JP2001068925A - Road side antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a narrow communication area even when there is a structure at an upper front part of a road side antenna that is suitable for an automatic toll collection system. SOLUTION: The road side antenna system is provided with a road side antenna 5 that is installed on a road 3 to form a prescribed communication area 6 and a roof structure 11 that is installed at an upper front part of the road side antenna 5 and has a radio wave absorbing body 12 placed on the side of the road side antenna 5. Then, radio communication is conducted within the communication area between the road side antenna 5 and an on-vehicle device 2 mounted on a vehicle 1 traveling on the road.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roadside antenna device suitable for an automatic toll collection system in which tolls are collected by wireless communication at a tollgate on a toll road and vehicles can pass without stopping.

[0002]

2. Description of the Related Art Conventionally, at a tollgate on a toll road, passing vehicles are temporarily stopped, and a driver and a staff member need to exchange a toll ticket and pay a toll, which has been a major factor of congestion. . Therefore, as a tollgate system that allows vehicles to pass through without stopping, ETC (Electronic Tol
l Collection: automatic toll collection system) is about to be commercialized.

FIG. 6 is a schematic configuration diagram showing an example of an automatic toll collection system that is scheduled to be put into practical use. A vehicle 1 has an on-vehicle device 2 mounted thereon, The wireless communication is performed with the roadside antenna 5 installed by the support 4.

In this configuration, when the vehicle 1 passes through the communication area 6 of the roadside antenna 5, wireless communication is performed between the roadside antenna 5 and the vehicle-mounted device 2, and a control (not shown) is performed based on the wireless information. The device is configured to charge a toll.

The automatic toll collection system uses 5.8G in a narrow communication area 6 formed by the roadside antenna 5 in order to avoid wireless communication with a vehicle traveling on an adjacent lane.
Wireless communication is performed using radio waves in the Hz band.

FIGS. 7A and 7B are diagrams showing the directivity of the roadside antenna 5, wherein FIG. 7A shows the directivity in the horizontal direction and FIG. 7B shows the directivity in the vertical direction. As is clear from this characteristic diagram, in the horizontal direction and the vertical direction, −20 from the center position.
It has a directional characteristic in which a communication area can be formed in a narrow range of up to +20 degrees.

FIG. 8 shows such a roadside antenna 5 installed at a height of 5 m above the ground at an installation angle of 23 degrees and a transmission output of 16 dBm.
EIRP (Equivalent Isotropically Radiated Power
: Equivalent isotropic radiated power), the received power at a height of 1 m above the ground is indicated by an EIRP value.

As is apparent from FIG.
m, a communication area 6 of 3 m is formed in the vehicle width direction, and a good power distribution is generated without generating leakage power before and after the communication areas 6L and 6R of the adjacent lane and the lane.

[0009]

However, at a tollgate on a toll road, a structure may be present in front of and above the roadside antenna due to a roof or an overpass. The presence of such a structure causes multiple reflections of radio waves.

FIG. 9 shows a roof 11 located in front of and above the antenna.
Shows how radio waves are reflected by the radio wave. That is,
The radio wave radiated from the roadside antenna 5 is reflected on the road 3,
The state where the reflected wave is reflected once again on the roof 11 is shown.

The analysis of the reflection of the roof 11 can be defined as radiation from a mirror image antenna on the opposite side of the roof 11 with the roof 11 as a mirror image plane. FIG. 10 shows the state of such radio wave radiation, and the mirror image antenna 5i
Is a mirror image antenna having the roof 11 as a mirror image surface.

Next, the intensity of radio waves due to the reflection from the roof 11 will be described. Assuming that there is no loss due to reflection on the road 3 and the roof 11, the reflected wave on the roof 11 is equivalent to radiating from the mirror image antenna 5i with the same output as the roadside antenna 5.

Therefore, the height above the ground is defined as “the height of the roof × 2 +
When a radio wave with an output of 16 dBm EIRP is radiated from the mirror image antenna 5 i imagined to be 5 degrees and the installation angle is 23 degrees, the received power at a height of 1 m above the ground is as shown in FIG. 11.

As is apparent from this figure, the reflected wave on the roof 11 causes leakage power in the communication areas 6L and 6R of the adjacent lanes in front of the communication area 6 (to the right in the figure) and to the left and right (up and down in the figure). . As a result, wireless communication is established between the vehicle running on the adjacent lane and the following vehicle on the own lane, and the toll is erroneously received.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a roadside antenna device capable of forming a narrow communication area even if there is a structure in front of the roadside antenna. The purpose is to provide.

[0016]

A roadside antenna device according to the present invention is provided on a roadside antenna installed on a road and setting a predetermined communication area on the road, and on a roadside antenna side surface installed above and in front of the roadside antenna. A roof-like structure provided with a radio wave absorber is provided, and wireless communication is performed between a roadside antenna and a vehicle-mounted device mounted on a vehicle running on a road in a communication area. As the radio wave absorber, a sheet-shaped thin radio wave absorber, a paint type radio wave absorber or a multilayer type radio wave absorber can be used.

In this configuration, the radio wave radiated from the roadside antenna is reflected on the road, but the reflected wave is absorbed by the radio wave absorber installed on the roof-like structure. A similar narrow communication area can be obtained.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is a configuration diagram showing Embodiment 1 of a roadside antenna device of the present invention. In FIG. 1, a vehicle 1 has an in-vehicle device 2 mounted thereon, and wirelessly communicates between the in-vehicle device 2 and a roadside antenna 5 installed by a support 4 above a road 3.
In addition, a sheet-like thin radio wave absorber 12 is installed on the lower surface of the roof 11 located above and in front of the roadside antenna 5.

FIG. 2 shows a structure 1 of the thin radio wave absorber 12.
It is sectional drawing explaining the absorption principle of a layer type radio wave absorber.

In FIG. 1, a thin radio wave absorber 12 is provided with a metal plate 12b on the rear surface of an absorber 12a. When a radio wave of an electric field Eo enters the front surface of the absorber 12a, the absorber 1
The electric field Er1 is reflected on the front surface of 2a, and the rest is transmitted inside the absorber. As the absorbent 12a, resistance fiber, FRP,
There are rubber ferrite and rubber carbon.

The radio wave transmitted through the absorber 12a is exponentially attenuated by the attenuation constant of the absorber 12a.
Since it does not become sufficiently small, it is completely reflected by the metal plate 12b. The completely reflected radio wave reaches the surface of the absorber 12a while being attenuated again by the absorber 12a. Then, a part is reflected on the boundary surface of the surface and returns to the inside of the absorber 12a again, and the rest is transmitted and becomes a reflected wave of the absorber 12a as an electric field Er2.

This process is repeated a number of times, and the reflected wave is emitted to the front. However, since the reflected wave is attenuated each time it reciprocates inside the absorber 12a, the magnitude of the electric field is gradually reduced each time the reflection is repeated. Become.

If the first reflected electric field Er1 and the second reflected electric field Er2 can have the same magnitude and opposite phases, the reflection coefficient of the absorber 12a becomes zero. However, actually, one round trip is not enough, and many round trips need to be considered. Thus, the radio wave absorber has the function of attenuating the electric field and delaying the phase of the electric field.

Next, the operation of the roadside antenna device according to the present embodiment will be described. The roadside antenna 5 is installed on the road 3 at a certain ground height and an installation angle, and radiates radio waves with a prescribed transmission EIRP value having beam-shaped directional characteristics.

Radio waves radiated from the roadside antenna 5 form a communication area 6 and are reflected on the road 3. The reflected wave of the road 3 reaches the roof 11, but is absorbed by the thin radio wave absorber 12 installed on the roof 11, and does not reflect on the roof 11.

As described above, according to the present embodiment, the thin radio wave absorber 1 is attached to the structure located in front of the roadside antenna 5.
By installing 2, it is possible to realize the same narrow communication area as when there is no communication area.

(Embodiment 2) FIG. 3 is a configuration diagram showing Embodiment 2 of the roadside antenna device of the present invention. In FIG. 1, a vehicle 1 has an in-vehicle device 2 mounted thereon, and wirelessly communicates between the in-vehicle device 2 and a roadside antenna 5 installed by a support 4 above a road 3.
Further, a paint type radio wave absorber 13 is installed on the lower surface of the roof 11 at the upper front of the roadside antenna 5. The absorption principle and material of the paint-type radio wave absorber 13 are the same as those of the thin radio wave absorber 12.

In this configuration, the roadside antenna 5 is installed on the road at a certain height above the ground and at an installation angle, has a beam-shaped directional characteristic, and radiates radio waves with a specified transmission EIRP value.

Radio waves radiated from the roadside antenna 5 form a communication area 6 and are reflected on the road 3. The reflected wave of the road 3 reaches the roof 11, but is absorbed by the radio wave absorbing sheet 13 installed on the roof 11, and does not reflect on the roof 11.

As described above, according to the present embodiment, by installing the paint-type radio wave absorber 13 on the structure in front of the roadside antenna 5, a good communication area similar to that without the paint-type radio wave absorber 13 can be obtained. Can be realized.

(Embodiment 3) FIG. 4 is a configuration diagram showing Embodiment 3 of a roadside antenna device of the present invention. In FIG. 1, a vehicle 1 has an in-vehicle device 2 mounted thereon, and wirelessly communicates between the in-vehicle device 2 and a roadside antenna 5 installed by a support 4 above a road 3.
In addition, a wedge-type multilayered electromagnetic wave absorber 14 is installed on the lower surface of the roof 11 at the upper front of the roadside antenna 5.

FIG. 5 shows a wedge-type multilayer electromagnetic wave absorber 1.
In the enlarged view of FIG. 4, a wedge 14a made of an absorbent material is provided on the front surface, a multilayer absorbent material 14b is provided in the middle, and a metal plate 14c is provided on the rear surface.

The one-layer type radio wave absorber has limitations in the frequency band and the incident characteristics. Therefore, near the surface of the absorber, a material whose material constant is close to air is selected, and a material with a large radio wave absorption is selected as it enters the interior. Broadband radio wave absorption characteristics that are transmitted through and gradually attenuated are obtained. In addition, by using a wedge structure or pyramid structure, the area near the surface is reduced, so that even if the same material is used, the dielectric constant is equivalently reduced to obtain a dielectric constant close to that of air. ing.

Next, the operation of the roadside antenna device according to the present embodiment will be described. The roadside antenna 5 has a beam-shaped directional characteristic, is installed on the road at a certain ground height and an installation angle, and radiates radio waves at a specified transmission EIRP value.

Radio waves radiated from the roadside antenna 5 form a communication area 6 and are reflected on the road 3. The reflected wave of the road 3 reaches the roof 11, but is absorbed by the multilayered radio wave absorber 14 installed on the roof 11, and does not reflect on the roof 11.

As described above, according to the present embodiment, the structure located above and in front of the roadside antenna 5 has
By installing 4, a communication area as narrow as when there is no communication area can be realized.

[0038]

As described above, according to the present invention, a radio wave absorber is provided on a roof-like structure located above and in front of a roadside antenna, so that such a structure is located above and in front of the roadside antenna. However, there is an advantageous effect that the same narrow communication area can be realized as when there is no communication area.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing Embodiment 1 of a roadside antenna device of the present invention.

FIG. 2 is a cross-sectional view for explaining the absorption principle of the single-layer radio wave absorber.

FIG. 3 is a configuration diagram showing Embodiment 2 of the roadside antenna device of the present invention.

FIG. 4 is a configuration diagram showing Embodiment 3 of the roadside antenna device of the present invention.

FIG. 5 is an enlarged view of a multilayered electromagnetic wave absorber.

FIG. 6 is a schematic configuration diagram of a conventional roadside antenna device.

FIG. 7 shows an example of a directional characteristic of a roadside antenna, and FIG.
Is a horizontal directional pattern, and (b) is a vertical directional pattern.

FIG. 8 is a diagram illustrating an example of a communication area formed by radio waves from a roadside antenna;

FIG. 9 is a diagram showing a state of reflection of a radio wave by a roof-like structure.

FIG. 10 is a diagram showing a state of radio wave radiation by a mirror image antenna.

FIG. 11 is a diagram illustrating an example of a communication area formed by a reflected wave from a roof-like structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vehicle 2 In-vehicle apparatus 3 Road 4 Prop 5 Roadside antenna 5i Mirror image antenna 6 Communication area 11 Roof 12 Thin radio wave absorber 12a Absorbing material 12b Metal plate 13 Paint type radio wave absorber 14 Multilayer type radio absorber 14a Wedge 14b Multilayer absorber 14c Metal plate

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akihiro Inui 4-3-1 Tsunashima Higashi, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture Inside Matsushita Communication Industrial Co., Ltd. (72) Inventor Masaki Terashima Higashi-Yoshina Tsunashima, Kohoku-ku, Kanagawa No.3-1, Matsushita Communication Industrial Co., Ltd. F-term (reference) 5H180 AA01 CC12 EE10 5J020 EA02 EA03 EA04 EA07 EA10

Claims (4)

[Claims] 1. A roadside antenna installed on a road and setting a predetermined communication area on the road, and a roof having a radio wave absorber installed above and in front of the roadside antenna on a surface on the roadside antenna side. A roadside antenna device, wherein wireless communication is performed between the roadside antenna and an in-vehicle device mounted on a vehicle running on the road in the communication area. 2. The roadside antenna device according to claim 1, wherein the radio wave absorber is a sheet-shaped thin radio wave absorber. 3. The roadside antenna device according to claim 1, wherein the radio wave absorber is a paint type radio wave absorber. 4. The roadside antenna device according to claim 1, wherein the radio wave absorber is a multilayer radio wave absorber.