CN114325132A - High-frequency 3M circular test tool of three-coaxial-method cable shielding effectiveness test system - Google Patents
High-frequency 3M circular test tool of three-coaxial-method cable shielding effectiveness test system Download PDFInfo
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Abstract
The invention provides a high-frequency 3M circular test tool of a three-coaxial cable shielding effectiveness test system, which comprises a vector network analyzer and a high-frequency 3M circular test tool. The high-frequency 3M circular test tool comprises an outer loop near-end short circuit structure, a shielding cap structure and a metal cylinder structure, wherein the outer loop near-end short circuit structure comprises a left end cover and a short circuit clamping piece; the shielding cap structure comprises an inner loop far-end shielding box, an outer loop far-end assembly, a supporting assembly and a connector; the metal cylinder comprises an outer copper pipe I and an outer copper pipe II.
Description
Technical Field
The invention belongs to the field of electrical measurement technology and instruments, and particularly relates to a cable shielding effectiveness testing system based on a three-coaxial method.
Background
The research patents distributed in the fields of electric automobiles, aerospace, ships and the like, relating to cable shielding effectiveness evaluation exist in China, a high-frequency band test system aiming at the shielding effectiveness of radio frequency coaxial cables based on a triple-axis method is provided, and the system is also in blank areas in the field of high-voltage shielding cables of rail transit.
With the continuous emergence of various communication services, the development of communication towards high frequency has become a trend, the demand of broadband communication becomes the power for the development and innovation of coaxial cables, and high-frequency communication puts higher requirements on coaxial cables for transmitting radio frequency signals. Radio frequency coaxial cables and CATV coaxial cables will be developed much longer in high frequency networks, as two of the field development directions and goals of the nine key products.
In practice, users often need to know the shielding effectiveness of the cable in order to use and design. Since the shielding layer structure of the shielded cable is various, and the shielding effectiveness of the cable can only be ideally analyzed. If the cable shielding effectiveness can be directly obtained through testing aiming at the shielding cables with different specifications, accurate investigation basis can be provided when the shielding cables are evaluated, compared, designed and used in engineering.
The cable shielding effectiveness testing method and system are basically implemented by slightly changing or even not changing based on an IEC standard method, the changing positions are mostly concentrated on input and output interfaces, the improvement schemes of the characteristics of the input and output interfaces of the testing equipment are more, but the prior art scheme with flexible operation and simple structure is less.
Related research of a cable and connector shielding effectiveness analysis algorithm is only related to Hunan university at present, adjustment is carried out on a surface transfer impedance model of a foreign keyli scholars, and related published technical schemes are still rare.
The control software of the cable and connector shielding effectiveness test system is only the winCOMET software of Rosenberger in the industry at present, but has no published prior art data.
Disclosure of Invention
The invention provides a high-frequency 3M circular test tool of a three-coaxial cable shielding effectiveness test system, which belongs to a part of the three-coaxial cable shielding effectiveness test system and aims to overcome the technical defects in the prior art, improve the scientificity and accuracy of high-frequency three-coaxial cable shielding measurement and simultaneously improve the simplicity and the flexibility and the convenience of the design of a device on the design of a short circuit structure at the near end of an outer loop, a shielding cap structure at the far end of the outer loop and an insulating support structure.
The three-coaxial cable shielding effectiveness testing system comprises a vector network analyzer and a high-frequency 3M circular testing tool. The high-frequency 3M circular test tool is mainly applied to testing of shielding attenuation of a tested cable when the frequency is 30MHz-3 GHz.
The testing principle of the high-frequency 3M circular testing tool is a short circuit-matching three-coaxial method, namely, the near end of an outer loop is short-circuited, and the terminal of an inner loop is connected with a matching resistor.
Aiming at a test frequency band of 30MHz-3GHz, a high-frequency 3M circular test tool of a cable shielding effectiveness test system adopting a three-coaxial method is provided, and comprises an outer loop near-end short circuit structure, a shielding cap structure and a metal cylinder structure, wherein the outer loop near-end short circuit structure comprises a left end cover and a short circuit clamping piece; the shielding cap structure comprises an inner loop far-end shielding box, an outer loop far-end assembly, a supporting assembly and a connector; the metal cylinder comprises an outer copper pipe I, an outer copper pipe II and an outer copper pipe connecting pipe; the outer copper pipe connecting pipe is matched according to different cable lengths; particularly, the first outer copper pipe, the second outer copper pipe and the connecting pipe of the outer copper pipe can also be integrated, namely, the metal cylinder can also be an integral copper pipe, but the test convenience is reduced.
The left end cover is arranged on the outer side of the outer copper tube II, and the short circuit clamping piece is arranged on the inner side of the left end cover; the outer loop far-end assembly is arranged on the outer side of the outer copper pipe I, the inner loop far-end shielding box and the supporting assembly are arranged in the outer loop far-end assembly, and the supporting assembly is used for fixing the inner loop far-end shielding box in the outer loop far-end assembly;
the short circuit clamping piece is used for fixedly clamping one end of a tested cable and is in contact with the cable shielding layer; the tested cable penetrates through the metal cylinder and is positioned on a central axis of the metal cylinder; and the shielding box at the far end of the inner loop fixedly clamps the other end of the tested cable.
The inner loop far-end shielding box comprises a shielding sleeve, a semicircular clamping piece and a conical ejector rod; the shielding sleeve is connected with the conical ejector rod through threads; the semicircular clamping piece is arranged in the shielding sleeve in a taper fit manner and used for clamping the other end of the tested cable, preferably, the semicircular clamping piece is matched and used for clamping the shielding layer of the tested cable with different outer diameters and is clamped on the shielding layer of the tested cable, and the matching of a proper clamping force can be realized when the shielding layer of the tested cable with different outer diameters is clamped, so that the influence of a clamping state on the deformation of the shielding layer is kept constant, and the measurement precision and the stability of a test system are improved; the conical ejector rod gradually compresses the semicircular clamping piece along with the screwing of the threads.
Preferably, the outer loop distal end assembly comprises a right end cap, a transition sleeve, an inner tapered adapter end cap; the right end cover is arranged on the outer side of the outer copper pipe I, the transition sleeve is connected with the right end cover, and the inner conical adaptive end cover is arranged on the outer side of the transition sleeve.
Preferably, the support assembly comprises a large insulating support and a small insulating support; the large insulating support is arranged between the transition sleeve and the inner conical adaptive end cover, the tail of the conical ejector rod penetrates through the large insulating support, the small insulating support is arranged at the top of the inner conical adaptive end cover, and the head of the conical ejector rod penetrates through the small insulating support.
Preferably, the connector is press-fitted outside the inner tapered fitting end cap by a screw; the connector is electrically connected with the tapered head portion.
Preferably, the end face of the inner conductor of the connector is butted with the head of the conical ejector rod through plugging.
Preferably, the inner tapered adapter end cap achieves a tapered transition with a ratio to the outer circuit inner diameter variation (difference in size of outer copper tube and coaxial connector) greater than 5.
Preferably, the large insulating support and the small insulating support realize nominal characteristic impedance matching through inner and outer diameter design, thickness design and circular groove design; the surfaces of the large insulating support and the small insulating support are provided with circular grooves, and the grooves are used for compensating impedance interference generated after the large insulating support and the small insulating support are introduced, so that the measurement precision of the system is improved.
The shielding layer of the tested cable, the matching resistor and the inner conductor of the tested cable form an inner loop; the cable shielding layer to be tested, the inner loop far-end shielding box, the outer loop far-end assembly and the metal cylinder body form an outer loop.
Preferably, the area of the short circuit clamping piece contacted with the cable shielding layer is 360 degrees around the cable shielding layer, and the area of the short circuit clamping piece contacted with the cable shielding layer is increased, so that the accuracy of system measurement is improved.
Preferably, the shielding sleeve and the conical ejector rod are connected through threads; during assembly, the conical ejector rod gradually compresses the semicircular clamping piece along with the screwing of the threads.
The design of the high-frequency 3M circular test tool copper pipe comprises one outer copper pipe, two outer copper pipes and four outer copper pipe connecting pipes. In the test process, the first outer copper pipe and the second outer copper pipe are indispensable and respectively realize the functions of far end matching of the inner loop and near end short circuit of the outer loop; the four outer copper pipe connecting pipes are used for adapting to the tested cables with different lengths and can be increased or decreased according to the lengths of the tested cables.
The implementation of the shielding sleeve assembly of the high-frequency 3M circular testing tool and the connection of the integral testing tool is described above, the characteristics and requirements of the three coaxial devices are considered in the integral design, a modularized design idea is embodied, and the assembly and the test of the whole set of device are facilitated while the reliable connection and the good electrical continuity of the device are ensured.
The invention has the beneficial effects that: the test system can be applied to the fields of rail transit, new energy automobiles, photovoltaic, aerospace and the like, and measures the shielding attenuation of the tested cable by a three-coaxial method so as to evaluate the shielding effectiveness of the cable. The test system has the characteristics of basically no requirement on the test environment, high precision of test results, wide application range and the like. The device design of the whole set of test system not only ensures the scientificity and accuracy of measurement, but also highlights the simplicity and the innovation of the device design on the design of the short circuit structure, the shielding cap structure and the insulating support structure at the near end of the outer loop. Based on the characteristic of simple design of the test system, the process of using the test system and butting the input and output interfaces is flexible and convenient.
Drawings
The advantages and spirit of the present invention can be further understood by the following detailed description of the invention and the accompanying drawings.
FIG. 1 is a schematic view of a high-frequency 3M circular test fixture of a cable shielding effectiveness test system by a three-coaxial method according to the present invention;
FIG. 2 is a cross-sectional view of a high-frequency 3M circular test fixture of a cable shielding effectiveness test system by a three-coaxial method according to the present invention;
fig. 3 is a schematic diagram of a left end cover of an external loop near-end short-circuit structure of a high-frequency 3M circular test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention;
fig. 4 is a schematic diagram of a short circuit clip of an external loop near-end short circuit structure of a high-frequency 3M circular test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention;
FIG. 5 is a schematic diagram of an outer copper tube II of a metal cylinder structure of a high-frequency 3M circular test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention;
FIG. 6 is a schematic diagram of an outer copper pipe I of a metal cylinder structure of a high-frequency 3M circular test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention;
fig. 7 is a schematic diagram of a transition sleeve of a shield cap structure of a high-frequency 3M circular test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention;
fig. 8 is a schematic diagram of a right end cover of a shielding cap structure of a high-frequency 3M circular testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;
fig. 9 is a schematic view of a shielding sleeve of a shielding cap structure of a high-frequency 3M circular testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;
fig. 10 is a schematic diagram of a semicircular clamping piece of a shielding cap structure of a high-frequency 3M circular testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;
fig. 11 is a schematic diagram of a conical ejector rod of a shielding cap structure of a high-frequency 3M circular testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;
fig. 12 is a schematic view of a large insulation support of a shield cap structure of a high-frequency 3M circular test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention;
FIG. 13 is a schematic view of an inner tapered adaptive end cap of a shield cap structure of a high-frequency 3M circular test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention;
fig. 14 is a schematic view of a small insulating support of a shield cap structure of a high-frequency 3M circular test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention;
fig. 15 is a schematic diagram of a connector N-KF50 of a shield cap structure of a high-frequency 3M circular test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention;
fig. 16 is a schematic diagram of a shield cap part structure of a high-frequency 3M circular test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention;
reference numerals:
1. a connector; 2. an inner conical adaptive end cap; 3. a large insulating support; 4. a transition sleeve; 5. a right end cap; 6. a left end cap; 7. a short circuit clip; 8. a shielding sleeve; 9. a semicircular clamping piece; 10. a conical ejector rod; 11. small insulating support
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to overcome the technical defects in the prior art and improve the scientificity and accuracy of measurement, meanwhile, the design simplicity and the flexibility and the convenience of use of the device are improved in the design of a short-circuit structure at the near end of an outer loop, a shielding cap structure at the far end of the outer loop and an insulating support structure, and a three-coaxial-method cable shielding effectiveness testing system is provided.
The invention provides a three-coaxial cable shielding effectiveness testing system which is composed of a vector network analyzer and a high-frequency 3M circular testing tool. The high-frequency 3M circular test tool is mainly applied to testing the shielding attenuation of a tested cable when the frequency is 30MHz-3 GHz.
The testing principle of the testing tool is a short circuit-matching three-coaxial method, namely, the near end of an outer loop is short-circuited, and the terminal of an inner loop is connected with a matching resistor.
The high-frequency 3M circular test tool comprises an outer loop near-end short-circuit structure, a shielding cap structure and a metal cylinder structure, wherein the outer loop near-end short-circuit structure comprises a left end cover 6 and a short-circuit clamping piece 7; the shielding cap structure comprises an inner loop far-end shielding box, an outer loop far-end assembly, a supporting assembly and a connector 1; the metal cylinder comprises an outer copper pipe I, an outer copper pipe II and an outer copper pipe connecting pipe;
the left end cover 6 is arranged on the outer side of the outer copper tube II, and the short circuit clamping piece 7 is arranged on the inner side of the left end cover 6; the outer loop far-end assembly is arranged on the outer side of the outer copper pipe I, the inner loop far-end shielding box and the supporting assembly are arranged in the outer loop far-end assembly, and the supporting assembly is used for fixing the inner loop far-end shielding box in the outer loop far-end assembly;
the short circuit clamping piece 7 is used for fixedly clamping one end of a tested cable and is in contact with the cable shielding layer; the tested cable penetrates through the metal cylinder and is positioned on a central axis of the metal cylinder; and the shielding box at the far end of the inner loop fixedly clamps the other end of the tested cable.
The inner loop far-end shielding box comprises a shielding sleeve 8, a semicircular clamping piece 9 and a conical ejector rod 10; wherein, the shielding sleeve 8 is connected with the conical mandril 10 through threads; the semicircular clamping piece 9 is arranged in the shielding sleeve 8 through taper fit and used for clamping the other end of the tested cable, preferably, the semicircular clamping piece 9 is matched and used for clamping the shielding layer of the tested cable according to different outer diameters and is clamped on the shielding layer of the tested cable, and the matching of proper clamping force can be realized when the shielding layer of the tested cable with different outer diameters is clamped, so that the influence of a clamping state on the deformation of the shielding layer is kept constant, and the measurement precision and the stability of a test system are improved;
preferably, the outer loop distal end assembly comprises a right end cover 5, a transition sleeve 4, an inner conical adapting end cover 2; the right end cover 5 is arranged on the outer side of the outer copper pipe I, the transition sleeve 4 is connected with the right end cover 5, and the inner conical adaptive end cover 2 is arranged on the outer side of the transition sleeve 4.
Preferably, the support assembly comprises a large insulating support 3, a small insulating support 11; the large insulating support 3 is arranged between the transition sleeve 4 and the inner conical adaptive end cover 2, the tail of the conical ejector rod 10 penetrates through the large insulating support 3, the small insulating support 11 is arranged at the top of the inner conical adaptive end cover 2, and the head of the conical ejector rod 10 penetrates through the small insulating support 11.
Preferably, the connector 1 is press-fitted outside the inner tapered adapter end cap 2 by screws; the connector 1 is electrically connected with the head part of the conical mandril 10.
Preferably, the end face of the conductor in the connector 1 is butted with the head of the conical mandril 10 through insertion.
Preferably, the inner conical adapter end cap 2 achieves a conical transition with a ratio of change of the inner diameter of the outer circuit greater than 5.
Preferably, the large insulating support 3 and the small insulating support 11 realize nominal characteristic impedance matching through inner and outer diameter design, thickness design and circular groove design; the surfaces of the large insulating support 3 and the small insulating support 11 are both provided with circular grooves, and the grooves are used for compensating impedance interference generated after the large insulating support 11 and the small insulating support 11 are introduced, so that the measurement precision of the system is improved.
The shielding layer of the tested cable, the matching resistor and the inner conductor of the tested cable form an inner loop; the cable shielding layer to be tested, the inner loop far-end shielding box, the outer loop far-end assembly and the metal cylinder body form an outer loop. Preferably, the area of the contact area of the short circuit clip 7 and the cable shielding layer surrounds the cable shielding layer for 360 degrees, and the improvement of the area of the contact area of the short circuit clip 7 and the cable shielding layer is helpful for improving the measurement accuracy of the system.
Preferably, the shielding sleeve 8 and the conical ejector rod 10 are connected through threads; during assembly, the conical ejector rod 10 gradually compresses the semicircular clamping piece 9 along with the screwing of the threads.
The design of the high-frequency 3M circular test tool copper pipe comprises one outer copper pipe, two outer copper pipes and four outer copper pipe connecting pipes. In the test process, the first outer copper pipe and the second outer copper pipe are indispensable and respectively realize the functions of far end matching of the inner loop and near end short circuit of the outer loop; the four outer copper pipe connecting pipes are used for adapting to the tested cables with different lengths and can be increased or decreased according to the lengths of the tested cables.
In addition, in a high-frequency test environment, the electrical continuity of the test system is directly affected by the skin effect, so that the contact resistance is increased. In order to ensure good electrical continuity of a test system, each part of the high-frequency 3M circular test tool is designed and processed by H62 brass, and the good processing characteristic, the mechanical strength, the corrosion resistance and the excellent conductivity of the high-frequency 3M circular test tool meet the design requirements.
On the one hand, the outer loop near-end short circuit structure of the high-frequency 3M circular test tool of the test system is provided, and the design idea of the outer loop near-end short circuit structure is to realize effective electrical short circuit of a shielding layer of a tested cable and a copper pipe of the test tool.
As shown in fig. 1-15, the outer loop proximal end short circuit structure of the high frequency 3M circular test fixture (as shown in fig. 1-2) is composed of a left end cap 6 shown in fig. 3 and a short circuit clip 7 shown in fig. 4. Implementation of outer loop near-end short circuit: selecting a short circuit clamping piece 7 matched with the tested cable, clamping the shielding layer of the tested cable by using a central hole arranged in the central position of the short circuit clamping piece 7, then placing the end 1 of the tested cable into the end A of the outer copper tube II shown in figure 5, enabling the end 2 of the tested cable to penetrate through the left end cover 6 shown in figure 3, and effectively realizing the electrical short circuit between the shielding layer of the tested cable and the metal cylinder by screwing the left end cover 6 shown in figure 3.
The central aperture of the first version of the short circuit clamping piece 7 only designs two specifications of phi 4 and phi 7, and the subsequent processing of corresponding adaptive size can be carried out according to the diameter of a cable to be tested or the diameter of the cable to be tested required by customers.
In one aspect (as shown in fig. 2), a shielding cap structure of the test system is provided, which comprises a right end cover 5, a transition sleeve 4, a shielding sleeve 8, a semicircular clip 9, a large insulating support 3, a conical ejector pin 10, a small insulating support 11, an inner conical fitting end cap 2, and a connector 1 (preferably an N-KF50 connector 1).
Inner loop far-end resistance matching and shielding cap structural design: the testing system is based on a triaxial short circuit-matching testing principle, the far-end resistance matching is realized by welding a patch resistor between a shielding layer 1 and an inner conductor of a tested cable end, and the resistance value of the patch resistor is equal to the characteristic impedance of the tested cable (aiming at a radio frequency coaxial cable which is a measuring object, a high-frequency 3M circular testing tool has common characteristic impedances of the radio frequency coaxial cable of 50 omega and 75 omega). The chip resistor has good radio frequency characteristics and smaller mechanical size, the structure size, the power capacity and the high-frequency characteristics of the chip resistor adaptive to the test system are comprehensively considered, and a 50-ohm CRS 0805 type chip resistor is preferably selected (a coaxial cable with the characteristic impedance of 50 ohms is selected in the specific implementation process). In order to prevent the direct coupling of the matching resistor and the outer loop, a shielding cap structure is required to be added at the end of the tested cable 1 for shielding; considering that the tested cable needs to be transited to the external connector 1, the shielding cap structure needs to perform the shielding function and also to function as a transition conductor.
The high-frequency 3M circular test fixture shielding cap structure is composed of a transition sleeve 4 shown in FIG. 7, a right end cover 5 shown in FIG. 8, a shielding sleeve 8 shown in FIG. 9, a semicircular clip 9 shown in FIG. 10, a conical ejector pin 10 shown in FIG. 11, a large insulating support 3 shown in FIG. 12, an inner conical adapting end cover 2 shown in FIG. 13, a small insulating support 11 shown in FIG. 14 and a connector 1 shown in FIG. 15.
The design of the high-frequency 3M circular test tool copper pipe comprises one outer copper pipe, two outer copper pipes and four outer copper pipe connecting pipes. In the test process, an outer copper tube I and an outer copper tube II are indispensable and respectively realize the functions of far end matching of the inner loop and near end short circuit of the outer loop, wherein in the figure 2, the left side is the outer copper tube II, and the right side is the outer copper tube I; the four outer copper pipe connecting pipes are used for adapting to the tested cables with different lengths and can be increased or decreased according to the lengths of the tested cables.
The realization method for the assembly of the shielding cap structure of the high-frequency 3M circular test tool and the connection of the whole test tool is as follows: the assembly implementation is described for the case where only the outer copper tube two as shown in fig. 5 and the outer copper tube one as shown in fig. 6 are selected. According to the implementation of the short circuit of the near end of the external loop of the high-frequency 3M circular test tool, the end 1 of the tested cable is placed from the end A of the external copper pipe II shown in the figure 5; the end B of the outer copper pipe II shown in figure 5 and the end B of the outer copper pipe I shown in figure 6 are screwed tightly through threads; then, butting the end A of the first outer copper pipe shown in FIG. 6 with the end B of the transition sleeve 4 shown in FIG. 7, and pressing the end A of the first outer copper pipe through the right end cover 5 shown in FIG. 8 and the end B of the transition sleeve 4 shown in FIG. 7 to the end A of the first outer copper pipe through threads; then the end 1 of the cable to be tested penetrates into the end of the shielding sleeve 8A shown in FIG. 9 and penetrates out from the end (threaded end) of the shielding sleeve 8B; after clamping the shielding layer at the end 1 of the tested cable by using the semicircular clamping piece 9 as shown in fig. 10, integrally placing the shielding layer into the shielding sleeve 8; then pulling the tested cable towards the end direction of the shielding sleeve 8A until the semicircular clamping piece 9 is tightly clamped to the tail end of the shielding sleeve 8A; then, the large insulating support shown in the figure 12 is sleeved at the tail end of the threaded end of the conical ejector rod 10 shown in the figure 11, and the conical ejector rod 10 shown in the figure 11 is connected with the end B of the shielding sleeve 8 shown in the figure 9 through threads to form a good shielding box structure; as shown in fig. 11, a blind hole with a certain depth is arranged at the inner side of the threaded end of the conical ejector rod 10, and the diameter of the blind hole is determined according to the outer diameter of the tested cable sheath and the inner diameter of the shielding sleeve 26 shown in fig. 9; finally, a small insulating support 11 shown in fig. 14 is placed at the top end inside the inner conical adaptive end cover 2 shown in fig. 13, the mandril end of the conical mandril 10 shown in fig. 11 is inserted into the small insulating support and then is integrally inserted into the inner conical adaptive end cover 2 shown in fig. 13, and connection is realized through the threads arranged at the tail end of the inner conical adaptive end cover 2 and the end of the transition sleeve 4A shown in fig. 7. The selected coaxial connector 1 (such as an N-KF50 type) is pressed on the top end of the inner conical adaptive end cover 2 through a screw, as shown in FIG. 11, the head of the conical ejector rod 10 is butted with the end face of the inner conductor of the coaxial connector 1 through plugging (a gap exists on the inner conductor of the plug of the common commercial N-type coaxial connector 1, the gap must be ground flat before plugging to ensure that the end face is flat, and the butting depth of the head of the conical ejector rod 10 and the inner conductor of the N-type connector 1 needs to be ensured to be more than 2mm to ensure the reliable connection between the two). Design of the inner taper of the conical mandril 10 and the end cover 2: since the tapered transition connection structure can exhibit a good impedance matching characteristic, the outer copper tube and the coaxial connector 1 are connected by the tapered transition connection structure. The taper of the inner tapered adapter end cap 2 and the tapered mandrel 10 can be further determined while ensuring that the characteristic impedance of the coaxial line of the tapered section is 50 Ω.
The shielding sleeve 8 shown in fig. 9, the semicircular clip 9 shown in fig. 10, the tapered ejector pin 10 shown in fig. 11, the large insulating support 3 shown in fig. 12, the internally tapered adapter end cap 2 shown in fig. 13, and the small insulating support 11 shown in fig. 14 can be assembled into an integral assembly which cannot be easily disassembled after the assembly is completed, thereby facilitating the subsequent repeatability test. The overall assembly is shown in fig. 16.
The implementation of the shielding sleeve assembly of the high-frequency 3M circular testing tool and the connection of the integral testing tool is described above, the characteristics and requirements of the three coaxial devices are considered in the integral design, a modularized design idea is embodied, and the assembly and the test of the whole set of device are facilitated while the reliable connection and the good electrical continuity of the device are ensured. The calculation method for copper tube and part sizing is described in detail later.
To is directed atThe size design method of the outer loop (which is composed of a tested coaxial cable shielding layer, an outer copper pipe and the like, and is regarded as a coaxial line in the design process) comprises the following steps: the coaxial lines all work in a TEM mode under a normal working state (a waveguide mode without electric field and magnetic field components in the transmission direction of electromagnetic waves in the TEM mode), and higher modes, namely a TE mode and a TM mode (the TE mode and the TM mode are evanescent fields and have no volatility and cannot be transmitted) can appear when the working wavelength is close to the size of the cross section of the coaxial lines. In order to ensure that only TEM modes are transmitted in the coaxial line at a given frequency, the cut-off wavelength problem of higher order modes must be taken into account in designing the outer copper tube dimensions. The lowest order TM mode in the coaxial line is TM01Mode, lowest order TE mode being TE11Mode, cut-off wavelength λcThe determination can be made according to the following two equations:
wherein D is the diameter mm of the inner conductor of the coaxial line, D is the diameter mm, epsilon of the outer conductor of the coaxial liner-filling medium relative dielectric constant, mu, between inner and outer conductors of a coaxial liner-filling medium relative permeability between inner and outer conductor of coaxial line
In order to ensure that only TEM mode exists in the coaxial line, the shortest operating wavelength must be ensured to be larger than the TE of the lowest order higher-order mode11The cutoff wavelength of the mode. Namely that make
From this, the value range of (D + D) can be determined. In order to obtain the actual values of D and D, further confirmation needs to be performed through the maximum transmission power or the minimum loss of the transmission line. Because the coaxial line can not give consideration to the maximum transmission power and the minimum loss, a compromise mode is adopted in the actual design process, at the moment, the loss is 10% larger than the minimum loss condition, the transmission power capacity is 15% smaller than the maximum transmission power capacity, and therefore the ratio relation between D and D can be obtained.
Cut-off frequency of use of coaxial line, i.e. TE11The frequency at which the mode begins to appear, the cut-off frequency fc at which the higher order modes appear, being a function of the dimensions of the inner and outer conductors and the propagation speed of the coaxial line, i.e.
Wherein C is0Speed of light,. epsilonre-the filling medium equivalent dielectric constant of the coaxial line.
The equivalent dielectric constant of the filling medium of the coaxial line can be calculated according to the following formula:
wherein epsilonr1Relative dielectric constant of the sheath of the cable to be tested, ∈r0Relative dielectric constant of air, d1Outer diameter mm of cable sheath to be tested
Considering that 50 omega characteristic impedance is formed at the shielding cap end of the triaxial device, part processing is facilitated, and a certain tested cable outer diameter range is ensured, the barrel diameter size of the shielding sleeve of the shielding box at the far end of the inner loop and the inner diameter size of the outer copper pipe can be finally determined on the basis of ensuring the 50 omega characteristic impedance.
And (3) checking and calculating according to the determined cylinder diameter size of the shielding sleeve and the inner diameter size of the outer copper pipe by the formula 1 to obtain the design requirement that the upper limit cutoff frequency of the coaxial line at the end of the shielding sleeve at the moment meets the test range to 3 GHz.
In the design process, in order to ensure the coaxial performance of the tested cable inner conductor, the inner loop distal end shielding box and the outer copper pipe of the three-coaxial cable connector 1 shielding performance testing system, a supporting structure must be added in the inner conical adaptive end cover as shown in fig. 13. However, the introduction of the supporting structure may cause the impedance characteristic of the outer loop of the test system to change, and the supporting structure may additionally increase electromagnetic reflection and dielectric loss, which ultimately affects the accuracy of the test result. Therefore, there is a need to take into account the material selection and the structural dimensioning of the support structure, in order to minimize the negative effects of the incorporation of the support structure.
First, the material of the support structure is considered. The selected material is the same as the insulation connecting plates 1 and 2 shown in figures 13 and 14, and is made of polytetrafluoroethylene, and the material has higher hardness, is easy to process and has smaller relative dielectric constant than other two common insulation materials, namely polystyrene and polyethylene. The introduction of the insulating support structure can inevitably cause the coaxial height difference of the inner conductor and the outer conductor to form a step capacitor, so that the electromagnetic field structure of the support part is changed, and the characteristic impedance of the support part is further influenced. In order to reduce the influence of the step capacitance on the accuracy of the test result, compensation needs to be made on the design size and the design process. The essence of the compensation is that a section of inductance is introduced into the supporting part, and the characteristic impedance of the supporting part is equal to that of the rest part by utilizing the better compensation stepped capacitance of the inductance.
The compensating design of the insulating support structure is as follows:
1. the inner and outer diameter (inner and outer conductor groove depth) and thickness of the insulating support structure are designed.
2. And (4) coplanar compensation design, namely determining the size of the annular grooves on the two end faces of the insulating support.
For the compensation design 1, the thickness of the insulating support member affects the highest operating frequency of the test system, and the thinner the insulating support member is, the closer the highest operating frequency is to the cut-off frequency under the condition of an air medium, but the too thin the thickness of the insulating support member is, so that it is difficult to ensure the sufficient support strength of the insulating support member. Therefore, the thickness of the insulating support needs to be designed as thin as possible while ensuring the working frequency and the supporting strength. To avoid the occurrence of higher order modes, the thickness B of the insulating support should satisfy the relationship shown in equation 2 and preferably ensure that the thickness is less than one quarter wavelength at the highest operating frequency.
Wherein: lambda [ alpha ]gOperating wavelength, fcTheoretical cutoff frequency of coaxial line using air as medium, f operating frequency, epsilonrPhase of insulating supportTo dielectric constant
And calculating to determine the specific dimension B of the insulating support structure.
The grooves on the inner and outer conductors will introduce discontinuous capacitance, and in order to ensure the minimum total step capacitance, the combination of the groove depths of the inner and outer conductors needs to be considered. The characteristic impedance calculation formula obtained according to the radio frequency coaxial cable transmission theory is
Wherein epsilonrRelative dielectric constant of the insulating medium, D-inner diameter mm of the outer conductor, D-inner diameter mm of the inner conductor
To ensure that the characteristic impedance at the insulating support is 50 Ω, the final insulating support inside and outside diameter dimensions can be determined by performing calculations according to equation 3.
Aiming at the compensation design 2, after the slotting combination of the compensation design 1 is added, the discontinuous capacitance introduced by the insulating support member is greatly improved, and in order to further reduce the electromagnetic reflection of a test frequency band, the insulating support member which is subjected to slotting treatment needs to be subjected to coplanar compensation design. The compensation mode of coplanar compensation is to process a ring groove on each of the two end faces of the insulating support, so that the compensation inductance can be introduced to realize the compensation of the discontinuous capacitance. The size and depth of the annular groove can be calculated as follows:
according to the above formula 3, when the inner and outer diameters of the supporting member are determined, the annular groove is processed to change the relative dielectric constant of the supporting member, so as to ensure that the characteristic impedance at the position of the insulating supporting member is still kept at 50 Ω, and after the annular groove is processed, the equivalent relative dielectric constant of the insulating supporting member can be calculated by the formula 4:
wherein: epsilonreEquivalent relative permittivity of the insulating support after incorporation in the annular groove
εr1Relative dielectric constant of insulating medium
εr2Relative dielectric constant of air
V1Volume of insulating support after introduction into annular groove
V2Volume of the annular groove
To sum up, the size of the complete insulating support piece can be obtained, and the related parameters comprise the thickness B of the insulating support piece, the outer diameter D, the inner diameter D, the large radius R of the circular groove, the small radius R of the circular groove and the depth B of the circular groove.
The embodiments described in the specification are only preferred embodiments of the present invention, and the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the present invention. Those skilled in the art can obtain technical solutions through logical analysis, reasoning or limited experiments according to the concepts of the present invention, and all such technical solutions are within the scope of the present invention.
It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program instructing relevant hardware, where the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.
The embodiments described in the specification are only preferred embodiments of the present invention, and the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the present invention. Those skilled in the art can obtain technical solutions through logical analysis, reasoning or limited experiments according to the concepts of the present invention, and all such technical solutions are within the scope of the present invention.
Claims (12)
1. A high-frequency 3M circular test tool of a three-coaxial cable shielding effectiveness test system is characterized by comprising an outer loop near-end short circuit structure, a shielding cap structure and a metal cylinder structure, wherein the outer loop near-end short circuit structure comprises a left end cover and a short circuit clamping piece; the shielding cap structure comprises an inner loop far-end shielding box, an outer loop far-end assembly, a supporting assembly and a connector; the metal cylinder comprises an outer copper pipe I and an outer copper pipe II;
the left end cover is arranged on the outer side of the outer copper tube II, and the short circuit clamping piece is arranged on the inner side of the left end cover; the outer loop far-end assembly is arranged on the outer side of the outer copper pipe I, the inner loop far-end shielding box and the supporting assembly are arranged in the outer loop far-end assembly, and the supporting assembly is used for fixing the inner loop far-end shielding box in the outer loop far-end assembly;
the short circuit clamping piece is used for fixedly clamping one end of a tested cable and is in contact with the cable shielding layer; and the shielding box at the far end of the inner loop fixedly clamps the other end of the tested cable.
2. The high-frequency 3M circular test fixture of the three-coaxial cable shielding effectiveness test system according to claim 1, wherein the metal cylinder further comprises an outer copper pipe connecting pipe, and the outer copper pipe connecting pipe is connected with the first outer copper pipe and the second outer copper pipe.
3. The high-frequency 3M circular test tool of the three-coaxial cable shielding effectiveness test system according to claim 1 or 2, wherein the inner loop far-end shielding box comprises a shielding sleeve, a semicircular clamping piece and a conical ejector rod; wherein the shielding sleeve is connected with the conical ejector rod; the semicircular clamping piece is arranged in the shielding sleeve in a taper fit mode and used for clamping the other end of the tested cable; the conical ejector rod compresses the semicircular clamping piece.
4. The high-frequency 3M circular test tool of the three-coaxial cable shielding effectiveness test system according to claim 1 or 2, wherein the outer loop distal end assembly comprises a right end cover, a transition sleeve and an inner conical adaptive end cover; the right end cover is arranged on the outer side of the outer copper pipe I, the transition sleeve is connected with the right end cover, and the inner conical adaptive end cover is arranged on the outer side of the transition sleeve.
5. The high-frequency 3M circular test tool of the three-coaxial cable shielding effectiveness test system according to claim 4, wherein the support assembly comprises a large insulating support and a small insulating support; the large insulating support is arranged between the transition sleeve and the inner conical adaptive end cover, the tail of the conical ejector rod penetrates through the large insulating support, the small insulating support is arranged at the top of the inner conical adaptive end cover, and the head of the conical ejector rod penetrates through the small insulating support.
6. The high-frequency 3M circular test fixture of the three-coaxial cable shielding effectiveness test system according to claim 5, wherein the connector is press-fitted outside the inner tapered adaptive end cover; the connector is electrically connected with the tapered head portion.
7. The high-frequency 3M circular test tool of the three-coaxial cable shielding effectiveness test system according to claim 6, wherein the end face of the inner conductor of the connector is butted with the head of the conical ejector rod through plugging.
8. The high-frequency 3M circular test fixture of the three-coaxial cable shielding effectiveness test system according to claim 4, wherein the inner conical adaptive end cover realizes conical transition with a ratio of change of inner diameter of an external loop larger than 5.
9. The high-frequency 3M circular test tool of the three-coaxial cable shielding effectiveness test system according to claim 3, wherein circular grooves are formed in the surfaces of the large insulating support and the small insulating support.
10. The high-frequency 3M circular test fixture of the three-coaxial cable shielding effectiveness test system according to claim 1 or 2, wherein an area where the short-circuit clip is in contact with the cable shielding layer surrounds the cable shielding layer by 360 degrees.
11. The high-frequency 3M circular test tool of the three-coaxial cable shielding effectiveness test system according to claim 3, wherein the shielding sleeve is in threaded connection with the conical ejector rod; during assembly, the conical ejector rod gradually compresses the semicircular clamping piece along with the screwing of the threads.
12. The high-frequency 3M circular test tool of the three-coaxial cable shielding effectiveness test system according to claim 1 or 2, wherein the cable to be tested passes through the metal cylinder and is positioned on a central axis of the metal cylinder.
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| CN202210022701.XA Pending CN114325132A (en) | 2021-11-15 | 2022-01-10 | High-frequency 3M circular test tool of three-coaxial-method cable shielding effectiveness test system |
| CN202220051141.6U Active CN217820584U (en) | 2021-11-15 | 2022-01-10 | Low-frequency cylinder testing tool of three-coaxial-method cable shielding effectiveness testing system |
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| KR100430879B1 (en) * | 2002-02-06 | 2004-05-17 | 남성훈 | Elastic collet for pcb mounting jig and pcb mounted jig assembly |
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| CN209961874U (en) * | 2019-04-15 | 2020-01-17 | 安徽伟光电缆股份有限公司 | Cable voltage resistance detection device |
| CN210092486U (en) * | 2019-07-08 | 2020-02-18 | 思库机电工程技术(上海)有限公司 | Shielded cable grounding type joint |
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