Method for producing a coaxial cable

Abstract

The invention relates to a method for producing a stranded inner conductor (1), and to a coaxial cable (9). In a first step, a stranded inner conductor (2) is provided, which consists of several wires (3) twisted together. Then the stranded inner conductor (1) is rotary swaged by means of a rotary swaging device (10). In a further step, the rotary swaged stranded inner conductor (3) is enclosed with a dielectric (4). In a further step, the dielectric (4) is enclosed with an outer conductor (5) and a cable sheath (6).

Claims

1. A method for producing a high-frequency coaxial cable (9) comprising the steps of: a) providing a litz inner conductor (1) comprising a plurality of wires (3) that have been stranded together along a longitudinal axis; b) rotary swaging the litz inner conductor (1) directly by means of a rotary swaging device (10) having an axis of rotation that is parallel to the longitudinal axis, for lowering signal transmission loss and increasing signal return loss; c) encasing the rotary swaged litz inner conductor (2) with a dielectric (4); and d) encasing the dielectric (4) with an outer conductor (5).

2. The method according to claim 1, wherein the stranded litz inner conductor (1) includes a constant and/or variable pitch.

3. The method according to claim 1, wherein the outer conductor (5) in encased with an outer sheath (6).

4. The method according to claim 1, wherein the outer conductor (5) is produced as a braided outer conductor and/or a tube outer conductor and/or a foil outer conductor and/or a tape outer conductor.

5. The method according to claim 1, wherein the dielectric (4) is designed in multiple layers.

6. The method according to claim 1, wherein a surface of the wires (3) is coated.

7. The method according to claim 6, wherein the surface of the wires (3) is coated with gold, silver or tin.

8. The method according to claim 1, wherein the inner conductor (1) is rotary swaged by means of a plurality of rotary swaging devices (10) connected one behind the other.

9. The method according to claim 8, wherein the litz inner conductor (2) is subjected to an additional method step between the rotary swaging processes.

10. The method according to claim 1, wherein the litz inner conductor is in direct contact with the rotary swaging device during the rotary swaging.

11. The method according to claim 1, wherein the rotary swaging reduces a diameter of the litz inner conductor.

12. The method according to claim 1, wherein the rotary swaging reduces spacing between the plurality of wires in the litz inner conductor.

13. The method according to claim 12, wherein the rotary swaging forms a polygonal cross sectional wire shape from a round cross sectional wire shape for each of the plurality of wires.

14. The method according to claim 12, further comprising rotary swaging a full length of the litz inner conductor.

15. The method according to claim 1, further comprising rotary swaging to obtain a homogeneous outer surface for the litz inner conductor homogeneous.

16. A method for producing a high-frequency coaxial cable (9) comprising the steps of: a) providing a litz inner conductor (1) comprising a plurality of wires (3) stranded together along a longitudinal axis and with gaps therebetween; b) rotary swaging the litz inner conductor (1) directly by means of a rotary swaging device (10) having an axis of rotation that is parallel to the longitudinal axis, to the wires abut each other without the gaps, for lowering signal transmission loss and increasing signal return loss; c) encasing the rotary swaged litz inner conductor (2) with a dielectric (4); and d) encasing the dielectric (4) with an outer conductor (5).

17. The method according to claim 16, further comprising rotary swaging a full length of the litz inner conductor.

18. The method according to claim 16, wherein the rotary swaging smooths an irregular outer surface of the litz inner conductor into a homogenous outer surface.

19. A method for producing a high-frequency coaxial cable (9) comprising the steps of: a) providing a litz inner conductor (1) comprising an outer surface and a plurality of wires (3) stranded together along a longitudinal axis and with gaps therebetween, wherein each of the wires comprises a round cross section; b) rotary swaging the litz inner conductor (1) directly on the outer surface by means of a rotary swaging device (10) having an axis of rotation that is parallel to the longitudinal axis, to reduce a size of the gaps by pressing the round cross sections into polygonal cross sections, wherein the rotary swaging lowers signal transmission loss and increases signal return loss; c) encasing the rotary swaged litz inner conductor (2) with a dielectric (4); and d) encasing the dielectric (4) with an outer conductor (5).

20. The method according to claim 19, further comprising rotary swaging a full length of the litz inner conductor, wherein the rotary swaging and the polygonal cross sections provide a homogeneous outer surface for the litz inner conductor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Additional aspects of the invention will now be described in greater detail with reference to the embodiment described in the following figures, in which:

(2) FIG. 1 shows a coaxial cable having periodic faults, which are shown symbolically by constrictions in the outer conductor;

(3) FIG. 2 is a first graph showing the frequency-dependent return loss progression of a coaxial cable according to FIG. 1;

(4) FIG. 3 is a second graph showing the frequency-dependent return loss progression of a coaxial cable according to the invention;

(5) FIG. 4 is a schematic view of the production of an inner conductor according to the invention for a coaxial cable according to the invention;

(6) FIG. 5 is a side view of the arrangement shown in FIG. 4;

(7) FIG. 6(a) is a micrograph of a stranded litz inner conductor;

(8) FIG. 6(b) shows the contours of the micrograph according to (a);

(9) FIG. 7(a) is a micrograph of a litz inner conductor according to the invention;

(10) FIG. 7(b) shows the contours of the micrograph according to (a); and

(11) FIG. 8 is a schematic view of the structure of a coaxial cable according to the invention.

(12) FIG. 1 is a schematic and highly simplified view of a conventional coaxial cable 100, as known from the prior art, comprising a stranded litz inner conductor. When viewed in the longitudinal direction (x-direction), said cable comprises flaws 101 (shown schematically as semicircles) in the outer conductor which are arranged periodically and have a negative effect on the transmission behaviour and system behaviour of the coaxial cable, depending on the frequency. The flaws 101 are arranged with a spacing of /2 or a multiple thereof (nth factor). The flaws 101 cause a part 102 of the input signal 103 fed in to be reflected at each flaw 101. Owing to the periodicity of the flaws 101, the signal parts that are scattered back are in the same phase position at the input of the coaxial cable and thus interfere constructively. This leads to an increase of the reflected signal part at a single frequency or in a narrow frequency band.

(13) FIG. 2 is a first graph schematically showing the frequency-dependent return loss behaviour of a conventional coaxial cable comprising a litz inner conductor according to FIG. 1. The x-axis shows the frequency (f) and the y-axis shows the return loss in dB. The permissible thresholds for the return loss are shown in the form of a horizontal line 105. The progression of the return flow can be seen in the form of a first curve 106 which fluctuates strongly. It can be seen that at two narrow-band points 107 and 108 the return loss has distinct minima and the permissible thresholds 105 are exceeded. The minima are given the term RL spikes.

(14) FIG. 3 is a second graph showing, in the form of a second curve 109, the return loss (y-axis) of a coaxial cable according to the invention comprising a litz inner conductor according to FIG. 4 as a function of the frequency (x-axis). The permissible thresholds for the return loss are again represented by a horizontal line 110. As can be seen, the cable according to the invention does not have the RL spikes that exceed the thresholds, as is the case with the cable known from the prior art according to the graph in FIG. 2.

(15) FIG. 4 is a perspective, diagonal front view from above of a stranded litz inner conductor in a non-processed state 1 and of the same litz inner conductor in a processed state 2. FIG. 5 is a side view of the arrangement according to FIG. 1. FIG. 6 is a sectional view through the litz inner conductor 1 along the section line EE according to FIG. 4. FIG. 7 is a sectional view through the litz inner conductor 2 along the section line FF according to FIG. 4. FIG. 8 is a schematic sectional view of a structure of a coaxial cable 9 comprising a litz inner conductor 2 according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(16) In the method according to the invention, the litz inner conductor I is deformed into the processed litz inner conductor 2 by means of a rotary swaging device 10.

(17) FIG. 6a is a photograph of a cross section (micrograph) of a conventional stranded litz inner conductor 1. FIG. 6b is a graphical view of the same cross section. FIG. 7a is a photograph of a cross section (micrograph) of a rotary swaged litz inner conductor 2 according to the invention. FIG. 7b is a graphical view of the same cross section.

(18) When comparing the sectional images of FIGS. 6 and 7, it is apparent that prior to the rotary swaging (cf. FIG. 6a or 6b) wires 3 are arranged comparatively loosely and at a large spacing with respect to one another and do not necessarily abut one another. In addition, the litz inner conductor 1 comprises an irregular and bumpy outer face 8.

(19) By contrast, the wires 3 in the rotary swaged litz inner conductor 2 according to FIG. 7a or 7b are arranged so as to closely abut one another and without any spaces in between. When viewed in cross section, they have a polygonal structure with generally four to six straight or slightly curved side walls 25, which merge into one another via kinks 26.

(20) In the embodiment shown, the rotary swaging device 10 comprises a tool 11 which in the embodiment shown has four jaws 12. The jaws 12 form a processing opening 13 which is continuous in the centre. The jaws 12 are driven by outer rams 14 so as to be deflected in the radial direction of an axis of rotation 15 (cf. arrow 22), meanwhile a working shaft 16, in which the jaws 12 and the outer rams 14 are arranged mounted in recesses 17, rotates about the axis of rotation 15 (cf. arrow 23). The outer rams 14 comprise ramp-like enlargements 18 which interact with rollers 21 that are arranged in an outer ring 19 and mounted in a cage 20. The outer ring 19 supports the rollers in the radial direction. By means of the rotation of the working shaft 16, the ramps 18 are moved over the rollers 21, which rotate therewith, and are thus deflected inwards. This movement is transferred to the jaws 12 of the tool 11. Other drive mechanisms are possible. The stranded litz conductor 1 is moved through the processing opening 13 of the tool 11 in the direction of the arrow 24. The wires 3 are thereby compressed and the cross section thereof is deformed as shown in the subsequent figures. The cross section of the stranded litz inner conductor is reduced thereby from a first diameter D1 to a second diameter D2. Depending on the field of application, the diameters D2 to D1 are typically at a ratio of 0.5-0.9 to one another. Below approximately 0.77, all the intermediate regions between the wires 3 are filled and the wires can be stretched in the longitudinal direction, which this leads to an increase of the length of the inner conductor 2.

(21) As is particularly recognizable from FIG. 7, following the rotary swaging the wires 3 closely abut one another and exhibit a cross section which is practically gap-free. In particular, the cross sections of the wires 3 are no longer round but are rather shaped polygonal. In the embodiment shown, the litz conductor comprises a circular outer face 8, which is highly constant over the length of the litz conductor. In some regions, the inner faces 7 abut one another in a toothed manner. They are formed such that the wires 3 can nevertheless be displaced relative to one another in the longitudinal direction.

(22) The coaxial cable 9 according to the invention and as shown in FIG. 8, comprises a stranded and rotary swaged litz inner conductor 2, which is surrounded by a dielectric 4. The dielectric 4 is in turn surrounded by an outer conductor 5 arranged concentrically with the outer face 8. Here, the outer conductor 5 is enclosed by a protective outer sheath 6. Other outer conductors 5 are possible, e.g. the litz inner conductor 2 and the dielectric 4 can also be surrounded by a rigid outer conductor or housing (not shown in greater detail), respectively. Good results are obtained using litz inner conductors having a diameter of from 0.1 to 3 mm. Said inner conductors (depending on the field of application) generally comprise 7, 19 or 37 individual wires. In this case, the diameter of the individual wires is in the range of from 0.02 to 0.6 mm prior to the rotary swaging. The litz inner conductors according to the invention are well suited for very high transmission frequencies of up to 110 GHz.