JP2537934Y2 - coaxial cable - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a coaxial cable having a center conductor and two layers of outer conductors, the two layers of outer conductors being separated from each other and to the center conductor by a dielectric material.

[0002]

2. Description of the Related Art In general, a coaxial cable having a structure in which a single braided conductor is used as an outer conductor is used as a coaxial cable for frequencies up to about 3 GHz, but a higher frequency band up to about 12 GHz is used. Is used, a coaxial cable having a double braided structure in which the shielding density is increased by using two braided conductors is used (see Japanese Utility Model Application Laid-Open No.
120119, JP-A-61-47017, etc.).
In a higher frequency band, a semi-rigid coaxial cable using a copper pipe as a shielding layer is used.

[0003] By the way, since this semi-rigid coaxial cable lacks flexibility, in the field where flexibility is required,
As an alternative, a thin copper tape is vertically attached to the outer periphery of the coaxial core, and further, a copper wire is braided outside the copper tape winding layer, and the copper tape winding layer and the copper wire braid are integrated. For this reason, a coaxial cable having a structure in which a low-melting metal layer such as tin is provided on the outer surface has been proposed (Japanese Patent Laid-Open No. 622-2 / 1987).
29608). In such a coaxial cable, it is possible to shield a wide frequency band by the copper tape winding layer and the copper wire braid, and by holding the copper tape winding layer by the low melting point metal layer and the copper wire braiding, the copper in bending can be prevented. The tape is prevented from breaking or slipping.

[0004]

However, in the above-mentioned coaxial cable in which the outer conductor is a combination of a copper tape winding layer and a copper wire braid, the stress when braiding the copper wire is applied to the copper tape wound around the coaxial core. This has an adverse effect, which tends to shift the overlapping portions of the side edges of the vertically attached copper tape and to cause wrinkles in the copper tape. Therefore, it is difficult to bring the copper tape winding layer into close contact with the outer peripheral surface of the coaxial core without any gap. Further, since the copper tape winding layer and the copper wire braid are joined and integrated via a low melting point metal layer such as tin, the outer conductor becomes hard, and the flexibility of the entire cable is not so good, and There was also a problem in terms of weight.

[0005] In view of these problems of the prior art, the present invention provides a coaxial cable which is excellent in flexibility and lighter in weight while having shielding properties close to those of a coaxial cable using a copper pipe as an outer conductor. Its purpose is to provide.

[0006]

In order to achieve the above object, the present invention is directed to a coaxial cable in which a two-layer outer conductor is provided outside a dielectric surrounding a center conductor. And the outer outer conductor is formed by a braided conductor, and a synthetic resin layer having a thickness of 0.03 to 0.15 mm is interposed therebetween.

In the present invention, the reason why the thickness of the synthetic resin layer is limited to the range of 0.03 to 0.15 mm is that if the thickness is outside this range, no particular effect of improving flexibility can be obtained. And preferably a thickness of 0.06 to 0.10 mm.

[0008]

In the coaxial cable according to the present invention, the metal tape forming the inner outer conductor is spirally wrapped around the outside of the dielectric, so that the resistance to bending is smaller than that of the longitudinal attachment and the flexibility is lower. This is advantageous. The distance between the metal tape winding layer and the outer conductor is 0.03.
Since a synthetic resin layer having a thickness of about 0.15 mm is provided, and the synthetic resin layer uniformly holds the inner metal tape winding layer over the entire outer peripheral surface and maintains the wound state, When the metal tape winding layer is bent, the metal tape winding layer does not shift, and the metal tape winding layer is closely adhered to the outer peripheral surface of the coaxial core without any gap, so that the stability of electric characteristics is remarkably improved.

In addition, due to the presence of the synthetic resin layer, the stress at the time of forming the outer braided conductor and the stress associated with bending are alleviated there and do not directly reach the inner metal tape winding layer. Even thin metal tapes are reliably protected without breaking. Since the thickness of the synthetic resin layer is small, the influence on the flexibility of the cable is negligible. Since the contact is prevented, slippage occurs between the inner and outer conductors via the synthetic resin layer at the time of bending, and good flexibility is obtained. In this case, if a fluorine-based resin is used for the synthetic resin layer, the flexibility of the cable is further improved due to its low friction property.

When the thickness of the synthetic resin layer is 0.15 mm or more, the rigidity due to the thickness appears more than the effect of improving the flexibility by inserting the synthetic resin layer. Flexibility decreases. On the other hand, if the thickness is less than 0.03 mm, it is too thin to obtain the effect of interposing the synthetic resin layer.

[0011]

FIG. 1 is a perspective view of an embodiment of a coaxial cable according to the present invention, wherein the coaxial cable has a center conductor 1, a dielectric 2, an inner outer conductor 3,
It has a synthetic resin layer 4, an outer conductor 5 outside and a jacket 6, and the outer conductor has a double structure. In this case, a low dielectric constant polymer material such as polyethylene or a fluororesin is used for the dielectric 2, and a material made porous by stretching or foaming is particularly preferably used.

The inner outer conductor 3 is formed by spirally winding a highly conductive metal tape such as copper foil or silver-plated copper foil, and the outer outer conductor 5 is formed by braiding a copper wire. ing. In the embodiment, a synthetic resin layer 4 made of a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer resin (PFA) is formed between these two outer conductors 3 and 5 by extrusion molding to have a thickness of 0.03 to 0.15 mm.
The thickness is provided. In addition, as the synthetic resin layer 4, in addition to the above-mentioned PFA, fluorine such as tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP), ethylene-tetrafluoroethylene copolymer resin (ETFE), polytetrafluoroethylene (PTFE), etc. Although the system resin is advantageous in terms of low friction, use of other synthetic resins is of course acceptable at all.

Next, the flexibility of a coaxial cable manufactured by changing the thickness of the synthetic resin layer 4 was examined together with a comparative example. In this case, as a method for evaluating flexibility, a coaxial cable cut to a length of 50 cm is placed on a horizontal table so that one end protrudes 30 cm, and a portion on the table is fixed.
The amount of bending when a 200 g weight was attached to the free end was used as an index of flexibility. Table 1 shows the results. In this flexibility test, a porous polytetrafluoroethylene tape as a dielectric was wound with a thickness of 0.70 mm around the outer periphery of a center conductor made of a silver-plated soft copper wire having an outer diameter of 0.912 mm, and the outer periphery was wound around the outer periphery. A copper foil having a thickness of 0.04 mm is spirally wrapped and wound to form an inner outer conductor. A PFA layer having a thickness shown in Table 1 is provided outside the copper foil layer, and an outer diameter of 0.14 mm is further provided on the outer periphery thereof. A coaxial cable having a configuration in which an outer outer conductor was formed by braiding 96 silver-plated annealed copper wires, and the outer periphery thereof was covered with a jacket made of FEP.

[0014]

[Table 1]

As is apparent from the results shown in Table 1, the distance between the inner outer conductor and the outer outer conductor is 0.03 to 0.15 mm.
It can be seen that the example in which the synthetic resin layer is provided with a thickness of 3 mm is superior in flexibility to the coaxial cable of the comparative example.

Note that the present invention is not limited to the above-described embodiment, and it is possible to change a polymer material such as a dielectric, a synthetic resin layer, and an outer cover to another material, or to use a center conductor, an outer conductor, or the like. It is of course possible to change the material.

[0017]

As described above, the coaxial cable according to the present invention has excellent effects in practical use such that good flexibility can be obtained without impairing the shielding characteristics, and the weight can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view of a coaxial cable according to the present invention, in which an end is cut away.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Center conductor 2 Dielectric 3 Inner outer conductor 4 Synthetic resin layer 5 Outer outer conductor 6 Outer jacket

 ──────────────────────────────────────────────────続 き Continued from the front page (56) References JP-A-63-170809 (JP, A) JP-A-6-20417 (JP, U) JP-A-60-166916 (JP, U) JP-A-1 66712 (JP, U)

Claims (1)

(57) [Scope of request for utility model registration] In a coaxial cable in which a two-layer outer conductor is provided outside a dielectric surrounding a center conductor, an inner outer conductor is formed by helical winding of a metal tape.
A coaxial cable comprising an outer outer conductor formed of a braided conductor and a synthetic resin layer having a thickness of 0.03 to 0.15 mm interposed therebetween.