Low-loss leaky coaxial cable and manufacturing method thereof

Abstract

The invention belongs to the field of wireless communication, and particularly relates to a low-loss leaky coaxial cable and a manufacturing method thereof. The leaky coaxial cable comprises an inner conductor, a composite insulating layer, an outer conductor and a sheath layer which are coaxially arranged in sequence, and each layer forms a concentric cylindrical structure by taking an axis as a center. The outer surface of the inner conductor and the outer surface of the outer conductor of the leaky coaxial cable are respectively roughened, so that the contact between the inner conductor and the insulating layer and the contact between the outer conductor and the sheath layer are improved, meanwhile, a solid inner skin layer originally used for bonding the inner conductor and the insulating layer is omitted, the signal transmission performance is improved, and the service life of the leaky coaxial cable is prolonged. And the transmission loss is reduced. Compared with an existing product, the leaky coaxial cable with the surfaces of the inner conductor and the outer conductor, provided by the invention, has the advantages that the attenuation index is integrally optimized by 2.6%-5.8% under multiple frequency bands of 900 MHz to 2700 MHz on the premise of meeting the test requirements of adhesive force, standing wave and insulating dielectric strength between the insulating layer and the inner conductor.

Description

Technical Field

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

[0002] Leaky coaxial cable radiates to the outside world and receives electromagnetic wave signals from the outside world by setting openings on its outer conductor. Therefore, it has the dual functions of signal transmission line and transceiver antenna. It is mainly used in places where radio signal propagation is poor, such as tunnels, tunnels, underground railways, underground buildings, mountainous areas and other environments.

[0003] Existing leaky coaxial cables are usually composed 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 to isolate the two and the supporting structure; the outer conductor is used to transmit signals and shield external signals, and there are openings on the outer conductor for signal leakage.

[0004] The product structure of conventional leaky coaxial cable complies with the industry standard YD / T 2491 "Communication Cable Physical Foamed Polyethylene Insulation Longitudinal Copper Tape Outer Conductor Radial Leaky Coaxial Cable". Its insulation layer is usually divided into three layers. The solid thin insulation layer close to the inner and outer conductors of the cable is mainly made of low-density polyethylene (LDPE) or high-density polyethylene (HDPE), mixed with ethylene-vinyl acetate (EVA) resin with bonding effect; the middle foam insulation layer is thicker, and its material composition is mainly LDPE and HDPE mixture mixed with nucleating agent, and is made by physical foaming continuous extrusion process. This kind of insulation structure can better take into account the requirements of attenuation, cost and production efficiency. However, there are problems in the leaky coaxial cable of the prior art, such as large dielectric constant of solid insulation layer and excessive cable transmission attenuation. The commonly used insulation 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 be well bonded to the surface of the inner conductor, which will cause the insulation layer and the inner conductor to separate, causing changes in the cable structure and affecting normal transmission. The outer conductor and the sheath layer are also made of two completely different materials, so there is also the problem of poor adhesion; in addition, if the cable is powered on for a long time, poor heat dissipation performance will also affect its service life.

[0005] In order 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 foam 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 mixture of solid polyethylene and glue EVA, the comprehensive dielectric constant is about 2.4 (data at 1 MHz), compared with the dielectric constant of 1.25 of the physical foam layer, the existence of the inner skin layer greatly increases the transmission loss of the cable.

[0006] Therefore, an improved leaky coaxial cable structure is urgently needed to solve the above problems. Summary of the invention

[0007] In view of the defects of the prior art, the purpose of the present invention is to provide a low-loss leaky coaxial cable and a method for manufacturing the same. By appropriately roughening the surfaces of the inner conductor and the outer conductor, respectively, the contact between the inner conductor and the insulation layer, as well as the outer conductor and the sheath layer is improved, and the solid inner skin layer is omitted, thereby reducing cable losses and improving signal transmission performance, thereby solving the technical problems of the prior art such as poor contact between the inner conductor and the insulation layer, as well as the outer conductor and the sheath layer, and high transmission losses.

[0008] To achieve the above object, the present invention provides a low-loss leaky coaxial cable, the cable comprising an inner conductor, a composite insulating layer, an outer conductor and a sheath layer coaxially arranged in sequence, each layer forming a concentric cylindrical structure with the axis as the center; The composite insulating layer comprises a foamed resin layer and a solid outer skin layer; wherein the outer surface of the inner conductor is in direct contact with the foamed resin layer, and the solid outer skin layer is in direct contact with the inner surface of the outer conductor; The outer 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 outer conductor is provided with a plurality of openings for allowing signal leakage; and the outer surface of the outer conductor also has a microscopic rough structure formed by roughening treatment, and the roughness thereof is 5 μm to 20 μm.

[0009] Preferably, the roughness of the outer surface of the inner conductor is 1 μm to 3 μm.

[0010] Preferably, the surface roughening treatment methods of the inner conductor and the outer conductor are independently laser roughening, chemical etching, mechanical grinding or electrochemical treatment.

[0011] According to another aspect of the present invention, there is provided a method for preparing the leaky coaxial cable, comprising the following steps: (1) performing a surface roughening treatment on the outer surface of the inner conductor so that the roughness thereof is controlled within a range of 0.5 μm to 5.0 μm, thereby obtaining a roughened inner conductor; (2) preparing the foamed resin layer and the solid outer skin layer on the outer surface of the inner conductor after the roughening treatment by a double-layer co-extrusion process; (3) performing a surface roughening treatment on the outer surface of the outer conductor so that the roughness thereof is controlled within a range of 5 μm to 20 μm, thereby obtaining a roughened outer conductor; (4) longitudinally wrapping the roughened outer conductor outside the solid outer skin layer; (5) The sheath layer is prepared on the outer surface of the outer conductor by an extrusion process.

[0012] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art: (1) By roughening the outer surface of the inner conductor of the leaky coaxial cable, the contact between the inner conductor and the insulation layer is significantly improved, and the solid inner skin layer originally used to bond the inner conductor and the insulation layer material is omitted, thereby reducing the transmission loss of the cable. At the same time, the outer surface of the outer conductor is also roughened, which not only enhances the bonding between the outer conductor and the sheath layer, but also helps the heat dissipation of the cable. Experimental tests show that, under the same other process conditions, the inner and outer conductor surfaces of the leaky coaxial cable are moderately roughened, and the inner skin layer is omitted. The overall attenuation index is reduced by 2.6% to 5.8% compared with the existing technology that is not roughened and contains an inner skin layer.

[0013] (2) The optimized cable structure has better signal transmission performance and anti-interference ability, and is suitable for high-frequency and high-speed communication scenarios.

[0014] (3) The surface roughness of the inner conductor is controlled within the range of 0.5 μm to 5.0 μm, and the surface roughness of the outer conductor is controlled within the range of 5 μm to 20 μm. This can not only ensure contact, but also avoid signal reflection and loss increase, and also improve its heat dissipation performance.

[0015] (4) The improved leaky coaxial cable manufacturing method of the present invention is simple and easy to implement and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the end face structure of the leaky coaxial cable of comparative example 1 of the present invention.

[0017] Figure 2 It is a schematic diagram of the side structure of the leaky coaxial cable of comparative example 1 of the present invention.

[0018] Figure 3 This is a schematic diagram of the end face structure of the leaky coaxial cable according to Example 1 of the present invention.

[0019] Figure 4 This is a schematic diagram of the side structure of the leaky coaxial cable according to Example 1 of the present invention.

[0020] In all the drawings, the same reference numerals are used to represent the same elements or structures, wherein: 1 - inner conductor; 2 - composite insulation layer; 3 - outer conductor; 4 - sheath layer; 5 - opening; 6 - identification structure; 21 - solid inner skin layer; 22 - foamed resin layer; 23 - solid outer skin layer. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0022] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and processes are given, but the protection scope of the present invention is not limited to the following embodiments. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0023] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0024] The "inside", "outside", "inner layer" and "outer layer" mentioned in the present invention are defined relative to the central axis of the leaky coaxial cable, where "inside" refers to the side close to the central axis and "outer" refers to the side away from the central axis.

[0025] The prior art leaky coaxial cable, such as Figure 1 and Figure 2 As shown, it comprises an inner conductor 1, a composite insulation layer 2, an outer conductor 3 and a sheath layer 4 which are coaxially arranged in sequence, and each layer forms a concentric cylindrical structure with the axis as the center. The composite insulation layer is composed of a solid inner skin layer 21, a foamed resin layer 22 and a solid outer skin layer 23; the solid inner skin layer 21 and the solid outer skin layer 23 are usually solid polyethylene layers. A resin with an adhesive effect is usually added to the solid inner skin layer to bond the metal inner conductor and the thermoplastic foamed polyolefin resin insulation layer. However, the addition of an adhesive resin often leads to a high dielectric constant of the solid inner skin layer, which increases the transmission loss of the cable. In addition, the metal surface of the inner conductor is directly bonded to the thermoplastic resin, and the contact between the two completely different materials is poor, which can easily lead to a decrease in the electrical performance of the cable. In view of these technical defects, the present invention provides a low-loss leakage coaxial cable, such as Figure 3 and Figure 4As shown, it comprises an inner conductor 1, a composite insulating layer 2, an outer conductor 3 and a sheath layer 4 which are coaxially arranged in sequence, and each layer forms a concentric cylindrical structure with the axis as the center. The composite insulating layer is composed of a foamed resin layer 22 and a solid outer skin layer 23. Compared with the above-mentioned prior art, the solid inner skin layer 21 is omitted; the outer surface of the inner conductor 1 is in direct contact with the foamed resin layer 22, and the solid outer skin layer 23 is in direct contact with the inner surface of the outer conductor 3. The outer 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 (Ra) ranges from 0.5 μm to 5.0 μm. The outer conductor 3 is provided with a number of openings 5 ​​for allowing signal leakage. Correspondingly, an identification structure 6 is provided on the sheath layer 4 on the other side of the opening to facilitate identification of the location of the outer conductor opening 5 during installation. Usually, the identification structure 6 is an outer conductor slot identification line arranged along the length direction of the sheath layer, and a single slot identification line is at 180° from the center of the slot, and the center of the double slot identification line is at 180° from the center of the slot. The outer surface of the outer conductor also has a microscopic rough structure formed by roughening treatment, and its roughness is 5 μm to 20 μm.

[0026] The present invention provides a leaky coaxial cable which improves the contact between the inner conductor and the insulating layer, the contact between the outer conductor and the sheath layer by improving the surface structure of the inner conductor and the outer conductor, and omits the inner skin layer. When the leaky coaxial cable is working, the signal is transmitted between the outer surface of the inner conductor and the inner surface of the outer conductor. Therefore, the traditional leaky coaxial cable requires the inner conductor and the outer conductor to remain smooth to prevent the reflection of the cable caused by the surface defects of the conductor from affecting the use. However, experiments have found that when the outer surface of the inner conductor is appropriately roughened, it does not actually affect the electrical performance of the product within the standard range. Moreover, the roughened outer surface of the inner conductor also improves its adhesion with the foamed polyolefin layer insulation layer. At the same time, since the contact between the inner conductor and the foamed insulation layer is increased by roughening the outer surface of the inner conductor, the original solid inner skin layer structure can be directly omitted, and omitting this structure means that the transmission loss of the original inner skin layer to the cable is avoided at the same time, so the transmission loss of the coaxial cable can be further reduced. The present invention also roughens the outer surface of the outer conductor at the same time. Experiments have shown that the roughened outer conductor surface does not affect the transmission of the signal, and its roughness can be greater than the roughness of the outer surface of the inner conductor. The invention roughens the outer surface of the outer conductor in order to improve the adhesion between the outer conductor and the sheath layer and improve the heat dissipation of the cable, thereby further increasing the service life of the cable.

[0027] The roughness (Ra) of the inner conductor surface ranges from 0.5 μm to 3.0 μm, and the 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. Experiments have found that compared with the inner conductor, the surface roughness of the outer conductor in the range of 5μm-20μm has little effect on the electrical performance of the leaky coaxial cable. The outer surface of the outer conductor does not involve signal transmission, and its roughness range can be controlled within the range of 5 μm to 20 μm.

[0028] The surface roughening treatment method of the inner conductor and the outer conductor of the present invention can adopt laser roughening, chemical etching, mechanical grinding or electrochemical treatment to form a uniform concave-convex structure on the surface of the inner conductor and the outer conductor, thereby increasing the contact area with the insulating layer / sheath layer. However, the roughening degree of the outer surface of the inner conductor needs to be strictly controlled to avoid the conductor surface size fluctuation due to excessive roughening affecting signal transmission, or the electric field concentration effect caused by the sharp metal edges due to excessive roughening causing electrical breakdown.

[0029] The outer surfaces of the inner conductor and the outer conductor of the present invention are roughened to form a microscopic rough structure. It is understandable that the present application does not limit the shape or material type of the inner conductor and the outer conductor themselves, and the types of inner conductors and outer conductors reported in the prior art are all applicable to the present application. In some embodiments, the inner conductor can be a copper-clad aluminum wire, a spiral corrugated copper tube, a smooth copper tube, etc., and in other embodiments, high-purity silver materials can also be used. The outer conductor can be a spiral corrugated metal outer conductor, an annular corrugated metal outer conductor, or a metal wire braided outer conductor. In some embodiments, the metal inner conductor and outer conductor are both copper conductors.

[0030] Compared with the prior art, the insulating layer between the inner conductor and the outer conductor of the leaky coaxial cable of the present invention omits the original solid inner skin layer used to bond the inner conductor and the foamed insulating layer, and the remaining foamed resin layer and the solid outer skin layer can also use the insulating layer materials reported in the prior art. For example, the foamed resin layer can be a foamed polyolefin, such as foamed polyethylene, etc., with a foaming degree of 40%-85% and a thickness of 3mm-15mm, and the solid outer skin layer is a solid polyolefin, such as low-density polyethylene LDPE (density range of 0.910 g / cm³ - 0.930 g / cm³), or high-density polyethylene HDPE (density range of 0.940 g / cm³ - 0.976 g / cm³); the thickness of the solid outer skin layer is the same as the thickness of the solid outer skin layer in the prior art, generally 0.05mm~0.15mm.

[0031] In some embodiments, the opening on the outer conductor is a straight hole, an elliptical hole, a U-shaped hole, an L-shaped hole, or a combination of holes.

[0032] In some embodiments, the sheath layer is a polyolefin sheath, such as polyethylene resin, polypropylene resin, polystyrene resin, etc., and the thickness of the sheath layer is 0.3 mm to 4 mm.

[0033] The improved leaky 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. Through the roughening treatment of the inner and outer conductor surfaces, the inner conductor is in direct contact with the foamed resin layer, which significantly improves the contact property and reduces the signal transmission loss; the sheath layer is in direct contact with the roughened outer conductor surface, which can understandably optimize its contact property to a certain extent and significantly improve the heat dissipation performance of the outer conductor.

[0034] The present invention also provides a method for manufacturing a leaky coaxial cable, comprising the following steps: (1) performing a surface roughening treatment on the outer surface of the inner conductor so that the roughness thereof is controlled within a range of 0.5 μm to 5.0 μm, thereby obtaining a roughened inner conductor; (2) preparing a foamed resin layer and a solid outer skin layer by double-layer co-extrusion on the outer surface of the inner conductor after the roughening treatment; (3) performing a surface roughening treatment on the outer surface of the outer conductor so that the roughness thereof is controlled within a range of 5 μm to 20 μm, thereby obtaining a roughened outer conductor; (4) longitudinally wrapping the roughened outer conductor outside the solid outer skin layer; (5) The sheath layer is prepared on the outer surface of the outer conductor by an extrusion process.

[0035] The roughening treatment in step (1) and step (3) of the present invention is not limited to a specific roughening method, for example, they can be laser roughening, chemical etching, mechanical grinding or electrochemical treatment independently. The preferred roughening method is the laser surface roughening process, which can ensure a high degree of consistency in the treatment process, and is easy to perform online synchronous processing, which is convenient for promotion. The inner conductor and outer conductor surfaces with different roughness can be obtained by adjusting the roughening process parameters. In some embodiments, the outer surface of the inner conductor in step (1) is roughened by chemical etching, the etching solution is a 0.1 mol / L-2 mol / L dilute nitric acid solution, the etching time is 1 minute to 30 minutes, and a uniform microscopic rough structure is formed, and the roughness is controlled within the range of 0.5 μm to 5.0 μm; in other embodiments, the outer surface of the outer conductor in step (3) is roughened by chemical etching, the etching solution is a 0.1 mol / L-2 mol / L dilute nitric acid solution, the etching time is 5 minutes to 60 minutes, and a uniform microscopic rough structure is formed, and the roughness is controlled within the range of 5.0 μm to 20.0 μm.

[0036] In other embodiments, the surface of the inner conductor in step (1) is treated by laser, specifically, the laser power is controlled between 10W-300W, 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 outer surface of the outer conductor in step (3) can also be roughened by laser, specifically, the laser power is controlled between 100W-450W, the scanning speed is between 600mm / s and 1200mm / s, the scanning pitch is between 0.05mm and 0.25mm, and the roughness is preferably controlled within the range of 5.0 μm to 20.0 μm. Laser processing can use common lasers, such as solid lasers (365nm solid lasers or 1064nm solid lasers), fiber lasers, gas lasers (carbon dioxide lasers or copper vapor lasers) or semiconductor lasers, preferably fiber lasers.

[0037] In some embodiments, the inner conductor with roughened surface is a preheated inner conductor. The surface preheating temperature is usually controlled at 80° C.-120° C. according to different products, so that the foaming layer can better adhere to the conductor surface.

[0038] In some embodiments, step (2) specifically comprises: uniformly mixing molten polyolefin and foaming gas to form an aerosol, and co-extruding the aerosol and molten polyolefin such as polyethylene used to prepare a solid outer skin layer on the surface of the inner conductor after roughening treatment to form a foamed resin layer and a solid outer skin layer coated on the outside of the foamed resin layer. The extrusion temperature is 130°C to 210°C to ensure that the foamed polyolefin material is tightly combined with the inner conductor to form a foamed resin layer.

[0039] The present invention performs surface roughening treatment on the outer surface of the outer conductor to control its roughness within the range of 5 μm to 20 μm to obtain the roughened outer conductor; then the roughened outer conductor is prepared by longitudinally wrapping the outer solid outer skin layer; finally, a sheath layer is extruded on the surface of the outer conductor to complete the manufacture of the cable.

[0040] The following are examples and comparative examples: Comparative Example 1 The leaky coaxial cable provided in this comparative example is applied to the traditional cable of model HLRCTYZ-50-32 in the YD / T 2491 standard (cable specification is -32), and its end face structure diagram is shown as follows: Figure 1 As shown, the side structure diagram is as follows Figure 2As shown. From the inside to the outside, an inner conductor 1, a composite insulation layer 2, an outer conductor 3 and a sheath layer 4 are coaxially nested in sequence, wherein the composite insulation 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, wherein the inner conductor 1 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 tube, the sheath layer 4 is polyethylene, the outer conductor 3 is provided with an opening 5 for allowing signal leakage, the sheath layer 4 is provided with an identification structure 6, the identification structure 6 is two identification lines arranged along the length direction of the sheath layer, and the center of the two identification lines is 180° at the center of the opening. The preparation method of the leaky coaxial cable of this comparative example is carried out according to the following steps: (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 the inner conductor of a smooth copper tube with a diameter of 13.1 mm to form a bonded solid inner skin layer with a thickness of 0.15 mm.

[0041] (2) High-density polyethylene, low-density polyethylene and 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 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 32.3 mm and a foaming degree of 80%.

[0042] (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.

[0043] (4) Use a copper strip with a thickness of 0.1 mm and pre-grooved holes to longitudinally wrap the copper tube through a forming mold. At the same time, insert the cable core into the longitudinally wrapped copper tube and directly enter the sheath machine head. A layer of low-smoke halogen-free flame-retardant sheath material with a thickness of 2 mm is evenly extruded on the outside of the copper tube to form a finished sheath. The outer diameter of the sheath is 37.1 mm.

[0044] Comparative Example 2 The other aspects are the same as those of Comparative Example 1, except that the outer surface of the outer conductor of Comparative Example 1 is subjected to surface laser roughening treatment in this comparative example, and the specific steps are as follows: Steps (1), (2) and (3) are the same as those in Comparative Example 1.

[0045] Step (4): The outer surface of the 0.1 mm thick copper strip with grooves engraved in advance is roughened by using a fiber laser. The laser power is 320 W, the scanning speed is 800 mm / s, the scanning interval is 0.08 mm, and the surface roughness is controlled at 10 μm, thereby obtaining an outer conductor with a roughened outer surface.

[0046] (5) The outer conductor with roughened outer surface is longitudinally wrapped in a copper tube through a forming mold. At the same time, the cable core is inserted into the longitudinally wrapped copper tube and directly enters the sheath machine head. A layer of low-smoke halogen-free flame-retardant sheath material with a thickness of 2 mm is evenly extruded on the outside of the copper tube to form a finished sheath. The outer diameter of the sheath is 37.1 mm.

[0047] Comparative Example 3 The other aspects are the same as those of Comparative Example 2, except that the laser roughening process parameters are controlled so that the roughness of the outer surface of the outer conductor after laser roughening is 20 μm.

[0048] Example 1 The leaky coaxial cable provided in this embodiment is applied to the traditional cable of model HLRCTYZ-50-32 in the YD / T 2491 standard (cable specification is -32), and its end face structure schematic diagram is shown as follows: Figure 3 As shown, the side structure diagram is as follows Figure 4 As shown. An inner conductor 1, a composite insulation layer 2, an outer conductor 3 and a sheath layer 4 are coaxially nested in sequence from the inside to the outside, wherein the composite insulation layer 2 includes a foamed resin layer 22 and a solid outer skin layer 23 in sequence from the inside to the outside, the outer surface of the inner conductor 1 is in direct contact with the inner surface of the foamed resin layer, and the outer surface of the solid outer skin layer 23 is in direct contact with the inner surface of the outer conductor 3. The inner conductor 1 is a solid copper-clad aluminum wire, the foamed resin layer 22 is foamed polyethylene, the solid outer skin layer 23 is low-density polyethylene, the outer conductor 3 is a copper strip welded corrugated tube, the sheath layer 4 is polyethylene, the outer conductor 3 is provided with an opening 5 for allowing signal leakage, the sheath layer 4 is provided with an identification structure 6, the identification structure 6 is two identification lines arranged along the length direction of the sheath layer, and the center of the two identification lines is at 180° from the center of the opening. The preparation method of the leaky coaxial cable of this embodiment is carried out according to the following steps: (1) The outer surface of a 13.1 mm diameter smooth copper tube was roughened using a fiber laser. The laser power was 60 W, the scanning speed was 1000 mm / s, the scanning spacing was 0.08 mm, and the surface roughness was controlled at 2 μm. Then it was preheated and the temperature before entering the foaming head was 80~120°C.

[0049] (2) High-density polyethylene, low-density polyethylene and 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 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, the mixture was directly attached to the inner conductor with roughened surface by high-pressure extrusion for foaming and cooling to form an insulating foamed cable core with a diameter of 32.3 mm and a foaming degree of 80%.

[0050] (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.

[0051] (4) The outer surface of the copper strip with a thickness of 0.1 mm and grooves engraved in advance was roughened by a fiber laser. The laser power was 320 W, the scanning speed was 800 mm / s, the scanning interval was 0.08 mm, and the surface roughness was controlled at 10 μm to obtain an outer conductor with a roughened outer surface.

[0052] (5) The outer conductor with roughened outer surface is longitudinally wrapped in a copper tube through a forming mold. At the same time, the cable core is inserted into the longitudinally wrapped copper tube and directly enters the sheath machine head. A layer of low-smoke halogen-free flame-retardant sheath material with a thickness of 2 mm is evenly extruded on the outside of the copper tube to form a finished sheath. The outer diameter of the sheath is 37.1 mm.

[0053] Example 2 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 after roughening treatment is 3 μm.

[0054] Example 3 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 after laser roughening is 4 μm.

[0055] Example 4 The rest is the same as in Example 1, except that the laser roughening process parameters are controlled so that the roughness of the inner conductor surface after laser roughening is 5 μm.

[0056] Comparative Example 4 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 after laser roughening is 0.3 μm.

[0057] Comparative Example 5 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 after laser roughening is 6 μm.

[0058] Comparative Example 6 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 after laser roughening is 8 μm.

[0059] The leaky coaxial cables of the above comparative examples and embodiments were verified and tested according to the test method in the YD / T 2491 standard. The test items were: a. Adhesion test between the insulation layer and the inner conductor (considering the effect of the roughening process on the stability of the product structure); b. Standing wave test (considering the effect of the roughening process on the standing wave index); c. Insulation dielectric strength test (considering whether the surface roughness of the inner conductor after roughening will produce metal sharp corners to cause local electric field concentration, thereby causing abnormal insulation withstand voltage index); d. Loss / attenuation test (considering the effect of the roughening process on the cable attenuation after removing the inner cortex layer). The measured results are shown in Table 1 (the " / " in Table 1 indicates that the roughening process was not performed).

[0060] Table 1

[0061] Comparative Examples 2 and 3 are based on Comparative Example 1, except that only the outer conductor surface is roughened to a roughness of 10 μm and 20 μm respectively. It can be seen from the data in Table 1 that when only the outer surface of the outer conductor is roughened, the electrical properties of the leaky coaxial cable are almost the same as those of Comparative Example 1 without roughening, indicating that roughening the surface of the outer conductor of the leaky coaxial cable does not affect the electrical properties of the cable. However, it can be understood that roughening the outer conductor can improve its adhesion with the sheath layer and can help dissipate heat from the outer conductor.

[0062] It can be seen from the test data of test item d in Table 1 that, compared with comparative example 1, in embodiments 1 to 4, under the condition that other process is the same, the outer surface of the outer conductor is roughened to the same extent (roughness is 10 μm), and the surface of the inner conductor is roughened to different degrees (roughness ranges from 2 μm to 5 μm), and the inner cortex is removed, and the attenuation index is optimized (reduced) by 2.6% to 5.8% as a whole.

[0063] From the test data of test item a in Table 1, it can be seen that the adhesion index between the insulating layer and the inner conductor increases with the increase of the surface roughness of the inner conductor. When the surface roughness of the inner conductor is reduced to 0.3μm (Comparative Example 4), the adhesion between the conductor and the insulating layer cannot meet the normal requirements. In addition, when the adhesion index is unqualified, it may be due to the unstable structure between the insulating layer and the inner conductor, which indirectly leads to the failure of the standing wave index of test item b.

[0064] 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 (Comparative Examples 5 and 6), the electric field concentration effect caused by the sharp corners of the metal surface may cause the insulation dielectric strength test to fail. At the same time, according to experimental data, when the outer surface of the inner conductor is too rough, the insulation dielectric strength test fails, while the standing wave test meets the standard; the insulation dielectric strength index has problems before the standing wave index, so the influence of the standing wave is not a priority consideration, which also shows that as long as the surface roughness of the inner conductor is controlled within an appropriate range, the standing wave test is usually up to standard.

[0065] From the above test data, it can be seen that the feasible surface roughness of the inner conductor of the leaky coaxial cable after roughening is 0.5μm~5μm, and the better roughness range is 1μm~3μm; the outer surface roughness of the outer conductor can be controlled at 5μm-20μm, and better at 10μm-20μm.

[0066] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-loss leaky coaxial cable, characterized in that: The cable comprises an inner conductor, a composite insulating layer, an outer conductor and a sheath layer which are coaxially arranged in sequence, and each layer forms a concentric cylindrical structure with the axis as the center; The composite insulating layer comprises a foamed resin layer and a solid outer skin layer; wherein the outer surface of the inner conductor is in direct contact with the foamed resin layer, and the solid outer skin layer is in direct contact with the inner surface of the outer conductor; The outer 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 outer conductor is provided with a plurality of openings for allowing signal leakage; and the outer surface of the outer conductor also has a microscopic rough structure formed by roughening treatment, and the roughness thereof is 5 μm to 20 μm.

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

3. The leaky coaxial cable according to claim 1, characterized in that: The surface roughening treatment methods of the inner conductor and the outer conductor are independently laser roughening, chemical etching, mechanical grinding or electrochemical treatment.

4. The leaky coaxial cable according to claim 1, characterized in that: 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; and / or, The solid outer skin layer is solid polyolefin; the thickness of the solid outer skin layer is 0.05mm-0.15mm.

5. The leaky coaxial cable according to claim 1, characterized in that: The opening on the outer conductor is a straight hole, an elliptical hole, a U-shaped hole, an L-shaped hole or a combined hole.

6. A method for preparing a leaky coaxial cable according to any one of claims 1 to 5, characterized in that: The steps include: (1) performing a surface roughening treatment on the outer surface of the inner conductor so that the roughness thereof is controlled within a range of 0.5 μm to 5.0 μm, thereby obtaining a roughened inner conductor; (2) preparing the foamed resin layer and the solid outer skin layer on the outer surface of the inner conductor after the roughening treatment by a double-layer co-extrusion process; (3) performing a surface roughening treatment on the outer surface of the outer conductor so that the roughness thereof is controlled within a range of 5 μm to 20 μm, thereby obtaining a roughened outer conductor; (4) longitudinally wrapping the roughened outer conductor outside the solid outer skin layer; (5) The sheath layer is prepared on the outer surface of the outer conductor by an extrusion process.

7. The method according to claim 6, characterized in that The roughening treatments in step (1) and step (3) are independently laser roughening, chemical etching, mechanical grinding or electrochemical treatment.

8. The method according to claim 7, characterized in that When step (1) uses laser roughening to perform the outer surface roughening treatment of the inner conductor, the laser power is 10W-300W, the scanning speed is between 600mm / s and 1200mm / s, and the scanning interval is between 0.05mm and 0.12mm; and / or, When step (3) uses laser roughening to perform the outer surface roughening treatment of the outer conductor, the laser power is 100W-450W, the scanning speed is between 600mm / s and 1200mm / s, and the scanning interval is between 0.05mm and 0.25mm.

9. The method according to claim 6, characterized in that Step (2) specifically comprises: uniformly mixing molten polyolefin and foaming gas to form an aerosol, and performing double-layer co-extrusion of the aerosol and the molten polyolefin material for preparing the solid outer skin layer on the outer 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.

10. The method according to claim 6, 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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