High-temperature resistant cable for mobile phone base station

Abstract

A high-temperature resistant cable for a mobile communication base station comprising, in succession, an inner conductor, a PTFE insulating layer, an outer conductor, and a sheath, wherein the PTFE insulating layer has at least one hollow channel extending in a direction of extension of the inner conductor, wherein the outer conductor is a spiral copper tube, wherein the PTFE insulating layer is formed by extruding and sintering a pasty PTFE material to form a PTFE insulating layer blank surrounding the inner conductor, wherein the extruded PTFE insulating layer blank is dried at a temperature of 100 to 250 °C, and subsequently the dried PTFE insulating layer blank is sintered and solidified at a temperature of 400-480 °C, and wherein nano-copper oxide is added to the pasty PTFE material.

Description

Technical field

[0001] The present invention relates to the technical field of accessories for mobile communication base stations and in particular relates to a high temperature resistant cable for a mobile communication base station. background

[0002] In the field of mobile communications, miniaturization and high gain in mobile base station antennas are the trends for future development. A conventional high-temperature cable currently used in base station antennas, such as semi-flexible RG141 cable, offers advantages like high temperature resistance, low intermodulation, good bending properties, and good mechanical phase stability. However, RG141 cable is unsuitable for high-gain antennas due to the high attenuation inherent in its structure and dimensions. Using RG250 instead of RG141 increases the cost of the coaxial cable used in the antenna by almost 200%, and the larger dimensions of RG250 lead to a larger bending radius, which is not conducive to cable routing within the antenna.

[0003] Prior art patent US 2005 / 0139377A1 discloses a paste-extruded insulated conductor with air channels, comprising a conductor and an insulator made of paste-extruded PTFE fine powder surrounding the conductor, wherein the insulator has at least one closed, continuous, longitudinal air channel separated from the conductor by a gap. The insulator is typically dried at temperatures between 100°C and 250°C and sintered at temperatures in the range of 327°C to 500°C.

[0004] Furthermore, the prior art typically uses a combined process of weaving a tinned copper wire and tin dipping for the outer conductor of the high-temperature cable, which will break after repeated bending. CN 1 02 646 464 A discloses an RF cable comprising, from the inside out, an inner conductor, an insulating layer, a knitted and tinned layer, and an outer sheath. The insulating layer is a PTFE layer with several porous cavities inside, and the knitted and tinned layer consists of tinned copper wire knitting. As in Fig.As shown in Figure 1, the strength of the weld point where one end of a connector in a high-temperature cable assembly used in the antenna is attached to the cable is poor, which can easily cause the outer conductor of the cable to break when bent. Even if a heat-shrinkable sleeve is used to increase the strength, it is still difficult to completely solve the problem of the outer conductor breaking easily.

[0005] Furthermore, CN 2 10 575 256 U discloses a foamed PTFE RF coaxial cable with stable amplitude and phase, comprising a coaxially arranged inner conductor core, an insulating layer, an outer conductor, an outer shielding layer, and a jacket layer. The insulating layer is a foamed polytetrafluoroethylene insulating layer with porous gaps along the cable axis direction, wherein the outer conductor has a helical tubular structure formed by helical winding of a silver-plated copper strip.

[0006] There is therefore an urgent need to develop a high-temperature cable with small dimensions, low loss, good bending properties, low intermodulation and high strength, in order to simultaneously meet the requirements for miniaturization and high gain of mobile base station antennas. Disclosure of the invention

[0007] To solve the aforementioned technical problem in the prior art, it is an object of the present invention to provide a high-temperature resistant cable for a mobile communication base station.

[0008] In order to solve the technical problems described in the present disclosure and to solve the problem of the present invention, a high-temperature resistant cable with the features of claim 1 is proposed.

[0009] Furthermore, the PTFE insulation layer of the cable according to the invention can have several hollow channels that are not connected to each other.

[0010] The multiple hollow channels can be arranged parallel to the inner conductor and symmetrically around the inner conductor.

[0011] Furthermore, in the cable according to the invention, the inner conductor can be a single silver-plated copper wire or a copper strand made of a plurality of silver-plated copper wires.

[0012] Furthermore, in the cable according to the invention, the PTFE insulation layer can have an outer diameter of 2.0 to 20.0 mm, preferably of 3.0 to 20.0 mm.

[0013] Furthermore, in the cable according to the invention, the hollow channel can have a diameter of 0.20 to 5.0 mm, preferably of 0.20 to 2.0 mm.

[0014] Furthermore, the sheathing of the cable according to the invention can be made of low-smoke halogen-free (LSZH type) or fluorinated ethylene propylene copolymer (FEP) and other high-temperature resistant materials.

[0015] In comparison to the nearest prior art, the high-temperature resistant cable for a mobile communication base station according to the present invention has the following advantageous effects.

[0016] The high-temperature resistant cable for a mobile communication base station of the present invention has the same dimensions as a conventional semi-flexible cable, but it has higher strength, better bending properties and lower intermodulation and losses and can follow the trend towards miniaturization and high gain of mobile communication antenna base stations. Brief description of the drawings Fig. Figure 1 is a photograph showing a crack in the outer conductor at a point where a connector of a high-temperature cable assembly is welded to the cable according to the state of the art. Fig. Figure 2 is a schematic view of the overall structure of a high-temperature resistant cable for a mobile communication base station according to the present invention. Fig.Figure 3 is a schematic cross-sectional view of the high-temperature resistant cable for a mobile communication base station according to the present invention. Detailed description of the embodiments

[0017] A high-temperature resistant cable for a mobile communication base station according to the present invention is further described below with reference to the specific embodiments in order to provide a more complete and clearer description of the technical solution of the present invention.

[0018] As in the Fig.As shown in Figures 2 to 3, the high-temperature-resistant cable for a mobile communication base station in this embodiment comprises, successively, an inner conductor 10, a PTFE insulating layer 20, an outer conductor 30, and a sheath 40. The PTFE insulating layer has at least one hollow channel extending along one direction of the inner conductor. The multiple hollow channels are parallel to the inner conductor and are symmetrically distributed around the inner conductor.

[0019] In the present invention, the inner conductor is preferably made of silver-plated copper wire to meet the requirements for high-frequency transmission properties. For example, a single silver-plated copper wire or a copper strand can be selected from a plurality of silver-plated copper wires. As a noble metal, silver is used as a plating layer for the conductive wire core, which can reduce conductor loss at high frequency / radio frequency and is advantageous for improving or guaranteeing the cable's performance at high temperatures and high frequencies. The silver plating layer can also provide good thermal conductivity and resistance to thermal oxidation, which are conducive to the formation of the PTFE insulating layer on the inner conductor by extrusion and sintering processes.

[0020] In contrast to the swelling microporous polytetrafluoroethylene (PTFE) insulating layer typically used in the prior art, the present invention uses a PTFE insulating layer comprising at least one hollow channel extending along the direction of the inner conductor. The PTFE insulating layer has an outer diameter of 2.0 to 20.0 mm, and preferably 2.0 to 10.0 mm. The hollow channel has a diameter of 0.20 to 5.0 mm, preferably 0.20 to 2.0 mm, and particularly preferably 0.30 to 1.50 mm.The PTFE insulation layer with the hollow channel not only guarantees the temperature resistance of the PTFE insulation layer, but can also reduce the dielectric constant of the PTFE insulation layer, since air is filled into the hollow channel; and since the PTFE insulation layer has a lower dielectric loss, it is suitable for the high-frequency and ultra-high-frequency working environments to which the present invention is applied.At the same time, compared to a standard expanding microporous polytetrafluoroethylene (PTFE) insulation layer, the use of a hollow-channel insulation layer can reduce the amount of PTFE material required and improve its utilization. For example, provided the strength and temperature resistance of the insulation layer are guaranteed, it is generally possible to reduce the amount of PTFE material by 10% to 50%, depending on the diameter and number of hollow channels. The PTFE insulation layer is formed by extruding and sintering a paste-like PTFE material.

[0021] In particular, the insulating layer with a hollow channel according to the present invention is obtained by extruding, drying, and sintering the pasty PTFE material using an extruder. The extruder comprises a die head and a die core, and the die head has a conically tapered section and a die hole connected to a base of the conically tapered section; the die core has a central hole for conveying the inner conductor and a plurality of rods extending in a direction parallel to an axis of the die core, the rods being arranged symmetrically around the central hole. The rods are arranged in the die hole to form the hollow channels.In detail, the process is as follows: the pasty PTFE material is extruded through the conically tapered section of the nozzle head and is extruded from an outlet of the nozzle hole to form a PTFE insulation layer blank surrounding the inner conductor, and the extruded PTFE insulation layer blank can be dried at a temperature of 100 to 250 °C so that lubricating oil in the PTFE insulation layer blank evaporates and is removed. When the drying process is carried out, a hot air stream can be introduced to accelerate the evaporation of the lubricating oil, then the dried PTFE insulation layer blank is sintered and solidified in a curing oven, and a sintering and solidification temperature can, for example, be higher than a PTFE melting temperature and lower than 500 °C, preferably from 400 to 480 °C, to obtain the PTFE insulation layer of the present invention.In the present invention, the pasty PTFE material is typically formed using PTFE, lubricating oil, or the like, or a commercially available pasty PTFE material can be used; for example, a pasty material with the trade name Fluon CD4 (Imperial Chemical Industries) can be used. Fluorine atoms in a PTFE molecular chain are symmetrically and uniformly distributed without an inherent dipole moment, which causes a dissipation factor tgδ and its relative dielectric constant to change slightly in a range from low to high frequency. tgδ is also nearly constant in the temperature range from room temperature to its operating temperature and even up to 300 °C, and theoretically, the tgδ value is approximately 0.0001. However, in the present invention, the pasty PTFE material is used.Since the lubricant contained therein is difficult to completely evaporate and sinter, the dielectric loss tgδ is typically 0.00035 to 0.00050. However, the applicant has found that adding a small amount of nano-copper oxide, in particular 0.05 to 0.5 wt% (preferably 0.05 to 0.30) of the pasty PTFE material, contributes to reducing the dissipation factor tgδ, but does not affect the bending properties and has little influence on the dielectric constant. This may result from the improved sintering performance of the PTFE insulation blank due to the nano-copper oxide and the reduction of crystallization loss. Table 1 below shows the influence of the nano-copper oxide content on the dielectric loss tgδ (resonant cavity method). Table 1 Salary 0 0,01 0,02 0,03 0,05 0,10 0,20 0,30 0,40 0,50 0,60 tgδ 0,00045 0,00042 0,00045 0,00041 0,00035 0,00030 0,0025 0,0028 0,00035 0,00040 0,0010

[0022] In the present invention, the outer conductor is a spiral copper tube. The structural strength and bending properties of the outer conductor are further improved by using the spiral copper tube instead of an outer conductor produced by a combined process of wire weaving and tin dipping. Furthermore, a dual air channel, formed by air between the spiral copper tube and the PTFE insulation layer and air within the hollow channels of the PTFE insulation layer, further reduces the insulation dielectric constant, advantageously resulting in a further reduction of the dielectric loss. In the present invention, the outer conductor is formed from a copper strip using conventional machining, welding, drawing, dimensioning, and stamping processes.To reduce loss and improve bending properties, the pitch, peak, and trough between the screw turns should be as uniform as possible. The copper strip should be thicker than 0.15 mm, and its surface should be smooth, clean, and free of defects such as flaking, burrs, inclusions, and the like.

[0023] In the present invention, the sheathing is arranged on an outermost layer to protect the inner conductor, the outer conductor, and the PTFE insulating layer therein. The sheathing can be made of materials such as low-smoke, halogen-free (LSZH type) or fluorinated ethylene propylene copolymer (FEP), or other materials with low smoke, low toxicity, low corrosion, and high flame-retardant properties, which not only impart good mechanical and flame-retardant properties to the cable but are also safe and environmentally friendly. First embodiment

[0024] The high-temperature resistant cable in this embodiment comprises a silver-plated copper wire inner conductor, a PTFE insulating layer with seven hollow channels arranged parallel to one direction of extension of the inner conductor and symmetrically around the inner conductor, a spiral copper tube, and a flame-retardant LSZH polyolefin. The silver-plated copper wire inner conductor has a diameter of 1.15 ± 0.02 mm, with the silver-plated layer having a thickness greater than 1 µm. The PTFE insulating layer has an outer diameter of 3.00 ± 0.05 mm. Seven hollow channels, each with a diameter of 0.3 to 0.5 mm, are symmetrically distributed within it. The spiral copper tube has an outer diameter of 4.25 ± 0.10 mm. The outer sheath has an outer diameter of 5.20 ± 0.10 mm. Second embodiment

[0025] The high-temperature resistant cable in this embodiment comprises a silver-plated copper wire inner conductor, a PTFE insulating layer with seven hollow channels arranged parallel to one direction of extension of the inner conductor and symmetrically around the inner conductor, a spiral copper tube, and a fluorinated ethylene-propylene copolymer FEP. The silver-plated copper wire inner conductor has a diameter of 1.15 ± 0.02 mm, with the silver-plated layer having a thickness greater than 1 µm. The PTFE insulating layer has an outer diameter of 3.00 ± 0.05 mm. Seven hollow channels, each with a diameter of 0.3 to 0.5 mm, are symmetrically distributed. The spiral copper tube has an outer diameter of 4.25 ± 0.10 mm. The sheathing has an outer diameter of 5.0 ± 0.10 mm.

[0026] According to the coaxial cable signal transmission principle, the transmission loss of the cable is primarily caused by heat generation in the inner conductor, insulation, and outer conductor. The present invention improves the structure and material of the cable, which not only solves problems related to the cable's mechanical properties, such as bending cracks and insufficient strength, but also significantly reduces the overall attenuation of the cable due to a substantial reduction in the overall dielectric constant and loss.

Claims

[1] High-temperature resistant cable for a mobile communication base station comprising successively an inner conductor, a PTFE insulating layer, an outer conductor and a sheath, wherein the PTFE insulating layer has at least one hollow channel extending in a direction of extension of the inner conductor, wherein the outer conductor is a spiral copper tube, wherein the PTFE insulating layer is formed by extruding and sintering a pasty PTFE material to form a PTFE insulating layer blank surrounding the inner conductor, wherein the extruded PTFE insulating layer blank is dried at a temperature of 100 to 250 °C, and subsequently the dried PTFE insulating layer blank is sintered and solidified at a temperature of 400-480 °C, and wherein nano-copper oxide is added to the pasty PTFE material. [2] High temperature resistant cable for a mobile communication base station according to claim 1, wherein the PTFE insulation layer comprises several hollow channels which are not interconnected. [3] High temperature resistant cable for a mobile communication base station according to claim 2, wherein the multiple hollow channels are parallel to the inner conductor and are distributed symmetrically around the inner conductor. [4] High temperature resistant cable for a mobile communication base station according to claim 1, wherein the inner conductor is a single silver-plated copper wire or a copper strand made of a plurality of silver-plated copper wires. [5] High temperature resistant cable for a mobile communication base station according to claim 1, wherein the PTFE insulation layer has an outer diameter of 2.0 to 20.0 mm. [6] High temperature resistant cable for a mobile communication base station according to claim 5, wherein the PTFE insulation layer has an outer diameter of 3.0 to 20.0 mm. [7] High temperature resistant cable for a mobile communication base station according to claim 5, wherein the hollow channel has a diameter of 0.20 to 5.0 mm. [8] High temperature resistant cable for a mobile communication base station according to claim 7, wherein the hollow channel has a diameter of 0.20 to 2.0 mm. [9] High temperature resistant cable for a mobile communication base station according to claim 1, wherein the sheathing is made of low smoke halogen-free or fluorinated ethylene propylene copolymer and other high temperature resistant materials.

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