JPS5910623B2 - bus detection device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a bus detection device.

Conventionally, the loop coupling method and the antenna coupling method have been used as bus detection methods. The loop coupling method is a method in which a conductor loop coil is buried in the road surface, and when a bus passes over the loop, it is detected by the loop current, but the burying work to bury the loop coil in the road surface is difficult, and There was a problem that the buried loop coil was easily broken by the load and vibration of passing vehicles.

In addition, the antenna coupling method involves attaching a circularly polarized wave radiation antenna with a directivity that radiates radio waves only in the forward direction to the side wall of the bus, and installing a circularly polarized wave receiving antenna on the roadside. This method uses a ground antenna that rotates in the same direction as the on-board antenna and receives circularly polarized waves. The rotation of the circularly polarized wave is in the same direction, so it is received, but when it is reflected from the on-board antenna by another object and received by the ground antenna, it is difficult to receive it because the rotation direction of the circularly polarized wave changes, and only directly received radio waves are detected. However, since the shape of the other object that is the reflector is not spherical, the reflected wave is not a completely circularly polarized wave with opposite rotation, but also contains circularly polarized wave components in the same direction. Therefore, some radio waves reflected from other objects are also received at the receiving point, which poses a problem.

The present invention improves the function of an antenna detection type bus detection device using a ground antenna and an on-vehicle antenna by specifying the position and directivity of the antenna.

In the present invention, the on-board antenna is installed as high as possible on the side wall of a vehicle such as a bus, and the ground antenna is installed as low as possible on the roadside, and the received signal strength is limited to a certain elevation angle range when looking from the ground antenna to the on-board antenna. is large,
In other elevation angle ranges, the directivity of the antenna is selected so that the received signal strength is close to o.

An embodiment of the present invention will be explained with reference to FIG.

In Figure 1, 1 is the road surface, 2 and 5 are vehicles such as buses, of which 2 is running on the lane that goes from the front to the back in the figure, and 5 is running on the opposite lane that goes from the back to the front. . 3 and 6 are on-board antennas attached to the upper side walls of vehicles such as buses, 4 is a ground antenna installed on the roadside, and r is another vehicle traveling in the same direction in the adjacent lane as vehicle 5 such as a bus. .

Further, C indicates the center separation line, H indicates the height of the on-board antenna, and h indicates the height of the ground antenna. In this embodiment, the on-board antenna is installed as high as possible on the side wall of a vehicle such as a bus, that is, close to the roof, and the ground antenna is installed as low as possible, that is, as close to the ground as possible and at least lower than the on-board antenna. will be installed.

In this way, when a vehicle such as a bus passes by the ground antenna, the ground antenna will look up at the on-board antenna.If the elevation angle when looking at the on-board antenna from this ground antenna is θ, then θ is Depending on how far a vehicle passes from the roadside ground antenna, the height difference between the on-board antenna and the ground antenna, that is, H-h.
Although it depends on the vehicle, if the width of the lane and the height of the on-board antenna and the ground antenna are determined, θ can be specified within a certain range, that is, θ1, θ, and θ2.

In this case, θ is the angle of elevation when the vehicle such as a bus passes the farthest position from the roadside, and θ2 is the angle of elevation when the vehicle such as the bus passes very close to the roadside.

Consider the case of a round-trip route with two lanes each way.

The ground antenna is retracted 0.5m from the edge of the wharf to the sidewalk side, and the height h is 1.5m. Alternatively, the width of a vehicle such as a bus is 3.0 m, and the height H of the on-board antenna is 3 m. The lanes are each 3.5 m wide and there are two lanes on each side. In such a case, assuming that the vehicle such as a bus passes through a position farthest from the ground antenna, the elevation angle θl when looking at the on-board antenna from the ground antenna is calculated as follows.

Also, the elevation angle θ2 when a vehicle such as a bus passes closest to the ground antenna is: 0? ．． Become.

Therefore, in such an embodiment, the elevation angle when looking at the on-vehicle antenna from the ground antenna is always K2O. This means that it is in the range of 6 × θ × 71.6.

Next, consider what route the radio waves emitted from the on-board antenna take to be received by the ground antenna. In Fig. 1, the radio wave paths are shown as Tl, t2, and t3. Route tl represents the case where the radio waves emitted from the on-board antenna are directly received by the ground antenna, and route T2 represents the case where the radio waves emitted from the on-board antenna are received directly. is reflected on the road surface 1 and received, route T3 is the radio wave emitted from the on-board antenna 6 of a vehicle 5 such as a bus traveling in the opposite direction in the opposite lane and reflected by another vehicle traveling in the opposite lane. This shows the case where the signal is received by a ground antenna.

In this case, signal reception on path T3 is undesirable because it is unnecessary signal reception and may lead to malfunction. Further, reception of the signal on the path T2 does not directly lead to malfunction, but is unnecessary, and it is sufficient to receive only the signal on the path t1. Considering the above-mentioned elevation angle as seen from the on-board antenna from the ground antenna and this radio wave path, the received signal strength becomes large in the elevation angle range of θ1 to θ2, and in other elevation angle ranges, especially in the range of θ to θ. It can be seen that by selecting the directivity of the ground antenna so that the received signal strength is close to 0, it is possible to block the signal on the radio wave path T2 or T3. Next, specific means for making the reception strength large in a certain elevation angle range and close to 0 in other elevation angle ranges will be described. The ideal directivity D(θ) of such an antenna is given by the following equation (1).

11 ゛ 8゛ - -6' Since it is impossible to realize a perfect antenna with such directional characteristics, we will choose one with characteristics that approximate those of the actual antenna. A fairly close approximation can be made using the vertical array antenna shown in .

A in Figure 2.

, Al. A2...An, A]', A25...
. . . An' is an array antenna element, and d is an element spacing. Motoko A. The excitation width is A. , Element Ail. If the complex excitation width of Ai is Ai+Jbi, the directivity Dψ is as follows. However, ψ Kdsinθ Using the composite directivity D1ψ of this vertical array antenna, (
In order to approximate the ideal directivity in formula 1) in the sense of least square error, the excitation amplitude should be determined so as to satisfy the following.

Here, the ideal directivity is given by the equation D(θ), and there is a relationship between θ and ψ of ψ=Kdsinθ. One embodiment will be explained using FIG. 3. Considering three elements with λ d=-, the excitation intensity and phase are (3
) (4) gives the following.

The degree of coupling of the ground antenna in this case was calculated by considering not only the radio wave path T, but also T2 and T3 for the above-mentioned example of the location of the on-board antenna and ground antenna such as height, and the dimension example of two lanes on each side. This is the graph shown in FIG.

According to this example, the range of elevation angles indicated as [D] is 20.6D to N. 6, this is the range of the elevation angle of the on-board antenna attached to a vehicle such as a bus traveling in the forward direction when viewed from the ground antenna, and in this range, the degree of coupling is , -10 db or more, and sufficient reception is achieved for practical purposes.

Also, the elevation angle range of an on-board antenna installed on a bus, etc. that is traveling in the opposite direction when viewed from the ground antenna in the forward direction is 0, and is shown as the range [U] in Figure 3. The degree of coupling is -17 db or less within the range, and because the degree of coupling is low, it will not be received as an erroneous signal.

Also, as can be seen from Figure 3, if the difference in height between the on-board antenna and the ground antenna is increased and θ is increased, the difference in coupling level between the range 1) and the range 2) will increase, so the on-board antenna should be adjusted as much as possible. The lower the ground antenna, the better. Further, when the present invention is put into practice, it is natural that if circularly polarized radio waves are used, the influence of reflected waves will be reduced and the characteristics will be further improved.

As described above, in the present invention, the ground antenna is installed as low as possible than the vehicle soil antenna, and the directivity of the ground antenna is adjusted to the elevation angle when looking at the vehicle antenna of a vehicle such as a bus traveling in the forward direction from the ground antenna. The received signal strength is selected so that the received signal strength is large in the range where the angle exists, and the received signal strength is close to 0 in other elevation angle ranges, so that the radio waves from the on-board antenna of a vehicle such as a bus traveling in the opposite lane are Excellent bus detection can be performed without being affected.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an embodiment of the present invention, FIG. 2 is an embodiment of the terrestrial antenna of the present invention, and FIG. 3 is a diagram showing the degree of coupling of the embodiment of the present invention. In the figure, 1 is the road surface, 2 and 5 are vehicles such as buses, 3 and 6 are on-board antennas, 4 is ground antenna, 7 is another vehicle, T,, t2
, t3 indicate the radio wave path, and C indicates the center separation line.

Claims (1)

[Claims] 1. A bus that travels along the forward lane by installing an on-board antenna on the side wall of a vehicle such as a bus, and receiving radio waves emitted from the on-board antenna with a ground antenna installed on the roadside. In a bus detection device that detects passage of a vehicle near the ground antenna, the ground antenna is installed at least at a lower position than the above-mentioned on-board antenna, and the directivity of the ground antenna is changed from the ground antenna to the ground antenna in the forward direction. The received signal strength is selected so that the received signal strength is large in the range of elevation angles when looking at the on-board antenna of a vehicle such as a bus passing by, and the received signal strength is close to 0 at least in the range of elevation angles below the above range of elevation angles. A bus detection device characterized in that it does not detect radio waves emitted from an on-board antenna of a vehicle such as a bus passing in the opposite direction in the opposite lane. 2. The bus detection device according to claim 1, wherein the terrestrial antenna is constituted by a vertical array antenna.