JP4194735B2 - Attenuator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio wave attenuator used for suppressing unnecessary radio waves generated in bidirectional communication between a roadside antenna and an onboard unit side antenna in an automatic toll collection system, for example.
[0002]
[Prior art]
Recently, an automatic toll collection system (also referred to as ETC (Electronic Toll Collection System)) has attracted attention as a means of relieving congestion at toll gates on toll roads. This system automatically collects tolls by two-way wirelessly communicating information about tolls between the roadside antenna and the onboard unit antenna in the onboard unit mounted on the vehicle. .
[0003]
In this system, the roadside antenna is installed at a toll gate or a display installed on the road, and radiates radio waves from above to a car passing through the gate.
[0004]
[Problems to be solved by the invention]
By the way, when a toll booth that uses an automatic toll collection system is provided on the lower road at a three-dimensional intersection, radio waves radiated from the roadside antenna are multiplexed between the road surface and the lower surface of the upper road. There is a possibility of reflection. For this reason, the reach of radio waves above the threshold that can be received by the vehicle-mounted device antenna is wider than the target range, and multiple vehicles running on the same lane or adjacent lanes enter the reach. There is a problem that the system may malfunction.
[0005]
Also, not only in the case of a three-dimensional intersection, the radio wave radiated from the roadside antenna is reflected multiple times between the road surface and the indicator installed on the road, or the radio wave radiated from the roadside antenna is And multiple reflections between the roof of the toll gate and the same problem may occur. Furthermore, the radio wave radiated from the roadside antenna may be reflected by the support part of the display or the side part of the gate of the toll gate, and the same problem may occur. In addition, when an automatic toll collection system is adopted in a plurality of lanes, radio waves radiated from a roadside antenna in a certain lane leak to other adjacent lanes, causing interference between adjacent lanes. It may occur.
[0006]
By the way, the electromagnetic wave absorber comprised using electromagnetic wave absorption materials, such as a ferrite, is conventionally known as what attenuates an unnecessary electromagnetic wave. Therefore, it is conceivable to use such a radio wave absorber to suppress unnecessary radio waves in the automatic toll collection system as described above.
[0007]
However, in the automatic toll collection system, when means for suppressing unnecessary radio waves, such as the above-described radio wave absorber, is provided, the means are inevitably installed outdoors. Therefore, as a means for suppressing unnecessary radio waves in the automatic toll collection system, a means with a simple configuration is desired in order to improve durability and ease of installation.
[0008]
Japanese Patent Application Laid-Open No. 11-261283 discloses a radio wave absorber using a reflector having an uneven surface shape that reverses the phase of a reflected wave. However, in Japanese Patent Application Laid-Open No. 11-261283, the fourth column, lines 11 to 13, describes that “the uneven waves with the wavelength λ or more of the communication radio wave are used to reduce the reflected waves on the uneven surfaces”. On the other hand, in FIG. 2B, the uneven step is described as “λ / 2”, and the size of the uneven step necessary to reduce the reflected wave is as follows. It is unknown.
[0009]
Further, as shown in FIG. 2B of Japanese Patent Laid-Open No. 11-261283, when the size of the uneven step is λ / 2, as will be described later in the embodiment, It hardly functions as a radio wave absorber for radio waves incident at an incident angle within a range of about 50 ° to 50 °. As can be seen from FIG. 1 of Japanese Patent Application Laid-Open No. 11-261283, as a radio wave absorber, it is necessary to practically absorb radio waves incident at an incident angle in the range of about 0 ° to 50 °. Although it is considered that there are many, the radio wave absorber shown in FIG. 2B of JP-A-11-261283 cannot satisfy this requirement.
[0010]
Furthermore, Japanese Patent Application Laid-Open No. 11-261283 does not consider the relationship between the incident angle of radio waves and the size of the uneven steps, and is necessary for reducing the reflected waves with respect to radio waves incident at a predetermined incident angle. The size of the uneven step is also unknown.
[0011]
Japanese Patent Application Laid-Open No. 11-261283 discloses a triangular wavefront shape and a rectangular wavefront shape as the uneven surface shape. However, in a radio wave absorber using a reflector having such a triangular wavefront shape or a rectangular wavefront shape, the shape of the reflective surface is not isotropic. The characteristics may change greatly depending on the polarization state.
[0012]
Japanese Patent Application Laid-Open No. 58-34602 and Japanese Patent Application Laid-Open No. 9-181474 disclose a technique for forming a concavo-convex surface on a radio wave absorber to widen the radio wave absorption band. However, in any of these technologies, radio wave absorption is mainly due to the radio wave absorber, not due to the uneven surface. In addition, these techniques have a problem in that manufacturing is difficult because an uneven surface is formed on the radio wave absorber.
[0013]
The present invention has been made in view of such problems, and an object of the present invention is to provide a radio wave attenuator capable of effectively attenuating a reflected wave with respect to a radio wave incident at a predetermined incident angle with a simple configuration. It is to provide.
[0014]
[Means for Solving the Problems]
The radio wave attenuator of the present invention includes a first reflective surface that reflects radio waves, and a second reflective surface that is disposed at a predetermined distance from the first reflective surface to the arrival side of radio waves and reflects radio waves. The incident angle of the radio wave with respect to the second reflecting surface is θ, the wavelength of the radio wave is λ, and the relative dielectric constant of the portion between the first reflecting surface and the second reflecting surface is ε. _r , M is an integer greater than or equal to 0, the distance d between the first reflecting surface and the second reflecting surface is d = (2m + 1) λ / {4√ (ε _r -Sin ² θ)}.
[0015]
In the radio wave attenuator of the present invention, when a radio wave is incident with an incident angle of θ with respect to the second reflecting surface, between the radio wave reflected by the first reflecting surface and the radio wave reflected by the second reflecting surface. A phase difference corresponding to an odd multiple of one-half wavelength occurs, and the radio wave after the two reflected waves overlap is attenuated by this phase difference.
[0016]
In the radio wave attenuator of the present invention, the total area of the first reflecting surface viewed from the radio wave reflected by the first reflecting surface and the area of the second reflecting surface viewed from the radio wave reflected by the second reflecting surface May be equal.
[0017]
In the radio wave attenuator of the present invention, the first reflecting surface and the second reflecting surface are alternately arranged in two directions parallel to and orthogonal to the first reflecting surface and the second reflecting surface. Also good. In this case, for each of the two directions, the interval between the boundary portions of the first reflecting surface and the second reflecting surface may be equal to or greater than the wavelength of the radio wave.
[0018]
In the radio wave attenuator of the present invention, the first reflecting surface and the second reflecting surface may be electrically continuous or electrically discontinuous.
[0019]
In the radio wave attenuator of the present invention, the first reflective surface and the second reflective surface are formed of a radio wave reflector having a concave portion serving as the first reflective surface and a convex portion serving as the second reflective surface. It may be.
[0020]
In the radio wave attenuator of the present invention, the first reflective surface is formed by a plate-shaped first radio wave reflector, and the second reflective surface is relative to the first reflective surface and the second reflective surface. The plate-shaped second radio wave reflectors may include a plurality of holes arranged at predetermined intervals in two directions that are parallel to each other and orthogonal to each other. In this case, the radio wave attenuator of the present invention may further include a filling member filled between the first radio wave reflector and the second radio wave reflector. The filling member may have sound absorbing properties. The filling member may be a dielectric.
[0021]
In the radio wave attenuator of the present invention, the first reflection surface and the second reflection surface may be formed of a radio wave reflector that transmits visible light. In this case, the radio wave reflector that transmits visible light may include an optically transparent dielectric and an optically transparent conductive thin film formed on the surface of the dielectric. The dielectric may be made of glass or a transparent organic polymer. The conductive thin film may be made of a metal oxide, a metal nitride, a metal, or a mixture thereof.
[0022]
In the radio wave attenuator of the present invention, at least one of the first reflection surface and the second reflection surface may be formed of a mesh formed of a material that reflects radio waves. In this case, the first reflecting surface may be formed of a mesh, and the radio wave attenuator may further include a sound absorbing material disposed on the opposite side of the mesh from the radio wave arrival side.
[0023]
The radio wave attenuator of the present invention further includes a first reflecting portion having a surface that functions as a first reflecting surface for radio waves of the first wavelength, and a second for radio waves of the first wavelength. A second reflecting portion having a surface that functions as a reflecting surface of the first reflecting portion, and the first reflecting portion receives the first reflecting surface and the second reflecting wave with respect to radio waves having a second wavelength shorter than the first wavelength. The second reflecting unit has two reflecting surfaces that function as reflecting surfaces, and the second reflecting unit has two reflecting surfaces that function as a first reflecting surface and a second reflecting surface with respect to radio waves of the second wavelength. It may be. In this case, the second wavelength may be 1/8 or less of the first wavelength.
[0024]
The radio wave attenuator of the present invention may be used to suppress unnecessary radio waves generated in bidirectional communication between the roadside antenna and the vehicle-mounted device-side antenna in the automatic toll collection system.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment]
First, an outline of a radio wave attenuator according to a first embodiment of the present invention and an automatic fee collection system to which the radio attenuator is applied will be described with reference to FIG.
[0026]
FIG. 1 is an explanatory diagram showing an example of a configuration around a toll gate in an automatic toll collection system to which the present embodiment is applied. In this example, the toll gate 1 is provided with a gate 2, and the roadside antenna 3 in the automatic toll collection system is provided above the gate 2. The automatic toll collection system automatically collects tolls by wirelessly communicating information about tolls between the roadside antenna 3 and the onboard unit antenna in the onboard unit 5 mounted on the car 4. To do. The roadside antenna 3 radiates radio waves toward the road 6 where the toll gate 1 is installed.
[0027]
Further, above the toll gate 1, another road 7 that intersects the road 6 is arranged. In such a situation, when the radio wave attenuator according to the present embodiment is not used, the radio wave radiated from the roadside antenna 3 is generated between the upper surface of the lower road 6 and the lower surface of the upper road 7. There is a possibility of multiple reflections between them. As a result, the reachable range of radio waves above the threshold that can be received by the onboard device-side antenna in the onboard device 5 is wider than the target range, and the same lane or a plurality of adjacent lanes are traveling within the reachable range. Multiple cars may enter and the system may malfunction.
[0028]
In order to prevent this, the radio wave attenuator 10 according to the present embodiment is attached to, for example, the upper road 7 that is a peripheral structure ahead of an unnecessary traveling direction of radio waves radiated from the roadside antenna 3. . Specifically, the radio wave attenuator 10 is located at the position below the traveling direction of the radio wave radiated from the roadside antenna 3 and reflected by the road 6 below the road 7 below the toll gate. Is attached.
[0029]
Next, the configuration of the radio wave attenuator 10 according to the present embodiment will be described with reference to FIGS. 2 is a front view of the radio wave attenuator 10, and FIG. 3 is a cross-sectional view taken along line AA of FIG.
[0030]
The radio wave attenuator 10 includes a radio wave reflector 11 formed of, for example, a metal plate. The radio wave reflector 11 is formed with concave portions and convex portions arranged in a lattice pattern. For the sake of convenience, in FIG. 2, the concave portions are indicated by hatching.
[0031]
The radio wave attenuator 10 is arranged at a position separated from the first reflection surface 21 by a predetermined distance from the first reflection surface 21 to the radio wave arrival side, and reflects the radio wave. The second reflecting surface 22 is provided. The first reflecting surface 21 is formed by a concave portion of the radio wave reflector 11, and the second reflecting surface 22 is formed by a convex portion of the radio wave reflector 11.
[0032]
The first reflecting surface 21 and the second reflecting surface 22 have a square shape with the same area. The first reflecting surface 21 and the second reflecting surface 22 are parallel to the first reflecting surface 21 and the second reflecting surface 22 and orthogonal to each other, that is, the up-down direction and the left-right direction in FIG. Alternating with respect to direction.
[0033]
2, the distance between the boundary portions of the first reflective surface 21 and the second reflective surface 22, that is, one side of the first reflective surface 21 and the second reflective surface 22, in each of the two directions of the vertical direction and the horizontal direction in FIG. Is preferably equal to or longer than the wavelength of the radio wave so that each of the reflecting surfaces 21 and 22 functions as a surface that actually reflects the radio wave. On the other hand, if the length L is too large, the way in which the radio wave reflected by the reflecting surface 21 and the radio wave reflected by the reflecting surface 22 are overlapped becomes small, so the length L may be three times or less the wavelength of the radio wave. preferable.
[0034]
In the present embodiment, as described later, the intensity of the radio wave is attenuated by superimposing the reflected wave on the first reflecting surface 21 having the phase difference and the reflected wave on the second reflecting surface 22. In the entire radio wave attenuator 10, the total area of the first reflecting surface 21 as viewed from the radio wave reflected by the first reflecting surface 21 and the second as viewed from the radio wave reflected at the second reflecting surface 22. The total area of the reflecting surfaces 22 is preferably equal or nearly equal.
[0035]
Here, with reference to FIG. 4, the total area of the first reflecting surface 21 as viewed from the radio wave reflected by the first reflecting surface 21 and the radio wave reflected from the second reflecting surface 22 are viewed. The meaning of the total area of the second reflecting surface 22 will be described. As shown in FIG. 4, when radio waves are incident on the first reflective surface 21 and the second reflective surface 22 from an oblique direction, the second reflective surface 22 has radio waves in the entire area A2. And all the incident radio waves are emitted in front of the second reflecting surface 22. On the other hand, on the first reflecting surface 21, only the radio wave incident on the partial area A <b> 1 is reflected by the first reflecting surface 21 and emitted forward of the second reflecting surface 22. Therefore, it is preferable that the sum of the areas of the regions A1 of the first reflecting surface 21 and the sum of the areas of the regions A2 of the second reflecting surface 22 be equal or substantially equal. The total area of the first reflecting surface 21 as viewed from the radio wave reflected by the first reflecting surface 21 is the total area of the region A1, and is the second as viewed from the radio wave reflected by the second reflecting surface 22. The total area of the reflective surfaces 22 is the total area of the region A2.
[0036]
In addition, when perpendicularly entering a radio wave with respect to the first reflecting surface 21 and the second reflecting surface 22, the area of the first reflecting surface 21 as viewed from the radio wave reflected by the first reflecting surface 21. The total is the total area of the entire region of the first reflecting surface 21.
[0037]
In the present embodiment, as shown in FIG. 3, the incident angle of the radio wave with respect to the second reflecting surface 22 is θ, the wavelength of the radio wave is λ, the first reflecting surface 21 and the second reflecting surface 22 The relative dielectric constant of the part between _r , M is an integer greater than or equal to 0, the distance d between the first reflecting surface 21 and the second reflecting surface 22 is expressed by the following formula (1).
[0038]
d = (2m + 1) λ / {4√ (ε _r -Sin ² θ)} (1)
[0039]
If the portion between the first reflecting surface 21 and the second reflecting surface 22 is air, ε _r = 1, and the above equation (1) becomes d = (2m + 1) λ / (4 cos θ). The distance d is the smallest when m = 0. In this case, the equation (1) is d = λ / (4 cos θ).
[0040]
Moreover, in this Embodiment, since the 1st reflective surface 21 and the 2nd reflective surface 22 were formed with the electromagnetic wave reflector 11 which has a recessed part and a convex part, the 1st reflective surface 21 and the 2nd reflective surface are formed. Surface 22 is electrically continuous. However, the first reflecting surface 21 and the second reflecting surface 22 may be electrically discontinuous.
[0041]
Next, the operation of the radio wave attenuator 10 according to the present embodiment will be described. As shown in FIG. 3, when radio waves having the same phase are incident on the second reflecting surface 22 at an incident angle θ, the distance d between the first reflecting surface 21 and the second reflecting surface 22 is expressed by the equation When (1) is satisfied, there is a phase difference corresponding to an odd multiple of one-half wavelength between the reflected wave on the first reflecting surface 21 and the reflected wave on the second reflecting surface 22. Arise. Since the reflected wave on the first reflecting surface 21 and the reflected wave on the second reflecting surface 22 are spread, the two reflected waves overlap at a position sufficiently away from the radio wave attenuator 10. Here, if the intensity of the reflected wave on the first reflecting surface 21 and the intensity of the reflected wave on the second reflecting surface 22 are equal, the intensity of the radio wave after the two reflected waves overlap is theoretically zero. Become. Further, even if the intensity of the reflected wave on the first reflecting surface 21 and the intensity of the reflected wave on the second reflecting surface 22 are slightly different, the intensity of the radio wave after the two reflected waves overlap is determined by each reflected wave alone. Compared to the strength of, it is greatly reduced and becomes a value close to zero. Thus, according to the radio wave attenuator 10 according to the present embodiment, it is possible to attenuate radio waves incident on the radio wave attenuator 10 at a predetermined incident angle θ.
[0042]
In the radio wave attenuator 10 according to the present embodiment, the first reflecting surface 21 and the second reflecting surface 21 are parallel to the first reflecting surface 21 and the second reflecting surface 22 and orthogonal to each other. The reflection surfaces 22 are alternately arranged. Therefore, the shape of the entire reflection surface of the radio wave attenuator 10 including the first reflection surface 21 and the second reflection surface 22 is substantially isotropic. Therefore, in the radio wave attenuator 10 according to the present embodiment, it is possible to prevent the characteristics from changing greatly depending on the incident direction of the radio wave and the polarization state of the radio wave. The polarization state of the radio wave includes a TE (Transverse Electronic) wave whose linear electric field is perpendicular to the incident surface, a TM (Transverse Magnetic) wave whose linear magnetic field is perpendicular to the incident surface, and a circular polarization. There are waves.
[0043]
FIG. 5 is a characteristic diagram showing an example of the characteristics of the radio wave attenuator 10 according to the present embodiment obtained by simulation. Here, the frequency of the radio wave is 5.8 GHz. In this case, the wavelength λ of the radio wave is about 51.7 mm. FIG. 5 shows the incident angle and the return loss for the six cases where the distance d between the first reflecting surface 21 and the second reflecting surface 22 is 13 mm, 14 mm, 15 mm, 17 mm, 26 mm, and 30 mm, respectively. Showing the relationship. According to equation (1), when d is 13 mm, 14 mm, 15 mm, 17 mm, 26 mm and 30 mm, the incident angle θ is about 4 °, about 23 °, about 30 °, about 40 °, about 60 This corresponds to the case of ° and about 64 °.
[0044]
In the example shown in FIG. 5, when d is 13 mm, 14 mm, 15 mm, 17 mm, 26 mm, and 30 mm, the incident angles are about 4 °, about 23 °, about 30 °, about 40 °, about The return loss increases in the vicinity of 60 ° and about 64 °.
[0045]
Here, when d is 26 mm, that is, λ / 2, the return loss reaches a peak when the incident angle is about 60 °. However, when the incident angle is within the range of 0 ° to 50 °, On the other hand, the return loss is small and it does not function as a radio wave attenuator. For this reason, in the radio wave absorber shown in FIG. 2B of Japanese Patent Laid-Open No. 11-261283, as a radio wave absorber for radio waves incident at an incident angle in the range of about 0 ° to 50 °. It can be seen that it does not fulfill the function. Further, when d is further increased, for example, 30 mm, the peak of the return loss moves to the larger incident angle.
[0046]
Next, an example of the measurement result of the characteristics of the prototype radio wave attenuator 10 will be described. The prototype radio wave attenuator 10 has d of 15 mm so as to attenuate radio waves having a frequency of 5.8 GHz incident at an incident angle of 30 °, and the distance between the boundary portions of the first reflection surface 21 and the second reflection surface 22. Is set to 100 mm, which is about twice the wavelength λ of the radio wave. In measuring the characteristics of the prototype radio wave attenuator 10, circularly polarized radio waves having a frequency of 5.8 GHz were incident on the radio wave attenuator 10 at incident angles of 2 °, 20 °, and 40 °, and the return loss was measured. . As a result, the reflection attenuation amounts by the radio wave attenuator 10 when the incident angles were 2 °, 20 °, and 40 ° were 13.4 dB, 15.6 dB, and 12.4 dB, respectively. Note that the calculated values of the return loss by the radio wave attenuator 10 when the incident angles are 2 °, 20 °, and 40 ° are 12.2 dB, 17.0 dB, and 15.2 dB, respectively.
[0047]
As described above, according to the radio wave attenuator 10 according to the present embodiment, unnecessary radio waves can be suppressed with a simple configuration including the first reflective surface 21 and the second reflective surface 22. become.
[0048]
Further, according to the present embodiment, since the distance d between the first reflecting surface 21 and the second reflecting surface 22 is set as represented by the formula (1), A reflected wave with respect to a radio wave incident at a predetermined incident angle can be effectively attenuated. In addition, in the radio wave attenuator 10 according to the present embodiment, the range of the incident angle where the return loss is sufficiently large is narrow. However, when the radio wave attenuator 10 is used in an automatic toll collection system, the incident angle of unnecessary radio waves with respect to the radio wave attenuator 10 is often limited to a certain narrow angle range. Unnecessary radio waves can be sufficiently attenuated.
[0049]
Further, according to the radio wave attenuator 10 according to the present embodiment, the shape of the entire reflection surface of the radio wave attenuator 10 including the first reflection surface 21 and the second reflection surface 22 is substantially isotropic. It is possible to suppress unnecessary radio waves without greatly changing characteristics depending on the incident direction of radio waves and the polarization state of radio waves.
[0050]
Further, according to the present embodiment, as shown in FIG. 1, the radio wave attenuator 10 is used for the path of unnecessary radio waves generated in bidirectional communication between the roadside antenna 3 and the vehicle-mounted device side antenna in the automatic toll collection system. By providing in, unnecessary radio waves can be suppressed. As a result, according to the present embodiment, it is possible to prevent malfunction of the automatic fee collection system.
[0051]
By the way, in this Embodiment, the electromagnetic wave reflector 11 is not restricted to what was formed by the metal plate, You may be formed by the other material. For example, the radio wave reflector 11 may be formed by coating a conductive thin film on a resin base material.
[0052]
The radio wave reflector 11 may transmit visible light. The radio wave reflector 11 that transmits visible light may have, for example, an optically transparent dielectric and an optically transparent conductive thin film formed on the surface thereof. . In this case, the optically transparent dielectric may be made of, for example, transparent glass, or an organic polymer such as polyethylene terephthalate (PET), polycarbonate, ABS resin, acrylic, vinyl chloride, or Teflon. May be. Examples of the conductive thin film include a thin film made of metal oxide, metal nitride, metal, or a mixture thereof. Specific examples of such a thin film include a thin film made of tin oxide, tin oxide-doped indium oxide (ITO), zinc oxide, titanium nitride, silver, or the like. Examples of a method for forming an optically transparent conductive thin film on the surface of an optically transparent dielectric material include vapor deposition, sputtering, and ion plating. Further, the surface resistance value of the optically transparent conductive thin film is preferably larger than 0Ω □ and not more than 50Ω □. That is, in this case, a sufficiently large amount of reflection can be obtained by the conductive thin film.
[0053]
When the radio wave reflector 11 is a metal plate that does not transmit visible light, the radio wave attenuator 10 cannot be installed in front of an object that requires visual observation, such as an existing illumination device or a display plate. On the other hand, when the radio wave reflector 11 transmits visible light, the radio wave attenuator 10 transmits light from the illumination device, or the display plate or the like can be visually observed through the radio wave attenuator 10. Therefore, it is possible to install the radio wave attenuator 10 in front of an existing lighting device or display panel.
[0054]
[Second Embodiment]
Next, with reference to FIG. 6 and FIG. 7, a radio wave attenuator 30 according to a second embodiment of the present invention will be described. 6 is a front view of the radio wave attenuator 30, and FIG. 7 is a cross-sectional view taken along the line BB of FIG.
[0055]
The radio wave attenuator 30 according to the present embodiment includes a plate-like first radio wave reflector 31 and a first radio wave at a position away from the first radio wave reflector 31 on the radio wave arrival side by a predetermined distance. A plate-like second radio wave reflector 32 arranged in parallel to the reflector 31, and a filling member 33 filled between the first radio wave reflector 31 and the second radio wave reflector 32. I have. The first radio wave reflector 31 and the second radio wave reflector 32 may be formed of, for example, a metal plate, or may be formed by coating a resin base material with a conductive thin film. . Further, the first radio wave reflector 31 and the second radio wave reflector 32 may transmit visible light.
[0056]
The second radio wave reflector 32 has predetermined directions in two directions parallel to and perpendicular to the first radio wave reflector 31 and the second radio wave reflector 32, that is, in the vertical direction and the horizontal direction in FIG. A plurality of square holes 32a arranged at intervals are formed. In the present embodiment, the first reflecting surface is formed by a portion of the first radio wave reflector 31 corresponding to the hole 32a of the second radio wave reflector 32, and the second reflective surface is the second wave reflector. It is formed by a portion other than the hole 32a of the radio wave reflector 32. The shape of the hole 32a is not limited to a square, but may be a circle or the like.
[0057]
The filling member 33 is made of a material that transmits radio waves. The filling member 33 may have sound absorbing properties. The filling member 33 may be a dielectric. As the filling member 33, for example, glass wool having a sound absorbing property and a dielectric may be used. The portion between the first radio wave reflector 31 and the second radio wave reflector 32 may be air without providing the filling member 33. In this case, the first radio wave reflector 31 and the second radio wave reflector 32 may be held at a predetermined interval by a frame, for example.
[0058]
In each of the two directions of the up and down direction and the left and right direction in FIG. 6, the interval between the boundary portions of the first reflecting surface and the second reflecting surface is preferably not less than the wavelength of the radio wave and not more than three times the wavelength of the radio wave. .
[0059]
Further, in the entire radio wave reflector 30, the total area of the first reflection surface viewed from the radio wave reflected by the first reflection surface and the second reflection surface viewed from the radio wave reflected by the second reflection surface The sum of the areas is preferably equal or approximately equal.
[0060]
The radio wave attenuator 30 according to the present embodiment is easy to manufacture because it is not necessary to form irregularities on the radio wave reflector.
[0061]
In the present embodiment, when the filling member 33 has a sound absorbing property, it is possible to reduce noise.
[0062]
Further, in the present embodiment, when the filling member 33 is a dielectric, the denominator on the right side in Equation (1) is increased, so the distance d between the first reflecting surface and the second reflecting surface is reduced. can do. Therefore, the distance between the first radio wave reflector 31 and the second radio wave reflector 32 can be reduced, and as a result, the thickness of the radio wave attenuator 30 can be reduced.
[0063]
Other configurations, operations, and effects in the present embodiment are the same as those in the first embodiment.
[0064]
[Third Embodiment]
Next, with reference to FIG. 8, a radio wave attenuator 40 according to a third embodiment of the present invention will be described. FIG. 8 is a cross-sectional view of the radio wave attenuator 40.
[0065]
The radio wave attenuator 40 according to the present embodiment includes a first radio wave reflector 41 made of a mesh formed of a material that reflects radio waves, and a predetermined distance from the first radio wave reflector 41 to the radio wave arrival side. And a second radio wave reflector 42 disposed in parallel to the first radio wave reflector 41 at a position separated by a distance. The first radio wave reflector 41 forms a first reflection surface, and the second radio wave reflector 42 forms a second reflection surface. It is preferable that the mesh | lattice space | interval of the mesh as the 1st electromagnetic wave reflector 41 is below 1/10 of the wavelength of an electromagnetic wave.
[0066]
The shape of the second radio wave reflector 42 is the same as that of the second radio wave reflector 32 in the second embodiment. The second radio wave reflector 42 may be formed by, for example, a metal plate, or may be formed by coating a resin base material with a conductive thin film, or the first radio wave reflector. It may be formed of the same mesh as 41.
[0067]
Further, a filling member may be provided between the first radio wave reflector 41 and the second radio wave reflector 42, or the first radio wave reflector 41 and the second radio wave reflector 42 may be connected to each other by a frame or the like. You may make it hold | maintain at intervals.
[0068]
In addition, as shown in FIG. 8, the sound absorbing material 43 may be disposed on the opposite side of the first radio wave reflector 41 from the second radio wave reflector 42, that is, on the opposite side from the radio wave arrival side. In this case, the noise can be reduced by the sound absorbing material 43. In addition, since the mesh as the first radio wave reflector 41 is disposed on the front surface of the sound absorbing material 43 instead of the metal plate, the sound absorbing effect by the sound absorbing material 43 can be enhanced.
[0069]
Other configurations, operations, and effects in the present embodiment are the same as those in the first or second embodiment.
[0070]
[Fourth Embodiment]
Next, a radio wave attenuator 50 according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 9 is an explanatory diagram showing a configuration of the radio wave attenuator 50.
[0071]
The radio wave attenuator 50 according to the present embodiment includes a first reflection unit 51 having a reflection surface S1 that functions as a first reflection surface for radio waves having a predetermined first wavelength λ1, and a first wavelength λ1. And a second reflecting part 52 having a reflecting surface S2 that functions as a second reflecting surface for the radio wave. The distance d1 between the reflecting surface S1 and the reflecting surface S2 is expressed by the following formula (2).
[0072]
d1 = (2m + 1) λ1 / {4√ (ε _r -Sin ² θ)} (2)
[0073]
Further, in two directions parallel to and perpendicular to the reflective surface S1 and the reflective surface S2, the distance between the boundary portions of the reflective surface S1 and the reflective surface S2 is not less than the first wavelength λ1 and not more than 3 times the wavelength λ1. Is preferred.
[0074]
In FIG. 9, as shown in an enlarged view of a part of the first reflecting portion 51, the first reflecting portion 51 responds to radio waves having a predetermined second wavelength λ2 shorter than the first wavelength λ1. The reflecting surface S11 and the reflecting surface S12 function as the first reflecting surface and the second reflecting surface. Similarly, the second reflecting section 52 has a reflecting surface S21 and a reflecting surface S22 that function as a first reflecting surface and a second reflecting surface for radio waves having a predetermined second wavelength λ2.
[0075]
The distance between the reflecting surface S11 and the reflecting surface S12 in the first reflecting portion 51 is equal to the distance between the reflecting surface S21 and the reflecting surface S22 in the second reflecting portion 52, which is d2. This distance d2 is expressed by the following formula (3).
[0076]
d2 = (2m + 1) λ2 / {4√ (ε _r -Sin ² θ)} (3)
[0077]
In addition, the distance L2 between the boundary portions of the reflecting surface S11 and the reflecting surface S12 in the two directions parallel to and orthogonal to the reflecting surfaces S11 and S12 in the first reflecting portion 51 is equal to or more than the second wavelength λ2. It is preferably 3 times or less of λ2. The interval between the boundary portions of the reflecting surface S21 and the reflecting surface S22 in the two directions parallel to and orthogonal to the reflecting surfaces S21 and S22 in the second reflecting portion 52 is the same as the interval L2.
[0078]
The second wavelength λ2 is, for example, 1/8 or less of the first wavelength λ1. Here, if the values of m in the equations (2) and (3) are equal (for example, 1), the distance d2 is also obtained when the second wavelength λ2 is equal to or less than one-eighth of the first wavelength λ1. It becomes 1/8 or less of the distance d1. In this case, the distance d2 is negligible when viewed from the radio wave having the first wavelength λ1.
[0079]
Further, when the second wavelength λ2 is equal to or less than one eighth of the first wavelength λ1, the interval L2 is, for example, equal to or less than one eighth of the interval L1. In this case, when viewed from the radio wave having the first wavelength λ1, the interval L2 is a negligible interval.
[0080]
Accordingly, the reflection surface S1 in the first reflection part 51 actually includes the reflection surface S11 and the reflection surface S12 having a step of the distance d2, but it is one when viewed from the radio wave having the first wavelength λ1. It can be regarded as the first reflecting surface. Similarly, the reflecting surface S2 in the second reflecting portion 52 actually includes the reflecting surface S21 and the reflecting surface S22 having a step of the distance d2, but is 1 when viewed from the radio wave having the first wavelength λ1. It can be regarded as two second reflecting surfaces.
[0081]
Other conditions regarding the positional relationship between the reflective surface S1 and the reflective surface S2, the positional relationship between the reflective surface S11 and the reflective surface S12, and the positional relationship between the reflective surface S21 and the reflective surface S22 are the first to third implementations. This is the same as the case of the positional relationship between the first reflecting surface and the second reflecting surface in the embodiment. The materials constituting the first reflecting portion 51 and the second reflecting portion 52 are the same as those of the radio wave reflector in the first to third embodiments.
[0082]
In the radio wave attenuator 50 according to the present embodiment, the radio wave having the first wavelength λ1 is attenuated by the reflection surface S1 of the first reflection unit 51 and the reflection surface S2 of the second reflection unit 52. On the other hand, the radio wave of the second wavelength λ2 is attenuated by the reflection surface S11 and the reflection surface S12 of the first reflection unit 51, and is attenuated by the reflection surface S21 and the reflection surface S22 of the second reflection unit 52. The Therefore, the radio wave attenuator 50 has a function of attenuating radio waves with respect to radio waves of two wavelengths.
[0083]
According to the radio wave attenuator 50 according to the present embodiment, it is possible to attenuate a plurality of radio waves having different wavelengths (frequencies). Therefore, the radio wave attenuator 50 according to the present embodiment is, for example, a radio wave (frequency 5.8 GHz) used in an automatic toll collection system or a radio wave (frequency 60 GHz or 77 GHz) used in a millimeter wave collision prevention on-vehicle radar. It can be used in a corner portion such as a tunnel or a highway that uses a plurality of radio waves having different wavelengths (frequencies). In this case, it is possible to improve radio interference due to a plurality of radio waves having different wavelengths (frequencies).
[0084]
Other configurations, operations, and effects in the present embodiment are the same as those in the first to third embodiments.
[0085]
In addition, this invention is not limited to said each embodiment, A various change is possible. For example, the radio wave attenuator of the present invention is not limited to a road disposed above a toll gate, and may be attached to a display or a support portion disposed in front of a toll gate, It may be attached under the roof or on the side of the gate. The radio wave attenuator of the present invention may be disposed between a plurality of lanes. Moreover, you may use the electromagnetic wave attenuator of this invention other than an automatic fee collection system.
[0086]
【The invention's effect】
As explained above, The present invention According to the radio wave attenuator, it is possible to suppress unnecessary radio waves with a simple configuration including the first reflection surface and the second reflection surface, and the incident angle of the radio wave with respect to the second reflection surface Is θ, the wavelength of the radio wave is λ, and the relative dielectric constant of the portion between the first reflecting surface and the second reflecting surface is ε. _r , M is an integer greater than or equal to 0, the distance d between the first reflecting surface and the second reflecting surface is expressed as d = (2m + 1) λ / {4√ (ε _r -Sin ² θ)}, the reflected wave with respect to the radio wave incident at a predetermined incident angle can be effectively attenuated. Furthermore, according to the present invention, since the first reflection surface and the second reflection surface are formed by the radio wave reflector that transmits visible light, the radio wave attenuator is installed in front of the illumination device or the display board. Also has the effect of becoming possible.
[0087]
Also, The present invention Since the first reflection surface and the second reflection surface are alternately arranged in two directions that are parallel to and orthogonal to the first reflection surface and the second reflection surface, There is an effect that unnecessary radio waves can be suppressed without greatly changing the characteristics depending on the polarization state of the radio waves.
[0093]
Also, The present invention The first reflecting portion having a surface that functions as a first reflecting surface for radio waves of the first wavelength, and the surface that functions as a second reflecting surface for radio waves of the first wavelength. And the first reflection unit has two reflections that function as a first reflection surface and a second reflection surface with respect to radio waves having a second wavelength shorter than the first wavelength. Since the second reflecting portion has two reflecting surfaces that function as the first reflecting surface and the second reflecting surface with respect to the radio wave of the second wavelength, a plurality of different wavelengths are provided. There is an effect that it becomes possible to attenuate the radio wave.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example of a configuration around a toll gate to which a first embodiment of the present invention is applied.
FIG. 2 is a front view of the radio wave attenuator according to the first embodiment of the present invention.
FIG. 3 is a cross-sectional view taken along line AA in FIG.
FIG. 4 is an explanatory diagram for explaining areas of a first reflecting surface and a second reflecting surface in the radio wave attenuator according to the first embodiment of the present invention.
FIG. 5 is a characteristic diagram showing an example of characteristics of the radio wave attenuator according to the first embodiment of the present invention obtained by simulation.
FIG. 6 is a front view of a radio wave attenuator according to a second embodiment of the present invention.
7 is a cross-sectional view taken along line BB in FIG.
FIG. 8 is a cross-sectional view of a radio wave attenuator according to a third embodiment of the present invention.
FIG. 9 is an explanatory diagram showing a configuration of a radio wave attenuator according to a fourth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Toll gate, 2 ... Gate, 3 ... Roadside antenna, 4 ... Car, 5 ... Onboard equipment, 6 ... Road, 7 ... Road, 10 ... Radio wave attenuator, 11 ... Radio wave reflector, 21 ... First reflection Surface, 22 ... second reflecting surface.

Claims (4)

A first reflecting surface that reflects radio waves;
A second reflecting surface that is disposed at a position away from the first reflecting surface by a predetermined distance on the radio wave arrival side and reflects the radio wave,
The incident angle of the radio wave with respect to the second reflecting surface is θ, the wavelength of the radio wave is λ, the relative dielectric constant of the portion between the first reflecting surface and the second reflecting surface is ε _r , and m is 0 or more. The distance d between the first reflecting surface and the second reflecting surface is represented by d = (2m + 1) λ / {4√ (ε _r −sin ² θ)},
The first reflecting surface and the second reflecting surface are formed by a radio wave reflector that transmits visible light,
The first reflective surface and the second reflective surface are alternately arranged in two directions parallel to and orthogonal to the first reflective surface and the second reflective surface,
The two directions of each interval of the first reflecting surface and the boundary portion of the second reflecting surface Ri der than the wavelength of the radio wave,
And a first reflecting portion having a surface that functions as a first reflecting surface for radio waves of the first wavelength;
A second reflecting portion having a surface that functions as a second reflecting surface for the radio wave of the first wavelength,
The first reflecting section has two reflecting surfaces that function as a first reflecting surface and a second reflecting surface for radio waves having a second wavelength shorter than the first wavelength,
The radio wave attenuator , wherein the second reflection unit has two reflection surfaces that function as a first reflection surface and a second reflection surface with respect to radio waves of the second wavelength .   The sum of the areas of the first reflecting surfaces viewed from the radio waves reflected by the first reflecting surface is equal to the sum of the areas of the second reflecting surfaces viewed from the radio waves reflected by the second reflecting surface. The radio wave attenuator according to claim 1. 3. The radio wave attenuator according to claim 1, wherein the second wavelength is 1/8 or less of the first wavelength. 4. Telecommunications damping body according to any one of claims 1 to 3, characterized in that it is used to suppress unnecessary radio waves generated in the two-way communication with the road-side antenna and the vehicle-mounted device side antenna in the automatic toll collection system .

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