Radio frequency coaxial cable with low attenuation leakage

Abstract

The application relates to the technical field of radio frequency coaxial cables, in particular to a radio frequency coaxial cable with low attenuation leakage, which comprises a cable main body, the cable main body comprises an inner conductor and an outer conductor, the outer conductor is located at the outer circle of the inner conductor, and the inner conductor and the outer conductor comprise a first foaming layer and a second foaming layer; the roughness of the outer surface of the inner conductor in contact with the first foaming layer is less than 0.5 microns; the second foaming layer contains a first filler and a second filler with consistent components, the total addition ratio of the first filler and the second filler is not greater than 1%; the foaming degree of the first foaming layer is greater than that of the second foaming layer, the extrusion temperature corresponding to the first foaming layer is greater than that of the second foaming layer, the thickness of the first foaming layer is greater than that of the second foaming layer, and the thermal conductivity of the first foaming layer is less than that of the second foaming layer. Through the improvement of the foaming degree and the thermal conductivity of the insulating layer, the attenuation of the cable can be reduced while the electrical performance of the cable is maintained, and the signal propagation speed of the radio frequency coaxial cable is improved.

Description

Technical Field

[0001] This application relates to the field of radio frequency coaxial cable technology, and more particularly to a radio frequency coaxial cable with low attenuation leakage. Background Technology

[0002] Radio frequency coaxial cables are core components for transmitting high-frequency electrical signals and are widely used in communications, broadcasting, radar, medical equipment, and testing instruments. With the development of technologies such as 5G, the Internet of Things (IoT), and ultra-high-definition video, higher requirements are placed on cable performance: lower signal attenuation (Loss), higher signal transmission speed (Velocity of Propagation, Vp), and excellent mechanical stability and environmental reliability.

[0003] Current RF coaxial cables mainly improve attenuation strength through protective sleeves. Once the protective sleeve is damaged, attenuation and leakage of the cable will be unavoidable. Summary of the Invention

[0004] At least one aspect and advantage of this application will be set forth in part in the description which follows, or may be apparent from the description, or may be acquired by practicing the subject matter of this application.

[0005] According to a first aspect of this application, a radio frequency coaxial cable with low attenuation leakage is provided, comprising a cable body including an inner conductor and an outer conductor, the outer conductor being located on the outer ring of the inner conductor, and a first foam layer and a second foam layer being included between the inner conductor and the outer conductor;

[0006] The surface roughness of the outer surface where the inner conductor and the first foam layer contact is less than 0.5 micrometers;

[0007] The second foamed layer contains a first filler and a second filler with identical components, and the total addition ratio of the first filler and the second filler is not greater than 1%.

[0008] The degree of foaming of the first foam layer is greater than that of the second foam layer, and the extrusion temperature of the first foam layer is greater than that of the second foam layer. The thickness of the first foam layer is greater than that of the second foam layer, and the thermal conductivity of the first foam layer is less than that of the second foam layer.

[0009] According to one embodiment of this application, the first foaming layer is low-density polyethylene, and the foaming gas is carbon dioxide.

[0010] According to one embodiment of this application, the matrix of the second foam layer is a mixture of low-density polyethylene and high-density polyethylene, and the foaming gas of the second foam layer is nitrogen.

[0011] According to one embodiment of this application, the first filler and the second filler are non-metallic compounds.

[0012] According to one embodiment of this application, the first filler and the second filler are spherical modified boron nitride nanoparticles;

[0013] The D50 value of the first packing is greater than that of the second packing.

[0014] According to one embodiment of this application, the addition ratio of the first filler and the second filler is 3:1 to 5:1.

[0015] According to one embodiment of this application, the thermal conductivity of the second foam layer is 1.01-1.03 times that of the first foam layer.

[0016] According to one embodiment of this application, the outer conductor layer is formed by longitudinal wrapping of a smooth metal.

[0017] According to one embodiment of this application, the inner conductor is a copper-plated steel wire with an average surface roughness of 0.4-0.7 micrometers.

[0018] According to one embodiment of this application, the copper layer thickness on the surface of the steel wire is 15-20 micrometers.

[0019] This application improves the foaming degree and thermal conductivity of the insulation layer, thereby reducing cable attenuation and increasing the signal propagation speed of the RF coaxial cable while maintaining the electrical performance of the cable. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] Figure 1 This is a schematic diagram of the cross-sectional structure of a radio frequency coaxial cable with low attenuation leakage, provided as an embodiment of this application.

[0022] Reference numerals: 1-Inner conductor; 2-Outer conductor; 3-First foam layer; 4-Second foam layer; 100-Coaxial cable. Detailed Implementation

[0023] The content of this application will now be discussed with reference to several exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and thus implement the content of this application, and are not intended to imply any limitation on the scope of this application.

[0024] As used herein, the term "comprising" and its variations are to be interpreted as open-ended terms meaning "including but not limited to". The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment". The term "another embodiment" is to be interpreted as "at least one other embodiment". These terms are primarily used to better describe this application and its embodiments and are not intended to limit the indicated components to having a particular orientation, or being constructed and operated in a particular orientation. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. Furthermore, the terms "first", "second", etc., are primarily used to distinguish different components (the specific types may be the same or different) and are not intended to indicate or imply the relative importance and number of the indicated components. Unless otherwise stated, "a plurality of" means two or more.

[0025] According to one embodiment of this application, a radio frequency coaxial cable with low attenuation leakage is provided, such as... Figure 1 As shown, the low-attenuation leakage radio frequency coaxial cable 100 includes a cable body, which includes an inner conductor 1 and an outer conductor 2. The outer conductor is located on the outer ring of the inner conductor. A first foam layer 3 and a second foam layer 4 are included between the inner conductor and the outer conductor. The surface roughness of the outer surface where the inner conductor and the first foam layer contact is less than 0.5 micrometers. The second foam layer contains a first filler and a second filler with the same composition, and the total addition ratio of the first filler and the second filler is not greater than 1%. The foaming degree of the first foam layer is greater than that of the second foam layer, and the extrusion temperature corresponding to the first foam layer is greater than that of the second foam layer. The thickness of the first foam layer is greater than that of the second foam layer, and the thermal conductivity of the first foam layer is less than that of the second foam layer.

[0026] The first and second foamed layers of this application are designed with a gradient in foaming degree, which makes the dielectric constant of the inner first foamed layer lower. This helps to reduce signal attenuation, improve thermal insulation performance, optimize impedance characteristics, and improve flexibility and reduce weight. At the same time, the low roughness (less than 0.5 micrometers) of the first foamed layer ensures the flow of high-frequency current, further reduces the skin effect, and achieves the purpose of low attenuation and high signal transmission speed.

[0027] This application, by adding a first filler and a second filler of identical composition, can make the thermal conductivity of the second foamed layer slightly higher than that of the first foamed layer. On the one hand, this can improve the strength of the second foamed layer to better protect the first foamed layer; on the other hand, the addition of this filler, while increasing its thermal conductivity, will not increase its dielectric constant and loss factor, thus not affecting its electrical performance.

[0028] Increasing the filler content leads to an increase in the dielectric constant of the insulating material, resulting in increased signal attenuation. A total addition ratio of no more than 1% has minimal impact on the dielectric constant of the second foaming layer. This ensures that the overall insulation characteristics of the second foaming layer are not altered, and the electrical performance is not affected, guaranteeing stable dielectric properties of the insulation layer and preventing increased RF signal transmission loss. In this embodiment, the addition ratio of the first and second fillers is set to 0.5%, with a thermal conductivity exceeding 0.045 W / mK. Although this value is still relatively low, it is an improvement over the original foaming layer and helps to avoid affecting the foaming process. In some parallel experiments, adding more than 3% BN particles resulted in a reduction in cable impedance characteristics compared to adding 0.5% insulation, while maintaining essentially the same signal attenuation. Furthermore, the dielectric constant increased to 1.28, a 2% increase compared to this application, and the characteristic resistance decreased by 0.13 Ω to 48.95 Ω. Based on typical performance considerations, this application provides a coaxial cable with better electrical performance by reducing the BN addition ratio.

[0029] The first foaming layer with high foaming density has a lower thermal conductivity, resulting in slower heat transfer. However, the second foaming layer with low foaming density has a higher thermal conductivity. This allows the second foaming layer to work with the first foaming layer to form a heat dissipation gradient, thus dissipating the heat from the inner conductor and preventing signal attenuation in the first foaming layer.

[0030] This application increases the thickness of the first foaming layer with high foaming density, and its thickness is greater than that of the second foaming layer. The high thickness provides space for the uniform foaming of the first foaming layer, which can minimize attenuation and improve signal propagation speed.

[0031] The first foaming layer in this application uses a high foaming coefficient. A high foaming coefficient maintains the characteristic impedance stability of the coaxial cable, ensuring signal transmission quality. The high foaming degree reduces energy loss during signal transmission, which is crucial for the transmission of medium and high frequency signals, and also reduces dielectric loss. When used in conjunction with the foaming gas, it also maintains a stable dielectric constant.

[0032] The first foaming layer uses a higher extrusion temperature in this application, which makes it easier to form a fine, uniform, and closed-cell structure at high foaming temperatures. In practical applications, the first foaming layer can be foamed using carbon dioxide, and the second foaming layer can be foamed using nitrogen.

[0033] The typical process for preparing the foamed layer is as follows:

[0034] The matrix material and foaming gas (such as nitrogen or carbon dioxide) used to prepare the first foamed layer are injected into an extruder under high pressure. Then, by controlling the extrusion temperature and pressure, the molten plastic forms a uniform and dense closed-cell structure at high temperature, thereby achieving a high degree of foaming. This embodiment mainly involves the preparation process of the first and second foamed layers. The first foamed layer can be prepared using a 150°C low-temperature extrusion and nitrogen foaming process. Performance differences can be achieved by adjusting the foaming pressure (e.g., selecting 200 bar and optimizing according to actual performance) and fillers, while maintaining uniform process parameters for easy industrial mass production. The second foamed layer can be prepared using a 160°C low-temperature extrusion and carbon dioxide foaming process, with adjustments made to the foaming pressure (e.g., selecting 370 bar to 200 bar and optimizing according to actual performance).

[0035] If the amount of foaming gas is large during the above process, the dispersion becomes more uncontrollable, which in turn affects the final performance.

[0036] To reduce the risk of cell rupture during the foaming process and to ensure that the cells are small, uniform, and closed, the degree of foaming was adjusted and controlled below 85%, preferably below 82%, and especially within the range of 60-80%. Within this range, the drawback of increased cost per unit introduced by more stringent processing techniques is avoided.

[0037] Specifically, the inner conductor is typically made of a highly conductive metal such as copper or aluminum. Due to the skin effect, current flows on the surface of the conductor; therefore, the inner conductor can be made of commonly used copper wire or copper-clad aluminum wire. To reduce the weight of the cable, a copper tube can also be used as the inner conductor, thus reducing cable weight and cost while maintaining conductivity. The inner conductor serves as the carrier for signal transmission, and signal current flows within it.

[0038] Specifically, the process of preparing the inner conductor may include: drawing a copper rod through a wire drawing machine step by step to achieve the radius required by the design; and then performing an annealing treatment to obtain the inner conductor used to prepare the coaxial cable.

[0039] Specifically, the first foamed layer can be prepared directly on the surface of the inner conductor, or the insulating material can be foamed by directly contacting the inner skin layer with the inner conductor. This application embodiment uses the method of directly foaming the insulating material on the surface of the inner conductor to form the first foamed layer.

[0040] In some embodiments, the inner skin layer can be a polyethylene insulation layer, which is prepared by extrusion at a high temperature (220°C); then a first foaming layer is prepared on the inner skin layer; or the inner skin layer can be a separate structure tightly wrapped around the inner skin layer; during preparation, appropriate materials can be selected according to the required performance requirements of the inner skin layer. For example, low-density polyethylene and EVA (ethylene-vinyl acetate copolymer) adhesive are mixed in a certain proportion, and then heated to 120-195°C to make the material reach an extrudable molten state. Then, the heated and molten inner skin layer material is uniformly extruded onto the surface of the inner conductor through an extruder screw. The parameters of the extruder, such as extrusion speed and temperature, are controlled to ensure that the thickness of the inner skin layer is uniform and meets the requirements. Generally, the thickness of the inner skin layer can be controlled at 0.05-0.1 mm. After the inner skin layer is extruded, it is cooled by air cooling or other methods to quickly solidify and shape the inner skin layer, forming a stable structure. At this point, the preparation of the inner conductor with the inner skin layer is completed. Then, it is processed according to the preparation process of the polyethylene insulation layer. Preparing the first foaming layer on the inner sheath avoids major modifications to existing processes and preserves its original performance to the greatest extent. Specifically, the outer conductor typically employs a seamless corrugated copper tube, longitudinally welded aluminum tube, or other structures with excellent sealing properties to prevent moisture, humidity, dust, and other environmental media from entering the cable, thus avoiding moisture-induced aging of the insulation layer and extending the cable's service life in outdoor, underground, and other environments.

[0041] In the above embodiments, EVA is used to improve foaming performance and enhance the flexibility and foaming properties of polyethylene. The amount added can be reduced or omitted as needed. When omitted, BN can be directly dispersed in the high-temperature melt of polyethylene.

[0042] In some embodiments, the outer conductor can also be formed by winding a dense metal wire; or by seamlessly welding a metal foil (e.g., copper foil) around the outside of the insulator. In most instances, the thickness of the outer conductor is not limited, and since the current mainly flows inside, it can be set as needed, for example, in the range of 0.1-0.5 mm.

[0043] According to one embodiment of this application, the first foamed layer is low-density polyethylene, and the foaming gas is carbon dioxide. Since carbon dioxide has high solubility with low-density polyethylene, using carbon dioxide as the foaming gas effectively ensures its dissolution, thereby forming a highly foamed, fine, and uniform closed-cell structure.

[0044] In some embodiments, the preparation process of the first foamed layer includes: firstly, feeding low-density polyethylene granules into an extruder, where the granules are melted into a viscous polymer melt; then, injecting CO2 into the polymer melt under high pressure to obtain a mixture; subsequently, cooling a corresponding section of the barrel to uniformly disperse the CO2 into the polymer melt to obtain a homogeneous solution; and finally, extruding and foaming the homogeneous solution to form the first foamed layer.

[0045] According to one embodiment of this application, the matrix of the second foam layer is a mixture of low-density polyethylene and high-density polyethylene, and the foaming gas of the second foam layer is nitrogen; the second foam layer with low foaming degree provides mechanical strength protection for the first foam layer.

[0046] Because low-density polyethylene (LDPE) suffers from poor rigidity, tensile strength, and abrasion resistance, blending it with high-density polyethylene (HDPE) can improve the overall crystallinity and melt strength of the matrix. Simultaneously, by increasing the difficulty of foaming the blowing agent, it is more conducive to forming an insulation structure with low foaming degree and high strength. Furthermore, nitrogen has lower solubility in the polymer matrix, further ensuring the formation of a second foamed layer with low foaming degree.

[0047] Specifically, the mixing ratio of low-density polyethylene and high-density polyethylene can be determined based on compatibility and processability factors.

[0048] Specifically, the mixing ratio of low-density polyethylene and high-density polyethylene can be between 8:2 and 6:4, preferably 7:3, at which point the strength value of the second foamed layer formed by foaming is the highest and the processing cost is the lowest.

[0049] According to one embodiment of this application, the first filler and the second filler are non-metallic compounds.

[0050] Because non-metallic compounds possess high thermal conductivity and high insulation properties, their addition does not affect the insulation properties of the second foaming layer, thus preventing signal leakage (attenuation spikes) or short circuits. Simultaneously, it allows the thermal conductivity of the second foaming layer to be greater than that of the first foaming layer, forming a heat dissipation gradient with the first foaming layer when heat is transferred to the second layer. Furthermore, the low dielectric constant of the non-metallic compound has minimal impact on signal attenuation, achieving the goal of low attenuation in the RF coaxial cable.

[0051] Specifically, the first foam layer and the second foam layer can be prepared in the following manner:

[0052] A foamed matrix (a mixture of low-density polyethylene and high-density polyethylene) and boron nitride (BN) were physically mixed and the resulting melt was then gas-foamed in an extruder and extruded onto a carrier. After irradiation crosslinking, the corresponding thermal conductivity was measured. For the unfilled foamed matrix, the thermal conductivity increased by 2-2.3% relative to the matrix. The BN filler used consisted of micro / nano materials of varying sizes. Although this increase in thermal conductivity appears relatively small, after fabricating coaxial cables and operating them at a high load of 1.5 GHz, the outer sheath temperature of the unfilled cable stabilized at 80-90 degrees Celsius after half an hour (measured by infrared), while the outer sheath temperature of the filled cable was 78-87 degrees Celsius (measured by infrared). This is because the increased thermal conductivity delayed and transferred some of the accumulated heat, resulting in a slight decrease in operating temperature.

[0053] In this application, if polyethylene with fibers or clear orientation and BN fibers are used, the performance should be greatly improved, but the cost will increase significantly.

[0054] In addition, tests revealed that providing only one type of filler had limited performance improvement, while providing different particle size ratios resulted in a higher actual performance improvement than using a single type. For example, using only 0.1-2 micrometer fillers increased the thermal conductivity by 0.7-0.8%. This is because BN particles with different particle size ratios and morphologies may form a three-dimensional structure during foaming, thereby improving thermal conductivity.

[0055] According to one embodiment of this application, the first filler and the second filler are spherical modified boron nitride nanoparticles;

[0056] The D50 value of the first packing is greater than that of the second packing.

[0057] The embodiments of this application use high-insulation, low-dielectric-loss boron nitride. The complementary sizes of two types of boron nitride (BN) with different particle size ratios can form complex pathways, which can radially conduct and spread out the dense heat (skin effect hotspots) on the inner surface of the outer conductor, and reduce local temperature peaks to a certain extent.

[0058] Modified boron nitride nanoparticles exhibit high compatibility with the matrix of the second foaming layer, improving compatibility and dispersibility with the resin matrix, preventing agglomeration, and enhancing dispersibility within the resin system. Furthermore, their spherical shape allows for better flowability in the resin melt, minimizing their impact on melt flowability and facilitating extrusion processing. Using silane-modified boron nitride nanoparticles with different particle size ratios allows smaller particles to fill the gaps between larger particles, achieving higher thermal conductivity with less filler.

[0059] According to one embodiment of this application, the addition ratio of the first filler and the second filler is 3:1 to 5:1.

[0060] Experiments have shown that when the ratio of the first filler to the second filler is 3:1 to 5:1, the surface of the second foamed layer can be kept smooth without causing an increase in melt viscosity that would affect processing.

[0061] The addition ratio of the first filler to the second filler in this application of 3:1 to 5:1 can most effectively construct a thermally conductive network, thereby significantly improving the thermal conductivity of the second foam layer, enabling it to better dissipate the heat of the inner conductor. This can prevent the cable from aging due to overheating, deforming of the foam structure, or deterioration of dielectric properties, thereby achieving the goal of maintaining the low attenuation performance of the cable in a long-term stable manner.

[0062] In this embodiment, the addition ratio of the first filler and the second filler is set to 4:1.

[0063] According to one embodiment of this application, the thermal conductivity of the second foam layer is 1.01-1.03 times that of the first foam layer.

[0064] The difference in thermal conductivity is the cause of interfacial thermal resistance. A difference in thermal conductivity of 1.01 to 1.03 times can allow heat to flow slowly from the inner layer to the outer layer, reducing the interfacial thermal resistance between the first foam layer and the second foam layer.

[0065] In practical applications, the thermal conductivity of the second foaming layer can be controlled to be 1.01-1.03 times that of the first foaming layer by adjusting the degree of foaming of the second foaming layer, as well as the total addition ratio and particle size of the spherical modified boron nitride nanoparticles.

[0066] According to one embodiment of this application, the outer conductor layer is formed by longitudinal wrapping of a smooth metal.

[0067] The outer conductor of this application is formed by smooth metal longitudinal wrapping, which can reduce the roughness of the inner surface of the outer conductor, reduce resistance, and further reduce the overall signal attenuation.

[0068] During preparation, a pre-rolled metal strip (usually aluminum or copper strip) is longitudinally wound and bent around an inner conductor covered with an insulating layer to complete the wrapping. The strip is then shaped and welded (or overlapped) using a mold to ultimately form a metal tubular shell. The thickness of the metal strip is typically chosen to be 0.08-0.20 mm.

[0069] According to one embodiment of this application, the inner conductor is a copper-plated steel wire with an average surface roughness of 0.4-0.7 micrometers. Setting the average surface roughness reduces high-frequency resistance, significantly mitigating resistance loss caused by the skin effect. Simultaneously, the use of steel wire ensures the strength of the inner conductor, preventing deformation due to excessive external force during the outer conductor's fabrication process, stabilizing impedance to reduce signal return loss, and further reducing overall cable attenuation.

[0070] According to one embodiment of this application, the copper layer thickness on the surface of the steel wire is 15-20 micrometers.

[0071] The skin depth of radio frequency signals is typically only a few micrometers. The 15-20μm thickness of the copper layer on the steel wire surface is much greater than the skin depth in common frequency bands, ensuring that the current flows entirely within the high-quality copper layer without touching the poorly conductive steel core. The preferred copper layer thickness on the steel wire surface is 18μm.

[0072] The following are some specific embodiments to illustrate the fabrication process of the radio frequency coaxial cable with low attenuation leakage of this application.

[0073] Example 1:

[0074] 1. High-purity oxygen-free copper is used as the inner conductor, and electrolytic polishing or ultra-precision mechanical polishing technology is employed to ensure a surface roughness of <0.5μm;

[0075] 2. The first melt uses nitrogen as a foaming agent, the extrusion temperature is 185-190℃, the extrusion pressure is 190 bar, and a first foamed layer with a foaming degree of 82% is obtained;

[0076] 3. The second melt uses nitrogen as a foaming agent, the extrusion temperature is 170-175℃, the extrusion pressure is 165 bar, and a second foamed layer with a foaming degree of 79% is obtained;

[0077] 4. An outer conductor is formed on the second foaming layer using a copper strip forming and welding method;

[0078] 5. A rubber outer sheath is formed on the surface of the outer conductor;

[0079] The parameters for the above steps are as follows:

[0080] The inner conductor has a radius of 5mm, the outer conductor has a radius of 12.5mm, the first foam layer has a thickness of 4mm, and the second foam layer has a thickness of 3.5mm.

[0081] Furthermore, the first melt is a mixture of high-density polyethylene and low-density polyethylene in a 1:1 ratio, and the foaming gas is nitrogen.

[0082] The second melt is a mixture of high-density polyethylene and low-density polyethylene in a 1:1 ratio. The foaming gas is nitrogen. The melt contains 0.7% BN particles (a mixture of particles with a D50 of 300 nm and particles with a D50 of 30 nm in a 3:1 ratio). These particles are pre-dispersed in EVA adhesive and then extruded after being mixed evenly with the second melt.

[0083] The coaxial cable maintains an impedance of approximately 49.13 ohms during long-term operation, and its outer sheath temperature is 1-1.5℃ lower than that of unfilled cables. The dielectric constant of the insulation layer is 1.263. The operating parameters are: communication bandwidth: 3GHz, peak power: 300W, and so on.

[0084] Example 2:

[0085] 1. High-purity oxygen-free copper is used as the inner conductor, and electrolytic polishing or ultra-precision mechanical polishing technology is employed to ensure a surface roughness of <0.5μm;

[0086] 2. The first melt uses nitrogen as a foaming agent, the extrusion temperature is 185-190℃, the extrusion pressure is 190 bar, and a first foamed layer with a foaming degree of 82% is obtained;

[0087] 3. The second melt uses nitrogen as a foaming agent, the extrusion temperature is 170-175℃, the extrusion pressure is 165 bar, and a second foamed layer with a foaming degree of 79% is obtained;

[0088] 4. An outer conductor is formed on the second foaming layer using a copper tube stretching method;

[0089] 5. A rubber outer sheath is formed on the surface of the outer conductor;

[0090] The parameters for the above steps are as follows:

[0091] The inner conductor has a radius of 5mm, the outer conductor has a radius of 12.5mm, the first foam layer has a thickness of 5mm, and the second foam layer has a thickness of 2.5mm.

[0092] Furthermore, the first melt is low-density polyethylene, and the foaming gas is carbon dioxide;

[0093] The second melt is medium-density polyethylene, the foaming gas is nitrogen, and the melt contains 1% BN particles (a mixture of particles with a D50 of 300nm and particles with a D50 of 30nm, with a blending ratio of 3:1). These particles are pre-dispersed in EVA glue and then mixed evenly with the second melt before being extruded.

[0094] The impedance of this coaxial cable remains at around 49.03 ohms during long-term operation, and its outer sheath temperature is 0.7-1.5℃ lower than that of unfilled cables.

[0095] Example 3:

[0096] 1. High-purity oxygen-free copper is used as the inner conductor, and electrolytic polishing or ultra-precision mechanical polishing technology is employed to ensure a surface roughness of <0.5μm;

[0097] 2. The first melt uses nitrogen as a foaming agent, the extrusion temperature is 185-190℃, the extrusion pressure is 190 bar, and a first foamed layer with a foaming degree of 82% is obtained;

[0098] 3. The second melt uses nitrogen as a foaming agent, the extrusion temperature is 170-175℃, the extrusion pressure is 175 bar, and a second foamed layer with a foaming degree of 79% is obtained;

[0099] 4. An outer conductor is formed on the second foaming layer using a copper tube stretching method;

[0100] 5. A rubber outer sheath is formed on the surface of the outer conductor;

[0101] The parameters for the above steps are as follows:

[0102] The inner conductor has a radius of 5mm, the outer conductor has a radius of 12.5mm, the first foam layer has a thickness of 6mm, and the second foam layer has a thickness of 1.5mm.

[0103] Furthermore, the first melt is low-density polyethylene, and the foaming gas is carbon dioxide;

[0104] The second melt is a mixture of high-density polyethylene and low-density polyethylene, the foaming gas is nitrogen, and the melt contains 1% BN particles (a mixture of particles with a D50 of 300nm and particles with a D50 of 30nm, with a blending ratio of 3.6:1). These particles are pre-dispersed in EVA glue and then mixed evenly with the second melt before being extruded.

[0105] The impedance of this coaxial cable remains at around 49.05 ohms during long-term operation, and its outer sheath temperature is 1.5-2.0℃ lower than that of unfilled cables.

[0106] In the above embodiments, low-density polyethylene (LDPE) is the lightest variety of polyethylene resin, appearing as milky white, tasteless, odorless, non-toxic, and matte waxy granules. It possesses good flexibility, extensibility, electrical insulation, transparency, ease of processing, and a certain degree of air permeability. It exhibits good chemical stability, is resistant to alkalis and common organic solvents, and its density is generally 0.91-0.93 g / cm³.

[0107] In the above embodiments, high-density polyethylene (HDPE) is a white powder or granular product. It is non-toxic, odorless, has a crystallinity of 80%–90%, a softening point of 125–135°C, and a service temperature up to 100°C. Its hardness, tensile strength, and creep resistance are superior to low-density polyethylene, and its density is generally 0.941–0.960 g / cm³.

[0108] In the above embodiments, medium-density polyethylene (MDPE), abbreviated as MDPE, is a synthetic resin formed by copolymerization of ethylene and α-olefins (such as propylene, 1-butene, etc.), with a density range of 0.926-0.953 g / cm³.

[0109] In the above embodiments, the strength of the formed foam layer can be further increased by electron irradiation.

[0110] In the above embodiments, EVA is used to improve foaming performance and enhance the flexibility and foaming properties of polyethylene. The amount added can be reduced or omitted as needed. When omitted, BN can be directly dispersed in the high-temperature melt of polyethylene.

[0111] During the above process, the parameters of the foaming process can be adjusted as needed to ensure that the degree of foaming meets the requirements.

[0112] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with technical features having similar functions disclosed in this application.

[0113] It should be understood that the sequence number of each step in the invention and embodiments of this application does not absolutely imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The foregoing description of the implementation of this application has been given for illustrative and descriptive purposes. The foregoing description is not exhaustive and is not intended to limit this application to the exact form disclosed. Various modifications and variations may exist based on the above teachings, or various modifications and variations may be derived from the practice of this application. These embodiments were chosen and described to illustrate the principles of this application and its practical application, so that those skilled in the art can utilize this application in various implementations and modifications to suit the specific purpose of the concept. Those skilled in the art will understand that the above-described embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of this application.

Claims

1. A radio frequency coaxial cable with low attenuation leakage, characterized in that, The cable includes a cable body, which comprises an inner conductor and an outer conductor, the outer conductor being located around the inner conductor, and a first foam layer and a second foam layer being located between the inner conductor and the outer conductor. The surface roughness of the outer surface where the inner conductor and the first foam layer contact is less than 0.5 micrometers; The second foamed layer contains a first filler and a second filler with identical components, and the total addition ratio of the first filler and the second filler is not greater than 1%. The degree of foaming of the first foam layer is greater than that of the second foam layer, and the extrusion temperature of the first foam layer is greater than that of the second foam layer. The thickness of the first foam layer is greater than that of the second foam layer, and the thermal conductivity of the first foam layer is less than that of the second foam layer.

2. The radio frequency coaxial cable with low attenuation leakage as described in claim 1, characterized in that, The first foaming layer is low-density polyethylene, and the foaming gas is carbon dioxide.

3. The radio frequency coaxial cable with low attenuation leakage as described in claim 1, characterized in that, The matrix of the second foam layer is a mixture of low-density polyethylene and high-density polyethylene, and the foaming gas of the second foam layer is nitrogen.

4. The radio frequency coaxial cable with low attenuation leakage as described in claim 1, characterized in that, The first and second packing materials are non-metallic compounds.

5. The radio frequency coaxial cable with low attenuation leakage as described in claim 4, characterized in that, The first and second fillers are spherical modified boron nitride nanoparticles; The D50 value of the first packing is greater than that of the second packing.

6. The radio frequency coaxial cable with low attenuation leakage as described in claim 5, characterized in that, The addition ratio of the first filler and the second filler is 3:1 to 5:

1.

7. The radio frequency coaxial cable with low attenuation leakage as described in claim 4, characterized in that, The thermal conductivity of the second foam layer is 1.01-1.03 times that of the first foam layer.

8. The radio frequency coaxial cable with low attenuation leakage as described in claim 1, characterized in that, The outer conductor layer is formed by longitudinal wrapping of a smooth metal.

9. A radio frequency coaxial cable with low attenuation leakage as described in claim 1, characterized in that, The inner conductor is a copper-plated steel wire with an average surface roughness of 0.4-0.7 micrometers.

10. A radio frequency coaxial cable with low attenuation leakage as described in claim 9, characterized in that, The copper layer on the surface of the steel wire is 15-20 micrometers thick.

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