JP2976816B2 - Semi-rigid coaxial cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semi-rigid type coaxial cable for transmitting a high frequency signal used in a mobile communication device or the like.

[0002]

2. Description of the Related Art A coaxial cable conventionally used for signal transmission in a high-frequency band exceeding several hundred megahertz is a circle in which a central conductor is uniformly coated with a fluorine-based resin having excellent electrical characteristics at high frequencies. A so-called semi-rigid coaxial cable with a structure in which a metal insulated wire is inserted into a metal tube such as copper or aluminum and then the metal tube is uniformly sinked so that there is no gap between the metal tube and the insulated wire is well known. ing.

[0003]

The above-mentioned semi-rigid coaxial cable uses a metal tube as an outer conductor.
Although the transmission characteristics at high frequencies are extremely excellent, there is a problem that connection with equipment is difficult. If the size is limited, you can make a dedicated connector and use it, but it is not economical to make a dedicated connector for all sizes. In particular, for small diameter cables with an outer diameter of 2 mm or less,
It is technically difficult to make a dedicated connector. Therefore, a connection method of soldering a metal tube, which is an external conductor, on a circuit board or a metal plate for shielding is inevitable. However, the above-mentioned semi-rigid type coaxial cable, which has a small diameter, has a thin outer conductor, cannot withstand the expansion of the insulator due to heat when soldering, and often causes cracks in the outer conductor. The workability of connection with the equipment was poor.

[0004]

Means for Solving the Problems The inventors of the present invention have solved the above problem, that is, to prevent cracks and the like from entering the outer conductor due to heat during soldering, and to facilitate connection with equipment. Various investigations were made on the method of performing the above. Although a method using an insulating material having a small coefficient of thermal expansion is conceivable, no insulating material having such a small coefficient of thermal expansion has been found as an insulating material for a cable for transmitting a signal at a high frequency. Also, we tried to reduce the thermal expansion force at the time of heating by foaming the insulator.However, with a foamed insulator made of closed cells, the thermal expansion force could not be reduced well. The outer conductor cracked.

[0005] Even after such trial and error, by adopting a structure in which a solid insulating layer and a porous layer having non-independent pores are combined, transmission characteristics at high frequencies are good, and cracks in the external conductor due to heat during soldering are eliminated. The present inventors have found that a semi-rigid type coaxial cable that does not cause any problem can be obtained, and completed the present invention. That is, the semi-rigid coaxial cable of the present invention is formed by, for example, extruding a fluororesin resin on a conductor, winding a porous tetrafluoroethylene tape having continuous pores thereon, and sintering the resultant. After inserting in the metal tube,
It is obtained by squeezing the metal tube with a die so that the insulator and the metal tube are tightly contacted.

[0006]

EXAMPLE A solid tetrafluoroethylene / perfluoroalkylvinyl ether (PFA resin) having a thickness of 0.1 mm was coated on a silver-plated copper alloy wire having an outer diameter of 0.2 mm, and continuous pores were formed thereon with a porosity of 70%. The porous tetrafluoroethylene tape having the above-mentioned structure was wrapped and sintered to prepare an insulated wire having an outer diameter of 0.65 mm. This insulated wire has an inner diameter of 0.8 mm,
After being inserted into a copper tube with an outer diameter of 1.0 mm, the copper tube is squeezed with a die so that the insulator and the copper tube adhere to each other without gaps.
A semi-rigid coaxial cable having an outer diameter of 0.85 mm was obtained. This is designated as Example Sample A.

For comparison, the following samples having similar dimensions and different structures were prepared. Sample B: 0.2 mm outside diameter on a silver-plated copper alloy wire.
225mm, thick tetrafluoroethylene layer is provided,
An insulated wire having an outer diameter of 0.65 mm was inserted into a copper tube having an inner diameter of 0.8 mm and an outer diameter of 1.0 mm, and then the copper tube was diced so that the insulator and the copper tube were in close contact with no gap. To obtain a semi-rigid coaxial cable having an outer diameter of 0.85 mm.

Sample C: An insulated wire having an outer diameter of 0.65 mm was formed by providing a foamed polyethylene layer having closed cells with a thickness of 0.225 mm on a silver-plated copper alloy wire having an outer diameter of 0.2 mm. After being inserted into a copper tube of 0.8 mm and an outer diameter of 1.0 mm, the copper tube was squeezed with a die so that the insulator and the copper tube were in close contact with each other without any gap, and a semi-rigid coaxial cable having an outer diameter of 0.85 mm was obtained. .

Sample D: A porous tetrafluoroethylene tape having a porosity of 70% and having continuous pores was directly wound around a silver-plated copper alloy wire having an outer diameter of 0.2 mm, and sintered to form an outer diameter of 0.1 mm. A 65 mm insulated wire was made. After inserting this insulated wire into a copper tube having an inner diameter of 0.8 mm and an outer diameter of 1.0 mm, the copper tube is squeezed with a die so that the insulator and the copper tube are in close contact with no gap, and the outer diameter is 0.85 mm. A semi-rigid coaxial cable was obtained.

[0010]

According to the present invention, sample A, sample B, sample C,
For Sample D, a heating test and a measurement of high-frequency reflection characteristics at room temperature were performed, respectively. As a result, as shown in Tables 1 and 2, only the sample A of the example had excellent high-frequency reflection characteristics and did not cause cracking of the outer conductor due to heating.

[0011]

[Table 1]

[0012]

[Table 2]

In sample B, since the solid tetrafluoroethylene was used as the insulator, the outer conductor could not withstand the thermal expansion of the insulator due to heating, and cracks occurred. In Sample C, foamed polyethylene having closed cells was used as an insulator, and the expansion force due to heating should have been weakened. However, the heating also caused cracks in the outer conductor. Sample D uses porous tetrafluoroethylene having continuous pores in the insulating layer. This porous tetrafluoroethylene has a form in which fine fibers are entangled, and the gaps between the fibers are connected both in the length direction and in the thickness direction. It is in a form that the expansion easily escapes in the length direction. As a result, in the sample D, no crack was generated in the outer conductor even when the sample was heated. However, since the insulating layer is composed only of porous tetrafluoroethylene, the adhesion between the center conductor and the insulating layer is unstable, and as shown in Table 2, there is a disadvantage that the high-frequency reflection characteristics are deteriorated.

Since only the sample A of the embodiment does not crack the outer conductor even when heated, it has both the characteristics that the connection work by soldering is easy and the excellent high frequency characteristics, It turns out that it is most suitable as a coaxial cable for signal transmission.

[Brief description of the drawings]

FIG. 1 shows a cross section of a semi-rigid coaxial cable of the present invention.

[Explanation of symbols]

 1: Conductor 2: Solid insulating layer 3: Porous layer having non-independent pores 4: Metal layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-41622 (JP, A) JP-A 63-162412 (JP, U) JP-A 63-70214 (JP, U) 503807 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01B 11/18 H01B 11/00 H01B 11/06

Claims (2)

(57) [Claims] 1. A semi-rigid coaxial cable characterized by sequentially providing a solid insulating layer, a porous layer having non-independent pores, and a metal layer concentrically on the outer periphery of a center conductor. 2. The semi-rigid coaxial cable according to claim 1, wherein the porous layer having non-independent pores is made of tetrafluoroethylene.