JP2008293729A - Coaxial cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency coaxial cable, particularly a fine-diameter coaxial cable having an insulator outer diameter of 1 mm or less which can exhibit attenuation amount characteristics and VSWR characteristics capable of being used in a wide frequency range of several tens of MHz to ten and several of GHz and which does not adversely affect the attenuation amount characteristics and the VSWR characteristics even if an external force such as bending and twisting is added. <P>SOLUTION: In the coaxial cable 1 for arranging a plastic tape 4 with a metal layer on the circumference of an insulator 3 to cover the inner conductor 2 and to have the outer conductor 5 thereon, the plastic tape 4 with the metal foil is formed by pasting together a metal foil 4a with thickness more than 4 μm and not more than 10 μm and the plastic tape 4b. In this coaxial cable 1, the plastic tape 4 with the metal layer is arranged on the outer periphery of the insulator 3 by longitudinal lapping. In this coaxial cable 1, the plastic tape 4 with the metal layer has a width of 1.00 time or more and 1.25 times or less of the outer periphery of the insulator 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a high-frequency coaxial cable, particularly a small-diameter coaxial cable having an insulator outer diameter of 1 mm or less, and can exhibit attenuation characteristics and VSWR (Voltage Standing Wave Ratio) characteristics that can be used in a wideband frequency, and can exhibit tension, vibration, The present invention relates to a device that does not adversely affect the attenuation characteristics and VSWR characteristics even when an external force such as bending is applied.

Coaxial cables are used as wiring materials for various electronic devices, and are frequently used especially for high frequency applications. In a so-called low attenuation coaxial cable that is generally used at a high frequency of 1 GHz to 10 GHz, for example, as shown in FIG. 1, the periphery of the inner conductor 2 is covered with an insulator 3 such as polyethylene, and the insulator 3 A plastic tape 4 with a metal layer is vertically or horizontally wound around the periphery, and an outer conductor 5 made of a metal braid or the like is provided around the periphery, and the outer conductor 5 is covered with an insulating jacket 6. It has a structure. The plastic tape 4 with the metal layer improves the shield characteristics and improves electrical characteristics such as attenuation characteristics and VSWR characteristics.

Here, as the plastic tape 4 with a metal layer, for example, Patent Document 1 discloses a single-sided conductor plastic film obtained by laminating (bonding) a plastic film to a metal foil made of aluminum or copper. For example, Patent Document 2 discloses a tape 14 with a metal layer in which a metal layer 14a is formed by vapor-depositing a metal or metal oxide on the surface of a plastic tape 14b (tape substrate) as shown in FIG. . Further, in Patent Document 3, as shown in FIG. 4, a first metal layer 24d is formed on the surface of a plastic tape 24b by vapor deposition of a metal such as copper, aluminum, silver or the like, and electroplating is further performed to form a second metal layer. A plastic tape 24 with a metal layer is disclosed in which a metal layer 24c is formed and these are used as the metal layer 24a. Here, the thickness of the metal layer 24a composed of the first metal layer 24d and the second metal layer 24c is assumed to be 1 μm or more and 4 μm or less.

Japanese Patent No. 3671729: Hitachi Cable Japanese Utility Model Publication No. 6-17044: Nissei Electric Japanese Patent No. 3671919: Hitachi Cable

In recent years, coaxial cables have been used in various applications such as digital terrestrial television broadcasting, mobile phones, wireless LANs, WiMAX, UWB, RFID, ITS, ETC, and a wide range of frequencies. A coaxial cable capable of exhibiting characteristics and VSWR characteristics has been required. To improve the attenuation characteristics simply, the outer diameter of the inner conductor or the outer diameter of the insulator may be increased. However, in mobile phones, PDAs, notebook PCs, etc. The cable has come to pass through the hinge portion of the device and the terminal, and there is a strong demand for reducing the diameter of the cable because of the need to make the device and the terminal thinner and lighter. Specifically, it is necessary to set the outer diameter of the insulator to 1 mm or less. Furthermore, since these devices and terminals are subjected to external forces such as bending and twisting at the hinge portion, they are not only excellent in high-frequency characteristics such as attenuation and VSWR but also in bending and twisting. There has been a need for a cable having excellent characteristics such as rotation.

In a coaxial cable using a plastic tape with a metal layer as in Patent Document 1, there is no thin metal layer in terms of manufacturing technology, and generally available ones have a thickness of the metal layer exceeding 10 μm. It was. When such a plastic tape with a metal layer is used, particularly in a coaxial cable having an insulator outer diameter of 1 mm or less, it is very difficult to perform vertical or horizontal winding, and the coaxial cable itself becomes hard. Become.

When the metal layer 14a is formed on the plastic tape 14b by vapor deposition as in Patent Document 2 (FIG. 3), the thickness of the metal layer 14a is generally 0.1 μm to 2.0 μm in the case of copper, and the case of aluminum. In this case, the limit is about 0.05 μm to 0.5 μm, and a sufficient thickness for obtaining desired electrical characteristics cannot be obtained. That is, in order to obtain a sufficient skin effect by the metal layer 14a, a thickness of at least 3 μm is required at a high frequency of 0.6 GHz, at least 2 μm at a high frequency of 1 GHz, and at least 1 μm at a high frequency of 5 GHz. There is an inconvenience that it is difficult to increase the thickness of the metal layer 14a and sufficient electrical characteristics cannot be exhibited.

Further, in the case of the plastic tape 24 with a metal layer in which the metal layer 24a is formed as in Patent Document 3 (FIG. 4), the thickness of the metal layer 24a can be set to 1 μm or more and 4 μm or less. However, such a metal layer 24a is actually vulnerable to cracking, and when an external force such as tension, vibration, or bending is applied to the coaxial cable 1, the crack is used as a base point between the plastic tape 24b and the metal layer 24a. Peeling occurs, which adversely affects the attenuation characteristics and VSWR characteristics.

The present invention has been made to solve the above-described problems, and can exhibit attenuation characteristics and VSWR characteristics that can be used in a wide frequency range. Even if an external force such as tension, vibration, or bending is applied, the attenuation characteristics are provided. Another object of the present invention is to provide a high-frequency coaxial cable that does not adversely affect the VSWR characteristics, particularly a small-diameter coaxial cable having an insulator outer diameter of 1 mm or less.

In order to achieve the above object, a coaxial cable according to claim 1 of the present invention is a coaxial cable in which a plastic tape with a metal layer is disposed on the circumference of an insulator covering an inner conductor, and the outer conductor is provided thereon. The layered plastic tape is obtained by laminating a metal foil having a thickness of 4 μm or more and 10 μm or less and a plastic tape.

According to a second aspect of the present invention, in the coaxial cable, the plastic tape with a metal layer is arranged vertically on the circumference of the insulator.

According to a third aspect of the present invention, in the coaxial cable, the plastic tape with a metal layer has a width of 1.00 times or more and 1.25 times or less of the outer periphery of the insulator.

The coaxial cable of various electronic devices to which the coaxial cable of the present invention is wired can exhibit attenuation characteristics and VSWR characteristics that can be used in a wide frequency range, and external forces such as tension, vibration, and bending are applied to the coaxial cable. Even in such a case, the plastic tape and the metal layer are not peeled off, and the attenuation characteristic and the VSWR characteristic are not adversely affected. Therefore, the present invention has a great effect on the industry.

Hereinafter, the contents of the present invention will be described in more detail with reference to embodiments shown in the drawings. Note that the present invention is not limited thereby.

FIG. 1 is a partially cutaway side view for explaining the structure of the coaxial cable 1 of the present invention. FIG. 2 is a schematic diagram showing the structure of a plastic tape with a metal layer used in the coaxial cable 1 of the present invention.

Each constituent material will be described. Of course, the present invention is not limited to these materials, and various conventionally known materials may be substituted. As the internal conductor 2, for example, a copper wire, a single wire of aluminum wire, a stranded wire or the like is used. As the insulator 3, for example, PE (polyethylene) resin, a solid or foamed fluororesin, or the like is used. As metal layer 4a of plastic tape 4 with a metal layer, metal foil, such as copper foil and aluminum foil, is used, for example. As the plastic tape 4b of the plastic tape 4 with a metal layer, for example, a plastic tape such as PET (polyethylene terephthalate) or Teflon (registered trademark) is used. As the external conductor 5, for example, an annealed copper wire braid, a plated annealed copper wire braid, or the like is used.

As the plastic tape 4 with a metal layer, one obtained by bonding a metal layer 4a made of metal foil and a plastic tape 4b is used. In the case where the metal layer 4a is formed by vapor deposition or metal plating, such as the plastic tape 14 with metal layer shown in FIG. 3 or the plastic tape 24 with metal layer shown in FIG. 4, the coaxial cable 1 is tensioned, vibrated, bent, etc. When the external force is applied, since there is no good adhesion between the plastic tapes 14b, 24b and the vapor deposition layers 14a, 24d, there is a high possibility that they will be easily peeled off. As a result, the attenuation characteristic and the VSWR characteristic are adversely affected, so that they are not used in the present invention.

The thickness of the metal layer 4a is 4 μm or more and 10 μm or less. If the thickness is less than 4 μm, it is very difficult to produce a laminate with the plastic tape 4b, and a sufficient skin effect cannot be obtained at a frequency of 0.6 GHz or less. When the thickness exceeds 10 μm, in particular, in the coaxial cable 1 having a thin outer diameter of 1 mm or less, it is very difficult to vertically or horizontally wind the insulator 3, and the plastic tape 4 with a metal layer is used. This is because the hardness of the cable increases and the coaxial cable 1 itself becomes hard. In order to reduce the diameter of the coaxial cable 1, the thickness of the metal layer 4a is particularly preferably less than 8 μm.

Further, when the plastic tape 4 is disposed on the insulator 3, it is preferable that the metal layer 4a be disposed outside (on the outer conductor 5 side). In this way, since the metal layer 4a is inserted into the gap between the outer conductors 5, the gap generated between the outer conductor strands is reduced. In addition, even when an external force such as tension, vibration, or bending is applied to the coaxial cable 1, a gap is hardly generated between the outer conductor 5 and the plastic tape 4 with a metal layer, and the outer conductor 5 and the plastic tape 4 with a metal layer are formed. Adhesion between each other becomes stronger. Therefore, the contact area between the outer conductor 5 constituting the shield layer and the plastic tape 4 with the metal layer is increased, the conductor resistance is reduced, the shield characteristic of the shield layer is improved, and electromagnetic noise is generated in the electric circuit of the electrical equipment. It can be surely prevented from mixing.

Moreover, when arrange | positioning the above-mentioned plastic tape 4 with a metal layer on the insulator 3, arrange | positioning by vertical attachment or horizontal winding can be considered, However, It is preferable to arrange | position by vertical attachment among these. This is because electromagnetic noise can be reliably prevented from being mixed in the same manner as described above, and the manufacturing cost can be greatly reduced as compared with the horizontal winding method. In that case, it is preferable that the plastic tape 4 with a metal layer has a width | variety of 1.00 times or more and 1.25 times or less of the insulator 3 outer periphery. When it is less than 1.00 times, when the coaxial cable 1 is bent, the overlapping portion of the plastic tape 4 with the metal layer opens, which may adversely affect the attenuation characteristic and the VSWR characteristic. On the other hand, if the ratio exceeds 1.25 times, the consumption of the plastic tape 4 with the metal layer increases, which is uneconomical. Also, the outer diameter of the finished coaxial cable 1 becomes thicker, and further, when bent, the metal tape There is a possibility that wrinkles may occur in the layered plastic tape 4.

The outer conductor 5 is exemplified by an annealed copper wire braid and a plated annealed copper wire braid, but is not limited to this. A metal wire that is not an annealed copper wire or a plated annealed copper wire may be used, and there is no problem as long as it is a conductor. Further, instead of the braiding, for example, a horizontal winding of a metal wire may be used.

A jacket 6 may be formed on the periphery of the outer conductor 5 as necessary. The material constituting the outer cover 6 may be appropriately selected depending on the intended use and the like. For example, PVC (polyvinyl chloride) resin, fluorine resin, or the like is used.

Example 1
As the inner conductor 2 of the coaxial cable 1 as shown in FIG. 1, a 32 AWG (outer diameter of about 0.24 mm) silver-plated annealed copper wire is used, and FEP (tetrafluoroethylene / hexafluoropropylene copolymer) is formed thereon. Resin is extruded to provide the insulator 3 to form an insulating core wire having an insulator outer diameter of 0.70 mm. As shown in FIG. 2, a plastic tape 4 with a metal layer in which a metal layer 4a made of copper foil with a thickness of 6 μm is bonded onto a plastic tape 4b made of PET with a thickness of 6 μm is used as the metal layer 4a. The tube was vertically attached so that the side was the outside. Further, a tin-plated annealed copper wire braid with an element wire diameter of 0.05 mm is formed thereon to form an outer conductor 5. Further, FEP resin is extruded and coated thereon to form a jacket 6, and the coaxial cable 1 according to the present invention is formed. Created.

(Comparative Example 1)
In the configuration shown in the first embodiment, instead of the plastic tape 4 with the metal layer, as shown in FIG. A coaxial cable 1 having the same structure as that of Example 1 was prepared except that the plastic tape 14 with a metal layer on which the metal layer was formed was used.

(Comparative Example 2)
In the configuration shown in Example 1, instead of the metal layer-attached plastic tape 4, as shown in FIG. 4, a vapor deposition layer 24d obtained by depositing copper on a 6 μm thick PET tape 24b and a metal plating layer 24c by electroplating. A coaxial cable 1 having the same structure as in Example 1 was prepared except that the metal layer-attached plastic tape 24 formed with the metal layer 24a having a thickness of 2 μm was used.

(Comparative Example 3)
In the configuration shown in Example 1, a coaxial cable 1 in which the plastic tape 4 with a metal layer was omitted was created.

(Comparative Example 4)
In the configuration shown in Example 1, the coaxial cable 1 having the same structure as that of Example 1 was tried except that the thickness of the metal layer 4a in the plastic tape 4 with the metal layer was set to 3 μm. However, since it became difficult to bond the metal layer 4a and the plastic tape 4b, the coaxial cable 1 could not be obtained.

(Comparative Example 5)
In the configuration shown in Example 1, the coaxial cable 1 having the same structure as that of Example 1 was tried except that the thickness of the metal layer 4a in the plastic tape 4 with the metal layer was 12 μm. However, since the plastic tape 4 with a metal layer has become hard and it has become difficult to vertically attach the insulator 3, the coaxial cable 1 has not been obtained.

The coaxial cable thus obtained was evaluated for the initial attenuation characteristic and VSWR characteristic, and the amount of change in the attenuation characteristic and VSWR characteristic after loading a predetermined amount of bending. The attenuation characteristic and the VSWR characteristic were measured in a frequency range of 45 MHz to 10 GHz with a network analyzer by attaching compatible connectors to both ends of the coaxial cable cut to 1 m. For the VSWR characteristic, the maximum value within a predetermined frequency was measured. The above bending conditions are based on the usage environment of a notebook computer and a mobile phone, and a 1 m cable is bent at a bending radius of R5 (radius 5 mm), bending angle ± 90 °, speed 20 times / minute, no load. The number of round trips was 20,000. Table 1 shows initial attenuation characteristics and VSWR characteristics, and Table 2 shows changes in attenuation characteristics and VSWR characteristics after a predetermined amount of bending is applied.

As a result, as shown in Table 1, with respect to the attenuation characteristic, an excellent attenuation characteristic which is lower than or equivalent to that of Comparative Examples 1, 2, and 3 which are conventional products was exhibited. In particular, when Example 1 and Comparative Example 1 are compared, Comparative Example 1 with a thin metal layer of 1 μm has a lower attenuation value than Example 1 in the low frequency region. Further, the VSWR characteristics of Example 1 exhibited better VSWR characteristics than Comparative Examples 1 and 2 over a wide frequency range.

As shown in Table 2, with respect to the amount of change in the attenuation characteristic after a predetermined amount of bending is applied, Comparative Examples 1 and 2 change +0.20 dB or more, while Example 1 has +0.20 dB. The deterioration of the attenuation characteristic was small as follows. In particular, in Comparative Examples 1 and 2, the amount of change in the attenuation characteristic is large at a high frequency. Further, the VSWR characteristics of Example 1 exhibited better VSWR characteristics than Comparative Examples 1 and 2 over a wide frequency range even after bending was applied. These are considered to be caused by peeling of the metal layer due to bending.

As described above in detail, the coaxial cable according to the present invention can exhibit attenuation characteristics and VSWR characteristics that can be used in a wide frequency range, and can exhibit attenuation characteristics and VSWR characteristics even when an external force such as tension, vibration, or bending is applied. It does not have an adverse effect. Therefore, it is effective for a high-frequency coaxial cable, particularly a small-diameter coaxial cable having an insulator outer diameter of 1 mm or less. Therefore, it can be suitably used in various electronic devices and information devices, specifically, for example, terrestrial digital television broadcast, mobile phone, wireless LAN, WiMAX, UWB, RFID, ITS, ETC, and the like.

It is a partially cutaway side view for demonstrating the structure of the coaxial cable of this invention. It is the schematic which shows the structure of the plastic tape with a metal layer used for the coaxial cable of this invention. It is the schematic which shows the structure of the plastic tape with a metal layer by a prior art and a comparative example. It is the schematic which shows the structure of the plastic tape with a metal layer by a prior art and a comparative example.

Explanation of symbols

1 Coaxial cable 2 Inner conductor 3 Insulator 4 Plastic tape with metal layer 4a Metal foil 4b Plastic tape 5 Outer conductor 6 Outer sheath

Claims (3)

In a coaxial cable in which a plastic tape with a metal layer is arranged on the periphery of an insulator covering an inner conductor and an outer conductor is provided thereon, the plastic tape with a metal foil has a thickness of 4 μm or more and 10 μm or less. Coaxial cable, characterized in that it is made by bonding plastic tape. The coaxial cable according to claim 1, wherein the plastic tape with a metal layer is arranged vertically on the circumference of the insulator. The coaxial cable according to claim 2, wherein the plastic tape with a metal layer has a width of 1.00 times or more and 1.25 times or less of the outer periphery of the insulator.

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