A metal cavity filter with a blade type capacitive cross-coupling structure

Abstract

The application discloses a metal cavity filter with a paddle type capacitive cross-coupling structure and belongs to the technical field of radio frequency communication. The metal cavity filter is provided with a main cavity, a resonant cavity, a tuning screw, a coupling screw and a paddle type coupling structure. The paddle type coupling metal sheet is in a flat plate structure and is arranged opposite to the side wall of the resonant rod. Capacitive coupling is realized through the flat plate opposite mode. The application increases the coupling opposite area through the flat plate type paddle structure. On the premise of ensuring the rated coupling strength, the safety distance between the coupling structure and the mushroom head of the resonant rod is greatly improved. The influence of the machining and assembly errors on the electrical performance of the filter is obviously reduced. The product mass production consistency and yield are improved. Meanwhile, the structure is simple, compatible with the existing cavity filter machining process and easy to mass produce.

Description

Technical Field

[0001] This invention belongs to the field of radio frequency communication technology, and specifically relates to a metal cavity filter with a paddle-type capacitive cross-coupling structure, which is particularly suitable for bandpass metal cavity filters used in wireless communication base stations and satellite communication systems. Background Technology

[0002] Metal cavity filters, with their advantages of low insertion loss, high out-of-band rejection, high power capacity, and excellent temperature stability, have become indispensable core components in radio frequency communication systems and are widely used in 5G / 6G base stations, satellite communications, radar, and other fields. The cross-coupling structure of cavity filters is an important technique for achieving high out-of-band rejection, with capacitive cross-coupling being widely adopted because it can introduce transmission zeros at the passband edge.

[0003] In CQ-type filters that achieve capacitive cross-coupling, a common technique involves stripping the outer conductors from both ends of a semi-rigid coaxial cable to create probes insulated from the cavity shell. This method exposes the center conductors at both ends of the semi-rigid cable as coupling probes, achieving capacitive coupling through the near-field electric field between the probes and the resonant rod. To ensure coupling strength, the probe tip must be close to the mushroom head of the resonant rod; even minor deviations in processing and assembly can cause drastic fluctuations in coupling, leading to filter center frequency shift and deterioration of return loss. Furthermore, even if the probe tip maintains a safe distance from the mushroom head of the resonant rod, the limited mechanical strength of the semi-rigid cable makes it prone to deformation over long-term use, resulting in coupling drift.

[0004] Another common capacitive cross-coupling structure is the dumbbell-shaped coupling structure, typically consisting of a central connecting rod and two disc-shaped coupling plates at both ends, forming an overall dumbbell shape. This structure achieves capacitive coupling between the discs at both ends and the resonant rod, which can improve coupling stability to some extent. However, the dumbbell-shaped structure still requires the discs at both ends to be close to the mushroom head of the resonant rod to obtain sufficient coupling, and it remains sensitive to machining tolerances and assembly deviations. Furthermore, the electric field concentration area between the discs and the resonant rod is relatively small, limiting the range of coupling adjustment. In addition, this structure has a symmetrical, protruding shape, occupying a large cavity space, which is not conducive to miniaturization design. Summary of the Invention

[0005] The purpose of this invention is to provide a metal cavity filter with a paddle-type capacitive cross-coupling structure to solve the problems of sensitive processing and assembly tolerances, easy drift of coupling, poor mass production consistency, and low product yield of existing CQ-type filter semi-rigid coaxial probe coupling structures and dumbbell-type capacitive cross-coupling structures. Without reducing the coupling strength, the invention reduces the impact of processing and assembly errors on the filter's electrical performance from the root by increasing the safety distance between the coupling structure and the mushroom head of the resonant rod, thereby improving product mass production consistency and yield. At the same time, the structure is simple and compatible with existing processing technology.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A metal cavity filter with a paddle-type capacitive cross-coupling structure includes: a metal cavity, four resonant rods, three coupling screws, and a paddle-type coupling structure;

[0008] The metal cavity is provided with a first resonant cavity, a second resonant cavity, a third resonant cavity and a fourth resonant cavity, which together constitute a CQ-type four-cavity cross-coupled filter topology.

[0009] The four resonant rods are the first resonant rod, the second resonant rod, the third resonant rod, and the fourth resonant rod. The first to the fourth resonant rods are all hollow structures and are respectively arranged in the first resonant cavity, the second resonant cavity, the third resonant cavity, and the fourth resonant cavity.

[0010] The three coupling screws are the first coupling screw, the second coupling screw, and the third coupling screw, respectively, and are respectively disposed between the first resonant cavity and the second resonant cavity, between the second resonant cavity and the third resonant cavity, and between the third resonant cavity and the fourth resonant cavity;

[0011] The paddle-type coupling structure is disposed between the first resonant cavity and the fourth resonant cavity; it includes a support member, a connecting rod, a first paddle-type coupling plate, and a second paddle-type coupling plate. One end of the connecting rod is connected to the first paddle-type coupling plate, and the other end passes through the support member and is connected to the second paddle-type coupling plate. The first paddle-type coupling plate extends into the first resonant cavity and is disposed opposite to the side wall of the first resonant rod. The second paddle-type coupling plate extends into the fourth resonant cavity and is disposed opposite to the side wall of the fourth resonant rod. Both the first and second paddle-type coupling plates are flat metal structures, and their plate surfaces are parallel to the central axis of the corresponding resonant rod, forming capacitive coupling with the resonant rod in a plate-to-plate manner.

[0012] Furthermore, the metal cavity filter also includes a cover plate, which is located on the top of the metal cavity. A tuning screw is threaded onto the cover plate for each resonant rod. The tuning screw passes downward through the cover plate and extends into the corresponding resonant rod, and the tuning screw is coaxially arranged with the hollow structure of the resonant rod.

[0013] Furthermore, the first resonant cavity is adjacent to the second resonant cavity, the second resonant cavity is adjacent to the third resonant cavity, the third resonant cavity is adjacent to the fourth resonant cavity, a common isolation rib is provided between the first resonant cavity and the fourth resonant cavity, and a groove is provided on the common isolation rib. The paddle-type coupling structure is embedded and installed between the first resonant cavity and the fourth resonant cavity through the groove.

[0014] Furthermore, a first coupling window is provided between the first resonant cavity and the second resonant cavity, a second coupling window is provided between the second resonant cavity and the third resonant cavity, and a third coupling window is provided between the third resonant cavity and the fourth resonant cavity; the first coupling screw, the second coupling screw and the third coupling screw are respectively disposed at the first coupling window, the second coupling window and the third coupling window.

[0015] Furthermore, the first resonant cavity, the second resonant cavity, the third resonant cavity, and the fourth resonant cavity are arranged in a 2×2 matrix within the metal cavity.

[0016] Furthermore, the support member is a hollow cylindrical structure, and the connecting rod passes through the central through hole of the support member and is coaxially arranged with the support member.

[0017] Furthermore, the connecting rod has an L-shaped chamfer.

[0018] Furthermore, the first and second blade-type coupling plates are integrally formed with the connecting rod, or are electrically connected by welding.

[0019] Furthermore, the substrates of the metal cavity, the first resonant rod, the second resonant rod, the third resonant rod, and the fourth resonant rod have a bulk conductivity range of 1×10⁻⁶. 7 S / m~6.1×10 7 A conductive metal with a bulk conductivity of not less than 4 × 10⁻⁶ S / m is provided on the surface of the substrate. 7 Conductive metal plating with S / m.

[0020] Furthermore, the support member is made of an insulating material with a relative permittivity of 2.0 to 2.2 and a dielectric loss tangent of ≤0.001.

[0021] Furthermore, the metal cavity is a one-piece milled structure.

[0022] The metal cavity filter provided by this invention adopts a planar blade coupling structure to replace the traditional probe-type and disk-type coupling structures. By increasing the coupling area through the planar blade structure, the safe distance between the coupling structure and the mushroom head at the top of the resonant rod is increased from less than 1mm in the traditional structure to more than 5mm while ensuring the rated coupling strength. This significantly improves the safe distance between the coupling structure and the mushroom head of the resonant rod. This design fundamentally reduces the interference of processing and assembly position errors on the coupling quantity, resulting in a significant reduction in the fluctuation range of key electrical performance indicators such as the filter's center frequency and return loss. This effectively mitigates the negative impact of processing and assembly errors on the filter's electrical performance, improving product mass production consistency and yield. At the same time, the overall structure is simple and adaptable to existing cavity filter processing procedures, facilitating large-scale mass production. Attached Figure Description

[0023] Figure 1 The overall structure diagram of the metal cavity filter with a paddle-type capacitive cross-coupling structure provided by the present invention is shown below.

[0024] Figure 2 The topology of a CQ-type four-cavity cross-coupled filter; topology;

[0025] Figure 3 A top view of the metal cavity filter provided in the embodiment;

[0026] Figure 4 A schematic diagram of the mounting groove for the paddle-type capacitive cross-coupling structure in the metal cavity filter provided in the embodiment;

[0027] Figure 5 The impeller-type capacitive cross-coupling structure provided in the embodiment;

[0028] Figure 6 A schematic front view of the paddle-type capacitive cross-coupling structure provided for the embodiment;

[0029] Figure 7 A top view of the paddle-type capacitive cross-coupling structure provided in the embodiment;

[0030] Figure 8 A 3D simulation model of a metal cavity filter provided for an embodiment;

[0031] Figure 9 For based on Figure 7 Simulation results of S-parameters for generating symmetrical transmission zeros;

[0032] Figure label:

[0033] 10. Metal cavity; 101. First resonant cavity; 102. Second resonant cavity; 103. Third resonant cavity; 104. Fourth resonant cavity; 201. First resonant rod; 202. Second resonant rod; 203. Third resonant rod; 204. Fourth resonant rod; 301. First tuning screw; 302. Second tuning screw; 303. Third tuning screw; 304. Fourth tuning screw; 401. First coupling screw; 402. Second coupling screw; 403. Third coupling screw; 501. Support member; 502. Connecting rod; 503. First paddle-shaped coupling plate; 504. Second paddle-shaped coupling plate; 601. First coupling window; 602. Second coupling window; 603. Third coupling window. Detailed Implementation

[0034] The technical solution of the present invention will be understood below with reference to the accompanying drawings and embodiments.

[0035] like Figures 1 to 8 As shown, this embodiment provides a metal cavity filter with a paddle-type capacitive cross-coupling structure, including: a metal cavity 10, four resonant rods, three coupling windows, three coupling screws, and a paddle-type coupling structure.

[0036] like Figure 1 As shown, the metal cavity 10 is divided into four independent resonant cavities by an integrally formed metal insulating rib. The four resonant cavities are designated as a first resonant cavity 101, a second resonant cavity 102, a third resonant cavity 103, and a fourth resonant cavity 104. The first resonant cavity 101, the second resonant cavity 102, the third resonant cavity 103, and the fourth resonant cavity 104 are arranged in a 2×2 matrix within the metal cavity 10, forming a structure as shown in the diagram. Figure 2 The CQ-type four-cavity cross-coupled filter topology is shown.

[0037] like Figures 3 to 4 As shown, the four resonant rods are the first resonant rod 201, the second resonant rod 202, the third resonant rod 203, and the fourth resonant rod 204. All four resonant rods 201 to 204 are hollow structures and are respectively disposed within the first resonant cavity 101, the second resonant cavity 102, the third resonant cavity 103, and the fourth resonant cavity 104. A cover plate is provided on the top of the metal cavity 10. A tuning screw is threaded onto the cover plate corresponding to each resonant rod, namely the first tuning screw 301, the second tuning screw 302, the third tuning screw 303, and the fourth tuning screw 304. Each tuning screw passes downward through the cover plate and extends coaxially into the hollow structure of the corresponding resonant rod, maintaining a preset distance from the resonant rod. By turning the tuning screws to change the insertion depth, the resonant frequency of each resonant cavity can be independently fine-tuned to ensure that the center frequency and passband specifications of the filter meet the design requirements.

[0038] The three coupling windows are three rectangular coupling windows, specifically including a first coupling window, a second coupling window, and a third coupling window. The first coupling window 601 is located between the first resonant cavity 101 and the second resonant cavity 102; the second coupling window is located between the second resonant cavity 102 and the third resonant cavity 103; and the third coupling window is located between the third resonant cavity 103 and the fourth resonant cavity 104. The three coupling screws are a first coupling screw 401, a second coupling screw 402, and a third coupling screw 403, respectively located between the first resonant cavity 101 and the second resonant cavity 102, between the second resonant cavity 102 and the third resonant cavity 103, and between the third resonant cavity 103 and the fourth resonant cavity 104, and corresponding one-to-one with the three coupling windows. Adjacent resonant cavities are magnetically coupled through corresponding coupling windows and coupling screws, forming the main signal transmission path of the filter. The signal transmission direction is first resonant cavity 101 → second resonant cavity 102 → third resonant cavity 103 → fourth resonant cavity 104. By adjusting the depth of the coupling screws inserted into the coupling windows, the main coupling amount between adjacent resonant cavities can be precisely controlled, thereby achieving precise control of the filter's passband characteristics.

[0039] In terms of materials and processes, the substrates of the metal cavity 10, the first resonant rod 201, the second resonant rod 202, the third resonant rod 203, and the fourth resonant rod 204 have a bulk conductivity range of 1×10⁻⁶. 7 S / m~6.1×10 7 A conductive metal with a bulk conductivity of not less than 4 × 10⁻⁶ S / m is provided on the surface of the substrate. 7 The conductive metal plating has a strength of S / m. The metal cavity 10 is a one-piece milled metal cavity with an overall cuboid structure.

[0040] The paddle-type coupling structure 50 is disposed between the first resonant cavity 101 and the fourth resonant cavity 104, and serves as a key component of the metal cavity filter in this embodiment. Its structure is as follows: Figures 5 to 7As shown, the system includes a support member 501, a connecting rod 502, a first paddle-type coupling plate 503, and a second paddle-type coupling plate 504. One end of the connecting rod 502 is connected to the first paddle-type coupling plate 503, and the other end passes through the support member 501 and is connected to the second paddle-type coupling plate 504. The first paddle-type coupling plate 503 extends into the first resonant cavity 101 and is positioned opposite to the side wall of the first resonant rod 201. The second paddle-type coupling plate 504 extends into the fourth resonant cavity 104 and is positioned opposite to the side wall of the fourth resonant rod 204. Both the first paddle-type coupling plate 503 and the second paddle-type coupling plate 504 are flat metal structures, and their plate surfaces are parallel to the central axis of the corresponding resonant rod, forming capacitive coupling with the resonant rod in a plate-to-plate manner. By setting a flat blade structure to increase the coupling area, the safe distance between the coupling structure and the mushroom head at the top of the resonant rod is increased from less than 1mm in the traditional structure to more than 5mm while ensuring the rated coupling strength. This significantly improves the safe distance between the coupling structure and the mushroom head of the resonant rod.

[0041] In this embodiment, the first resonant cavity 101 is adjacent to the second resonant cavity 102, the second resonant cavity 102 is adjacent to the third resonant cavity 103, and the third resonant cavity 103 is adjacent to the fourth resonant cavity 104. A common isolation rib is provided between the first resonant cavity 101 and the fourth resonant cavity 104. A groove 505 is provided on the common isolation rib. The paddle-type coupling structure 50 is embedded and installed between the first resonant cavity 101 and the fourth resonant cavity 104 through the groove 505. It is used to introduce capacitive cross-coupling for the filter, generate transmission zeros at the upper and lower edges of the filter passband, and significantly improve the out-of-band rejection performance of the filter.

[0042] In some other implementations, the paddle-type coupling structure 50 has a hollow cylindrical support 501 made of an insulating material with a relative permittivity of 2.0 to 2.2 and a dielectric loss tangent ≤ 0.001. Both ends of the connecting rod 502 are L-shaped chamfers, and the connecting rod 502 passes through the central through-hole of the support 501 and is coaxially arranged with the support 501. To eliminate losses and coupling misalignment caused by assembly gaps, the first paddle-type coupling plate 503 and the second paddle-type coupling plate 504 are integrally formed with the connecting rod 502, or are electrically connected by welding to ensure the reliability of the electrical connection and the consistency of coupling performance.

[0043] Figure 9 The simulation results of the S-parameters for generating symmetric transmission zeros are shown in the figure. Figure 9The filter shown in this embodiment operates in the 2.913GHz~3.069GHz frequency band with an in-band insertion loss better than 0.1dB and a return loss better than 21dB. It forms transmission zeros at 2.836GHz and 3.136GHz on both sides of the passband, and has an out-of-band rejection of up to 67dB. It has excellent passband performance and out-of-band rejection capability. At the same time, the paddle-type coupling structure significantly improves the tolerance of processing and assembly errors, meeting the requirements of engineering applications.

Claims

1. A metal cavity filter with a paddle-type capacitive cross-coupling structure, characterized in that, include: Metal cavity, four resonant rods, three coupling screws, and paddle-type coupling structure; The metal cavity is provided with a first resonant cavity, a second resonant cavity, a third resonant cavity and a fourth resonant cavity, which together constitute a CQ-type four-cavity cross-coupled filter topology. The four resonant rods are the first resonant rod, the second resonant rod, the third resonant rod, and the fourth resonant rod. The first to the fourth resonant rods are all hollow structures and are respectively arranged in the first resonant cavity, the second resonant cavity, the third resonant cavity, and the fourth resonant cavity. The three coupling screws are the first coupling screw, the second coupling screw, and the third coupling screw, respectively, and are respectively disposed between the first resonant cavity and the second resonant cavity, between the second resonant cavity and the third resonant cavity, and between the third resonant cavity and the fourth resonant cavity; The paddle-type coupling structure is disposed between the first resonant cavity and the fourth resonant cavity; it includes a support member, a connecting rod, a first paddle-type coupling plate, and a second paddle-type coupling plate. One end of the connecting rod is connected to the first paddle-type coupling plate, and the other end passes through the support member and is connected to the second paddle-type coupling plate. The first paddle-type coupling plate extends into the first resonant cavity and is disposed opposite to the side wall of the first resonant rod. The second paddle-type coupling plate extends into the fourth resonant cavity and is disposed opposite to the side wall of the fourth resonant rod. Both the first and second paddle-type coupling plates are flat metal structures, and their plate surfaces are parallel to the central axis of the corresponding resonant rod, forming capacitive coupling with the resonant rod in a plate-to-plate manner.

2. The metal cavity filter according to claim 1, characterized in that, The metal cavity filter also includes a cover plate, which is located on the top of the metal cavity. A tuning screw is threaded onto the cover plate for each resonant rod. The tuning screw passes downward through the cover plate and extends into the corresponding resonant rod. The tuning screw and the hollow structure of the resonant rod are coaxially arranged.

3. The metal cavity filter according to claim 1, characterized in that, The first resonant cavity is adjacent to the second resonant cavity, the second resonant cavity is adjacent to the third resonant cavity, and the third resonant cavity is adjacent to the fourth resonant cavity. A common isolation rib is provided between the first resonant cavity and the fourth resonant cavity. A groove is provided on the common isolation rib. The paddle-type coupling structure is embedded and installed between the first resonant cavity and the fourth resonant cavity through the groove.

4. The metal cavity filter according to claim 1, characterized in that, A first coupling window is provided between the first resonant cavity and the second resonant cavity, a second coupling window is provided between the second resonant cavity and the third resonant cavity, and a third coupling window is provided between the third resonant cavity and the fourth resonant cavity; the first coupling screw, the second coupling screw and the third coupling screw are respectively provided at the first coupling window, the second coupling window and the third coupling window.

5. The metal cavity filter according to claim 1, characterized in that, The first resonant cavity, the second resonant cavity, the third resonant cavity, and the fourth resonant cavity are arranged in a 2×2 matrix within the metal cavity.

6. The metal cavity filter according to claim 1, characterized in that, The support member is a hollow cylindrical structure, and the connecting rod passes through the central through hole of the support member and is coaxial with the support member.

7. The metal cavity filter with a paddle-type capacitive cross-coupling structure according to claim 1, characterized in that, The connecting rod has an L-shaped chamfer.

8. The metal cavity filter according to claim 1, characterized in that, The first and second blade-type coupling plates are integrally formed with the connecting rod, or are electrically connected by welding.

9. The metal cavity filter according to claim 1, characterized in that, The substrates of the metal cavity, the first resonant rod, the second resonant rod, the third resonant rod, and the fourth resonant rod have a bulk conductivity range of 1×10⁻⁶. 7 S / m~6.1×10 7 A conductive metal with a bulk conductivity of not less than 4 × 10⁻⁶ S / m is provided on the surface of the substrate. 7 Conductive metal plating with S / m.

10. The metal cavity filter according to any one of claims 1 to 9, characterized in that, The support is made of an insulating material with a relative permittivity of 2.0 to 2.2 and a dielectric loss tangent of ≤0.001.

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