A low-loss flexible coaxial cable and a method for manufacturing the same

Abstract

The present invention provides a low-loss flexible coaxial cable and a manufacturing method thereof, belonging to the field of cable technology. The coaxial cable comprises an inner conductor, a dielectric layer, a shielding layer and a sheath layer which are coaxially arranged in sequence, wherein the dielectric layer comprises a cylindrical inner layer and a spiral layer, the spiral layer is a spiral structure, the outer circumferential surface of the cylindrical inner layer is provided with a spiral groove matching the spiral structure, the depth of the spiral structure sunk into the spiral groove is less than half of the wire diameter of the spiral structure, the dielectric layer also comprises an outer pressure layer located outside the spiral layer, the outer pressure layer is used to provide a preset force to hold the spiral layer tightly to the cylindrical inner layer. The present invention also provides a manufacturing method for the above-mentioned coaxial cable. The coaxial cable of the present invention can have both low loss and flexibility.

Description

Technical Field

[0001] The present application relates to the field of cable technology, and in particular to a low-loss flexible coaxial cable and a manufacturing method thereof. Background Art

[0002] In order to ensure timely communication over a large area in open outdoor areas (such as some emergency communications), higher requirements are placed on the loss and flexibility of antenna feed lines.

[0003] The transmission loss of the feeder includes resistance loss, dielectric loss, radiation loss, shielding loss, etc. Among them, dielectric loss refers to the loss of the dielectric layer of the feeder. The electric field causes polarization effect in the dielectric layer, resulting in energy loss. The dielectric constant and dielectric loss factor of the dielectric material are the key parameters affecting the dielectric loss. In order to reduce dielectric loss, the prior art improves the uniformity of dielectric materials by selecting dielectric materials with lower dielectric loss factors, and uses foaming materials to further reduce the equivalent dielectric constant. In other words, in order to reduce the transmission loss of the dielectric layer, the prior art usually improves the design of the material itself, but these improvements often cannot take into account the flexibility of the dielectric layer. For example, when using materials with lower dielectric loss factors, such as polytetrafluoroethylene (PTFE), the molecular structure of these materials is stronger to improve electrical performance, but it may limit its flexibility. Therefore, the existing method of reducing dielectric loss by improving materials cannot effectively take into account flexibility. Summary of the invention

[0004] An object of the first aspect of the present invention is to provide a coaxial cable that can achieve both low loss and flexibility.

[0005] Another object of the present invention is to ensure the stability of cable performance during long-term use.

[0006] An object of the second aspect of the present invention is to provide a method for manufacturing the above-mentioned coaxial cable.

[0007] An embodiment of the present invention provides a low-loss flexible coaxial cable, comprising an inner conductor, a dielectric layer, a shielding layer and a sheath layer coaxially arranged in sequence, wherein the dielectric layer comprises a cylindrical inner layer and a spiral layer, the spiral layer is a spiral structure, the outer circumferential surface of the cylindrical inner layer is provided with a spiral groove matching the spiral structure, the depth of the spiral structure sunk into the spiral groove is less than half of the wire diameter of the spiral structure, the dielectric layer also comprises an outer pressure layer located outside the spiral layer, the outer pressure layer is used to provide a preset force to hold the spiral layer tightly to the cylindrical inner layer.

[0008] Optionally, the cylindrical inner layer and the spiral layer are made of the same target material, and the outer pressure layer is made of a foamed material of the target material.

[0009] Optionally, the target material is polytetrafluoroethylene, polyethylene, polyvinyl chloride or fluorinated ethylene propylene.

[0010] Optionally, the thickness of the inner layer of the cylinder, the wire diameter of the spiral layer and the thickness of the outer pressure layer decrease in sequence.

[0011] Optionally, the thickness of the inner layer of the cylinder, the wire diameter of the spiral layer, the pitch of the spiral layer, the thickness of the outer pressure layer, the depth of the spiral groove, and the foaming ratio of the outer pressure layer are determined according to design target values, and the design target values ​​include the bending radius threshold and loss threshold of the coaxial cable.

[0012] Optionally, the external pressure layer is formed on the outer peripheral sides of the cylindrical inner layer and the spiral layer by an extrusion process, so that the external pressure layer contacts the outer peripheral surface of the cylindrical inner layer and presses the spiral layer.

[0013] Optionally, a difference between an equivalent dielectric constant of a mixed region of the external pressure layer and the helical layer and a dielectric constant of the external pressure layer is smaller than a preset value.

[0014] In particular, an embodiment of the present invention further provides a method for manufacturing the above-mentioned coaxial cable, comprising:

[0015] forming a first dielectric structure on the outer peripheral side of the inner conductor;

[0016] Processing the spiral groove on the outer circumference of the first dielectric structure to form the inner layer of the cylinder;

[0017] Winding a preformed second dielectric wire in the spiral groove of the inner layer of the cylinder to form the spiral layer;

[0018] Forming an outer pressure layer on the outer peripheral side of the spiral layer by an extrusion molding process;

[0019] The shield layer and the sheath layer are sequentially formed on the outer peripheral side of the helical layer.

[0020] According to the first aspect of the present invention, the coaxial cable is configured as a multilayer structure including a cylindrical inner layer and a spiral layer. The spiral layer and the layered design of the spiral structure can make the dielectric layer have better flexibility. In addition, the configuration of the cylindrical inner layer and the spiral layer in this embodiment can gradually reduce the effective dielectric constant of the dielectric layer in the direction from the inside to the outside. The smooth transition of the effective dielectric constant helps to reduce reflections and standing wave fields in signal transmission, thereby reducing signal loss. Furthermore, the outer surface of the cylindrical inner layer is provided with a spiral groove matching the spiral layer, which helps to establish a smoother contact surface between the cylindrical inner layer and the spiral layer, avoids large impedance differences between the interfaces, and thus reduces losses caused by changes in the electric field. The spiral design of the spiral layer makes the electric field distribution more uniform, which helps to reduce electric field concentration and energy loss (especially in high-frequency transmission).

[0021] According to the second aspect of the present invention, the outermost side of the dielectric layer of the coaxial cable also includes an outer pressure layer, which is used to press the spiral layer against the inner layer of the cylinder. In this way, when the cable is deformed during use, the spiral layer is not easy to fall out of the spiral groove, and the spiral layer is always kept in close contact with the inner layer of the cylinder. This can reduce signal loss and improve the transmission performance of the cable when the cable is bent or deformed during long-term use.

[0022] Furthermore, the cylindrical inner layer and the spiral layer are made of the same material, and the outer pressure layer is made of a foamed material of the spiral layer material, which can ensure that the effective dielectric constant of the dielectric layer decreases from the inside to the outside.

[0023] Furthermore, the inner layer of the cylinder serves as the main supporting layer of the dielectric layer, the spiral layer serves as the deformation layer, and the outer pressure layer serves only as a compression layer and may have a smaller thickness, so that the dielectric layer as a whole forms a structural layer with flexible properties.

[0024] Furthermore, the coaxial cable has a better dielectric layer structure, which can have lower loss and be more flexible while maintaining the size of the cable.

[0025] Furthermore, by further optimizing the difference between the equivalent dielectric constant of the mixed area of ​​the outer pressure layer and the helical layer and the dielectric constant of the outer pressure layer, it is beneficial to reduce the overall transmission loss of the cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A partial cross-sectional view of a coaxial cable according to an embodiment of the present invention;

[0027] Figure 2 is a schematic structural diagram of a coaxial cable according to another embodiment of the present invention;

[0028] Figure 3 for Figure 2 Schematic diagram of the exploded dielectric layer of the coaxial cable;

[0029] Figure 4 for Figure 2 A partial cross-sectional view of a coaxial cable;

[0030] Figure 5 for Figure 4 A partial enlarged view of the middle A;

[0031] Figure 6 is a flow chart of a method for manufacturing a coaxial cable according to one embodiment of the present invention;

[0032] Reference numerals:

[0033] 100-coaxial cable, 10-inner conductor, 20-dielectric layer, 201-gap, 21-cylindrical inner layer, 211-spiral groove, 22-spiral layer, 23-outer pressure layer, 30-shielding layer, 40-jacket layer. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0035] It should be noted that when a component is referred to as being "fixed to" or "disposed on" another component, it may be directly on the other component or there may also be a central component. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may be a central component at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in the specification of this application are for illustrative purposes only and do not represent the only implementation method.

[0036] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0037] In the present application, unless otherwise clearly specified and limited, a first feature being “above” or “below” a second feature may mean that the first feature is directly in contact with the second feature, or the first feature and the second feature are in contact indirectly through an intermediate medium. Moreover, a first feature being “above”, “above”, or “above” a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being “below”, “below”, or “below” a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0038] Unless otherwise defined, all technical and scientific terms used in the specification of this application have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used in the specification of this application includes any and all combinations of one or more related listed items.

[0039] Figure 1 FIG. 1 is a partial cross-sectional view of a coaxial cable 100 according to an embodiment of the present invention. Figure 1 As shown, in one embodiment, the low-loss flexible coaxial cable 100 of the present invention includes an inner conductor 10, a dielectric layer 20, a shielding layer 30 and a sheath layer 40 which are coaxially arranged in sequence. The inner conductor 10 and the shielding layer 30 here can be made of common materials of coaxial cables for communication, such as copper, aluminum, etc., and the sheath layer 40 can be made of a material with a certain flexibility, such as polyvinyl chloride (PVC), thermoplastic polyurethane elastomer (TPU) or polyethylene (PE) and other common sheath materials. The dielectric layer 20 includes a cylindrical inner layer 21 and a spiral layer 22. The spiral layer 22 is a spiral structure, and the outer peripheral surface of the cylindrical inner layer 21 is provided with a spiral groove 211 matching the spiral structure. The depth D of the spiral layer 22 sunk into the spiral groove 211 is less than half of the wire diameter d of the spiral structure, that is, The center of the circular cross section of the spiral layer 22 is located outside the outer circumference of the cylindrical inner layer 21. The materials of the cylindrical inner layer 21 and the spiral layer 22 can be selected from the materials commonly used in the cable dielectric layer 20, such as polytetrafluoroethylene, polyethylene, polyvinyl chloride or fluorinated ethylene propylene, which are not limited here.

[0040] In this embodiment, the coaxial cable is configured as a multilayer structure including a cylindrical inner layer 21 and a spiral layer 22. The spiral layer 22 of the spiral structure and the layered design can make the dielectric layer 20 have good flexibility. In addition, the configuration of the cylindrical inner layer 21 and the spiral layer 22 in this embodiment can gradually reduce the effective dielectric constant of the dielectric layer 20 in the direction from the inside to the outside. The smooth transition of the effective dielectric constant helps to reduce reflection and standing wave fields in signal transmission, thereby reducing signal loss. Furthermore, the outer surface of the cylindrical inner layer 21 is provided with a spiral groove matching the spiral layer 22, which helps to establish a smoother contact surface between the cylindrical inner layer 21 and the spiral layer 22, avoiding a large impedance difference between the interfaces, thereby reducing the loss caused by the change of the electric field. The spiral design of the spiral layer 22 makes the electric field distribution more uniform, which helps to reduce electric field concentration and energy loss (especially in high-frequency transmission).

[0041] like Figure 1 As shown, since there is a gap 201 between two adjacent spiral lines of the spiral layer 22 in the axial direction, the equivalent dielectric constant of the dielectric layer 20 gradually decreases from the outer peripheral surface of the cylindrical inner layer 21 along the direction of arrow a (i.e., in the radial direction away from the axis OO' of the cylindrical inner layer 21). Along the direction of arrow a, the volume of the spiral layer 22 increases first and then decreases. If the volume of the spiral layer 22 exposed to the cylindrical inner layer 21 is directly reduced, it is equivalent to further reducing the equivalent dielectric constant, which will cause a large change in the equivalent dielectric constant, which is not conducive to the smooth transition of the effective dielectric constant. In this embodiment, the depth of the spiral groove 211 is set to be less than half of the wire diameter of the spiral layer 22, which can weaken the reduction of the equivalent dielectric constant at the interface, thereby facilitating the smooth transition of the effective dielectric constant and further reducing the loss.

[0042] Figure 2 FIG. 1 is a schematic structural diagram of a coaxial cable 100 according to another embodiment of the present invention. Figure 3 for Figure 2 FIG. 1 is an exploded schematic diagram of the dielectric layer 20 of the coaxial cable 100 . Figure 4 for Figure 2 A partial cross-sectional view of the coaxial cable 100 in FIG. Figure 5 for Figure 4 In another embodiment, as shown in FIG. Figure 2 See also Figure 3 and Figure 4The dielectric layer 20 also includes an external pressure layer 23 located outside the spiral layer 22. The external pressure layer 23 is used to provide a preset force to hold the spiral layer 22 tightly to the cylindrical inner layer 21. The external pressure layer 23 can be formed on the outer peripheral side of the cylindrical inner layer 21 and the spiral layer 22 by an extrusion process, so that the external pressure layer 23 contacts the outer peripheral surface of the cylindrical inner layer 21 and presses the spiral layer 22. In one embodiment, the cylindrical inner layer 21 and the spiral layer 22 are made of the same target material, and the external pressure layer 23 is made of a foaming material of the target material. The target material is a commonly used dielectric layer 20 material such as polytetrafluoroethylene, polyethylene, polyvinyl chloride or fluorinated ethylene propylene. For example, the cylindrical inner layer 21 and the spiral layer 22 are both made of polytetrafluoroethylene material, and the external pressure layer 23 is made of a foaming material of polytetrafluoroethylene.

[0043] The outermost side of the dielectric layer 20 of the coaxial cable 100 of this embodiment also includes an outer pressure layer 23, which is used to press the spiral layer 22 against the cylindrical inner layer 21, so that when the cable is deformed during use, the spiral layer 22 is not easy to fall out of the spiral groove 211, and the spiral layer 22 is always kept in close contact with the cylindrical inner layer 21, which can reduce signal loss and improve the transmission performance of the cable when the cable is bent or deformed during long-term use. In one embodiment, the outer pressure layer 23 is formed on the outer peripheral side of the cylindrical inner layer 21 and the spiral layer 22 by an extrusion process, so that the outer pressure layer 23 contacts the outer peripheral surface of the cylindrical inner layer 21 and presses the spiral layer 22.

[0044] Furthermore, the cylindrical inner layer 21 and the spiral layer 22 are made of the same material, and the outer pressure layer 23 is made of a foamed material of the spiral layer 22, which can ensure that the effective dielectric constant of the dielectric layer 20 decreases from the inside to the outside.

[0045] In a further embodiment, the thickness of the cylindrical inner layer 21, the wire diameter of the spiral layer 22 and the thickness of the outer pressure layer 23 decrease in sequence.

[0046] In this embodiment, the cylindrical inner layer 21 serves as the main supporting layer of the dielectric layer 20, the spiral layer 22 serves as the deformation layer, and the outer pressure layer 23 serves only as a compression layer and may have a smaller thickness, so that the dielectric layer 20 as a whole forms a structural layer with flexible properties.

[0047] In one embodiment, the thickness of the cylindrical inner layer 21 and the wire diameter d of the spiral layer 22 (see Figure 5 ), the pitch of the helical layer 22, the thickness of the outer pressure layer 23, the depth D of the helical groove 211 (see Figure 5 ), the foaming ratio of the outer pressure layer 23 is determined according to the design target value, and the design target value includes the bending radius threshold and loss threshold of the coaxial cable 100.

[0048] For a coaxial cable of a specific specification, it has a certain impedance. In order to make the cable have lower loss and be more flexible while keeping the cable size unchanged, the structure of the dielectric layer 20 can be optimized to determine a better structure of the dielectric layer 20.

[0049] In this embodiment, it is assumed that the coaxial cable has a certain impedance, and the total thickness of the dielectric layer 20 is kept at a fixed value. The structure of the dielectric layer 20 is optimized with the optimization goals of improving the flexibility of the coaxial cable 100 and reducing the loss of the dielectric layer 20.

[0050] First, the region including both the external pressure layer 23 and the spiral layer 22 is referred to as a mixed region (i.e. Figure 5 The area between the dotted line M and the dotted line N in the figure), since the materials of the external pressure layer 23 and the spiral layer 22 are different, their respective dielectric constants are different, so the equivalent dielectric constant of this area is determined by the volume proportion of the spiral layer 22 and the external pressure layer 23, thus, by changing the wire diameter and pitch of the spiral layer 22, the equivalent dielectric constant of the mixed area can be adjusted, thereby changing the transition smoothness of the effective dielectric constant of the entire dielectric layer 20, thereby changing the loss of the dielectric layer 20. Furthermore, the foaming ratio of the external pressure layer 23 is used to determine the effective dielectric constant of the external pressure layer 23, so adjusting the foaming ratio of the external pressure layer 23 will also affect the effective dielectric constant of the mixed area, thereby affecting the loss of the dielectric layer 20.

[0051] Secondly, the thickness distribution of the cylindrical inner layer 21, the spiral layer 22 and the outer pressure layer 23 of the dielectric layer 20 will affect the final flexibility of the dielectric layer 20. Since the total thickness of the dielectric layer 20 is a constant for a cable with a certain impedance and unchanged size, setting the thickness of the cylindrical inner layer 21 and the thickness of the outer pressure layer 23 as adjustment parameters can be used to change the overall flexibility of the dielectric layer 20.

[0052] Again, the depth of the spiral groove 211 determines the volume of the spiral layer 22 in the mixing area, and will also affect the effective dielectric constant of the mixing area. In addition, as mentioned above, the depth of the spiral groove 211 will also affect the change pattern of the spiral layer 22 in the radial direction away from the axis of the cylindrical inner layer 21, that is, it will also affect the smooth transition degree of the effective dielectric constant.

[0053] In summary, the thickness of the cylindrical inner layer 21, the wire diameter of the spiral layer 22, the pitch of the spiral layer 22, the thickness of the outer pressure layer 23, the depth of the spiral groove 211, and the foaming ratio of the outer pressure layer 23 are used as the optimization adjustment parameters, which can effectively achieve the purpose of adjusting the flexibility of the coaxial cable 100 and the loss of the dielectric layer 20, that is, the bending radius of the coaxial cable 100 is less than the bending radius threshold and the overall transmission loss is less than the loss threshold as the optimization target, thereby achieving the structural optimization purpose of taking into account flexibility and reducing losses. Here, since only the relevant parameters of the dielectric layer 20 of the cable are changed, the change in the overall transmission loss of the coaxial cable 100 directly reflects the change in the loss of the dielectric layer 20. The optimization process can be realized through simulation software or experiments. When performing transmission loss, a certain range of variation is given to each of the above-mentioned optimization adjustment parameters, and then the corresponding working frequency band is set. The optimization simulation is performed with the overall transmission loss of the coaxial cable 100 being less than the loss threshold as the optimization target. This process can be simulated by commonly used loss simulation software such as CST StudioSuite, ANSYS HFSS or COMSOL Multiphysics, and then the bending radius simulation is performed on each coaxial cable 100 that meets the required loss requirements, such as commonly used mechanical property simulation software such as ANSYS structural analysis module. The specific simulation process is a conventional method in this field and will not be repeated here.

[0054] The coaxial cable of this embodiment has a better dielectric layer 20 structure, and can have lower loss and be more flexible while keeping the size of the cable unchanged.

[0055] In a further embodiment, the optimization target also includes that the difference f between the equivalent dielectric constant of the mixed area of ​​the outer pressure layer 23 and the helical layer 22 and the dielectric constant of the outer pressure layer 23 is less than a preset value. That is, the optimization is performed with the bending radius of the coaxial cable 100 being less than the bending radius threshold, the loss of the dielectric layer 20 being less than the loss threshold, and the difference f as the optimization target.

[0056] like Figure 5 As shown, due to the junction of the mixed area and the outer pressure layer 23 (i.e. Figure 5 The dotted line N in the middle is the interface where the equivalent dielectric constant changes significantly. If the difference in the equivalent dielectric constants on both sides of the interface is too large, it will lead to stronger interface loss at the interface. Especially at high frequencies, this difference will make electromagnetic waves more likely to scatter, increase surface loss and volume loss, and ultimately lead to a decrease in the overall transmission efficiency of the cable. The foaming ratio of the outer pressure layer 23, the wire diameter and pitch of the spiral layer 22 in the above-mentioned optimization adjustment parameters will affect the above-mentioned difference f. Therefore, the purpose of optimizing the difference f can be achieved at the same time by changing the above-mentioned optimization adjustment parameters.

[0057] This embodiment further optimizes the difference between the equivalent dielectric constant of the mixed region of the outer pressure layer 23 and the helical layer 22 and the dielectric constant of the outer pressure layer 23 , which is beneficial to reducing the overall transmission loss of the cable.

[0058] Figure 6 FIG. 1 is a flow chart of a method for manufacturing a coaxial cable 100 according to an embodiment of the present invention. Figure 6 As shown, the present invention also provides a method for manufacturing the above coaxial cable 100, comprising:

[0059] Step S100, forming a first dielectric structure on the outer circumference of the inner conductor 10;

[0060] Step S200, processing a spiral groove 211 on the outer circumference of the first dielectric structure to form a cylindrical inner layer 21;

[0061] Step S300, winding a pre-formed second dielectric wire in the spiral groove 211 of the cylindrical inner layer 21 to form a spiral layer 22;

[0062] Step S400, forming an outer pressure layer 23 on the outer peripheral side of the spiral layer 22 by an extrusion molding process;

[0063] In step S500 , a shielding layer 30 and a sheath layer 40 are sequentially formed on the outer circumference of the helical layer 22 .

[0064] In step S100, the existing extrusion molding process can be used to form a first dielectric structure on the outside of the inner conductor 10, and then in step S200, a spiral groove 211 can be processed on the outer peripheral surface of the first dielectric structure by a tool. Here, the spiral groove 211 can be processed by controlling the first dielectric structure and the inner conductor 10 to move and rotate while the tool remains stationary.

[0065] In step S300, a linear second dielectric wire can be prepared first, that is, the material is processed into a filament through a conventional melt extrusion or wire drawing process, and then the second dielectric wire is wound into the spiral groove 211 of the cylindrical inner layer 21. Here, the cylindrical inner layer 21 can move using the movement and rotation parameters in step S200 to ensure the precise winding of the second dielectric wire.

[0066] In step S500, a shielding layer 30 is first formed on the outside of the external pressure layer 23, and then a TPU protective layer is formed on the outside of the shielding layer 30. This processing step can use the existing processing technology and will not be described in detail here.

[0067] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A low-loss flexible coaxial cable, characterized in that: The invention comprises an inner conductor, a dielectric layer, a shielding layer and a sheath layer which are coaxially arranged in sequence, wherein the dielectric layer comprises a cylindrical inner layer and a spiral layer, the spiral layer is a spiral structure, the outer peripheral surface of the cylindrical inner layer is provided with a spiral groove matching the spiral structure, the depth of the spiral structure sunk into the spiral groove is less than half of the wire diameter of the spiral structure, the dielectric layer also comprises an outer pressure layer located outside the spiral layer, the outer pressure layer is used to provide a preset force for holding the spiral layer tightly to the cylindrical inner layer, the cylindrical inner layer is formed by extruding a first dielectric structure on the outer peripheral side of the inner conductor, and then machining the spiral groove at the outer peripheral surface of the first dielectric structure, the difference between the equivalent dielectric constant of the mixed area of ​​the outer pressure layer and the dielectric constant of the outer pressure layer is less than a preset value, the cylindrical inner layer and the spiral layer are made of the same target material, the outer pressure layer is made of a foamed material of the target material, and the target material is polytetrafluoroethylene, polyethylene, polyvinyl chloride or fluorinated ethylene propylene.

2. The low-loss flexible coaxial cable according to claim 1, characterized in that: The thickness of the inner layer of the cylinder, the wire diameter of the spiral layer and the thickness of the outer pressure layer decrease in sequence.

3. The low-loss flexible coaxial cable according to claim 2, characterized in that: The thickness of the inner layer of the cylinder, the wire diameter of the spiral layer, the pitch of the spiral layer, the thickness of the outer pressure layer, the depth of the spiral groove, and the foaming ratio of the outer pressure layer are determined according to design target values, and the design target values ​​include the bending radius threshold and loss threshold of the coaxial cable.

4. The low-loss flexible coaxial cable according to claim 3, characterized in that: The external pressure layer is formed on the outer peripheral sides of the cylindrical inner layer and the spiral layer through an extrusion process, so that the external pressure layer contacts the outer peripheral surface of the cylindrical inner layer and presses the spiral layer.

5. A method for manufacturing a coaxial cable according to any one of claims 1 to 4, characterized in that: include: forming a first dielectric structure on the outer peripheral side of the inner conductor by extrusion molding; Processing the spiral groove on the outer circumference of the first dielectric structure to form the inner layer of the cylinder; Winding a preformed second dielectric wire in the spiral groove of the inner layer of the cylinder to form the spiral layer; Forming an outer pressure layer on the outer peripheral side of the spiral layer by an extrusion molding process; The shield layer and the sheath layer are sequentially formed on the outer peripheral side of the helical layer.

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