High-power cavity low-pass filter
By introducing a parallel-series resonant equivalent circuit with transmission zeros into the low-pass filter, the problems of large volume in the low-frequency band or difficult processing in the high-frequency band are solved, achieving miniaturization and low insertion loss, and improving out-of-band rejection performance.
Patent Information
- Application Number
- CN202422942706.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-28
- Publication Date
- 2025-10-31
- Estimated Expiration
- 2034-11-28
AI Technical Summary
Existing low-pass filters are bulky or have high insertion loss when designed for low frequencies, and are difficult to manufacture when designed for high frequencies, making it difficult to find a balance between high suppression and low insertion loss.
A distributed semi-lumped approach is adopted, using inductors to realize the equivalent circuit of a low-pass filter with zeros in the lumped element series inductor, and combining high and low impedance lines to realize the equivalent circuit of parallel series resonance. By introducing transmission zeros, out-of-band rejection is improved and insertion loss is reduced.
It achieves miniaturization and low insertion loss of filters under the same suppression requirements, reduces the requirements for manufacturing precision, and improves out-of-band suppression performance.
Smart Images
Figure CN223502166U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of microwave device technology, and in particular to a high-power cavity low-pass filter. Background Technology
[0002] In modern applications, low-pass filters are generally required to have low insertion loss, high out-of-band rejection, low port reflection, and miniaturization. Generally, achieving high rejection requires increasing the filter order, which inevitably increases insertion loss, makes port impedance matching more difficult, and increases the filter's size (mainly in the length direction). In high-rejection, low-insertion-loss, high-power applications, common low-pass filters include LC low-pass filters, skein low-pass filters, tubular low-pass filters, and various printed circuit board (PCB) low-pass filters.
[0003] LC low-pass filters are easy to implement in various topologies (including introducing transmission zeros), but the presence of the printed circuit board (PCB) inevitably introduces dielectric loss, increasing insertion loss. At frequencies above 1GHz, the inductance is relatively small, often necessitating the abandonment of the PCB to avoid parasitic parameters introduced by it. Device assembly requires a three-dimensional structure, which is inconvenient for assembly and debugging. The "candied hawthorn" low-pass filter, while offering high suppression at 15th order or higher in the low-frequency range, is relatively large (mainly in the length direction) and cannot introduce transmission zeros to compress the length. At high frequencies, it requires integrated processing, demanding high tolerances and making it difficult to manufacture. Tubular low-pass filters are similar to the "candied hawthorn" type and will not be discussed further. Although various PCB-based low-pass filters are small in size, the dielectric loss inherent in the PCB results in relatively high insertion loss, which increases more significantly at higher frequencies. While suspended wire low-pass filters transfer most of their energy to the air and have a high Q-factor, it is still relatively small compared to cavity low-pass filters.
[0004] This invention addresses the problems of existing low-pass filters designed for high suppression at low frequencies (15th order or higher) having large size (mainly in the length direction) or high insertion loss; and the difficulty in fabricating cavity low-pass filters designed for high frequencies (15th order or higher); and improves suppression and insertion loss performance. Utility Model Content
[0005] To address the shortcomings of existing technologies, this invention provides a high-power cavity low-pass filter. By using a distributed semi-lumped design, it utilizes inductors to realize the series inductor equivalent circuit of the low-pass filter with zero-point lumped elements, and uses high and low impedance lines to realize the parallel series resonant equivalent circuit of the low-pass filter with zero-point lumped elements.
[0006] This utility model discloses a high-power cavity low-pass filter through embodiments, comprising a metal cavity, a cover plate matching the metal cavity, several inductors connected in series inside the metal cavity, and connectors connected to both ends of the series inductors outside the metal cavity; the inductors and connectors, and the inductors and inductors connected inside the metal cavity are also connected with the same or different zero-point stubs; each zero-point stub is disposed in a cylindrical stub cavity, and a dielectric sleeve is disposed between the stub cavity and the zero-point stub; the zero-point stub includes a cylindrical first stub and a second stub, and the outer diameter of the first stub is larger than the outer diameter of the second stub; one end of the second stub is connected to the part between the inductors and the connector, or electrically connected to the part between the two inductors; the other end of the second stub is connected to the first stub, and both the first and second stubs are coaxial with the stub cavity.
[0007] Furthermore, the zero-point stub is integrally milled from high and low impedance lines. The second stub is high impedance, which can be equivalent to an inductor; the first stub is low impedance, which can be equivalent to a capacitor.
[0008] Furthermore, the differences between the zero-point branches include: the first and second branches of the same zero-point branch have different lengths; the first branches of different zero-point branches have different diameters and / or different lengths; and the second branches of different zero-point branches have different diameters and / or different lengths.
[0009] Furthermore, inductors include helical inductors and linear inductors. The differences between these inductors include: variations in the thickness of the materials used to compose them, differences in the pitch of the lead screw, and / or differences in the diameter of the lead screw. The choice between helical and linear inductors depends on whether the required inductance is easy to wind. A linear inductor is a straight metal wire, constructed from a profile. Here, the profile refers to commercially available metal wire or rod obtained through drawing.
[0010] Furthermore, the media sleeve is located between the branch cavity and the two-point branch, and is bonded with silicone.
[0011] Furthermore, the connector includes an input connector and an output connector, each of which is connected to both ends of the series-connected inductor.
[0012] Furthermore, the metal cavity and the cover plate are each provided with several screw holes. The metal cavity and the cover plate are connected by screw holes and screws to seal the space inside the metal cavity.
[0013] Furthermore, the metal cavity, cover plate, each inductor, and each zero-point stub surface are all covered with a silver plating layer. Silver plating can improve the quality factor of the series inductor and the parallel-series resonant components.
[0014] Furthermore, it also includes a dielectric rod that runs through each of the inductors, with both ends of the dielectric rod fixed to the two sides of the metal cavity.
[0015] Furthermore, this includes a medium block fixed to the metal cavity by screws.
[0016] The purpose of using dielectric rods or dielectric blocks is to take into account the need to fix the inductor in a metal cavity under vibration and shock conditions.
[0017] Compared to existing technologies, this invention offers the following advantages: By employing a distributed semi-lumped design, this invention utilizes inductors to realize the series inductor equivalent circuit of a low-pass filter with zeros in lumped elements. It also uses high and low impedance lines to realize the parallel series resonant equivalent circuit of the low-pass filter with zeros in lumped elements. This solves the problems of large size (mainly in the length direction) or high insertion loss in existing low-pass filters designed for 15th order or higher high suppression in the low-frequency band, and the difficulty in fabricating cavity low-pass filters designed for 15th order or higher in the high-frequency band. It improves suppression and insertion loss performance. Under the same suppression requirements, it achieves miniaturization and low insertion loss; under the same size requirements, it improves out-of-band suppression; and compared to commonly used low-insertion-loss "candied hawthorn" low-pass filters, it reduces the requirements for processing precision. Attached Figure Description
[0018] To more clearly illustrate the technical solution of this utility model and facilitate a further understanding of its technical effects, features, and objectives, the utility model will be described in detail below with reference to the accompanying drawings. The drawings constitute an essential part of the specification and are used together with the embodiments of this utility model to illustrate its technical solution, but do not constitute a limitation on this utility model.
[0019] Figure 1 This is a top view of the filter described in the embodiments of this utility model;
[0020] Figure 2 This is a front view of the filter described in an embodiment of this utility model;
[0021] Figure 3 This is the equivalent circuit diagram of the filter described in the embodiments of this utility model. Detailed Implementation
[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Of course, the specific embodiments described below are only for explaining the technical solutions of the present invention, and not for limiting the present invention. Furthermore, the parts described in the embodiments or drawings are merely illustrative examples of relevant parts of the present invention, and not the entirety of the present invention. At the same time, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention should naturally fall within the protection scope of the present invention.
[0023] like Figure 1As shown, this utility model proposes a high-power cavity low-pass filter through the following embodiments, which includes a metal cavity 1, a cover plate (not shown in the figure) matching the metal cavity 1, four inductors connected in series inside the metal cavity 1, and a connector 2 connected to both ends of the series inductors outside the metal cavity 1; zero-point stubs are also connected at the connection points between the inductors and the connector 2, and at the connection points between the inductors inside the metal cavity 1; each zero-point stub is set in a cylindrical stub cavity, and a dielectric sleeve 7 and a dielectric sleeve 8 are provided between the stub cavity and the zero-point stub; the zero-point stub includes a cylindrical first stub and a second stub, and the outer diameter of the first stub is larger than the outer diameter of the second stub; one end of the second stub is connected to the part between the inductors and the connector, or electrically connected to the part between the two inductors; the other end of the second stub is connected to the first stub, and both the first stub and the second stub are coaxial with the stub cavity.
[0024] In this embodiment, both zero-point stubs 5 and 6 are integrally milled from high and low impedance lines. The second stub is high impedance, which can be equivalent to an inductor; the first stub is low impedance, which can be equivalent to a capacitor. To enable the reflected and incident waves to cancel each other out, a trapezoidal LC low-pass prototype filter topology is used. The capacitor in the parallel branch is connected in series with the inductor, generating zeros to improve out-of-band rejection. Due to the introduction of zeros, out-of-band rejection is improved at the same order. Therefore, when the rejection meets certain requirements, the filter order can be reduced.
[0025] In this embodiment, the difference between the zero-point branches is that the lengths of the first and second branches of the same zero-point branch are different, and the lengths of the first branches of different zero-point branches are different.
[0026] In this embodiment, both inductor 3 and inductor 4 are spiral inductors. The difference between the spiral inductors lies in their pitch. Of course, in other embodiments, the choice between spiral and straight inductors depends on whether the required inductance is easy to wind. A straight inductor is a straight metal wire, constructed from a profile. Here, the profile refers to commercially available metal wire or metal rod obtained through drawing. In this embodiment, taking the low-frequency band as an example, a spiral inductor with a compressed inductance is chosen because the main series inductor has a larger inductance. Figure 1 , Figure 2 As shown in the diagram. The main spiral inductors can be wound as a single unit or composed of several independent spiral inductors wound and welded together. In the high-frequency range, because the inductance of the main series inductors is relatively small and difficult to wind, straight inductors are chosen. The position of the straight inductor is the same as... Figure 1 , Figure 2 Position of the spiral inductor. The two ends of the linear inductor are soldered to the input and output respectively, or a long linear inductor is used to replace the pins and inserted into the input and output connectors to form a whole.
[0027] In this embodiment, dielectric sleeves 7 and 8 are located between the stub cavity and the two-point stub, and are bonded together with silicone. It is worth noting that in some other embodiments, when considering the power carrying capacity, since the structure is a cavity and all parts are made of metal, the power carrying capacity is mainly considered as the peak power, which depends on two aspects: firstly, the gap between the low-impedance line and the cylindrical cavity of the metal cavity, i.e., the dielectric thickness; secondly, the gap between the spiral inductor and the cavity wall. When a wide stopband needs to be considered, due to the semi-distributed method used, the low-pass filter will generate a parasitic response. The location of the parasitic response depends on the half-wavelength of the high and low impedance lines, the position of the higher-order mode of the coaxial line, and the self-resonant frequency of the spiral inductor. Therefore, the location of the parasitic response can be changed by selecting different diameters and lengths of the high and low impedance lines, or by selecting the thickness, pitch, and diameter of the spiral inductor. When vibration and shock need to be considered, silicone is added between the zero-point stub, the dielectric sleeve, and the metal cavity, and the main inductor needs to be made of a thicker profile to reduce the problems caused by vibration and shock. If high vibration and impact requirements are needed, a dielectric rod should be inserted through the middle of the spiral inductor and fixed on both sides of the cavity input and output. Alternatively, several dielectric blocks with holes in the middle can be selected and fixed between the metal cavity and the cover plate with screws.
[0028] In this embodiment, the connector includes an input connector and an output connector, each of which is connected to both ends of the series-connected inductor.
[0029] In this embodiment, the metal cavity is also provided with several screw holes, and the metal cavity and the cover plate are connected by screw holes and screws to seal the space inside the metal cavity.
[0030] In this embodiment, the metal cavity, cover plate, each inductor, and each zero-point stub are all covered with a silver plating layer. The silver plating can improve the quality factor of the series inductor and the parallel-series resonant components.
[0031] It is worth noting that, due to the introduction of zero-point stubs and the use of silver plating, the length of the filter can be reduced and the insertion loss lowered under the same suppression requirements; while the out-of-band suppression can be improved under the same length.
[0032] The equivalent circuit diagram of the high-power cavity low-pass filter described in the above embodiments is as follows: Figure 3 As shown, Figure 1 , 2 3 is Figure 3 Inductor L1, Figure 1 , 2 4 is Figure 3 L2 inductor, Figure 1 , 2 5 is Figure 3 In the middle section, L3 and C1 are connected in series (the thin stem in section 5 is equivalent to L3, and the thick stem is equivalent to C1). Figure 1 ,2 6 is Figure 3 In the middle, L3 and C2 are connected branches (the thin stem in 6 is equivalent to L3, and the thick stem is equivalent to C2).
[0033] Introducing transmission zeros into a low-pass filter can achieve the following effects: First, it improves out-of-band rejection while keeping the filter order (number of series inductors in the main path and number of parallel capacitors in the branches) constant. Second, while keeping the out-of-band rejection constant, it can reduce the filter order, the number of inductors in the main path, and the number of capacitors in the branches (the number of series inductors in the main path and parallel capacitors in the branches is reduced by almost half), thereby reducing the length of the filter and lowering the insertion loss of the filter.
[0034] Meanwhile, there are two ways to introduce transmission zeros into a low-pass filter. One is to introduce a parallel resonant circuit in series with the main path. For example... Figure 3 One approach is to connect a capacitor in parallel with either the main inductor L1 or L2. Another approach is to introduce a series resonant circuit by connecting a capacitor in parallel with a branch. For example... Figure 3 A capacitor C1 or C2 is connected in series with an inductor. This patent uses the second method. Figure 3 The low-pass filter has five series resonant circuits in its five parallel branches. Each series resonant circuit in a parallel branch generates a transmission zero outside the band, improving the low-pass filter's out-of-band rejection. The five series resonant circuits generate five transmission zeros outside the band, which can be superimposed to further improve the low-pass filter's out-of-band rejection. The effect of this is that if a series inductor L3 were not introduced into the parallel branches, the number of main circuit inductors would increase from four to eight, and the number of branch capacitors would increase from five to nine, while still achieving the same level of out-of-band rejection. The inductance of the introduced series inductor (…). Figure 1 , 2 The diameter and length of the thin rods in parts 5 and 6 may be different. In this embodiment, the same series inductor L3 is selected.
[0035] Of course, it should be noted that the scope of protection of this invention is not limited to... Figure 1 , Figure 2 The structure shown includes its dual circuit form. The zero-point structure can be a cylindrical cavity, a rectangular cavity, and a circular, square, or modified zero-point stub structure. The above embodiments are only for more clearly illustrating the technical solution of this utility model. Those skilled in the art will understand that the implementation of this utility model is not limited to the above content. Any obvious changes, substitutions, or replacements made based on the above content do not exceed the scope of the technical solution covered by this utility model; other implementations will naturally fall within the scope of this utility model without departing from the concept of this utility model.
Claims
1. A high-power cavity low-pass filter, characterized in that, Includes a metal cavity, a cover plate matching the metal cavity, several inductors connected in series inside the metal cavity, and connectors connecting the two ends of the inductors connected in series outside the metal cavity. The inductor and connector connection points and inductor-to-inductor connection points within the metal cavity are also connected to the same or different zero-point stubs; each zero-point stub is disposed within a cylindrical stub cavity, and a dielectric sleeve is disposed between the stub cavity and the zero-point stub. The zero-point stub includes a cylindrical first stub and a second stub, with the outer diameter of the first stub being larger than that of the second stub; one end of the second stub is either connected to the portion between the inductor and the connector, or electrically connected to the portion between the two inductors. The other end of the second branch is connected to the first branch, and both the first and second branches are coaxial with the branch cavity.
2. The high-power cavity low-pass filter as described in claim 1, characterized in that: The zero-point stub is machined from a single high- and low-impedance line, with the second stub being high-impedance and the first stub being low-impedance.
3. The high-power cavity low-pass filter as described in claim 2, characterized in that, The differences between the zero-point branches include: the first and second branches of the same zero-point branch have different lengths; the first branches of different zero-point branches have different diameters and / or different lengths; and the second branches of different zero-point branches have different diameters and / or different lengths.
4. The high-power cavity low-pass filter as described in claim 1, characterized in that, The inductors include helical inductors and linear inductors. The differences between the inductors include: the different thicknesses of the materials that make up the inductors, the different pitches of the inductors, and / or the different diameters of the inductors.
5. The high-power cavity low-pass filter as described in claim 1, characterized in that: The medium sleeve is located between the branch cavity and the two-point branch, and is bonded with silicone.
6. The high-power cavity low-pass filter as described in claim 1, characterized in that: The connector includes an input connector and an output connector, each of which is connected to one end of a series-connected inductor.
7. The high-power cavity low-pass filter as described in claim 1, characterized in that: The metal cavity and the cover plate are respectively provided with a number of screw holes. The metal cavity and the cover plate are connected by the screw holes and screws to seal the space of the metal cavity.
8. The high-power cavity low-pass filter as described in claim 1, characterized in that: The surfaces of the metal cavity, the cover plate, each inductor, and each zero-point stub are all covered with a silver plating layer.
9. The high-power cavity low-pass filter as described in claim 1, characterized in that: It also includes a dielectric rod that runs through each of the inductors, with both ends of the dielectric rod fixed to the two sides of the metal cavity.
10. The high-power cavity low-pass filter as described in claim 1, characterized in that, It also includes a medium block that is fixed to the metal cavity by screws.