Coaxial cable

Abstract

The present application provides a coaxial cable which maintains stable high-frequency transmission performance and has a hollow core with improved side pressure strength compared with the existing structure. In the hollow core (1) constituting the coaxial cable (10), the inner annular portion (2) insulatingly covering the inner conductor (12), the plurality of rib portions (3) extending radially from the inner annular portion (2), and the outer annular portion (4) connected to the outer ends of the rib portions (3) are an integral structure of thermoplastic resin, have three or more void portions (5) surrounded by the inner annular portion (2), the rib portions (3), and the outer annular portion (4), the outer side reinforcing portions (7) are formed on both sides of the outer ends of the rib portions (3), and the size ratio of the minimum value (W1) of the rib width of the rib portions (3) to the maximum value (W2) of the rib width of the rib portions (3) is in the range of 1:1.6 to 1:3.0.

Description

TECHNICAL FIELD

[0001] The present application relates to a coaxial cable. BACKGROUND

[0002] Conventionally, a coaxial cable provided with a hollow core is known (Patent Document 1: Japanese Patent No. 5255529).

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENT

[0005] Patent Document 1: Japanese Patent No. 5255529 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] Electronic devices mounted on mobile body communication equipment are being miniaturized and high-density-ized with use in high frequency bands. Along with this, coaxial cables used in the electronic devices are also used in higher frequency bands than ever before, and are required to be thin in diameter. In such a situation, it has recently been found that when a thin-diameter coaxial cable is routed inside a small antenna, the hollow core is sometimes crushed by side pressure.

[0008] MEANS FOR SOLVING THE PROBLEMS

[0009] The present application was completed in view of the above-described situation, and aims to provide a coaxial cable that maintains stable high frequency transmission performance, and has a hollow core with a structure that improves side pressure strength compared to conventional structures.

[0010] The above-described problems are solved by the following disclosed technical means as one embodiment.

[0011] The coaxial cable of the present application is characterized by having a hollow core that is a one-piece structure of a thermoplastic resin of an inner annular portion that insulates an inner conductor, a plurality of rib portions that extend radially from the inner annular portion, and an outer annular portion that is connected to outer ends of the rib portions, the hollow core having three or more void portions surrounded by the inner annular portion, the rib portions, and the outer annular portion, outer side reinforcing portions being formed on both sides of the outer ends of the rib portions, a rib width of the rib portions having a minimum value in the circumferential direction at a position close to the inner annular portion, the rib width of the rib portions having a maximum value in the circumferential direction at the outer ends, a size ratio of the minimum value to the maximum value being 1:1.6 to 1:3.0, and inner side reinforcing portions smaller than the outer side reinforcing portions being formed on both sides of inner ends of the rib portions connected to the inner annular portion in the hollow core.

[0012] According to the structure, it is possible to maintain stable high-frequency transmission performance and realize a structure with improved lateral pressure strength compared to conventional structures. That is, when current flows through the inner conductor, an electric field is formed around the inner conductor. The electric field strength at this time is stronger closer to the inner conductor and weaker farther from the inner conductor. Therefore, by providing the outer side reinforcing portions on both sides of the outer end of each rib portion of the hollow core, it is possible to improve the strength of the hollow core that functions as an insulating covering. In addition, since the dielectric constant in the vicinity of the inner conductor remains unchanged at a small value, it is possible to maintain stable high-frequency transmission performance. The shape of the outer side reinforcing portions can be a circular arc shape, a triangular shape, a shape obtained by combining triangular shapes, or other known thickened shapes, in a cross-sectional view.

[0013] Effects of Invention

[0014] According to the present application, it is possible to realize a coaxial cable with a hollow core that maintains stable high-frequency transmission performance and has a structure with improved lateral pressure strength compared to conventional structures. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a cross-sectional view schematically showing a first example of a hollow core of an embodiment of the present application.

[0016] Figure 2 is a cross-sectional view schematically showing a second example of a hollow core of an embodiment of the present application.

[0017] Figure 3 is a cross-sectional view schematically showing a third example of a hollow core of an embodiment of the present application.

[0018] Figure 4 is a cross-sectional view schematically showing a fourth example of a hollow core of an embodiment of the present application.

[0019] Figure 5 is a cross-sectional view schematically showing a fifth example of a hollow core of an embodiment of the present application.

[0020] Figure 6 is an explanatory view explaining a lateral pressure test of a coaxial cable.

[0021] Figure 7A is a schematic configuration view showing a first example of a coaxial cable, Figure 7B is a schematic configuration view showing a second example of a coaxial cable, Figure 7C is a schematic configuration view showing a third example of a coaxial cable. DETAILED DESCRIPTION

[0022] Hereinafter, an embodiment of the present application will be described in detail with reference to the drawings. As an example, a coaxial cable 10 provided with the hollow core 1 of the present embodiment is suitable for a signal transmission cable for wiring inside an antenna supporting 5G, inside an antenna supporting 6G. Further, in all the drawings for explaining the embodiment, the same reference numerals are sometimes attached to components having the same function, and repeated explanation thereof is omitted.

[0023] [Coaxial cable]

[0024] Hereinafter, based on Figures 7A-7C The coaxial cable 10 will be described.

[0025] Figure 7A The coaxial cable 10A is a first example, and is structured such that the inner conductor 12 is insulated by the hollow core 1, and a seamless metal pipe 17 is provided on the outer periphery of the hollow core 1 as an outer conductor. In addition, on the basis of the above structure, an insulating sheath is sometimes provided on the outer periphery of the metal pipe 17.

[0026] Figure 7B The coaxial cable 10B is a second example, and is structured such that the inner conductor 12 is insulated by the hollow core 1, and a braided wire 14 formed of a metal wire is provided on the outer periphery of the hollow core 1 as an outer conductor, and an insulating sheath 15 is provided on the outermost periphery.

[0027] Figure 7C The coaxial cable 10C is a third example, and is structured such that the inner conductor 12 is insulated by the hollow core 1, and a metal foil 13 is spirally wound on the outer periphery of the hollow core 1, and a braided wire 14 formed of a metal wire is provided on the outer periphery of the metal foil 13 as an outer conductor. An insulating sheath 15 is provided on the outermost periphery.

[0028] The inner conductor 12 is made of copper or a copper alloy, a copper-clad steel wire, aluminum or an aluminum alloy, a composite material such as copper-clad aluminum, or a material obtained by plating a metal having excellent weldability on these materials. As an example, the inner conductor 12 is a silver-plated soft copper wire or a soft copper wire. The inner conductor 12 is not limited to a single wire, and a stranded wire can be used. As an example, a copper wire is subjected to wire drawing processing to form the inner conductor 12 having a circular shape such as a circular or an elliptical cross section.

[0029] The hollow core 1 is made of an insulating resin capable of being formed by melting, and as an example, the hollow core 1 is a fluorine-based resin or a polyolefin-based resin.

[0030] The outer conductor is composed of a metal pipe 17 provided on the outer periphery of the hollow core 1, or a metal foil 13 spirally wound or longitudinally attached, a resin tape for cushioning, or a braided wire 14 composed of a metal wire, or a metal wire transversely wound, or a combination of these. The metal foil 13 is made of stainless steel, nickel alloy, copper or copper alloy, aluminum or aluminum alloy, or a combination thereof. The braided wire 14 is a braided wire, and the metal wire is made of stainless steel, nickel alloy, copper or copper alloy, aluminum or aluminum alloy, or a combination thereof. The sheath 15 is an outer covering for insulation from the outside, and constitutes the outermost layer in the coaxial cable 10. As an example, the sheath 15 is composed of a fluorine-based resin FEP.

[0031] As an example, a metal foil 13 is sometimes longitudinally attached. As an example, transverse winding of a metal wire is sometimes performed. Therefore, the outer conductor is composed of a metal pipe 17 provided on the outer periphery of the hollow core 1, or a metal foil 13 spirally wound or longitudinally attached, a resin tape for cushioning, or a braided wire 14 composed of a metal wire, or a metal wire transversely wound, or a combination of these.

[0032] [Hollow Core]

[0033] Hereinafter, based on the above-described structure, the hollow core 1 will be described. Figures 1-5 The hollow core 1 will be described.

[0034] Figure 1 The hollow core 1A is a first example, and the inner annular portion 2 that insulates the inner conductor 12, the plurality of rib portions 3 that extend radially from the inner annular portion 2, and the outer annular portion 4 that is connected to the outer ends of the rib portions 3 are a unit structure of a thermoplastic resin. The hollow core 1A is formed with three or more gap portions 5 surrounded by the inner annular portion 2, the rib portions 3, and the outer annular portion 4 in the circumferential direction. In this example, the gap portions 5 are formed at six positions. The thermoplastic resin is a fluorine-based resin or a polyolefin-based resin. As a preferred fluorine-based resin, a fluorinated resin copolymer (perfluoroalkoxy fluororesin: PFA) or the like can be given.

[0035] In the above-described structure, the hollow core 1 is formed with the inner annular portion 2 that insulates the inner conductor 12, the plurality of rib portions 3 that extend radially from the inner annular portion 2, and the outer annular portion 4 that is connected to the outer ends of the rib portions 3. Figure 1In the hollow core 1A of the first example shown, the portion surrounded by the single-dot chain line on both sides of the outer end of the rib portion 3 is formed with an outer side reinforcing portion 7. The outer side reinforcing portion 7 narrows the space on the outer peripheral side of the void portion 5, and is a thickened portion in a triangular shape in a cross-sectional view. The length of one side of the triangular shape forming the outer side reinforcing portion 7 coincides with the full length of the columnar shape of the rib portion 3. The rib width of the rib portion 3 has a minimum value Wl of the rib width in the circumferential direction at a position close to the inner annular portion 2, and has a maximum value W2 of the rib width in the circumferential direction at the outer end. Here, the size ratio of the minimum value Wl of the rib width to the maximum value W2 of the rib width is in the range of 1:1.6 to 1:3.0.

[0036] Figure 2 The hollow core 1B of the second example shown is formed with an outer side reinforcing portion 7 on both sides of the outer end of the rib portion 3. The outer side reinforcing portion 7 narrows the space on the outer peripheral side of the void portion 5, and is a thickened portion in a triangular shape in a cross-sectional view. Also, in the triangular shape forming the outer side reinforcing portion 7, the length of the one side of the outer side reinforcing portion 7 in the rib portion 3 that is in contact with the void portion 5 is 0.5 times the full length of the columnar shape of the rib portion 3. This point is different from the first example.

[0037] Figure 3 The hollow core 1C of the third example shown is formed with an outer side reinforcing portion 7 on both sides of the outer end of the rib portion 3. The outer side reinforcing portion 7 narrows the space on the outer peripheral side of the void portion 5, and is a thickened portion in a shape in which two triangular shapes are combined in a cross-sectional view. Also, in the shape in which the two triangular shapes forming the outer side reinforcing portion 7 are combined, the total length of the two sides of the outer side reinforcing portion 7 in the rib portion 3 that are in contact with the void portion 5 is 0.5 times the full length of the columnar shape of the rib portion 3. This point is different from the first example.

[0038] Figure 4 The hollow core 1D of the fourth example shown is formed with an outer side reinforcing portion 7 on both sides of the outer end of the rib portion 3. The outer side reinforcing portion 7 narrows the space on the outer peripheral side of the void portion 5, and is a thickened portion in an R shape in a cross-sectional view. Also, the radius of the R shape forming the outer side reinforcing portion 7 is 0.5 times the full length of the columnar shape of the rib portion 3. This point is different from the first example.

[0039] Figure 5The hollow core 1E of the fifth example shown is formed with an outer side reinforcing portion 7 in the portion surrounded by the single-dot chain line on both sides of the outer end of the rib portion 3. Also, the hollow core 1E is formed with an inner side reinforcing portion 6 in the portion surrounded by the broken line on both sides of the inner end of the rib portion 3 that is connected to the inner annular portion 2. The outer side reinforcing portion 7 narrows the space on the outer peripheral side of the void portion 5, and is a thickened portion in an R shape in a cross-sectional view. The radius of the R shape that forms the outer side reinforcing portion 7 is 0.5 times the full length of the columnar shape of the rib portion 3. Also, the inner side reinforcing portion 6 narrows the space on the inner peripheral side of the void portion 5, and is a thickened portion in an R shape in a cross-sectional view. The size of the R shape that forms the inner side reinforcing portion 6 is smaller than the size of the R shape that forms the outer side reinforcing portion 7. If the cross-sectional area is compared, the size of the inner side reinforcing portion 6 is 0.2 to 0.5 times the size of the outer side reinforcing portion 7. This is different from the first example.

[0040] In the hollow cores 1A to 1E, the number of void portions 5 (the number of rib portions 3) is three or more, and can be appropriately set according to the desired hollow ratio and mechanical characteristics, and the like. However, if the number of void portions 5 (the number of rib portions 3) is ten or more, the physical hollow ratio becomes small, and the electrical characteristics can decrease. Therefore, the number of void portions 5 (the number of rib portions 3) is preferably three to nine, more preferably four to eight, and particularly preferably six.

[0041] In the hollow core 1 (the hollow cores 1A to 1E), the thickness T1 of the inner annular portion 2 is 15 μm to 70 μm, the thickness T2 of the outer annular portion 4 is 25 μm to 80 μm, the minimum value W1 of the rib width is 25 μm to 80 μm, and the maximum value W2 of the rib width is 37 μm to 240 μm. Also, regarding the relationship of the respective thicknesses, the thickness T2 of the outer annular portion 4 is larger than the thickness T1 of the inner annular portion 2 (T2 > T1), the maximum value W2 of the rib width is larger than the minimum value W1 of the rib width (W2 > W1), and the maximum value W2 of the rib width is the same as or larger than the thickness T2 of the outer annular portion 4 (W2 ≥ T2). According to this structure, a coaxial cable 10 of a fine diameter can be formed, and can be formed in a strong structure, so that when wiring is performed inside a small antenna, the hollow core 1 can be prevented from being crushed due to side pressure. Therefore, a structure of a signal transmission cable that is suitable for wiring inside an antenna that supports 5G, inside an antenna that supports 6G, and the like can be realized.

[0042] The manufacturing method of the hollow core 1 of the present embodiment uses a mold having a central hole, an inner annular hole formed adjacent to the outer edge of the central hole so as to surround the central hole, three or more prescribed shape holes extending radially from the outer periphery of the inner annular hole and having a width wider than the inner annular hole, and an outer annular hole connecting the outer ends of the prescribed shape holes and having a width wider than the inner annular hole. Then, while inserting an inner conductor through the central hole, molten resin is extruded from the inner annular hole, the prescribed shape holes, and the outer annular hole, thereby forming a hollow core 1A to 1E composed of an inner annular portion, a rib portion extending radially from the inner annular portion, an outer annular portion connecting the outer ends of the rib portion, and a gap portion surrounded by the inner annular portion, the outer annular portion, and the rib portion and continuous in the length direction around the inner conductor.

[0043] According to the manufacturing method of the hollow core 1 of the present embodiment, the thickness of the inner side portion, which has an influence on the electrical characteristics, is made thin, and the thickness of the outer side portion, which has little influence on the electrical characteristics, is made thick. Thus, a hollow core 1A to 1E having high electrical characteristics and high mechanical strength, particularly high side pressure strength, can be obtained. Therefore, a coaxial cable 10 having a structure that maintains stable high-frequency transmission performance and has improved side pressure strength compared with the conventional structure can be realized.

[0044] [Side pressure test]

[0045] Next, a side pressure test was performed on an example of the coaxial cable 10B using the hollow core 1E having the shape shown in the fifth example described above and a comparative example of a coaxial cable of another company. Figure 6 The number of samples was one each, and the measurement positions of the ribs were changed. The example was measured at six positions, and the comparative example was measured at two positions. As for the measurement timing, the measurement was performed 30 minutes after the side pressure as a reference value, and the measurement was performed 3 minutes after the side pressure release as a change value, and the change amount of the measured value was evaluated. The evaluation criteria were that the change amount of the transmission loss was set to OK within 10%, and the change amount of the transmission loss was set to NG exceeding 10%. In addition, the change amount of the impedance was set to OK within 1Ω, and the change amount of the impedance was set to NG exceeding 10%. The evaluation results of the side pressure test of each sample are shown in Table 1.

[0046] [Table 1]

[0047]

[0048] OK: change amount ≤ ±10%, OK: change amount ≤ ±1Ω

[0049] As shown in Table 1, in the embodiment, the variation in the transmission loss is within 10%, and the variation in the impedance is within 1 Ω, and thus it is a good result. On the other hand, in the comparative example, the variation in the transmission loss exceeds 10%, and the variation in the impedance exceeds 1 Ω, and thus it is known that deterioration has occurred. In the embodiment, the size ratio of the minimum value W1 of the rib width to the maximum value W2 of the rib width is 1:1.6 or more. On the other hand, in the comparative example, the size ratio of the minimum value W1 of the rib width to the maximum value W2 of the rib width is 1:1.4 or less.

[0050] According to the evaluation results of the side pressure test, by providing the size ratio of the minimum value W1 of the rib width to the maximum value W2 of the rib width to be 1:1.6 or more, a structure in which the side pressure strength is improved compared to the existing structure can be realized. On the other hand, in order to maintain the physical void ratio of the void portion 5 and maintain the electrical characteristics, it is preferable to provide the size ratio of the minimum value W1 of the rib width to the maximum value W2 of the rib width to be 1:3.0 or less. Thus, it is clear that by providing the size ratio of the minimum value W1 of the rib width to the maximum value W2 of the rib width to be within the range of 1:1.6 to 1:3.0, stable high-frequency transmission performance can be maintained, and a structure in which the side pressure strength is improved compared to the existing structure can be realized.

[0051] The present application is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present application.

Claims

1. A coaxial cable characterized by comprising: the coaxial cable is provided with a hollow core, the structure of the hollow core is: an inner annular part for insulating covering an inner conductor, a plurality of rib parts extending radially from the inner annular part, and an outer annular part connected with the outer end of the rib part are an integral structure of thermoplastic resin, the hollow core has 3 or more gap parts surrounded by the inner annular part, the rib part and the outer annular part, the outer side reinforcing part is formed on both sides of the outer end of the rib part, the rib width of the rib part has a minimum value in the circumferential direction near the inner annular part, the rib width of the rib part has a maximum value in the circumferential direction at the outer end, the size ratio of the minimum value to the maximum value is 1:1.6-1:3.0, in the hollow core, the inner side reinforcing part smaller than the outer side reinforcing part is formed on both sides of the inner end of the rib part connected with the inner annular part.

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