JP6888282B2 - Leaky coaxial cable, wireless communication system - Google Patents

Description

The present invention relates to a leaky coaxial cable that radiates a weak electromagnetic wave.

Patent Document 1 discloses a leaky coaxial cable that radiates an electromagnetic wave by a slot formed periodically on an outer conductor of the coaxial cable. This type of leaky coaxial cable is used, for example, for FM broadcasting that provides information to vehicles on highways, road management broadcasting, train radio, and the like.

By the way, the strength of the electric field leaking from the leaking coaxial cable becomes weaker as the distance from the connection end connected to the wireless communication device increases. Therefore, in order to use it over a longer range, prepare multiple types of leaky coaxial cables with different radiant intensities so that they do not fall below the minimum size required for communication. Leakage coaxial cables with higher radiant intensity are gradually used as the distance from the communication device increases. The radiant intensity of the leaky coaxial cable is generally adjusted by the size of the slot.

Japanese Unexamined Patent Publication No. 2013-255175

However, the above-mentioned method has a problem that it is necessary to prepare various kinds of leakage coaxial cables having different radiation intensities. In addition, since it is necessary to connect the leaky coaxial cables to each other, there is also a problem that the laying work requires time and effort.

The present disclosure provides a technique for easily forming a communication area over a long range by using a leaky coaxial cable.

One aspect of the present disclosure is a leaky coaxial cable comprising an inner conductor, an insulator, an outer conductor, and an outer skin portion. The inner conductor is formed in a long shape. The insulator is formed so as to cover the inner conductor. The outer conductor covers an insulator, and a plurality of slots are formed along the longitudinal direction of the inner conductor. The outer skin portion is formed of a dielectric material that covers the outer conductor, and is configured such that the dielectric constant changes in one direction from one end to the other end.

According to such a configuration, even if the slot size is the same, the larger the dielectric constant of the outer skin, the shorter the wavelength of the leaked radiated wave, and even if the slot size is the same, electricity In terms of the above, it is equivalent to providing a larger slot, and the strength of the leakage electric field becomes stronger. Therefore, according to the leakage coaxial cable according to the present disclosure, a communication area in which the electric field strength equal to or higher than the minimum required for communication can be easily maintained over a longer range without changing the size of the slot. Can be formed.

It is explanatory drawing which shows the structure of the wireless communication system using the leakage coaxial cable which concerns on one aspect of this disclosure, and the strength of the leakage electric field from the leakage coaxial cable. It is a perspective view which shows the structure of the leakage coaxial cable. It is explanatory drawing which shows the structure of the wireless communication system using the leakage coaxial cable which concerns on another aspect of this disclosure, and the strength of the leakage electric field from the leakage coaxial cable.

Hereinafter, modes for carrying out the invention will be described with reference to the drawings.
[1. Constitution]
As shown in FIG. 1, the communication system 1 according to one aspect of the present disclosure includes a leaky coaxial cable 2 and a radio 5. The radio 5 functions as a fixed station of a wireless LAN, and is well known to transmit and receive signals in a preset frequency band using the leaky coaxial cable 2 as an antenna.

The leaky coaxial cable 2 is laid in a place where radio waves are hard to reach, a place where spot-like communication is possible, and the like.
The leaky coaxial cable 2 has a cable body 3 and an outer skin 4.

As shown in FIG. 2, the cable main body 3 is configured by sequentially providing an insulator 32, an outer conductor 33, and a sheath 34 on the outer periphery of the inner conductor 31.
As the inner conductor 31, for example, a conductor wire formed in a long shape with a metal having good conductivity such as a copper pipe or a copper covered wire can be exemplified. Examples of the insulator 32 include those formed of polyethylene resin, fluororesin, or low dielectric constant resin obtained by foaming these resins, or those in which strings formed of these resins are bundled. be able to. As the outer conductor 33, for example, a braid made of a metal foil or a metal wire rod formed of a metal having good conductivity such as copper or aluminum can be exemplified. The sheath 34 protects the outer conductor 33, and preferably has flame retardancy, wear resistance, low friction resistance, low temperature resistance, heat resistance, and the like. For example, fluororesins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene / hexafluoropropylene (FEP) can be preferably used. The materials of the inner conductor 31, the insulator 32, the outer conductor 33, and the sheath 34 are not limited to these, and can be appropriately selected depending on the operating frequency band, the operating environment, and the like.

A plurality of slots 35 are formed in the outer conductor 33 along the longitudinal direction of the cable body 3 (hereinafter, the cable axial direction). The slot 35 is formed by punching an outer conductor 33 formed in a sheet shape. However, the method of forming the slot 35 is not limited to this.

The slots 35 are formed in a straight line (here, a rectangular shape), and are designed to repeat the same pattern at regular intervals (hereinafter, pitch) P along the cable axis direction. In this embodiment, there are four slots SL1 to SL4 per pitch P. Of these, the two slots SL1 and SL2 are inclined at an angle α in the longitudinal direction of the slot 35 (hereinafter, the slot direction) with respect to the cable axial direction, and the remaining two slots SL3 and SL4 are inclined with respect to the cable axial direction. The slot direction is formed so as to incline at an angle -α.

In the leaky coaxial cable 2, the cutoff frequency is determined by the outer diameter (that is, the inner diameter of the outer conductor 33) D of the insulator 32, and the smaller the cable diameter, the higher the cutoff frequency. The cutoff frequency needs to be set to be higher than the frequency of the signal transmitted / received by the radio 5 (hereinafter referred to as the frequency used).

Further, in the present embodiment, the outer diameter D of the insulator 32 is set so as to satisfy D / λ> 0.12, where λ is the wavelength of the signal at the operating frequency. This is because, in a general leakage coaxial cable, radiation generated by a magnetic flow induced along the longitudinal direction of the slot around the slot by a current flowing through the inner conductor 31 is mainly used. On the other hand, the above-mentioned setting increases the radiation generated by the electric field component of the signal propagating in the TM mode inside the outer conductor 33 of the leaky coaxial cable 2 leaking from the slot 35.

Returning to FIG. 1, the leaky coaxial cable 2 is divided into three sections, and the sections S1, S2, and S3 are provided in this order from the one closest to the connection end of the radio 5. The section S1 is formed with the sheath 34 exposed, and the sections S2 and S3 are provided with an outer skin 4. In the present embodiment, these sheaths 34 and exodermis 4 correspond to the exodermis portion of the present invention. Further, the outer skin 4 is formed by winding a tape formed of a dielectric material (hereinafter referred to as a dielectric tape) around the outer circumference of the sheath 34. However, a dielectric tape having a higher dielectric constant is used in the outer skin 42 of the section S3 than in the outer skin 41 of the section S2. Further, the dielectric tape has at least a higher dielectric constant than the dielectric forming the sheath 34. Although the case where the number of sections is three is illustrated here, the number of sections may be two or four or more.

[2. design]
In the sections S2 and S3 where the outer skin 4 is provided, the wavelength of the signal radiated to the outside by the electric field component leaking from the slot 35 is shortened by the dielectric constant of the outer skin 4. When the wavelength is shortened, even if the size of the slot 35 is the same, it is electrically equivalent to the provision of a larger slot, and the leakage from the slot 35 increases. As a result, a larger electric field strength can be obtained around the section S2 as compared with the section S1 and around the section S3 as compared with the section S2.

Further, as shown in the graph in FIG. 1, the electric field strength observed around each section has a characteristic that decreases as the distance from the radio 5 increases. However, a serrated characteristic is obtained by increasing the electric field strength at the boundary between the section S1 and the section S2 and the boundary between the section S2 and the section S3. The length of each section S1 to S3 and the dielectric constants of the outer skins 41 and 42 of sections S2 and S3 are such that the electric field strength measured at a point separated from the leaky coaxial cable 2 by a preset communicable distance is determined. It is set so as not to fall below the electric field threshold Eth, which is determined by the minimum electric field strength required for communication with the radio 5.

[3. effect]
According to the embodiment described above, the following effects can be obtained.
(1) By providing the outer skin 4 around the cable main body 3, the strength of the electric field leaking from the leaky coaxial cable 2 is made different for each section S1 to S3. Therefore, it is possible to easily form a communication area in which an electric field strength larger than the electric field threshold value Eth can be obtained over a longer range without changing the size of the slot 35 formed in the outer conductor 33.

(2) Since the outer skin 4 is formed by winding a dielectric tape around the cable main body 3, only one type of cable main body 3 having the same slot 35 size can be used. Moreover, the length of the range S1 to S3 can be easily and arbitrarily changed according to the function of the radio device 5 to be used (for example, the frequency band used and the output power).

[4. Other embodiments]
Although the embodiment for carrying out the present invention has been described above, the present invention is not limited to the above-described embodiment and can be implemented in various modifications.

(1) In the above embodiment, the outer skin 4 is formed of a dielectric tape, but the present invention is not limited to this. For example, a paint formed of a dielectric, a sheet formed of a dielectric, a tube formed of a dielectric, or a case-shaped member that can be attached to and detached from the outside of the cable body 3 may be used.

(2) In the above embodiment, the outer skin 4 is provided separately from the sheath 34, but the outer skin 4 is omitted as in the leaky coaxial cable 2a shown in FIG. 3, and the sheath 34a is formed for each section S1 to S3. The dielectric constants ε1 to ε3 of the dielectric material to be formed may be formed so that ε1 <ε2 <ε3. In this case, the sheath 34 corresponds to the exodermis portion of the present invention.

(3) In the above embodiment, the slot pattern per pitch P is composed of four slots SL1 to SL4, but the present invention is not limited to this. The slots 35 forming the slot pattern may have a shape that is line-symmetrical with respect to the center of the pitch. For example, the number of slots 35 per pitch may be 3 or less or 5 or more. The tilt angles of the slots 35 in the same pitch do not necessarily have to be the same.

(4) The functions of one component in the above embodiment may be dispersed as a plurality of components, or the functions of the plurality of components may be integrated into one component. Further, a part of the configuration of the above embodiment may be omitted. In addition, at least a part of the configuration of the above embodiment may be added or replaced with the configuration of the other above embodiment. It should be noted that all aspects included in the technical idea specified from the wording described in the claims are embodiments of the present invention.

1 ... Communication system, 2,2a ... Leakage coaxial cable, 3 ... Cable body, 4,41,42 ... Outer skin, 5 ... Radio, 31 ... Inner conductor, 32 ... Insulator, 33 ... Outer conductor, 34,34a ... Sheath, 35 ... slot.

Claims (6)

With the long inner conductor
An insulator formed to cover the inner conductor and
An outer conductor that covers the insulator and has a plurality of slots formed along the longitudinal direction of the inner conductor.
An exodermis portion formed of a dielectric material covering the outer conductor and configured so that the dielectric constant changes in one direction from one end to the other end.
Bei to give a,
The outer skin is a leaky coaxial cable formed around a sheath that protects the outer conductor. In the outer skin portion, the strength of the leaked electric field based on the signal input from one end of the leaked coaxial cable changes in a sawtooth shape along the axial direction of the coaxial cable, and the magnitude is equal to or larger than the preset electric field threshold. The leaky coaxial cable according to claim 1, wherein the dielectric constant of each part is set to be changed stepwise so as to be maintained. The leaky coaxial cable according to claim 1 or 2, wherein the outer diameter of the insulator is D, the wavelength of the signal to be used is λ, and D / λ> 0.12 is set. The leaky coaxial cable according to claim 1 to 3 , wherein the outer skin portion is formed so as to be removable from the sheath. The leaky coaxial cable according to any one of claims 1 to 4 , wherein the plurality of slots are formed so as to repeat the same pattern at regular pitch intervals. With wireless communication equipment
A leaky coaxial cable used as an antenna for the wireless communication device,
It is a wireless communication system equipped with
The leaky coaxial cable
With the long inner conductor
An insulator formed to cover the inner conductor and
An outer conductor that covers the insulator and has a plurality of slots formed along the longitudinal direction of the inner conductor.
An exodermis portion formed of a dielectric material covering the outer conductor and having a large dielectric constant as the distance from the connection end with the wireless communication device increases.
Bei to give a,
The outer skin portion is a wireless communication system formed around a sheath that protects the outer conductor.

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