Spread spectrum leaky coaxial cable compatible with super cut-off frequency transmission task

Abstract

The invention provides a spread spectrum leaky coaxial cable compatible with a super cut-off frequency transmission task, which comprises an inner conductor, an insulating layer and an outer conductor which are coaxially nested from inside to outside, a plurality of slot arrays are arranged on the outer conductor, any slot array comprises a plurality of rows of slot groups, and the slot groups are arranged in the slot groups. Each row of slotted hole group is composed of a plurality of slotted hole pairs which are arranged in the radial direction and are symmetrical about the same axial symmetric axis, the shapes and the sizes of the two slotted holes forming any slotted hole pair are the same, and the length of the long axis of the slotted hole pair in any row of slotted hole group is gradually increased from the two ends to the symmetric axis in the radial direction; a plurality of pairs of slotted holes which are symmetric about the same axial symmetry axis in the radial direction are formed, the length of a long axis is gradually increased from the two ends to the symmetry axis in the radial direction, and the instability problem of a high-order mode during super-cut-off frequency transmission is effectively relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of communication cables, and particularly to a spread spectrum leaky cable compatible with ultra cut-off frequency transmission tasks. Background Art

[0002] A leaky coaxial cable (hereinafter referred to as leaky cable) is a composite communication medium with both signal transmission and wireless transceiver functions. Through a periodically slotted structure preset on the outer conductor surface, the leaky cable can achieve directional radiation of electromagnetic wave energy and environmental signal reception, and thus complete two-way information interaction. Currently, the leaky cable technology has been successfully applied in the rail transit field (such as enclosed spaces like subway tunnels and railway tunnels), providing stable mobile communication coverage for train passengers and on-vehicle equipment.

[0003] Existing leaky cable products for 4G and below mid-low frequency bands (such as 2.6 GHz and below) mostly adopt the 13 / 8 type structure, and its theoretical cut-off frequency is about 2.8 GHz. Among them, the critical frequency (Cut-off Frequency) of the leaky cable refers to the highest frequency threshold for maintaining signal integrity in its single-mode transmission state. When the frequency of the actual transmitted signal breaks through this critical value, multi-path interference and energy loss will be generated inside the leaky cable due to the excitation of higher-order modes, resulting in deterioration of the communication link quality and making it difficult to meet the stringent communication requirements of low latency and high reliability in tunnel scenarios. Therefore, when facing the ultra cut-off frequency transmission task of 5G communication signals with a frequency of 3.5 GHz and above, this type of leaky cable will cause signal degradation problems due to the excitation of higher-order modes. Especially in the ultra-long tunnel environment where the 13 / 8 type leaky cable has been widely deployed, the existing infrastructure cannot directly adapt to the communication requirements of the 5G high-frequency band, becoming a technical bottleneck restricting 5G coverage in the rail transit scenario.

[0004] Currently, when facing the above ultra cut-off frequency transmission task, the down-conversion method is mostly used to convert the high-frequency 5G signal into an intermediate-frequency signal with a frequency lower than the cut-off frequency of the leaky cable, and then use the leaky cable to transmit this intermediate-frequency signal. Subsequently, the in-vehicle relay device in the train carriage running in the tunnel is used to up-convert this intermediate-frequency signal into a high-frequency signal with the target operating frequency, so as to use the existing leaky cable for 5G mobile communication transmission. However, although this solution can temporarily solve the high-frequency support problem of the old leaky cable, it has multiple limitations. This solution requires additional configuration of a base station end down-converter and an in-vehicle relay up-converter, which not only greatly increases the hardware cost and volume, but also deteriorates the signal quality due to the phase noise and frequency offset error introduced in the frequency conversion link, especially affecting the transmission accuracy of high-order modulation signals. The microsecond-level delay accumulated in the two-way frequency conversion process is also difficult to meet the requirements of the 5G ultra-low latency communication scenario, and the practice of compressing the intermediate-frequency band width directly sacrifices the spectrum utilization rate of the high-frequency signal, resulting in a decrease in network capacity. In addition, the train-end relay device depends on the in-vehicle power supply and installation space, has poor compatibility with old vehicle models, and lacks sustainability. Summary of the Invention

[0005] The present invention provides a spread spectrum leaky cable compatible with ultra-cutoff frequency transmission tasks, so as to solve the defects in the prior art that the transmission of high-frequency signals by down-conversion technology leads to an increase in hardware costs and the transmission accuracy and efficiency are interfered by the frequency conversion link.

[0006] The present invention provides a spread spectrum leaky cable compatible with ultra-cutoff frequency transmission tasks, including an inner conductor, an insulating layer and an outer conductor coaxially nested from the inside out;

[0007] Wherein, a plurality of slot hole arrays are formed on the outer conductor;

[0008] Any one of the slot hole arrays includes multiple columns of slot hole groups, and each column of slot hole groups is composed of multiple pairs of slot hole pairs arranged radially and symmetric about the same axial symmetry axis; the shapes and sizes of the two slot holes forming any one of the slot hole pairs are the same, and the major axis lengths of the slot hole pairs in any one column of slot hole groups gradually increase along the radial direction from both ends to the symmetry axis direction.

[0009] According to the spread spectrum leaky cable compatible with ultra-cutoff frequency transmission tasks provided by the present invention, the total slot hole length of any one column of slot hole groups in any one of the slot hole arrays is less than half of the circumference of the outer conductor; the total slot hole length of any one column of slot hole groups is composed of the slot hole lengths of each slot hole in any one column of slot hole groups and the slot hole gap lengths between adjacent slot holes.

[0010] According to the spread spectrum leaky cable compatible with ultra-cutoff frequency transmission tasks provided by the present invention, the slot hole lengths of the slot holes in any one column of slot hole groups satisfy the following conditions:

[0011] c / (12f(e r ) 1 / 2 )<l i <c / (4f(e r ) 1 / 2 )-(iδ) / n

[0012] Wherein, c is the propagation speed of electromagnetic waves in free space, f is the center frequency, e r is the relative permittivity of the insulating layer, l i is the slot hole length of slot hole i, and δ is a correction coefficient, and its range is 0.5 to 10 mm.

[0013] According to the spread spectrum leaky cable compatible with ultra-cutoff frequency transmission tasks provided by the present invention, the farther any one of the slot hole arrays is from the signal transmitting end, the longer the total slot hole length of the slot hole groups in any one of the slot hole arrays is.

[0014] According to the spread spectrum leaky cable compatible with ultra-cutoff frequency transmission tasks provided by the present invention, the distance between adjacent slot hole groups in any one of the slot hole arrays satisfies the following conditions:

[0015] Pdif = P / m(ξ + 1)

[0016] Wherein, P dif is the pitch between adjacent slot groups in any one of the slot arrays; P is the pitch between adjacent slot arrays; ξ is the number of slot groups in any one of the slot arrays; m is the order of the target high-order mode, and the target high-order mode is the interfering high-order mode caused when the leaky cable transmits signals at frequencies above the cut-off frequency;

[0017] The number of slot groups in any one of the slot arrays is determined based on the following method:

[0018] Based on the current test number of slot groups in any one of the slot arrays, determine the pitch between adjacent slot groups in any one of the slot arrays, and calculate the standing wave ratio at each leaky cable transmission frequency based on the current test number of slot groups in any one of the slot arrays and the pitch between adjacent slot groups; increase the current test number of slot groups in any one of the slot arrays until the standing wave ratio at each leaky cable transmission frequency meets the preset requirements, and determine the current test number of slot groups in any one of the slot arrays as the number of slot groups in any one of the slot arrays.

[0019] According to a spread spectrum leaky cable compatible with the super cut-off frequency transmission task provided by the present invention, the slots in any one of the slot arrays are inclined with respect to the axial direction; non-through cuts corresponding to each slot array are provided on the surface of the inner conductor; the width of the non-through cut in the axial direction is the same as the total width of the corresponding slot array in the axial direction.

[0020] According to a spread spectrum leaky cable compatible with the super cut-off frequency transmission task provided by the present invention, the opening direction of the non-through cut forms an angle of 0 degrees and / or 180 degrees with the opening direction of the central slot pair of the corresponding slot array.

[0021] According to a spread spectrum leaky cable compatible with the super cut-off frequency transmission task provided by the present invention, the opening direction of the non-through cut forms an angle of 90 degrees and 270 degrees with the opening direction of the central slot pair of the corresponding slot array.

[0022] A spread spectrum leaky cable compatible with ultra-cutoff frequency transmission tasks according to the present invention. When the opening direction of the non-through cut is at a 0-degree angle to the opening direction of the central slot pair of the corresponding slot array, the length, width, and depth of the non-through cut satisfy the condition that the inductance change amount of the region where the non-through cut is added to the inner conductor is equal to the inductance change amount of the region where the corresponding slot array is provided on the outer conductor; the inductance change amount of the region of any slot array is the sum of the inductance change amounts corresponding to all the slots in the any slot array, and the inductance change amount corresponding to any slot is determined based on the angle of the any slot relative to the axial direction, the slot length of the any slot, the characteristic impedance per unit length of the leaky cable and the current propagation speed, and the radius of the outer conductor.

[0023] A spread spectrum leaky cable compatible with ultra-cutoff frequency transmission tasks according to the present invention. Each of the slot arrays in the leaky cable includes multiple slot groups with different numbers of slots, and the slot groups with different numbers of slots are alternately arranged on the outer conductor.

[0024] A spread spectrum leaky cable compatible with ultra-cutoff frequency transmission tasks according to the present invention includes an inner conductor, an insulating layer, and an outer conductor coaxially nested from the inside out. Among them, multiple slot arrays are provided on the outer conductor. Each of the slot arrays includes multiple columns of slot groups, and each column of slot groups is composed of multiple pairs of slots arranged radially and symmetric about the same axial symmetry axis. The shapes and sizes of the two slots forming any slot pair are the same, and the major axis lengths of the slot pairs in any column of slot groups gradually increase along the radial direction from both ends to the symmetry axis direction; by providing multiple pairs of slots symmetric about the same axial symmetry axis in the radial direction and setting the major axis length to increase along the radial direction from both ends to the symmetry axis direction, the instability problem of high-order modes during ultra-cutoff frequency transmission is effectively alleviated. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0026] Figure 1 One of the schematic diagrams of the slot layout after the outer conductor is unfolded in the circumferential direction provided by the present invention;

[0027] Figure 2 Another schematic diagram of the slot layout after the outer conductor is unfolded in the circumferential direction provided by the present invention;

[0028] Figure 3 One of the schematic cross-sectional diagrams of the leaky cable provided by the present invention;

[0029] Figure 4 The second cross-sectional schematic diagram of the leaky cable provided by the present invention;

[0030] Figure 5 The schematic diagram of the slot structure provided by the prior art;

[0031] Figure 6 The schematic diagram of the attenuation curve of the leaky cable provided by the prior art;

[0032] Figure 7 The schematic diagram of the attenuation curve of the leaky cable provided by the present invention. Detailed implementation manners

[0033] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts fall within the scope of protection of the present invention.

[0034] Most of the existing leaky cable products for 4G and below mid-low frequency bands (such as 2.6 GHz and below) adopt the 13 / 8 type structure, and its theoretical cut-off frequency is about 2.8 GHz. When the frequency of the actual transmitted signal breaks through this critical value, multipath interference and energy loss will be generated due to the excitation of higher-order modes inside the leaky cable, resulting in the deterioration of the communication link quality and making it difficult to meet the stringent communication requirements of low latency and high reliability in tunnel scenarios. Therefore, when this type of leaky cable faces the task of transmitting 5G communication signals with a frequency of 3.5 GHz and above beyond the cut-off frequency, signal degradation problems will be caused due to the excitation of higher-order modes. Especially in the ultra-long tunnel environment where the 13 / 8 type leaky cable has been widely deployed, the existing infrastructure cannot directly adapt to the communication requirements of the 5G high-frequency band, which has become a technical bottleneck restricting the 5G coverage in the rail transit scenario.

[0035] Currently, when facing the above-mentioned ultra-cutoff frequency transmission task, the down-conversion method is mostly used to convert the high-frequency 5G signal into an intermediate-frequency signal with a frequency lower than the cutoff frequency of the leaky cable, and then the leaky cable is used to transmit the intermediate-frequency signal. Subsequently, the in-vehicle relay device in the train carriages traveling in the tunnel is used to up-convert the intermediate-frequency signal into a high-frequency signal with the target operating frequency, so as to utilize the existing leaky cable for 5G mobile communication transmission. However, although this solution can temporarily solve the problem of high-frequency support for the old leaky cables, it has multiple limitations. This solution requires additional configuration of a base station end down-converter and an in-vehicle relay up-converter, which not only greatly increases the hardware cost and volume, but also deteriorates the signal quality due to the phase noise and frequency offset error introduced in the frequency conversion link, especially affecting the transmission accuracy of high-order modulation signals. The microsecond-level time delay accumulated in the two-way frequency conversion process is also difficult to meet the requirements of the 5G ultra-low latency communication scenario, and the practice of compressing the intermediate-frequency band width directly sacrifices the spectrum utilization rate of the high-frequency signal, resulting in a decrease in network capacity. In addition, the relay device at the train end relies on in-vehicle power and installation space, has poor compatibility with old vehicle models, and lacks sustainability.

[0036] In response to this, the present invention provides a spread-spectrum leaky cable compatible with ultra-cutoff frequency transmission tasks, which can effectively transmit signals within the cutoff frequency range and beyond the cutoff frequency. By optimizing the slot structure of the outer conductor and the inner conductor structure of the leaky cable, this improved leaky cable can directly transmit high-frequency signals beyond the current cutoff frequency of the leaky cable. By adjusting the size gradient and distribution pattern of the outer conductor slots, this solution can stabilize the high-order modes excited during the ultra-cutoff frequency transmission process, without the need for external frequency conversion equipment, fundamentally eliminating the problems of noise superposition and time delay accumulation caused by signal conversion, and can match high-real-time scenarios. At the same time, the leaky cable directly transmitting the original high-frequency signal can maximize the spectrum efficiency and provide a larger communication capacity for the tunnel environment. More importantly, this structural improvement solution only requires the transformation of the existing leaky cable body, without the need for train equipment upgrade, providing a smooth upgrade path of "one cable for multiple uses" for the evolution of the rail transit communication system.

[0037] Specifically, the leaky cable includes an inner conductor, an insulating layer, and an outer conductor coaxially nested from the inside out. Figure 1 One of the schematic diagrams of the slot layout after the outer conductor is unfolded in the circumferential direction provided by the present invention is as Figure 1 shown, and a plurality of slot arrays 120 are formed on the outer conductor 110.

[0038] Among them, any one slot array 120 includes multiple columns of slot groups 130, and each column of slot groups 130 is composed of multiple pairs of slots arranged radially and symmetric about the same axial symmetry axis (i.e., the axial symmetry axis of the leaky cable). As Figure 1As shown, the shapes and dimensions of the two slots forming each slot pair 131, 132, 133, and 134 are the same, that is, the shapes and dimensions of slot 1311 and slot 1312 are the same, the shapes and dimensions of slot 1321 and slot 1322 are the same, the shapes and dimensions of slot 1331 and slot 1332 are the same, and the shapes and dimensions of slot 1341 and slot 1342 are the same. At the same time, the two slots forming each slot pair 131, 132, 133, and 134 are symmetric about the axial symmetry axis Y. In addition, the major axis lengths of the slot pairs in any column of slot groups 130 gradually increase in the radial direction from both ends towards the symmetry axis. Taking slot pairs 131, 132, 133, and 134 as an example, the major axis lengths of slot 1311 and slot 1312 are less than the major axis lengths of slot 1321 and slot 1322, the major axis lengths of slot 1321 and slot 1322 are less than the major axis lengths of slot 1331 and slot 1332, and the major axis lengths of slot 1331 and slot 1332 are less than the major axis lengths of slot 1341 and slot 1342. It should be noted that the angle between the major axis of the slot and the radial direction is smaller than the angle between the minor axis of the slot and the radial direction.

[0039] In some specific embodiments, the centers of the two slots in the slot pair can have a slight left - right offset in the radial direction, and the offset distance does not exceed 8 mm.

[0040] Relative to Figure 5 the slot structures commonly used in the prior art shown in Figure 6 and Figure 7 ( Figure 6 and Figure 7In it, the abscissa is the frequency and the ordinate is the attenuation amount. It can be seen that in the embodiments of the present invention, through two complementary slot setting methods, that is, by setting multiple pairs of slots that are axially symmetric about the same axial symmetry axis in the radial direction, and setting the major axis length to gradually increase from both ends to the symmetry axis direction in the radial direction, its attenuation curve is smoother than the attenuation curve of the prior art. Therefore, the leaky cable provided by the embodiments of the present invention effectively alleviates the instability problem of higher-order modes during super cutoff frequency transmission. First, the slots are arranged on the outer conductor in a radial arrangement and are axially symmetric about the same axial symmetry axis. This symmetric layout is equivalent to setting a perturbation structure to fix the electric field direction of the higher-order mode, which can ensure the stability of the cutting current in the circumferential direction. The symmetric slot pairs can make the electromagnetic field evenly distributed in all directions, reduce the over-strong or insufficient local electromagnetic field caused by asymmetry, and thus reduce the unnecessary interference and coupling between higher-order modes. This balanced field distribution helps to suppress those higher-order modes that are prone to generating standing waves and local resonances, making the overall transmission more stable. In addition, by setting slot pairs with the major axis length gradually increasing from both ends to the symmetry axis in the radial direction, this gradient design actually forms a "trapezoidal" leakage characteristic on the surface of the leaky cable, which can make the signal converge towards the middle, strengthen the intensity of the middle signal, and improve the coverage effect. At the same time, the smaller slots are located at both ends, which can appropriately limit the leakage of high-frequency signals and prevent premature attenuation; while the larger slots in the middle can enhance the leakage efficiency in the required area, making the energy distribution of high-frequency signals along the axis in the leaky cable more smooth. Such a size gradient can make the signal leakage process more continuous and gradual, avoiding problems such as local impedance mismatch and over-strong excitation of higher-order modes caused by sudden changes in slot size.

[0041] More importantly, when these two settings are combined, a more significant regulation effect on higher-order modes can be achieved. The radially symmetric slot arrangement ensures the balance of the overall field distribution, and the gradient of the major axis length enables the leakage characteristics to smoothly transition in different regions, reducing both local resonance phenomena and selectively enhancing or suppressing the leakage of specific modes. When the leaky cable transmits high-frequency signals above its cutoff frequency such as 3.5G, the instability of higher-order modes is effectively controlled, the signal transmission is more uniform and stable, and at the same time, the coverage requirements of the entire frequency band are taken into account.

[0042] In some alternative embodiments, the total length of the slots in any column of slot groups 130 of any slot array 120 is less than half of the circumference of the outer conductor. Herein, the total length of the slots in any column of slot groups 130 is composed of the slot lengths (i.e., the lengths of the major axes of the slots) of the respective slots 1311, 1312, 1321, 1322, 1331, 1332, 1341, 1342 in that slot group 130 and the slot gap lengths between adjacent slots. Here, since in the high-order mode state, the distribution of the electromagnetic field may have a specific symmetry. If the slot arrangement range exceeds half of the circumference of the outer conductor (and may also exceed half of the wavelength), it may cover regions with opposite electric field directions, resulting in the cancellation of the radiated or coupled electric fields, thereby weakening the signal. Specifically, when the total slot length exceeds half of the circumference, the phases of the electric fields may be different at different positions along the circumferential direction. If the slots cover more than half of the circumference, then some slots may be in the region of the positive electric field direction and the other part in the negative direction region, leading to the cancellation of the radiation fields and weakening of the overall signal. Therefore, to avoid signal weakening in the high-order mode, all the slots of the slot groups 130 of the slot array 120 are arranged within the range of the semi-circumference of the outer conductor. By restricting the total slot length to be less than half of the circumference, it can be ensured that all the slots are in the region where the electric field phases are consistent, thereby enhancing the radiation efficiency of the signal.

[0043] In some specific embodiments, to ensure the signal synthesis degree and the signal radiation efficiency, the slot length of slot i in any column of slot groups satisfies the following conditions:

[0044] c / (12f(e r ) 1 / 2 )<l i <c / (4f(e r ) 1 / 2 )-(iδ) / n(1)

[0045] Wherein, c is the propagation speed of electromagnetic waves in free space, f is the center frequency, e r is the relative dielectric constant of the insulating layer, l i is the slot length of slot i, and δ is a correction factor, and its range is 0.1 - 10 mm.

[0046] In some alternative embodiments, to determine the slot lengths of the slots in any column of slot groups, the total slot length of the slot group and the slot gap length between adjacent slots may be set first. Based on the setting of the total slot length of the slot group and the slot gap length between adjacent slots, the slot lengths of the center slots of each slot pair can be determined sequentially from both ends along the radial direction towards the symmetry axis. Taking slot pairs 131, 132, 133, and 134 as an example, the slot lengths of slots 1311 and 1312, the slot lengths of slots 1321 and 1322, the slot lengths of slots 1331 and 1332, and the slot lengths of slots 1341 and 1342 are determined in sequence. Among them, the effective total length of the slots (the sum of the slot lengths corresponding to each slot) can be determined based on the total slot length of the slot group and the slot gap length between adjacent slots. When determining the slot lengths of the slots in the current slot pair, the upper and lower limits of the slot lengths of the slots in the slot pair can be determined based on Equation (1), and in combination with the effective total length of the slots and the known slot lengths of the slots in the slot pair, a suitable value can be selected from within the range of the upper and lower limits as the slot length of the slots in the current slot pair.

[0047] In some other specific embodiments, the length of a single slot in the short-axis direction (referred to as the slot width) is 0.5 - 8 mm.

[0048] In some alternative embodiments, as Figure 2 shown, the farther any slot array is from the signal transmitting end, the longer the total slot length of the slot group of the slot array. Since the system loss of high-frequency signals in the high-order mode state will increase, through this design, the system loss during the transmission of high-frequency signals in the leaky cable can be balanced, and the signal transmission performance can be improved.

[0049] In some other alternative embodiments, the spacing between adjacent slot groups in any slot array satisfies the following conditions:

[0050] P dif = P / m(ξ + 1) (2)

[0051] where P dif is the spacing between adjacent slot groups in the slot array; P is the spacing between adjacent slot arrays; ξ is the number of slot groups in the slot array; m is the order of the target high-order mode, which is the interfering high-order mode caused by the leaky cable when transmitting signals above the cut-off frequency, that is, the high-order mode that causes interference to the transmission of high-frequency signals and is not conducive to the transmission of high-frequency signals, such as the -2nd mode. By determining the spacing between adjacent slot groups in the slot array in this way, the high-order modes that are not conducive to the transmission of high-frequency signals can be suppressed, and the stability of the high-order mode can be further improved.

[0052] In some specific embodiments, the number of slot groups in any slot array can be determined based on the following method:

[0053] Based on the current test quantity of the slot groups in any slot array, use Equation (2) to determine the spacing between adjacent slot groups in this slot array, and calculate the standing wave ratio at each leaky cable transmission frequency based on the current test quantity of the slot groups in this slot array and the spacing between adjacent slot groups; then increase the current test quantity of the slot groups in this slot array, and calculate the standing wave ratio at each leaky cable transmission frequency according to the above steps until the standing wave ratio at each leaky cable transmission frequency meets the preset requirements. At this time, the current test quantity of the slot groups in this slot array can be determined as the quantity of the slot groups in this slot array.

[0054] When the leaky cable transmits high-frequency signals with frequencies above the cut-off frequency, it will inevitably excite higher-order modes. The higher-order modes will be excited and propagated strongly on the surface of the smooth inner conductor, so that the higher-order modes form local standing waves or resonances in some areas, resulting in uneven distribution of signal energy, thus deteriorating the voltage standing wave ratio. In addition, due to the condition that the surface of the inner conductor remains uniform, it is easy to cause strong interference and coupling between the higher-order modes. This instability of the higher-order modes will cause uneven signal transmission, affecting the coverage and reliability of the communication system.

[0055] Therefore, in some alternative embodiments, the slots in the slot array 120 are arranged obliquely with respect to the axial direction, that is, the included angle between the long axis direction of the slot and the axial direction of the leaky cable is greater than 0 degrees and less than 180 degrees. On this basis, non-through cuts corresponding to each slot array are provided on the surface of the inner conductor. Among them, the width of the non-through cut in the axial direction is the same as the total width of the corresponding slot array in the axial direction. By providing non-through cuts corresponding to each slot array on the surface of the inner conductor, the perturbation is increased, which helps to stably excite higher-order modes during the transmission of signals with frequencies above the cut-off frequency.

[0056] Specifically, in a non-notch inner conductor, the current is distributed along the uniform conductor. After adding a non-penetrating notch to the inner conductor surface, the non-penetrating notch can be understood as a non-through groove formed on the inner conductor surface in the radial direction. This notch will perturb the local current distribution and magnetic field distribution. Such perturbation is usually small, so it can be regarded as a perturbation of the system. On the one hand, the non-penetrating notch forms a local groove on the inner conductor surface, enabling the current to bypass in this area, thus changing the original uniform current distribution. This bypass effect can interrupt or weaken the over-excitation of high-order modes in a specific area, reduce the local impedance mutation and reflection phenomenon, and further make the energy distribution of high-order modes in the overall transmission more uniform and smoother. At the same time, the perturbation introduced by the non-penetrating notch can change the local electromagnetic field distribution, reduce the interaction between certain modes, and make it difficult for different high-order modes to strongly couple and interfere with each other. On the other hand, by setting a non-penetrating notch on the inner conductor surface, the perturbation brought by the notch can break the continuity of the inner conductor surface, thereby destroying the resonance condition of high-order modes and making the excitation of high-order modes more tend to be dispersed and stable.

[0057] In some specific embodiments, Figure 3 is one of the cross-sectional schematic diagrams of the leaky cable provided by the present invention. As Figure 3 shown, the opening direction of the non-penetrating notch 310 forms an angle of 0 degrees and / or 180 degrees with the opening direction of the central slot pair 320 of the corresponding slot array. Among them, as Figure 3 shown in the left schematic diagram, from the cross-sectional view of the leaky cable, a non-penetrating notch 310 can be opened at the position of the inner conductor facing the central slot pair 320 of the slot array, so that the opening direction of the non-penetrating notch 310 forms an angle of 0 degrees with the opening direction of the central slot pair 320 of the corresponding slot array; as Figure 3 shown in the middle schematic diagram, from the cross-sectional view of the leaky cable, a non-penetrating notch 310 can be opened at the position of the inner conductor facing away from the central slot pair 320 of the slot array, so that the opening direction of the non-penetrating notch 310 forms an angle of 180 degrees with the opening direction of the central slot pair 320 of the corresponding slot array; as Figure 3 shown in the right schematic diagram, from the cross-sectional view of the leaky cable, non-penetrating notches 310 can be opened at the positions of the inner conductor facing and facing away from the central slot pair 320 of the slot array respectively, so that the opening directions of the two non-penetrating notches 310 form angles of 0 degrees and 180 degrees with the opening direction of the central slot pair 320 of the corresponding slot array respectively.

[0058] In some other specific embodiments, Figure 4 is the second cross-sectional schematic diagram of the leaky cable. As Figure 4As shown, the opening directions of the non-through cuts 410 form an angle of 90 degrees and 270 degrees with the opening direction of the central slot pair 420 of the corresponding slot array. That is, from the cross-sectional view of the leaky cable, a non-through cut 410 can be respectively arranged on the side of the inner conductor, so that the opening directions of the two non-through cuts 410 form an angle of 90 degrees and 270 degrees with the opening direction of the central slot pair 420 of the corresponding slot array respectively. The field distribution of the higher-order modes will show changes in the circumferential current and electric field under different modes. By setting non-through cuts with opening directions forming an angle of 90 degrees and 270 degrees with the opening direction of the central slot pair 420 of the corresponding slot array respectively, the resonance conditions of these modes can be destroyed, the standing wave effect can be weakened, the mode distribution can be made more uniform, and thus the instability of the higher-order mode transmission can be reduced. In addition, under the higher-order mode, certain specific resonant modes will cause local accumulation of signal energy, resulting in unnecessary mode interference and loss, and this cut method can destroy the formation of these resonant modes, reduce signal loss, and improve the transmission efficiency.

[0059] For the case where the opening direction of the non-through cut forms an angle of 0 degrees with the opening direction of the central slot pair of the corresponding slot array, for the problem that local standing waves are likely to occur and the voltage standing wave ratio is likely to deteriorate under the higher-order mode, it is necessary to further set the size of the cut (the radial length and the depth relative to the surface of the inner conductor) to suppress the reflected waves generated at each slot position and optimize the voltage standing wave ratio.

[0060] Specifically, due to the inclined slots being set, the current on the outer conductor causes the current path to become longer and the inductance to increase when passing through the slots of the slot array, resulting in characteristic impedance interference in each slot, and this characteristic impedance interference may cause the voltage standing wave ratio at the slot to deteriorate. Considering that after the non-through cut is set, the current will bypass the cut, and the increased bypass path is equivalent to adding an additional inductance, and this additional inductance can be equivalent to a series inductance, which affects the overall transmission characteristics. Therefore, by setting the size of the non-through cut, the additional inductance increased when the inner conductor current bypasses the cut can be offset by the inductance increased when the outer conductor current passes through the slots, so as to eliminate the characteristic impedance interference in the slots. That is, the length, width, and depth of the non-through cut satisfy the following conditions: the change in inductance of the region of the inner conductor where the non-through cut is added is equal to the change in inductance of the region of the outer conductor where the corresponding slot array is set.

[0061] Among them, the change in inductance of the region of any slot array is the sum of the changes in inductance corresponding to all the slots in the slot array, and the change in inductance corresponding to any slot is determined based on the angle of the slot relative to the axial direction, the slot length of the slot, the characteristic impedance per unit length of the leaky cable and the current propagation speed, and the radius of the outer conductor. Here, the change in inductance corresponding to any slot can be calculated based on the following formula:

[0062]

[0063] Among them, ΔC is the capacitance change corresponding to the slot, ΔL is the inductance change corresponding to the slot, S is the slot length of the slot, θ is the angle of the slot relative to the axial direction, Z0 is the characteristic impedance per unit length of the leaky cable, V c is the current propagation speed, and r is the radius of the outer conductor.

[0064] Those skilled in the art should understand that in the disclosure of the present invention, the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the system or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

[0065] In the description of this specification, the description with reference to "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiments or examples are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A spread spectrum leaky cable compatible with super-cutoff frequency transmission tasks, characterized in that: It includes an inner conductor, an insulating layer and an outer conductor coaxially nested from inside to outside; Wherein, the outer conductor is provided with a plurality of slot arrays; Any slot array contains multiple columns of slot groups, each column of slot groups consists of multiple pairs of slot pairs that are radially arranged and symmetrical about the same axial symmetry axis; the two slots that constitute any slot pair have the same shape and size, and the long axis length of the slot pairs in any column of slot groups gradually increases from both ends toward the symmetry axis along the radial direction.

2. A spread spectrum leaky cable compatible with super cut-off frequency transmission tasks according to claim 1, characterized in that: The total length of the slots in any row of slot groups in any slot array is less than half of the circumference of the outer conductor; the total length of the slots in any row of slot groups is composed of the slot lengths of each slot in any row of slot groups and the slot gap lengths between adjacent slots.

3. A spread spectrum leaky cable compatible with super cut-off frequency transmission tasks according to claim 2, characterized in that: The slot lengths of the slots in any row of slot groups satisfy the following conditions: c / (12f(e r ) 1 / 2 )<l i <c / (4f(e r ) 1 / 2 )-(iδ) / n Where c is the propagation speed of electromagnetic waves in free space, f is the center frequency, and e is the r is the relative dielectric constant of the insulating layer, l i is the slot length of slot i, δ is the correction coefficient, and its range is 0.5~10mm.

4. A spread spectrum leaky cable compatible with super-cutoff frequency transmission tasks according to claim 2, characterized in that: The farther any slot array is from the signal transmitting end, the longer the total length of the slots of the slot group of any slot array.

5. A spread spectrum leaky cable compatible with super-cutoff frequency transmission tasks according to claim 1, characterized in that: The spacing between adjacent slot groups in any slot array meets the following conditions: P dif =P / m(ξ+1) Among them, P dif is the spacing between adjacent slot groups in any slot array; P is the spacing between adjacent slot arrays; ξ is the number of slot groups in any slot array; m is the order of the target high-order mode, and the target high-order mode is the interfering high-order mode caused by the leaky cable when transmitting a super-cutoff frequency signal; The number of slot groups in any slot array is determined based on the following method: Based on the current tested number of slot groups in any slot array, the spacing between adjacent slot groups in any slot array is determined, and the standing wave ratio at each leaky cable transmission frequency is calculated based on the current tested number of slot groups in any slot array and the spacing between adjacent slot groups; the current tested number of slot groups in any slot array is increased until the standing wave ratio at each leaky cable transmission frequency reaches a preset requirement, and the current tested number of slot groups in any slot array is determined as the number of slot groups in any slot array.

6. A spread spectrum leaky cable compatible with super cut-off frequency transmission tasks according to claim 1, characterized in that: The slots in any slot array are arranged obliquely relative to the axial direction; the surface of the inner conductor is provided with non-penetrating cutouts corresponding to each slot array.

7. A spread spectrum leaky cable compatible with super cut-off frequency transmission tasks according to claim 6, characterized in that: The opening direction of the non-through cutout forms an angle of 0 degree and / or 180 degrees with the opening direction of the central slot pair of the corresponding slot array.

8. A spread spectrum leaky cable compatible with super cut-off frequency transmission tasks according to claim 6, characterized in that: The opening direction of the non-through cutout forms an angle of 90 degrees and 270 degrees with the opening direction of the central slot pair of the corresponding slot array.

9. A spread spectrum leaky cable compatible with super cut-off frequency transmission tasks according to claim 7, characterized in that: When the opening direction of the non-through cut forms an angle of 0 degrees with the opening direction of the central slot pair of the corresponding slot array, the length, width and depth of the non-through cut satisfy the condition that the inductance change of the area of ​​the inner conductor where the non-through cut is added is equal to the inductance change of the area of ​​the outer conductor where the corresponding slot array is set; the inductance change of the area of ​​any slot array is the sum of the inductance changes corresponding to all the slots in any slot array, and the inductance change corresponding to any slot is determined based on the angle of any slot relative to the axial direction, the slot length of any slot, the characteristic impedance per unit length of the leaky cable and the current propagation speed, and the radius of the outer conductor.

10. The spread spectrum leaky cable compatible with super cut-off frequency transmission tasks according to claim 1, characterized in that: Any slot array includes multiple slot groups with different numbers of slots, and the slot groups with different numbers of slots are alternately arranged on the outer conductor.

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