A low-loss radio frequency coaxial cable and its manufacturing method

Abstract

The present invention belongs to the field of wireless communication, and more specifically, relates to a low-loss radio frequency coaxial cable and a manufacturing method thereof. By performing surface treatment on the inner conductor of the radio frequency coaxial cable, the adhesion between the inner conductor and the insulating layer is improved, the transmission loss is reduced, and the signal transmission performance is enhanced. After moderate process treatment on the surface of the inner conductor, the contact performance can be improved while avoiding signal reflection and increased loss. On the premise of meeting the requirements of insulation adhesion, standing wave, and insulation withstand voltage tests, the surface of the inner conductor of the radio frequency coaxial cable is moderately treated, so that the overall attenuation index is optimized by 3.3% - 6.0% compared with the existing products in the attenuation values of the radio frequency coaxial cable in frequency bands such as 900 MHz, 1800 MHz, and 2700 MHz.

Description

Technical Field

[0001] The present invention belongs to the field of wireless communication, and more specifically, relates to a low-loss radio frequency coaxial cable and a manufacturing method thereof. Background Art

[0002] A radio frequency coaxial cable is a cable used to transmit electromagnetic energy within the radio frequency range and is widely used in fields such as radio communication, broadcasting, television, radar, and navigation. Existing radio frequency coaxial cables generally consist of an inner conductor, an insulating layer, an outer conductor, and a sheath layer. The inner conductor is usually made of high-purity copper or silver and is responsible for transmitting radio frequency signals; the insulating layer is located between the inner conductor and the outer conductor, used to isolate the two and play a role in supporting the structure, and the outer conductor is used to transmit signals and shield against external signals.

[0003] The product structure of conventional radio frequency coaxial cables complies with the industry standard YD / T1092 "50 Ω Foamed Polyolefin Insulated Corrugated Copper Tube Outer Conductor Radio Frequency Coaxial Cable for Wireless Communication of Communication Cables". Its insulating layer is usually divided into three layers. The solid thin insulating layers near the inner and outer conductors of the cable are mainly made of low-density polyethylene (LDPE) or high-density polyethylene (HDPE), and ethylene-vinyl acetate (EVA) resin with a bonding effect is incorporated; the middle foam insulating layer is thicker, and its material composition is mainly a mixture of LDPE and HDPE with a nucleating agent incorporated, and is made by a physical foaming continuous extrusion process. This kind of insulating structure can better balance the requirements in terms of attenuation, cost, and production efficiency. However, in the prior art, there are problems of a large dielectric constant of the solid insulating layer and too high transmission attenuation of the cable. The commonly used insulating layer between the inner and outer conductors is a polyolefin physical foaming structure, and its dielectric constant is about 1.25. However, the physical foaming layer cannot bond well with the surface of the inner conductor, which will cause the insulating layer to separate from the inner conductor, resulting in a change in the cable structure and affecting normal transmission.

[0004] To solve the above problems, the usual practice is to first extrude a solid inner skin layer on the surface of the inner conductor, and then extrude a foaming layer on the inner skin layer. The role of the solid inner skin layer is to bond the inner conductor and the foamed polyethylene layer. However, since the inner skin layer is generally a mixed material of solid polyethylene and glue EVA, the comprehensive dielectric constant is about 2.4 (data at 1 MHz), and compared with the dielectric constant of 1.25 of the physical foaming layer, the existence of the inner skin layer greatly increases the transmission loss of the cable.

[0005] Therefore, there is an urgent need for an improved radio frequency coaxial cable structure to solve the above problems. Summary of the Invention

[0006] Aiming at the defects of the prior art, the purpose of the present invention is to provide a low-loss radio frequency coaxial cable and its manufacturing method. By roughening the surface of the inner conductor, the contact between the inner conductor and the insulating layer is improved, and the solid inner skin layer is omitted, thereby reducing the cable loss and enhancing the signal transmission performance, and solving the technical problems such as poor contact between the inner conductor and the insulating layer and high transmission loss in the prior art.

[0007] To achieve the above object, the present invention provides a low-loss radio frequency coaxial cable, comprising an inner conductor, a composite insulating layer, an outer conductor, and an outer sheath that are concentrically nested from the inside out;

[0008] The composite insulating layer includes a foamed resin layer and a solid outer skin layer; wherein, the foamed resin layer is in direct contact with the inner conductor, and the solid outer skin layer is in direct contact with the outer conductor;

[0009] The surface of the inner conductor in direct contact with the foamed resin layer has a microscopic rough structure formed by roughening treatment, and its roughness is 0.5 μm to 5.0 μm.

[0010] Further preferably, the surface roughness of the inner conductor is 1 μm to 3 μm.

[0011] Further preferably, the method for roughening the surface of the inner conductor is laser roughening, chemical etching, mechanical polishing, or electrochemical treatment.

[0012] According to another aspect of the present invention, a manufacturing method of the radio frequency coaxial cable is provided, comprising the following steps:

[0013] (1) Perform surface roughening treatment on the inner conductor to control its roughness within the range of 0.5 μm to 5.0 μm;

[0014] (2) Double-extrude the foamed resin layer and the solid outer skin layer on the surface of the roughened inner conductor;

[0015] (3) Prepare the outer conductor and the outer sheath in sequence outside the solid outer skin layer.

[0016] Generally speaking, compared with the prior art by the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0017] (1) By roughening the surface of the inner conductor, the present invention significantly improves the contact between the inner conductor and the insulating layer. Meanwhile, the solid inner skin layer is omitted, reducing the transmission loss of the cable. Experimental tests show that, under the same other technological processes, when the surface of the inner conductor of the radio frequency coaxial cable is moderately roughened and the inner skin layer is removed, the attenuation index is overall optimized (reduced) by 3.3% - 6.0% compared with the prior art without roughening and with an inner skin layer at the frequency bands of 900 MHz, 1800 MHz, and 2700 MHz.

[0018] (2) The optimized cable structure of the present invention has better signal transmission performance and anti-interference ability, and is applicable to radio frequency communication scenarios.

[0019] (3) The surface roughness of the low-loss radio frequency coaxial inner conductor provided by the present invention is controlled within the range of 0.5 μm to 5.0 μm, which can not only improve the contact between the inner conductor and the insulating layer, but also avoid signal reflection and increased loss.

[0020] (4) The manufacturing method of the low-loss radio frequency coaxial cable provided by the present invention is simple and easy to implement, and is suitable for large-scale production. Description of the Drawings

[0021] Figure 1 It is a schematic end face structure diagram of the radio frequency coaxial cable of Comparative Example 1 of the present invention.

[0022] Figure 2 It is a schematic side structure diagram of the radio frequency coaxial cable of Comparative Example 1 of the present invention.

[0023] Figure 3 It is a schematic end face structure diagram of the radio frequency coaxial cable of Embodiment 1 of the present invention.

[0024] Figure 4 It is a schematic side structure diagram of the radio frequency coaxial cable of Embodiment 1 of the present invention.

[0025] Figure 5 It is a schematic microscopic structure diagram of the surface roughening treatment of the inner conductor of Embodiment 1 of the present invention.

[0026] In all the drawings, the same reference numerals are used to represent the same elements or structures, where: 1 - inner conductor; 2 - composite insulating layer; 3 - outer conductor; 4 - outer sheath; 21 - solid inner skin layer; 22 - foamed resin layer; 23 - solid outer skin layer. Detailed Embodiments

[0027] To make the objectives, technical solutions and advantages of the present invention clearer, the following will, in combination with the embodiments of the present invention, clearly and completely describe the technical solutions in the embodiments of the present invention. Those skilled in the art should understand that the described embodiments are only for helping to understand the present invention and should not be construed as specific limitations to the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0028] The embodiments of the present invention are implemented on the premise of the technical solutions of the present invention, and detailed implementation manners and processes are given. However, the scope of protection of the present invention is not limited to the following embodiments. For the process parameters without specific conditions noted in the following embodiments, they are usually in accordance with conventional conditions.

[0029] In the present invention, the endpoints and any values within the disclosed ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0030] In the present invention, unless otherwise specified and / or described, throughout, all numerical values related to the amounts of components are in "parts by weight". For the process parameters without specific conditions noted in the following embodiments, they are usually in accordance with conventional conditions.

[0031] The existing radio frequency coaxial cables, such as Figure 1 and Figure 2 shown, include an inner conductor 1, a composite insulating layer 2, an outer conductor 3 and an outer sheath 4 that are concentrically nested from the inside out. The composite insulating layer is composed of a solid inner skin layer 21, a foamed resin layer 22 and a solid outer skin layer 23; the function of the solid inner skin layer is to bond the metal inner conductor and the thermoplastic foamed polyolefin resin insulating layer. To improve the bonding effect, the solid inner skin layer usually contains a resin with a bonding effect. However, incorporating the bonding resin will result in a high dielectric constant of the solid inner skin layer and increase the transmission loss of the cable; on the other hand, directly connecting the metal surface of the inner conductor to the thermoplastic resin results in poor contact between the two due to different material types, and poor contact is also likely to cause a decline in the electrical performance of the cable. To address these technical defects, the present invention provides a low-loss radio frequency coaxial cable, the schematic diagrams of its end face and side structure are respectively as Figure 3 and Figure 4As shown, it includes an inner conductor 1, a composite insulation layer 2, an outer conductor 3, and an outer sheath 4 that are concentrically nested from the inside out. The composite insulation layer is composed of a foamed resin layer 22 and a solid outer skin layer 23; the foamed resin layer 22 is in direct contact with the inner conductor 1, and the solid outer skin layer 23 is in direct contact with the outer conductor 3. The surface of the inner conductor 1 in direct contact with the foamed resin layer 22 also has a microscopic rough structure formed by roughening treatment, and its roughness (Ra) ranges from 0.5 μm to 5.0 μm.

[0032] The present invention provides a radio frequency coaxial cable that improves the contact between the inner conductor and the insulation layer by improving the surface structure of the inner conductor and omits the inner skin layer. Traditional radio frequency coaxial cables require the surfaces of the inner conductor and the outer conductor to be smooth to prevent reflections caused by conductor surface defects and affect the use of the cable. However, the inventors of this application unexpectedly found that when the surface of the inner conductor is moderately roughened, it actually does not affect the electrical performance of the product within the standard range. Moreover, the roughened inner conductor surface also improves its adhesion to the foamed polyolefin layer insulation. At the same time, since the contact with the foamed insulation layer is increased by roughening the inner conductor surface, the original solid inner skin layer structure can be directly omitted. Omitting this structure also means avoiding the transmission loss of the original solid inner skin layer to the cable. Therefore, the transmission loss of the coaxial cable can be further reduced.

[0033] The roughness (Ra) of the inner conductor surface ranges from 0.5 μm to 3.0 μm, and a better range is from 1.0 μm to 3.0 μm. This roughness range can not only ensure good contact between the inner conductor and the insulation layer but also avoid signal reflection and increased loss caused by excessive roughness.

[0034] The method for roughening the surface of the inner conductor of the present invention can adopt laser roughening, chemical etching, mechanical polishing, or electrochemical treatment to form a uniform concave-convex structure on the surface of the inner conductor and increase the contact area with the insulation layer. However, it is necessary to strictly control the degree of roughening of the inner conductor surface to avoid affecting signal transmission due to size fluctuations on the conductor surface caused by excessive roughening, or causing electric breakdown due to the occurrence of an electric field concentration effect on sharp metal edges caused by excessive roughening.

[0035] The surface of the inner conductor of the present invention has been roughened to form a microscopic rough structure. It can be understood that the present application does not limit the shape or material type of the inner conductor and the outer conductor itself, and the inner conductors and outer conductors reported in the prior art are all applicable to the present application. In some embodiments, the above-mentioned inner conductor includes but is not limited to copper-clad aluminum wire, spiral corrugated copper tube, smooth copper tube, etc. In some other embodiments, high-purity silver material can also be used. The above-mentioned outer conductor is one of a spiral corrugated metal outer conductor, an annular corrugated metal outer conductor, or a metal wire braided outer conductor. In some embodiments, both the above-mentioned metal inner conductor and the outer conductor are copper conductors.

[0036] In the present invention, the insulating layer between the inner conductor and the outer conductor of the radio frequency coaxial cable omits the original solid inner skin layer that plays a bonding role for the inner conductor and the foamed insulating layer compared with the prior art. The remaining foamed resin layer and the solid outer skin layer can adopt the insulating layer materials reported in the prior art. For example, the foamed resin layer can be foamed polyolefin, including but not limited to foamed polyethylene, with a foaming degree of 40% - 85% and a thickness of 3 mm - 15 mm. The solid outer skin layer is solid polyolefin, such as low-density polyethylene LDPE (density range: 0.910 g / cm³ - 0.930 g / cm³) or high-density polyethylene HDPE (density range: 0.940 g / cm³ - 0.976 g / cm³), and the thickness is 0.05 mm - 0.15 mm.

[0037] In some embodiments, the above-mentioned outer sheath is a polyolefin sheath, including but not limited to polyethylene resin, polypropylene resin, polystyrene resin, etc., and the thickness of the outer sheath is 0.3 mm - 4 mm.

[0038] The improved radio frequency coaxial cable of the present invention has a composite insulating layer composed of a foamed resin layer and a solid outer skin layer, omitting the traditional solid inner skin layer. After surface roughening treatment, the surface of the inner conductor directly contacts the foamed resin layer, significantly improving its contact property and reducing signal transmission loss.

[0039] The present invention also provides a manufacturing method of the above-mentioned radio frequency coaxial cable, including the following steps:

[0040] (1) Perform surface roughening treatment on the inner conductor to control its roughness within the range of 0.5 μm to 5.0 μm;

[0041] (2) Double-layer co-extrusion is performed on the surface of the roughened inner conductor to prepare a foamed resin layer and a solid outer skin layer;

[0042] (3) An outer conductor and an outer sheath are sequentially prepared outside the solid outer skin layer.

[0043] The roughening treatment in step (1) of the present invention does not limit the specific roughening method. For example, it can be laser roughening, chemical etching, mechanical grinding or electrochemical treatment. The preferred roughening method is the laser surface roughening process, which can ensure a high degree of consistency in the treatment process, is easy to perform online synchronous treatment, and is convenient for popularization.

[0044] In some embodiments, in step (1), the surface of the inner conductor is treated by chemical etching method, the etching solution is dilute nitric acid solution, and the etching time is 5 - 10 minutes to form a uniform microscopic rough structure, and the roughness is preferably controlled within the range of 1.0 μm to 3.0 μm.

[0045] In some other embodiments, the surface of the inner conductor is processed by laser. Specifically, the laser power is controlled within 10W - 400W, the scanning speed is between 600mm / s and 1200mm / s, the scanning pitch is between 0.05mm and 0.12mm, and the roughness is preferably controlled within the range of 1.0 μm to 3.0 μm. The laser can be a common one such as a solid-state laser (365nm solid-state laser or 1064nm solid-state laser), a fiber laser, a gas laser (carbon dioxide laser or copper vapor laser), or a semiconductor laser. Preferably, a fiber laser is used.

[0046] In some embodiments, the inner conductor with roughened surface is a preheated inner conductor. Generally, according to different products, the surface preheating temperature is controlled at 80°C - 120°C so that the foamed layer can better adhere to the conductor surface.

[0047] In some embodiments, step (2) is specifically as follows: The molten polyolefin and the foaming gas are mixed evenly to form an aerosol. The aerosol and the molten polyolefin for preparing the solid outer skin are co-extruded in a double layer on the surface of the inner conductor after roughening treatment to form the foamed resin layer and the solid outer skin coated on the outside of the foamed resin layer. The extrusion temperature is 130°C - 210°C to ensure that the foamed polyolefin material is tightly combined with the inner conductor to form the foamed resin layer.

[0048] In step (3) of the present invention, the outer conductor and the outer sheath are sequentially arranged outside the insulating layer according to the conventional process to complete the manufacture of the cable.

[0049] The following are the examples and comparative examples:

[0050] Comparative Example 1

[0051] The radio frequency coaxial cable provided in this comparative example is applied to the traditional cable with the model HCAAY - 50 - 12 in the YD / T1092 standard (the cable specification is -12). The schematic diagrams of its end face and side structure are respectively as Figure 1 and Figure 2 shown. From the inside to the outside, there are coaxially arranged an inner conductor 1, a composite insulating layer 2, an outer conductor 3, and an outer sheath 4 in sequence. Among them, the composite insulating layer 2 includes a solid inner skin layer 21, a foamed resin layer 22, and a solid outer skin layer 23 from the inside to the outside. The inner conductor is a solid copper-clad aluminum wire, the solid inner skin layer 21 and the solid outer skin layer 23 are low-density polyethylene, the foamed resin layer 22 is foamed polyethylene, the outer conductor 3 is a copper strip welded corrugated pipe, and the outer sheath 4 is polyethylene. The preparation method of this radio frequency coaxial cable is carried out according to the following steps:

[0052] (1) Low-density polyethylene and glue (EVA resin) are mixed in a ratio of 3:1 and extruded at 130-220°C, and evenly coated on the surface of a solid copper-clad aluminum inner conductor with a diameter of 4.8 mm to form a bonded solid inner skin layer with a thickness of 0.1 mm.

[0053] (2) High-density polyethylene, low-density polyethylene and nucleating agent (a mixture of cyclodextrin nanosponge (NS) and vinyl triethoxysilane (VTES), mass ratio of 1:1) were mixed in a mass ratio of 70:29:1, and after high-temperature plasticization at 130-195°C, high-pressure gas (carbon dioxide) was injected into the molten state. After being fully mixed in the screw, they were extruded at high pressure and attached to the inner skin layer for foaming and cooling to form an insulating foamed cable core with a diameter of 12.6 mm and a foaming degree of 75%.

[0054] (3) At the same time as the foaming layer in the previous step, a low-density polyethylene solid outer layer with a thickness of about 0.1 mm is extruded, which is evenly coated on the periphery of the foaming layer, so that the insulation layer has better sealing properties.

[0055] (4) A 0.21 mm thick smooth copper strip is welded into a copper tube by forming argon arc welding and then inserted into the foam cable core for corrugation. The corrugation trough sinks into the cable core insulation layer, so that the outer conductor and the insulation layer fit tightly into a whole. The outer diameter of the corrugation peak is 13.85 mm.

[0056] (5) A layer of polyethylene sheath material is extruded on the surface of the outer conductor, and the sheath thickness is 0.8 mm.

[0057] Example 1

[0058] The radio frequency coaxial cable provided in this embodiment is applied to the traditional cable of model HCAAY-50-12 in the YD / T1092 standard (cable specification is -12), and its end face and side face structure schematic diagrams are shown as follows: Figure 3 and Figure 4 As shown, an inner conductor 1, a composite insulating layer 2, an outer conductor 3 and an outer sheath 4 are coaxially arranged from the inside to the outside, wherein the composite insulating layer 2 includes a foamed resin layer 22 and a solid outer skin layer 23 from the inside to the outside, wherein the inner conductor is a copper-clad aluminum wire with a surface roughness of 1 μm after roughening treatment, the solid outer skin layer 23 is low-density polyethylene with a thickness of 0.1 mm, the foamed resin layer 22 is foamed polyethylene, the outer conductor 3 is a corrugated copper strip, and the outer sheath 4 is polyethylene with a thickness of 0.8 mm. The preparation method of the radio frequency coaxial cable is carried out according to the following steps:

[0059] (1) The copper-clad aluminum with a diameter of 4.8 mm was roughened by a fiber laser. The laser power was 50 W, the scanning speed was 1000 mm / s, the scanning spacing was 0.08 mm, and the surface roughness was controlled at 1 μm. The schematic diagram of the inner conductor surface after roughening is shown in the figure.Figure 5 Then it is preheated and the temperature before entering the foaming machine head is 80~120℃.

[0060] (2) High-density polyethylene, low-density polyethylene and a nucleating agent (a mixture of cyclodextrin nanosponge (NS) and vinyl triethoxysilane (VTES), mass ratio 1:1) were mixed in a mass ratio of 70:29:1, and after being plasticized at a high temperature of 130-195°C, high-pressure gas (carbon dioxide) was injected into the molten state. After being fully mixed in the screw, the mixture was directly attached to the inner conductor with a roughened surface by high-pressure extrusion for foaming and cooling to form an insulating foamed cable core with a diameter of 12.6 mm and a foaming degree of 75%, thereby obtaining a foamed resin layer.

[0061] (3) At the same time as the foaming layer in the previous step, a low-density polyethylene solid outer layer with a thickness of about 0.1 mm is extruded, which is evenly coated on the periphery of the foaming resin layer, so that the insulation layer has better sealing properties.

[0062] (4) A 0.21 mm thick smooth copper strip is welded into a copper tube by forming argon arc welding and then inserted into the foam cable core for corrugation. The corrugation trough sinks into the cable core insulation layer, so that the outer conductor and the insulation layer fit tightly into a whole. The outer diameter of the corrugation peak is 13.85 mm.

[0063] (5) A layer of polyethylene sheath material is extruded on the surface of the outer conductor, and the sheath thickness is 0.8 mm.

[0064] Example 2

[0065] The other aspects are the same as those of Example 1, except that the laser roughening process parameters are controlled so that the roughness of the inner conductor surface is 2 μm.

[0066] Example 3

[0067] The other aspects are the same as those of Example 1, except that the laser roughening process parameters are controlled so that the roughness of the inner conductor surface is 3 μm.

[0068] Example 4

[0069] The other aspects are the same as those of Example 1, except that the laser roughening process parameters are controlled so that the roughness of the inner conductor surface is 4 μm.

[0070] Example 5

[0071] The other aspects are the same as those of Example 1, except that the laser roughening process parameters are controlled so that the roughness of the inner conductor surface is 5 μm.

[0072] Comparative Example 2

[0073] The other aspects are the same as those of Example 1, except that the laser roughening process parameters are controlled so that the roughness of the inner conductor surface is 6 μm.

[0074] Comparative Example 3

[0075] Other conditions are the same as in Example 1, except that the roughness of the roughened inner conductor surface is controlled to be 7 μm by adjusting the laser roughening process parameters.

[0076] Comparative Example 4

[0077] Other conditions are the same as in Example 1, except that the roughness of the roughened inner conductor surface is controlled to be 8 μm by adjusting the laser roughening process parameters.

[0078] Comparative Example 5

[0079] Other conditions are the same as in Example 1, except that the roughness of the roughened inner conductor surface is controlled to be 0.3 μm by adjusting the laser roughening process parameters.

[0080] Comparative Example 6

[0081] Other conditions are the same as in Example 1, except that the roughness of the roughened inner conductor surface is controlled to be 0.2 μm by adjusting the laser roughening process parameters.

[0082] Verify and test the RF coaxial cables of the above comparative examples and examples according to the test methods in the YD / T 1092 standard. The test items are as follows: a. Adhesion test between the insulation layer and the inner conductor (considering the influence of the roughening process on the structural stability of the product); b. Standing wave test (considering the influence of the roughening process on the standing wave index); c. Insulation dielectric strength test (considering whether the surface roughness after roughening the inner conductor will generate metal sharp corners, resulting in local electric field concentration and abnormal insulation withstand voltage index); d. Loss / attenuation test (considering the influence of the roughening process on the cable attenuation after removing the inner skin layer). The measured results are shown in Table 1.

[0083] It can be seen from the test data of test item d in Table 1 that, compared with Comparative Example 1, in the case of the same other process conditions, after the inner conductor surface roughening process and removing the inner skin layer, the attenuation index of Examples 1 to 5 is overall optimized (decreased) by 3.3% - 6.0%.

[0084] It can be seen from the test data of test item a in Table 1 that the index of insulation adhesion increases with the increase of the surface roughness of the inner conductor. When the surface roughness of the inner conductor drops to 0.3 μm or less, after removing the inner skin layer, the adhesion between the conductor and the insulation layer cannot meet the normal requirements. And when the adhesion index is unqualified, it may indirectly lead to the unqualified standing wave index of test item b due to the unstable structure between the insulation layer and the inner conductor.

[0085] It can be seen from the test data of test item c in Table 1 that when the surface roughness of the inner conductor exceeds 5μm, the electric field concentration effect caused by the sharp corners on the metal surface may result in the failure of the insulation dielectric strength test. At the same time, according to the experimental data, when the coarsening degree is too high (Comparative Example 2, Comparative Example 3, and Comparative Example 4), the insulation dielectric strength test fails while the standing wave test meets the standard; since this index fails first before the standing wave index, the influence of the standing wave is not considered as a priority, which also indicates that as long as the surface roughness of the inner conductor is controlled within a suitable range, the standing wave test is usually qualified.

[0086] Table 1

[0087]

[0088] Based on the above test data, the present invention recommends that the surface roughness of the inner conductor of the radio frequency coaxial cable after using the coarsening process be controlled within 0.5μm to 5μm, and the better roughness range is 1μm to 3μm.

[0089] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A low-loss radio frequency coaxial cable, characterized in that: It includes an inner conductor, a composite insulation layer, an outer conductor and an outer sheath which are concentrically nested from the inside to the outside; The composite insulating layer is composed of a foamed resin layer and a solid outer skin layer; wherein the foamed resin layer is in direct contact with the inner conductor, and the solid outer skin layer is in direct contact with the outer conductor; The material of the foamed resin layer is foamed polyolefin; the foaming degree of the foamed polyolefin is 40%-85%; the thickness of the foamed resin layer is 3mm-15mm; The solid outer skin layer is solid polyolefin; the thickness of the solid outer skin layer is 0.05mm~0.15mm; The surface of the inner conductor directly in contact with the foamed resin layer has a microscopic rough structure formed by roughening treatment, and the roughness thereof is 0.5 μm to 5.0 μm; The inner conductor is a copper-clad aluminum wire or a smooth copper tube.

2. The radio frequency coaxial cable according to claim 1, characterized in that: The surface roughness of the inner conductor is 1 μm to 3 μm.

3. The radio frequency coaxial cable according to claim 1, characterized in that: The inner conductor surface roughening treatment method is laser roughening, chemical etching, mechanical grinding or electrochemical treatment.

4. A method for preparing a radio frequency coaxial cable according to any one of claims 1 to 3, characterized in that: The steps include: (1) The inner conductor is subjected to surface roughening treatment so that its roughness is controlled within the range of 0.5 μm to 5.0 μm; (2) preparing the foamed resin layer and the solid outer skin layer by double-layer co-extrusion on the surface of the inner conductor after the roughening treatment; (3) The outer conductor and the outer sheath are sequentially prepared outside the solid outer skin layer.

5. The method according to claim 4, characterized in that The roughening treatment in step (1) is specifically laser roughening, chemical etching, mechanical grinding or electrochemical treatment.

6. The method according to claim 5, characterized in that When the roughening process is performed by laser roughening, the laser power is 10W-400W, the scanning speed is 600mm / s-1200mm / s, and the scanning interval is 0.05mm-0.12mm.

7. The method according to claim 4, characterized in that Step (2) specifically comprises: uniformly mixing molten polyolefin and foaming gas to form an aerosol, and co-extruding the aerosol and the molten polyolefin for preparing the solid outer skin layer on the surface of the inner conductor after the roughening treatment to form the foamed resin layer and the solid outer skin layer coated on the outside of the foamed resin layer.

8. The method according to claim 4, characterized in that The inner conductor in step (1) is an inner conductor that has been preheated at a temperature of 80°C-120°C.

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