COAXIAL CABLE WITH THIN CORRUGATED OUTER CONDUCTOR AND METHOD OF FORMING SAME

A method of manufacturing a coaxial cable includes: providing an intermediate construction for a coaxial cable comprising an inner conductor, a dielectric layer circumferentially surrounding the inner conductor, and a smooth outer conductor circumferentially surrounding and adhered to the dielectric layer; and impressing corrugations into the outer conductor and corresponding protrusions in the dielectric layer.

FIELD OF THE INVENTION

The present invention relates generally to cable, and more specifically to coaxial cable.

BACKGROUND

Coaxial cable typically includes an inner conductor, an outer conductor, a dielectric layer that separates the inner and outer conductors, and a jacket that surrounds the outer conductor. The outer conductor can take many forms, including flat, braided, and corrugated.

A typical corrugated outer conductor is manufactured by welding a thin wall cylindrical tube from a flat strip. This tube is then formed into a corrugated outer conductor with a specific shape by using use of one of several available forming methods. A typical shape for an outer conductor1010of a corrugated cable1000is shown inFIGS. 1 and 2. The thickness of the outer conductor1010is typically greater than 0.007 inch (even in relatively small cables) due to manufacturing limitations (particularly for reliable welding of the seam) and mechanical strength requirements for bending, crush and tensile loading. The corrugated outer conductor1010is then slipped over a dielectric layer1014that has already been extruded over an inner conductor (seeFIG. 2).

While the illustrated corrugation shape is relatively easy to make and results in a cable with adequate bending performance, it may be desirable to further improve on the design and to reduce the metal content of the cable without sacrificing cable bending performance.

SUMMARY

As a first aspect, embodiments of the invention are directed to a method of manufacturing a coaxial cable. The method comprises: providing an intermediate construction for a coaxial cable comprising an inner conductor, a dielectric layer circumferentially surrounding the inner conductor, and a smooth outer conductor circumferentially surrounding and adhered to the dielectric layer; and impressing corrugations into the outer conductor and corresponding protrusions in the dielectric layer.

As a second aspect, embodiments of the invention are directed to a coaxial cable, comprising: an inner conductor; a dielectric layer circumferentially surrounding the inner conductor; an outer conductor circumferentially surrounding the dielectric layer, the outer conductor having a thickness of less than 0.065 inch. The outer conductor has corrugations and the dielectric layer has protrusions that fill the corrugations.

As a third aspect, embodiments of the invention are directed to a coaxial cable, comprising: an inner conductor; a foamed dielectric layer circumferentially surrounding the inner conductor; and an outer conductor circumferentially surrounding the dielectric layer. The outer conductor has corrugations and the dielectric layer as protrusions that fill the corrugations. The dielectric layer has a density gradient that increases with radial distance from the inner conductor.

As a fourth aspect, embodiments of the invention are directed to a coaxial cable, comprising: an inner conductor; a dielectric layer circumferentially surrounding the inner conductor; and an outer conductor circumferentially surrounding the dielectric layer, the outer conductor having a thickness of less than 0.065 inch. The outer conductor has impressed dimples.

DETAILED DESCRIPTION

The present invention is described with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments that are pictured and described herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It will also be appreciated that the embodiments disclosed herein can be combined in any way and/or combination to provide many additional embodiments.

Unless otherwise defined, all technical and scientific terms that are used in this disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the above description is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this disclosure, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when an element (e.g., a device, circuit, etc.) is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

Referring now to the drawings,FIG. 3shows an intermediate construction of a coaxial cable during manufacturing. The intermediate construction10includes an inner conductor (not shown inFIG. 3—shown at112inFIG. 6a), a dielectric layer14(typically foamed) circumferentially surrounding the inner conductor, and a smooth wall outer conductor16circumferentially surrounding the dielectric layer14. An adhesive layer18is interposed between the dielectric layer14and the outer conductor16to weld these layers together.

The inner conductor12and dielectric layer14may be of conventional construction, The smooth wall outer conductor16is thin; the thickness of the outer conductor16may be below 0.065 inch, and in some embodiments between about 0.0025 and 0.007 inch, which is sufficiently thick to provide adequate electrical properties to the coaxial cable. In some embodiments, the outer conductor16may be formed of copper.

The intermediate construction10proceeds to a corrugation station, wherein corrugations22are formed in the outer conductor16(seeFIG. 4). The corrugations22may be of conventional size and configuration. As can be seen inFIG. 4, as the corrugations22are formed, the inner surface of the outer conductor16remains adhered to the dielectric layer14, such that protrusions15in the dielectric layer14fill in the inner spaces of the corrugations22. A jacket20of conventional construction is then added to cover the outer conductor16.

Because the outer conductor16is adhered to the dielectric layer14, these layers form a composite structure with considerable strength. As such, the composite structure can provide the mechanical strength required for acceptable bending, crush and tensile loading performance for a coaxial cable which are typically not achievable with a thin outer conductor that is not adhered to the dielectric layer14. This performance can be achieved with a much thinner (and therefore much less expensive) copper layer as the outer conductor16.

As shown schematically inFIG. 5, in some embodiments the dielectric layer14′ has a density gradient, such that the radially inward portion of the dielectric layer14′ is denser than the radially outward portion. Such a construction may enable the dielectric layer14′ to be more easily deformed during the formation of the corrugations22. In addition, the lower density of the radially outward portion of the dielectric layer14′ may enable the protrusions15′ of the dielectric layer14′ to maintain a desired dielectric constant when compressed.

Referring now toFIGS. 6a-6e,alternative configurations for the outer conductor are shown in which the corrugations are replaced with dimpled impressions, wherein the dimples form indentations in the dielectric layer.FIG. 6aillustrates an outer conductor116in which a plurality of dimples118are dispersed thereon in a random pattern.FIG. 6bshows an outer conductor216in which dimples218are impressed in a series of longitudinal rows.FIG. 6cillustrates an outer conductor316in which dimples318are formed in multiple circumferential rings. InFIG. 6d,an outer conductor416includes dimples418in a helical pattern, and inFIG. 6e, an outer conductor516has dimples518a,518b(represented by “A” and “B” inFIG. 6e) in a dual helical pattern. Other arrangements will be apparent to those of skill in this art.