Cavity Filter

Abstract

This application provides a cavity filter, relating to the field of filter technology. The cavity filter includes a housing portion forming a first cavity and a second cavity, with a first coupling window formed between the first and second cavities. A quarter-wavelength resonant unit is disposed within the first cavity, and a first coupled resonant unit and a second coupled resonant unit are symmetrically arranged about the longitudinal center plane of the second cavity within the second cavity. The quarter-wavelength resonant unit includes a first cylinder and a second cylinder coaxially arranged, with the diameter of the first cylinder being larger than the diameter of the second cylinder. The first coupled resonant unit includes a first resonant section and a second resonant section, with the impedance of the first resonant section being greater than the impedance of the second resonant section. The second coupled resonant unit includes a third resonant section and a fourth resonant section, with the impedance of the third resonant section being greater than the impedance of the fourth resonant section. The cavity filter provided by this application has the advantages of wide stopband and miniaturization.

Description

Technical Field

[0001] This application relates to the field of filter technology, and in particular to a cavity filter. Background Technology

[0002] Filters are indispensable passive devices in wireless communication systems. Their core function is to filter signals at both the transmitting and receiving ends, selecting target frequency band signals and suppressing interference frequency band signals to ensure the purity and transmission quality of system signals.

[0003] For cavity filters, the disordered distribution of higher harmonics directly affects their out-of-band suppression performance, causing the microwave system to form parasitic passbands in non-target frequency bands, thereby interfering with the frequency selection and noise reduction functions of the microwave system.

[0004] Existing technologies for suppressing higher harmonics in filters mainly include: first, introducing transmission zeros to suppress harmonics by extending the stopband range; second, using resonators with the same fundamental mode frequency but different higher-order modes to avoid parasitic passband generation by staggering harmonic frequencies; and third, combining the filter with a specific frequency suppression structure to directly block out-of-band harmonic transmission. However, current filter designs face problems such as insufficient miniaturization and difficulty in suppressing higher-order modes. Summary of the Invention

[0005] This application provides a cavity filter with the advantages of wide stopband and miniaturization.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] This application provides a cavity filter, comprising: a housing portion forming a first cavity and a second cavity, and a first coupling window formed between the first cavity and the second cavity; a quarter-wavelength resonant unit disposed within the first cavity, the quarter-wavelength resonant unit comprising a first cylinder and a second cylinder coaxially arranged, the bottom end of the first cylinder being connected to the top end of the second cylinder, the diameter of the first cylinder being larger than the diameter of the second cylinder; a first coupling resonant unit and a second coupling resonant unit disposed within the second cavity; the first coupling resonant unit comprising a first resonant portion and a second resonant portion, the top end of the first resonant portion being connected to the bottom end of the second resonant portion, the impedance of the first resonant portion being larger than the impedance of the second resonant portion; the second coupling resonant unit comprising a third resonant portion and a fourth resonant portion, the top end of the third resonant portion being connected to the bottom end of the fourth resonant portion, the impedance of the third resonant portion being larger than the impedance of the fourth resonant portion; the first coupling resonant unit and the second coupling resonant unit being symmetrically arranged about the longitudinal center plane of the second cavity, the longitudinal center plane being perpendicular to the plane containing the extension direction of the first coupling window.

[0008] In one possible implementation, the top wall of the outer casing is recessed inward to form a first partition, and the bottom wall of the outer casing is recessed inward to form a second partition. The first partition and the second partition are opposite to each other along a first direction and are spaced apart. A first coupling window is formed between the first partition and the second partition. The first direction is the direction from the top wall of the outer casing to the bottom wall. The first cavity and the second cavity are located on both sides of the first partition and the second partition along a second direction, which is perpendicular to the first direction.

[0009] In one possible implementation, the first resonant part and the third resonant part are cylinders with the same diameter.

[0010] In one possible implementation, the second resonant part is a column extending axially along the first resonant part, the column has a segmental cross-section, and the side of the column includes a connected arc surface and a first plane, the arc surface being coaxially arranged with the first resonant part; the fourth resonant part is a column extending axially along the third resonant part, the column has a segmental cross-section, and the side of the column includes a connected arc surface and a second plane, the arc surface being coaxially arranged with the third resonant part; the first plane and the second plane are opposite each other along the longitudinal center plane of the second cavity.

[0011] In one possible implementation, the bottom end of the second cylinder contacts the bottom wall of the first cavity, and a gap is provided between the top end of the first cylinder and the top wall of the first cavity; the bottom ends of the first resonant part and the third resonant part respectively contact the bottom end of the second cavity, and a gap is provided between the top ends of the second resonant part and the fourth resonant part respectively and the top end of the second cavity.

[0012] In one possible implementation, it further includes: a first feed probe and a second feed probe, the first feed probe being inserted into the first cavity and connected to the 1 / 4 wavelength resonant unit, and the second feed probe being inserted into the second cavity and connected to the second coupled resonant unit.

[0013] In one possible implementation, it further includes: a non-resonant node, which includes a first connecting portion, a second connecting portion, and a bending portion, one end of the first connecting portion being connected to a 1 / 4 wavelength resonant unit, one end of the second connecting portion being connected to a second coupled resonant unit, and the bending portion being connected between the first connecting portion and the second connecting portion.

[0014] In one possible implementation, the first connecting portion and the second connecting portion extend along the same straight line, and the bent portion is located on one side of the axial extension direction of the first connecting portion and the second connecting portion; the first connecting portion is perpendicularly connected to the 1 / 4 wavelength resonant unit, and the second connecting portion is perpendicularly connected to the second coupled resonant unit.

[0015] In one possible implementation, the bending portion includes two first extension segments and one second extension segment; the two first extension segments extend along an extension direction perpendicular to the first connecting portion and are opposite to each other and spaced apart along the extension direction perpendicular to the first connecting portion; one end of each of the two first extension segments is connected to the first connecting portion and the second connecting portion respectively, and the other end of each of the two first extension segments is connected to the second extension segment; the second extension segment extends along the extension direction of the first connecting portion.

[0016] In one possible implementation, it further includes: a coupling boss, which is disposed between the first coupled resonant unit and the second coupled resonant unit, and the bottom end of the coupling boss is connected to the bottom wall of the second cavity.

[0017] The cavity filter provided in this application includes a housing portion, which is configured to form a first cavity and a second cavity, and a first coupling window is configured between the first cavity and the second cavity. Energy is transferred between the first cavity and the second cavity through the first coupling window.

[0018] The first cavity houses a quarter-wavelength resonant unit, while the second cavity houses a first coupled resonant unit and a second coupled resonant unit. The quarter-wavelength resonant unit comprises a first cylinder and a second cylinder coaxially arranged, with the bottom of the first cylinder connected to the top of the second cylinder. The diameter of the first cylinder is larger than the diameter of the second cylinder. The quarter-wavelength resonant unit achieves a step impedance characteristic through the abrupt change in the diameters of the first and second cylinders.

[0019] The first coupled resonant unit includes a first resonant section and a second resonant section. The impedance of the first resonant section is greater than the impedance of the second resonant section. The top end of the first resonant section is connected to the bottom end of the second resonant section, forming an impedance abrupt change interface. The second coupled resonant unit includes a third resonant section and a fourth resonant section. The impedance of the third resonant section is greater than the impedance of the fourth resonant section. The top end of the third resonant section is connected to the bottom end of the fourth resonant section, forming an impedance abrupt change interface.

[0020] In this way, by using the stepped impedance structure of the quarter-wavelength resonant unit, the first coupled resonant unit, and the second coupled resonant unit, the cavity filter can shorten the electrical length of the resonant unit without reducing the quality factor, thus achieving miniaturization. At the same time, the stepped impedance structure can effectively suppress higher harmonics by utilizing impedance discontinuities, thereby significantly extending the stopband width of the cavity filter.

[0021] Furthermore, the first and second coupled resonant units are symmetrically arranged about the longitudinal center plane of the second cavity, with the longitudinal center plane perpendicular to the plane containing the extension direction of the first coupling window. In this way, the first and second coupled resonant units can form a strongly coupled resonant pair structure. Based on the antiphase characteristics of odd-mode and even-mode electromagnetic fields, the symmetrically arranged first and second coupled resonant units can form a mixed odd-even mode coupling, thereby increasing the coupling degrees of freedom. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the cavity filter structure provided in an embodiment of this application;

[0024] Figure 2 A top view of the cavity filter provided in an embodiment of this application;

[0025] Figure 3 The S-parameter frequency response curve of the cavity filter provided in this application embodiment is shown.

[0026] Explanation of reference numerals in the attached figures:

[0027] 1-Cavity filter;

[0028] 100 - Outer shell; 200 - Non-resonant node; 300 - Coupling boss; 400 - First feed probe; 500 - Second feed probe;

[0029] 110 - First cavity; 120 - Second cavity; 130 - First coupling window; 210 - First connecting part; 220 - Second connecting part; 230 - Bending part;

[0030] 111 - 1 / 4 wavelength resonant unit; 121 - First coupled resonant unit; 122 - Second coupled resonant unit; 231 - First extension segment; 232 - Second extension segment;

[0031] 1111 - First cylinder; 1112 - Second cylinder; 1211 - First resonant part; 1212 - Second resonant part; 1221 - Third resonant part; 1222 - Fourth resonant part;

[0032] 12121 - First plane; 12122 - First arc surface; 12221 - Second plane; 12222 - Second arc surface. Detailed Implementation

[0033] As described in the background section, in wireless communication systems, filters, as key passive components, have the core function of filtering out spurious noise at the transmitting end to ensure the purity of the transmitted signal. Simultaneously, at the receiving end, they accurately extract the target frequency band signal from the complex electromagnetic signals received by the antenna, suppressing out-of-band interference. The out-of-band rejection capability and frequency selectivity of the filter directly affect the spurious signal suppression performance of the transmitter, the noise figure optimization effect of the receiver, and the anti-interference capability, signal receiving sensitivity, and spectrum utilization efficiency of the entire wireless communication link.

[0034] Currently, filters can be classified into cavity filters, planar filters (such as microstrip filters and stripline filters), and dielectric filters according to their structural form. Among them, cavity filters are widely used in scenarios with stringent requirements for signal purity and power processing, such as base stations and radar, due to their high quality factor, low insertion loss, and high power handling capacity.

[0035] However, compared to planar filters, the three-dimensional resonant structure of cavity filters makes their higher harmonic distribution more complex. When operating at the fundamental mode frequency, the electromagnetic coupling between the metal cavity wall and the resonant rod can easily excite unexpected higher mode resonances, resulting in parasitic passbands at frequencies that are integer multiples or non-integer multiples of the fundamental frequency, which seriously interferes with the signal suppression effect outside the target frequency band.

[0036] In related technologies, the parasitic passband problem caused by higher harmonics in cavity filters is mainly suppressed through the following technical approaches: one is to construct transmission zeros within the target stopband by introducing parallel short-circuit stubs or loading reactive components into the resonant structure of the cavity filter. While this method can extend the stopband, the reduction in lateral dimensions is limited, and the suppression effect on higher harmonics depends on complex parameter adjustments.

[0037] Secondly, a filter network is constructed using multiple resonator units with the same fundamental mode frequency but different resonant characteristics in higher-order modes. By precisely adjusting the geometric parameters of each resonator, their fundamental frequency resonant points are made to coincide to ensure passband consistency, while the resonant frequencies of higher-order modes are staggered to avoid resonance superposition at integer or non-integer multiples of the fundamental frequency. However, in practical applications, passband consistency is easily deteriorated due to manufacturing errors.

[0038] Third, the cavity filter housing is electromagnetically coupled with an additional structure having frequency selectivity to form a "filter-suppression structure" composite system. This method has poor integration and low electromagnetic coupling efficiency.

[0039] Therefore, wide stopband filters designed based on existing technologies often face challenges such as insufficient miniaturization and difficulty in suppressing high-order modes.

[0040] In view of this, embodiments of this application provide a cavity filter.

[0041] This application employs a quarter-wavelength resonant unit and two coupled resonant units. The fundamental mode resonance of the quarter-wavelength resonant unit forms the first-order passband, while the two symmetrically distributed coupled resonant units form the latter two orders through odd-mode and even-mode resonance. In this way, a third-order passband can be formed through the coordinated resonance of multiple resonant units. Compared with traditional multi-stage cavity cascade structures, this reduces the number of cavities, thus enabling miniaturized design.

[0042] Furthermore, the researchers noted that traditional uniform impedance resonant units suffer from drawbacks such as large size and reliance on complex parameter adjustments for harmonic suppression. Step impedance structures, however, can shorten the electrical length of the resonant unit without reducing the quality factor through impedance abrupt changes. Therefore, the researchers constructed a step impedance structure with one quarter-wavelength resonant unit and two coupled resonant units. By combining the quarter-wavelength step impedance resonant unit with symmetrically arranged strongly coupled step impedance resonant units, miniaturization was further achieved. Moreover, the impedance abrupt change characteristic of the step impedance structure alters the resonant frequency of higher-order modes, avoiding parasitic passband concentration.

[0043] In addition, the design of the step impedance structure, combined with the symmetrical layout of the coupled resonant unit, can induce multi-path signal inversion, thereby forming multiple transmission zeros in a wide frequency band to jointly suppress out-of-band interference.

[0044] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0045] Figure 1 This is a schematic diagram of the cavity filter provided in an embodiment of this application. (Refer to...) Figure 1 As shown, this application provides a cavity filter 1, which can be used in wireless communication scenarios of indoor distributed systems, such as shopping malls, airports, subways, and other places with high-frequency communication demand. The cavity filter 1 can effectively improve the purity of signal processing and anti-interference capability, ensuring the reliability and efficiency of the communication system. Alternatively, the cavity filter 1 can also be used in high-density communication environments where multiple frequency bands coexist, such as scenarios where 5G and 4G spectrums are shared. The cavity filter 1 can accurately extract the target frequency band signal and suppress out-of-band interference, ensuring the signal purity and spectrum utilization efficiency of the base station link.

[0046] Reference Figure 1As shown, the cavity filter 1 includes a housing portion 100. In this embodiment, the housing portion 100 is described as having a rectangular structure. The housing portion 100 may include a top wall, a bottom wall, a front wall, a rear wall, a left side wall, and a right side wall. The top wall and the bottom wall are along... Figure 1 The walls are arranged opposite each other and spaced apart along the Z-axis, with the front and rear walls along... Figure 1 The walls are arranged opposite each other and spaced apart along the Y-axis, with the left and right walls along... Figure 1 The X-axis direction is relative and spaced apart.

[0047] The outer shell 100 is configured to form a first cavity 110 and a second cavity 120, and a first coupling window 130 is configured between the first cavity 110 and the second cavity 120. The first coupling window 130 serves as an internal coupling channel between the first cavity 110 and the second cavity 120, enabling energy transfer between the first cavity 110 and the second cavity 120.

[0048] In some embodiments, the top wall of the outer casing 100 may be recessed inward to form a first partition, and the bottom wall of the outer casing 100 may be recessed inward to form a second partition. In this embodiment, the direction from the top wall of the outer casing 100 to the bottom wall is defined as the first direction (corresponding to...). Figure 1 (Z-axis direction), second direction (corresponding to) Figure 1 The first cavity 110 and the second cavity 120 are located on opposite sides of the first partition and the second partition along the second direction, respectively. Furthermore, the first partition and the second partition are opposite to each other along the first direction and are spaced apart; therefore, the gap between the first partition and the second partition forms a first coupling window 130. (The X-axis direction is perpendicular to the first direction.)

[0049] In other embodiments, the outer casing 100 may further include a metal partition (not shown in the figure), which extends vertically along a first direction and is fixedly connected between the top wall and the bottom wall of the outer casing 100, thereby dividing the internal space of the outer casing 100 into a first cavity 110 and a second cavity 120 distributed along a second direction. A first coupling window 130 is provided on the metal partition, which serves as an electromagnetic coupling channel connecting the first cavity 110 and the second cavity 120.

[0050] It should be noted that as long as effective electromagnetic coupling can be achieved between the first cavity 110 and the second cavity 120, the embodiments of this application do not specifically limit the construction form of the first coupling window 130.

[0051] Continue to refer to Figure 1 As shown, a quarter-wavelength resonant unit 111 is disposed in the first cavity 110. The quarter-wavelength resonant unit 111 refers to the resonant unit whose electrical length is one-quarter of the operating wavelength. The quarter-wavelength resonant unit 111 adopts a stepped impedance resonant structure.

[0052] Specifically, the quarter-wavelength resonant unit 111 includes a first cylinder 1111 and a second cylinder 1112 arranged coaxially, with the bottom end of the first cylinder 1111 connected to the top end of the second cylinder 1112. The diameter of the first cylinder 1111 is larger than the diameter of the second cylinder 1112, and a step impedance characteristic is formed by the abrupt change in the diameters of the first cylinder 1111 and the second cylinder 1112.

[0053] The bottom end of the second cylinder 1112 contacts the bottom wall of the first cavity 110, which is equivalent to a short circuit. The top end of the first cylinder 1111 is separated from the top wall of the first cavity 110, which is equivalent to an open circuit.

[0054] Continue to refer to Figure 1 As shown, a first coupled resonant unit 121 and a second coupled resonant unit 122 are disposed within the second cavity 120. The first coupled resonant unit 121 and the second coupled resonant unit 122 are symmetrically arranged about the longitudinal center plane of the second cavity 120. In this embodiment, the longitudinal center plane is parallel to the plane formed by the X-axis and Z-axis directions, and the second cavity 120 is symmetrical about the longitudinal center plane along the Y-axis direction.

[0055] In this way, the first coupled resonant unit 121 and the second coupled resonant unit 122 can form a strongly coupled resonant pair structure. Based on the antiphase characteristics of odd-mode and even-mode electromagnetic fields, the symmetrically arranged first coupled resonant unit 121 and second coupled resonant unit 122 can form a mixed coupling of odd and even modes at the longitudinal central plane, thereby increasing the coupling degree of freedom.

[0056] The first coupled resonant unit 121 includes a first resonant section 1211 and a second resonant section 1212. The top end of the first resonant section 1211 is connected to the bottom end of the second resonant section 1212. The impedance of the first resonant section 1211 is greater than the impedance of the second resonant section 1212. An impedance abrupt change interface is formed at the junction of the top end of the first resonant section 1211 and the bottom end of the second resonant section 1212. The second coupled resonant unit 122 includes a third resonant section 1221 and a fourth resonant section 1222. The top end of the third resonant section 1221 is connected to the bottom end of the fourth resonant section 1222. The impedance of the third resonant section 1221 is greater than the impedance of the fourth resonant section 1222. An impedance abrupt change interface is formed at the junction of the top end of the third resonant section 1221 and the bottom end of the fourth resonant section 1222.

[0057] The bottom ends of the first resonant part 1211 and the third resonant part 1221 respectively contact the bottom end of the second cavity 120, forming a short circuit. The top ends of the second resonant part 1212 and the fourth resonant part 1222 are respectively spaced from the top end of the second cavity 120, forming an open circuit.

[0058] Figure 2 This is a top view of a cavity filter provided in an embodiment of this application. (Refer to...) Figure 2 The second resonant part 1212 includes a first plane 12121, and the fourth resonant part 1222 includes a second plane 12221. Furthermore, the first plane 12121 and the second plane 12221 are arranged opposite to each other along the longitudinal center plane of the second cavity 120, and the longitudinal center plane is perpendicular to the plane where the extension direction of the first coupling window 130 is located.

[0059] In one embodiment, the first resonant part 1211 and the third resonant part 1221 can each be a cylinder with the same diameter. The second resonant part 1212 is a cylinder extending along the axial direction of the first resonant part 1211. The cross-section of the cylinder is segmental, and the side surface of the cylinder includes a first arc surface 12122 and a first plane 12121 connected to each other. The first arc surface 12122 is coaxially arranged with the first resonant part 1211. The fourth resonant part 1222 is a cylinder extending along the axial direction of the third resonant part 1221. The cross-section of the cylinder is segmental, and the side surface of the cylinder includes a second arc surface 12222 and a second plane 12221 connected to each other. The second arc surface 12222 is coaxially arranged with the third resonant part 1221.

[0060] In this context, a segmental shape refers to the area remaining after a circle is cut by a non-diameter chord, which is enclosed by the chord and the corresponding arc. In the embodiments of this application, the chord in the segmental shape corresponds to the first plane 12121 and the second plane 12221, and the arc in the segmental shape corresponds to the first arc surface 12122 and the second arc surface 12222.

[0061] In this way, by setting the first plane 12121 and the second plane 12221, the effective overlap area of ​​the first coupled resonant unit 121 and the second coupled resonant unit 122 at the open-circuit end can be significantly increased. According to electromagnetic coupling theory, the edge electric field effect between parallel conductor surfaces will increase with the increase of the facing area, thereby increasing the equivalent capacitance value between the first coupled resonant unit 121 and the second coupled resonant unit 122. The increase in equivalent capacitance can enhance the electric field coupling strength between the first coupled resonant unit 121 and the second coupled resonant unit 122.

[0062] Compared to uniform impedance resonators, the quarter-wavelength resonant unit 111, the first coupled resonant unit 121, and the second coupled resonant unit 122 of this application, through a step impedance resonant structure, can construct an impedance ratio. By adjusting the impedance ratio, the distribution of equivalent inductance and capacitance can be optimized, thereby shortening the electrical length of the resonant unit without reducing the quality factor, achieving structural miniaturization. Simultaneously, the step impedance structure can effectively suppress higher harmonics by utilizing impedance discontinuities, thus significantly extending the stopband width of the cavity filter 1.

[0063] The fundamental mode resonant frequency of the quarter-wavelength resonant unit 111 within the first cavity 110 can constitute the first-order response of the passband. The first coupled resonant unit 121 and the second coupled resonant unit 122 within the second cavity 120 form a strongly coupled structure through symmetrical arrangement. Utilizing the anti-phase electromagnetic field characteristics of the odd-mode and even-mode resonant modes, two independent resonant responses can be excited within the second cavity 120. Thus, the quarter-wavelength resonant unit 111, the first coupled resonant unit 121, and the second coupled resonant unit 122 can complete the third-order passband response within both the first cavity 110 and the second cavity 120. Compared to the traditional structure requiring three cascaded cavities, the cavity filter 1 of this application can reduce the volume of one physical cavity, further realizing the miniaturization design of the cavity filter 1.

[0064] Reference Figure 1 and Figure 2 As shown, the cavity filter 1 also includes a non-resonant node 200, which is a 1 / 4 wavelength transmission line non-resonant node 200.

[0065] The non-resonant node 200 includes a first connecting portion 210, a second connecting portion 220, and a bending portion 230. One end of the first connecting portion 210 is connected to the 1 / 4 wavelength resonant unit 111, one end of the second connecting portion 220 is connected to the second coupled resonant unit 122, and the bending portion 230 is connected between the first connecting portion 210 and the second connecting portion 220.

[0066] The non-resonant node 200, through its quarter-wavelength transmission line characteristics, can effectively block the propagation path of spurious modes induced by capacitive loading effects, suppress the interference of spurious resonance on the main passband signal, and significantly improve the passband return loss performance of the cavity filter 1. Furthermore, the non-resonant node 200 can also reconstruct the coupling phase relationship between the quarter-wavelength resonant unit 111 and the second coupled resonant unit 122 while maintaining efficient passband signal transmission, thereby optimizing the impedance matching characteristics of the cavity filter 1.

[0067] In some embodiments, the first connecting portion 210 and the second connecting portion 220 may extend along the same straight line, and the first connecting portion 210 is perpendicularly connected to the 1 / 4 wavelength resonant unit 111, and the second connecting portion 220 is perpendicularly connected to the second coupled resonant unit 122. The bending portion 230 is located on one side of the axial extension direction of the first connecting portion 210 and the second connecting portion 220.

[0068] Specifically, the bending portion 230 may include two first extension segments 231 and one second extension segment 232. The two first extension segments 231 extend in a direction perpendicular to the first connecting portion 210, and are opposite to each other and spaced apart in the same direction. One end of each of the two first extension segments 231 is connected to the first connecting portion 210 and the second connecting portion 220, respectively, and the other end of each of the two first extension segments 231 is connected to the second extension segment 232. The second extension segment 232 extends in the direction of the first connecting portion 210.

[0069] With this configuration, the bending section 230 can reduce the axial length of the non-resonant node 200 by folding the transmission line, thereby meeting the miniaturization requirements while maintaining the 1 / 4 wavelength electrical characteristics.

[0070] In addition, continue to refer to Figure 1 As shown, the cavity filter 1 also includes a coupling boss 300. The coupling boss 300 is disposed between the first coupled resonant unit 121 and the second coupled resonant unit 122. Furthermore, the bottom end of the coupling boss 300 is connected to the bottom wall of the second cavity 120. Current conduction exists on the surface of the coupling boss 300, enabling magnetic coupling between the first coupled resonant unit 121 and the second coupled resonant unit 122. The coupling strength increases with the height of the boss. By fine-tuning the height of the coupling boss 300, the coupling coefficient between the first coupled resonant unit 121 and the second coupled resonant unit 122 can be optimized to compensate for frequency shift.

[0071] Continue to refer to Figure 1 and Figure 2 As shown, the cavity filter 1 further includes a first feed probe 400 and a second feed probe 500. The first feed probe 400 extends into the first cavity 110 and is connected to the quarter-wavelength resonant unit 111. The second feed probe 500 extends into the second cavity 120 and is connected to the first coupling resonant unit 121. Exemplarily, the first feed probe 400 and the second feed probe 500 can be Sub-Miniature Version A (SMA) connector feed probes. The first feed probe 400 and the second feed probe 500 can effectively reduce signal reflection and ensure efficient energy transmission at the filter's input and output ports.

[0072] The first feed probe 400 serves as the RF input port of the cavity filter 1. Connected to the quarter-wavelength resonant unit 111, it inputs an external RF signal into the first cavity 110, exciting the fundamental mode of the quarter-wavelength resonant unit 111. The second feed probe 500 serves as the RF output port of the cavity filter 1, connected to the first coupling resonant unit 121, and is used to extract the RF signal after cavity filtering, completing the signal transmission link. Alternatively, the second feed probe 500 can serve as the RF input port, and the first feed probe 400 as the RF output port. This embodiment does not impose specific limitations on this.

[0073] The cavity filter 1 of this application can be manufactured using multi-jet fusion 3D printing technology. For example, this application can be manufactured using multi-jet fusion (MJF).

[0074] Specifically, a movable build unit containing the 3D model data of cavity filter 1 is first placed into the printing equipment. The material recovery system reciprocates in the build area, applying powder material layer by layer. During printing, the printing and melting carriages move synchronously, preheating the powder to the process-set temperature. Then, the melt is precisely sprayed into a designated area of ​​the powder bed through inkjet nozzles, achieving selective material fusion. After each material layer is printed, the build unit automatically descends by one layer thickness, creating space for the next layer of powder deposition. This cycle continues until the overall structure is formed. The printing accuracy is controlled within ±0.15mm / 100mm.

[0075] Among them, the powder material can be selected from polydodecanone (PA12) material with excellent impact resistance and chemical stability to ensure that the printed cavity filter 1 structure has sufficient mechanical strength.

[0076] After printing, the following post-processing steps are required: First, a cooling process is performed on the printed cavity filter 1 component. Operators can allow the cavity filter 1 component to cool and solidify fully by natural placement or using dedicated cooling equipment. Next, a powder recovery process is performed, collecting unmelted powder material from the printing chamber into a dedicated storage container for recycling. Following this, a surface cleaning process is executed, using techniques such as sandblasting, air blasting, or water rinsing to thoroughly remove residual powder from the surface of the cavity filter 1 component. Finally, a metallization process is performed, including: first, deep cleaning of the component using a dedicated degreasing agent; then, chemical activation of the component surface; next, chemical copper plating; and finally, electroplating to form a uniform copper layer 10μm thick. After drying, the entire processing flow is complete.

[0077] Thus, the cavity filter 1 of this application, manufactured using 3D printing technology, can achieve one-piece molding, maintaining high molding precision. Furthermore, the printed filter component possesses both excellent electromagnetic and mechanical properties.

[0078] Figure 3 The S-parameter frequency response curve of the cavity filter 1 provided in this embodiment of the application is shown in the figure. (Refer to...) Figure 3 As shown, cavity filter 1 forms a passband response at a center frequency of 2.645 GHz, with a passband bandwidth of 690 MHz. The first harmonic is located at 12.05 GHz, with a ratio of 4.55 to the center frequency. The return loss within the passband is better than 16 dB, verifying good impedance matching characteristics.

[0079] In addition, cavity filter 1 generates four transmission zeros at frequencies of 1.9 GHz, 3.98 GHz, 9.02 GHz, and 10.03 GHz. The transmission zero at 1.9 GHz is formed by the phase inversion effect of the multipath signal between the first coupled resonant unit 121 and the second coupled resonant unit 122. The generation of the transmission zero at 3.98 GHz depends on the asymmetric layout characteristics of the first feed probe 400 and the second feed probe 500. The transmission zeros at 9.02 GHz and 10.03 GHz originate from the electromagnetic hybrid coupling mechanism between the quarter-wavelength resonant unit 111, the first coupled resonant unit 121, and the second coupled resonant unit 122, as well as the interaction of higher-order resonant modes not used in the passband. The synergistic effect of these transmission zeros significantly extends the stopband suppression range, enabling cavity filter 1 to achieve wide stopband characteristics while possessing excellent frequency selectivity.

[0080] It should be noted that the embodiments referred to in the specification, such as "one embodiment," "embodiment," "exemplary embodiment," and "some embodiments," may include specific features, structures, or characteristics, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not, is within the knowledge scope of those skilled in the art.

[0081] Generally speaking, terms should be understood at least in part by their use in context. For example, at least in part by context, the term "one or more" as used in the text can be used to describe any feature, structure, or characteristic of the singular meaning, or a combination of features, structures, or characteristics of the plural meaning. Similarly, at least in part by context, terms such as "one" or "" can also be understood to convey either singular or plural usage.

[0082] It should be readily understood that the terms “on,” “above,” and “on top of” in this application should be interpreted in the broadest possible sense, such that “on” means not only “directly on something” but also “on something” with an intermediate feature or layer therebetween, and that “above” or “on top of” means not only “on something” but also “on something” without an intermediate feature or layer therebetween (i.e., directly on something).

[0083] Furthermore, for ease of explanation, spatially relative terms such as "below," "below," "under," "above," and "above" may be used to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation other than those shown in the figures. The device may have other orientations (rotated 90° or in other orientations), and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A cavity filter, characterized in that, include: The outer shell portion is configured to form a first cavity and a second cavity, and a first coupling window is configured between the first cavity and the second cavity; The first cavity is provided with a 1 / 4 wavelength resonant unit, which includes a first cylinder and a second cylinder arranged coaxially. The bottom end of the first cylinder is connected to the top end of the second cylinder, and the diameter of the first cylinder is larger than the diameter of the second cylinder. The second cavity is provided with a first coupled resonant unit and a second coupled resonant unit; The first coupled resonant unit includes a first resonant part and a second resonant part, the top end of the first resonant part is connected to the bottom end of the second resonant part, and the impedance of the first resonant part is greater than the impedance of the second resonant part; The second coupled resonant unit includes a third resonant section and a fourth resonant section, the top end of the third resonant section is connected to the bottom end of the fourth resonant section, and the impedance of the third resonant section is greater than the impedance of the fourth resonant section; The first coupled resonant unit and the second coupled resonant unit are symmetrically arranged about the longitudinal center plane of the second cavity, and the longitudinal center plane is perpendicular to the plane where the extension direction of the first coupling window is located.

2. The cavity filter according to claim 1, characterized in that, The top wall of the outer casing is recessed inward to form a first partition, and the bottom wall of the outer casing is recessed inward to form a second partition. The first partition and the second partition are opposite to each other along a first direction and are spaced apart. A first coupling window is formed between the first partition and the second partition. The first direction is the direction from the top wall of the outer casing to the bottom wall. The first cavity and the second cavity are located on both sides of the first partition and the second partition along the second direction, respectively, and the second direction is perpendicular to the first direction.

3. The cavity filter according to claim 1, characterized in that, The first resonant part and the third resonant part are both cylinders with the same diameter.

4. The cavity filter according to claim 3, characterized in that, The second resonant part is a column extending along the axial direction of the first resonant part. The cross-section of the column is a segmental shape. The side of the column includes a connected arc surface and a first plane. The arc surface is arranged coaxially with the first resonant part. The fourth resonant part is a column extending along the axial direction of the third resonant part. The cross-section of the column is a segmental shape. The side of the column includes a connected arc surface and a second plane. The arc surface is arranged coaxially with the third resonant part. The first plane and the second plane are opposite each other along the longitudinal center plane of the second cavity.

5. The cavity filter according to claim 1, characterized in that, The bottom end of the second cylinder contacts the bottom wall of the first cavity, and a gap is provided between the top end of the first cylinder and the top wall of the first cavity. The bottom ends of the first resonant part and the third resonant part are respectively in contact with the bottom end of the second cavity, and the top ends of the second resonant part and the fourth resonant part are respectively spaced apart from the top ends of the second cavity.

6. The cavity filter according to claim 1, characterized in that, Also includes: A first feed probe and a second feed probe, the first feed probe being inserted into the first cavity and connected to the 1 / 4 wavelength resonant unit, and the second feed probe being inserted into the second cavity and connected to the first coupled resonant unit.

7. The cavity filter according to claim 1, characterized in that, Also includes: The non-resonant node includes a first connecting part, a second connecting part, and a bending part. One end of the first connecting part is connected to the 1 / 4 wavelength resonant unit, one end of the second connecting part is connected to the second coupled resonant unit, and the bending part is connected between the first connecting part and the second connecting part.

8. The cavity filter according to claim 7, characterized in that, The first connecting portion and the second connecting portion extend along the same straight line, and the bent portion is located on one side of the axial extension direction of the first connecting portion and the second connecting portion; The first connecting part is vertically connected to the 1 / 4 wavelength resonant unit, and the second connecting part is vertically connected to the second coupled resonant unit.

9. The cavity filter according to claim 7, characterized in that, The bent portion includes two first extension sections and one second extension section; The two first extension segments extend in a direction perpendicular to the first connecting portion, and are opposite to each other and spaced apart in the same direction. One end of each of the two first extension segments is connected to the first connecting portion and the second connecting portion, respectively, and the other end of each of the two first extension segments is connected to the second extension segment; The second extension extends along the extension direction of the first connecting portion.

10. The cavity filter according to claim 1, characterized in that, Also includes: A coupling boss is disposed between the first coupled resonant unit and the second coupled resonant unit, and the bottom end of the coupling boss is connected to the bottom wall of the second cavity.

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