Coaxial cable with braided silica core

Abstract

The cable includes a central conductor and at least one layer formed of silica fibers braided around the central conductor to form a braided dielectric core layer on the central conductor. The outer conductor layer is formed on the braided silica core layer in the form of a wrapping tape or a semi-rigid conductor. In a flexible embodiment of the cable, one or more outer strength layers and sheaths may be applied on the outer conductor layer. In the embodiment of the invention, the dielectric core layer comprises a plurality of sub-layers of silicon dioxide fibers, and each sub-layer is sequentially woven on the previous sub-layer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 320,395 (pending), filed on March 16, 2022, the disclosure of which is incorporated herein by reference. Technical Field

[0003] 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 characteristics. Background Art

[0004] Existing coaxial cables need to remain temperature stable over a wide temperature range, so certain dielectric materials are used. Specifically, high temperature cables have been constructed using porous extruded amorphous or crystalline silica (SiO2) extruded around a center conductor as a dielectric core. The extruded core is typically joined into a semi-rigid cable using connectors that are welded and hermetically sealed. In such cable constructions using silica for the extruded core, the cable core tends to be hygroscopic and therefore easily absorbs moisture over time. This is a characteristic of the construction of the core material, but the hydroscopicity of the core material can have an adverse effect on the loss characteristics of such cables. In order to prevent the absorption of moisture, current high temperature coaxial cables require an airtight seal at the end of the cable to reduce moisture absorption and thereby prevent the loss characteristics of the cable from changing over time. The additional losses can have a serious impact on the overall electrical performance of the cable and attenuate the signals handled by the cable in an undesirable manner.

[0005] The silica material used in the construction of existing coaxial cables is first extruded. The extruded core is then loaded into a semi-rigid cable, and the outer cable jacket is sunk into the extruded core. Extruded silica cores tend to be brittle. Therefore, during the cable construction process, serious problems may occur when the semi-rigid cable is bent into its final position. Specifically, the brittle core may crack, which allows direct line of sight from the center conductor to the outer conductor in the cable. This defect can lead to dielectric breakdown failures, voltage standing wave ratio problems, and increased signal insertion loss, resulting in performance degradation. If the defect is severe, it can even lead to catastrophic failure of the coaxial cable. Summary of the invention

[0006] The cable comprises a center conductor and at least one layer formed of silica fibers, which are woven around the center conductor to form a braided dielectric core layer on the center conductor. The outer conductor layer is formed on the braided silica core layer. In certain embodiments of the cable, one or more outer strength layers and a sheath may be applied to the outer conductor layer. In a specific embodiment of the invention, the dielectric core layer comprises a plurality of sublayers of silica fibers, wherein each sublayer is woven on the previous sublayer in sequence. The sublayers may be woven using different braiding parameters to improve coverage on the center 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 center conductor and the braided dielectric core layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with the detailed description given below, serve to explain various aspects of the present invention.

[0008] Figure 1 is a partial cross-sectional perspective view of a cable according to an embodiment of the present invention.

[0009] Figure 2 yes Figure 1 Cross-section diagram of the cable.

[0010] Figure 3 is a partial cross-sectional perspective view of a cable according to another embodiment of the present invention.

[0011] Figure 4 yes Figure 2 Cross-section diagram of the cable.

[0012] Figure 5 is a partial cross-sectional perspective view of a cable according to another embodiment of the present invention.

[0013] Figure 6 yes Figure 5 Cross-section diagram of the cable.

[0014] It should be understood that the drawings are not necessarily drawn to scale, but rather present a somewhat simplified representation of various features of the basic principles of the invention. Specific design features of the sequence of operations disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes of the various illustrated components, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to other features for ease of viewing and clarity of understanding. In particular, for example, thin features may be thickened for clarity or illustration. DETAILED DESCRIPTION

[0015] The present invention relates to a coaxial cable construction that implements silica material as a dielectric, but implements a braided portion formed of braided silica fibers in the cable construction. That is, the present invention eliminates the silica extruded core and all of the physical and performance issues presented by such an extruded core as described above. More specifically, the present invention provides a coaxial cable that is constructed using a unique manufacturing process in which the silica material is braided onto the center conductor rather than extruded onto the conductor. Fibers of the silica material are formed into a braid having one or more braided layers. The outer conductor is then formed on the silica braid, and one or more strength layers and jacket layers may then be applied. By braiding the silica material onto the center conductor, the present invention presents a flexible cable and eliminates concerns about cracking of the extruded dielectric. In order to address the issue of coverage not being present in the extruded core, the dielectric is braided in layers so that coverage on the center conductor is provided in a manner that eliminates direct line of sight between the center conductor and the outer conductor.

[0016] According to one embodiment of the present invention, a hydrophobic form of silica fiber is used to make a cable core. Specifically, the fiber is made of a material that is initially a crystalline structured quartz material, which is then ground and melted so that in the final bonded form, the fiber becomes a non-porous amorphous silica fiber with hydrophobic properties. Because the silica braid and fiber material do not absorb a large amount of moisture, the braid can be used in traditional flexible coaxial cable constructions, such as using a spirally wrapped outer conductor, with open pores on the outer conductor layer to improve flexibility. In contrast to porous, hygroscopic extruded cores, the hydrophobicity of the braided silica core with a quartz-like structure allows for higher propagation speeds and lower losses because the core layer does not absorb moisture. By combining a braided silica core wire on a center conductor and a spirally wrapped outer conductor on a silica braid, an embodiment of a cable is provided that has all the temperature and performance advantages of silica, but the package is very flexible and does not have the brittleness and damage problems of an extruded core. The structure of the core material also has advantages in other cable constructions.

[0017] The cable of the present invention is capable of operating at high temperatures with a linear phase to temperature response. Due to the braided silica core, the cable has good phase stability and low losses under extreme temperatures and pressures. In addition, the cable provides higher speed signal propagation. The speed of propagation is increased as a result of the voids in the braid of the silica braided core. The unique, novel manufacturing method and construction make it easier to manufacture than previous cable designs, and due to the hydrophobic structure of the silica braided core used, the need for the cable to be hermetically sealed at its ends is eliminated. Therefore, conventional terminal styles and connectors can be used for termination of the innovative cable.

[0018] The innovative cable's dielectric withstand voltage (DWV) is addressed and improved by layering the braided core in sub-layer braid components. This offsets gaps in the braided sub-layers. The cable meets the DWV parameters and levels of similar sized cables utilizing conventional extruded cores. In addition, with the innovative cable, voltage standing wave ratio (VSWR) performance is excellent while maintaining ideal insertion loss characteristics. In addition, the innovative cable maintains ideal phase vs. temperature characteristics consistent with conventional silica extruded cores, but without the drawbacks of brittle cores.

[0019] Figure 1 1 is a partial cross-sectional perspective view showing those components of a coaxial cable according to one embodiment of the present invention. Specifically, the cable 10 includes a center conductor 12, a braided dielectric core layer 14, an outer conductor layer 16, a strength layer 18, and a jacket layer 20. The center conductor can be a suitable conductive material or metal, such as copper or other suitable materials and metals conventionally used to conduct electrical signals. The center conductor 12 can be a solid or stranded conductor.

[0020] In accordance with one feature of the present invention, the dielectric core 14 is a braided core made using braided fibers made of silica (SiO2). The fibers are braided around the center conductor 12 to form the braided core 14. More specifically, to form the core 14, one or more layers of silica fibers are braided around the center conductor to provide a desired outer diameter for the specific dimensions and electrical characteristics of the cable 10. In accordance with one feature of the present invention, the braided core 14 is configured to provide a flexible silica dielectric layer while providing coverage on the center conductor 12 in a manner that eliminates a direct line of sight between the center conductor 12 and the outer conductive layer or outer conductor 16. In this way, the cable 10 maintains ideal dielectric withstand voltage (DWV) characteristics and avoids potential DWV breakdown issues.

[0021] According to one aspect of the present invention, the braid is formed using fused, non-porous, amorphous, hydrophobic silica fibers. That is, the braided silica core 14 is unlikely to absorb significant amounts of water. Thus, the braided silica core 14 can provide greater flexibility and can be implemented in conjunction with the flexible outer conductor layer 16, allowing the cable 10 to be utilized in a conventional flexible coaxial cable configuration.

[0022] For example, in Figure 1In one embodiment of the present invention shown, the outer conductor layer 16 is a wrapping layer, such as a spirally wrapped tape or foil layer, which can be used to improve the flexibility of the cable 10. However, in such a spiral wrapping layer, openings are present in the outer conductor layer 16. Therefore, the properties of the braided silica core layer 14 allow the use of a wrapped outer conductor layer 16 without significant moisture issues. By combining the braided silica core layer 14 and the wrapped outer conductor layer 16 (such as a spirally wrapped tape), the cable 10 can provide a very flexible cable with all the advantages of using silica without the concerns of traditional brittle extruded silica cores as in previous cable solutions. In addition, the cable 10 does not require an airtight seal at the connector interface. Therefore, the cable 10 and its design can be provided as a solution to replace traditional flat phase FEP / PFA foam core designs.

[0023] exist Figure 1 In the embodiment of the cable 10 shown, the outer conductor layer 16 is formed by a wound tape or foil that is wound in a spiral overlapping manner to provide complete coverage on the braided core layer 14 for the desired electrical properties of the cable. For example, the overlap percentage of the wrap forming the layer can be in the range of 35%-50% overlap. The wrapped outer conductor is formed by 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 of two metal materials that form the tape or foil. For example, copper is used as a tape layer material, and stainless steel is used as another tangential tape layer material located on one side of the copper. The layer facing the copper faces inward in the wrap, toward the center conductor 12, and the stainless steel is located on the outside of the tape layer. In this way, the outer conductor 16 provides high electrical connection characteristics for the internal circuit of the cable 10, while providing strong corrosion resistance to the external environment on the outside of the outer conductor layer 16. In another embodiment, for the tape, a silver layer on the copper layer can be used for the tape. Alternatively, silver and copper can be sewn into the braid to form the outer conductor 16. In another embodiment of the present invention, the carbon tape may be implemented on the outside of the braided silica core layer. Additionally, as described herein, a semi-rigid outer conductor, such as a copper or aluminum tube, may be used as the outer conductor of the semi-rigid cable.

[0024] In one embodiment, to complete the cable construction 10, an outer strength layer 18 may be used. For example, the outer strength layer 18 may be a braided layer using fibers (such as Kevlar or other aramid fibers) to provide protection and high tensile strength to the cable. Other materials forming the strength layer 18 may include glass fibers interwoven with other composite or aramid fibers (such as Kevlar, nylon, etc.). Regarding the formation of the strength layer 18, the present invention is not limited thereto.

[0025] Finally, one or more outer jacket layers 20 may be employed to complete the cable construction of the cable 10. Such jacket layers are well known and may be made of a variety of different materials such as FEP, TEFZEL, PFA, etc. The composition of the jacket layer 20 is also not limited for purposes of the present invention.

[0026] Figure 2 A cross-sectional view of the cable 10 is shown, illustrating the various layers of the center conductor 12 and the braided silica core layer 14. The relative thickness of the various layers are shown for illustration purposes only. Figure 2 It does not reflect actual layers and layer thicknesses relative to one another. One of ordinary skill in the art will appreciate that the thickness of the center conductor 12 as well as the braided silica 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.

[0027] Figure 3 and Figure 4 An alternative embodiment of the present invention is shown in which the braided silica core layer of the cable comprises multiple layers, one layer stacked on top of the other to stack the entire braided silica core layer to a desired thickness. This unique construction provides stacking characteristics to allow the braided core layer to have a desired thickness while also addressing the line-of-sight distance characteristics between the outer conductor layer and the center conductor to address any potential DWV breakdown issues. More specifically, Figure 3 The system comprises a center conductor 42, a braided silica core layer 44, an outer conductive layer 52, one or more strength layers 54, and one or more jacket layers 56. Figure 3 As shown, the braided silica core is made of a plurality of braided sub-layers 46, 48, 50, each of which is braided on the center connector 42 and on the previous braided sub-layer to form an overall braided silica core 44 of a specific thickness or outer diameter. According to one aspect of the present invention, each braided sub-layer 46, 48, 50 can be braided using different braiding parameters so that the braiding characteristics of each layer are slightly different from the previous sub-layer. In this way, the sub-layers 46, 48 and 50 of the braided silica core cable 44 can be adjusted to achieve the desired physical and electrical characteristics of the cable 40. For example, the multiple braided sub-layers provided by the braided silica core 44 result in greater coverage to improve DWV performance.

[0028] In one embodiment of the invention, silica fibers in the form of yarn are sewn into multiple layers on the center conductor. One suitable fiber material is Quartzel plant fiber produced by St. Gobain Quartz USA of Louisville, Kentucky. More specifically, a Quartzel yarn of size QS1318 is used, which is composed of a plurality of 9 micron fibers and has the U.S. customary system designation 300 2 / 4QS13 4Z3.8S yarn, which has four layers of two-ply twisted filaments, providing a nominal linear density of 133 tex.

[0029] According to the present invention, for the braided structure and use as a braided silicon dioxide dielectric layer, such as Figure 3 and Figure 4 As shown, each coil of each layer in the three layers uses one end of the fiber. In one embodiment, the coil used is a NEB fine No. 2 coil with a transverse length of 2.75 inches, and each coil holds 120 grams of material. In order to braid the first layer 46 on the center conductor, a 16-carrier NED Butt braiding machine is run at half load. That is, four carriers run in one direction, four carriers run in the other direction, and all carriers are equally spaced. Overlay braiding is applied to the center conductor 42 using 25 needles per inch (+ / -1). When applying the first layer 46, the outer diameter is 0.060 inches (+ / -0.002 inches). Next, in order to form layer 48, a similar 16-carrier NEB Butt braiding machine is used, again running at half load, four carriers run in one direction, four carriers run in the other direction, and all carriers are equally spaced, thereby applying silica yarn. Layer 48 is applied to layer 46 as an overlay braid using 20 needles per inch (+ / -1) construction. This increases the outer diameter to approximately 0.075 inches (+ / - 0.002 inches). Finally, layer 50 is applied using a similar 12-carrier NEB Butt braiding machine. However, for layer 50, the operator is running at full capacity, with all 12 carriers used to form the superimposed braided layer applied to the first two layers 46 and 48 at a 20 stitches per inch (+ / - 1) configuration. This brings the outer diameter of the braided coil layer 44 to 0.090 inches (+ / - 0.002 inches). Thereafter, once the braided core layer 44 having multiple sub-layers 46, 48, 50 is formed, the outer conductor can be formed on the core material. Different outer conductor configurations can be implemented depending on the finished cable design, such as a flexible cable, a semi-rigid cable, or a rigid cable.

[0030] For the flexible cable embodiment of the present invention, refer to Figure 3, the outer conductor layer 52 may include a wrapping tape layer. In one embodiment, a foil tape such as the copper / stainless steel tape discussed herein may be used. The tape may be as Figure 3 The outer conductor 52 is then braided or otherwise applied with a strength layer 54, and a jacket 56 is extruded or otherwise applied to the strength layer 54 to complete the cable designation. The materials of the outer conductor 52, the strength layer 54, and the jacket 56 can be the same as those of the Figure 1 and Figure 2 The materials of embodiment 10 in are similar.

[0031] Figure 4 yes Figure 3 A cross-sectional view of an inventive cable embodiment 40 is shown. Braided sublayers 46, 48, and 50 are shown relative to each other within the braided silica core layer, and their total thickness compared to the thickness of additional layers 52, 54, and 56, for reference only, and the present invention is not intended to imply or limit a particular relative size configuration.

[0032] exist Figure 1 , Figure 3 In the configuration of the wrapped outer conductor, as previously described, the tape may be helically wrapped with an overlap ranging between 35%-50% to form a conductive layer having a thickness of 0.001-0.012 inches, providing an overall outer diameter of the cable of approximately 0.098 inches. The relative thickness of the strength layer 54 is 0.001-0.012 inches, providing an outer diameter of this layer of 0.110 inches. Finally, the jacket layer 56 has a thickness of 0.001-0.022 inches, providing an overall diameter of the cable of approximately 0.130 inches. Of course, it will be appreciated by those of ordinary skill in the art that a variety of different dimensional configurations may be utilized using the cables of the present invention to achieve desired impedance and other electrical characteristics.

[0033] Although Quartzel yarn is shown in one embodiment, the present invention is not limited to this particular brand of silica fiber. Other suitable silica yarns can be used to form the braided silica core layer 14, 44 or 64 disclosed herein.

[0034] Figure 5 and Figure 6 Another embodiment of the present invention is shown for a rigid or semi-rigid design. Figure 3-4 Similar to the embodiment of the present invention, the cable 60 is implemented with multiple layers of braided silica core layer, one layer is stacked on top of the other layer, and the entire braided silica core layer is stacked to a desired thickness. More specifically, Figure 5The invention comprises a central conductor 62, a braided silica core layer 64, and an outer conductive layer 80 which can be generally formed as rigid or semi-rigid. For example, the outer conductor can be a copper tube into which the central conductor 62 and the braided core 64 are inserted. In an alternative embodiment, the outer conductive layer can be a semi-rigid layer having an inner material of copper and an outer material of stainless steel. Figure 5 As shown, the braided silica core layer can be made of multiple braided sub-layers 66, 68, 70, each of which is braided on the center connector 62 and the previous braided sub-layer to form an overall braided silica core layer 64 of a specific thickness or outer diameter. As previously described, each braided sub-layer can be braided using different braiding parameters so that the braiding characteristics of each layer are slightly different from the previous sub-layer to achieve the ideal coverage on the center conductor and achieve the desired physical and electrical characteristics of the cable. The braided core 64 can be as Figure 3-4 The cable may be formed as discussed in the illustrated embodiment. In such a rigid or semi-rigid construction, the strength layer and outer jacket would not be implemented. A semi-rigid outer conductor 80, such as a semi-rigid conductive tube formed of copper or aluminum or copper and stainless steel, may form the outer conductor element, with the center conductor and braided dielectric core layer inserted into the semi-rigid conductive tube to complete the cable, as is known in semi-rigid cable construction. The semi-rigid embodiment will have the desired characteristics of a flexible embodiment using a braided silica dielectric core layer.

[0035] Although the present invention has been illustrated by the description of various embodiments, and although these embodiments have been described in some detail, it is not the intention of the inventors to restrict or in any way limit the scope of the appended claims to these details. Therefore, other advantages and modifications of the present invention will be readily apparent to those skilled in the art. The various features of the present invention may be used alone or in any combination according to the needs and preferences of the user.

Claims

1. A cable, comprising: Center conductor; a dielectric core layer, the dielectric core layer comprising at least one layer formed of silica fibers; The silica fibers are braided around the center conductor and form a braided dielectric core layer on the center conductor; An outer conductor layer is formed on the braided dielectric core layer.

2. The cable according to claim 1, further comprising a strength member layer formed on the outer conductor layer.

3. The cable according to claim 2, further comprising a jacket layer formed on the strength member layer.

4. The cable according to claim 1, wherein the braided dielectric core layer comprises a plurality of sub-layers formed of silica fibers, the sub-layers being sequentially braided on the center conductor to form the braided dielectric core layer.

5. The cable of claim 4, wherein at least two of the sub-layers of silica fibers are braided using different braiding parameters to improve coverage of the braided dielectric core layer on the center conductor.

6. The cable of claim 4, wherein the braided dielectric core layer comprises at least three sub-layers of silica fibers, each of the at least three sub-layers being braided using different braiding parameters to improve coverage on the center conductor.

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

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

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

10. The cable of claim 1, wherein the outer conductor layer formed on the braided core layer comprises a semi-rigid conductive tube, and the center conductor and the braided dielectric core layer are inserted into the semi-rigid conductive tube.

11. A method of forming a cable, comprising: Providing a center conductor; braiding at least one silica fiber around an outer surface of the center conductor to form a braided dielectric core layer on the center conductor; An outer conductor layer is formed on the braided core layer to form a cable.

12. The method of claim 11, further comprising forming a strength member layer on 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 sequentially braiding a plurality of sub-layers of silica fiber on the center conductor to form a braided dielectric core layer.

15. The method of claim 14, further comprising braiding at least two sub-layers of silica fiber using different braiding parameters to improve coverage of the braided dielectric core layer on the center conductor.

16. The method of claim 14, further comprising braiding at least three sub-layers of silica fiber on the center conductor, each of the at least three sub-layers being braided using different braiding parameters to improve coverage of the braided dielectric core layer on the center conductor.

17. The method of claim 11, wherein forming the outer conductor layer on the braided 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 stainless steel.

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

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

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