Filter and tuning method thereof
By using a metallurgical connection to form a dense alloy layer with hot melt material in the filter, the nonlinear effect of the threaded contact surface in traditional cavity filters is solved, improving the performance and stability of the PIM and making it suitable for modern communication systems.
Patent Information
- Application Number
- CN202511638378.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-10
- Publication Date
- 2026-02-10
AI Technical Summary
Traditional cavity filters suffer from poor intermodulation performance and insufficient stability due to the threaded connection between the tuning screw and the cover plate. They are particularly prone to oxidation and degradation under high-power radio frequency signals, leading to PIM performance deterioration and electrical performance parameter drift.
Hot melt material is used to fill the gap between the tuning screw and the cover plate through hole. By heating, it melts and penetrates to form a dense alloy layer, realizing the metallurgical integral connection between the tuning screw and the cover plate and eliminating the nonlinear effect of the thread contact surface.
It significantly improves the passive intermodulation performance and long-term mechanical stability of the filter, meeting the performance requirements of modern communication systems.
Smart Images
Figure CN121507352A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a filter, in particular to a filter and a tuning method thereof. BACKGROUND
[0003] The conventional cavity filter usually adopts the structure of setting a tuning screw on the cover plate to realize the tuning of frequency and coupling amount. The basic structure includes a cavity, a resonant column fixed in the cavity, and a metal cover plate covering above the cavity. A threaded hole is opened on the cover plate corresponding to the center of the resonant column (for frequency tuning) or the coupling window (for coupling tuning), and a metal tuning screw is screwed into the threaded hole. By rotating the tuning screw to change its depth into the cavity, the equivalent capacitance of the cavity or the coupling strength is changed, so as to realize the tuning of electrical performance. After the tuning is completed, the locking nut above the tuning screw is tightened to prevent the screw from loosening by using the friction force between the nut and the surface of the cover plate.
[0004] However, the conventional structure has inherent defects: Poor intermodulation performance: the threaded hole between the tuning screw and the cover plate is a mechanical connection of point contact or line contact. Under the action of high-power radio frequency signals, the current is concentrated on the microscopic contact point, generating Joule heat, which causes the oxidation and deterioration of the contact point. More importantly, the nonlinear contact between metals is one of the main sources of passive intermodulation (PIM). Even if the contact surface has a silver or other good conductor plating, a small amount of loosening, surface contamination, or microscopic uneven contact will cause nonlinear changes in contact resistance, thereby deteriorating the PIM performance.
[0005] Insufficient stability: only relying on the friction force of the nut for locking, under the environmental stress of long-term vibration, temperature change (thermal expansion and cold contraction), etc., micron-level slip or loosening may occur inside the threaded pair, causing changes in contact resistance, resulting in drift of filter electrical performance parameters (such as center frequency, bandwidth), affecting its long-term reliability.
[0006] Therefore, in order to solve the inherent PIM defects and stability problems of the conventional threaded tuning structure, there is an urgent need for a new tuning scheme that can improve the electrical contact characteristics of the threaded connection physically while retaining the convenient tuning function. SUMMARY
[0007] The purpose of the present application is to provide a filter and a tuning method thereof that completely eliminate the nonlinear effects of the threaded contact surface.
[0008] The first aspect of the present application provides a tuning method of a filter, the filter comprising an open-ended cavity, a cover plate installed at the open end of the cavity, a resonant post installed in the cavity, and a tuning screw; the cover plate is provided with a through hole, the tuning screw is threadedly connected with the inner wall of the through hole and extends into the cavity; the method comprises the following steps: S1, a receiving groove is arranged at the edge of the through hole at the top end of the cover plate, and a solid hot melt material is filled into the receiving groove; S2, the tuning screw is rotated to adjust the resonant frequency or coupling amount of the filter; when the end of the tuning screw moves to a preset distance from the top end of the resonant post to reach a preset resonant frequency or a preset coupling amount of the filter, the tuning screw is locked at the position where the end of the tuning screw is at the preset distance from the top end of the resonant post by a locking nut; S3, the filter is heated to completely melt the solid hot melt material into a liquid state and sufficiently penetrate into the gap between the threads of the tuning screw and the inner wall of the through hole which are threadedly connected; after the filter is cooled, the tuning screw and the cover plate form a one-piece whole.
[0009] Preferably, before step S2, the outer surface of the tuning screw and the outer surface of the cover plate are plated with a conductive layer.
[0010] Preferably, the hot melt material is a tin-silver or tin-copper alloy or a tin-silver-copper alloy composed of tin, silver and copper.
[0011] Preferably, the melting point of the solid hot melt material ranges from 150 to 250 degrees; the melting points of the cavity, the cover plate, the resonant post and the tuning screw are all higher than the melting point of the solid hot melt material.
[0012] Preferably, the conductive layer on the outer surface of the tuning screw and the outer surface of the cover plate is a silver plating layer; the thickness of the silver plating layer ranges from 0.3 to 1 μm.
[0013] Preferably, in step S3, the heating method of the filter is reflow soldering.
[0014] Preferably, in step S3, the liquid hot melt material penetrates into the gap between the threads of the tuning screw and the inner wall of the through hole which are threadedly connected through capillary action; after the liquid hot melt material is cooled in the gap, a dense alloy layer is formed to form a one-piece whole of the tuning screw and the cover plate by metallurgy.
[0015] Preferably, in step S2, the thread connection between the threads of the tuning screw and the inner wall of the through hole is a mechanical connection of point contact or line contact.
[0016] The second aspect of the present application provides a filter, which comprises an open-ended cavity, a cover plate installed at the open end of the cavity, a resonant column installed in the cavity, and a tuning screw and a locking nut; the cover plate is provided with a through hole, the tuning screw is threadedly connected with the inner wall of the through hole and extends into the cavity, the locking nut is threadedly connected with the tuning screw and abuts against the top end of the cover plate to lock the tuning screw, a dense alloy layer is filled in the gap between the threads of the tuning screw and the threads of the inner wall of the through hole to fixedly connect the tuning screw and the cover plate into an integral whole, and the top end of the cover plate is provided with a receiving groove at the edge of the through hole, and the dense alloy layer is melted into a molten liquid to flow into the gap.
[0017] Preferably, the receiving groove and the through hole are stepped holes of the cover plate, and the inner diameter of the receiving groove is greater than the inner diameter of the through hole.
[0018] The solid hot melt material is completely melted into a liquid state by heating and sufficiently penetrates into the gap between the threads of the tuning screw and the threads of the inner wall of the through hole, and after the filter is cooled, a dense alloy layer is formed in the gap between the threads of the tuning screw and the threads of the inner wall of the through hole, thereby completely eliminating the nonlinear effect of the threaded contact surface of the filter. BRIEF DESCRIPTION OF DRAWINGS
[0019] Figure 1 A longitudinal sectional structure schematic diagram of the filter provided by the embodiment of the present application before heating is shown in Figure 2 is Figure 1 a connection schematic diagram of the cover plate of the filter and the thread connection between the through hole of the cover plate and the tuning screw and showing the gap therebetween is shown in Figure 3 A longitudinal sectional structure schematic diagram of the filter provided by the embodiment of the present application after heating is shown in Figure 4 is Figure 3 a connection schematic diagram of the cover plate of the filter and the fixed connection between the through hole of the cover plate and the tuning screw with a dense alloy layer therebetween is shown in Figure 5 A flowchart schematic diagram of the tuning method of the filter provided by the embodiment of the present application is shown in DETAILED DESCRIPTION
[0020] The present application is further described below in combination with the drawings and embodiments.
[0021] Please refer to Figure 1 and Figure 2The application provides a filter 100, which comprises an open-ended cavity 10, a cover plate 20 installed at the open end of the cavity 10, a resonant column 30 installed in the cavity 10, and a tuning screw 50. Specifically, the cover plate 20 is provided with a through hole 21, and the through hole 21 is provided with a thread. The tuning screw 50 is provided with a threaded section, and the threaded section of the tuning screw 50 is screwed with the inner wall of the through hole 21, and one end of the threaded section of the tuning screw 50 extends into the cavity 10. In the embodiment, the end of the threaded section of the tuning screw 50 extending into the cavity 10 is the end of the tuning screw 50.
[0022] The tuning screw 50 is rotated to change the distance between the end of the tuning screw and the top end of the resonant column 30, so as to adjust the resonant frequency of the filter 100. Alternatively, the depth of the tuning screw 50 extending into the coupling window 9 is changed to change the coupling amount of the filter 100.
[0023] Further, the filter 100 further comprises a locking nut 60. When the preset resonant frequency or the preset coupling amount of the filter 100 is reached, the locking nut 60 locks the tuning screw 50, so that the tuning screw 50 cannot be rotated. Specifically, the locking nut 60 is screwed with the tuning screw 50, and the locking nut 60 pulls the tuning screw 50 away from the resonant column 30, and when the locking nut 60 abuts against the top end of the cover plate 20, the tuning screw 50 is locked and cannot be rotated.
[0024] Please refer to Figure 3 and Figure 4 In the embodiment, the threaded section of the tuning screw 50 is fixedly connected with the thread in the through hole 21 and the inner wall of the through hole 21 in a metallurgical way, and the tuning screw 50 is fixedly connected with the cover plate 20 in one piece, so that the mechanical thread connection between the tuning screw 50 and the cover plate 20 is changed into a firm metallurgical connection, the non-linear effect of the thread contact surface can be completely eliminated, and the passive intermodulation (PIM) performance and long-term mechanical stability of all tuning points of the filter 100 can be significantly improved.
[0025] In the embodiment, the metallurgical way is reflow soldering, and specifically, the filter 100 is placed in a reflow soldering furnace and heated according to a set temperature curve, so that the solid hot melt material 70 is melted into a liquid state, and the liquid hot melt material penetrates into the gap 211 between the thread of the tuning screw 50 and the thread of the inner wall of the through hole 21. After the filter 100 is cooled, the liquid hot melt material is solidified to form a dense alloy layer 70A.
[0026] In order to make the hot melt material better penetrate into the thread section of the tuning screw 50 in the through hole 21 and the thread of the inner wall of the through hole 21, preferably, a containing groove 22 is arranged at the edge of the through hole 21 at the top end of the cover plate 20; the solid hot melt material 70 is placed in the containing groove 22. It can be understood that the containing groove 22 is a stepped hole of the through hole 21 of the cover plate 20. Preferably, the inner diameter of the stepped hole is larger than the inner diameter of the through hole 21. In this way, the liquid hot melt material can flow down from the containing groove 22 along the gap between the through hole 21 and the tuning screw 50.
[0027] Further, in order to make the filter 100 as a whole not be deformed in the metallurgical process, the melting points of the cavity 10, the cover plate 20, the resonant column 30, the tuning screw 50 and the locking nut 60 are all higher than the melting point of the solid hot melt material 70. For example, the solid hot melt material 70 is a tin-based solder with a melting point between 150°C and 250°C. The cover plate 3 is an aluminum alloy material with a melting point higher than 250°C. The tuning screw 50 is a stainless steel material with a melting point higher than 250°C. The tin-based solder includes a tin-silver-copper alloy composed of a combination of any one of silver or copper or a mixture of tin, silver and copper.
[0028] Preferably, the outer surface of the cover plate 20 and the outer surface of the tuning screw 50 are plated with a conductive layer; to ensure their electrical conductivity. At the same time, the conductive layer can also ensure that the thread of the tuning screw 50 has good weldability with the thread in the through hole 21 of the cover plate 20. Specifically, the conductive layer is a silver plating layer. The thickness of the silver plating layer ranges from 0.3 to 1 μm. It can be understood that the outer surface of the cover plate 20 includes the thread of the inner wall of the through hole 21 and the inner surface of the containing groove 22. That is, the thread of the inner wall of the through hole 21 and the containing groove 22 are plated with a conductive layer.
[0029] Based on the structure of the filter 100 described above, a tuning method of the filter 100 is introduced as follows, please refer to Figure 5 The method comprises the following steps: S1, arranging a containing groove 22 at the edge of the through hole 21 at the top end of the cover plate 20, and filling the solid hot melt material 70 into the containing groove 22; S2, rotating the tuning screw 50 to adjust the resonant frequency or the coupling amount of the filter 100; when the end of the tuning screw 50 moves to a preset distance from the top end of the resonant column 30 to reach a preset resonant frequency or a preset coupling amount of the filter 100, the tuning screw 50 is locked at the position where the end of the tuning screw 50 is at the preset distance from the top end of the resonant column 30 by the locking nut 60; S3, heating the filter 100, so that the solid hot melt 70 is completely melted into a liquid state and fully penetrates into the gap 211 between the threads of the tuning screw 50 and the threaded connection of the inner wall of the through hole 21; after the filter 100 is cooled, the tuning screw 50 and the cover plate 20 form a one-piece whole. In this way, the tuning screw 50 and the cover plate 20 are changed from mechanical threaded connection to firm metallurgical connection, which can completely eliminate the nonlinear effect of the threaded contact surface and significantly improve the passive intermodulation (PIM) performance and long-term mechanical stability of all tuning points of the filter 100.
[0030] Preferably, before step S2, the outer surface of the tuning screw 50 and the outer surface of the cover plate 20 are plated with a conductive layer. While ensuring good electrical conductivity of the filter 100, it also ensures good weldability or said fusion of the threads of the tuning screw 50 and the threads in the through hole 21 of the cover plate 20.
[0031] In step S3, the heating method of the filter 100 is reflow soldering. Specifically, the melting point of the solid hot melt 70 is lower than that of other components of the filter 100. The liquid hot melt penetrates into the gap 211 between the threads of the tuning screw 50 and the threaded connection of the inner wall of the through hole 21 by capillary action; after the liquid hot melt is cooled at the gap 211, a dense alloy layer 70A is formed, and the tuning screw 50 and the cover plate 20 are formed into a one-piece whole by metallurgical means.
[0032] Understandably, in step S2, the threaded connection between the threads of the tuning screw 50 and the inner wall of the through hole 21 is a point or line contact mechanical connection.
[0033] The above tuning method of the present application can completely solve the nonlinear problem of the threaded contact, greatly improve the PIM performance of the filter, and at the same time ensure its super strong stability in harsh environments, meeting the extreme requirements of modern communication systems such as 5G on filter performance.
[0034] As shown in Figure 1 and Figure 3 The present application is not only suitable for tuning frequency, but also suitable for tuning coupling amount. The tuning screw 50 extends into the through hole 21 of the cover plate 20 and extends to the coupling window 9 between the two resonant columns 2 to tune the coupling amount.
[0035] The above embodiments only express the preferred embodiments of the present application, which are described in detail and specifically, but cannot be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, such as combination of different features in each embodiment, which all belong to the protection scope of the present application.
Claims
1. A method for tuning a filter, the filter comprising a cavity open at one end, a cover plate mounted on the open end of the cavity, a resonant post mounted inside the cavity, and a tuning screw; the cover plate having a through hole, the tuning screw being threadedly connected to the inner wall of the through hole and extending into the cavity; characterized in that, The method includes the following steps: S1. A receiving groove is provided at the edge of the through hole at the top of the cover plate, and the solid hot melt material is filled into the receiving groove; S2. Rotate the tuning screw to adjust the resonant frequency or coupling of the filter; when the end of the tuning screw moves to a preset distance from the top of the resonant post, reaching the preset resonant frequency or preset coupling of the filter, lock the tuning screw at the preset distance from the top of the resonant post by tightening the lock nut. S3. The filter is heated so that the solid hot melt material is completely melted into a liquid state and fully penetrates into the gap between the thread of the tuning screw and the inner wall thread of the through hole; after the filter is cooled, the tuning screw and the cover plate form a one-piece integral unit.
2. The filter tuning method according to claim 1, characterized in that, It also includes, before step S2, plating a conductive layer on the outer surface of the tuning screw and the outer surface of the cover plate.
3. The filter tuning method according to claim 1, characterized in that, The hot melt material is a combination of tin and any one of silver or copper, or a tin-silver-copper alloy made of tin, silver and copper.
4. The filter tuning method according to claim 1, characterized in that, The melting point of the solid hot melt material is between 150 and 250 degrees Celsius; the melting points of the cavity, cover plate, resonant column and tuning screw are all higher than the melting point of the solid hot melt material.
5. The filter tuning method according to claim 2, characterized in that, The conductive layer on the outer surface of the tuning screw and the outer surface of the cover plate is a silver plating layer; the thickness of the silver plating layer ranges from 0.3 to 1 μm.
6. The filter tuning method according to claim 1, characterized in that, In step S3, the filter is heated by reflow soldering.
7. The filter tuning method according to claim 1, characterized in that, In step S3, the liquid hot melt material penetrates through capillary action into the gap between the thread of the tuning screw and the inner wall thread of the through hole; after the liquid hot melt material cools in the gap, it forms a dense alloy layer, and the tuning screw and the cover plate are formed into a one-piece integral through metallurgy.
8. The filter tuning method according to claim 1, characterized in that, In step S2, the threaded connection between the thread of the tuning screw and the inner wall of the through hole is a mechanical connection of point contact or line contact.
9. A filter, comprising a cavity open at one end, a cover plate mounted on the open end of the cavity, a resonant post mounted into the cavity, a tuning screw, and a locking nut; the cover plate has a through hole, the tuning screw is threadedly connected to the inner wall of the through hole and extends into the cavity; the locking nut is threadedly connected to the tuning screw and abuts against the top of the cover plate to lock the tuning screw; characterized in that, The thread gap between the tuning screw and the thread gap on the inner wall of the through hole is filled with a dense alloy layer, so that the tuning screw and the cover plate are fixedly connected to form a one-piece integral unit; the top of the cover plate is provided with a receiving groove at the edge of the through hole, and the dense alloy layer is formed by the solid hot melt material placed in the receiving groove melting into molten liquid and flowing into the gap.
10. The filter according to claim 9, characterized in that, The receiving groove and the through hole are stepped holes in the cover plate; the inner diameter of the receiving groove is larger than the inner diameter of the through hole.