Coaxial cable with braided SiO2 core

Abstract

The cable includes a central conductor and at least one layer formed of silicon dioxide fibers braided around the central conductor to form a braided dielectric core layer over the central conductor. An outer conductor layer, either as a wrapped tape or a semi-rigid conductor, is formed over the braided silicon dioxide core layer. In flexible embodiments of the cable, one or more outer strength layers and a jacket may be applied over the outer conductor layer. In an embodiment of the invention, the dielectric core layer includes multiple sub-layers of silicon dioxide fibers, each sub-layer being successively braided on the previous sub-layer.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 320,395, filed March 16, 2022 (pending), the disclosure of which is incorporated herein by reference.

[0002] The present invention relates generally to coaxial cables, and more particularly to coaxial cables capable of operating at high temperatures while still maintaining desirable electrical properties. [Background technology]

[0003] Existing coaxial cables that are intended to be thermally stable over a significant range of temperatures have used certain dielectric materials. Specifically, high temperature cables have been constructed using porous extruded amorphous or crystalline SiO2 as a dielectric core that is extruded around a central conductor. The extruded core is secured in a semi-rigid cable, usually with a connector that is welded and hermetically sealed. In the construction of such cables with extruded cores using SiO2, the cable core is hygroscopic and therefore tends to readily absorb moisture over time. While this is a feature of the core's construction, the hygroscopic nature of the core can adversely alter the loss characteristics of such cables. To prevent moisture absorption, current high temperature coaxial cables require hermetic sealing at the ends of the cable to reduce moisture absorption, thereby preventing changes in the loss characteristics of the cable over time. The added loss can significantly affect the overall electrical performance of the cable and can undesirably attenuate the signals that the cable handles.

[0004] The SiO2 cores used in the construction of existing coaxial cables are first extruded. The extruded cores are then fitted into a semi-rigid cable and an outer cable jacket is sunk over the extruded core. The extruded SiO2 cores tend to be brittle. Thus, the cable construction process can be quite problematic when the semi-rigid cable is bent into its final position. In particular, the brittle cores can crack, which allows a line of sight directly from the center conductor to the outer conductor in the cable. Such defects can lead to failures in dielectric breakdown, problems with voltage standing wave ratio, and increased signal insertion loss, thus degrading performance. If the defects are large, they can even lead to catastrophic failure of the coaxial cable. Summary of the Invention [Means for solving the problem]

[0005] The cable includes a central conductor and at least one layer formed of silicon dioxide fibers braided around the central conductor to form a braided dielectric core layer over the central conductor. An outer conductor layer is formed over the braided silicon dioxide core layer. In some embodiments of the cable, one or more outer reinforcement layers and a jacket may be applied over the outer conductor layer. In certain embodiments of the invention, the dielectric core layer includes multiple sub-layers of silicon dioxide fibers, each sub-layer being successively braided on the previous sub-layer. The sub-layers may be braided using different braiding parameters to improve coverage over the central conductor. The outer conductor layer may include a tape wrapped around the braided dielectric core layer. Alternatively, a semi-rigid outer conductor may cover the central conductor and the braided dielectric core layer.

[0006] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention as well as the detailed description provided below, and serve to explain various aspects of the invention. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view, partially in section, of a cable according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the cable of FIG. 1. [Diagram 3] FIG. 2 is a perspective view, partially in section, of a cable according to another embodiment of the present invention. [Figure 4] FIG. 3 is a cross-sectional view of the cable of FIG. 2. [Diagram 5] FIG. 2 is a perspective view, partially in section, of a cable according to another embodiment of the present invention. [Figure 6] FIG. 6 is a cross-sectional view of the cable of FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] It should be understood that the accompanying drawings are not necessarily drawn to scale and present somewhat simplified representations of various features illustrating the underlying principles of the present invention. For example, the specific design features of the sequences of operations disclosed herein, including the specific dimensions, orientations, locations, and shapes of the various illustrated components, are determined, in part, by the specific intended application and environment of use. Certain features of the described embodiments have been enlarged or distorted relative to others to facilitate visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity or illustration.

[0009] The present invention relates to a coaxial cable configuration that implements SiO2 material as a dielectric, but with a braid formed from SiO2 fibers braided in the cable structure. That is, the present invention eliminates the SiO2 extruded core and all the physical and performance problems that such extruded cores present, as discussed above. More specifically, the present invention provides a coaxial cable that is configured with a unique manufacturing process, in which the SiO2 material is braided onto the central conductor, rather than extruded onto the conductor. The fibers of the SiO2 material are formed into a braid with one or more braid layers. An outer conductor is then formed over the SiO2 braid, and one or more reinforcing and jacket layers can then be attached. By braiding the SiO2 material onto the central conductor, the present invention presents a flexible cable and eliminates the problem of extruded dielectrics cracking. To address the coverage problem that does not exist in the extruded core, the dielectric is braided in layers, so that coverage over the central conductor is achieved in a manner that eliminates the direct line of sight between the central conductor and the outer conductor.

[0010] According to one embodiment of the present invention, a cable core is made using a hydrophobic SiO2 fiber form. Specifically, the fiber is made from a material that is a crystalline structured quartz material in its initial form, which is then ground and melted so that in its final form, the fiber is essentially hydrophobic, amorphous SiO2 with no pores. Because the SiO2 braid and fiber material do not significantly absorb moisture, the braid can be utilized in traditional flexible coaxial cable configurations, such as using a spirally wound outer conductor with openings in the outer conductor to improve flexibility. The hydrophobicity of the braided SiO2 core with a quartz-like structure, as opposed to a porous, hygroscopic extruded core, allows for higher speed propagation and lower losses due to the core layer not absorbing moisture. By combining both a braided SiO2 core over a central conductor and a spirally wrapped outer conductor over a SiO2 braid, one embodiment of a cable is provided that offers all the temperature and performance benefits of SiO2, but in a very flexible package without the fragility and damage issues to the extruded core. The core configuration has advantages over other cable configurations as well.

[0011] The cable of the present invention is capable of operating at high temperatures with a linear phase vs. temperature response. Due to the braided SiO2 core layer, the cable has good phase stability and low loss over extreme temperatures and pressures. In addition, the cable achieves high speed signal propagation. The propagation speed is accelerated as a result of the presence of voids in the braided layer of the SiO2 braided core. The unique and novel manufacturing techniques and configurations make it easier to manufacture than previous cable designs and eliminate the need for hermetic sealing of the cable at the cable ends due to the hydrophobic structure of the SiO2 braided core used. Therefore, traditional termination shapes and connectors can be used to terminate the cable of the present invention.

[0012] The dielectric withstand voltage (DWV) of the inventive cable is addressed and improved by laminating the braided core to the lower layer braided component, thereby offsetting the gaps in the braided lower layer. The cable matches the DWV parameters and levels of a similarly sized cable with a traditional extruded core. Also, the voltage standing wave ratio (VSWR) performance is an exception for the inventive cable, while maintaining the desired insertion loss characteristics. Additionally, the inventive cable maintains the desired phase vs. temperature characteristics consistent with a traditional SiO2 extruded core, without the disadvantages of a brittle core.

[0013] 1 is a perspective view, partially in section, showing components of a coaxial cable in accordance with one embodiment of the present invention. Specifically, cable 10 incorporates a center conductor 12, a braided dielectric core layer 14, an outer conductor layer 16, a reinforcement layer 18, and a jacket layer 20. The center conductor may be of any suitable conductive material or metal, such as copper or other suitable materials and metals conventionally utilized to conduct electrical signals. Center conductor 12 may be a solid or stranded conductor.

[0014] According to one feature of the invention, the dielectric core layer 14 is a braided core layer formed utilizing braided fibers made of silicon dioxide (SiO2). To form the braided core layer 14, the fibers are braided around the center conductor 12. More specifically, to form the core layer 14, one or more layers of SiO2 fibers are braided around the center conductor to provide a desired outer diameter for a cable 10 of a particular size and electrical characteristics. According to one feature of the invention, the braided core layer 14 is configured to provide a flexible SiO2 dielectric layer while providing coverage over the center conductor 12 in a manner that eliminates a direct line of sight between the center conductor 12 and the outer conductor layer or conductor 16. In that manner, the cable 10 maintains the desired dielectric withstand voltage (DWV) characteristics and avoids potential DWV breakdown issues.

[0015] According to one aspect of the present invention, the braid is formed utilizing fibers that are in a molten, non-porous, amorphous form of SiO2, which is hydrophobic. That is, the braided SiO2 core layer 14 is not likely to absorb significant moisture. The braided SiO2 core layer 14 can thus achieve greater flexibility and can be implemented in combination with a flexible outer conductor layer 16, such that the cable 10 can be utilized in a traditional flexible coaxial cable configuration.

[0016] For example, in one embodiment of the present invention as illustrated in FIG. 1, the outer conductor layer 16 is a wound layer, such as a layer of spirally wrapped tape or foil, which can be used to achieve improved flexibility for the cable 10. However, in such a spirally wrapped layer, there are openings in the outer conductor layer 16. Thus, the nature of the braided SiO2 core layer 14 allows the use of the wound outer conductor layer 16 without significant moisture issues. By combining both the braided SiO2 core layer 14 and the wound outer conductor layer 16, such as a spirally wrapped tape, the cable 10 can achieve a very flexible cable with all the benefits of using SiO2, without the problems of traditional brittle extruded SiO2 cores, as in previous cable solutions. Furthermore, the cable 10 does not need to be hermetically sealed at the connector interface. Therefore, the cable 10 and its design can be provided as a solution to replace traditional flat phase FEP / PFA shaped core designs.

[0017] In the embodiment of cable 10 illustrated in FIG. 1, the outer conductor layer 16 is formed of a wrapped tape or foil that is wrapped in a helical overlapping manner to achieve complete coverage over the braided core layer 14 for the desired electrical properties of the cable. For example, the overlap percentage of the wraps to form the layers may range from 35% to 50% overlap. The wrapped outer conductor is formed from a suitable conductive tape / foil material, such as including one or more metal layers. In one embodiment of the present invention, the outer conductor is made using two metal materials to form a tape or foil. For example, copper is utilized as one tape layer material and stainless steel is utilized as another tangential tape layer material on the copper side. The copper facing layer faces inward in the wrap toward the center conductor 12, and the stainless steel is disposed on the outside of the tape layer. In that manner, the outer conductor 16 achieves high electrical connectivity characteristics for the internal electrical circuitry of the cable 10, while still achieving strong corrosion resistance to the external environment outside the outer conductor layer 16. In another embodiment, the tape can use a layer of silver over a layer of copper. Alternatively, silver and copper can be woven into a braid to form the outer conductor 16. In another embodiment of the invention, a carbon tape can be implemented on the outside of the braided SiO2 core layer. Still further, as discussed herein, a semi-rigid outer conductor, such as a copper or aluminum tube, can be used as the outer conductor for the semi-rigid cable.

[0018] In one embodiment, an outer strength layer 18 may be utilized to complete the cable configuration 10. For example, the outer strength layer 18 may be a braided layer utilizing fibers, such as Kevlar fibers or other aramid fibers, to provide protection and high tensile strength to the cable. Other materials for forming the strength layer 18 may include glass fibers braided with other composite fibers or aramid fibers, such as Kevlar, nylon, and others. The present invention is not limited with respect to the formation of the strength layer 18.

[0019] Finally, one or more outer jacket layers 20 may be utilized to complete the cable construction of cable 10. Such jacket layers are conventionally known and may be made of a number of different materials, such as FEP, TEFZEL, PFA, etc. The composition of jacket layer 20 is also not limiting with respect to the present invention.

[0020] FIG. 2 illustrates a cross-sectional view of cable 10 showing the various layers of center conductor 12 and braided SiO2 core layer 14. The relative thicknesses of the various layers are shown for illustrative purposes only. FIG. 2 does not reflect the actual layers and their thickness relative to each other. Those skilled in the art will understand that the thicknesses of center conductor 12 and braided SiO2 core layer 14, outer conductor layer 16, and other remaining layers 18, 20 will vary depending on the desired electrical and physical properties of the cable.

[0021] 3 and 4 illustrate an alternative embodiment of the present invention in which the braided SiO2 core layer of the cable incorporates multiple layers on top of each other to build up the overall braided SiO2 core layer to a desired thickness. Such a unique configuration provides overlapping properties so that the braided core layer has a desired thickness and line-of-sight distance properties between the outer conductor layer and the center conductor are addressed to resolve any potential DMW yield issues. More specifically, FIG. 3 incorporates a center conductor 42, a braided SiO2 core layer 44, an outer conductor layer 52, one or more reinforcing layers 54, and one or more jacket layers 56. As shown in FIG. 3, the braided SiO2 core layer is made of multiple braided sublayers 46, 48, 50, each braided over the center connector 42 and previous braided sublayers to form an overall braided SiO2 core layer 44 of a particular thickness or outer diameter. According to one aspect of the present invention, each of the braided sub-layers 46, 48, 50 can be braided utilizing different braiding parameters, so that each layer has slightly different braiding characteristics than the previous sub-layer. In that manner, the sub-layers 46, 48, and 50 of the braided SiO2 core cable 44 can be tailored to achieve the desired physical and electrical properties of the cable 40. For example, the multiple stacking of braided sub-layers provided by the braided SiO2 core layer 44 provides greater coverage for improved DWV performance.

[0022] In one embodiment of the present invention, SiO2 fibers in the form of yarn are woven into multiple layers covering the central conductor. One suitable fiber material is Quartzel vegetable fiber available from St. Gobain Quartz USA, Louisville, Kentucky. More specifically, a Quartzel yarn of size QS1318 is utilized, having a US Customary System grade of 300 2 / 4 QS 13 4Z 3.8 S yarn, consisting of multiple 9 micron fibers and having 4 plies of 2 strands of filament twisted together to produce a nominal linear density yarn of 133 tex.

[0023] In constructing and using the braid as a braided SiO2 dielectric layer in accordance with the present invention, one end of the fiber is used per bobbin for each of the three layers, as shown in Figures 3 and 4. In one embodiment, the bobbins used are NEB Fine No. 2 wire bobbins at 2.75 inch traverse, each bobbin holding 120 grams of material. To braid the first layer 46 over the center conductor, a 16-carrier NED Butt braiding machine is run at half load; that is, four carriers run in one direction and four run in the other direction, with all carriers equally spaced. An over braid is applied to the center conductor 42 at 25 picks (±1) per inch. The outside diameter after application of the first layer 46 is 0.060 inches (±0.002''). Next, to form layer 48, the braided SiO2 yarn is applied using a similar 16-carrier NEB Butt braider, again operating at half load, with four carriers operating in one direction and four in the other, all equally spaced. Layer 48 is applied as an overbraid to layer 46 in a 20 picks per inch (±1) configuration. This adds to the outside diameter, increasing the outside diameter to approximately 0.075 inches (±0.002''). Finally, layer 50 is applied on a similar 12-carrier NEB Butt braider. However, for layer 50, the operator operates all 12 carriers used at full load to form an overbraid layer that is applied to the two previous layers 46, 48 in a 20 picks per inch (±1) configuration. This results in an outside diameter of 0.090 inches (±0.002'') for the braided core layer 44. Thereafter, once the braided core layer 44 having multiple sub-layers 46, 48, 50 is formed, the outer conductor can be formed over the core. Depending on the final cable design, such as for a flexible cable or a semi-rigid cable or a rigid cable, different outer conductor configurations may be implemented.

[0024] In an embodiment of the flexible cable of the present invention, referring to FIG. 3, the outer conductor layer 52 may incorporate a wrapped tape layer. In one embodiment, a foil tape, such as a copper / stainless steel tape as discussed herein, may be used. The tape may be spirally wrapped as shown in FIG. 3 to form the outer conductor. A reinforcing layer 54 is then braided or otherwise applied over the outer conductor, and a jacket 56 is extruded or otherwise applied to the reinforcing layer 54 to complete the cable construction. The materials of the outer conductor 52, reinforcing layer 54, and jacket 56 may be similar to those mentioned with respect to embodiment 10 of FIGS. 1 and 2.

[0025] Figure 4 illustrates a cross-sectional view of embodiment 40 of the cable of the present invention illustrated in Figure 3. For illustrative purposes only, braided sublayers 46, 48, and 50 are illustrated to show their relative positions within the braided SiO2 core layer and their overall thickness versus the thickness of additional layers 52, 54, 56, without any particular relative dimensional configuration being implied or limiting in the present invention.

[0026] In the wrapped outer conductor configuration of Figures 1 and 3, the tape may be helically wrapped, as noted, with an overlap ranging from 35% to 50% overlap to form a conductor layer having a thickness of 0.001 to 0.012 inches, giving the cable a total outer diameter of approximately 0.098 inches. The reinforcing layer 54 may have a relative thickness of 0.001 to 0.012 inches, giving that layer an outer diameter of 0.110 inches. Finally, the jacket layer 56 may have a thickness of 0.001 to 0.022 inches, giving the cable a total diameter of approximately 0.130 inches. Of course, those skilled in the art will appreciate that cables employing the present invention may be constructed in a number of different dimensions to achieve the desired impedance and other electrical characteristics.

[0027] In one embodiment, Quartzel yarn is illustrated, however the invention is not limited to that particular brand of SiO2 fiber. Other suitable SiO2 yarns may be utilized to form the braided SiO2 core layer 14, 44, or 64 as disclosed herein.

[0028] 5 and 6 illustrate yet another alternative embodiment of the present invention for a rigid or semi-rigid design. The cable 60 implements a braided SiO2 core layer with multiple layers on top of each other, building up the overall braided SiO2 core layer to a desired thickness similar to the embodiment of FIG. 3, FIG. 4. More specifically, FIG. 5 incorporates a center conductor 62, a braided SiO2 core layer 64, and an outer conductor layer 80 that can be generally formed to be rigid or semi-rigid. For example, the outer conductor can be a copper tube into which the center conductor 62 and braided core 64 are inserted. In an alternative embodiment, the outer conductor layer can be a semi-rigid layer with an inner material of copper and an outer material of stainless steel. As shown in FIG. 5, the braided SiO2 core layer can be made of multiple braided sublayers 66, 68, 70, each braided over the center connector 62 and previous braided sublayers to form the overall braided SiO2 core layer 64 of a particular thickness or outer diameter. As mentioned, each braided sublayer can be braided utilizing different braiding parameters to achieve the desired coverage over the center conductor for the desired physical and electrical properties of the cable, so that each layer has slightly different braiding properties than the previous sublayer. The braided core 64 can be formed as discussed herein for the embodiments of Figures 3 and 4. In such rigid or semi-rigid configurations, the reinforcing layer and outer jacket are not implemented. As is known in semi-rigid cable constructions, a semi-rigid outer conductor 80, such as a semi-rigid conductive tube formed of copper or aluminum, or copper and stainless steel, forms the outer conductor element, and the center conductor and braided dielectric core layer can be inserted inside the semi-rigid conductive tube to complete the cable. The semi-rigid embodiment will have the desired properties of the flexible embodiment using a braided SiO2 dielectric core layer.

[0029] While the present invention has been illustrated by the description of various embodiments, and these embodiments have been described in a certain degree of detail, it is not the intention of the inventors to restrict or in any way limit the scope of the appended claims to such details. Accordingly, further advantages and modifications will readily occur to those skilled in the art. The various features of the present invention may be used alone or in any combination, depending on the needs and preferences of the user. [Explanation of symbols]

[0030] 10 Cable 12 Center conductor 14 Braided dielectric core layer, dielectric core layer, braided core layer, braided SiO2 core layer 16 Outer conductor layer 18 reinforcement layer 20 Jacket layer 40 Cable 42 Center conductor, center connector 44 Braided SiO2 core layer, braided core layer 46 Braided lower layer, first layer 48 Braided lower layer 50 Braided Lower Layer 52 Outer conductor layer 54 Reinforcement layer 56 Jacket layer 60 Cable 62 Center conductor, center connector 64 Braided SiO2 core layer, braided core 66 Braided lower layer 68 Braid lower layer 70 Braided lower layer 80 Outer conductor layer

Claims

1. A central conductor; a dielectric core layer, comprising at least one layer formed of silicon dioxide fibers; a dielectric core layer, the silicon dioxide fibers being braided around the central conductor to form a braided dielectric core layer over the central conductor; an outer conductor layer formed over the braided dielectric core layer; A cable comprising:

2. The cable of claim 1 , further comprising a strength member layer formed over said outer conductor layer.

3. The cable of claim 2 , further comprising a jacket layer formed over said strength member layer.

4. 10. The cable of claim 1, wherein said braided dielectric core layer includes a plurality of sub-layers formed from silicon dioxide fibers, said sub-layers being continuously braided over said central conductor to form said braided dielectric core layer.

5. 5. The cable of claim 4, wherein at least two of the sub-layers of silicon dioxide fibers are braided using different braiding parameters to provide improved coverage of the braided dielectric core layer over the center conductor.

6. 5. The cable of claim 4, wherein the braided dielectric core layer comprises at least three sub-layers of silicon dioxide fibers, each of the at least three sub-layers being braided using different braiding parameters to provide improved coverage over the center conductor.

7. 10. The cable of claim 1, wherein the outer conductor layer formed over the braided core layer comprises a conductive tape wrapped around the braided dielectric core layer.

8. 8. The cable of claim 7, wherein the conductive tape comprises at least one of layers of copper and stainless steel.

9. 8. The cable of claim 7, wherein the conductive tape has a layer of copper on one side and a layer of stainless steel on an opposite side to the copper layer, the conductive tape being wrapped around the braided dielectric core layer with the copper layer facing the center conductor.

10. 2. The cable of claim 1, wherein the outer conductor layer formed over the braided core layer comprises a semi-rigid conductive tube, the center conductor and the braided dielectric core layer being inserted inside the semi-rigid conductive tube.

11. providing a central conductor; braiding at least one layer of silicon dioxide fibers about an outer surface of the central conductor to form a braided dielectric core layer over the central conductor; forming an outer conductor layer over the braided core layer to form a cable; A method of forming a cable comprising:

12. The method of claim 11 , further comprising forming a strength member layer over the outer conductor layer.

13. The method of claim 12 , further comprising forming a jacket layer over the strength member layer.

14. The method of claim 1 , further comprising the step of continuously braiding a plurality of sub-layers of silicon dioxide fibers over the central conductor to form the braided dielectric core layer.

15. 15. The method of claim 14, further comprising braiding at least two of the sub-layers of silicon dioxide fibers using different braiding parameters to achieve improved coverage of the braided dielectric core layer over the center conductor.

16. 15. The method of claim 14, further comprising braiding at least three sub-layers of silicon dioxide fibers over the central conductor, each of the at least three sub-layers being braided using different braiding parameters to provide improved coverage of the braided dielectric core layer over the central conductor.

17. The method of claim 11 , wherein forming an outer conductor layer over the braided dielectric core layer comprises wrapping a conductive tape around the braided dielectric core layer.

18. The method of claim 17 , wherein the conductive tape comprises at least one of a layer of copper and a layer of stainless steel.

19. 20. The method of claim 17, wherein the conductive tape has a layer of copper on one side and a layer of stainless steel on an opposite side to the copper layer, the method further comprising wrapping the conductive tape around the braided dielectric core layer with the copper layer facing the center conductor.

20. 12. The method of claim 11 , wherein the outer conductor layer formed over the braided core layer comprises a semi-rigid conductive tube, the method further comprising inserting the central conductor and the braided dielectric core layer inside the semi-rigid conductive tube.

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