JP3734857B2 - Leaky coaxial cable - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a leaky coaxial cable that radiates a radio wave used in, for example, a mobile radio communication system, a radio control system, and the like.
[0002]
[Prior art]
In general, a leaky coaxial cable used in a mobile radio communication system or the like is provided with a center conductor 12 and an insulator 14 on the center conductor 12 via an insulator 14 as shown in FIG. An outer conductor 16 with a slot 18 and an outer covering 24 provided on the outer conductor 16 are provided. In this leaky coaxial cable 10, as shown in FIG. 6, the slot 18 of the outer conductor 16 is formed in a specific direction, and depending on the position of this slot 18, a certain amount of radio waves are transmitted within the cross section of the leaky coaxial cable 10. Radiating with directivity is going to realize stable wireless communication.
[0003]
However, when the cross-sectional diameter of the leaky coaxial cable 10 is smaller than the wavelength of the radio wave, the radio wave diffraction phenomenon appears so large that the cross-section of the leaky coaxial cable 10 can hardly exhibit the shielding effect. Was radiated in all directions of the circumference of the leaky coaxial cable 10 without showing sufficient directivity.
[0004]
For this reason, as shown in FIG. 7, when the leaky coaxial cable 10 is installed in the tunnel 26 or the like, the radio wave r radiated in all directions of the circumference of the leaky coaxial cable 10 is reflected on the wall surface 26A or the ceiling surface 26B of the tunnel 26. Then, since it is received by the antenna 32 of the moving body 28 (track 30 in the figure) through various routes, the electric field fluctuates or the leaking coaxial cable 10 and the antenna 32 of the moving body 28 that receives the radio wave r There is a problem that stable reception cannot be performed because the amount of coupling between the channels changes. In particular, when the separation distance between the leaky coaxial cable 10 and the wall surface 26A, etc. is small, or depending on the medium or state of the wall surface 26A, etc., the amount of attenuation is affected, and the electric field changes depending on the installation location of the leaky coaxial cable 10. There was also a problem.
[0005]
In consideration of the fact that radio waves are radiated in all directions of the circumference of the leaky coaxial cable in this manner, it is generally performed to reflect the radio waves by attaching a reflector to the wall of the tunnel or the like (Japanese Patent Laid-Open No. Sho 52-52). In this case, the reflector is separate from the leaky coaxial cable and cannot be used in an open space other than a tunnel having a wall surface.
[0006]
In addition, a superconductor is provided in the slot portion of the outer conductor of the leaky coaxial cable to prevent radio wave leakage, and directivity is given to the radio wave as a normal conducting state by a superconducting magnet attached to the moving body only where necessary. Means are also provided (see JP-A-2-66086). However, in this prior art, in order to receive radio waves, it is necessary to provide means such as a superconducting magnet for destroying this superconducting state on the receiving antenna, etc., so that the radio wave receiving equipment becomes complicated, and the elevator Unlike the moving body such as the track 30, the moving body 28 such as the track 30 shown in FIG. 7 does not always move at a fixed interval with respect to the leaky coaxial cable 10. There is a possibility that radio waves cannot be received reliably and stably without being affected by the magnetic field of the superconducting magnet.
[0007]
[Problems to be solved by the invention]
In order to solve the above problems, the problem of the present invention is to suppress the fluctuation of the electric field by giving sufficient directivity so as to radiate the radio wave only in the specific direction that requires the use of the radio wave, An object of the present invention is to provide a leaky coaxial cable that can easily receive a stable radio wave.
[0008]
[Means for Solving the Problems]
As a means for solving the above-mentioned problems, the present invention provides a leaky coaxial cable including a center conductor and a slotted outer conductor provided on the center conductor via an insulator. It further includes a reflector that is disposed so as to surround the outer conductor with a space and has an opening that emits radio waves in a certain direction, and the opening of the reflector is continuous in the longitudinal direction and is disposed corresponding to the slot of the outer conductor. it is intended to provide a leaky coaxial cable, characterized in being.
[0009]
This reflector reflects the radio waves radiated in all directions of the outer conductor around the cable cross section and radiates the radio waves from the opening, so that the radio waves have sufficient directivity in the direction of the opening. There is no occurrence of electric field fluctuations due to reflection, and radio waves can be easily and stably received. In particular, even when the cross-sectional diameter of the leaky coaxial cable is smaller than the wavelength of the radio wave, the cross-section of the leaky coaxial cable exhibits a sufficient shielding effect by the reflector, so that the directivity of the radio wave is improved. In addition , since the openings of the reflectors are continuously arranged in the longitudinal direction so as to correspond to the slots of the outer conductor, it is possible to further improve the directivity in the slot direction that requires the use of radio waves.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described in detail with reference to the drawings. FIGS. 1 and 2 show a leaky coaxial cable 10 according to the present invention. The leaky coaxial cable 10 includes a center conductor 12 and the center conductor 12. And an external conductor 16 provided via an insulator 14.
[0011]
The central conductor 12 is made of an appropriate conductor such as a copper wire or an aluminum wire, and the insulator 14 is made of an insulator having stable insulation and moldability, such as polyethylene or fluororesin. The insulator 14 is formed so as to cover the entire length of the central conductor.
[0012]
As shown in FIG. 1, the outer conductor 16 is provided with a slot group 18, and in the illustrated embodiment, the slot group 18 is a plurality of slots arranged in a so-called C-shape in which the inclination is directed in the opposite direction. Slot 18A, 18B. These slot groups 18 are provided as appropriate over the entire length of the leaky coaxial cable 10 at locations where radio wave radiation is required or at predetermined intervals. Radio waves radiated by the slot group 18 provided in the outer conductor 16 are radiated with a certain degree of directivity within the cross section of the leaky coaxial cable 10. Therefore, the leaky coaxial cable 10 is usually laid so that the slot group 18 faces the antenna 32 (see FIG. 3) of the moving body 28 that should receive radio waves. Needless to say, the slots 18A and 18B may be arranged other than the so-called C shape shown in FIG.
[0013]
As shown in FIGS. 1 and 2, the leaky coaxial cable 10 of the present invention further includes a reflector 20 disposed so as to surround the outer conductor 16 with a space from the outer conductor 16 with the slots 18A and 18B. ing. In the illustrated embodiment, the reflector 20 is provided on the outer conductor 16 via the second insulator 22 so as to be spaced from the outer conductor 16. Thus, since the reflector 20 is disposed at a distance from the outer conductor 16, it can reflect radio waves radiated from the outer conductor 16.
[0014]
Further, as shown in FIGS. 1 and 2, the reflector 20 has an opening 20 a that radiates radio waves radiated from the outer conductor 16 in a certain direction. The opening 20 a is formed over the entire length of the leaky coaxial cable 10 . Further, as shown in FIGS. 1 and 2, the opening 20a is disposed so as to correspond to the slots 18A and 18B so that the slots 18A and 18B face the opening 20a.
[0015]
As a result, as shown in FIG. 3, the radio wave r radiated from the slots 18 </ b> A and 18 </ b> B provided in the outer conductor 16 in all directions including the radiation due to diffraction is reflected within the cross section of the leaky coaxial cable 10. 20 is reflected from the opening 20a and radiated from the opening 20a. Therefore, the directivity in the direction of the slots 18A and 18B, which is the direction in which the radio wave r needs to be used, can be sufficiently obtained. Thus, the electric field fluctuation or the like does not occur, and the antenna 32 which is the receiver of the track 30 which is the moving body 28 can receive the radio wave r stably.
[0016]
In particular, even when the cross-sectional diameter of the leaky coaxial cable 10 is smaller than the wavelength of the radio wave r, the cross-section of the leaky coaxial cable 10 exhibits a sufficient shielding effect by the reflector 20, and thus the directivity of the radio wave r is improved. To do. Further, in this case, the radio wave r can be stably received even with respect to the mobile body 28 such as the track 30 that does not always move at a constant distance from the leaky coaxial cable 10. 28 can easily and stably receive the radio wave r without providing complicated equipment such as a superconducting magnet, and the leaky coaxial cable 10 itself is provided with the reflector 20 so that it is not open except for the tunnel 26 and the like. This is advantageous in that the radio wave r can be given sufficient directivity even in a confined space. In addition, there is a preferable advantage from the viewpoint of effective use of the radio wave r in that the radio wave r is not radiated so much except in a necessary direction.
[0017]
The reflector 20 can be used regardless of the type as long as it is a metal that reflects radio waves as a material. Specifically, the reflector 20 can be formed of a copper tape, an aluminum tape, or the like. In the illustrated embodiment, the reflector 20 is formed by winding this copper tape or the like on the second insulator 22 in consideration of the flexibility of the leaky coaxial cable 10 to some extent. It is not limited to this, It can also form by other appropriate methods, such as vertical attachment. Further, an outer coating 24 is provided on the reflector 20 as shown in FIGS. As shown in FIG. 4, a coating 34 may be further provided between the second insulator 22 and the reflector 20. Further, the coating 34 may be provided on the outer conductor 16 (between the outer conductor 16 and the second insulator 22). Therefore, the existing leaky coaxial cable that does not include the reflector 20 used in the present invention can be dealt with by applying the second insulator 22, the reflector 20 and the outer coating 24 later.
[0018]
In the above embodiment, the opening 20a of the reflector 20 is arranged corresponding to the slots 18A and 18B. However, if necessary, the opening 20a can be formed in the slot 18A, as shown in FIG. You may arrange | position so that an electromagnetic wave may be radiated | emitted in other predetermined directions other than 18B.
[0019]
3 shows that the moving body 28 is a track 30. Of course, the moving body 28 is not limited to this track 30, and the leaky coaxial cable of the present invention is not limited to the moving body. Regardless of the type of 28, it can be used for a wireless communication system and a wireless control system.
[0020]
【The invention's effect】
According to the present invention, as described above, the reflector having an opening that is spaced from the outer conductor and radiates radio waves in a certain direction is provided. Therefore, the reflector is arranged in all directions of the circumference of the outer conductor. Since the radiated radio wave is reflected in the cable cross section and radiated from the opening, the radio wave shows sufficient directivity in the opening direction, and it is not reflected on the wall surface of the tunnel or the like to cause fluctuation of the electric field. There is an advantage that radio waves can be received simply and stably. In particular, even when the cross-sectional diameter of the leaky coaxial cable is smaller than the wavelength of the radio wave, the cross-section of the leaky coaxial cable exhibits a sufficient shielding effect by the reflector, so that the directivity of the radio wave is improved. Further, in this case, since the openings of the reflector are arranged corresponding to the slots of the outer conductor continuously in the longitudinal direction, the directivity in the slot direction can be further improved.
[0021]
In particular, according to the present invention, compared with the prior art, radio waves can be stably received even for mobile bodies such as trucks that do not always move with a constant distance from the leaky coaxial cable, In addition, it is possible to easily receive radio waves easily and stably without providing complicated equipment such as a superconducting magnet in the moving body, and further, since the leaky coaxial cable itself has a reflector, it is open except for tunnels and the like. It is advantageous in that sufficient directivity can be given to the radio wave even in a limited space.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view of a leaky coaxial cable according to the present invention.
FIG. 2 is a cross-sectional view of a leaky coaxial cable taken along line AA in FIG.
FIG. 3 is a schematic view showing a radio wave radiation state of a leaky coaxial cable according to the present invention installed in a tunnel.
FIG. 4 is a cross-sectional view of another embodiment of a leaky coaxial cable according to the present invention.
FIG. 5 is a cross-sectional view of another embodiment of a leaky coaxial cable according to the present invention.
FIG. 6 is a schematic perspective view of a conventional general leaky coaxial cable.
FIG. 7 is a schematic view showing a radiation state of a conventional general leaky coaxial cable installed in a tunnel.
[Explanation of symbols]
10 Leakage coaxial cable 12 Central conductor 14 Insulator 16 Outer conductor 18 Slot group 18A, 18B Slot 20 Reflector 20a Opening 22 Second insulator 24 Outer coating 26 Tunnel 26A Tunnel wall 28 Mobile 30 Track 32 Antenna 34

Claims (1)

In a leaky coaxial cable comprising a center conductor and a slotted outer conductor provided on the center conductor via an insulator, the radio wave is arranged by surrounding the outer conductor at a distance from the outer conductor. A leaky coaxial cable, further comprising a reflector having an opening that radiates in a direction, the opening of the reflector being continuous in a longitudinal direction and disposed corresponding to a slot of the outer conductor .

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