A radio frequency signal long-distance vertical transmission conversion structure

Abstract

This invention discloses a long-distance vertical transmission conversion structure for radio frequency (RF) signals, belonging to the field of RF and microwave technology. It includes a housing with stepped holes and transmission through-holes, an RF connector, PTFE pillars, a printed circuit board (PCB), a PTFE clamping block, and a cover plate. The conductor pins of the RF connector pass through the central hole of the PTFE pillar, and the PTFE pillar provides rigid, full-path positioning within the transmission through-hole through an interference fit. The ends of the conductor pins pass through metallized vias on the PCB and are soldered. An anti-overflow solder mask layer is provided on the back of the PCB. The PTFE clamping block has grooves to avoid microstrip lines and is further secured by the grooves in the cover plate. This invention utilizes a fully dielectric-filled structure to achieve long-distance precision impedance matching, eliminates the oscillation space of the conductor pins in vibration environments, significantly optimizes phase noise, effectively prevents solder overflow and short circuits, and improves the reliability of vertical interconnects.

Description

Technical Field

[0001] This invention belongs to the field of radio frequency and microwave, specifically, it relates to a long-distance vertical transmission conversion structure for radio frequency signals. Background Technology

[0002] In radio frequency (RF) and microwave communication applications, system design is increasingly moving towards miniaturization and high integration. To achieve complex functions within limited installation space, multiple modules with unique functions are typically overlapped and interconnected based on actual system requirements. Traditionally, RF signal exchange between these modules relies heavily on cable assemblies. However, these cable assemblies consume significant system space, resulting in a less compact overall structure. To address this issue, current design approaches are shifting towards overlapping module installations and vertical interconnection of RF ports, achieving optimized layout within limited space through vertical conversion structures.

[0003] Due to the spatial stacking distribution of each module, during vertical RF conversion, a certain wall thickness is usually required to accommodate the installation of internal structural components for screw holes. The problem at this time is that the vertical RF signal transmission distance is relatively long. When the RF connector conductor pins are conducted over long distances, they may experience eccentricity or displacement in the air dielectric hole. For example, if the RF connector conductor pin is φ0.38mm, the corresponding air dielectric hole is approximately φ0.9mm. Especially in the high-frequency range, even slight displacement of the RF connector conductor pin can easily cause instability of the RF signal and deterioration of phase noise.

[0004] Furthermore, when RF equipment is exposed to vibration or shock, the conductor pins, lacking effective support, will experience severe displacement impacts. These impacts not only further affect the transmission quality of electromagnetic signals but also significantly increase the mechanical stress at the solder joints between the RF connector and the printed circuit board, easily leading to solder joint fatigue damage or even conductor pin root breakage, thus causing the entire RF system to fail. Simultaneously, existing vertical structures also present process risks during assembly and soldering, such as solder seepage along through-holes causing short circuits that are difficult to observe. Therefore, designing a vertical RF conversion structure that can achieve stable long-distance transmission, effectively resist external environmental vibration and shock, and possess excellent phase noise and high reliability is of great significance for the engineering application of RF and microwave products. Summary of the Invention

[0005] The purpose of this invention is to provide a long-distance vertical transmission conversion structure for radio frequency signals, which mainly solves the problems of unstable signal transmission, poor vibration resistance, and low process reliability of existing long-distance radio frequency vertical interconnect structures.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A long-distance vertical transmission conversion structure for radio frequency signals includes a housing, an RF connector, a polytetrafluoroethylene (PTFE) pillar, a printed circuit board (PCB), and a cover plate. The housing has a coaxially through-hole and a transmission through-hole. The RF connector is installed in the through-hole and has a conductor pin extending axially and passing through the transmission through-hole. The PTFE pillar is installed in the transmission through-hole via an interference fit and has an axial central hole through which the conductor pin passes. The PCB has a metallized via, and the end of the conductor pin passes through the metallized via and is electrically connected to the PCB. The cover plate is screwed to the housing to encapsulate the PCB within the housing.

[0008] Furthermore, the present invention also includes a polytetrafluoroethylene pressure block disposed between the cover plate and the printed circuit board.

[0009] Furthermore, in this invention, the polytetrafluoroethylene pressing block has a first groove on the side facing the printed circuit board, and the first groove covers the microstrip transmission line on the printed circuit board.

[0010] Furthermore, in this invention, the cover plate has a second groove on the side facing the printed circuit board, and the polytetrafluoroethylene pressing block is embedded in the second groove.

[0011] Furthermore, in this invention, the side of the printed circuit board facing the radio frequency connector is provided with an anti-overflow solder mask layer in the circumferential area of ​​the metallized via.

[0012] Furthermore, in this invention, the bottom of the stepped hole of the housing is provided with a stepped support surface, which abuts against the insulating support of the radio frequency connector.

[0013] Furthermore, in this invention, a solder sintering layer is provided between the housing of the RF connector and the stepped hole of the housing.

[0014] Furthermore, in this invention, the inner walls of the stepped hole and the transmission through hole are provided with a gold plating layer.

[0015] Furthermore, in this invention, the axial depth of the transmission through hole is equal to the axial length of the polytetrafluoroethylene column, and the outer diameter of the polytetrafluoroethylene column has an interference fit relative to the inner diameter of the transmission through hole.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The present invention adopts a structure of full-path filling transmission through hole of polytetrafluoroethylene pillar, combined with interference fit design to realize full-path rigid limit of RF connector conductor pin, eliminating the eccentric displacement space of conductor pin during long-distance transmission, and realizing full-path precise impedance calibration through dielectric parameter matching, effectively optimizing the phase noise index of RF signal transmission and ensuring the stability of high-frequency signal transmission.

[0018] (2) The present invention constructs a multi-level rigid protection system by using the nested limiting structure of the polytetrafluoroethylene pressure block and the cover plate groove, combined with the interference constraint of the shell on the polytetrafluoroethylene column. This system can effectively resist mechanical stress under complex working conditions such as vibration and impact, avoid fatigue damage or breakage of the solder joint at the root of the conductor needle, and greatly improve the environmental adaptability and operational reliability of the radio frequency vertical interconnect structure.

[0019] (3) The present invention sets an anti-overflow solder resist layer in the circumferential area of ​​the metallized via of the printed circuit board, which cuts off the path of molten solder seeping down during the soldering process and avoids the short circuit risk caused by solder overflow. At the same time, the overall structure can be adapted to different frequency bands and different impedance requirements of radio frequency transmission scenarios by adjusting the inner and outer diameter of the polytetrafluoroethylene column. There is no need to make major modifications to the general structural components such as the shell and cover plate, which has strong versatility and expandability. Attached Figure Description

[0020] Figure 1 This is a schematic cross-sectional view of the assembly structure of the present invention.

[0021] Figure 2 This is a schematic cross-sectional view of the shell structure in this invention.

[0022] Figure 3 This is a schematic cross-sectional view of the polytetrafluoroethylene column structure in this invention.

[0023] Figure 4 This is a schematic diagram of the inner side of the cover plate in this invention.

[0024] Figure 5 This is a schematic diagram of one side of the printed circuit board in this invention.

[0025] Figure 6 The figure shows the phase noise simulation curve of a traditional RF conversion structure.

[0026] Figure 7 The figure shows the phase noise simulation curve of the conversion structure of the present invention.

[0027] The names corresponding to the reference numerals in the attached figures are as follows:

[0028] 1. Housing; 2. RF connector; 3. PTFE pillar; 4. Printed circuit board; 5. PTFE clamping block; 6. Cover plate; 7. Stepped hole; 8. Transmission through hole; 9. Conductor pin; 10. Axial center hole; 11. Metallized via; 12. Anti-overflow solder mask layer; 13. Second groove. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.

[0030] like Figure 1 As shown, the present invention discloses a long-distance vertical transmission conversion structure for radio frequency signals. In practical application scenarios, it is mainly used in microwave systems that require modular stacked design, such as high-performance radar, satellite communication terminals, and avionics equipment.

[0031] refer to Figures 1-5 The conversion structure of this invention consists of a housing 1, an RF connector 2, a PTFE pillar 3, a printed circuit board 4, a PTFE clamping block 5, and a cover plate 6. The housing 1, serving as the mechanical support base and electrical ground plane of the entire structure, is made of highly conductive aluminum alloy or brass and has undergone surface gold plating. A stepped hole 7 is precisely machined on the housing 1, the diameter of which matches the outer diameter of the RF connector 2, providing a precise mounting position for the RF connector 2. A transmission through-hole 8 is coaxially connected to the stepped hole 7, and the axial depth of the transmission through-hole 8 is H. In this embodiment, the depth H of the transmission through-hole 8 is defined as 4mm. This length falls within the typical long-distance transmission range; without constraint, the conductor pin 9 is highly susceptible to simple harmonic vibration at this length.

[0032] The RF connector 2 is a through-wall SMPJ type connector, whose core component is a slender conductor pin 9. The outer diameter of the conductor pin 9 is D1, which is 0.38 mm in this embodiment. When the RF connector 2 is installed in the stepped hole 7, the conductor pin 9 passes through the transmission through hole 8 axially. To solve the support problem in long-distance transmission, a polytetrafluoroethylene (PTFE) pillar 3, calculated for impedance matching, is filled in the transmission through hole 8. The axial length L of the PTFE pillar 3 is exactly the same as the depth H of the transmission through hole 8, i.e., L=H=4 mm. This equal-length design ensures that after assembly, the top surface of the PTFE pillar 3 is at the same level as the plane on which the printed circuit board 4 is installed inside the housing 1, eliminating any stepped gaps that may cause impedance mismatch.

[0033] like Figure 3As shown, an axial center hole 10 is machined at the radial center position of the PTFE column 3, and the diameter of the axial center hole 10 is D2. To achieve a tight fit around the conductor needle 9, the nominal size of D2 is set to 0.38 mm, which is equal to the outer diameter D1 of the conductor needle 9. In actual machining, the axial center hole 10 adopts a slight positive tolerance, while the conductor needle 9 adopts a slight negative tolerance, thus forming a precise small clearance fit or sliding fit, ensuring that the conductor needle 9 does not experience radial wobble inside the PTFE column 3. The outer diameter of the PTFE column 3 is D3, and the inner diameter of the transmission through hole 8 of the housing 1 is D. To ensure the stability of the PTFE column 3 within the housing 1, an interference fit design is adopted between D3 and D. By designing D3 to be slightly larger than D by 0.02 mm, after the PTFE column 3 is pressed into the transmission through hole 8, it is subjected to radial compression by the hole wall, generating a huge axial friction force, so that even when subjected to high G-value vibration acceleration, no axial or radial movement can occur.

[0034] In this embodiment, because the transmission path changes from air to PTFE, its dielectric constant changes from 1.0 to approximately 2.1. To maintain the standard characteristic impedance of 50 ohms, the outer diameter D must be recalculated according to the coaxial transmission line formula. In this embodiment, by establishing a 3D equivalent model, setting excitation and boundary conditions, and confirming through electromagnetic simulation optimization, when the outer diameter of the conductor needle 9 is 0.38 mm, the corresponding inner diameter D of the housing transmission through-hole 8 and the outer diameter D3 of the PTFE pillar 3 are both set to 1.3 mm. This dimensional ratio effectively offsets the resistance fluctuations caused by the change in dielectric constant, ensuring that the VSWR remains at an extremely low level when the RF signal passes perpendicularly through a distance of 4 mm.

[0035] The end of the conductor pin 9 is designed to protrude from the end face of the PTFE pillar 3. The length of the protrusion is set according to the welding process requirements, typically 0.5mm to 0.8mm. A printed circuit board 4 is placed on the internal mounting plane of the housing 1. The printed circuit board 4 has metallized vias 11 machined at the positions corresponding to the conductor pins 9. The diameter of the metallized via 11 is D4, which is set to 0.55mm. This size ensures that there is an annular gap of approximately 0.085mm on one side between the metallized via 11 and the conductor pin 9 with an outer diameter of 0.38mm. This gap serves to accommodate solder during the welding process, allowing the solder to form a full annular solder joint, thus enhancing the reliability of the electrical connection.

[0036] like Figure 5As shown, to prevent potential quality issues during soldering, an anti-overflow solder mask layer 12 is provided on the back side of the printed circuit board 4 (i.e., the side facing the PTFE pillar 3) in the circumferential area of ​​the metallized via 11. The anti-overflow solder mask layer is achieved by removing the copper foil around the via and applying solder resist ink. This design cuts off the path of molten solder flowing downwards along the conductor pin 9, avoiding the risk of solder seeping into the tiny gap between the PTFE pillar 3 and the metallized via 11, which could lead to a short circuit with the housing 1. Simultaneously, the anti-overflow solder mask layer also serves as impedance compensation, reducing parasitic capacitance generated at the solder joint.

[0037] A polytetrafluoroethylene (PTFE) pressure block 5 is mounted on the other side of the printed circuit board 4. The PTFE pressure block 5 not only serves as a physical limiter but also possesses excellent microwave dielectric properties. A first groove is machined on the side of the PTFE pressure block 5 facing the printed circuit board 4. The position of the first groove corresponds perfectly to the microstrip transmission line on the printed circuit board 4. The design of the first groove avoids the pressure block directly pressing the microstrip line, thus maintaining a certain thickness of air layer above the microstrip line, preserving the original electromagnetic field distribution of the microstrip line, and preventing impedance shift caused by dielectric loading.

[0038] like Figure 4 As shown, the cover plate 6 is fixed to the housing 1 with screws, and a second groove 13 is machined on its back. The outline dimensions of the second groove 13 are precisely matched with the outer dimensions of the PTFE pressure block 5. When the cover plate 6 is locked, the PTFE pressure block 5 is completely enclosed within the second groove 13, forming a closed, rigid constraint space. The cover plate 6 transmits downward pressure evenly to the printed circuit board 4 through the PTFE pressure block 5, making the printed circuit board 4 tightly adhere to the mounting bottom surface of the housing 1. This layered pressing structure greatly enhances the natural frequency of the printed circuit board 4, eliminates its elastic deformation under vibration, thereby ensuring that the mechanical stress at the solder joint is at an extremely low level and preventing fatigue fracture at the root of the conductor pin 9.

[0039] The specific assembly process of the conversion structure of the present invention is as follows:

[0040] S1. First, prepare a gold-plated housing 1 and insert the RF connector 2 into the stepped hole 7 of the housing 1. Use a high-frequency heating device to locally heat the housing 1, and then use a soldering process to fix the RF connector 2 into the stepped hole 7. This step establishes a common ground connection between the RF connector 2 and the housing 1 and achieves primary positioning.

[0041] S2. Align the axial center hole 10 of the PTFE post 3 with the conductor pin 9 of the RF connector 2 and install it. Then, using a vertical press-fitting machine, smoothly push the PTFE post 3 axially into the transmission through hole 8 of the housing 1. During the pressing process, due to the interference fit, the outer wall of the PTFE post 3 will undergo a slight elastic compression, thus locking it tightly within the transmission through hole 8. Continue until the bottom end face of the PTFE post 3 contacts the bottom step of the stepped hole 7, and the top end face is flush with the inner plane of the housing 1. At this point, the end of the conductor pin 9 accurately protrudes from the center of the PTFE post 3.

[0042] S3. Apply an appropriate amount of conductive adhesive to the printed circuit board mounting area of ​​the housing 1, and then place the printed circuit board 4 into the housing 1, so that the conductor pin 9 passes through the metallized via 11. The conductive adhesive is cured by baking, thus achieving initial fixation and good grounding between the printed circuit board 4 and the housing 1.

[0043] S4. Using a temperature-controlled soldering iron or an automated soldering robot, solder the conductor pins 9 to the metallized vias 11 on the front side of the printed circuit board 4. Due to the presence of the anti-overflow solder mask layer 12, the solder is confined within the metallized vias 11. After soldering, perform a visual inspection to ensure that the solder joints are smooth and free of excess solder.

[0044] S5. Cover the printed circuit board 4 with the PTFE clamping block 5, ensuring that the first groove is aligned with the microstrip line area. Then, fasten the cover plate 6 so that the PTFE clamping block 5 is embedded in the second groove 13 on the back of the cover plate 6. Finally, tighten the cover plate 6 diagonally by passing four high-strength screws through the mounting holes of the cover plate 6 and screwing them into the threaded holes of the housing 1 to a predetermined torque.

[0045] The conversion structure achieved through the above assembly process exhibits extremely high stability in actual operation. In the comparative structure without the PTFE pillar 3, the conductor needle 9 is suspended, and the diameter of the surrounding air cavity typically needs to be about 2.3 times the diameter of the conductor needle to achieve impedance matching (e.g., a 0.38mm needle corresponding to a 0.9mm hole). Within this large air cavity, the conductor needle 9 will oscillate significantly when subjected to external vibrations and impacts, and this oscillation is directly converted into phase jitter in the radio frequency signal. In contrast, this invention completely fills the space around the conductor needle 9 with the PTFE pillar 3, and each micro-segment of the conductor needle 9 is radially supported by the PTFE medium, completely eliminating the oscillation space.

[0046] refer to Figure 6 and Figure 7The electrical performance simulation results show that the present invention performs excellently in the 6GHz to 12GHz frequency band. Under simulated strong vibration and shock conditions, the phase noise curve of the structure without the present invention exhibits drastic fluctuations, especially in the frequency offset range of 100Hz to 1kHz, where the phase noise performance is poor. Specifically, at 100Hz, its phase noise is only -95dBc per Hz. However, after adopting the long-distance vertical RF conversion structure of the present invention, the phase noise curve is very flat and stable. Under the same vibration conditions, the phase noise of this structure is optimized to -105dBc per Hz at 100Hz, an improvement of 10dB compared to the traditional structure. At 1kHz, this structure reaches -121dBc per Hz, an improvement of 3dB compared to -118dBc per Hz of the traditional structure. This significant performance improvement directly demonstrates the technical advantage of the present invention in maintaining the stability of high-frequency signal transmission.

[0047] In actual high and low temperature cycling tests, although the coefficient of linear expansion of PTFE differs from that of the aluminum alloy shell, this invention, through interference fit and physical compression of the cover plate 6, offsets the displacement tendency caused by the thermal expansion and contraction of the materials. When the PTFE pressure block 5 expands due to heat, the additional pressure it generates is converted into a tighter limiting force by the rigid cavity formed by the cover plate 6 and the shell 1, ensuring consistent RF transmission performance across the entire temperature range from -55 degrees Celsius to +85 degrees Celsius.

[0048] The long-distance vertical RF conversion structure described in this invention cleverly solves the challenges of RF conversion in long-distance, high-frequency, and high-vibration environments through a simple combination of mechanical parts. It not only provides a stable electromagnetic transmission path but also constructs a reliable mechanical protection system. This structural form is not strictly limited by specific frequency bands; by adjusting the inner and outer diameters of the PTFE column 3, it can be easily adapted to RF systems with different frequency and impedance requirements.

[0049] In summary, this invention achieves high-quality transmission of radio frequency signals over long-distance vertical paths through the dielectric filling and physical support of the PTFE column 3, combined with the composite locking of the PTFE pressure block 5 and the cover plate 6. This solution achieves groundbreaking technical results in improving phase noise performance, enhancing vibration and shock resistance, and simplifying assembly processes, providing a high-performance solution for vertical conversion of radio frequency and microwave products.

[0050] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

Claims

1. A long-distance vertical transmission conversion structure for radio frequency signals, characterized in that, The device includes a housing (1), an RF connector (2), a polytetrafluoroethylene (PTFE) pillar (3), a printed circuit board (4), and a cover plate (6). The housing (1) has a coaxial through-hole (7) and a transmission through-hole (8). The RF connector (2) is installed in the through-hole (7) and has a conductor pin (9) extending axially and passing through the transmission through-hole (8). The PTFE pillar (3) is installed in the transmission through-hole (8) by interference fit and has an axial center hole (10) through which the conductor pin (9) passes. The printed circuit board (4) has a metallized via (11) through which the end of the conductor pin (9) passes and is electrically connected to the printed circuit board (4). The cover plate (6) is connected to the housing (1) by screws and is used to encapsulate the printed circuit board (4) in the housing (1).

2. The radio frequency signal long-distance vertical transmission conversion structure according to claim 1, characterized in that, It also includes a polytetrafluoroethylene pressure block (5) disposed between the cover plate (6) and the printed circuit board (4).

3. The radio frequency signal long-distance vertical transmission conversion structure according to claim 2, characterized in that, The polytetrafluoroethylene block (5) has a first groove on the side facing the printed circuit board (4), and the first groove covers the microstrip transmission line on the printed circuit board (4).

4. The radio frequency signal long-distance vertical transmission conversion structure according to claim 3, characterized in that, The cover plate (6) has a second groove (13) on the side facing the printed circuit board (4), and the polytetrafluoroethylene block (5) is embedded in the second groove (13).

5. The radio frequency signal long-distance vertical transmission conversion structure according to claim 4, characterized in that, The side of the printed circuit board (4) facing the radio frequency connector (2) has an anti-overflow solder mask layer (12) in the circumferential area of ​​the metallized via (11).

6. The radio frequency signal long-distance vertical transmission conversion structure according to claim 5, characterized in that, The bottom of the stepped hole (7) of the housing (1) is provided with a stepped support surface, which abuts against the insulating support of the radio frequency connector (2).

7. The radio frequency signal long-distance vertical transmission conversion structure according to claim 6, characterized in that, A solder sintering layer is provided between the housing of the radio frequency connector (2) and the stepped hole (7) of the housing (1).

8. The radio frequency signal long-distance vertical transmission conversion structure according to claim 7, characterized in that, The inner walls of the stepped hole (7) and the transmission through hole (8) are provided with a gold plating layer.

9. The radio frequency signal long-distance vertical transmission conversion structure according to claim 8, characterized in that, The axial depth of the transmission through hole (8) is equal to the axial length of the polytetrafluoroethylene column (3), and the outer diameter of the polytetrafluoroethylene column (3) has an interference fit relative to the inner diameter of the transmission through hole (8).

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