JP4888974B2 - Antenna for in-vehicle communication device and method for determining mounting position thereof - Google Patents

Description

  The present invention relates to an antenna for an in-vehicle communication device mounted on a vehicle in order to use an ETC system, for example, and a method for determining a mounting position thereof.

Conventionally, for example, as an aspect of mounting an ETC antenna of an ETC on-board unit, an ETC antenna is mounted at a position where the distance from the window glass satisfies a predetermined condition in order to avoid a decrease in antenna gain caused by the presence of the window glass. The structure which performs is provided (for example, refer patent document 1).
JP 2002-246817 A

  By the way, the windshield is generally provided with a wiper. Since the wiper has a structure having metal parts, the presence of the wiper may cause a decrease in antenna gain. However, the device described in Patent Document 1 does not consider the presence of the wiper, and there is a problem that the antenna gain is reduced due to the presence of the wiper.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an antenna for an in-vehicle communication device and a mounting position determination method thereof that can avoid a decrease in antenna gain caused by the presence of a wiper. It is to provide.

According to the antenna for an in-vehicle communication device according to claim 1, the in-vehicle communication device that performs at least one of reception of radio waves from an external device and transmission of radio waves to the external device through a window glass provided with a wiper. The antenna moves as the vehicle moves on the electric field intensity distribution generated by the combination of the direct wave coming directly from the external device to the antenna and the scattered wave coming from the external device through the wiper to the antenna. The electric field intensity on the trajectory is acquired, the acquired electric field intensity is converted into antenna reception power, and the antenna is mounted at a position where the operating area where the converted antenna reception power is equal to or greater than a threshold value is maximized . Accordingly, in consideration of the presence of the wiper, working area antenna reception power is equal to or greater than the threshold value by mounting the position became maximum, to avoid a decrease in antenna gain caused by the presence of the wiper in advance be able to.

According to the method for determining the mounting position of the antenna for the in-vehicle communication device according to claim 2, the electric field generated by combining the direct wave coming directly from the external device to the antenna and the scattered wave coming from the external device to the antenna through the wiper. Acquires the electric field strength on the trajectory where the antenna moves as the vehicle moves on the intensity distribution, converts the acquired electric field strength into the antenna received power, and the converted antenna received power exceeds the threshold Since the position where the area is maximized is determined as the optimum mounting position of the antenna, the same effect as that described in the first aspect can be obtained.

  Hereinafter, an embodiment in which the present invention is applied to an ETC antenna of an ETC onboard device mounted on a vehicle in order to use an ETC system (automatic toll collection system on a toll road) will be described with reference to the drawings.

  In the ETC system, a roadside radio device (external device in the present invention) is disposed on the toll gate on the road, and an ETC onboard device is mounted on the vehicle side, and the ETC onboard device and the roadside radio device communicate wirelessly. By paying, the toll is automatically paid and it is possible to pass without stopping the toll booth. The ETC antenna of the ETC on-board unit is configured such that, for example, a radiator and a feed line are formed from a copper foil pattern on the surface of a high-frequency substrate, and radio waves are received from a roadside radio device disposed in an overhead and connected to the roadside radio device. Radio waves are transmitted through the windshield.

  Hereinafter, a procedure for determining the optimum mounting position of the ETC antenna will be described. Since the front window glass is provided with a wiper having metal parts (for example, iron or stainless steel), the optimum mounting position of the ETC antenna is determined in consideration of the presence of the wiper.

  First, the radiated radio wave from the road unit antenna is a right-handed plane wave, and the wiper is regarded as a cylinder made of a metal body, and the electric field intensity distribution generated around the wiper is calculated. In this case, as shown in FIG. 2, a synthesis (addition) of a direct wave directly coming from the roadside antenna 1 to the ETC antenna 2 and a scattered wave coming from the roadside antenna 1 via the cylinder 3 to the ETC antenna 2. Thus, a standing wave can be observed in the electric field intensity distribution generated around the cylinder 3. In FIG. 2, the x-axis represents the vehicle longitudinal direction, the y-axis represents the vehicle left-right direction, and the z-axis represents the vehicle height direction.

  Here, when a vehicle equipped with an ETC vehicle-mounted device passes under a roadside radio device, when the position of the column 3 is fixed, the electric field intensity distribution rotates around the column 3 as a rotation center. If the two paths indicated by the arcs P and Q shown in FIG. 2 are described as trajectories for the movement of the ETC antenna 2, the electric field strength on the arrows P and Q corresponds to the received power of the ETC antenna 2. In this case, at the arrow P, the ETC antenna 2 passes through the antinode a, node A, and antinode b of the electric field intensity distribution sequentially, while at the arrow Q, the ETC antenna sequentially passes through the antinode a and node A of the electric field intensity distribution. . The belly is a place where radio waves interfere and strengthen each other, and the node is a place where radio waves interfere and weaken each other. In FIG. It is a part corresponding to a clause.

At this time, as shown in FIG. 3, when the ETC antenna 2 moves in accordance with the arrow P, the received power is equal to or higher than a threshold value (“about −40 dBm” in the present embodiment). The horizontal distance between them (shown by a broken line arrow) is about “about 1200 mm”, but when the ETC antenna 2 moves according to the arrow Q, the ETC antenna 2 and the roadside device antenna whose received power is equal to or greater than a threshold value. The distance in the horizontal direction from 1 (indicated by a solid arrow) is about “about 2000 mm”. That is, when the ETC antenna 2 is mounted at a position that moves according to the arrow P and when the ETC antenna 2 is mounted at a position that moves according to the arrow Q, the latter enlarges the operating area of the ETC antenna 2 than the former. be able to. In FIG. 3, the horizontal distance between the ETC antenna 2 and the roadside antenna 1 is indicated as “0” when the ETC antenna 2 exists immediately below the roadside antenna 1.

  FIG. 4 shows the optimum mounting position in the mountable range of the ETC antenna 2. The mountable range of the ETC antenna 2 is limited to be formed between the dashboard (metal plate for separating the engine room and the vehicle interior space) and instrument panel mounting parts (such as meters and audio equipment) and the dashboard. It is a space, and in this embodiment, the horizontal width is “about 60 mm” and the width in the height direction is the intersection of the diagonal line “about 130 mm” behind the vehicle and “about 40 mm” below from the position where the wiper is mounted. Is a space of “about 60 mm”. The position where the ETC antenna 2 does not pass through the node A of the electric field intensity distribution within the mountable range of the ETC antenna 2, specifically, when the (x coordinate, z coordinate) of the wiper is (0, 0) (109 , −36) is the optimum mounting position. That is, the position where the part of the radiator formed from the copper foil pattern is (109, −36) is the optimum mounting position of the ETC antenna 2. In the present embodiment, since the arrival direction of the radio wave from the roadside antenna 1 is the front upper direction when viewed from the vehicle, the vehicle left-right direction (y-axis direction) is determined when determining the optimum mounting position of the ETC antenna 2. Does not need to be considered.

  FIG. 1 is a flowchart showing a procedure for determining the optimum mounting position of the ETC antenna 2. First, wiper modeling and radio wave propagation analysis are performed (step S1), and a mounting position in the mountable range of the ETC antenna 2 is provisionally determined (step S2). Next, the electric field strength three components (x component, y component, z component) on the locus along which the ETC antenna 2 moves on the electric field strength distribution as the vehicle moves is acquired (step S3). Next, the acquired electric field strength is converted into antenna reception power (step S4), and the horizontal distance between the ETC antenna 2 and the roadside antenna 1 where the converted antenna reception power is equal to or greater than a threshold is determined as an operating area. (Step S5).

Then, it is determined whether or not the above-described processing has been performed for the entire mountable range of the ETC antenna 2 (for example, several dispersed positions) (step S6), and the entire mountable range of the ETC antenna 2 is described above. If the process has not been performed (“NO” in step S6), the mounting position of the ETC antenna 2 is changed within the mountable range (step S7), the process returns to step S3 described above, and the same process is repeated. To do. On the other hand, if the implementing process described above for whole mounting range of the ETC antenna 2 ( "YES" in step S6), and working area, and outputs the determined as the optimum mounting position position became maximum ( For example, display) (step S8). In this way, the optimum mounting position of the ETC antenna 2 can be determined by simulation. In the above, the position where the operating area is maximized is determined as the optimum mounting position. However, the position where the operating area required by the system specifications is secured can be optimized even if the operating area is not maximized. The mounting position may be determined.

  As described above, according to the present embodiment, the electric field generated by the combination of the direct wave directly coming from the roadside antenna 1 to the ETC antenna 2 and the scattered wave coming from the roadside antenna 1 through the wiper to the ETC antenna 2. Acquires the electric field strength on the trajectory along which the ETC antenna 2 moves as the vehicle moves on the intensity distribution, converts the acquired electric field strength into antenna received power, and the converted antenna received power is equal to or greater than a threshold value. Since the ETC antenna 2 is mounted at the position where the operating area becomes the maximum, it is possible to avoid a decrease in antenna gain caused by the presence of the wiper.

The present invention is not limited to the above-described embodiment, and can be modified or expanded as follows.
The present invention can be applied not only to the ETC antenna but also to determining the optimum mounting position of the antenna used in other systems. In addition to the presence of the wiper provided on the front window glass, when the antenna is mounted on the rear side of the vehicle, the optimum mounting position of the antenna is determined in consideration of the presence of the wiper provided on the rear window glass. It can also be applied to.
The present invention can be applied not only to the wiper but also to determining the mounting position of the antenna with respect to the on-vehicle component having a rotationally symmetric shape or a similar shape.

The flowchart which shows one Embodiment of this invention and shows the procedure which determines the optimal mounting position of an ETC antenna Diagram showing electric field strength distribution The figure which shows the correspondence of the distance of the horizontal direction between an ETC antenna and a roadside antenna, and received power The figure which shows the optimal mounting position of the ETC antenna

Explanation of symbols

  In the drawings, reference numeral 1 denotes a road unit antenna (external device), and 2 denotes an ETC antenna (antenna for an in-vehicle communication device).

Claims (4)

An antenna for an in-vehicle communication device that performs at least one of reception of radio waves from an external device and transmission of radio waves to the external device through a window glass provided with a wiper,
The antenna moves as the vehicle moves on the electric field intensity distribution generated by the combination of the direct wave coming directly from the external device to the antenna and the scattered wave coming from the external device through the wiper to the antenna. The electric field strength on the trajectory to be acquired is acquired, the acquired electric field strength is converted into the antenna reception power, and the operation area where the converted antenna reception power is equal to or greater than the threshold is mounted at the maximum position. An antenna for in-vehicle communication devices. A method for determining a mounting position of an antenna for an in-vehicle communication device that performs at least one of reception of radio waves from an external device and transmission of radio waves to the external device through a window glass provided with a wiper,
The antenna moves as the vehicle moves on the electric field intensity distribution generated by the combination of the direct wave coming directly from the external device to the antenna and the scattered wave coming from the external device through the wiper to the antenna. The electric field strength on the locus to be acquired is converted, the acquired electric field strength is converted into the antenna reception power, and the position where the operation area where the converted antenna reception power is equal to or greater than the threshold is the maximum is set as the optimum mounting position of the antenna. An antenna mounting position determination method for an in-vehicle communication device, comprising: Mounted at a position where the operating area where the antenna reception power is equal to or greater than a threshold value is maximized, is moved by 36 mm downward from the position of the wiper by 109 mm downward from the position of the wiper. The antenna for vehicle-mounted communication apparatuses described in Claim 1. As the position where the operating area where the antenna received power is equal to or greater than the threshold value is the maximum, the position where the wiper position is moved by 36 mm downward from the wiper position by 109 mm is determined as the optimum mounting position of the antenna. An antenna mounting position determination method for an in-vehicle communication device according to claim 2, wherein: