JP2007250387A - Leakage coaxial cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a leakage coaxial cable having excellent manufacturability and excellent flexibility, and allowing leakage at high frequency. <P>SOLUTION: The leakage coaxial cable 1 is composed of: an internal conductor 3; an insulator 5 arranged in the circumference of the internal conductor 3; an external conductor 7 arranged in the circumference of the insulator 5; and an outer cover 9 arranged in the circumference of the external conductor 7, and the cable is characterized in that the external conductor 7 is formed in a braid; and the strand of the braid is formed by overlaying an insulating layer around a conductor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a leaky coaxial cable, and more particularly to a leaky coaxial cable excellent in flexibility that can be applied to various fields mainly using wireless communication.

  Conventionally, a leaky coaxial cable that leaks radio waves in the longitudinal direction of the cable has been used to ensure communication with mobile objects such as train radios and automobile radios of high-speed cars in places where radio waves are difficult to propagate, such as tunnels and highways. Has been developed.

  In general, a conventional leaky coaxial cable is formed in a cylindrical shape, and is used by being laid along a road or a track because of its controllability and stability.

  Referring to FIG. 7, as a conventional leaky coaxial cable 101, for example, an inner conductor 103 made of an annealed copper pipe (or an annealed copper wire), a polyethylene string 105 is wound around the outer periphery of the inner conductor 103, and a polyethylene covering 107 is placed thereon. An insulator 109 provided with a polyethylene tube, an outer conductor 113 provided on the outer periphery of the insulator 109 and provided with a hole referred to as a slot 111, and an outer sheath 115 coated with the outer conductor 113 with, for example, polyethylene , A long coaxial element portion 117 is provided.

  The outer conductor 113 is a copper tape (or aluminum tape) vertically attached to the outer periphery of the insulator 109, and the slot 111 is perforated.

  The leaky coaxial cable 101 is provided with a long cable support line portion 123 in which the periphery of a tensile body 119 as a suspension line is covered with a sheath resin 121. The cable support line portion 123 and the coaxial element portion described above are provided. 117 are integrated in parallel with each other via a neck portion 125.

  Therefore, in the leaky coaxial cable 101, an electromagnetic field generated by the circumferential current induced by the slot 111 is radiated to the outside as a leaked radio wave. Currently, it is used in a specific frequency range (for example, several tens of MHz to 900 MHz, 900 MHz to 2400 MHz, etc.) with a frequency of about several tens of MHz to 2.5 GHz, and is mainly used in a tunnel or along a train line. Has been.

  Referring to FIG. 8, as another conventional leaky coaxial cable 127, a helical leaky coaxial cable has been put into practical use. The leaky coaxial cable 127 is used at a low frequency of 1600 kHz. That is, the same members as those of the leaky coaxial cable 101 of FIG. 7 described above are described with the same reference numerals. In the leaky coaxial cable 127, an annealed copper wire 131 is spirally wound around the outer periphery of the ferrite core 129 to constitute the internal conductor 133. . Further, the outer periphery of the annealed copper wire 131 is coated with polyethylene and a polyethylene tube is provided as an insulator 135. An annealer copper wire is spirally wound around the outer periphery of the insulator 135 to form an external conductor 137. The outer conductor 137 is sheathed with a jacket 115 covered with, for example, polyethylene, and a long coaxial element portion 139 is provided.

  The leaky coaxial cable 127 is provided with a long cable support line portion 123 in which the periphery of the tensile body 119 serving as a suspension line is covered with a sheath resin 121. The cable support line portion 123 and the coaxial element portion described above are provided. 139 are integrated in parallel with each other via a neck portion 125.

  In addition, the leaky coaxial cable disclosed in Patent Document 1 is provided with a plastic insulator on the outer periphery of an inner conductor (also referred to as a center conductor), and a hot-melt adhesive is previously provided on the outer periphery of the plastic insulator. A braided outer conductor of a metal wire coated with is provided, and the outer periphery of the braided outer conductor is covered with a sheath. The purpose of applying the hot melt adhesive on the metal wire of the braided outer conductor is to apply heat in the manufacturing process so that the plastic insulator and the sheath positioned above and below the braided outer conductor are the braided outer conductor. It is to integrate.

  The leaky coaxial cable shown in Patent Document 2 has basically the same configuration as that of Patent Document 1, except that at least one of an outer conductor and an inner conductor (also referred to as a center conductor) Braided, that is, the braided wire is composed of metal wire in one direction and the braided wire in the other direction alternately with non-conductive fibers (plastic), and opens electromagnetic waves outside the leaky coaxial cable. Yes.

  Further, the leaky coaxial cable shown in Patent Document 3 has basically the same configuration as that of Patent Document 1, and the difference is that the outer conductor is composed of, for example, a spiral wound metal wire, and the outer conductor is connected to the outer conductor. There is a gap. This gap is intended to leak electromagnetic waves. The outer conductor is not coated with hot melt adhesive.

Further, the leaky coaxial cable shown in Patent Document 4 has basically the same configuration as that of Patent Document 1, except that the outer conductor is a braid and a gap is provided in the braid. This gap is intended to leak electromagnetic waves. The outer conductor is not coated with hot melt adhesive.
JP 58-34510 A JP-A-63-88708 JP 2003-123555 A US4599121

  By the way, in the leaky coaxial cable 101 shown in FIG. 7 as described above, it is necessary to pre-perforate the slot 111 in the copper tape of the outer conductor 113, so that the productivity is excellent. In addition, although the outer conductor 113 is corrugated, it is a metal tape, so that it cannot be said that it is excellent in flexibility.

  Further, the leaky coaxial cable 127 of FIG. 8 has a problem that it is limited to the use at a low frequency of about 1600 kHz. In addition, since the ferrite core 129 is used, there is a problem that the cable becomes expensive and cannot be said to be excellent in flexibility.

  Further, the conventional leaky coaxial cable disclosed in Patent Document 1 has a problem in that the cost increases because it is necessary to previously apply a hot-melt adhesive to the braided metal wire constituting the outer conductor. Further, among the braids constituting the outer conductor, the plastic insulator and the sheath positioned in the outer layer are integrated by the braided outer conductor, so that even if there is an effect of preventing friction of the braid, it is excellent in flexibility. There was a problem that could not be said.

  In addition, the conventional leaky coaxial cable of Patent Document 2 has relatively good flexibility, but it is necessary to suppress the non-conductive fiber used for the outer conductor with a plastic tape from the outside. There was a problem that the outer conductor was easy to move.

  Further, the leaky coaxial cable disclosed in Patent Document 3 requires a gap in the outer conductor when it is spirally wound with the metal wire of the outer conductor at the time of manufacture, which requires a complicated manufacturing process and deteriorates manufacturability. There was a problem.

  In addition, the conventional leaky coaxial cable disclosed in Patent Document 4 has a problem that a complicated manufacturing process is required because it is necessary to provide a gap with a size and a space as needed in the braid as an outer conductor in advance. .

In order to achieve the problem to be solved by the above-described invention, a leaky coaxial cable of the present invention includes an inner conductor, an insulator provided on the outer periphery of the inner conductor, and an outer conductor provided on the outer periphery of the insulator. In a long leaky coaxial cable composed of a jacket provided on the outer periphery of the outer conductor,
The outer conductor is formed of a braid and the braided wire is formed by covering the conductor with an insulating layer.

  In the leaky coaxial cable according to the present invention, when the braid has a braid pitch L (mm) and a leak frequency peak value F (MHz) in the leaky coaxial cable, F = A / (√ε · L) (A: constant, ε: equivalent dielectric constant of coaxial cable) is satisfied, and a configuration that provides a desired amount of leakage is preferable.

  As can be understood from the means for solving the problems as described above, according to the present invention, the insulating layer of the braided strand of the outer conductor becomes an opening (window) for electromagnetic wave leakage, and the electromagnetic wave is formed outside the leaky coaxial cable. Can be leaked. Moreover, since the insulating layer on the strand of the outer conductor braid is thin, it can be used as a leaky coaxial cable only in a specific frequency range, and can be used as a normal coaxial cable outside the specific frequency range, so the applicable range is wide Is.

  In addition, the leaky coaxial cable of the present invention has the same productivity as a conventional general coaxial cable, for example, a coaxial cable in which the outer conductor is formed of a general braid, and has excellent flexibility. Leakage can be made possible at high frequencies in the GHz band.

  Embodiments of the present invention will be described below with reference to the drawings.

  Referring to FIG. 1, a leaky coaxial cable 1 according to this embodiment includes an inner conductor 3, an insulator 5 provided on the outer periphery of the inner conductor 3, and an outer conductor 7 provided on the outer periphery of the insulator 5. And an outer jacket 9 covering the outer periphery of the outer conductor 7.

  Further, the outer conductor 7 is constituted by a braid, and each of the strands of the braid is characterized by covering an insulating layer around a metal wire which is a good conductor.

  The inner conductor 3 may be, for example, an annealed copper wire, or may be tin plated or silver plated, or may be a copper alloy, single wire, stranded wire, pipe, etc. Various materials and structures are applicable.

  Further, for example, polyethylene can be used for the insulator 5, and in addition, cross-linked polyethylene, foamed polyethylene, polypropylene, fluorine resin such as PTFE, PFA, and FEP (all of which includes foam) may be used.

  In addition, for the outer conductor 7 described above, a metal wire that is a good conductor of each strand of the braid can be, for example, an annealed copper wire, or can be a tin-plated or silver-plated copper alloy. The one using may be used. On the other hand, the material of the insulating layer that insulates the wire may be any other material as long as it is an insulating material such as urethane, polyethylene, cross-linked polyethylene, polypropylene, fluororesin such as PTFE, PFA and FEP, polyester, and polyesterimide. Applicable.

  In addition, for example, PVC can be used for the jacket 9 described above, and various other resins may be used.

  With the above configuration, in the leaky coaxial cable 1 according to this embodiment, the insulating layer of the braided strand of the outer conductor 7 becomes an opening (window) for electromagnetic wave leakage, and electromagnetic waves can be leaked to the outside of the leaky coaxial cable 1. it can. Moreover, since the insulating layer on the braided wire of the outer conductor 7 is thin, it can be used as the leaky coaxial cable 1 only in a specific frequency range, and can be used as a normal coaxial cable outside the specific frequency range. Is wide.

  Further, the leaky coaxial cable 1 of the present invention has the same productivity as a conventional general coaxial cable, for example, a coaxial cable in which the outer conductor is formed of a general braid, and has excellent flexibility. It has a feature that enables leakage at a high frequency of several GHz band.

  More specifically, as shown in Table 1, as the leaky coaxial cable 1 of this embodiment, the inner conductor 3 is composed of seven annealed copper wires having a diameter φ of 0.18 mm and stranded wires with a diameter φ0. The insulator 5 is made of polyethylene and has a diameter of 1.6 mm. Further, as the outer conductor 7, the strand is coated with urethane as an insulating layer on a soft copper wire portion having a diameter of φ0.08 mm, and the outer diameter φ is 0.1 mm. Braided. Furthermore, the jacket 9 is made of PVC having a standard thickness of 0.4 mm. As described above, the diameter φ of the leaky coaxial cable 1 is 3.0 mm.

Furthermore, in order to confirm the effectiveness of the leaky coaxial cable 1 of this embodiment, as shown in Table 1, this implementation is performed with a coaxial cable 11 using a braided outer conductor that has been conventionally used. A structure very similar to the leaky coaxial cable 1 of the form is used as a comparative example. That is, the coaxial cable 11 of the comparative example is different from the leaky coaxial cable 1 of this embodiment in the outer conductor, and the outer conductor of the comparative example is a general braid, and an annealed copper wire having a diameter of 0.1 mm It is braided with 5 strands × 16 strokes with a strand of wire. Other configurations are the same as those of the leaky coaxial cable 1 of this embodiment. In Table 1, the same components as the leaky coaxial cable 1 are indicated by ←.

  The attenuation frequency characteristics and the amount of radiation leakage were measured for the samples of the leaky coaxial cable 1 of this embodiment and the coaxial cable 11 of the comparative example.

  As shown in FIG. 2, the attenuation frequency characteristics are shown in FIG. 2, when the frequency is changed at a sample length of 1 m under an environment where the temperature is 20 ° C., and the attenuation at each frequency (MHz) is confirmed. In the sample 15B, there is almost no change, but in the 15A of this embodiment, there is an attenuation amount of about −17 dB around the frequency of 2600 MHz.

  Further, referring to FIG. 3, the radiation leakage amount measuring device 13 for measuring the radiation leakage amount is such that the sample 15A of this embodiment or the sample 15B of the comparative example is vertically aligned by a sample support rotating device (not shown). It is configured to be stretched and rotated 360 ° in the horizontal direction as shown by the arrow in FIG. 3, and forms a ring shape for measuring the amount of radiation leakage of the sample 15A or 15B in the middle of the sample 15A or 15B. The loop antenna 17 is provided by a support member (not shown). The loop antenna 17 is configured such that the ring-shaped surface can be switched in both the horizontal direction and the vertical direction, and is electrically connected to the network analyzer 21 by a conductive line 19.

  The lower end of the sample 15A or 15B is electrically connected to the network analyzer 21. Then, as indicated by the arrows in FIG. 3, a signal is input from the network analyzer 21 to the sample 15A or 15B. The amount of radiation leakage of the sample 15A or 15B is measured by the loop antenna 17 and output to the network analyzer 21 via the conduction line 19.

  With the radiation leakage amount measuring device 13 as described above, the loop antenna 17 is brought into contact with the outer cover 9 of the sample 15A or 15B at a point 200 cm from the incident end (lower end) of the sample 15A or 15B. The amount of radiation leakage at a part, that is, the separation distance from the outer cover 9 of the sample 15A or 15B to the loop antenna 17 was 0 (zero) cm was measured by the loop antenna 17. The results are shown in the graphs of the vertical radiation amount measurement result of FIG. 4 and the horizontal radiation amount measurement result of FIG. The frequency at this time is 2600 MHz based on the graph of FIG.

  4 and 5, the horizontal direction and the vertical direction are the components in the circumferential direction of the sample 15A or 15B in FIG. 3 (in other words, the circumferential direction of the center of rotation of the sample 15A or 15B, and left and right in FIG. (Direction) is defined as the horizontal direction, and the longitudinal component of the sample 15A or 15B (in other words, the vertical direction in FIG. 3) is defined as the vertical component.

  In FIG. 4, the direction of the loop antenna 17 (the direction of the surface formed by the ring shape) is vertical, and each sample at each rotation angle when the sample 15A or 15B is rotated 360 ° horizontally as indicated by the arrow in FIG. The radiation leakage amounts of 15A and 15B are shown. In FIG. 4, the solid black line indicates the amount of radiation leakage of the sample 15A of the leaky coaxial cable 1 of this embodiment, and the solid white line indicates the amount of radiation leakage of the sample 15B of the coaxial cable 11 of the comparative example. Yes.

  In FIG. 5, the direction of the loop antenna 17 (the direction of the surface formed by the ring shape) is the horizontal direction, and each sample at each rotation angle when the sample 15A or 15B is rotated 360 ° horizontally as indicated by the arrow in FIG. The radiation leakage amounts of 15A and 15B are shown. In FIG. 5, the solid black line indicates the amount of radiation leakage of the sample 15A of the leaky coaxial cable 1 of this embodiment, and the solid white line indicates the amount of radiation leakage of the sample 15B of the coaxial cable 11 of the comparative example. Yes.

  As described above, also in FIGS. 4 and 5, it can be seen that the leakage coaxial cable 1 of this embodiment has been confirmed to have a leakage amount of 10 to 20 dB from the coaxial cable 11 of the comparative example.

  Further, referring to FIG. 6, the structure of the leaky coaxial cable 1 according to the embodiment of the present invention is further developed so that the braid pitch of the outer conductor 7 is L (mm) and the leak frequency peak value is F (MHz). As a result of investigating the correlation, it was confirmed that the correlation equation was established as shown in the graph of FIG.

That is, the correlation equation in FIG.
F = A / (√ε · L) (1)
However, A: constant, ε: equivalent dielectric constant of coaxial cable, correlation coefficient R = 0.9975.

  From the above equation (1), the structure of the leaky coaxial cable 1 according to the embodiment of the present invention can be obtained by arbitrarily selecting the braiding pitch L of the outer conductor 7 and the equivalent dielectric constant ε of the leaky coaxial cable 1. It will be possible to leak at a high frequency of several GHz band.

  Further, as can be seen from FIG. 2, except for the selected arbitrary frequency, since it has the same amount of attenuation as that of the conventional general coaxial cable 11 (comparative example), it is leaked only to the arbitrary frequency, and other Since it is possible to transmit at a frequency, a wide design range can be set.

  Moreover, the leaky coaxial cable 1 of this embodiment is a conventional general coaxial cable, that is, a coaxial cable 11 of a comparative example in which the outer conductor is formed of a general braid. Since the outer conductor 7 of this embodiment can be manufactured under the same manufacturing conditions using a conventional manufacturing facility, it can be manufactured by replacing the outer conductor 7 with the conventional configuration. This is an excellent leaky coaxial cable 1 that has the same manufacturability as a typical coaxial cable 11 and is excellent in flexibility and capable of leaking at a high frequency of several GHz band.

It is sectional drawing of the leaky coaxial cable of embodiment of this invention. It is a graph which shows the attenuation amount frequency characteristic of the leaky coaxial cable of embodiment of this invention, and the coaxial cable of a comparative example. It is the schematic of a radiation leak amount measuring apparatus. It is a graph which shows the measurement result of the perpendicular direction radiation amount of the leaky coaxial cable of embodiment of this invention. It is a graph which shows the measurement result of the horizontal radiation amount of the leaky coaxial cable of embodiment of this invention. It is a graph which shows the correlation of the braiding pitch L (mm) of the outer conductor 7 in the leaky coaxial cable of embodiment of this invention, and the leak frequency peak value F (MHz). It is sectional drawing of the conventional leaky coaxial cable. It is sectional drawing of the other conventional leaky coaxial cable.

Explanation of symbols

1 Leaky coaxial cable (in this embodiment)
3 Inner conductor 5 Insulator 7 Outer conductor 9 Outer jacket 11 Coaxial cable (for comparative example)
13 Radiation leakage measuring device 15A, 15B Sample 17 Loop antenna 19 Conducting wire 21 Network analyzer

Claims (2)

A long leaky coaxial cable comprising an inner conductor, an insulator provided on the outer periphery of the inner conductor, an outer conductor provided on the outer periphery of the insulator, and a jacket provided on the outer periphery of the outer conductor In
The leaky coaxial cable, wherein the outer conductor is formed of a braid, and the strands of the braid cover an insulating layer around the conductor.   When the braid has a braid pitch L (mm) and a leakage frequency peak value F (MHz), F = A / (√ε · L) (A: constant, ε: equivalent dielectric constant of coaxial cable) The leaky coaxial cable according to claim 1, wherein the following relational expression is satisfied and a desired leakage amount is obtained.

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