JPH0234735Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] This invention relates to a coaxial cable using a porous tetrafluoroethylene resin tape as an insulator, and particularly relates to a coaxial cable with improved signal propagation speed. [Conventional technology] With the advancement of technology in recent years, computers and
There is a growing demand for faster speeds in IC testers and the like. Coaxial cables for high-speed signal transmission are used in these high-speed computers, high-speed IC testers, etc., and in order to increase the signal propagation speed and reduce the distortion of the transmitted pulse waveform, It is necessary to minimize the dielectric constant of the insulating layer between the conductors. For this reason, the dielectric constant of the insulating layer is lowered by making the insulator porous by foaming, etc. The current method is, for example, porous tetrafluoroethylene resin made by the method of Japanese Patent Publication No. 18991/1983. A coaxial cable with a structure in which a tape is wound around a central conductor to form an insulating layer has a signal propagation delay time of 3.8 ns/m, and is said to have the best characteristics. However, in the above coaxial cable,
The porosity of the porous tetrafluoroethylene resin tape used for the insulating layer is approximately 70%, and if a tape with a porosity higher than this is used to lower the dielectric constant of the insulating layer, It was considered difficult to further increase the signal propagation speed. In order to solve these problems, Japanese Utility Model Application No. 60-5015 discloses a method in which a porous tetrafluoroethylene resin tape is roughly wound around the center conductor at appropriate intervals. This first winding layer and a second winding layer made of the same material but with the opposite winding direction are provided to serve as an insulating layer, and an outer conductor and a protective coating are sequentially formed on the outer periphery of the first winding layer. A coaxial cable is disclosed. Such a coaxial cable uses a porous tetrafluoroethylene resin tape with a higher porosity than conventional ones, and has a gap between a first winding layer and a second winding layer having a different winding direction. This effectively increases the porosity of the insulating layer, which combines with the pores inherent in the tape, resulting in a faster signal propagation speed. [Problem to be solved by the invention] However, in the above invention, increasing the signal propagation speed is achieved by increasing the porosity (low dielectric constant).
Although the signal propagation delay time can be improved to 3.65 ns/m due to the effect of the porous tetrafluoroethylene resin tape and the effect of the voids in the insulating layer, further improvement has been difficult. The main reason for this is that the voids in the porous tetrafluoroethylene resin tape and the insulating layer are crushed by the tension when wrapped around the center conductor, reducing the improvement effect.
In addition, simply increasing the pitch of the porous tetrafluoroethylene resin tape, that is, rolling it coarsely to increase the gap area and further increasing the signal propagation speed, will not work.
This leaves the problem that local variations in transmission characteristics and bending characteristics tend to occur in the longitudinal direction of the cable. This invention solves the problems of the conventional technology, has a signal propagation speed faster than the conventional one,
The purpose of the present invention is to provide a coaxial cable with uniform transmission characteristics. [Means for Solving the Problems] In view of the problems of the prior art described above, this idea was developed after intensive study and found that in this type of coaxial cable, a porous tetrafluoroethylene resin tape is wound around the axis of the center conductor. We found that the angle has a significant effect on the signal propagation speed. Therefore, according to this invention, in a coaxial cable equipped with an insulating layer formed by winding a porous tetrafluoroethylene resin tape, the signal propagation delay time of the coaxial cable is
In order to make it smaller than 3.65 ns/m, a porous tetrafluoroethylene resin tape with a porosity greater than 70% is used, and the winding angle θ of the porous tetrafluoroethylene resin tape with respect to the axis of the center conductor is set to 20.゜≧
By setting θ>0°, a coaxial cable is constructed in which the reduction in porosity of the porous tetrafluoroethylene resin tape is reduced. In this configuration, it is advantageous to use a fired porous polytetrafluoroethylene resin tape in order to maintain the porosity stably, and in addition, two or more wound layers of porous polytetrafluoroethylene resin tape are used. If the winding directions are alternated, it is advantageous in terms of bending characteristics and the like. [Function] According to this invention, as mentioned above, a porous tetrafluoroethylene resin tape is used as the insulating layer of the coaxial cable, and is wound at an angle of 20 degrees or less to the axis of the central conductor. The tension when wrapping the porous tetrafluoroethylene resin tape around the center conductor can be made smaller than that of conventional tapes. Even when a fluorinated ethylene resin tape is used, the porosity of the insulating layer is maintained stably, and the signal propagation speed is increased. Furthermore, since there is no need to roughly wrap the tape at intervals to form voids, the insulation layer of the cable will not be displaced or deformed.
As a result, local variations in transmission characteristics and bending characteristics can be prevented from occurring in the longitudinal direction of the cable. [Embodiment] FIG. 1 is a perspective view showing an embodiment of the coaxial cable according to this invention. This coaxial cable 1 is
A first wound layer 4 made of porous tetrafluoroethylene resin tape 3 is placed around the outer periphery of the central conductor 2 provided in the center.
Further, on the outer periphery of this first wound layer 4, a second wound layer 5 made of the same material but with the winding direction reversed is provided to form an insulating layer 6, and an external conductor 7 is provided on the outer periphery of the second wound layer 5. This is the basic configuration. A protective coating 8 made of synthetic resin or the like is provided on the outer periphery of the external conductor 7 as required. The outer conductor is formed by horizontally winding a copper wire, spirally winding a metal tape, vertically wrapping, or the like. FIG. 2 shows the center conductor 2 and the wound layer 3 made of porous tetrafluoroethylene resin tape in the above embodiment.
The winding angle θ with respect to the axis of the center conductor 2 is 20° or less. At this time, it is convenient to use a porous tetrafluoroethylene shaft tape that has been fired in advance because it allows the use of a tape with a higher porosity. Tape can be used. Next, the following table shows the results of measuring signal propagation delay times for coaxial cables made by changing the winding angle θ of the porous tetrafluoroethylene resin tape. The coaxial cable used in the test has an outer diameter of
0.254mm silver-plated annealed copper wire is used as the center conductor, and the porosity is
Using 85% porous tetrafluoroethylene resin tape,
An insulating layer was formed by winding to a coating thickness of 0.193 mm.
A polyester film laminated with aluminum foil is vertically attached on the outer periphery to serve as an external conductor, and a protective coating made of ethylene-tetrafluoroethylene resin is further provided.

[Effect of idea]

As explained above, according to this invention, in a coaxial cable equipped with an insulating layer formed by winding a porous tetrafluoroethylene resin tape, the porous tetrafluoroethylene resin tape is aligned with the axis of the center conductor.
Because it is wrapped at an angle of 20 degrees or less,
It is possible to use a porous tetrafluoroethylene resin tape with a porosity greater than 70%, resulting in a signal propagation time of less than 3.65 ns/m. Furthermore, since it is not necessary to wrap the tape at a coarse pitch, the shape of the insulating layer is stably maintained, and variations in transmission characteristics and bending characteristics in the longitudinal direction of the cable are eliminated. Note that this invention is not limited to the above embodiments, and may include changing the number of winding layers of the porous tetrafluoroethylene resin tape, changing the winding direction thereof, or providing the drain wire inside or outside the external conductor. Of course, various modifications can be made within the technical concept of this invention.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a coaxial cable according to this invention, and FIG. 2 is an explanatory diagram showing the relationship between the center conductor and the porous tetrafluoroethylene resin tape in the embodiment shown in FIG. 2: Center conductor, 3: Porous tetrafluoroethylene resin tape, 6: Insulating layer, 7: Outer conductor.

Claims (1)

[Claims for Utility Model Registration] (1) Signal propagation delay time of a coaxial cable having an insulating layer formed by winding a porous tetrafluoroethylene resin tape between a center conductor and an outer conductor. In order to make it smaller than 3.65 ns/m, a porous tetrafluoroethylene resin tape with a porosity greater than 70% is used, and the winding angle θ of the porous tetrafluoroethylene resin tape with respect to the axis of the center conductor is By setting 20゜≧θ＞0゜,
A coaxial cable characterized in that the decrease in porosity of the porous tetrafluoroethylene resin tape is reduced. (2) The coaxial cable according to Claim 1 of the Utility Model Registration Claim, characterized in that the porous tetrafluoroethylene resin tape is fired.