Data cable for high-speed data transmissions

Abstract

A data cable for high-speed data transmissions includes at least one wire pair formed of wires extending in a longitudinal direction and being surrounded by a shielding foil to form a pair shielding. A dielectric intermediate film or foil having a varying lay length is spun around the wire pair between the shielding foil and the wire pair, in order to effectively avoid a damping peak at high transmission frequencies.

Claims

1. A data cable for high-speed data transmissions, the data cable comprising: at least one wire pair, each wire pair being formed of two wires extending in a longitudinal direction; at least one shielding foil, each shielding foil surrounding a respective wire pair to form a pair shielding; and at least one dielectric intermediate film, each dielectric intermediate film being spun around a respective wire pair as an additional film between said shielding foil and said wire pair, said dielectric intermediate film being spun around said wire pair with a varying length of lay.

2. The data cable according to claim 1, wherein said length of lay varies at least within a range of +/5% relative to a mean length of lay.

3. The data cable according to claim 1, wherein said length of lay varies at least within a range of at least up to +/10% relative to a mean length of lay.

4. The data cable according to claim 1, wherein said intermediate film has a mean length of lay lying within a range of a few millimeters.

5. The data cable according to claim 1, wherein said intermediate film has a mean length of lay lying within a range of from 5 mm to 15 mm.

6. The data cable according to claim 1, wherein said intermediate film has a mean length of lay amounting in particular standards to approximately 6 mm to 8 mm.

7. The data cable according to claim 1, wherein said length of lay varies uniformly in said longitudinal direction.

8. The data cable according to claim 1, wherein said length of lay varies periodically in said longitudinal direction with a period length lying within a range of a few meters.

9. The data cable according to claim 1, wherein said length of lay varies periodically in said longitudinal direction with a period length lying within a range of from 1 m to 5 m.

10. The data cable according to claim 1, wherein said length of lay varies periodically in said longitudinal direction with a period length of 2 m.

11. The data cable according to claim 1, which further comprises a further outer film spun around said pair shielding.

12. The data cable according to claim 11, wherein said further outer film has a varying length of lay.

13. The data cable according to claim 1, wherein said further outer film is an adhesive.

14. The data cable according to claim 1, wherein said at least one dielectric intermediate film is spun around said at least one wire pair with a length of lay being different than a length of lay of said at least one shielding foil.

15. The data cable according to claim 1, wherein said at least one shielding foil and said at least one dielectric intermediate film are spun around said at least one wire pair with opposite-sense lays.

16. The data cable according to claim 1, wherein said at least one shielding foil is spun around said at least one wire pair with a constant length of lay.

17. The data cable according to claim 1, wherein said at least one shielding foil is at least one longitudinally folded foil.

18. The data cable according to claim 1, wherein said at least one shielding foil has a multilayered structure with an insulating backing layer and a conductive layer attached to said insulating backing layer.

19. The data cable according to claim 1, wherein a course of a feed of a high-frequency data signal within a GHz range, at least within a frequency band up to 25 GHz, causes no signal peak to occur either in an insertion loss or in a return loss.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a diagrammatic, cross-sectional view of a pair of wires, surrounded by a pair shielding, of a data cable;

(2) FIG. 2 is a side-elevational view showing the pair of wires, wrapped with an intermediate film, according to FIG. 1;

(3) FIG. 3 is a cross-sectional view of a data cable with two shielded pairs of wires;

(4) FIG. 4 is a diagram showing a variation of a length of a lay of an intermediate film;

(5) FIG. 5A is a diagram showing an insertion loss in the case of a conventionally shielded pair of wires;

(6) FIG. 5B is a diagram showing the insertion loss in the case of a pair of wires that has been provided with an intermediate film wound with a varying length of lay;

(7) FIG. 6A is a diagram, correlated with FIG. 5A, showing a return loss in the case of the conventionally shielded pair of wires; and

(8) FIG. 6B is a diagram, correlated with FIG. 5B, showing the return loss in the case of the pair of wires that has been provided with an intermediate film wound with a varying length of lay.

DETAILED DESCRIPTION OF THE INVENTION

(9) Referring now to the figures of the drawings in detail and first, particularly, to FIGS. 1-3 thereof, there is seen at least one wire pair 2, formed of two wires 4, in which each wire 4 in turn exhibits a central conductor 6 which is surrounded by a wire insulation 8. The wire pair 2 is surrounded in each instance by a pair shielding 10 which surrounds the wire pair 2, with the insertion or interposition of an intermediate film 12.

(10) In the embodiment variant according to FIG. 1, the pair shielding 10 has been formed by a single multilayered shielding foil 14 which is formed of a backing layer 16a taking the form of a PET backing film and also an aluminum coating, attached thereto, by way of a conductive layer 16b. The conductive layer 16b is oriented outward. In the case of the shielding foil 14, a longitudinally folded shielding foil 14 is used having longitudinal edges which therefore run parallel to the wires 4 in a longitudinal direction 17. The wires 4 run in the longitudinal direction 17, untwisted and parallel to one another.

(11) Furthermore, the entire pair structure has been wrapped by an adhesive outer film 20, with the aid of which the entire structure is fixed. This outer film 20 is, in turn, a plastic film.

(12) Drain wires 18, which are in electrical contact with the conductive layer 16b, have furthermore been disposed between the pair shielding 10 and the outer film 20. The drain wires 18 serve for simplified connection of the pair shielding 10 in a connector region. The drain wires 18 lie on a common line of centers which also passes through the center axes of the wires 4. They are situated, in particular, outside the intermediate film 12 and hence also outside filler regions between the wires 4. By virtue of the bilateral opposing configuration, a highly symmetrical structure has been obtained. In principle, alternative configurations with no drain wire or with only one drain wire are possible.

(13) All of the foils/films exhibit a thickness ordinarily within the range of merely a few pm. Insofar as it is a question of spun films, as is the case, in particular, with the intermediate film 12 and also the outer film 20, these typically exhibit a width B within a range from 4 mm to 6 mm.

(14) Whereas in the case of the shielding foil 14 it is preferentially a longitudinally folded foil, the intermediate film 12 has been wound around the wire pair 2. This can be gathered, in particular, from the side view according to FIG. 2. The intermediate film 12 has been wound around the wire pair 2 in this case with a mean length of lay I.sub.m. The length of lay I and hence the pitch of the intermediate film 12 varies in this case by a difference around the mean length of lay I.

(15) In FIG. 2 the representation of the pair shielding 10 has been dispensed with for a better overall view, and merely the intermediate film 12 can still be discerned.

(16) A data cable 22, as represented in an exemplary manner in FIG. 3, typically exhibits one or more wire pairs 2, each provided with a pair shielding 10. Each pair element preferably exhibits a structure such as has been described with reference to FIGS. 1 and 2. The individual wire pairs 2, which are surrounded by the pair shielding 10, form a transmission core which subsequently is also surrounded by an outer shielding 24 which is galvanically separated from the pair shielding 10. In this embodiment, the outer shielding 24 is a multilayered structure which, in this case, has an exterior braiding shield 24A and an interior overall shielding foil 24B which preferably has been formed like the shielding foil 14. The outer shielding 24 may also have been formed in one layer. A further insulating film 25 has been spun between the outer shielding and the transmission core in this embodiment. Finally, a cable jacket 26 has been disposed around the outer shielding 24, by way of an outer protective sheath of the data cable 22. In this case it is typically an extruded cable jacket 26.

(17) In FIG. 4 an exemplary curve of the variation of the mean length of lay I of the intermediate film 12 is represented. As can be discerned, the length of lay L varies around the mean length of lay I.sub.m by the difference between a maximum length of lay I.sub.max and a minimum length of lay I.sub.min. In this case the variation occurs uniformly and periodically and, in particular, in accordance with a sine curve represented in an exemplary manner in FIG. 4. This curve therefore exhibits a periodicity with a period length P which typically lies within the range of a few meters.

(18) In the following, the effect of the variation of the length of lay L in the case of the intermediate film 12 will be elucidated with reference to FIGS. 5A and 5B and also 6A and 6B. The diagrams represented show, schematically in each instance, measurement curves in which the attenuation a in decibels dB has been plotted over the frequency fin gigahertz GHz. The measurement curves were implemented in the case of data cables 22 having a fundamental structure according to FIG. 1 for the pair-shielded wire pair 2. In the case of the measurement according to FIGS. 5A and 6A, the basis was a conventional structure with an intermediate film 12 having a constant length of lay L, and in the case of the measurement curves of FIGS. 5B and 6B the basis was a structure having a varying length of lay L of the intermediate film 12. The measurements were made with a mean length of lay I.sub.m of the intermediate film 12 of approximately 6 mm. The length of lay L therefore lies distinctly above the conventionally chosen length of lay of, typically, approximately 3 mm, which is required, if no varying length of lay has been set, in order to shift the attenuation peak toward sufficiently high frequencies above 25 GHz.

(19) The pair of diagrams of FIGS. 5A and 5B shows the curve of the insertion loss [in dB] in a comparison of the two cable variants, and the diagram pair of FIGS. 6A and 6B shows the curve of the return loss [in dB] in a comparison of the two cable variants, in each instance plotted against the frequency.

(20) As can be readily discerned, the insertion loss generally increases continuously with increasing frequency. At approximately 19 GHz the data cable 22 in the variant with the constant length of lay displays a very strong attenuation peak which, in the example shown therein, displays an excursion of over 50 dB. Correspondingly, the return loss displays a similar curve and a reflection peak likewise at approximately 19 GHz. The height of the peak depends on the absolute attenuation and on the length of the line.

(21) In contrast, in the case of the data cable 22 with the intermediate film 12 having the varying length of lay L neither a peak in the insertion loss nor a peak in the return loss exists within the corresponding frequency range. By virtue of the varying length of lay, the base of the peak is accordingly distinctly widened to a width of, preferentially, several GHz, in particular from 3 GHz to 6 GHz, for example. Correspondingly, the height of the peak is also distinctly reduced, and merely a wavy curve in the manner of a noise is evident over the width. The signal level of this noise amounts to only a fraction of the original peak height, for example less than 10% of the original peak height.