Low standing wave leaky coaxial cable and radio frequency coaxial cable

Abstract

The invention belongs to the technical field of communication transmission cables, and particularly relates to a low standing wave leaky coaxial cable and a radio frequency coaxial cable. The corrugated pitch of the copper pipes of the outer conductor and the inner conductor and the synchronous phase difference between the outer conductor and the inner conductor are optimized correspondingly, and the standing-wave ratio of the radio frequency coaxial cable and the leaky coaxial cable finished product is reduced to the maximum extent. Under the condition that the requirements of the YD / T1092 standard and the YD / T2491 standard are met, the average value of the voltage standing wave ratio of the leaky coaxial cable can be reduced to 1.21, the average value of the voltage standing wave ratio of the radio-frequency coaxial cable can be reduced to 1.11, and meanwhile the leaky coaxial cable has the advantages of being convenient to control, high in adjusting precision and the like.

Description

Technical Field

[0001] The present application belongs to the technical field of communication transmission cables, and more specifically, relates to a low standing wave leakage coaxial cable and a radio frequency coaxial cable. Background Art

[0002] As common types of coaxial cables, RF coaxial cables and leaky coaxial cables have been widely used in many fields such as communications, radio and television, and satellite communications. Existing RF coaxial cables and leaky coaxial cables usually include structures such as inner conductor, foam insulation layer, outer conductor and sheath layer from the inside to the outside. RF coaxial cables are mostly used for RF signal transmission between mobile base stations and antennas, and leaky coaxial cables are mostly used for wireless signal coverage in narrow and long areas such as tunnels.

[0003] Voltage standing wave ratio (VSWR) is an important indicator to measure the impedance matching degree between the transmission line and the load in the RF transmission system, and has a significant impact on the cable transmission effect. The closer the VSWR is to 1, the better the impedance matching between the transmission line and the load, the smaller the reflected power, and the higher the signal transmission efficiency; high VSWR means more signal reflection and transmission loss. This reflected signal will not only reduce the signal strength, but also may cause damage to the transmitting equipment. Therefore, how to effectively reduce the voltage standing wave ratio of coaxial cable has always been one of the hot technical topics in this field.

[0004] In the prior art, whether it is RF coaxial cable or leaky coaxial cable, in order to ensure the consistency of cable impedance during processing and prevent signal reflection caused by impedance mutation and increase in standing wave ratio, the conventional practice is to control the equipment to operate according to fixed parameters as much as possible during the manufacturing process, so as to produce cables with uniform and stable dimensions.

[0005] However, further research shows that the RF cable production process often causes periodic failures in the system due to unstable factors such as equipment or raw materials. This periodic effect on the cable is manifested as periodic structural size fluctuations of the cable, and periodic structural size fluctuations can easily cause the cable's standing wave ratio to have a high peak value. Accordingly, further research is urgently needed in this field to better meet the high quality control requirements for reducing the voltage standing wave ratio of RF coaxial cables. Summary of the invention

[0006] In response to the above defects or improvement needs of the prior art, the present application provides a low standing wave leakage coaxial cable and a radio frequency coaxial cable, wherein targeted improvements are made by selecting the pitch design of specific structures such as the inner conductor and the outer conductor and the pitch variation model, etc., which can not only more accurately and effectively reduce the voltage standing wave ratio of various coaxial cables, but also simultaneously improve the cable bending stress and reduce the attenuation of high-frequency signals. At the same time, it has the advantages of easy processing and control, high reliability, etc., and is particularly suitable for high-frequency signal transmission application scenarios such as 5G communication base stations.

[0007] To achieve the above objectives, in a first aspect, the present application provides a low standing wave leakage coaxial cable, which comprises an inner conductor, an insulating medium, an outer conductor and a protective sleeve from inside to outside: The inner conductor is composed of a spiral corrugated copper tube for transmitting signals and its thread direction is kept rightward, wherein the corrugation pitch of the inner conductor is distributed in sections along the length direction of the cable and changes continuously, and adjacent sections each have different gradient characteristics; The outer conductor is composed of an annular corrugated copper tube or a spiral corrugated copper tube and has periodic openings or gaps on its surface for uniformly radiating and receiving signals. The corrugation pitch of the outer conductor is also distributed in segments along the length of the cable and is continuously gradient. Adjacent segments each have different gradient characteristics, and the pitch change of the inner conductor maintains a synchronous phase difference with the outer conductor.

[0008] As a further preferred embodiment of the present application, a synchronous phase difference of 0.6 to 0.8 times of the pitch change is maintained between the inner conductor and the outer conductor.

[0009] As a further preferred embodiment of the present application, the inner conductor and the outer conductor include at least three adjacent sections along the length direction of the cable, wherein the corrugation pitches in the first to third sections change according to the following first to third functional formulas respectively: The first function: P i =g+t×func Second function: P j =gt×func The third function: P r =g+t×sinα Among them, P i represents the wrinkle pitch at the i-th change in the first section, in mm; P j represents the wrinkle pitch when the jth change occurs in the second section, in mm; P rrepresents the wrinkle pitch at the rth change in the third section, in mm; g represents the preset wrinkle pitch reference value, in mm; t represents the preset wrinkle pitch tolerance value, in mm; func represents a preset random function, which is used to randomly output a value between (0, 1) each time; α represents the wrinkle pitch change period in the third section, and its value range is (0, π).

[0010] As a further preference of the present application, the first to third sections are repeatedly distributed along the length direction of the cable, and are repeatedly distributed at least twice or more.

[0011] As a further preferred embodiment of the present application, the inner and outer conductors are processed to achieve the wrinkle pitch in the following manner: The smooth copper strip is longitudinally wrapped through a forming table, and then the seams of the smooth copper strip are welded by argon arc welding or laser welding to form a corrugated copper tube; The corrugated copper tube is clamped and pulled by a servo motor and fed into a corrugating machine for processing at a speed corresponding to the first to third functional formulas, thereby forming the above-mentioned continuous and gradual corrugation pitch.

[0012] As a further preference of the present application, the insulating medium is a double-layer insulating structure of polyolefin adhesive layer / polyolefin closed-cell foam layer, or a three-layer insulating structure of polyolefin adhesive layer / polyolefin closed-cell foam layer / polyolefin outer skin layer.

[0013] As a further preference of the present application, the protective sheath is made of polyethylene sheath material or halogen-free, low-smoke, flame-retardant polyolefin sheath material.

[0014] In a second aspect, a low standing wave radio frequency coaxial cable is provided, which comprises an inner conductor, an insulating layer, an outer conductor and a protective sleeve from the inside to the outside, wherein the inner conductor is composed of a spiral corrugated copper tube for transmitting signals and its thread direction is kept rightward, and the corrugation pitch of the inner conductor is continuously gradient distributed in segments along the length direction of the cable as a whole, and adjacent segments each have different gradient characteristics; The outer conductor is composed of an annular corrugated copper tube or a spiral corrugated copper tube, wherein the corrugation pitch of the outer conductor is also distributed in segments along the length direction of the cable and continuously changes, and adjacent segments each have different gradient characteristics, and the pitch change of the inner conductor maintains a synchronous phase difference with the outer conductor.

[0015] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the prior art: (1) The present application makes targeted improvements by selecting the wrinkle pitch design form of specific structures such as the outer conductor and the inner conductor at the same time. This not only makes full use of the characteristics of the wrinkle structures of both being more sensitive to electromagnetic field distribution interference to break the resonance effect with the wavelength of the high-frequency signal and reduce signal reflection, but also effectively avoids the superposition of the standing wave ratio peak in the length direction of the cable, thereby further improving the effect of reducing the voltage standing wave ratio; (2) By selecting a targeted improvement in the design of the corrugation pitch, the present application can achieve better processing control in terms of precision and quality compared to solutions such as improving the insulation layer, and is not prone to losing low standing wave performance due to aging and other reasons; in addition, this partitioned continuous gradient design achieves differentiated bending performance at different positions of the same cable section during the production process, and accordingly better meets the comprehensive requirements of RF coaxial cables for low standing wave and special bending performance; compared to other methods of adjusting standing wave by adjusting the density or dielectric constant of the insulation layer, the method of the present application is more suitable for batch online production and is convenient for online monitoring and rapid online precise adjustment, and has higher stability; (3) This application further optimizes the design of the variation model of the corrugation pitch. Many actual tests have shown that the variation model can successfully avoid the high peak value of the cable's standing wave ratio even in high-frequency signal transmission application scenarios; taking the 50-12 feeder in the YD / T1092 standard as an example, when the frequency band is 700MHz~3700MHz, the standing wave ratio can be reduced from 1.5 to 1.2; by adjusting the pitch variation law of each section of the cable and calculating the optimal segmentation design based on the cable's frequency band and cable loss, it is possible to more effectively avoid the generation of new standing wave peaks caused by the continuous use of an algorithm; (4) The present application further optimizes the synchronous phase difference between the outer conductor and the inner conductor, thereby minimizing the standing wave ratio of the finished RF coaxial cable. In addition, the processing of the outer and inner conductors is fully compatible with the standard production process of YD / T 1092, thereby expanding the adaptability. The inner and outer conductors are produced simultaneously using this method, which more effectively prevents the problem of standing wave superposition that may be caused by the periodicity of the two layers of the cable conductors. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram for showing that the outer conductor / inner conductor includes at least three sections along the length direction of the cable according to a preferred embodiment of the present application, wherein the corrugation pitch changes continuously and gradually in each section and each section has a different gradual change feature; Figure 2 is a schematic diagram for exemplarily showing the structure of a leaky coaxial cable according to the present application; Figure 3is a schematic diagram for exemplarily showing the structure of a radio frequency coaxial cable according to the present application; In all the drawings, the same reference numerals are used to represent the same structures or elements, wherein: 1-inner conductor; 2-insulating medium; 3-outer conductor; 4-protective sheath; 5-periodic openings or gaps; 11-inner conductor; 12-insulating layer; 13-outer conductor; 14-protective sheath. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0018] It should be understood that expressions such as "include" and "may include" used in this application indicate the existence of the disclosed functions, operations or constituent elements, and do not limit one or more additional functions, operations and constituent elements. In this application, terms such as "include" and / or "have" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components or combinations thereof.

[0019] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0020] As analyzed in the previous "Background Technology" section, the existing leaky coaxial cable generally includes an inner conductor, a foamed insulation layer, an outer conductor and a sheath layer from the inside to the outside. In order to reduce the voltage standing wave ratio, the existing technology usually improves the specific composition of the insulation layer or its thickness and other processing parameters. However, it still has relatively poor effects under high-frequency transmission conditions, difficult to accurately control the quality, and insufficient stability after aging.

[0021] In view of the above technical problems, according to the first aspect of the present application, a low standing wave leakage coaxial cable is provided. Figure 2 The basic structure of the leaky coaxial cable is similar to that of the RF coaxial cable. Both have similar nested structures. The main difference is that the outer conductor of the leaky coaxial cable has periodic openings or gaps 5 to allow signal leakage for specific coverage areas.

[0022] As the most critical improvement, the present application has made special targeted designs for both the inner conductor and the outer conductor. Specifically, the inner conductor 1 is composed of a spiral corrugated copper tube for transmitting signals, and its thread direction is kept rightward, wherein the corrugation pitch of the inner conductor 1 is distributed in segments along the length direction of the cable as a whole and continuously changes, and adjacent segments each have different gradient characteristics; In coordination with this, the outer conductor 3 is composed of an annular corrugated copper tube or a spiral corrugated copper tube and has periodic openings or gaps on its surface for uniformly radiating and receiving signals, wherein the corrugation pitch of the outer conductor 3 is also distributed in segments along the length of the cable as a whole and continuously changes gradually, and adjacent segments each have different gradual characteristics, and the pitch change of the inner conductor 1 maintains a synchronous phase difference with the outer conductor 3. The reason for this design is that each cable has a corresponding attenuation value at the corresponding frequency point. When the attenuation value reaches a certain level, the strength of both the system signal and the periodic interference signal will be weakened (that is, the standing wave will no longer be superimposed / increased). In view of the above theoretical support, this application first makes full use of the characteristic that the corrugated structure is more sensitive to electromagnetic field distribution interference, and chooses to design the corrugation pitch of the inner conductor and the outer conductor as different periodic changes in segmented distribution. This not only breaks the resonance effect with the wavelength of the high-frequency signal and reduces signal reflection, but also can more effectively avoid the superposition of the periodic standing wave ratio peak in the length direction of the cable, and also helps to achieve processing control in terms of precision and quality, and is not easily lost due to aging and other reasons. Low standing wave performance.

[0023] In addition, the inventor of the present application also realized that after introducing the continuous gradient wrinkle pitch, when the RF coaxial cable is produced in a long length, unpredictable periodic changes may be formed again in the length direction, and new standing wave problems may be caused; in this case, considering that each cable has its corresponding attenuation value at the corresponding frequency point, when the attenuation value reaches a certain level, both the system signal and the periodic interference signal strength will be weakened. In view of the above theoretical support, the present application specifically designs the outer conductor wrinkle pitch as a segmented variation control form, so that even if a periodic standing wave ratio peak is generated along the length of the cable, it cannot be superimposed due to the passive attenuation of the signal, which further improves the effect of reducing the voltage standing wave ratio.

[0024] In a preferred embodiment of the present application, see Figure 1 , the inner conductor and the outer conductor include at least three adjacent sections along the length direction of the cable, wherein the corrugation pitches in the first to third sections change according to the following first to third functional expressions respectively: The first functional formula: Pi=g+t×func Second functional formula: Pj=gt×func The third function: Pr = g + t × sin α Among them, P i represents the wrinkle pitch at the i-th change in the first section, in mm; P j represents the wrinkle pitch when the jth change occurs in the second section, in mm; P r represents the wrinkle pitch at the rth change in the third section, in mm; g represents the preset wrinkle pitch reference value, in mm; t represents the preset wrinkle pitch tolerance value, in mm; func represents a preset random function, which is used to randomly output a value between (0, 1) each time; α represents the wrinkle pitch change period in the third section, and its value range is (0, π).

[0025] Through the above design, many actual tests have shown that the pitch variation model can successfully avoid the high peak value of the cable's standing wave ratio even in high-frequency signal transmission application scenarios; taking the 50-12 feeder in the YD / T1092 standard as an example, when the frequency band is 700MHz~3700MHz, the standing wave ratio can be reduced from 1.5 to 1.2, and it has the advantages of easy control and high adjustment accuracy. For example, the random function can be a pseudo-random number generation function that obeys a uniform distribution.

[0026] In another preferred embodiment of the present application, the first to third sections are repeatedly distributed along the length direction of the cable, and are repeatedly distributed at least twice or more.

[0027] In another preferred embodiment of the present application, when the first to third sections are repeated along the length direction of the cable, an intermediate section is provided as a spacing area, and the length L of the intermediate section is designed according to the following relationship: L<A÷A min Wherein, L is defined as the total length of all corrugation pitches in the middle section divided by 1000, in m; A represents the cable system loss value within the corresponding length when the actual voltage standing wave V1 of a coaxial cable is tested to be reduced to the target voltage standing wave V2, in dB; A min Represents the attenuation value of the coaxial cable at the lowest frequency point within the standard frequency band, in dB / 100m.

[0028] The present application also provides a method for manufacturing a corresponding low standing wave leakage coaxial cable, comprising the following steps: (1) Processing the inner conductor 1; (2) preparing an insulating medium 2 on the surface of the inner conductor; (3) wrapping an outer conductor 3 around the insulating medium 2; (4) A protective cover 4 is prepared on the surface of the outer conductor 3.

[0029] In the forming process of the inner conductor and the outer conductor, the wrinkle pitch is designed to be a continuous gradient distributed in segments along the length direction of the cable, and adjacent segments each have different gradient characteristics.

[0030] In another preferred embodiment of the present application, the inner and outer conductors are processed to achieve the wrinkle pitch in the following manner: The smooth copper strip is longitudinally wrapped through a forming table, and then the seams of the smooth copper strip are welded by argon arc welding or laser welding to form a corrugated copper tube; The corrugated copper tube is clamped and pulled by a servo motor and fed into a corrugating machine for processing at a speed corresponding to the first to third functional formulas, thereby forming the above-mentioned continuous and gradual corrugation pitch.

[0031] To explain more specifically, compared with the traditional spiral corrugated copper tube production line, the present application can use the following functional modules to implement the corresponding functions: such as corrugation main traction module, corrugation processing module and corrugation processing module, etc. The corrugation main traction module is used to adjust the line speed in real time according to the preset input change function; the corrugation processing module is used to adjust the motor speed according to the preset input change function, and then corrugate the conductor output to set the pitch.

[0032] According to the second aspect of the present application, a low standing wave radio frequency coaxial cable is also proposed, see Figure 3 The basic component structure of the RF coaxial cable is similar to that of existing products, that is, from the inside to the outside, it includes an inner conductor 11, an insulating layer 12, an outer conductor 13 and a protective cover 14, and may also include some other supporting functional structural layers; the main difference is that in the present application, an optimized design is made for the inner conductor 11 composed of a spiral corrugated copper tube, wherein the inner conductor 11 is composed of a spiral corrugated copper tube for transmitting signals and its thread direction remains right-handed, and the corrugation pitch of the inner conductor 11 is a continuous gradient distributed in segments along the length direction of the cable as a whole, and adjacent segments each have different gradient characteristics.

[0033] In addition, the outer conductor 13 of the low standing wave RF coaxial cable can also be designed based on the above principle, and the corrugation pitch of the spiral corrugated copper tube is processed into a continuous gradient with segmented distribution along the length direction of the cable, and the adjacent segments each have different gradient characteristics. The above pitch variation model can also be applied to the processing of the outer conductor and the inner conductor.

[0034] A specific example is given below to better explain the present application, wherein all test samples are made from the same batch of copper strip raw materials and are manufactured on the same equipment, with only the wrinkle pitch control algorithm being changed to eliminate equipment error interference.

[0035] In this specific example, the coaxial cable provided is applied to the radio frequency coaxial cable model HHTAYZ-50-42 (cable specification is -42) in the YD / T1092 standard and the leaky coaxial cable model HLRHTYZ-50-42 in the YDT 2491-2013 standard. The processing steps are as follows: The smooth copper strip is formed into a copper tube by argon arc welding, and then the surface of the copper tube is corrugated to form a corrugated copper tube inner conductor with a diameter of 17.6mm. A polyolefin foam layer is extruded on the surface of the inner conductor to form an insulating semi-finished product with a diameter of 42.8 mm; The semi-finished insulation product is inserted into a smooth copper tube formed by welding copper strips for corrugation. The cable core and the copper tube are tightly combined to obtain the outer conductor semi-finished product of the RF coaxial cable. A layer of low-smoke halogen-free flame-retardant sheath is extruded outside the outer conductor to obtain the HHTAYZ-50-42 finished product; or, the semi-finished insulation product is inserted into a copper tube formed by the longitudinal wrapping of the roller-corrugated copper strip, and a layer of low-smoke halogen-free flame-retardant sheath is directly extruded outside the outer conductor of the longitudinally wrapped copper tube after the drawing die is finalized, which is the HLRHTYZ-50-42 leaky coaxial cable.

[0036] The inner conductor and insulation processing steps of the above HHTAYZ-50-42 RF coaxial cable and HLRHTYZ-50-42 leaky coaxial cable are the same, and the inner conductor and insulation semi-finished products can be shared.

[0037] The processing and control process of the inner conductor / outer conductor is illustrated as follows: A 50-42 inner conductor was produced using a welding corrugation equipment with a worn main traction gearbox. The worn main traction gearbox had periodic speed fluctuations when traction was moving forward. The insulating semi-finished products produced by the manufactured inner conductor were used in both HHTAY-50-42 RF coaxial cable and HLRHTYZ-50-42 leakage coaxial cable. The voltage standing wave ratio (VSWR) measured for both finished cables showed high peak values, with a peak frequency of 1812MHz. The above control method of the present application is applied to the main traction of the welding corrugation to control the pitch of the inner conductor for continuous gradient production. 10 groups of insulating semi-finished products were produced using conventional technology and the control method of the present application, 5 groups produced HLRHTYZ-50-42 leaky coaxial cables, and 5 groups produced HHTAYZ-50-42 radio frequency coaxial cables. The standing wave VSWR test results of the finished products are shown in Tables 1 and 2: Table 1

[0038] Table 2

[0039] Comparing Table 1 and Table 2, it can be seen that the VSWR peak value of the RF coaxial cable and leaky coaxial cable produced by the present application has been significantly reduced, with a decrease of 0.24 to 0.31. Accordingly, it is confirmed that the VSWR peak value caused by systematic periodic faults caused by equipment failure and other reasons during the production process of RF coaxial cables and leaky coaxial cables can be improved according to the present application.

[0040] In summary, compared with the prior art, the present application can not only more accurately and effectively reduce the voltage standing wave ratio of the RF coaxial cable, but also simultaneously improve the cable bending stress and reduce the attenuation of high-frequency signals, and at the same time has the advantages of easy processing and control and high reliability; the designed product structure and processing technology are fully compatible with the YD / T 1092 standard production process, suitable for large-scale batch production, and therefore have good practical value and application prospects.

[0041] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A low standing wave leaky coaxial cable, the leaky coaxial cable comprising an inner conductor, an insulating medium, an outer conductor and a protective sleeve from inside to outside, characterized in that: The inner conductor is composed of a spiral corrugated copper tube for transmitting signals and its thread direction is kept rightward, wherein the corrugation pitch of the inner conductor is distributed in sections along the length direction of the cable and changes continuously, and adjacent sections each have different gradient characteristics; The outer conductor is composed of an annular corrugated copper tube or a spiral corrugated copper tube and has periodic openings or gaps on its surface for uniformly radiating and receiving signals. The corrugation pitch of the outer conductor is also distributed in segments along the length of the cable and is continuously gradient. Adjacent segments each have different gradient characteristics, and the pitch change of the inner conductor maintains a synchronous phase difference with the outer conductor.

2. The low standing wave leakage coaxial cable according to claim 1, characterized in that: The inner conductor and the outer conductor maintain a synchronous phase difference of 0.6 to 0.8 times of the pitch change.

3. The low standing wave leakage coaxial cable according to claim 2, characterized in that: The inner conductor and the outer conductor include at least three adjacent sections along the length direction of the cable, wherein the corrugation pitches in the first to third sections change according to the following first to third functional expressions respectively: The first function: P i =g+t×func Second function: P j =gt×func The third function: P r =g+t×sinα Among them, P i represents the wrinkle pitch at the i-th change in the first section, in mm; P j represents the wrinkle pitch when the jth change occurs in the second section, in mm; P r represents the wrinkle pitch at the rth change in the third section, in mm; g represents the preset wrinkle pitch reference value, in mm; t represents the preset wrinkle pitch tolerance value, in mm; func represents a preset random function, which is used to randomly output a value between (0, 1) each time; α represents the wrinkle pitch change period in the third section, and its value range is (0, π).

4. The low standing wave leakage coaxial cable according to claim 3, characterized in that: The first to third sections are repeatedly distributed along the length direction of the cable, and are repeatedly distributed at least twice.

5. The low standing wave leakage coaxial cable according to claim 3 or 4, characterized in that: The inner and outer conductors are processed in the following manner to achieve the wrinkle pitch: The smooth copper strip is longitudinally wrapped through a forming table, and then the seams of the smooth copper strip are welded by argon arc welding or laser welding to form a corrugated copper tube; The corrugated copper tube is clamped and pulled by a servo motor and fed into a corrugating machine for processing at a speed corresponding to the first to third functional formulas, thereby forming the above-mentioned continuous and gradual corrugation pitch.

6. The low standing wave leakage coaxial cable according to claim 1, characterized in that: The insulating medium is a double-layer insulating structure of a polyolefin adhesive layer / a polyolefin closed-cell foam layer, or a three-layer insulating structure of a polyolefin adhesive layer / a polyolefin closed-cell foam layer / a polyolefin outer skin layer.

7. The low standing wave leakage coaxial cable according to claim 6, characterized in that: The protective sheath is made of polyethylene sheath material or halogen-free, low-smoke, flame-retardant polyolefin sheath material.

8. A low standing wave radio frequency coaxial cable, comprising an inner conductor, an insulating layer, an outer conductor and a protective sleeve from inside to outside, characterized in that: The inner conductor is composed of a spiral corrugated copper tube for transmitting signals and its thread direction is kept rightward, wherein the corrugation pitch of the inner conductor is distributed in sections along the length direction of the cable and changes continuously, and adjacent sections each have different gradient characteristics; The outer conductor is composed of an annular corrugated copper tube or a spiral corrugated copper tube, wherein the corrugation pitch of the outer conductor is also distributed in segments along the length direction of the cable and continuously changes, and adjacent segments each have different gradient characteristics, and the pitch change of the inner conductor maintains a synchronous phase difference with the outer conductor.

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