JPH10276036A - Leaky coaxial cable - Google Patents

Abstract

(57) [Problem] To provide a leaky coaxial cable which is hardly affected by twisting of the cable itself and change in a relative angle in a circumferential direction of a communication partner. SOLUTION: A cylindrical outer conductor 12 having a plurality of leakage slots 12a arranged in a longitudinal direction, and an outer conductor 1 are provided.
2 and a linear center conductor 11 supported coaxially with the outer conductor 1.
2 and a support wire 14 for fixedly supporting the center conductor 11. The leakage slot 12a is formed at an arbitrary angle in the circumferential direction of the outer conductor 12 with respect to the support wire 14. A sheath 13 covering the outer conductor 12;
A marker 15 is formed in the longitudinal direction at a position corresponding to the plurality of leakage slots 12a on the outer peripheral surface of No. 3. In this case, the outer peripheral radius of the outer conductor 12 exceeds one-tenth of the wavelength of the high-frequency current flowing through the outer conductor 12 and the center conductor 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a leaky coaxial cable used for mobile communication and the like.

[0002]

2. Description of the Related Art A leaky coaxial cable (generally referred to simply as a leaky cable or LCX) is a type of aerial having the appearance of a normal coaxial cable and radiating electromagnetic waves in any direction on the outer periphery. .

The leaky coaxial cable is widely used for communication in a building or a cavity such as a tunnel. In addition, since communication with little fluctuation of electric field intensity and little mobility fading is possible over a wide range, it has recently been used for communication of a moving object traveling at high speed on the ground.

FIG. 4 is a perspective view showing a schematic configuration of a conventional leaky coaxial cable 50, and FIG. 5 is a similar front sectional view.
As shown in FIG. 4 and FIG.
Are supported at a predetermined distance from the central conductor 51 by a support member (not shown).
, An outer sheath 52 covering the outer conductor 52, and a support wire 54 attached to the outer peripheral surface of the sheath 53 for suspending the leaky coaxial cable 50.

[0005] In the outer conductor 52, leakage slots 52 a, 52 a... Are arranged in a row at a position (a position at 180 °: the lower end in this figure) facing the support wire 54. Electromagnetic fields are radiated from the slots 52a, 52a,.

By the way, the above-described leaky coaxial cable 50
The directional characteristic in the circumferential direction about the axis is substantially determined by the ratio between the diameter (radius R) of the outer conductor of the leaky coaxial cable 50 and the wavelength λ of the radiated electric field.

FIG. 6 is a diagram showing the directional characteristics based on the radiation direction of the electromagnetic field shown in FIG. 5 (arrow A in the figure).
The B (Front Back) ratio and the FS (Front Side) ratio are shown.

In the conventional leaky coaxial cable, the wavelength λ of the radiated electric field to be handled is determined by the radius R of the outer conductor of the leaky coaxial cable.
Was big enough for. Therefore, as can be seen from FIG. 6, both the FB ratio and the FS ratio are small. Therefore, the directivity of the leaky coaxial cable 50 in the circumferential direction was treated as almost non-directional.

[0009]

However, in a high frequency band where the wavelength is not negligible with respect to the diameter of the outer conductor, the leaky coaxial cable has a constant directivity in the circumferential direction (specifically, the directivity is not limited). Is 3 when R / λ exceeds 0.1.
An FB ratio exceeding [dB] occurs). FIG. 7 is a diagram showing an example of the directional characteristics of the leaky coaxial cable 50 at a high frequency in the circumferential direction based on FIG.

As can be seen from this figure, when the frequency becomes higher, ± 90 ° in the circumferential direction from the leakage slot 52a.
The electric field strength for the above is significantly reduced. In this case, if the leaky coaxial cable 50 is twisted at the time of laying the leaky coaxial cable 50, communication may be hindered.

FIG. 8 is a diagram showing a state of a radiated electric field when the leaky coaxial cable 50 is laid in a clockwise direction (in this figure, leftward of the support wire 54 for suspending the leaky coaxial cable 50) by approximately 30 °. is there. FIG. 8 shows a mobile communication device 6 located in the horizontal direction (rightward direction in this figure) on the opposite side of the twist.
0 shows a case where communication is performed.

In general, a leaky coaxial cable is often laid on the side wall of a tunnel or a passageway. Therefore, in mobile communication using such a leaky coaxial cable, the intensity of a horizontal radiated electric field with respect to the leaky coaxial cable is low. This is an important issue.

However, the leaky coaxial cable 5 shown in FIG.
At 0, the electric field strength is low above the horizontal direction, and if twisted as shown in FIG. 8, communication with a mobile object in the direction of a weak electric field will be performed. Becomes impossible.

The present invention has been made under such a background, and an object of the present invention is to provide a leaky coaxial cable which is hardly affected by twisting of the cable itself and a change in a relative angle in a circumferential direction of a communication partner. And

[0015]

According to the first aspect of the present invention, there is provided a cylindrical first conductor having a plurality of leakage slots arranged in a longitudinal direction. And a linear second conductor coaxially supported with the first conductor, and support means for fixedly supporting the first conductor and the second conductor, wherein the leakage slot comprises: The first conductor is formed at an arbitrary angle in the circumferential direction of the first conductor with respect to the supporting means. According to the invention as set forth in claim 2, in the leaky coaxial cable according to claim 1, the covering means for covering the first conductor and the plurality of leakage slots on the outer peripheral surface of the covering means. Display means formed in a corresponding position in the longitudinal direction. According to a third aspect of the present invention, in the leaky coaxial cable according to any one of the first and second aspects, the outer peripheral radius of the first conductor is equal to the first conductor and the second conductor. The wavelength of the high-frequency current flowing through the conductor exceeds one-tenth of the wavelength.

According to the present invention, a cylindrical first conductor having a plurality of leakage slots arranged in a longitudinal direction, a linear second conductor supported coaxially with the first conductor, Support means for fixedly supporting the first conductor and the second conductor, wherein the leakage slot is formed at an arbitrary angle in the circumferential direction of the first conductor with respect to the support means. A covering means for covering the first conductor and a longitudinal direction are formed at positions corresponding to the plurality of leakage slots on the outer peripheral surface of the covering means. In this case, the outer radius of the first conductor exceeds one-tenth of the wavelength of the high-frequency current flowing through the first conductor and the second conductor.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below.
FIG. 1 is a perspective view showing a schematic configuration of a leaky coaxial cable 10 according to one embodiment of the present invention. FIG. 2 is a similar front sectional view.

In FIGS. 1 and 2, reference numeral 11 denotes a center conductor formed of a metal such as copper in the shape of a thin column (linear shape). Reference numeral 12 denotes an outer conductor formed of a metal having high conductivity at a high frequency in a cylindrical shape and surrounding the center conductor 11.

This embodiment is applied when R / λ exceeds 0.1, where R is the outer radius of the outer conductor and λ is the wavelength of the high-frequency current flowing through the center conductor 11 and the outer conductor 12. Shall be.

The outer conductor 12 is supported coaxially with the center conductor by a support member made of a material having a high frequency loss and a low dielectric constant. However, since this is a known technique, its illustration and detailed description are omitted. I do.

Reference numeral 13 denotes an insulating sheath that covers the outer conductor 12. A support wire 14 is attached to the outer peripheral surface of the sheath 13 and suspends and supports the leaky coaxial cable 10.

At arbitrary positions of the outer conductor 12 (in this figure, 90 ° clockwise from the support line 14), slots for leakage 12a, 12a,. Electromagnetic fields are radiated from the slots 12a. These leakage slots 2a, 2a
Are also known technologies, and detailed description is omitted.

On the outer peripheral surface of the sheath 13, a marker 15 is attached along a position corresponding to the above-mentioned leakage slots 12a, 12a,. I have. This marker 1
Numeral 5 is made of a material having a high frequency loss or a low dielectric constant, for example, and is formed in a quadrangular prism shape.

FIG. 3 is a diagram showing the directional characteristics of the leaky coaxial cable 10 shown in FIGS. 1 and 2 in the circumferential direction. Note that FIG. 3 shows a case where communication is performed with the mobile communication device 20 located in the horizontal right direction of the leaky coaxial cable 10.

As shown in FIG. 3, in the direction of the leakage slots 12a, 12a,... The fluctuation is small and there is no problem in communication.

Further, since the marker 15 is attached in the direction of the radiated electromagnetic field, the point where the radiated power density becomes maximum can be easily directed toward the communication partner when the leaky coaxial cable 10 is laid.

It should be noted that the shape of the leakage slot, the support line, the marker, and the like shown in the above-described embodiment is an example for embodying the present invention.
The invention is not limited to these shapes.

[0028]

As described above, according to the present invention, a cylindrical first conductor having a plurality of leakage slots arranged in a longitudinal direction, and a wire supported coaxially with the first conductor. And a supporting means for fixedly supporting the first conductor and the second conductor, and the leakage slot is formed at an arbitrary angle in the circumferential direction of the first conductor with respect to the supporting means. Is formed at the position. A covering means for covering the first conductor and a longitudinal direction are formed at positions corresponding to the plurality of leakage slots on the outer peripheral surface of the covering means. in this case,
Since the outer peripheral radius of the first conductor exceeds one-tenth of the wavelength of the high-frequency current flowing through the first conductor and the second conductor, the twist of the cable itself and the relative angle in the circumferential direction of the communication partner are made. The effect is that a leaky coaxial cable that is less susceptible to the change of the coaxial cable can be realized.

That is, the fluctuation of the electromagnetic field strength due to the twist of the leaky coaxial cable or the like in the direction (main radiation direction) in which the leaky slot faces can be reduced. Further, the main radiation direction can be easily recognized by the marker along the leakage slot on the sheath.

Further, the main radiation direction can be controlled in an arbitrary direction by controlling the angle of the leakage slot with respect to the leakage coaxial cable. In this case, since the radiated electromagnetic field is weak in directions other than the main radiation direction, the direction of spurious (unwanted radiation) can be controlled. Thereby, the influence of the communication due to the spurious can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of a leaky coaxial cable according to an embodiment of the present invention.

FIG. 2 is a front sectional view showing a schematic configuration of the leaky coaxial cable according to the embodiment;

FIG. 3 is a diagram showing directional characteristics of the leaky coaxial cable shown in FIGS. 1 and 2 in a circumferential direction.

FIG. 4 is a perspective view showing a schematic configuration of a conventional leaky coaxial cable.

FIG. 5 is a front sectional view showing a schematic configuration of a conventional leaky coaxial cable.

6 is a diagram showing directivity characteristics based on the radiation direction of the electromagnetic field shown in FIG.

FIG. 7 is a diagram illustrating an example of a directional characteristic in a circumferential direction of a leaky coaxial cable at a high frequency.

FIG. 8 is a diagram showing a state of a radiated electric field when the leaky coaxial cable is laid by being twisted approximately 30 ° clockwise.

[Explanation of symbols]

Reference numeral 11: central conductor (second conductor), 12: outer conductor (first conductor), 12a: leakage slot, 13: sheath (covering means), 14: support line (support means), 15: marker (display) means).

Claims (3)

[Claims] A cylindrical first conductor (12) having a plurality of leakage slots (12a) arranged longitudinally.
A linear second conductor (11) supported coaxially with the first conductor, and a supporting means (14) for fixing and supporting the first conductor and the second conductor, The leakage coaxial cable according to claim 1, wherein the leakage slot is formed at an arbitrary angle in a circumferential direction of the first conductor with respect to the support means. 2. A covering means (13) for covering said first conductor.
A display means (1) formed in a longitudinal direction at a position corresponding to the plurality of leakage slots on an outer peripheral surface of the covering means;
5. The leaky coaxial cable according to claim 1, comprising: (5). 3. The method according to claim 1, wherein an outer peripheral radius of the first conductor exceeds one-tenth of a wavelength of a high-frequency current flowing through the first conductor and the second conductor. A leaky coaxial cable according to any of the preceding claims.