JPH10107540A - Radio wave reflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection sensitivity of a vehicle position using a radio wave by improving a scattering characteristic of the surface of the radio wave reflector. SOLUTION: A plurality of radiation elements 13 in resonance with a radio wave are arranged in an array at an interval of (d) on the surface of the radio reflector 11. A reflected signal level is increased with respect to a resonated radio wave. The reflected signal level is selectively increased with respect to a radio wave made incident at a prescribed incident angle depending on a wavelength of a radio wave and the interval (d) so as to improve the rear scattering characteristic much more thereby improving the detection sensitivity furthermore.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave reflector installed on a road surface for detecting the position of a vehicle using radio waves.

[0002]

2. Description of the Related Art Conventionally, there has been known a technique for detecting a relative position of a vehicle with respect to a traveling road in order to automatically drive the vehicle.

For example, Japanese Patent Application Laid-Open No. 1-109910 discloses a technique in which a light reflecting tape is laid on a track, and a pair of optical sensors is provided in a vehicle below the width of the reflecting tape to detect a vehicle attitude. Have been. In addition, there is also known a technique of detecting a relative position of a vehicle with respect to a white line by photographing a road surface with an in-vehicle camera and extracting a white line in a screen.

[0004]

However, when a light reflecting tape is used, sufficient light reflection may not be obtained due to contamination of the tape. Also, aside from indoors, actual roads are affected by rain, snow, etc. In the case of rainy weather, light is well reflected not only by light reflecting tapes but also by puddles, so the vehicle position cannot be detected with high accuracy. There was a problem. Similarly, when an in-vehicle camera is used, the vehicle is easily affected by the weather, and there is a problem that the contrast between the white line and other portions of the road surface is not sufficient in rainy weather or the like, and the white line cannot be accurately extracted.

Therefore, as shown in FIG. 7, there is a method of detecting a vehicle position using radio waves having a wavelength equal to or longer than a millimeter wave.
That is, a radio wave reflector 2 as a lane marker is provided at a predetermined position on the road surface 1, for example, at the center of the road surface 1, a radio wave transceiver 4 is provided on the vehicle 3, and the presence or absence of the radio wave reflector 2 is detected from the reflection intensity of the transmitted radio wave. Thus, the vehicle position is detected. However, since the reflection intensity may change due to changes in the radio wave scattering characteristics on the surface of the radio wave reflector 2, some measures are required to accurately detect the vehicle position. In particular, as shown in FIG. 8, when the radio wave is transmitted from the antenna 5 to the oblique front 7 inclined by an angle に 対 し て with respect to the traveling direction 6 of the vehicle 3 and the position of the radio wave reflector 2 in front is detected, It is necessary to improve the reflection characteristics to the light.

SUMMARY OF THE INVENTION An object of the present invention is to provide a radio wave reflector capable of improving the scattering characteristics of the surface of the radio wave reflector and improving the detection sensitivity of a vehicle position using radio waves.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a radio wave reflector installed on a road surface for detecting the position of a vehicle using radio waves having a wavelength of a millimeter wave or more. A radio wave reflector having a radiating element on its surface that resonates at the frequency of the radio wave and reflects an incident radio wave. According to the present invention, the surface of the radio wave reflector has a radiating element that resonates at the frequency of the position detection radio wave and reflects the incident radio wave. For example, a radiating element can be formed by printing a shape such as a half-wave dipole antenna or a patch antenna. Since the reflection intensity of the radio wave from the surface of the radio wave reflector increases, the backscattering characteristic can be improved, and the detection sensitivity (S / C ratio) can be improved.

In the present invention, the radio wave has a predetermined wavelength λ, is transmitted downward at a predetermined angle with respect to the traveling direction of the vehicle, and is incident on the radiating element at an incident angle θ. The radiating element is arranged at a distance d along the traveling direction of the vehicle.
And a product of sin θ is arranged at intervals d such that the product is an integral multiple of the wavelength λ. According to the present invention, the radio wave used for vehicle position detection has a predetermined wavelength λ, is transmitted downward at a predetermined angle with respect to the traveling direction of the vehicle, and is incident on the radiating element at an incident angle θ. You. The difference in the traveling distance of the radio wave reflected by the adjacent radiating element and returned in the incident direction is the product of the interval d and sin θ,
Since this value is an integral multiple of the wavelength λ of the radio wave, the reflected signal level can be maximized without canceling each other.

Further, the present invention is a radio wave reflector installed on a road surface for detecting the position of a vehicle using radio waves having a wavelength of a millimeter wave or more, wherein the radio wave reflector is provided on a surface thereof.
A radio wave reflector having irregularities formed thereon. According to the present invention, since irregularities are formed on the surface of the radio wave reflector, the backscattering characteristic for radio waves incident on the surface is improved as compared with a smooth surface, and the detection sensitivity of a vehicle position using radio waves is improved. be able to.

Further, in the present invention, the unevenness has a saw-tooth shape, and reflects an incident radio wave in an incident direction. According to the present invention, since saw-tooth irregularities are formed on the surface of the radio wave reflector and the incident radio wave is reflected in the incident direction, the incident radio wave can be strongly reflected in the incident direction, , The detection sensitivity of the vehicle position can be improved.

[0011]

1 and 2 show a schematic configuration of a radio wave reflector 11 as one embodiment of the present invention. FIG. 1 is a partial perspective view, and FIG. 2 is a partial side sectional view. The radio wave reflector 11 is installed on a road surface 12 of a road in order to perform position detection and the like using a radio wave having a wavelength of a millimeter wave or more while a vehicle such as an automobile is traveling. On the surface of the radio wave reflector 11, a plurality of radiating elements 13 are printed and arranged in an array using a conductive material such as a metal foil. A fixed interval d is provided between the radiating elements 13. Such an arrangement of the radiating elements 13 has the same structure as a microstrip antenna (abbreviated as “MSA”) in which there is no feed line for supplying high-frequency power at a predetermined phase and the parasitic radiating elements are arranged and printed in an array. is there.

The main body of the radio wave reflector 11 is formed of an insulator 14 having durability and electrical insulation. As the insulator 14, a durable paint or the like used for display on a road is used. When it is installed on an actual road or the like, the surface of the radio wave reflector 11 and the radiating element 13 may be further covered with a protective insulating film.

The radiating element 13 has a circular patch and notches provided at both ends of one diameter. The radiating element 13 has a resonance frequency determined by its shape. When a radio wave of the resonance frequency enters as an electromagnetic wave, it is excited and selectively emits a radio wave of that frequency. The size of the radiating element 13 roughly corresponds to the wavelength λ with respect to the resonance frequency,
It becomes smaller as the wavelength λ is shorter. As another form of the radiating element 13, a rectangular patch, a half-wave dipole antenna, or the like can be used. Further, by using radio waves of a plurality of frequencies for position detection and changing the resonance frequency, it is possible to realize a system in which the radio wave reflector 11 identifies frequencies.

FIG. 3 shows the change in the reflection coefficient with respect to the incident angle when the radiating elements 13 are arranged in an array at a constant interval d as shown in FIG. FIG. 4 shows a plurality of radiating elements 13.
2 shows a state in which a radio wave is incident as an incident wave 17, respectively. Each incident wave 17 is incident on the normal 18 of each radiating element 13 at a constant incident angle θ. As a result, a path difference Δ is generated between the radio waves reflected by the radiating elements 13 adjacent to each other in the incident direction as shown in the following first equation.

Δ = d × sin θ (1) When the path difference Δ becomes an integral multiple of the wavelength λ of the radio wave, the radio wave reflected by the adjacent radiating element 13 in the incident direction of the radio wave is directed in another direction. Is emphasized compared to the reflected radio waves. That is, n is an integer (n = 1, 2, 3,...)
When the following second expression is satisfied, the reflection signal level can theoretically be suppressed to about 13 dB as compared with the case where the reflection signal level is incident at θ = 0 in the direction of the normal 18.

[0016]

(Equation 1)

Generally, the incident wave 17 is, as shown in FIG.
A certain angle に 対 し て (ψ = π /
The radiation is radiated from the antenna 20 inclined by (2-θ).
If ψ = π / 2, that is, θ = 0, the reflection signal level becomes maximum, but only sensing of the radio wave reflector 11 corresponding to the current position value of the vehicle can be performed. When driving a vehicle traveling at a practical speed by obliquely looking ahead, the position of the radio wave reflector 11 can be detected to some extent earlier.

FIG. 5 shows a schematic shape of a radio wave reflector 41 according to still another embodiment of the present invention. FIG. 5A is a partial side sectional view, and FIG. 5B is a partial plan view. The radio wave reflector 41 of the present embodiment is entirely made of the same insulator as the insulator 14 of the embodiment of FIG. 1, and the surface thereof is formed with irregularities 42 acting as a quadrangular pyramid-shaped corner reflector. . The size of the unevenness 42 is set to such an extent that it is not considered to be smooth with respect to the wavelength of the position detecting radio wave. By forming such irregularities 42 on the surface, it is possible to improve the backscattering characteristic with respect to the radio wave as compared with a flat plate, and to improve the detection sensitivity by the radio wave.

FIG. 6 shows a radio wave reflector 51 having a saw-toothed unevenness formed on the surface as still another embodiment of the present invention.
Shows a state where the incident wave 45 is reflected in the incident direction as the reflected wave 46. FIG. 6A shows a state where the reflected wave 46 is returned in a direction parallel to the incident direction with respect to the incident wave 45 incident from a direction inclined with respect to the normal to the surface of the radio wave reflector 51. FIG. 6B shows a state in which an incident wave 45 that is perpendicularly incident on the surface of the radio wave reflector 51 is directly returned to the incident direction as a reflected wave 46. FIG. 6C shows a partial appearance of the radio wave reflector 51. By making the irregularities on the surface of the radio wave reflector 51 into an asymmetric saw-tooth shape having a gentle inclination in the radio wave incident direction, the radio wave incident is reflected in the incident direction or in a direction parallel thereto, as shown in FIG. The backscattering characteristic can be improved as compared with the symmetrical irregularities 42 having a quadrangular pyramid shape.

[0020]

As described above, according to the present invention, on the surface of the radio wave reflector, there is provided a radiating element which resonates at the frequency of the radio wave and reflects the incident radio wave. Since the reflection intensity of the radio wave from the surface of the radio wave reflector increases, the backscattering characteristics can be improved and the detection sensitivity can be improved.

Further, according to the present invention, since the interval d between the radiating elements is set so as to maximize the reflected signal level, the detection sensitivity can be improved.

Further, according to the present invention, only by forming irregularities on the surface of the radio wave reflector, the backscattering characteristic for radio waves incident on the surface is improved as compared with a smooth surface, and the detection sensitivity of the vehicle position is improved. be able to.

Further, according to the present invention, a sawtooth-shaped unevenness is formed on the surface of the radio wave reflector to reflect an incoming radio wave in the incident direction to improve the backscattering characteristic, and the position of the vehicle using the radio wave is improved. Can be improved.

[Brief description of the drawings]

FIG. 1 is a partial perspective view showing a schematic configuration of a radio wave reflector 11 according to an embodiment of the present invention.

FIG. 2 is a side sectional view of the radio wave reflector 11 of FIG.

FIG. 3 is a graph showing the relationship between the angle of incidence on the radio wave reflector 11 of FIG. 1 and the reflection coefficient.

FIG. 4 shows an incident wave 17 at an incident angle θ on the radio wave reflector 11 of FIG.
FIG. 3 is a schematic side cross-sectional view showing a state where light is incident.

FIG. 5 is a radio wave reflector 4 according to still another embodiment of the present invention.
1 is a partial side sectional view and a plan view showing a schematic configuration of FIG.

FIG. 6 shows a radio wave reflector 5 according to still another embodiment of the present invention.
FIG. 2 is a partial side sectional view and a perspective view showing a schematic shape of No. 1;

FIG. 7 is a simplified front view showing a schematic configuration related to vehicle position detection according to the related art.

FIG. 8 is a simplified side view showing a schematic configuration related to vehicle position detection by a radio wave reflector according to the prior art.

[Explanation of symbols]

 11, 41, 51 Radio wave reflector 12 Road surface 13 Radiating element 14 Insulator 17, 45 Incident wave 18 Normal line 20 Antenna 46 Reflected wave 42 Irregularity

Claims (4)

[Claims] 1. A radio wave reflector installed on a road surface for detecting a position of a vehicle using radio waves of a wavelength equal to or greater than a millimeter wave, wherein the radio wave reflector has a surface on which a radio wave frequency is set. A radio wave reflector having a radiation element that resonates and reflects an incident radio wave. 2. The radio wave has a predetermined wavelength λ,
It is transmitted downward at a predetermined angle with respect to the traveling direction of the vehicle, and is incident on the radiating element at an incident angle θ. The radiating element has a distance d and sin along the traveling direction of the vehicle.
2. The radio wave reflector according to claim 1, wherein a plurality of the wave reflectors are arranged at an interval d such that a product of [theta] and the wavelength is an integral multiple of the wavelength [lambda]. 3. A radio wave reflector installed on a road surface for detecting the position of a vehicle using a radio wave of a wavelength equal to or greater than a millimeter wave, wherein the radio wave reflector has irregularities formed on a surface thereof. A radio wave reflector. 4. The radio wave reflector according to claim 3, wherein the unevenness has a saw-tooth shape, and reflects an incident radio wave in an incident direction.