Coaxial cable

Abstract

To provide a coaxial cable with low attenuation in the high-frequency range. [Solution] A coaxial cable comprising a conductor, an insulator containing fluororesin disposed outside the conductor, a shield layer disposed outside the insulator, and an outer sheath disposed outside the shield layer, wherein the insulator contains voids, and the shield layer comprises a first shield layer in which metal foil tape is arranged spirally along the longitudinal side of the insulator, and a second shield layer containing a plurality of metal strands.

Description

Technical Field

[0001] This disclosure relates to coaxial cables.

Background Art

[0002] Patent Document 1 discloses a coaxial cable including a conductor, an insulator covering the periphery of the conductor, a shield layer having a spiral shield formed by winding a plurality of metal strands around the insulator, and a sheath covering the periphery of the shield layer. The insulator has recesses fitting the plurality of metal strands on the surface of the portion contacting the plurality of metal strands. The shield layer has the portion contacting the insulator in the circumferential direction of the plurality of metal strands fitting into the recesses of the insulator, and the plurality of metal strands adjacent to each other in the circumferential direction of the shield layer are in surface contact with each other.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, coaxial cables having a shield layer have been used in various applications.

[0005] By the way, in recent years, signals have been transmitted in the high-frequency range, and there has been a demand for coaxial cables with small attenuation in the high-frequency range.

[0006] Therefore, an object of this disclosure is to provide a coaxial cable with small attenuation in the high-frequency range.

Means for Solving the Problems

[0007] The coaxial cable of this disclosure comprises a conductor, an insulator containing a fluororesin disposed outside the conductor, a shield layer disposed outside the insulator, and a sheath disposed outside the shield layer, wherein the insulator contains voids, and the shield layer comprises a first shield layer in which metal foil tape is arranged spirally along the longitudinal side of the insulator, and a second shield layer containing a plurality of metal strands. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide a coaxial cable with low attenuation in the high-frequency range. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a perspective view of a coaxial cable according to one aspect of the present disclosure. [Figure 2] Figure 2 is a cross-sectional view of a coaxial cable in a plane perpendicular to its longitudinal direction according to one aspect of the present disclosure. [Figure 3] Figure 3 is a partial perspective view of an extruder that can be used to manufacture an insulator for a coaxial cable according to one aspect of the present disclosure. [Figure 4] Figure 4 is an explanatory diagram of the bending tests performed in Experimental Example 2 and Experimental Example 3. [Figure 5] Figure 5 is a table showing the structure of the coaxial cable fabricated in the experimental example. [Figure 6] Figure 6 is a table showing the evaluation results for Experimental Example 1. [Figure 7] Figure 7 is a table showing the evaluation results for Experimental Example 2. [Figure 8] Figure 8 is a table showing the evaluation results for Experiment Example 3. [Modes for carrying out the invention]

[0010] The implementation methods are described below.

[0011] [Description of Embodiments in this Disclosure] First, embodiments of the present disclosure will be listed and described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description thereof will not be repeated.

[0012] (1) A coaxial cable according to one aspect of the present disclosure includes a conductor, an insulator containing a fluororesin disposed outside the conductor, a shield layer disposed outside the insulator, and an outer jacket disposed outside the shield layer. The insulator includes voids. The shield layer has a first shield layer in which a metal foil tape is spirally disposed along the longitudinal direction of the conductor, and a second shield layer including a plurality of metal strands.

[0013] Since the insulator contains a fluororesin, the dielectric constant of the insulator can be reduced, and the attenuation amount in the high-frequency region of the coaxial cable can be reduced.

[0014] Since the insulator contains voids, the capacitance of the coaxial cable can be reduced, and the attenuation amount in the high-frequency region of the coaxial cable can be reduced.

[0015] Since the coaxial cable has a first shield layer and a second shield layer as the shield layer, signal leakage to the outside and radio wave intrusion from the outside can be particularly reduced. Also, the attenuation amount in the high-frequency region of the coaxial cable can be reduced.

[0016] In this specification, the high-frequency region means a region of 10 GHz or more.

[0017] (2) In (1), the second shield layer may have a transverse winding structure, and the winding direction of the metal foil tape of the first shield layer and the winding direction of the metal strands of the second shield layer may be opposite.

[0018] By forming the second shield layer into a transverse winding structure, the thickness of the second shield layer can be reduced, so that the coaxial cable can be made thinner and its flexibility can be enhanced. Also, by forming the second shield layer into a transverse winding structure, the productivity of the second shield layer and the coaxial cable can be increased and the cost can be reduced.

[0019] By reversing the winding direction of the metal foil tape of the first shield layer and the winding direction of the metal wire of the second shield layer, even when the coaxial cable is bent or the like, the attenuation in the high-frequency region can be reduced.

[0020] Whether the winding direction of the metal foil tape and the winding direction of the metal wire are the same or opposite can be determined by observing from the first end along the longitudinal direction of the coaxial cable. Specifically, when observed from the first end, the winding direction of the metal foil tape and the metal wire wound from the second end located opposite to the first end along the longitudinal direction of the coaxial cable toward the first end along the outer periphery of the insulator is their respective winding directions. And when the winding directions along the outer periphery of the insulator of the metal foil tape and the metal wire are different, it can be determined that the winding directions are opposite.

[0021] (3) In (1) or (2), the second shield layer may have a cross-wound structure, and the metal wire of the second shield layer may be arranged to have an angle of 10 degrees or more with respect to the longitudinal direction of the conductor.

[0022] By making the second shield layer have a cross-wound structure, the thickness of the second shield layer can be reduced, so that the coaxial cable can be made thinner and the flexibility can also be enhanced. Also, by making the second shield layer have a cross-wound structure, the productivity of the second shield layer and the coaxial cable can be improved and the cost can be reduced. By making the angle of the metal wire of the second shield layer with respect to the longitudinal direction of the conductor 10 degrees or more, even after the coaxial cable is repeatedly bent, the attenuation in the high-frequency region can be made sufficiently small.

[0023] (4) In any of (1) to (3), the shield layer may be arranged such that the first shield layer and the second shield layer are sequentially arranged from a position close to the conductor.

[0024] The first shield layer is a layer in which metal foil tape is arranged spirally along the length of the insulator, and therefore its surface is smoother compared to the second shield layer, which is made by twisting together multiple metal strands. For this reason, by positioning the first shield layer closer to the conductor than the second shield layer, the distance between the shield layer and the conductor can be made uniform, and the electrical characteristics of the coaxial cable can be stabilized.

[0025] (5) In any of (1) to (4), the porosity of the insulator may be 20% or more and 50% or less.

[0026] By setting the porosity of the insulator to 20% or more, the capacitance of the coaxial cable can be reduced, thereby reducing the attenuation of the coaxial cable in the high-frequency range.

[0027] By reducing the void ratio of the insulator to 50% or less, the strength of the coaxial cable can be increased, preventing damage and other issues.

[0028] (6) In any of (1) to (5), the outer diameter may be 1.2 mm or less.

[0029] By making the outer diameter of the coaxial cable 1.2 mm or less, it becomes possible to create a coaxial cable with excellent electrical characteristics in the high-frequency range and a small diameter, which was previously particularly difficult to achieve.

[0030] (7) In any of (1) to (6), the conductor may be a single wire or a compressed conductor.

[0031] By using a single wire or a compressed conductor as the conductor, variations in the impedance of the coaxial cable can be reduced, and attenuation in the high-frequency range can be particularly minimized.

[0032] (8) In any of (1) to (7), the outer diameter of the conductor may be 0.32 mm or less.

[0033] By reducing the outer diameter of the conductor to 0.32 mm or less, the outer diameter of the coaxial cable can also be reduced, improving handling.

[0034] (9) In any of (1) to (8), the gap may have a shape in which the width decreases as it moves away from the conductor in the cross-section of the coaxial cable.

[0035] The air gap has a shape in the cross-section of the coaxial cable where its width decreases as it moves away from the conductor. This makes it less likely for the air gap to collapse when the coaxial cable is bent, thus making it easier to maintain the cross-sectional shape of both the coaxial cable and the air gap.

[0036] [Details of the embodiments of this disclosure] A specific example of a coaxial cable according to one embodiment of this disclosure (hereinafter referred to as "this embodiment") will be described below with reference to the drawings. However, the present invention is not limited to these examples and is intended to be shown in the claims, with all modifications in the sense and scope equivalent to the claims being included.

[0037] Figures 1, 2, and 3 are schematic diagrams illustrating the arrangement of each component and do not accurately represent the size, shape, etc. of each component. [Coaxial cable] Figure 1 shows a perspective view of the coaxial cable 10 of this embodiment, and Figure 2 shows a cross-sectional view of the coaxial cable 10 of this embodiment perpendicular to its longitudinal side.

[0038] In Figures 1 and 2, the axis along the longitudinal direction of the coaxial cable is defined as the X-axis, and the plane perpendicular to the longitudinal direction of the coaxial cable 10 is defined as the YZ plane.

[0039] As shown in Figures 1 and 2, the coaxial cable 10 of this embodiment includes a conductor 11, an insulator 12 disposed outside the conductor 11, a shield layer 13 disposed outside the insulator 12, and an outer sheath 14 disposed outside the shield layer 13.

[0040] The following describes each component of the coaxial cable 10 in this embodiment. (1) Regarding the components of a coaxial cable (1-1) Conductor In Figures 1 and 2, the conductor 11 is shown as a single cylinder or circle, but since Figures 1 and 2 are schematic diagrams, it is not limited to these forms. The conductor 11 may be a single wire, a stranded wire made by twisting together multiple conductor strands, or a compressed conductor made by compressing a stranded wire.

[0041] The conductor 11 may be a single wire or a compressed conductor. By using a single wire or a compressed conductor for the conductor 11, the variation in impedance of the coaxial cable 10 can be reduced, and the attenuation in the high-frequency range can be particularly reduced.

[0042] For the conductor 11, one or more conductive materials selected from, for example, copper alloy, copper, silver-plated soft copper, and tin-plated soft copper may be used. Soft copper may be used as the copper.

[0043] The outer diameter D11 of the conductor 11 may be 0.32 mm or less. By making the outer diameter D11 of the conductor 11 0.32 mm or less, the outer diameter D10 of the coaxial cable 10 can also be reduced, improving handling.

[0044] The lower limit of the outer diameter D11 of the conductor 11 may be 0.1 mm or more, or 0.2 mm or more. By setting the outer diameter D11 of the conductor 11 to 0.1 mm or more, the resistance of the conductor 11 can be reduced, the variation in the impedance of the coaxial cable 10 can be reduced, and the attenuation in the high-frequency range can be reduced in particular.

[0045] Therefore, the outer diameter D11 of the conductor 11 may be 0.1 mm or more and 0.32 mm or less, or 0.2 mm or more and 0.32 mm or less. (1-2) Insulator (1-2-1) Fluororesin The insulator 12 may contain fluororesin.

[0046] By including fluororesin in the insulator 12, the dielectric constant of the insulator 12 can be reduced, thereby reducing the attenuation of the coaxial cable 10 in the high-frequency range.

[0047] As the fluororesin, one or more selected from, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), etc. may be used. The fluororesin contained in the insulator 12 may or may not be crosslinked.

[0048] The resin material contained in the insulator 12 may be formed solely from fluororesin.

[0049] The insulator 12 may contain one or more additives selected from flame retardants, flame retardant enhancers, antioxidants, lubricants, colorants, reflective agents, opacifiers, processing stabilizers, plasticizers, etc., in addition to fluororesin. (1-2-2)Void (shape) As shown in Figure 2, the insulator 12 can contain air gaps 121.

[0050] The insulator 12 includes an air gap 121, which reduces the capacitance of the coaxial cable 10 and minimizes the attenuation of the coaxial cable 10 in the high-frequency range.

[0051] The shape of the air gap 121 in the insulator 12 may be triangular in cross-section of the coaxial cable 10, as shown in Figure 2, and may have a columnar shape along the longitudinal side of the conductor 11. Specifically, the air gap 121 may be provided continuously along the longitudinal side of the conductor 11.

[0052] If the void 121 has a columnar shape, it becomes easier to control the porosity of the insulator 12 and the arrangement of the void 121 within the insulator 12.

[0053] Figure 2 shows an example of a void with a triangular cross-section, i.e., a triangular prism shape. However, the form is not limited to this, and the shape of the cross-section perpendicular to the central axis may be a cylindrical shape, or a columnar shape with polygons other than triangles, such as a quadrilateral. Note that the sides constituting the polygon, such as a triangle, do not have to be straight lines, but may be curved, such as a bow shape.

[0054] Furthermore, the air gap 121 may have a shape in the cross-section of the coaxial cable 10 such that one vertex faces the first shield layer 131 and one side faces the conductor 11, with the width decreasing as it moves away from the conductor 11. That is, the cross-sectional shape of the air gap 121 may include a tapered portion in the air gap 121 where the width decreases from the first end 121A, which is closest to the conductor 11, to the second end 121B, which is furthest from the conductor 11. In the air gap 121 of Figure 2, the width W121B at the second end 121B is smaller than the width W121A at the first end 121A. The width of the air gap 121 in the cross-section of the coaxial cable 10 represents the radius and vertical length of the coaxial cable 10 passing through the center of the air gap 121.

[0055] The gap 121 has a shape in which its width decreases as it moves away from the conductor 11 in the cross-section of the coaxial cable 10. This makes it less likely for the gap 121 to collapse even when the coaxial cable 10 is bent, and makes it easier to maintain the cross-sectional shape of the coaxial cable 10 and the gap 121.

[0056] An insulator 12 containing columnar shaped voids 121 can be manufactured, for example, using an extruder 30 that combines a die 31 and a point jig 32, as shown in Figure 3. The manufacturing method for the insulator 12 containing columnar shaped voids 121 shown in Figure 2 will be explained using Figure 3.

[0057] The point jig 32 can be provided with as many columnar members 33 as there are columnar gaps to be created. Figure 3 shows an example in which cylindrical members are provided as columnar members 33, in which case an insulator 12 having cylindrical gaps 121 can be manufactured.

[0058] The die 31 has a circular outlet 311, and resin can be extruded from the flow paths 34 and 35 between the point jig 32 and the die 31. At the same time, the conductor can be drawn out from the central hole 322 of the cylindrical part 321 of the point jig 32. By performing the above operations, the extruded resin can be used to coat the surface of the conductor. Alternatively, the conductor may be coated with resin by a pull-down method, in which the resin that has come out of the outlet of the die 31 is stretched to reduce its diameter and then used to coat the conductor. Resin does not flow into the columnar member 33, and by providing ventilation holes 331 in the columnar member 33, a void can be formed in the resin extruded from the die 31. The void can be shaped to match the columnar member 33; for example, if the columnar member 33 is cylindrical, the cross-sectional shape of the void can be circular or elliptical. Even if the columnar member 33 is cylindrical, by adjusting the resin pressure, etc., some of the resin can enter the void, and the cross-sectional shape can be made triangular or other shapes.

[0059] In the extruder 30 described above, the void ratio of the insulating layer can be easily adjusted by changing the diameter and number of columnar members 33 provided on the point jig 32.

[0060] The shape of the voids 121 in the insulator 12 is not limited to a columnar shape. For example, the voids 121 can be spherical and randomly arranged along the longitudinal side of the conductor 11. In this case, the spherical shape does not mean only a sphere in the strict sense, i.e., a perfect sphere, but also includes distorted spheres such as ellipsoids.

[0061] The insulators 12, which have spherical voids 121 and are randomly arranged, can be manufactured, for example, by molding a resin to which a foaming agent has been added. (porosity) The porosity of the insulator may be 20% to 50%, or 25% to 45%.

[0062] By setting the porosity of the insulator to 20% or more, the capacitance of the insulator 12 can be reduced, thereby reducing the attenuation of the coaxial cable 10 in the high-frequency range.

[0063] By reducing the void ratio of the insulator to 50% or less, the strength of the coaxial cable 10 can be increased, preventing damage and other issues. (1-3) Shield layer The coaxial cable 10 of this embodiment may have a shield layer 13. The shield layer 13 may have a first shield layer 131 in which a metal foil tape 1311 is arranged spirally along the longitudinal side of the insulator 12, and a second shield layer 132 which includes a plurality of metal strands 1321.

[0064] The coaxial cable 10 has a first shielding layer 131 and a second shielding layer 132 as its shielding layer 13, which significantly reduces signal leakage to the outside and interference from external radio waves. Furthermore, it can reduce the attenuation of the coaxial cable 10 in the high-frequency range.

[0065] Each shield layer will be explained below. (1-3-1) First Shield Layer The first shielding layer 131 is a layer formed outside the insulator 12 by arranging a metal foil tape 1311 spirally along the longitudinal side of the insulator 12, and may include the metal foil tape 1311. The first shielding layer 131 can be formed by spirally winding the metal foil tape 1311 along the longitudinal side of the insulator 12 such that parts of it overlap each other.

[0066] The material of the metal foil tape 1311 of the first shield layer 131 can be one or more metal materials selected from copper, copper alloys, aluminum, aluminum alloys, etc. The metal layer 22 may be formed from a single metal species, or two or more metal layers of different metal species may be laminated. In addition, a non-metallic material, such as a protective film containing an organic material, may be placed on the surface of the metal layer 22.

[0067] The metal foil tape 1311 may be formed solely from metal foil. (1-3-2) Second Shield Layer The second shield layer 132 is a layer containing multiple metal wires 1321.

[0068] The material for the metal wire 1321 may be a metal material such as copper, copper alloy, aluminum, or aluminum alloy, or a material with a plating applied to its surface, such as tin-plated soft copper or silver-plated soft copper. Soft copper may be used as the copper.

[0069] The structure of the multiple metal wires 1321 in the second shield layer 132 may be, for example, a horizontally wound structure or a braided structure.

[0070] As described above, the second shield layer 132 may have a horizontal winding structure. That is, the second shield layer 132 may be a layer in which metal strands 1321 are arranged in parallel and wound in a spiral shape. By making the second shield layer 132 a horizontal winding structure, the thickness of the second shield layer 132 can be reduced, so the coaxial cable 10 can be made thinner and its flexibility can be increased. In addition, by making the second shield layer 132 a horizontal winding structure, the productivity of the second shield layer 132 and the coaxial cable 10 can be increased and costs can be reduced. (Angle of horizontal winding) The metal wires 1321 in the second shield layer 132 may be arranged such that, for example, the lateral winding angle θ is 10 degrees or more.

[0071] The lateral winding angle θ represents the angle between the metal wires 1321 of the second shield layer 132 and the longitudinal direction of the conductor 11. Therefore, as shown in Figure 1, the lateral winding angle θ represents the angle between a straight line L1 along the longitudinal direction of the conductor 11 and a straight line L2 along the metal wires 1321.

[0072] By setting the angle of the metal strands 1321 of the second shield layer 132 with respect to the longitudinal direction of the conductor 11 to 10 degrees or more, the amount of attenuation in the high-frequency range can be sufficiently reduced even after the coaxial cable 10 has been repeatedly bent.

[0073] There is no particular upper limit to the lateral winding angle, but it may be 35 degrees or less, for example. By setting the lateral winding angle θ to 35 degrees or less, the length of the metal wire 1321 required when manufacturing the second shield layer 132 can be shortened, and productivity can be increased, thus reducing costs.

[0074] Therefore, the lateral winding angle may be between 10 degrees and 35 degrees. (winding direction) If the second shield layer 132 has a horizontal winding structure, the winding direction of the metal foil tape 1311 of the first shield layer 131 and the winding direction of the metal wires 1321 of the second shield layer 132 may be in the forward direction, i.e., the same direction.

[0075] Furthermore, the winding direction of the metal foil tape 1311 in the first shield layer 131 and the winding direction of the metal wires 1321 in the second shield layer 132 may be opposite.

[0076] By reversing the winding direction of the metal foil tape 1311 in the first shielding layer 131 and the winding direction of the metal wires 1321 in the second shielding layer 132, the amount of attenuation in the high-frequency range can be reduced even when the coaxial cable 10 is bent or otherwise subjected to bending. (1-3-3) Regarding the arrangement The shield layer 13 may be arranged in order, for example, with a second shield layer 132 and a first shield layer 131 positioned closer to the conductor 11.

[0077] Furthermore, the shield layer 13 may be arranged in order, for example, with a first shield layer 131 and a second shield layer 132 positioned closer to the conductor 11.

[0078] The first shield layer 131 is a layer in which metal foil tape 1311 is arranged spirally along the longitudinal side of the insulator 12, and therefore its surface is smoother compared to the second shield layer 132, which is made up of multiple strands of metal wire 1321 twisted together. For this reason, by positioning the first shield layer 131 closer to the conductor 11 than the second shield layer 132, the distance between the shield layer 13 and the conductor 11 can be made uniform, and the electrical characteristics of the coaxial cable 10 can be stabilized. (1-4) Outer covering The outer covering 14 can be placed outside the shield layer 13.

[0079] The outer covering 14 may include, for example, a resin material. Examples of resin materials include one or more selected from polyester resins such as polyethylene terephthalate (PET), polyolefin resins such as polyethylene, polyvinyl chloride (PVC), and fluororesins such as FEP and PFA.

[0080] The outer covering 14 may also contain various additives other than resin materials, such as flame retardants.

[0081] The resin material of the outer covering 14 may or may not be crosslinked.

[0082] The outer covering 14 may be formed, for example, by spirally wrapping a resin tape containing a resin material around the surface of the shield layer 13, or by extrusion molding or the like. (2) Regarding the size of coaxial cables The outer diameter D10 of the coaxial cable 10 may be 1.2 mm or less. By setting the outer diameter D10 of the coaxial cable 10 to 1.2 mm or less, it is possible to create a coaxial cable with excellent electrical characteristics in the small diameter and high frequency range, which has been particularly difficult to achieve conventionally. Note that the outer diameter D10 of the coaxial cable 10 refers to the outer diameter up to the outer sheath 14.

[0083] The lower limit of the outer diameter D10 of the coaxial cable 10 may be 1.0 mm or more. By setting the outer diameter D10 of the coaxial cable 10 to 1.0 mm or more, the outer diameter and thickness of each component such as the conductor 11 can be made sufficiently large, thereby increasing productivity.

[0084] Therefore, the outer diameter D10 of the coaxial cable 10 may be between 1.0 mm and 1.2 mm. [Examples]

[0085] The present invention will be described with specific examples below, but it is not limited to these examples. (1) Evaluation method First, we will explain the evaluation method for the coaxial cable fabricated in the following experimental example. (1-1) Outer diameter of conductor, outer diameter of insulator, outer diameter of shielding layer, outer diameter of coaxial cable, thickness of insulator, thickness of sheath The outer diameter D11 of the conductor 11, the outer diameter D12 of the insulator 12, the outer diameter D13 of the shielding layer 13, and the outer diameter D10 of the coaxial cable 10 were measured using a micrometer or caliper according to the method described in JIS C 3005 (2014).

[0086] To explain using the conductor 11 as an example, the lengths of two orthogonal diameters of the conductor 11 were measured in an arbitrary cross section perpendicular to the longitudinal side of the coaxial cable 10, and the arithmetic mean was taken as the outer diameter D11 of the conductor 11. The outer diameter D12 of the insulator 12, the outer diameter D13 of the shielding layer 13, and the outer diameter D10 of the coaxial cable 10 were measured using the same procedure, except that the objects of measurement were changed to the insulator 12, the shielding layer 13, and the coaxial cable 10.

[0087] The thickness T12 of the insulator 12 was calculated by subtracting the outer diameter D11 of the conductor 11 from the outer diameter D12 of the insulator 12 and dividing by 2. That is, T12 was calculated as T12 = (D12 - D11) ÷ 2.

[0088] The thickness T14 of the outer sheath 14 was calculated by subtracting the outer diameter D13 of the shield layer 13 from the outer diameter D10 of the coaxial cable 10 and dividing by 2. That is, T14 = (D10 - D13) ÷ 2. (1-2) Porosity The porosity, which is the ratio of the area of ​​air gaps 121 to the area of ​​the insulator 12, was determined for five different cross-sections perpendicular to the longitudinal side of the coaxial cable 10, and the arithmetic mean of the porosities for the five cross-sections was taken as the porosity. (1-3) Horizontal winding angle The outer sheath 14 was removed to expose the second shield layer 132, and the lateral winding angle θ was measured at an arbitrary point for each of five arbitrarily selected metal strands 1321 between a straight line L1 along the longitudinal direction of the conductor 11 and a straight line L2 along the longitudinal direction of the metal strand 1321. The arithmetic mean of the obtained lateral winding angles θ was then taken as the lateral winding angle of the metal strands 1321 in the evaluated coaxial cable 10. (1-4) Damping A 1-meter coaxial cable was measured using a network analyzer (Agilent E5071A).

[0089] (Pass / fail criteria for each frequency) The pass / fail criteria were determined by setting reference values ​​for attenuation at each frequency. The reference values ​​for each frequency are the same for Experimental Examples 1 to 3 below.

[0090] Specifically, at 5GHz, a device was deemed acceptable if the attenuation was 3.0dB / m or less.

[0091] At 10GHz, a signal was considered acceptable if the attenuation was 4.3dB / m or less.

[0092] At 15GHz, a signal was considered acceptable if the attenuation was 5.3dB / m or less.

[0093] At 20GHz, a signal was considered acceptable if the attenuation was 6.0dB / m or less.

[0094] The details of the attenuation test and the method of determination for each experimental example are explained. (Experimental Example 1) In Experimental Example 1, pass / fail was determined for each frequency, with a rating of A for pass and a rating of B for fail. At least in the high-frequency range of 10 GHz and above, a rating of A indicates that the coaxial cable has low attenuation.

[0095] (Experimental Example 2) In Experimental Example 2, the attenuation after a bending test was evaluated. As shown in Figure 4, the coaxial cable 10 to be evaluated was placed vertically between two mandrels with a diameter of 40 mm, the first mandrel 411 and the second mandrel 412, which were arranged horizontally and parallel to each other. The upper end of the coaxial cable 10 was then bent 90° so that it abutted the upper side of the first mandrel 411, and then bent 90° so that it abutted the upper side of the second mandrel 412, and this process was repeated 100 times. In the above bending test, one bend was defined as the time from bending the coaxial cable 10 to the left in Figure 4, then to the right, and then back to the left. During the bending test, a load of 5N was applied to the coaxial cable 10 along the block arrow 42 in Figure 4.

[0096] After conducting bending tests, attenuation evaluations were performed, and the number of coaxial cables that passed the tests was evaluated.

[0097] For the attenuation evaluation, coaxial cables that passed at all frequencies (5GHz, 10GHz, 15GHz, and 20GHz) were deemed acceptable, while coaxial cables that failed at any of these frequencies were deemed unacceptable.

[0098] In each of the experimental examples from Experimental Example 2-1 to Experimental Example 2-5, 10 coaxial cables manufactured under the same conditions were evaluated. A rating was given if 8 or more cables passed, a B rating if 2 or more cables passed but less than 8 cables passed, and a C rating if less than 2 cables passed. An A rating indicates that the coaxial cable has excellent bending resistance. (Experimental Example 3) In Experiment Example 3, the attenuation of the fabricated coaxial cable was evaluated with the cable bent at a 90° angle in the middle. As shown in Figure 4, the coaxial cable 10 to be evaluated was placed vertically between two 40mm diameter mandrels, the first mandrel 411 and the second mandrel 412, which were positioned horizontally and parallel to each other. The attenuation was then evaluated with the upper end of the coaxial cable 10 bent at a 90° angle so that it abutted against the upper side of the first mandrel 411.

[0099] In Experimental Examples 3-1 and 3-2, ten coaxial cables manufactured under the same conditions were evaluated. The number of passing coaxial cables for each frequency was evaluated, with a rating of A if eight or more cables passed, a B if two or more cables passed but less than eight, and a C if fewer than two cables passed. A rating of A indicates that the coaxial cable can reduce attenuation even when bent. (2) Experimental conditions and results The coaxial cables used in each experimental example are described below. (2-1) Experimental Example 1 The following coaxial cables were fabricated: Experimental Examples 1-1, 1-2, and 1-3. Experimental Example 1-1 is the embodiment, and Experimental Examples 1-2 and 1-3 are comparative examples. [Experimental Example 1-1] As shown in Figure 1, a coaxial cable 10 was fabricated having a conductor 11, an insulator 12 placed outside the conductor 11, a shield layer 13 placed outside the insulator 12, and an outer sheath 14 placed outside the shield layer 13, in a cross section perpendicular to the longitudinal direction. As shown in Figure 2, the insulator 12 has multiple air gaps 121 along the outer circumference of the conductor 11. The air gaps 121 have a triangular cross section and are continuously provided along the longitudinal direction of the conductor. As shown in Figure 2, in the cross section of the coaxial cable 10, the air gaps 121 are arranged such that one vertex faces the first shield layer 131 and one side faces the conductor 11, and the width decreases as it moves away from the conductor 11. The shield layer 13 has a first shield layer 131 and a second shield layer 132 in order from the position closest to the conductor 11.

[0100] The structure of each component, including its material and thickness, is shown in Figure 5. A single wire was used for the conductor 11.

[0101] In Figure 5, FEP refers to tetrafluoroethylene-hexafluoropropylene copolymer, and PFA refers to tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.

[0102] Furthermore, the winding direction of the metal foil tape in the first shield layer 131 is left-handed, and the winding direction of the metal wires in the second shield layer 132 is right-handed, meaning they are wound in opposite directions. It is also possible for the metal foil tape to be right-handed and the metal wires to be left-handed.

[0103] Attenuation tests were conducted on the fabricated coaxial cable 10. The evaluation results are shown in Figure 6.

[0104] The lateral winding angle of the metal wire 1321 in the second shield layer 132 was evaluated and found to be 15°. [Experimental Example 1-2] A coaxial cable was fabricated under the same conditions as in Experimental Example 1-1, except that no air gap 121 was provided in the insulator 12, and an attenuation test was conducted. The evaluation results are shown in Figure 6. [Experimental Examples 1-3] The first shield layer 131 was omitted, and the shield layer 13 consisted only of the second shield layer 132. Aside from these points, a coaxial cable was fabricated under the same conditions as in Experimental Example 1-1, and attenuation tests were conducted. The evaluation results are shown in Figure 6.

[0105] As shown in Figure 6, the coaxial cable in Experimental Example 1-1 met the reference values ​​at all frequencies of 5 GHz, 10 GHz, 15 GHz, and 20 GHz, confirming that it is a coaxial cable with low attenuation.

[0106] In contrast, the coaxial cables in Experimental Example 1-2, where the insulator 12 does not have an air gap 121, and in Experimental Example 1-3, where the first shield layer 131 is not present, failed to meet the attenuation requirements at all frequencies, confirming that the attenuation could not be reduced. (2-2) Experimental Example 2 The following coaxial cables were fabricated: Experimental Examples 2-1, 2-2, 2-3, 2-4, and 2-5. All of Experimental Examples 2-1 through 2-5 are examples of actual implementations. [Experimental Example 2-1] The second shield layer 132 was formed outside the first shield layer 131 so that the lateral winding angle of the metal wires 1321 in the second shield layer 132 was 8°. Except for the above, ten coaxial cables were fabricated under the same conditions as in Experimental Example 1-1. It was confirmed that all of the fabricated coaxial cables had the desired lateral winding angle. [Experimental Examples 2-2 to 2-5] The second shield layer 132 was formed outside the first shield layer 131 so that the lateral winding angle of the metal wires 1321 in the second shield layer 132 was the value shown in Figure 7. Except for the above, ten coaxial cables were fabricated under the same conditions as in Experimental Example 2-1. It was confirmed that the lateral winding angle of all fabricated coaxial cables was the desired value.

[0107] We evaluated the attenuation of the coaxial cables used in Experimental Examples 2-1 to 2-5 after bending tests.

[0108] Figure 7 shows the number of coaxial cables that passed the attenuation evaluation and the evaluation results.

[0109] In all experimental examples, it was confirmed that coaxial cables with low attenuation were obtained. Furthermore, it was confirmed that the attenuation could be sufficiently reduced even after repeated bending by setting the lateral winding angle to 10° or more. (2-3) Experimental Example 3 The coaxial cables described in Experimental Examples 3-1 and 3-2 below were fabricated. Both Experimental Examples 3-1 and 3-2 serve as examples of actual implementations. [Experimental Example 3-1] Ten coaxial cables identical to those used in Experimental Example 1-1 were fabricated.

[0110] Figure 8 shows the results of the attenuation evaluation, including the number of coaxial cables that passed the evaluation at each frequency, and the evaluation results. [Experimental Example 3-2] The winding direction of the metal wires 1321 in the second shield layer 132 was set to left-handed winding, the same as the copper foil, which is the metal foil tape of the first shield layer 131. Except for the above, ten coaxial cables were fabricated under the same conditions as in Experimental Example 3-1.

[0111] Figure 8 shows the results of the attenuation evaluation, including the number of coaxial cables that passed the evaluation at each frequency, and the evaluation results.

[0112] In all experimental examples, it was confirmed that coaxial cables with low attenuation were obtained. Furthermore, it was confirmed that by reversing the winding direction of the metal foil tape 1311 of the first shielding layer 131 and the winding direction of the metal wires 1321 of the second shielding layer 132, the attenuation could be made particularly small even when the coaxial cable was bent. [Explanation of symbols]

[0113] 10 Coaxial Cables D10 Coaxial Cable Outer Diameter 11 Conductors D11 Outer diameter of the conductor 12 Insulators D12 Outer diameter of the insulator T12 Insulator thickness 121 void 121A 1st end W121A Width at the first end 121B 2nd end W121B Width at the second end 13 Shield Layer D13 Outer diameter of the shield layer 131 First Shield Layer 1311 Metal foil tape 132 Second Shield Layer 1321 Metal wire 14 Outer cover T14 Thickness of the outer covering L1 straight line L2 straight line θ Transverse winding angle 30 Extruders 31 dice 311 Exit 32-point jig 321 Cylindrical section 322 Center hole 33 components 331 Ventilation holes 34 Flow channels 35 channels 411 First Mandrel 412 Second Mandrel 42 Block Arrows

Claims

1. A conductor and An insulator containing a fluororesin disposed outside the conductor, A shielding layer disposed outside the insulator, It has an outer covering disposed outside the shield layer, The insulator includes air gaps, The coaxial cable comprises a first shield layer in which a metal foil tape is arranged spirally along the longitudinal side of the insulator, and a second shield layer containing a plurality of metal strands.

2. The aforementioned second shield layer has a horizontal winding structure, The coaxial cable according to claim 1, wherein the winding direction of the metal foil tape in the first shielding layer and the winding direction of the metal wires in the second shielding layer are opposite.

3. The aforementioned second shield layer has a horizontal winding structure, The coaxial cable according to claim 1 or 2, wherein the metal strands of the second shield layer are arranged at an angle of 10 degrees or more with respect to the longitudinal direction of the conductor.

4. The coaxial cable according to claim 1 or claim 2, wherein the shield layers are arranged in order from a position close to the conductor, with the first shield layer and the second shield layer being arranged in that order.

5. The coaxial cable according to claim 1 or claim 2, wherein the void ratio of the insulator is 20% or more and 50% or less.

6. A coaxial cable according to claim 1 or claim 2, wherein the outer diameter is 1.2 mm or less.

7. The coaxial cable according to claim 1 or claim 2, wherein the conductor is a single wire or a compressed conductor.

8. The coaxial cable according to claim 1 or claim 2, wherein the outer diameter of the conductor is 0.32 mm or less.

9. The coaxial cable according to claim 1 or claim 2, wherein the gap has a shape in which the width decreases as it moves away from the conductor in the cross-section of the coaxial cable.

Images