JP2010009835A - Thin coaxial cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin coaxial cable that has improvements in thinning, flexibility and flex resistance, and limits deterioration of shield property and attenuation. <P>SOLUTION: A thin coaxial cable 1 is constructed of a central conductor 2 having a conductor cross-sectional area between 0.003 mm<SP>2</SP>and 0.09 mm<SP>2</SP>, an insulator 3, a spiral shield conductor 6 and an outer sheath 7, which are arranged coaxially. The spiral shield conductor 6 has a winding angle between 73° and 83° and is formed of two layers differing from each other in a spiral winding direction. A ratio of a strand diameter of the spiral winding conductor 4 forming the shield conductor 6 to a diameter of a shield portion of the cable is between 0.05 and 0.12. If a winding angle of an inner spiral winding conductor 4 of the two-layered spiral shield conductor 6 is θ1, and a winding angle of an outer spiral winding conductor 5 is θ2, then θ1≥θ2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a small-diameter coaxial cable used for wiring or the like in communication equipment using a high-frequency signal.

  In an electronic device provided with wireless communication means such as a mobile phone, a notebook personal computer (wireless LAN), a game machine, an in-vehicle wireless device (ETC, GPS, etc.), an antenna and a transmission / reception circuit are required. In general, the antenna portion is often arranged in the vicinity of the housing of the electronic device, and the transmission / reception circuit portion is often formed on a circuit board such as a mother board and arranged inside the device main body. In this case, the antenna portion and the transmission / reception circuit portion are connected using a high-frequency coaxial cable. The coaxial cable needs to have a small diameter, low attenuation, high flexibility, high bending resistance, and the like. .

  With recent downsizing of electronic devices, diversification of opening and closing functions, and widening and high frequency of use frequency, it has become difficult to provide coaxial cables having these needs. Conventionally, as this type of coaxial cable, a thin central conductor, an insulator, a shield conductor, and a jacket are generally arranged in a coaxial structure, and the shield conductor is formed of a braided conductor (for example, Patent Documents). 1). However, if a braided conductor is used for the shield conductor, it is difficult to further reduce the diameter of the coaxial cable, and considering the cable end workability, the flexibility and bending resistance are reduced, and the productivity and cost are also improved. It has been demanded.

On the other hand, it has also been proposed to improve the reduction in diameter, flexibility, bending resistance, and cost resistance by forming the shield conductor by lateral winding (see, for example, Patent Document 2). However, if the shield conductor is made of a laterally wound conductor, the amount of attenuation is worse than that of a braided conductor, so forming the insulator with a heat-resistant fluorinated resin material compensates for the deterioration of the amount of attenuation. ing.
JP-A-8-102222 JP 2007-188782 A

  As disclosed in Patent Document 2, if the shield conductor is formed of a single layer of laterally wound conductors in order to reduce the diameter, improve flexibility, and bend resistance, there is a gap between the conductors when the cable is bent or twisted. The shield may be insufficient, and the shielding characteristics are inferior to the braided conductor. In order to improve this, if the horizontal winding conductor is wound in two layers in the same direction to make a shield conductor, the shielding characteristic is improved to the same extent as the braided conductor, but the attenuation is reduced, compared with the case of a normal braided conductor. There is a problem of getting worse.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a small-diameter coaxial cable in which a decrease in shield characteristics and attenuation is suppressed, as well as an increase in diameter, flexibility, and bending resistance.

Thin coaxial cable according to the present invention, the center conductor of the conductor cross-sectional area of 0.003mm ² ~0.09mm ^2, insulator, at laterally wound shield conductor and the outer diameter coaxial cable arranged to be a coaxial structure, transverse wound The shield conductor is formed of two layers having winding angles of 73 ° to 83 ° and different in the horizontal winding direction. The strand diameter of the horizontal winding conductor forming the shield conductor is 0.05 of the diameter of the shield portion of the cable. It is characterized by being -0.12 times. When the winding angle of the inner horizontal winding conductor of the two-layer horizontal winding shield conductor is θ1, and the winding angle of the outer horizontal winding conductor is θ2, it is preferable that θ1 ≧ θ2.

  According to the thin coaxial cable of the present invention, it is possible to obtain the same shielding characteristics as those of the thin coaxial cable having a braided shield conductor and reduce the signal attenuation by about 10% compared to the shield conductor of the braided structure. It becomes possible to do. Further, it is excellent in flexibility, and wiring in the device is easy, and the cost can be reduced.

  Embodiments of the present invention will be described with reference to the drawings. 1A is a cross-sectional view of a thin coaxial cable according to the present invention, FIG. 1B is a perspective view thereof, FIG. 2 is a schematic side view thereof, and FIG. 3 illustrates the evaluation results of the thin coaxial cable according to the present invention. FIG. 4 is a diagram for explaining the shielding characteristics of the thin coaxial cable according to the present invention. In the figure, 1 is a thin coaxial cable, 2 is a central conductor, 3 is an insulator, 4 is an inner horizontal winding conductor, 5 is an outer horizontal winding conductor, 6 is a shield conductor, and 7 is a jacket.

  As shown in FIGS. 1A and 1B, a thin coaxial cable 1 according to the present invention includes a central conductor 2 surrounded by an insulator 3 and two layers of laterally wound conductors 4 and 5 on the outside thereof. The shield conductor 6 is disposed, and the outer side is covered with a jacket 7. The center conductor 2, the insulator 3, the shield conductor 6, and the jacket 7 are formed in a coaxial shape over the entire length of the cable so that the characteristic impedance is uniform.

  The center conductor 2 can be formed by a single wire or a stranded wire, and in the case of a stranded wire, it is usually formed by seven strands. In the case of a single wire, if the conductor cross-sectional area is made the same as that of the stranded wire, the wire diameter becomes somewhat smaller, and the diameter can be further reduced, and there is an advantage that it can be easily soldered to a contact portion such as a connector. . On the other hand, the stranded wire is advantageous in that it is superior in flexibility and hard to break as compared with a single wire. In this invention, it can apply to any of a single wire or a strand wire according to the use.

In the present invention, the center conductor 2, in 0.003 mm ² ～0.09Mm ² about a conductor cross-sectional area, AWG (American Wire Gauge) of # 28 to the coaxial cable using the small-diameter wires corresponding to # 42 Is targeted. As the wire for the center conductor 2, for example, a tinned annealed copper wire is used, and seven strands having an outer diameter of 0.05 mm are twisted, and the center of the outer diameter is 0.15 mm (equivalent to 0.014 mm ² AWG # 36). A conductor is used, or seven strands having an outer diameter of 0.102 mm are twisted to form a central conductor having an outer diameter of 0.31 mm (equivalent to 0.057 mm ² AWG # 29).

As the insulator 3, a fluororesin, a cross-linked polyolefin, a fluorinated FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and a fluorinated PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) are used. Can do. In order to obtain a predetermined characteristic impedance (50Ω), the thickness and the outer diameter of the insulator 3 are 0.14 mm in the case of the center conductor outer diameter of 0.15 mm and the outer diameter of the insulator is 0.43 mm. When the conductor outer diameter is 0.31 mm, the thickness is 0.30 mm and the insulator outer diameter is 0.90 mm. The fluorinated fluororesin (FEP, PFA) is a fluororesin having terminal groups fluorinated (for example, CF ₃ attached).

  The shield conductor 6 is formed of two layers of laterally wound (form wound in a spiral) conductor, and is composed of an inner laterally wound conductor 4 and an outer laterally wound conductor 5, and the laterally wound conductors 4 and 5 are in contact with each other. And wound in different winding directions. The winding direction of the inner horizontal winding conductor 4 and the outer horizontal winding conductor 5 may be right-handed or left-handed as long as the winding directions are different from each other.

  FIG. 2 is a diagram for explaining a winding state of the shield conductor. The shield conductor 6 winds the inner horizontal winding conductor 4 at a winding angle θ1 (hereinafter referred to as a winding angle) and the outer horizontal winding conductor 5 at a winding angle θ2. The “winding angle” refers to an angle with a transverse line orthogonal to the axial direction of the cable. Generally, the winding angles θ1 and θ2 are preferably in the range of 70 ° to 85 ° in order to prevent the horizontally wound shield conductor of the small-diameter coaxial cable from being broken at the time of terminal processing of connection to a connector or the like. Has been. In the present invention, as a more preferable form, the winding angles θ1 and θ2 of the horizontal winding are 73 ° to 83 °.

  The smaller the winding angle θ1, θ2 of the horizontal winding conductor, the larger the winding interval between the horizontal winding conductors when the cable is bent. However, when the shield conductor 6 has a two-layer winding, when the cable is bent, the force applied to the outer horizontal winding conductor 5 is larger than the force applied to the inner horizontal winding conductor 4. Therefore, it is desirable that the winding angle θ2 of the outer horizontal winding conductor is slightly smaller than the winding angle θ1 of the inner horizontal winding conductor 4. That is, by satisfying θ1 ≧ θ2, the resistance to bending of the outer horizontal winding conductor 5 and the inner horizontal winding conductor 4 can be made the same, and mechanical reliability can be ensured.

  Further, when the cable is twisted, when the winding of the inner horizontal winding conductor 4 is in the direction of loosening, the winding of the outer horizontal winding conductor 5 is in the opposite direction. However, as described above, by setting θ1 ≧ θ2, the conductor length of the outer horizontal winding conductor 5 becomes longer and the inner horizontal winding conductor 4 loosens and rises outward, whereas the outer horizontal winding conductor 5 tightening amount is reduced. As a result, the frictional force between the inner horizontal winding conductor 4 and the outer horizontal winding conductor 5 when the cable is twisted is reduced, the resistance to disconnection is improved, and the mechanical reliability can be increased.

  For the laterally wound conductors 4 and 5, for example, a tin-plated annealed copper wire similar to the central conductor 2 can be used. For the above-mentioned one having an outer diameter of 0.15 mm for the central conductor, for example, the inner horizontal winding conductor 4 and the outer horizontal winding conductor 5 both have dozens of wires having a wire diameter of 0.05 mm (for example, about 60 wires). ) In parallel and wound at a pitch of 7 mm (θ1 = 78 °, θ2 = 75 °). In this case, the strand diameter of the horizontal winding conductor forming the shield conductor is (0.05 / 0.53) in the inner horizontal winding conductor 4 with respect to the diameter of the shield portion of the cable (hereinafter referred to as shield winding diameter). = 0.094 times, and in the case of the outer laterally wound conductor 5, (0.05 / 0.63) = 0.079 times.

  Also, for the central conductor having an outer diameter of 0.31 mm, the inner horizontal winding conductor 4 having a strand diameter of 0.05 mm is used, and the outer lateral winding conductor 5 having a strand diameter of 0.064 mm. It is formed by winding at a pitch of 12 mm (θ1 = 76 °, θ2 = 73 °). In this case, the strand diameter of the horizontal winding conductor forming the shield conductor is (0.05 / 1.0) = 0.05 times as large as the outer horizontal winding conductor 5 in the inner horizontal winding conductor 4 with respect to the shield winding diameter. Then, (0.064 / 1.128) = 0.057 times.

When the center conductor 2 has a conductor cross-sectional area of 0.03 mm ² (equivalent to AWG # 42), the outer diameter of the insulator 3 is set to 0.2 mm in order to obtain a predetermined characteristic impedance (50Ω). In this case, it is desirable that the strand diameter of the inner laterally wound conductor 4 is 0.03 mm or less. In this case, the wire diameter of the horizontal winding conductor forming the shield conductor is (0.03 / 0.26) = 0.115 times in the inner horizontal winding conductor 4 with respect to the shield winding diameter, and the outer horizontal winding conductor 5 Then, (0.03 / 0.32) = 0.09 times.

  As described above, the strand diameter of the horizontally wound conductor forming the shield conductor in the reduced coaxial cable is set to 0.05 to 0.12 times the shield wound diameter. If the wire diameter of the horizontal winding conductor is less than 0.05 times the shield winding diameter, it is difficult to ensure the shielding characteristics, the resistance value of the shielding conductor is increased, and this is disadvantageous in terms of attenuation characteristics. . Further, when the wire diameter of the horizontally wound conductor exceeds 0.12 times the shield winding diameter, the wire is easily cut by repeated bending, which is disadvantageous in terms of mechanical reliability.

  The jacket 7 can be formed by extrusion molding using an extruder, and as the jacket material, PTFE (polytetrafluoroethylene) and ETFE (tetrafluoroethylene-ethylene copolymer) are used in addition to the FEP and PFA described above. be able to. Since these fluororesins have good thin-wall processability, it is easy to reduce the diameter of the coaxial cable by using these fluororesins as a jacket. In addition, since the dynamic friction coefficient is low, the bending resistance is improved, so that it is suitable for a coaxial cable of an electronic device having a twisted portion.

  The thickness of the jacket 7 can be formed with a thickness of 0.09 mm and a jacket outer diameter of 0.81 mm, for example, using PFA for the above-mentioned center conductor outer diameter of 0.15 mm. In addition, with respect to the central conductor having an outer diameter of 0.31 mm, the thickness can be set to 0.12 mm and the jacket outer diameter is 1.35 mm.

FIG. 3 is a diagram comparing and evaluating the characteristics of the above-described product of the present invention, a conventional standard product (braided shield), and a comparative example (horizontal winding one-layer shield, same-direction two-layer shield). In each evaluation product, the center conductor is a twist of seven tin-plated annealed copper wires having an outer diameter of 0.102 mm and an outer diameter of 0.31 mm (equivalent to 0.057 mm ² AWG # 29). 3 is made of fluorinated PFA with an outer diameter of 0.9 mm (standard braided product is ordinary fluororesin), tin-plated annealed copper wire is used for the shield conductor 6, and the outer sheath 7 is made of ordinary PFA. It was formed by extrusion molding so as to have a diameter of 1.35 mm.

  As for the shield conductor, the conventional standard product (braided) has a strand diameter of 0.05 mm and one layer, and the comparative example (one layer horizontal winding) has one strand with a strand diameter of 0.1 mm and the comparative example (two layers in the same direction horizontal winding) ) Is an inner strand diameter of 0.05 mm, an outer strand diameter of 0.064 mm, and the product of the present invention (two-layer horizontal winding in different directions) has an inner strand diameter of 0.05 mm and an outer strand diameter of 0.064 mm.

  As a result of the evaluation, the characteristic impedance of each evaluated product was able to ensure 50Ω ± 2. As shown in FIG. 4, the shield characteristic (low leakage voltage) is inferior to the conventional standard product (braid) in the comparative example (one-layer horizontal winding). However, the comparative example (two-layer same-direction horizontal winding) and the product of the present invention (two-layer different-direction horizontal winding) were able to ensure the same level of shielding characteristics as the conventional standard product (braid). Regarding cost, the comparative example (one-layer horizontal winding) was the cheapest, the conventional standard product (braided) was the most expensive, and the comparative example (two-layer same-direction horizontal winding) and the product of the present invention were in the middle.

  Regarding the signal attenuation, the comparative example (one-layer horizontal winding) is reduced compared to the conventional standard product (braided) and shows good results, but the comparative example with improved shielding characteristics (two-layer horizontal winding in the same direction) ), The loss increased as the frequency increased (6.0 GHz). However, in the case of the present invention, it was reduced by about 10% compared with the conventional standard product (braided), and was able to be suppressed to the same extent as the comparative example (one-layer horizontal winding). The attenuation of the high-frequency signal is affected by the contact resistance between the shield conductors and the skin effect. For this reason, as in the present invention, when the winding angles θ1 and θ2 of the two-layer horizontally wound shield conductors are 73 ° to 83 ° and the winding direction is the reverse direction, the two layers of shield conductors have a small contact resistance. It is considered that the skin is in contact and the influence of the skin effect is small.

  That is, according to the coaxial cable of the present invention, it is possible to keep the shield characteristics at the same level as the braided shielded coaxial cable, and to reduce the signal attenuation. In addition, the cost can be lower than that of a coaxial cable having a braided shield structure, and it is excellent in flexibility by lateral winding, facilitating wiring in the device, and enabling a reduction in diameter.

It is a figure explaining the outline of the thin coaxial cable by this invention. It is a figure explaining the structure of the shield conductor of the thin coaxial cable by this invention. It is a figure which shows the evaluation result of the thin coaxial cable by this invention. It is a figure explaining the shielding characteristic of the thin coaxial cable by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Small diameter coaxial cable, 2 ... Center conductor, 3 ... Insulator, 4 ... Inner side winding conductor, 5 ... Outer side winding conductor, 6 ... Shield conductor, 7 ... Outer jacket.

Claims (2)

Center conductor of the conductor cross-sectional area of 0.003mm ² ~0.09mm ^2, insulator, laterally wound shield conductor and the jacket a small diameter coaxial cable arranged in coaxial structure,
The horizontal winding shield conductor is formed of two layers having a winding angle of 73 ° to 83 ° and different in the horizontal winding direction. The strand diameter of the horizontal winding conductor forming the shield conductor is the diameter of the shield portion of the cable. A thin coaxial cable characterized by being 0.05 to 0.12 times.   2. The small diameter according to claim 1, wherein θ1 ≧ θ2 when the winding angle of the inner horizontal winding conductor of the two-layer horizontal winding shield conductor is θ1 and the winding angle of the outer horizontal winding conductor is θ2. coaxial cable.

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