. A fixing tool 13 for fixing the fixing tool 13 to the pole, and a fixing screw 14 for fixing the fixing tool 13 to the pole. In addition, the reflector material is aluminum or stainless steel, and the surface is made of Teflon (registered trademark), urethane coating, etc., to improve water repellency, prevent rain and snow from sticking, or apply titanium oxide. The rain water is made uniform.

  FIG. 2 shows an example of a radar system 1 including a millimeter wave radar reflector 3. The radar system 1 detects intrusion of a person or a vehicle into a predetermined outdoor area, transmits a radio wave to the monitoring area, and receives a reflected radio wave from an obstacle, a radar device 2, And a millimeter wave radar reflector 3 for detecting a reflected radio wave as a reference signal.

  The millimeter wave radar reflectors 3 are provided at both corners of the monitoring area, and a reference value is observed around −90 degrees in the observation signal from the right transmitting / receiving antenna. This reference value changes depending on the rain and snow conditions blowing into the monitoring area, but the change in the millimeter wave radar reflector 3 itself is small. Further, by correcting the threshold value in accordance with the change in the reference value, it becomes possible to reduce detection omissions and false detections of people and vehicles that have entered the monitoring area.

  FIG. 3 schematically shows the reflection characteristics of the reflector 10. From the top, (A) weight characteristics, (B) element block, (C) reflection element, and (D) a front view of the reflector are shown. Yes. The cross-shaped holding member shown in the reflector 10 of FIG. 1 is omitted.

  The reflector 10 reflects the radio wave transmitted from the radar apparatus. However, if the reflector 10 has strong directivity (the beam width is narrow), not only fine adjustment is required when installing the reflector 10, but also a small displacement such as vibration. However, since the reflected intensity of the reflected wave varies, it is desirable to have a predetermined wide beam width. Therefore, the weight characteristic of the reflector 10 has a convex weight characteristic as shown in FIG. In order to realize such weight characteristics, the reflector 10 is divided into concentric element blocks as shown in FIG. 3 (B), and a reflective element is provided in each element block as shown in FIG. 3 (C). A ring-shaped reflector 10 as shown in FIG.

FIG. 4 shows a reference reflection characteristic for comparison using a rectangular aperture as a reflector and a millimeter wave of 60.5 GHz. The rectangular opening is a flat and horizontal plate of 100 mm, and was obtained by simulation as a reflector made of aluminum or stainless steel. As a simulation result, a calculation level which is a calculation level and an RCS (dBsm) using RCS (Radar Cross Section) as a scale for evaluating the reflection characteristic with respect to the radar were obtained. Note that dBsm = 10 · log (measured RCS / RCS of unit m ² ), and in general, the RCS increases as the frequency increases. As shown in FIG. 4, the calculation level was 46.1 dB, the RCS was as high as 17.08 dBsm, and the beam width was 2.7 degrees. Further, the side lobe showing the next highest value after the peak level was -13 dB at a θ angle of 3 degrees, -18 dB at a θ angle of 6 degrees, and -22 dB at a θ angle of 10 degrees, and the beam characteristics were gentle. .

  FIG. 5 shows a reflection characteristic of a millimeter wave of 60.5 GHz obtained by using a circular aperture with a flat plate having a radius of 50 mm as a reflector. The calculation level is 45.1 dB, RCS is 16.08 dBsm, and the beam width is 3.8 degrees. It showed the characteristics. Further, the side lobe showing the next highest value after the peak level is −18 dB at a θ angle of 6 degrees and −25 dB at a θ angle of 9 degrees, and the side lobe value is reduced as compared with the rectangular opening of FIG. Thus, when the side lobe level is reduced, the influence of multipath from the ground and other reflecting objects is reduced, so that a favorable characteristic is exhibited as a reflector. Therefore, it was decided to increase the beam width by providing a slot in a circular opening made of a flat plate having a radius of 50 mm.

  FIG. 6 shows a reflector in which a slot is provided in a circular opening of a flat plate having a radius of 50 mm. Here, since the reflectivity of the outer peripheral portion decreases, a reflector having a radius of 35.3 mm is formed by forming a gap. Similarly, when the reflection characteristics of a millimeter wave of 60.5 GHz were obtained, the calculation level showed characteristics of 38.07 dB, RCS of 9.05 dBsm, and the beam width of 5.22 degrees. Thus, by providing a slot, it becomes possible to have a beam width of about 5 degrees, and the side lobe that shows the next highest value of the peak level is −19 dB at a θ angle of 30 degrees and −22 dB at a θ angle of 25 degrees. It became. From this, it was confirmed that the beam characteristics of the reflector provided with a slot in the circular aperture are improved as compared with the reflector of the circular aperture type in FIG. 5, and the influence of multipath from the ground and other reflectors is reduced. In addition, in order to reduce the side lobe level and further reduce the size of the reflector, a reflector with an overall reduction of the side lobe and the number of slots was examined.

  FIG. 7 shows a reflector aimed at reducing the overall side lobe and reducing the size by reducing the number of slots from 3 to 2. By reducing the number of slots, it became possible to reduce the outer dimensions, and the radius was reduced from 35.3 mm to 30.7 mm. Similarly, when 60.5 GHz millimeter wave reflection characteristics were obtained, the calculation level showed 37.71 dB, RCS 8.69 dBsm, and beam width 5.94 degrees. Thus, depending on the setting, the beam width can be maintained or increased even if the number of slots is reduced, and the required beam width exceeding about 5 degrees can be provided. Also, the side lobe values were -23 dB at a θ angle of 37 degrees and -25 dB at a θ angle of 29 degrees, and the side lobe level was reduced as a whole compared to the reflector of FIG. By optimizing in this way, the side lobe can be reduced and the reflector can be downsized.

  As described above, by using the reflector for millimeter wave radar according to the present embodiment, it is possible to provide a reflector for millimeter wave radar with little variation in reflectance due to rain or snow. Further, the millimeter wave radar reflector according to the present invention can further reduce the side lobe and reduce the size by selecting an appropriate number of slots and slot width.

  In the present embodiment, the reflection distribution has been described as a convex shape. However, the present invention is not limited to this, and a double convex shape may be used as a weight shape that increases the beam width. A line of rectangular shapes may be used. Further, the numerical values shown in the present embodiment are not limited to this, and needless to say, they should be set as optimum parameters according to the millimeter wave frequency, the beam width required by the system, and the like. Absent.

  In addition, in the present embodiment, the reflector is reduced in size, but it is also possible to reduce the side lobes and further improve the performance associated with the reflector in the installation of the reflector. As an example, when the pole 15 in FIG. 1 is made of metal, the diameter of the pole 15 is reduced to, for example, about 1/3 of the current state in order to reduce the reflection of millimeter waves, or the pole 15 May be made of a low reflection material such as FRP.

It is an external view which shows the external appearance of the reflector for millimeter wave radar which concerns on this embodiment. It is explanatory drawing explaining the outline | summary of the radar system which used the reflector for millimeter wave radar as a reference signal detector. It is explanatory drawing explaining the reflective characteristic of the reflector for millimeter wave radars concerning this embodiment. It is explanatory drawing explaining the reflection characteristic at the time of using a rectangular opening as a reflector for millimeter wave radar. It is explanatory drawing explaining the reflection characteristic at the time of using circular opening as a reflector for millimeter wave radar. It is explanatory drawing explaining the reflection characteristic at the time of setting it as a ring opening of radius 35.3mm as a reflector for millimeter wave radars. It is explanatory drawing explaining the reflection characteristic at the time of setting it as a ring opening of radius 30.7mm as a reflector for millimeter wave radars. It is explanatory drawing explaining the outline | summary of the conventional reflector apparatus for millimeter wave radars.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 radar system, 2 radar apparatus, 3 millimeter wave radar reflector, 4 transmission / reception antenna, 10 reflector, 11 support part, 12 reflector fixing screw, 13 fixing tool, 14 fixing screw, 15 pole, 16 base part, 20 reflector apparatus, 22, 24, 26 Reflector.

Claims (5)

In the millimeter wave radar reflector that reflects the millimeter wave transmitted from the radar transmitter,
A reflecting plate in which reflecting portions and non-reflecting portions are alternately provided so as to have a predetermined reflection distribution;
A support member for supporting the reflector at a predetermined angle;
With
A reflector for millimeter wave radar, characterized in that a change in reflection performance due to adhesion of rain or snow is suppressed by opening a non-reflective portion. In the reflector for millimeter wave radars of Claim 1,
A reflector for a millimeter wave radar, wherein the reflector has a convex reflection distribution, and the width of the reflection portion and the width of the opening are set. In the reflector for millimeter wave radars of Claim 1,
The reflector for a millimeter wave radar, wherein the reflector has a convex reflection distribution at a central portion and an outer periphery thereof. The reflector for millimeter wave radar according to any one of claims 1 to 3,
The reflector for a millimeter wave radar, wherein the reflector has a convex reflection distribution in which a reflection characteristic at an outer periphery thereof is lowered by a predetermined value with respect to a reflection characteristic at a central portion. The reflector for millimeter wave radar according to any one of claims 1 to 4,
The reflector for millimeter wave radar, wherein the reflector is coated with a water-repellent paint in order to keep the surface of the reflector part uniform.

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