Conductive connection structure with limited inner conductor single end and radio frequency coaxial adapter

Abstract

The invention discloses an inner conductor single-end limited conductive connection structure and a radio frequency coaxial adapter, the conductive connection structure comprises an inner conductor, a central insulating medium and an outer conductor which are coaxially arranged, the central insulating medium is axially fixed in an inner cavity of the outer conductor, and the inner conductor coaxially penetrates through a central inner hole of the central insulating medium; the inner conductor is provided with diameter mutation steps adaptive to the specifications of the interfaces at the two ends of the cross-specification adapter, only the steps abut against the end face of the medium to form unique axial hard limiting, the inherent structure is reused to achieve integration of limiting and impedance transition, and no extra axial hard limiting structure is arranged on the other portions. And the inner conductor and the medium inner hole are in interference fit to form axial static friction constraint. According to the invention, the technical prejudice that the conductor in the adapter must be limited at two ends in two directions is broken through, the problem that the performance and the reliability in the prior art are difficult to consider at the same time is solved, the radio frequency performance, the limiting reliability and the mass production economy are synchronously optimized in a very small design space, and the requirements of a high-frequency broadband radio frequency system are met.

Description

Technical Field

[0001] This invention relates to the field of conductive connection technology, and in particular to a conductive connection structure with single-end limiting of the inner conductor and a radio frequency coaxial adapter. Background Technology

[0002] RF coaxial adapters are core components in RF and microwave transmission systems, enabling signal interconnection and switching. They are primarily used for interconnecting RF signals between RF transmission cables, active / passive functional devices, system modules, test and measurement instruments, and complete equipment. They also provide stable impedance matching, reliable electromagnetic shielding, and mechanical connection guarantees for the transmission link. Among these, cross-specification adapters (such as N-type to SMA type adapters) that adapt to different standard RF interface series are essential components for solving the interconnection needs of devices with different interface standards in RF systems. They are widely used in 5G / 6G mobile communications, millimeter-wave radar, satellite communications, aerospace, and electronic test and measurement fields.

[0003] A typical RF coaxial adapter uses a coaxial transmission line structure, mainly consisting of an inner conductor (also known as a pin), an outer conductor, a central insulating medium (also known as an insulator) located between the inner and outer conductors, and a matching locking connection mechanism. It can support low-loss, high-fidelity transmission of transverse electromagnetic waves (TEM mode). As RF systems continue to evolve towards higher frequency broadband, smaller integration, and higher reliability, increasingly stringent design requirements are being placed on the RF transmission performance, mechanical stability, and environmental adaptability of various cross-specification RF coaxial adapters.

[0004] It is important to note that the structural design of cross-specification RF coaxial adapters is subject to the dual rigid constraints of mandatory international standards and the physical laws of transmission lines, leaving extremely limited room for optimization. Firstly, the dimensions and tolerances of the mating interfaces at both ends of the adapter are strictly limited by the IEC 60169 series of international standards and cannot be arbitrarily adjusted; otherwise, compatibility with standard components will be lost. Secondly, the RF transmission link must strictly match the industry-standard 50Ω characteristic impedance, requiring the ratio of the outer conductor's inner diameter to the inner conductor's outer diameter to be consistently maintained at approximately 3.44. Even slight adjustments to the inner conductor's outer diameter will directly cause a significant deviation in the local characteristic impedance, resulting in degraded RF performance. Thirdly, with the industry trend towards miniaturization, the internal mounting space of the adapter is fixed, leaving no redundant space for adding additional impedance compensation structures and limiting components. Under such stringent constraints, the inner conductor's structural design simultaneously undertakes two core functions: impedance matching and axial limiting. The design requirements of these two functions inherently conflict, further compressing the already extremely limited space for optimization.

[0005] According to the basic theory of coaxial transmission lines, the characteristic impedance of an RF coaxial structure is determined by the outer diameter of the inner conductor, the inner diameter of the outer conductor, and the relative permittivity of the intermediate insulating medium. Uniform characteristic impedance throughout the transmission link is a core prerequisite for ensuring distortion-free and low-loss transmission of RF signals. For cross-specification RF coaxial adapters, the diameter transition structure of the inner conductor is both the core object of impedance matching design and the natural carrier of the axial limiting structure. Therefore, the axial positioning and limiting reliability of the inner conductor is a core design dimension that is equally important as the RF transmission performance. The design of its limiting structure directly determines the adapter's assembly consistency, mechanical connection stability, long-term operational reliability, and impedance matching performance across the entire operating frequency band.

[0006] There has long been a fixed design consensus and a prevalent technical bias in this field: to ensure the axial stability of the inner conductor of a cross-specification RF coaxial adapter during mating and unmating at both ends, axial hard limiting structures must be set at corresponding positions at both ends of the inner conductor to form a bidirectional limiting constraint, thus preventing axial movement of the inner conductor under insertion and unmating forces; it is generally believed that a structure with only single-end limiting cannot meet the mechanical reliability requirements under mating conditions. This design consensus has not undergone rigorous verification under all operating conditions and is based solely on empirical design under traditional insertion and unmating conditions. Within the already extremely limited design space, it further restricts the possibility of structural optimization, leading the industry to generally ignore the limiting value of the inherent diameter transition structure of the inner conductor, and hindering the technical research and development of synergistic optimization of limiting structures and RF performance.

[0007] Based on this design consensus, the existing cross-specification RF coaxial adapter inner conductor limiting schemes all adopt a bidirectional two-end limiting design approach.

[0008] For example, the utility model patent with authorization announcement number CN215266993U discloses a high-frequency adapter. This adapter is an integrated special cross-specification coaxial adapter structure that adapts to SMA type ports and N type ports. It achieves bidirectional axial positioning of the inner conductor by relying on the variable diameter stepped surface of the plug and the end faces of the insulator respectively to fit and contact. A barb structure is set between the plug and the insulator to further enhance the bidirectional limiting reliability of the inner conductor. While simplifying the number of parts, it ensures the electrical performance and assembly consistency of the adapter.

[0009] For example, the utility model patent with authorization announcement number CN222826774U discloses an RF coaxial adapter that is compatible with multiple types of ports such as N-type and SMA-type. It is another mainstream general-purpose architecture for cross-specification adapters in this field. For the axial limiting of the inner conductor, it sets a retaining step and a top retaining mating surface at both ends of the center pin. By the front medium holding the retaining step and the rear medium holding the rear end surface of the center pin, a complete bidirectional axial limiting constraint at both ends is formed. It is equipped with multiple sets of bushings and top retaining sleeve assemblies to further enhance the reliability of the limiting at both ends, and can flexibly adapt to the port conversion needs of different specifications.

[0010] Furthermore, this bidirectional end-limiting design consensus is not limited to the field of cross-specification RF coaxial adapters, but has become a universally followed design principle across all application scenarios in the entire RF connector industry and globally. There has never been a design attempt that omitted the hard limit structure at the non-limiting end and only used a single-end limit, fully demonstrating that this design consensus has become a long-standing and universally followed technical principle in this field. For example, the utility model patent with authorization announcement number CN223167816U discloses an aerospace-grade radio frequency cable connector for low-orbit satellites. Designed for the extreme high-reliability conditions of space vacuum and strong vibration, it features a raised stepped surface in the middle of the inner conductor. The front and rear insulating media axially abut against the two end faces of the stepped surface, respectively. At the same time, the limiting steps at both ends of the outer shell provide bidirectional locking for the two sets of insulating media, forming a complete bidirectional axial limiting constraint on both ends of the inner conductor. This is a typical general design for aerospace-grade high-reliability radio frequency connectors.

[0011] For example, the utility model patent with authorization announcement number CN223390900U discloses a civilian high-reliability radio frequency coaxial connector. It not only forms a bidirectional axial limit for the inner conductor through the cooperation of the insulating medium and the inner conductor mounting boss and the inner wall step of the shell, but also sets a barb structure on the inner wall of the shell to strengthen the axial fixing effect of the insulating medium, further improving the reliability of the bidirectional limit of the inner conductor. This fully reflects the design understanding in the field that "basic bidirectional limit alone is not enough to guarantee reliability, and additional reinforcement structures are required".

[0012] For example, the invention patent application with publication number CN121618256A discloses a high-temperature, high-voltage, and high-current resistant connector for use in eVTOL aircraft and aerospace. It is designed for extreme conditions of high temperature, strong vibration, and high current. It uses two sets of insulators to axially support and limit the two ends of the inner conductor, and the stepped structure of the shell forms a complete bidirectional axial constraint at both ends. This is a general design principle in the field of RF / electrical connectors under extreme conditions.

[0013] Even leading companies in the global RF test and measurement field follow this approach. A utility model patent with authorization announcement number CN212485605U discloses a high-frequency RF connection component suitable for DC to millimeter-wave bands. It adopts an industry-leading pin-bead component structure, which forms a bidirectional axial abutment with the waist step of the inner conductor and the inner wall step of the sleeve through the bead, ultimately achieving bidirectional end-to-end constraint on the inner conductor. Even high-frequency millimeter-wave products from leading international manufacturers strictly adhere to the design concept that the inner conductor must be equipped with bidirectional axial constraints, and have never attempted a single-end constraint technology route.

[0014] The aforementioned existing technical solutions cover a full range of applications, including civilian general use, aerospace, low-orbit satellites, and high-frequency millimeter waves. They encompass the entire industry's technical routes from mainstream domestic manufacturers and leading international companies. All of them strictly adhere to the inherent design consensus of bidirectional end-to-end limiting of the inner conductor. Therefore, they share the same technical defects as the aforementioned solutions and cannot avoid the inherent pain points brought about by the bidirectional limiting structure. On the one hand, regardless of the insulation support structure or limiting reinforcement method used, as long as bidirectional hard limiting is set at both ends, at least two limiting mating steps / structures must be processed on the inner conductor. This inevitably introduces at least two axially separated impedance discontinuities in the coaxial transmission link, forming a signal reflection superposition effect in the high-frequency band, which deteriorates core RF performance such as VSWR and insertion loss, and limits the expansion of the product's operating bandwidth. Even with a millimeter-wave high-frequency solution using bead limiting, the bidirectional contact structure between the bead and the inner conductor and sleeve will still form two independent impedance discontinuities, which cannot solve the core problem of signal reflection superposition in the high-frequency band.

[0015] On the other hand, the bidirectional end-limiting design inevitably leads to the problem of tolerance accumulation in dual-reference positioning, which increases the processing accuracy requirements and assembly difficulty of the inner conductor. In order to enhance the reliability of bidirectional limiting, additional structures such as barbs, multiple sets of insulating media, and bushing components are added, which not only further increases the number of parts and assembly processes, but also introduces more impedance discontinuities, falling into a vicious cycle of "strengthening the limit → deteriorating RF performance → adding compensation structures → further compressing the design space", and can never solve the core pain point of the industry that it is difficult to balance the reliability of the limit and the RF performance.

[0016] Meanwhile, in existing technologies, the bidirectional mechanical limiting structure of the inner conductor and the RF impedance optimization structure are mutually restrictive. The design of the limiting structure at both ends must prioritize the mechanical limiting requirements, making it impossible to simultaneously consider the optimal design of RF transmission performance. Independent structural design and electromagnetic simulation optimization are required, significantly increasing product development cycle and design difficulty. This prevents deep synergistic optimization of the inner conductor's mechanical limiting performance and RF transmission performance, making it difficult to meet the current comprehensive design requirements of RF systems for high performance, miniaturization, and low cost of adapters. In summary, the notion that "the inner conductor of cross-specification RF coaxial adapters must have bidirectional axial hard limiting at both ends to ensure axial stability during insertion and removal; setting only a single-end limiting cannot meet the mechanical reliability requirements under all operating conditions" has become a long-standing and widespread technical bias in this field globally, across all application scenarios, and in all product categories from civilian to aerospace applications. This bias, without rigorous verification under all operating conditions, is based solely on empirical design under traditional insertion and removal conditions, guiding all manufacturers in the industry to optimize and improve the architecture around bidirectional two-end limiting, generally ignoring the limiting value of the inherent diameter transition structure of the inner conductor, and completely hindering the technical development direction of synergistic optimization of limiting structure and RF performance. Therefore, breaking through this deep-rooted technical bias in the field, and under the premise of being rigidly constrained by both international interface standards and the physical laws of transmission lines, and with extremely narrow space for optimization design, developing a conductive connection structure that can simultaneously take into account the reliability of the inner conductor axial limit and high-frequency broadband transmission performance, with a simplified structure and low processing and assembly difficulty, as well as a cross-specification RF coaxial adapter, has become a core technical problem that urgently needs to be solved in this field. Summary of the Invention

[0017] In view of the shortcomings of the prior art, the purpose of this invention is to break through the deep-rooted technical prejudices in this field, and to develop a conductive connection structure and cross-specification RF coaxial adapter that can simultaneously take into account the reliability of the inner conductor axial limit and high-frequency broadband transmission performance, with a simplified structure and low processing and assembly difficulty, under the premise of being constrained by the dual rigidity of international interface standards and transmission line physical laws and the extremely narrow space for optimization design.

[0018] The technical solution of the invention is as follows: A conductive connection structure with single-end limiting of the inner conductor, applied to a cross-specification RF coaxial adapter, includes an inner conductor, a central insulating medium, and an outer conductor arranged coaxially. The inner conductor has a large end and a small end, respectively. The inner conductor has a diameter abrupt step corresponding to the large and small ends, adapting to the rated specifications of the interfaces at both ends. The diameter abrupt step faces the small end. The central insulating medium is axially fixedly installed within the inner cavity of the outer conductor. The inner conductor coaxially passes through the central inner hole of the central insulating medium. The inner conductor axially abuts against the end face of the central insulating medium facing the large end only through the diameter abrupt step, forming a unique axial hard limiting structure. The rest of the inner conductor has no axial hard limiting structure that rigidly abuts against the central insulating medium or the outer conductor. The outer wall of the inner conductor, from the abrupt diameter step to the small end, is interference-fitted with the central inner hole of the central insulating medium, forming a static friction constraint on the axial movement of the inner conductor.

[0019] The above solution achieves the following results: Under the dual constraints of international interface standards and the physical laws of transmission lines, and with extremely limited space for optimization, this invention overcomes the long-standing global bias that "cross-specification RF coaxial adapters must have bidirectional axial hard limiting structures at both ends of the inner conductor to ensure axial stability during insertion and removal; single-end limiting alone cannot meet mechanical reliability and RF performance requirements." Even high-reliability products used in extreme conditions such as aerospace and low-orbit satellites, as well as high-frequency millimeter-wave products from leading international companies, strictly adhere to this bidirectional end-limiting design consensus. This invention omits the second set of axial hard limiting structures located in the non-transition section of the inner conductor, which is generally considered essential for bidirectional axial limiting of the inner conductor. Simultaneously, it does not reduce the axial limiting reliability of the inner conductor. Instead, without breaking any standard constraints or adding any extra structures, it achieves a comprehensive improvement in RF transmission performance, mechanical compatibility, and mass production economics. This constitutes an omitted invention in the sense of patent law, with the following specific beneficial effects: 1. Optimize RF transmission performance from the source and significantly expand the operating bandwidth: This invention eliminates the redundant impedance discontinuities inherent in existing end-limiting structures by using a design where the inner conductor forms a unique axial hard-limiting structure solely through a diameter abrupt step, with no additional axial hard-limiting structures elsewhere. According to the characteristic impedance theory of coaxial transmission lines, any abrupt change in the outer diameter of the inner conductor directly causes the local characteristic impedance to deviate from the standard value, forming impedance discontinuities. Even with an impedance compensation structure, the parasitic reactance and signal reflection caused by the abrupt change cannot be completely eliminated. At high frequencies, the superposition effect of multiple impedance discontinuities drastically degrades RF performance. Furthermore, within the extremely limited design space in this field, there is no redundant space to add independent impedance compensation structures for multiple impedance discontinuities, preventing existing technologies from resolving the core contradiction between limiting requirements and RF performance.

[0020] This invention retains only one diameter abrupt step to adapt to the inherent requirements of the adapter specification transition as the sole limiting structure, eliminating the need for additional steps, slots, or other structures for limiting. The non-limiting end is a smooth, uniform diameter structure, fundamentally eliminating the second impedance discontinuity point caused by the limiting at both ends in the prior art. Only one impedance compensation is needed for a single step to achieve continuous and uniform characteristic impedance across the entire operating frequency band, significantly reducing the difficulty of impedance compensation design. At the same time, it completely avoids the in-band resonance spike caused by the superposition of two impedance discontinuities. Under the premise of the same interface specifications and without changing the standard installation dimensions, it can significantly improve the highest usable operating frequency of the adapter and greatly broaden the usable operating bandwidth of the product.

[0021] Meanwhile, this invention directly reuses the diameter abrupt step inherent in cross-specification adapters as a limiting structure, realizing the integrated design of the limiting structure and impedance transition structure. This completely solves the industry pain point of mutual constraints between mechanical limiting structure and RF impedance optimization structure in the prior art. It does not require sacrificing RF performance for limiting requirements, nor does it require reducing limiting reliability for RF performance. It achieves deep synergistic optimization of mechanical limiting performance and RF transmission performance, which can significantly reduce product development cycle and electromagnetic simulation optimization workload.

[0022] 2. A single rigid support reference simultaneously improves the reliability of the limit switch and the assembly accuracy: This invention, through its design of axially fixing the central insulating medium to the inner cavity of the outer conductor and coaxially passing through the central inner hole of the central insulating medium, provides a single, absolutely fixed rigid support reference for the unique axial rigid restraint structure, ensuring the constraint effectiveness of the single-end restraint structure. When the inner conductor is subjected to axial insertion and extraction forces, the central insulating medium will not undergo axial displacement with the inner conductor, and the restraint force can be completely transmitted to the fixed outer conductor, ensuring the stable and reliable rigid constraint capability of the single-end restraint structure. This fundamentally refutes the core prejudiced argument in this field that single-end restraint cannot withstand mating insertion and extraction forces.

[0023] Meanwhile, the design of a single rigid support reference avoids the problems of reference misalignment and cumulative assembly tolerance caused by the existing dual support reference with two ends limiting. Under the premise of the same processing technology and the same standard tolerance requirements, the position tolerance band of the inner conductor mating end face can be significantly reduced, the fitting accuracy is greatly improved, the processing accuracy requirements of the inner conductor and the difficulty of assembly error control are significantly reduced, and it is suitable for high-precision assembly requirements in high-frequency scenarios.

[0024] 3. Construct a two-way closed-loop limiting system of "rigid hard limit + elastic soft constraint" to simultaneously improve adaptability to a wide temperature range environment: This invention uses the interference fit between the outer wall of the inner conductor, which transitions abruptly from a diameter step to the small end, and the inner hole of the central insulating medium to form a static friction damping constraint on the axial movement of the inner conductor. This, together with the single-end hard limiting structure, forms a complete bidirectional closed-loop limiting system, fully covering all stress conditions at the connection of the two ends of the adapter. Without the need for hard limiting at both ends or additional limiting components, the axial movement constraint of the inner conductor in all directions can be achieved within a fixed standard installation space.

[0025] When the large end of the inner conductor is connected to an external device, it is subjected to an axial pushing force towards the outside of the adapter. This force is directly offset by the rigid contact between the abrupt diameter step surface of the inner conductor and the central insulating medium, forming a rigid hard limit constraint that completely restricts the inner conductor from moving towards the large end. The axial movement of the inner conductor can be controlled at the micrometer level, fully meeting the industry standard requirements for the position accuracy of the connection interface. When the small end of the inner conductor is connected to an external device, it is subjected to an axial pushing force towards the outside of the adapter. This force is completely offset by the static friction damping constraint generated by the interference fit from the "diameter abrupt step to the small end", achieving full constraint on the movement of the inner conductor towards the small end. By optimizing the length of the interference fit section, the elastic modulus of the medium, and the interference amount, this solution can make the pull-out resistance provided by the static friction constraint far exceed the 100N required by the industry standard, fully covering the force requirements of all working conditions of bidirectional insertion and extraction, without the need for an additional reverse rigid limit structure.

[0026] Meanwhile, the design without rigid constraints at the non-limiting end allows deformation caused by the difference in thermal expansion coefficients between the inner conductor, the dielectric, and the outer shell to be released freely along the axial direction. This completely avoids the problems of dielectric cracking, interference reduction, and inner conductor deformation caused by thermal stress concentration in existing end-limiting structures, greatly improving the product's wide temperature range environmental adaptability and significantly reducing the product performance degradation rate under high and low temperature cycling conditions.

[0027] Furthermore, this invention eliminates the need for additional barbs, multiple sets of insulating media, bead assemblies, or other structures for reverse positioning. Compared to existing technologies that add extra structures to enhance bidirectional positioning, this invention simplifies the structure, reduces costs, and completely avoids problems such as dielectric scratches, impedance abrupt changes, and poor assembly consistency caused by additional positioning structures. Actual testing has verified that the long-term positioning reliability of this solution far exceeds that of existing barb-reinforced, multi-media bidirectional positioning solutions, completely overturning the core prejudice in this field that "single-end positioning cannot guarantee the mechanical reliability of bidirectional insertion and removal under all working conditions."

[0028] In a further preferred embodiment, the central insulating medium is made of glass fiber or silica-filled modified polytetrafluoroethylene.

[0029] The advantages of the above solution are as follows: The above setup specifically limits the material of the central insulating medium, selecting glass fiber or silica-filled modified polytetrafluoroethylene (PTFE). This fundamentally solves the inherent defects of industry-standard pure PTFE, such as low elastic modulus and strong cold flow creep, significantly improving the structural rigidity and long-term dimensional stability of the medium. Without altering the original single-end limiting structure or adding any additional reverse limiting components, it significantly enhances the radial contact pressure and static friction constraint capability generated by the interference fit between the inner conductor and the central insulating medium. This strengthens the reliability of the bidirectional closed-loop limiting system of "single-end rigid hard limiting + interference static friction soft constraint" in the basic solution, further verifying that the single-end limiting solution can fully cover the force requirements of bidirectional plugging and unplugging of the adapter under all working conditions, effectively overturning the inherent technical prejudice in this field that "single-end limiting cannot guarantee mechanical reliability." Simultaneously, the dielectric properties of this modified filling material are highly similar to those of general pure PTFE, allowing for direct implementation without adjusting the original impedance matching design and standard mating dimensions, achieving synergistic optimization of mechanical reliability and RF transmission performance.

[0030] In a further preferred embodiment, the elastic modulus of the filled modified polytetrafluoroethylene is not less than 1500 MPa, the relative permittivity at 25°C is 2.2 to 2.4, and the loss tangent at 10 GHz is not greater than 0.0008.

[0031] The effect of the above solution is that, based on the aforementioned limitations on the filled modified polytetrafluoroethylene material, it further refines the core performance parameters of the material at different levels, forming a complete protective boundary for material performance. The formula for calculating the maximum axial static friction force of a coaxial interference fit is as follows: The formula for calculating radial contact pressure is: The parameters in the above formula are defined as follows: Fmax: The maximum axial static friction force between the inner conductor and the central insulating medium, i.e. the maximum pull-out force for reverse restraint, in N; f: The static friction coefficient between the mating surfaces of the inner conductor and the central insulating medium. In this scheme, the static friction coefficient between the gold-plated beryllium copper and the filled modified polytetrafluoroethylene is taken as 0.35~0.45. p: Radial contact pressure at the mating surface between the inner conductor and the central insulating medium, in MPa; π: Pi, taken as a constant 3.1416; d: Nominal outer diameter of the interference fit section between the inner conductor and the central insulating medium, in mm; L: Effective axial length of the interference fit between the inner conductor and the central insulating medium, that is, the total length of the fit section of the inner conductor from the diameter abrupt step to the small end, in mm; E m : The elastic modulus of the central insulating medium, in MPa; Δd: The interference fit between the inner conductor and the central inner hole of the central insulating medium on one side, in mm; υ m Poisson's ratio of the central insulating medium; in this scheme, the Poisson's ratio of the modified polytetrafluoroethylene filling is taken as 0.32~0.38. D: Nominal diameter of the outer circle of the central insulating medium, in mm.

[0032] The elastic modulus E of the medium can be clearly derived from the formula. m The effective length L of the interference fit is related to the radial contact pressure p and the maximum axial static friction force F. max They show a direct positive correlation.

[0033] By limiting the elastic modulus to no less than 1500MPa, the radial contact pressure of the interference fit can be stably guaranteed, and the reverse limiting force can be stably increased by more than 3 times. This completely eliminates the problem of limiting force attenuation caused by medium creep during high and low temperature cycles and long-term use, providing quantitative and feasible performance support for the bidirectional closed-loop limiting system. By limiting the relative permittivity to 2.2~2.4 at 25℃, the dielectric properties of the medium are fully compatible with industry-standard pure polytetrafluoroethylene (PTFE). The original impedance compensation design can achieve precise matching of the 50Ω standard impedance across the entire frequency band without any adjustment, avoiding RF performance fluctuations caused by material changes. By limiting the loss tangent to no more than 0.0008 at 10GHz, it is fully adaptable to high-frequency operating scenarios from DC to 18GHz, ensuring extremely low transmission loss, and fully meets the stable supply level of mass-produced filled modified PTFE in the industry, taking into account both the comprehensiveness of the solution's protection range and the feasibility of mass production. At the same time, by precisely limiting the core performance parameters, the optimal implementation method of the solution is locked, further improving the stability and protection of the solution.

[0034] In a further preferred embodiment, the inner conductor is provided with a large-end adapter section, an intermediate transition section and a small-end adapter section with decreasing diameters along the axial direction, and the axial length of the intermediate transition section accounts for 20% to 21% of the total length of the inner conductor.

[0035] The advantages of the above solution are as follows: By precisely limiting the axial length ratio of the intermediate transition section, this solution completely departs from the general design logic of bidirectional two-end limiting architectures in this field. Conventional bidirectional limiting solutions in the industry require two axially separated limiting steps at each end of the intermediate transition section, thus necessitating that the length ratio of the intermediate transition section be maintained above 25%. This is an inevitable design in this field, and therefore inevitably creates two independent impedance nodes separated by the complete transmission line, leading to the inherent defect of high-frequency signal reflection and superposition degradation. This solution, however, compresses the length ratio of the intermediate transition section to 20%–21%, deeply integrating with the core design of single-end centralized limiting, and controlling the internal guide... The diameter abrupt change limiting structure is concentrated and compressed into an extremely narrow axial range. While ensuring a smooth impedance transition across different adapter specifications, it makes the two diameter abrupt changes electrically equivalent to a concentrated impedance node at the same location. Only a single compensation is needed to complete precise impedance matching across the entire frequency band. This completely avoids the inherent pain points of multi-node impedance abrupt changes and signal reflection superposition in conventional industry designs. It fundamentally optimizes the VSWR and insertion loss in the high-frequency band above 12GHz, and significantly expands the usable operating bandwidth of the adapter. At the same time, the compact design of the transition section compresses the cantilever length of the inner conductor, improves the structure's vibration and deformation resistance and assembly coaxiality accuracy, and further enhances the mechanical stability of the single-end limiting structure.

[0036] In a further preferred embodiment, the outer diameter of the intermediate transition section is between the outer diameter of the large-end adapter section and the outer diameter of the small-end adapter section, forming a continuous and smooth diameter decreasing structure; the ratio of the outer diameter of the intermediate transition section to the outer diameter of the large-end adapter section is 0.68 to 0.78, and the ratio of the outer diameter of the intermediate transition section to the outer diameter of the small-end adapter section is 1.58 to 1.85.

[0037] The effect of the above solution is that, based on the limitation of the length ratio of the intermediate transition section, this solution further precisely limits the ratio of the outer diameter of the intermediate transition section to the outer diameter of the two end adapter sections. This ratio range completely deviates from the general design logic of existing bidirectional limiting architectures—as per authorization announcement number CN215266993U. Existing industry-standard bidirectional limiting solutions, such as those using conventional methods, require a significant reduction in the outer diameter of the intermediate transition section to accommodate the axially separated limiting steps at both ends. The ratio of the transition section's outer diameter to the larger end adapter section is only about 0.52, and to the smaller end adapter section, it's only about 1.18. This inevitably creates a steep diameter abrupt change and multi-node impedance discontinuities, leading to inherent defects such as high-frequency signal reflection and degradation. In contrast, this solution utilizes a dedicated ratio range of 0.68–0.78 and 1.58–1.85, forming a clear boundary with existing technologies that completely avoids overlap. This overcomes the limitation of fixed-size adapters only being compatible with a single model, covering all cross-specification RF coaxial adapters using this single-ended limiting architecture. It is independent of specific interface standards and overall dimensions, greatly expanding the solution's applicability and protection scope. Furthermore, it deeply integrates with the core design of single-ended centralized limiting, forming a continuous... The smooth, decreasing diameter structure, combined with the coaxial transmission line characteristic impedance calculation formula, ensures that the characteristic impedance of the inner conductor consistently matches the 50Ω standard value from the large-end adapter section to the small-end adapter section. Regardless of adjustments to the overall adapter specifications, it significantly reduces local impedance deviations caused by the centralized limiting structure. A single impedance compensation is sufficient for precise matching across the entire frequency band, completely resolving the multi-node signal reflection problem caused by steep diameter abrupt changes in conventional industry solutions. This significantly improves the smoothness and consistency of RF transmission. Furthermore, this ratio range fully adapts to industry-standard machining tolerances, ensuring strong mass production feasibility. It forms a stable fit gap with the central inner hole of the central insulating medium, guaranteeing smooth interference fit assembly and coaxiality accuracy. This avoids the problems of jamming between the limiting structure and the dielectric assembly, and inner conductor misalignment, which are common in conventional industry solutions. This further enhances the mechanical stability and long-term reliability of the single-end limiting structure.

[0038] In a further preferred embodiment, the axial length of the large-end adapter segment accounts for 44% to 47% of the total length of the inner conductor, and the axial length of the small-end adapter segment accounts for 32% to 35% of the total length of the inner conductor.

[0039] The advantages of the above solution are as follows: Based on the structural constraints of the transition section, this solution precisely optimizes the length ratio of the large-end adapter section to the small-end adapter section, completely overturning the segmented length design logic of conventional bidirectional limiting solutions in the industry. In conventional solutions, independent limiting structures must be set at the large-end and small-end ends, thus requiring the large-end adapter section to be shortened and the small-end adapter section to be lengthened. Sufficient axial space cannot be reserved to achieve long-distance interference fit, and reverse limiting can only be achieved through additional barbs and slot structures, inevitably introducing additional impedance defects. In contrast, this solution, with a large-end adapter section ratio of 44% to 47% and a small-end adapter section ratio of 32% to 35%, achieves optimal synergy between limiting reliability and RF performance within a fixed total inner conductor length. The length ratio of the large-end adapter section ensures the reference positioning and fitting accuracy with the central insulating medium, providing stable rigidity for the single-end hard limiting structure. The system provides a support benchmark, avoiding the tolerance accumulation problem caused by dual-benchmark positioning in conventional industry solutions. The combined length of the small-end adapter section and the intermediate transition section maximizes the effective length of the interference fit between the inner conductor and the central insulating medium. Based on the calculation formula for the axial static friction force of coaxial interference fit, the stable guarantee of the fit length can significantly improve the static friction constraint capability generated by the interference fit. This perfectly realizes a bidirectional closed-loop limiting system of single-end hard limiting and interference soft constraint, eliminating the need for additional reverse limiting structures and completely eliminating the impedance defects caused by additional limiting structures in conventional industry solutions. This further verifies that the single-end limiting solution can fully cover the force requirements of bidirectional insertion and removal under all working conditions, effectively overturning the inherent technical prejudice in this field that "single-end limiting cannot guarantee mechanical reliability." At the same time, the length ratio of the two-end adapter sections is fully adapted to the docking size requirements of N-type and SMA-type standard interfaces, allowing for direct application without modifying the standard docking interface.

[0040] In a further preferred embodiment, both ends of the outer conductor adopt a straight wall structure without a flared opening. The inner wall of the outer conductor has two cylindrical center holes of different diameters opened sequentially along the axial direction. The connection between the two cylindrical center holes forms a single annular positioning groove. The central insulating medium is clamped into the annular positioning groove through the annular positioning step of the outer wall, thereby achieving axial non-movement locking of the central insulating medium.

[0041] The advantages of the above solution are as follows: The structure of the outer conductor is specifically optimized to fully adapt to the single-end limiting core architecture. The use of a straight-wall structure without flared ends and a double-cylindrical center hole design completely eliminates the additional impedance discontinuities caused by the flared end structure of conventional adapters. This avoids electric field distortion and high-frequency signal reflection loss caused by the flared end. Combined with the core design of single-end centralized limiting of the inner conductor to eliminate multi-node reflections, it forms a smooth impedance optimization across the entire link, further reducing the VSWR and insertion loss across the DC-18GHz full-band. Simultaneously, the double-cylindrical center holes are integrally formed along the axial direction, creating only a single annular positioning slot, which can achieve... The single-reference axial positioning of the core insulating medium completely avoids the tolerance accumulation problem caused by the multi-segment stepped holes and multiple positioning surfaces of the outer conductor in the existing technology. During processing, the precision machining of the entire hole type can be completed in one clamping, which greatly improves the coaxiality and dimensional accuracy of the inner cavity of the outer conductor. This ensures the assembly coaxiality of the core insulating medium and the inner conductor, and significantly improves the fitting accuracy between the single-end limiting step of the inner conductor and the end face of the core insulating medium. This further enhances the reliability and long-term stability of the single-end hard limiting structure. At the same time, the machining process of the straight-walled cylindrical hole is simpler, without the need for an additional flared mouth forming process, resulting in a higher mass production yield and a machining cost reduction of more than 20% compared to the conventional multi-step flared mouth structure.

[0042] In a further preferred embodiment, a connecting screw sleeve is fitted on the outer edge of the outer conductor corresponding to the large end. An axial limiting structure is provided between the connecting screw sleeve and the outer conductor, which cooperates with an annular limiting groove and an elastic retaining spring. The axial limiting structure restricts the axial movement and detachment of the connecting screw sleeve relative to the outer conductor, so that the axial position of the connecting screw sleeve relative to the outer conductor remains stable, and the connecting screw sleeve can rotate freely in the circumferential direction.

[0043] The advantages of the above solution are as follows: Conventional outer conductors with flared ends can only have a limiting structure at the flared end, inevitably resulting in a large axial movement gap. During insertion and removal, the impact of the connecting screw sleeve's movement is directly transmitted to the limiting fit of the inner conductor. Long-term use can easily lead to problems such as loosening of the inner conductor, excessive coaxiality, and continuous deterioration of RF performance. In contrast, this solution relies on the continuous cylindrical outer edge of the straight-walled outer conductor without a flared end to set a stable axial limiting structure. While ensuring that the connecting screw sleeve can rotate freely in the circumferential direction and fully meet the docking and locking function, it effectively limits the axial movement and risk of detachment of the connecting screw sleeve, keeping the axial position of the connecting screw sleeve always stable. The uniform force distribution during the process prevents axial impact caused by excessive movement, completely avoiding damage to the single-end limiting structure of the inner conductor from impact loads. This further enhances the long-term reliability of the bidirectional closed-loop limiting system with single-end hard limiting and interference static friction constraint. At the same time, the axially stable connecting screw can always ensure that the coaxiality accuracy of the adapter during docking remains within the design range, avoiding additional impedance changes and signal reflections caused by docking deviations. This, together with the core design of single-end centralized limiting of the inner conductor to eliminate multiple reflection nodes and the outer conductor's flared structure to optimize the smoothness of the entire link impedance, forms a complete synergistic gain, further improving the batch consistency and long-term stability of high-frequency transmission performance.

[0044] In a further preferred embodiment, the inner wall of the mating end of the connecting threaded sleeve is provided with an annular assembly guide chamfer, which extends axially toward the mating direction and protrudes entirely from the mating end face of the outer conductor.

[0045] The advantages of the above solution are as follows: The assembly guide chamfer on the inner wall of the connecting threaded sleeve protrudes axially from the mating end face of the outer conductor. When the adapter mates with the external interface, it provides a pre-guiding function. Before the external interface contacts the outer and inner conductors, the chamfered conical surface pre-calibrates the coaxiality of the mating, completely avoiding issues such as thread misalignment and interface misalignment during the mating process. This significantly reduces the difficulty of on-site assembly and mating. Simultaneously, it effectively protects the mating end face of the outer conductor and the mating pins of the inner conductor, preventing metal-on-metal damage during long-term insertion and removal, and extending the product's service life. This guide chamfer protruding from the outer conductor end face... Located entirely on the axial outside of the coaxial cavity for RF signal transmission, without extending into the coaxial transmission path, it does not disrupt the structural uniformity and electric field continuity of the coaxial transmission line. It completely avoids the additional impedance abruptness and high-frequency signal reflection problems caused by conventional guide chamfers, forming a synergistic gain with the core design of full-link impedance smoothing optimization, further ensuring the stability of RF transmission performance across the entire frequency band. At the same time, the precise docking after pre-calibration can significantly reduce the radial skew load and axial impact generated during insertion and removal, avoiding damage to the single-end limiting structure of the inner conductor caused by skew forces, and further enhancing the long-term reliability of the bidirectional closed-loop limiting system of single-end hard limiting combined with interference static friction constraint.

[0046] A radio frequency (RF) coaxial adapter is provided for interconnecting RF interfaces across different specifications. The RF coaxial adapter includes the conductive connection structure with a single-end limit on the inner conductor as described above. Since the RF coaxial adapter incorporates all the technical features of the conductive connection structure with a single-end limit on the inner conductor, it also incorporates all its technical effects, which will not be elaborated further.

[0047] Compared with existing technologies, this invention breaks through the long-standing technical prejudice in the field that "the inner conductor of cross-specification RF coaxial adapters must be set with bidirectional hard limits at both ends to ensure docking reliability." Under the premise of being constrained by both international interface standards and the physical laws of transmission lines, and with extremely narrow space for optimization design, it omits the non-limiting end hard limit structure that is recognized as indispensable in the field. It eliminates the redundant impedance discontinuities caused by the bidirectional limit of existing technologies from the root. At the same time, it forms a bidirectional closed-loop limit system through single-end rigid limit and interference static friction constraint, achieving a deep synergistic improvement in RF transmission performance, mechanical adaptation reliability and mass production economy. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the conductive connection structure with single-end limiting of the inner conductor provided by the present invention when applied to an RF coaxial adapter.

[0049] Figure 2 This is a schematic diagram of the structure of the inner conductor used in the conductive connection structure in a preferred embodiment of the present invention.

[0050] Figure 3 This is a schematic diagram of the structure of the central insulating medium used in the conductive connection structure in a preferred embodiment of the present invention. Detailed Implementation

[0051] This invention provides a conductive connection structure with single-end limiting of the inner conductor and an RF coaxial adapter. To make the objectives, technical solutions and effects of this invention clearer and more explicit, the invention will be further described in detail below with reference to the accompanying drawings and examples.

[0052] In this invention, the large end of the inner conductor refers to the end of the inner conductor that is adapted to the large-size interface of the cross-specification adapter; the small end of the inner conductor refers to the end of the inner conductor that is adapted to the small-size interface of the cross-specification adapter; the abrupt diameter step surface refers to the annular step surface on the inner conductor between the large end and the small end, facing the small end of the inner conductor.

[0053] Taking the most commonly used N-type male to SMA-type female cross-specification coaxial adapter in RF systems as an example, both ends of this adapter have a standard 50Ω characteristic impedance. The N-type male connector (N-male) has a standard inner conductor outer diameter of 3.04mm and an outer conductor inner diameter of 7.00mm; the SMA female connector (SMA female) has a standard inner conductor outer diameter of 1.27mm and an outer conductor inner diameter of 4.10mm. The central insulating medium uses industry-standard polytetrafluoroethylene (PTFE) material with a relative permittivity εr = 2.2. The characteristic impedance calculation formula for a standard 50Ω coaxial system is as follows: Where D is the inner diameter of the outer conductor and d is the outer diameter of the inner conductor. According to calculations, the ratio of the inner and outer diameters D / d corresponding to the standard 50Ω system needs to be stably controlled at around 3.44. Any sudden change in the outer diameter of the inner conductor will directly cause a deviation in the characteristic impedance, forming an impedance discontinuity point.

[0054] Regarding the aforementioned N-type male to SMA-type female cross-specification coaxial adapter, the prior art solution cited in the background section, with authorization announcement number CN215266993U, employs two sets of independent and opposite structures to achieve bidirectional axial limiting of the inner conductor. Its structure and limiting logic strictly match the assembly method disclosed in the patent: the inner conductor (the socket component described in the patent) is a three-section variable diameter structure adapted to the larger outer diameter of the N-type end and the smaller outer diameter of the SMA-type end. During assembly, the slender section of the inner conductor corresponding to the SMA-type end is inserted into the inner hole of the SMA-type mating end side of the insulator with the larger diameter and pressed into place, forming two sets of independent axial limiting in completely opposite directions. (1) The first group is a two-stage stepped axial limit. The inner conductor has two stepped surfaces that are completely aligned and point to the SMA type mating end. One is the stepped surface of the third section of the inner conductor facing the second section, which is in close contact with the end face of the insulator facing the SMA type mating end; the other is the stepped surface of the second section of the inner conductor facing the first section, which is in close contact with the inner stepped surface of the insulator. The two stepped surfaces together constitute an independent first limit system, which is only used to limit the axial movement of the inner conductor towards the outside of the N male end.

[0055] (2) The second group is a barbed snap-fit ​​axial limiter. The barbs are set on the outer wall of the inner conductor and snap into the groove corresponding to the inner wall of the insulator, forming an independent second limiter system that is completely opposite to the step limiter mentioned above. It is only used to limit the axial movement of the inner conductor toward the outside of the SMA mother end.

[0056] Meanwhile, the fixing of the insulator and the outer conductor in this scheme also adopts the same bidirectional fixing logic of "step unidirectional limit + barb reverse limit". The insulator is restricted from moving towards the N-type end by the contact between the step surface of the insulator and the step surface inside the shell, and the insulator is restricted from moving towards the SMA-type end by the interference fit of the barbs of the shell.

[0057] To achieve independent constraints in both directions, this bidirectional limiting structure requires machining two radially protruding limiting steps and a set of radially protruding anti-detachment barbs on the inner conductor. All three elements cause abrupt changes in the non-transmission function of the inner conductor's outer diameter, resulting in three independent impedance discontinuities spaced axially along the RF transmission path. This makes full-band matching optimization impossible through single impedance compensation. According to the standard characteristic impedance calculation formula for coaxial transmission lines, any increase in the inner conductor's outer diameter d will directly lead to a decrease in the D / d ratio, causing the local characteristic impedance Z0 to fall below the standard 50Ω, forming impedance discontinuities, as detailed below: Impedance mutation caused by anti-detachment barbs: To ensure the reliability of the anti-detachment snap-fit ​​of the barbs, the industry-standard minimum radial protrusion height of the anti-detachment barbs is Δd1≥0.15mm (if the protrusion height is too small, an effective interference snap-fit ​​force cannot be formed, and anti-detachment failure is likely to occur). That is, the outer diameter of the inner conductor at the barb is d+Δd1, and the barb is an irregular toothed protrusion structure, not a smooth annular step, which will introduce irregular parasitic reactance. Even if the minimum protrusion height in the industry is adopted, the relative deviation of the local characteristic impedance at this position from the standard 50Ω can still reach more than 12%, and this irregular impedance mutation cannot be completely eliminated by conventional impedance compensation structures.

[0058] The impedance discontinuities introduced by the additional barbs, in high-frequency scenarios with a rated maximum operating frequency of 18GHz for SMA interfaces, will have a superimposed effect with the signal reflections of the adapter's inherent transmission structure, resulting in a voltage standing wave ratio (VSWR) ≥1.45 and an insertion loss ≥0.28dB@18GHz. Simultaneously, the axially spaced impedance nodes form an equivalent resonant cavity structure, which is highly susceptible to in-band resonance spikes above 12GHz, causing RF signal transmission distortion and directly limiting the adapter's maximum operating frequency and usable bandwidth, making it unsuitable for the development requirements of high-frequency, broadband RF systems. Furthermore, the barbed interference fit structure of this design is prone to scratches on the inner hole of the insulating medium and misalignment of the inner conductor during assembly, leading to batch-to-batch performance fluctuations and making it difficult to maintain stable production yield.

[0059] For the same type N-type male to SMA-type female adapter, the prior art solution cited in the background section, with authorization announcement number CN222826774U, also adopts a bidirectional limiting structure at both ends of the inner conductor. To achieve bidirectional axial constraint, clamping steps are set at both ends of the inner conductor. Two sets of independent insulating media must be used to support the steps at both ends. At the same time, multiple sets of fixing components such as bushings, clamping sleeves, and connecting sleeves are added to enhance the reliability of the limiting. In order to achieve bidirectional limiting at both ends, this structure adds multiple sets of non-transmission functional cooperation structures in addition to the inherent transmission structure of the adapter. This results in at least three independent impedance discontinuities that are axially spaced along the RF transmission path, making it impossible to achieve full-band matching optimization through single impedance compensation.

[0060] Specifically, to achieve bidirectional limiting at both ends, the additional structure in this scheme introduces the following impedance abrupt changes: First, to accommodate the bidirectional clamping and limiting of the two sets of insulating media, the inner conductor requires the additional machining of two non-transmission functional clamping steps. The industry-standard minimum radial protrusion of the clamping step is ≥0.3mm, corresponding to a sudden change in the outer diameter of the inner conductor from the working outer diameter d to d+0.3mm. At the clamping step on the N-type end, the corresponding inner diameter of the outer conductor is 7.00mm, and calculations show that the relative deviation of the local characteristic impedance at this location from the standard 50Ω is over 40%. At the clamping step on the SMA-type end, the corresponding inner diameter of the outer conductor is 4.10mm, and calculations show that the relative deviation of the local characteristic impedance at this location from the standard 50Ω is over 22%. Second, to accommodate the assembly of multiple sets of fixing components, the inner conductor requires additional auxiliary mating steps. The impedance discontinuity caused by these auxiliary steps also results in a relative deviation of over 15% from the standard 50Ω. Third, the two independent insulating dielectrics will form an additional dielectric-air interface, resulting in additional impedance discontinuities and parasitic capacitances, which will further exacerbate the degradation of impedance matching.

[0061] The additional structural elements introduced by the aforementioned additional structure create multiple axially spaced impedance discontinuities. In high-frequency scenarios with a maximum rated operating frequency of 18GHz for SMA interfaces, this results in a superposition effect of multiple signal reflections, leading to a voltage standing wave ratio (VSWR) ≥1.52 and an insertion loss ≥0.32dB@18GHz for the adapter, significantly degrading its high-frequency performance. Simultaneously, these multiple axially spaced impedance abrupt changes form an equivalent resonant cavity structure, which is highly susceptible to in-band resonance spikes above 10GHz, causing RF signal transmission distortion and directly limiting the adapter's maximum operating frequency and available bandwidth, making it unsuitable for the development of high-frequency broadband RF systems. Furthermore, the multi-component combined bidirectional limiting structure of this solution involves a large number of parts, complex assembly processes, and large cumulative assembly tolerances. This can easily lead to inner conductor coaxiality deviations and out-of-tolerance mating interface positions, resulting in batch performance fluctuations and hindering improvements in mass production yield and assembly efficiency.

[0062] To address the technical problems existing in the prior art, this invention provides a radio frequency coaxial connection structure with a single-end limiting inner conductor 100, applicable to cross-specification coaxial adapters (such as the N-type male to SMA-type female adapter mentioned above), such as... Figure 1 As shown, it includes an inner conductor 100 arranged coaxially and a central insulating medium 200 (such as...). Figure 3As shown in the diagram, the outer conductor 300 and the central insulating medium 200 are axially fixed in the inner cavity of the outer conductor 300. The inner conductor 100 is coaxially inserted into the central inner hole of the central insulating medium 200. The inner conductor 100 is provided with a diameter abrupt step 110 corresponding to the N-type large end and the SMA-type small end of the adapter to adapt to the rated specifications of the two end interfaces. (It should be understood that the N-type male to SMA-type female adapter scheme used in the specific embodiments of this specification is only an exemplary embodiment. The application scenarios of this invention are not limited to this, and it can also be applied to N-type to 3.5mm type, N-type to 2.92mm type, SMA type to 2.4mm type, 7...) (This refers to cross-specification RF coaxial adapters with different rated coaxial transmission specifications at both ends, such as 7 / 16 to N-type and 7 / 16 to SMA-type, which require transition in inner conductor diameter). The inner conductor 100 only axially abuts against the end face of the central insulating medium 200 through the diameter abrupt step 110, forming a unique axial hard limiting structure. The rest of the inner conductor 100 has no axial hard limiting structure that rigidly abuts against the central insulating medium 200 or the outer conductor 300. From the diameter abrupt step to the outer wall of the small end, the inner conductor 100 is interference-fitted with the central inner hole of the central insulating medium 200, forming a static friction constraint on the axial movement of the inner conductor 100. It should be clarified here that the aforementioned "unique axial hard limiting structure" refers to the existence of only one type of axial hard limiting form based on the contact between the inner conductor diameter abrupt step and the end face of the central insulating medium, rather than limiting the number of diameter abrupt steps corresponding to this limiting structure to only one. In the preferred embodiment, to optimize the impedance matching performance in the high-frequency band, the diameter transition of the inner conductor 100 from the N male end to the SMA female end adopts a smooth transition structure with two consecutive reductions, corresponding to two coaxially arranged diameter abrupt steps 110. Both steps are axially contacted with the end face of the central insulating medium on the same side facing the large end, together forming the same type of axial hard limiting structure. The N male end of the inner conductor is a smooth, equal-diameter cylindrical structure, without any other form of axial hard limiting structure. However, it is not difficult to understand that the present invention does not limit the number of steps to ensure limiting stability. The specific number can be adaptively adjusted and modified by those skilled in the art according to actual needs, and these solutions should also fall within the protection scope of the present invention, which will not be elaborated further.

[0063] In terms of RF transmission performance, this solution concentrates all diameter abrupt steps 110 used for limiting at the same axial position, forming only one concentrated impedance discontinuity point. This completely eliminates the redundant impedance discontinuities with axial spacing introduced by bidirectional limiting in existing technologies, fundamentally avoiding the signal reflection superposition effect between multiple impedance nodes. For this single concentrated impedance discontinuity point, precise matching with the standard characteristic impedance across the entire operating frequency band can be achieved through a single impedance compensation design, significantly reducing the design difficulty of impedance compensation. At the same time, it completely solves the technical problem in existing technologies where multiple spaced impedance discontinuities cannot achieve full-band matching optimization through a single compensation. Based on the fundamental theory of transmission lines, eliminating redundant impedance discontinuities and the reflection superposition effect of multiple nodes can effectively reduce the voltage standing wave ratio and insertion loss of the transmission link, optimize the RF transmission performance across the entire frequency band, and completely avoid the in-band resonance spike problem caused by the formation of an equivalent resonant cavity by multiple axially spaced impedance nodes, effectively expanding the highest usable operating frequency and operating bandwidth of the adapter.

[0064] In terms of mechanical reliability, the single-end axial hard limiting structure of this solution, through the abrupt diameter step 110 of the inner conductor 100 and the rigid contact with the end face of the axially fixed central insulating medium 200, can directly offset the axial force during the insertion and removal of the corresponding mating ends, forming a stable rigid axial constraint, which fully meets the mechanical reliability requirements of the industry standard for insertion and removal conditions. The static friction constraint formed by the interference fit between the inner conductor 100 and the central insulating medium 200, together with the single-end rigid limiting structure, forms a two-way closed-loop axial limiting system, which can cover all axial force conditions when the two ends of the adapter are mated, effectively limiting the axial movement of the inner conductor 100 and ensuring that the position of the mating interface meets the requirements of the industry standard. At the same time, this solution omits the barbs, multiple sets of insulating media, and additional fixing components used for reverse limiting in the prior art, avoiding the problems of insulating medium scratches and inner conductor coaxiality deviation caused by barb interference assembly, and eliminating the cumulative dimensional tolerances caused by the assembly of multiple parts, effectively improving the assembly consistency and mass production yield of the product.

[0065] It is particularly important to note that in the design of RF coaxial adapters, the ratio of the inner to outer diameter corresponding to the 50Ω standard characteristic impedance must be strictly controlled at around 3.44. The adjustable design space is extremely small, and any slight adjustment to the inner conductor structure will directly cause significant fluctuations in RF performance. For a long time, it has been widely believed in the art that bidirectional axial hard limiting structures must be set at both ends of the inner conductor to ensure the mechanical reliability of the adapter during docking. This understanding has created a long-standing technical bias, leading those skilled in the art to sacrifice RF performance for mechanical reliability, thus failing to resolve the core contradiction between the two. This invention, by omitting the axial hard limiting structure at the non-limiting end, which is generally considered indispensable in the art, constructs a bidirectional closed-loop limiting system using a single type of axial hard limiting structure combined with interference fit static friction constraints. Without reducing mechanical reliability, it fundamentally eliminates the redundant impedance discontinuities caused by the limiting at both ends in existing technologies. It achieves simultaneous improvement in RF performance and mechanical reliability within a very small design space, completely breaking through and resolving the long-standing technical bias in the art.

[0066] In summary, despite extremely limited design space, this invention still possesses the following significant differences compared to existing technologies: (1) This invention overcomes the long-standing technical bias in the field: It is generally believed in the field that cross-specification RF coaxial adapters must have bidirectional axial hard limits set at both ends of the inner conductor to ensure the reliability of the two-end connection, and that setting only a single-end limit cannot meet the usage requirements. This invention breaks this inherent understanding and proves that a single-end limit combined with an interference constraint can achieve a better bidirectional limit effect, providing a brand-new technical idea for the design of cross-specification adapters.

[0067] (2) The present invention omits the non-limiting end hard limit structure that is recognized as essential in the art, and at the same time achieves dual optimization of limit function and radio frequency performance: the second set of axial hard limit structure that is recognized as essential in the art is omitted. After omitting it, not only is all the functions of bidirectional axial limit of the inner conductor retained, but also the radio frequency performance, mechanical reliability and environmental adaptability are comprehensively improved. At the same time, the structure is simplified, the manufacturing cost is reduced, and positive technical effects are produced.

[0068] (3) The present invention has achieved technical effects that are not expected by those skilled in the art: Based on the general understanding of the prior art, those skilled in the art could not have predicted that after omitting one end of the limiting structure, the limiting reliability, radio frequency performance and environmental adaptability of the product would be comprehensively improved. This effect exceeded the conventional expectations of those skilled in the art.

[0069] (4) The prior art does not provide any technical teachings related to the present invention: The series of prior art cited in this application covers the two mainstream architectures of cross-specification adapters, namely integrated special type and combined general type, as well as the full-scenario application solutions such as civilian general, aerospace, and high frequency millimeter wave. The core improvement direction of all prior art is to enhance the reliability of bidirectional end-to-end limiting, and even gives the opposite technical teaching that "the more limiting structures, the more reliable the limiting". Based on the general understanding of the prior art, those skilled in the art cannot obviously obtain the single-end limiting technical solution of the present invention.

[0070] The following description explains the solution of the present invention through specific values ​​in the N-to-SMA cross-specification RF coaxial adapter. However, it should be understood that this is not intended to limit the scope of protection of the present solution. Those skilled in the art can make adaptive adjustments within the core design framework of the present solution according to the interface standards, operating frequency bands, and application scenario requirements of different cross-specification RF coaxial adapters.

[0071] In this embodiment, the inner conductor 100 is made of gold-plated beryllium copper. After overall heat treatment, the hardness is controlled at HV360~380, and the thickness of the gold plating layer is 1~3μm. While taking into account wear resistance and high-frequency signal transmission performance, it also ensures the stability of the fit with the central insulating medium 200. The total length of the inner conductor 100 is 32.65mm. Along the axial direction from the N male end to the SMA female end, there are a large end adapter section 120, an intermediate transition section 130, and a small end adapter section 140 with continuously and smoothly decreasing diameters (e.g., ...). Figure 2As shown in the diagram, the axial length of the large-end adapter section 120 is 15mm, accounting for 45.9% of the total length of the inner conductor 100, falling within the design range of 44% to 47%. The axial length of the intermediate transition section 130 is 6.6mm, accounting for 20.2% of the total length of the inner conductor 100, falling within the design range of 20% to 21%. The axial length of the small-end adapter section 140 is 11.05mm, accounting for 33.8% of the total length of the inner conductor 100, falling within the design range of 32% to 35%. The intermediate transition section 130 and the small-end adapter section 140 together constitute the inner conductor 100. The interference fit between the inner conductor 100 and the central insulating medium 200 has an effective axial length of 17.65 mm, maximizing the effective length of static friction constraint and providing sufficient structural support for the bidirectional closed-loop constraint of the single-end limiting system. The machining tolerances of the outer diameters of each segment of the inner conductor 100 are controlled within ±0.005 mm, the axial length tolerance within ±0.03 mm, and the perpendicularity tolerance of the step end face is no greater than 0.01 mm. This ensures the fitting accuracy and consistency with the central insulating medium 200, preventing limiting failure due to machining tolerances. Or impedance deviation, where the nominal outer diameter of the large-end adapter section 120 is 3.04mm, adapting to the standard size of the N-type male connector; the nominal outer diameter of the intermediate transition section 130 is 2.16mm, falling between the outer diameters of the large-end adapter section 120 and the small-end adapter section 140, forming a continuous and smooth diameter decreasing structure; the nominal outer diameter of the small-end adapter section 140 is 1.27mm, adapting to the standard size of the SMA-type female connector; the ratio of the outer diameter of the intermediate transition section 130 to the outer diameter of the large-end adapter section 120 is 0.71, falling within the design range of 0.68 to 0.78. The ratio of the outer diameter of the intermediate transition section 130 to the outer diameter of the small-end adapter section 140 is 1.70, which is within the design range of 1.58 to 1.85. This ratio range forms a clear boundary with the general design of the existing bidirectional limiting architecture, which is completely non-overlapping. This not only breaks through the limitation that the fixed size can only adapt to a single model of adapter, but also covers all cross-specification RF coaxial adapters that adopt this single-end limiting architecture. It does not depend on a specific interface standard and overall size. Furthermore, it can be deeply linked with the core design of single-end centralized limiting, and ensures the consistency of characteristic impedance through a continuous and smooth diameter reduction structure.

[0072] Preferably, in this embodiment, the central insulating medium 200 is made of glass fiber / silica-filled modified polytetrafluoroethylene, which is prepared by molding and sintering process. The sintering temperature is controlled at 370℃~380℃, the holding time is 4~6h, and precision machining is performed after furnace cooling, which can ensure the density and dimensional stability of the material.

[0073] Example A: Glass fiber filled modified PTFE: The material uses alkali-free glass fiber as the filling medium, accounting for 25% of the total mass. The core performance parameters of the material are as follows: the elastic modulus at 25℃ is 1900MPa, which meets the design requirement of not less than 1500MPa; the relative permittivity at 25℃ is 2.30, which is within the design range of 2.2~2.4; the loss tangent at 10GHz is 0.0005, which meets the design requirement of stability not exceeding 0.0008; the elongation at break is not less than 200%; the dimensional change rate after high and low temperature cycling from -55℃ to 125℃ is not greater than 0.3%; and the cold flow creep is only 1 / 10 of that of pure polytetrafluoroethylene.

[0074] Example B: Silica-modified PTFE: This method uses nano-sized silica as the filling medium, accounting for 30% of the total mass. The core performance parameters of the material are: an elastic modulus of 1600 MPa at 25°C, meeting the design requirement of no less than 1500 MPa; a relative permittivity of 2.28 at 25°C, within the design range of 2.2 to 2.4; a loss tangent of 0.0006 at 10 GHz, consistently not exceeding the design requirement of 0.0008; superior dielectric constant uniformity compared to glass fiber filling schemes; and batch-to-batch performance fluctuations of no more than 2%. It is suitable for high-precision testing and measurement scenarios. These are the core characteristics of the two implementation examples. All performance parameters are within the range defined by this solution and can be directly replaced. The nominal inner diameter of the central inner hole of the central insulating medium 200 is 2.14mm, which forms an interference fit of 0.02mm on one side with the middle transition section and the small end fitting section (i.e. the part from the diameter abrupt step to the small end) of the inner conductor. The interference amount can be adjusted in the range of 0.01~0.05mm according to the actual working conditions. The outer diameter of the annular positioning step on the outer wall of the medium is adapted to the inner cavity of the outer conductor. The coaxiality tolerance is not greater than 0.02mm and the end face perpendicularity tolerance is not greater than 0.01mm, which can ensure the fitting accuracy with the inner conductor step.

[0075] The core proportion design of this solution is not limited to a single model of N-type male to SMA-type female adapter. It can be extended to adapt to all cross-specification RF coaxial adapters, including the full range of models such as N to SMC, TNC to SMA, 7 / 16 to N, and SMA to MCX. In the design of adapters of different specifications, it is only necessary to adapt to the standard size of the corresponding interface and keep the length ratio and outer diameter ratio of each segment within the range defined by this solution to achieve the same performance gain. At the same time, the two diameter abrupt step end faces of the inner conductor are provided with a small chamfer of 0.05×45° to avoid sharp edges scratching the contact end face of the central insulating medium, and to optimize the electric field distribution at the step, further reducing local resistance. To resist sudden changes, the central insulating medium features a 1×30° chamfer at the inlet end of the central inner hole, reducing resistance during inner conductor press-fitting, preventing scratches on the inner hole, and ensuring consistent interference fit. The material and dimensional design of this solution is suitable for a wide temperature range of -55℃ to 150℃. Under extreme high and low temperature conditions, the dielectric constant fluctuation is no greater than 3%, and the dimensional change rate is no greater than 0.5%, making it suitable for extreme environmental applications such as aerospace and automotive. Furthermore, the structural design reduces the machining steps for the inner conductor and dielectric, eliminating two machining steps for the inner conductor and one for the dielectric, significantly improving mass production yield and substantially reducing production costs.

[0076] In this solution, the outer conductor 300 is made of HPb59-1 leaded brass, which is commonly used in the industry. The overall surface adopts a composite plating process of first plating nickel and then plating gold. The nickel layer thickness is 3~5μm and the gold layer thickness is 2~3μm. It has excellent conductivity, wear resistance and salt spray corrosion resistance, and is suitable for long-term use in various scenarios such as industry, communication, and test and measurement. Both ends of the outer conductor 300 adopt a straight-wall structure without a flared opening. The inner and outer walls of both the large and small ends are continuous cylindrical straight-wall structures with equal diameters, without any flared opening structure, which is completely different from the design logic of the flared end of conventional adapters in the industry. The inner wall of the outer conductor 300 has two cylindrical center holes with different diameters opened sequentially along the axial direction. The central axes of the two cylindrical center holes are completely coincident. The nominal inner diameter of the large-diameter cylindrical center hole corresponding to the large end is 7.00mm, which is compatible with the medium installation size of the N-type interface standard. The nominal inner diameter of the small-diameter cylindrical center hole corresponding to the small end is 4.10mm, which is compatible with the medium installation size of the SMA-type interface standard. The connection between the two cylindrical center holes is formed by precision machining to form a flat annular step surface, which constitutes a single annular positioning groove for axially limiting the central insulating medium 200. The perpendicularity tolerance of the end face of the groove is not greater than 0.01mm, and the flatness tolerance of the end face is not greater than 0.005mm. The outer conductor 300, with its full inner cavity, is precision CNC turned in a single clamping operation, eliminating the need for secondary clamping and reversing. After machining, the overall coaxiality tolerance of the inner cavity is no greater than 0.02mm, completely avoiding the tolerance accumulation problem caused by multi-segment clamping. This ensures the coaxiality of the central insulating medium 200 and the inner conductor 100, providing a stable reference support for the precise fit of the single-end limiting structure of the inner conductor 100. Therefore, the single-clamping machining of the outer conductor, achieved without a flared opening and with a straight wall structure, significantly improves the coaxiality accuracy of the inner cavity, ensuring uniform fit across the entire circumference of the single-end limiting step of the inner conductor and the end face of the central insulating medium. This avoids the coaxiality deviation caused by secondary clamping in conventional flared opening structures, further enhancing the long-term reliability of the single-end hard limiting structure from a manufacturing process perspective. Together with the single-end limiting core solution, this creates a complete synergistic gain of "RF performance optimization + enhanced mechanical reliability."

[0077] A connecting threaded sleeve 400 is fitted onto the outer edge of the outer conductor 300 corresponding to the large end, such as... Figure 1 As shown, the connecting threaded sleeve 400 is made of leaded brass HPb59-1 nickel-plated material, and its inner wall has an internal thread adapted to the corresponding interface standard. The thread accuracy meets the industry-standard 6H grade, which can form a stable locking fit with the external interface. An axial limiting structure is provided between the connecting threaded sleeve 400 and the outer conductor 300. In this embodiment, the axial limiting structure adopts a structure in which an annular limiting groove cooperates with an open elastic retaining spring 500 (e.g., Figure 1As shown), a continuous annular limiting groove is formed on the outer edge of the large end of the outer conductor 300. An open elastic retaining spring 500 made of 304 stainless steel is installed in the groove. The wire diameter of the retaining spring is adapted to the groove depth and the limiting stroke. An annular limiting step is integrally formed on the inner wall of the connecting screw sleeve 400 at the corresponding position. After assembly, the end face of the elastic retaining spring and the end face of the annular limiting step form an axial limiting fit, which not only prevents the connecting screw sleeve 400 from moving and falling off in the docking direction, but also prevents the connecting screw sleeve 400 from moving in the opposite direction through the fixed step on the outer edge of the outer conductor 300. The radial clearance between the connecting threaded sleeve 400 and the outer conductor 300 is controlled at 0.02~0.05mm, and the axial clearance is controlled at 0.03~0.08mm. This clearance is only used to ensure that the connecting threaded sleeve can rotate freely in the circumferential direction to complete the threaded locking and docking with the external interface. At the same time, it can control the axial movement of the connecting threaded sleeve within a very small range, which is completely different from the 0.2~0.5mm movement clearance of conventional adapters in the industry. This effectively limits the axial movement and dislodgement risk of the connecting threaded sleeve, ensuring that the axial position of the connecting threaded sleeve remains stable relative to the outer conductor. It is understood that those skilled in the art can also adopt other axial limiting structures such as riveted flanges, integrated limiting retaining rings, and retaining rings, depending on actual mass production needs, interface specifications, and application scenarios. All of these fall within the protection scope of this solution.

[0078] The inner wall of the mating end of the connecting threaded sleeve 400 is provided with an annular assembly guide chamfer. The taper of the chamfer is 30°~45°, and a 30° taper is preferred in this embodiment to balance the guiding effect and structural strength. The assembly guide chamfer extends axially toward the mating direction, and its outermost axial end protrudes 0.5~1.2mm toward the mating direction relative to the large end face of the outer conductor 300. In this embodiment, a 0.8mm protrusion is preferred, forming a pre-guided structure. The radial starting position of the chamfer is located radially outside the inner hole of the mating end of the outer conductor 300. The overall structure of the chamfer is completely located on the axial and radial outside of the coaxial cavity for radio frequency signal transmission, without extending into the coaxial transmission path. This avoids disrupting the structural uniformity and electric field continuity of the coaxial transmission line, thus preventing the guide chamfer from affecting the radio frequency transmission performance at the structural source.

[0079] The assembly process of the outer conductor 300 and connecting sleeve 400 structure described in this solution is fully compatible with the existing mass production process of RF adapters in the industry. No additional special processing equipment or procedures are required, which greatly reduces the threshold for mass production. Before assembly, the outer conductor 300, connecting sleeve 400, and elastic retainer are ultrasonically cleaned to remove cutting oil, metal burrs, and impurities from the surface. After drying, they are ready for use. During assembly, the central insulating medium 200 and the outer conductor 300 are pre-assembled. The central insulating medium 200 is coaxially pressed into the inner cavity from the large end of the outer conductor 300 until the annular positioning step on the outer wall of the medium completely fits the annular positioning groove of the inner cavity of the outer conductor 300, thus achieving axial locking of the central insulating medium 200. Then, the connecting sleeve 400 is coaxially fitted onto the outer edge of the large end of the outer conductor 300 and adjusted to the corresponding position of the limiting step and the groove. The elastic retainer is then inserted into the annular limiting groove of the outer conductor 300 to complete the assembly of the axial limiting structure. After assembly, the connecting sleeve 400 needs to be rotated circumferentially to confirm that its circumferential rotation is smooth and without jamming, and that there is no obvious axial movement. Finally, the inner conductor 100 is pressed in and the finished product is inspected to ensure that the coaxiality and position of each component meet the design requirements.

[0080] Through actual testing under the same conditions, the outer conductor and connecting screw sleeve structure described in this solution exhibits significant performance advantages compared to conventional adapter solutions with flared ends and large axial movement gaps. In terms of mechanical performance, the coaxiality of the inner cavity of the outer conductor after a single clamping process is improved by more than 60% compared to conventional solutions, and the axial movement of the connecting screw sleeve is reduced by more than 85%. After 500 insertion and removal cycles, the axial movement of the inner conductor shows no significant change, and the fitting accuracy of the single-end limiting structure shows no attenuation, completely solving the problems of inner conductor loosening and limiting failure caused by the axial movement impact of the screw sleeve in conventional solutions. In terms of RF performance, the flared-end-less straight-wall structure eliminates the additional impedance discontinuities caused by conventional flared ends, significantly improving the overall impedance smoothness. Actual measurements show that the DC-1... With a full-band VSWR of ≤1.09 and insertion loss of ≤0.19dB@18GHz, the high-frequency performance is improved by more than 30% compared with conventional solutions, and the batch-to-batch RF performance fluctuation is ≤5%, with significantly better consistency than conventional solutions. In terms of environmental adaptability, after 100 cycles of high and low temperature cycling from -55℃ to 125℃ and random vibration testing from 10 to 2000Hz, the connecting screw sleeves showed no loosening or significant wear, and the mechanical and RF performance of the adapter did not show significant attenuation. It can be adapted to the use requirements of harsh working conditions such as aerospace, automotive, and industrial sites.

[0081] A radio frequency (RF) coaxial adapter is provided for interconnecting RF interfaces across different specifications. The RF coaxial adapter includes the conductive connection structure with a single-end limit on the inner conductor as described above. Since the RF coaxial adapter incorporates all the technical features of the conductive connection structure with a single-end limit on the inner conductor, it also incorporates all its technical effects, which will not be elaborated further.

[0082] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments; for example, any one of the claimed embodiments can be used in any combination.

[0083] It should be noted that the above embodiments are illustrative of the invention and not restrictive, and that those skilled in the art can devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses should not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in a claim. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names. The steps in the above embodiments, unless otherwise specified, should not be construed as limiting the order of execution.

Claims

1. A conductive connection structure with single-end limiting of the inner conductor, applied to a cross-specification RF coaxial adapter, comprising an inner conductor, a central insulating medium, and an outer conductor arranged coaxially, wherein the two ends of the inner conductor are a large end and a small end, respectively, and the inner conductor is provided with a diameter abrupt step corresponding to the large end and the small end to adapt to the rated specifications of the interfaces at both ends, the diameter abrupt step facing the small end, the central insulating medium being axially fixedly installed in the inner cavity of the outer conductor, and the inner conductor being coaxially inserted through the central inner hole of the central insulating medium; characterized in that, The inner conductor axially abuts against the end face of the central insulating medium facing the large end only through the diameter abrupt step, forming a unique axial hard limiting structure. The rest of the inner conductor has no axial hard limiting structure that rigidly abuts against the central insulating medium or the outer conductor. The outer wall of the inner conductor, from the abrupt diameter step to the small end, is interference-fitted with the central inner hole of the central insulating medium, forming a static friction constraint on the axial movement of the inner conductor.

2. The conductive connection structure with single-end limiting of the inner conductor according to claim 1, characterized in that, The central insulating medium is made of glass fiber or silica-filled modified polytetrafluoroethylene.

3. The conductive connection structure with single-end limiting of the inner conductor according to claim 2, characterized in that, The modified polytetrafluoroethylene has an elastic modulus of not less than 1500 MPa, a relative permittivity of 2.2 to 2.4 at 25°C, and a loss tangent of not more than 0.0008 at 10 GHz.

4. The conductive connection structure with single-end limiting of the inner conductor according to claim 1, characterized in that, The inner conductor is provided with a large-end adapter section, an intermediate transition section and a small-end adapter section with decreasing diameters along the axial direction. The axial length of the intermediate transition section accounts for 20% to 21% of the total length of the inner conductor.

5. The conductive connection structure with single-end limiting of the inner conductor according to claim 4, characterized in that, The outer diameter of the intermediate transition section is between the outer diameter of the large-end adapter section and the outer diameter of the small-end adapter section, forming a continuous and smooth diameter decreasing structure; the ratio of the outer diameter of the intermediate transition section to the outer diameter of the large-end adapter section is 0.68 to 0.78, and the ratio of the outer diameter of the intermediate transition section to the outer diameter of the small-end adapter section is 1.58 to 1.

85.

6. The conductive connection structure with single-end limiting of the inner conductor according to claim 5, characterized in that, The axial length of the large-end adapter section accounts for 44% to 47% of the total length of the inner conductor, and the axial length of the small-end adapter section accounts for 32% to 35% of the total length of the inner conductor.

7. The conductive connection structure with single-end limiting of the inner conductor according to claim 1, characterized in that, Both ends of the outer conductor have a straight wall structure without a flared opening. The inner wall of the outer conductor has two cylindrical center holes of different diameters opened sequentially along the axial direction. The connection between the two cylindrical center holes forms a single annular positioning groove. The central insulating medium is clamped into the annular positioning groove through the annular positioning step on the outer wall, so as to achieve axial non-movement locking of the central insulating medium.

8. The conductive connection structure with single-end limiting of the inner conductor according to claim 7, characterized in that, The outer conductor is fitted with a connecting screw sleeve on the outer edge corresponding to the large end. An axial limiting structure with an annular limiting groove and an elastic retaining spring is provided between the connecting screw sleeve and the outer conductor. The axial limiting structure restricts the axial movement and detachment of the connecting screw sleeve relative to the outer conductor, so that the axial position of the connecting screw sleeve relative to the outer conductor remains stable, and the connecting screw sleeve can rotate freely in the circumferential direction.

9. The conductive connection structure with single-end limiting of the inner conductor according to claim 8, characterized in that, The inner wall of the mating end of the connecting threaded sleeve is provided with an annular assembly guide chamfer. The assembly guide chamfer extends axially toward the mating direction and protrudes out of the mating end face of the outer conductor.

10. A radio frequency coaxial adapter for interconnecting cross-specification radio frequency interfaces, characterized in that, The radio frequency coaxial adapter includes a conductive connection structure with a single-end limit on the inner conductor as described in any one of claims 1 to 9.

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