Cavity filter

Abstract

The invention provides a cavity filter, and relates to the technical field of filters. The cavity filter comprises a shell part, the shell part is constructed to form a first cavity and a second cavity, and a first coupling window is constructed between the first cavity and the second cavity. Wherein the first cavity is internally provided with a 1 / 4 wavelength resonance unit, and the second cavity is internally provided with a first coupling resonance unit and a second coupling resonance unit which are symmetrically arranged about the longitudinal center plane of the second cavity. The 1 / 4 wavelength resonance unit comprises a first cylinder and a second cylinder which are coaxially arranged, and the diameter of the first cylinder is larger than that of the second cylinder. The first coupling resonance unit comprises a first resonance part and a second resonance part, and the impedance of the first resonance part is larger than that of the second resonance part. The second coupling resonance unit comprises a third resonance part and a fourth resonance part, and the impedance of the third resonance part is larger than that of the fourth resonance part. The cavity filter provided by the invention has the advantages of wide stop band and miniaturization.

Description

Technical Field

[0001] The present application relates to the field of filter technology, and in particular to a cavity filter. Background Art

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

[0003] For cavity filters, the chaotic distribution of high-order harmonics will directly affect their out-of-band suppression performance, causing the microwave system to form parasitic passbands in non-target frequency bands, thereby interfering with the microwave system's frequency selection and noise removal functions.

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

[0005] The present application provides a cavity filter having the advantages of wide stopband and miniaturization.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions:

[0007] The present application provides a cavity filter, comprising: an outer shell, the outer shell 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 is arranged in the first cavity, the quarter-wavelength resonant unit comprising a first cylinder and a second cylinder arranged coaxially, the bottom end of the first cylinder being connected to the top end of the second cylinder, and 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 are arranged in the second cavity; the first coupling resonant unit comprises 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 larger than the impedance of the second resonant part; the second coupling resonant unit comprises a third resonant part and a fourth resonant part, the top end of the third resonant part is connected to the bottom end of the fourth resonant part, and the impedance of the third resonant part is larger than the impedance of the fourth resonant part; the first coupling resonant unit and the second coupling resonant unit are symmetrically arranged about a 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.

[0008] In one possible embodiment, the top wall of the outer shell portion is recessed inward to form a first partition portion, and the bottom wall of the outer shell portion is recessed inward to form a second partition portion. The first partition portion and the second partition portion are opposite to each other and have a gap along a first direction, and a first coupling window is formed between the first partition portion and the second partition portion; wherein the first direction is the direction from the top wall of the outer shell portion toward the bottom wall; the first cavity and the second cavity are respectively located on both sides of the first partition portion and the second partition portion along the second direction, and the second direction is perpendicular to the first direction.

[0009] In a possible implementation manner, the first resonant part and the third resonant part are cylinders with equal diameters.

[0010] In one possible embodiment, the second resonant portion is a cylinder extending axially along the first resonant portion, the cross-section of the cylinder is in the shape of a circular segment, the side surface of the cylinder includes a connected arc surface and a first plane, and the arc surface is coaxially arranged with the first resonant portion; the fourth resonant portion is a cylinder extending axially along the third resonant portion, the cross-section of the cylinder is in the shape of a circular segment, the side surface of the cylinder includes a connected arc surface and a second plane, and the arc surface is coaxially arranged with the third resonant portion; the first plane and the second plane are opposite to each other along the longitudinal center plane of the second cavity.

[0011] In a possible embodiment, 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 end of the first resonant part and the bottom end of the third resonant part respectively contact the bottom end of the second cavity, and the top end of the second resonant part and the top end of the fourth resonant part respectively have a gap provided between them and the top end of the second cavity.

[0012] In a possible implementation, the system further includes: a first feeding probe and a second feeding probe, wherein the first feeding probe is inserted into the first cavity and connected to the 1 / 4 wavelength resonance unit, and the second feeding probe is inserted into the second cavity and connected to the second coupling resonance unit.

[0013] In a possible embodiment, it further includes: a non-resonant node, the non-resonant node including a first connecting portion, a second connecting portion and a bending portion, one end of the first connecting portion is connected to the 1 / 4 wavelength resonance unit, one end of the second connecting portion is connected to the second coupling resonance unit, and the bending portion is connected between the first connecting portion and the second connecting portion.

[0014] In a possible embodiment, the first connecting portion and the second connecting portion extend along the same straight line, and the bending 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 vertically connected to the 1 / 4 wavelength resonant unit, and the second connecting portion is vertically connected to the second coupling resonant unit.

[0015] In a possible embodiment, 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 the two first extension segments is respectively connected to the first connecting portion and the second connecting portion, and the other end 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 a possible implementation, the system further includes: a coupling boss, the coupling boss is disposed between the first coupling resonance unit and the second coupling resonance 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 the present application includes a shell portion, wherein the shell portion is structured to form a first cavity and a second cavity, and a first coupling window is structured to form a first coupling window between the first cavity and the second cavity. The first cavity and the second cavity realize energy transfer through the first coupling window.

[0018] A quarter-wavelength resonant unit is disposed within the first cavity, and a first coupled resonant unit and a second coupled resonant unit are disposed within the second cavity. The quarter-wavelength resonant unit comprises a first cylinder and a second cylinder arranged coaxially, with the bottom end of the first cylinder connected to the top end of the second cylinder, and the diameter of the first cylinder being larger than the diameter of the second cylinder. The quarter-wavelength resonant unit forms a step impedance characteristic through the sudden change in the diameter of the first cylinder and the diameter of the second cylinder.

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

[0020] In this way, through 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, achieving a miniaturized design. Furthermore, the stepped impedance structure effectively suppresses higher harmonics by utilizing impedance discontinuities, significantly expanding the cavity filter's stopband width.

[0021] Furthermore, the first and second coupling resonant units are symmetrically arranged about the longitudinal center plane of the second cavity, with the longitudinal center plane being perpendicular to the plane in which the first coupling window extends. Thus, the first and second coupling resonant units form a strongly coupled resonant pair structure. Due to the anti-phase characteristics of odd-mode and even-mode electromagnetic fields, the symmetrical arrangement of the first and second coupling resonant units enables mixed odd- and even-mode coupling, thereby increasing the coupling degrees of freedom. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0023] Figure 1 A schematic structural diagram of a cavity filter provided in an embodiment of the present application;

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

[0025] Figure 3 An S-parameter frequency response curve of the cavity filter provided in an embodiment of the present application.

[0026] Description of reference numerals:

[0027] 1- Cavity filter;

[0028] 100 - housing; 200 - non-resonant node; 300 - coupling boss; 400 - first feeding probe; 500 - second feeding probe;

[0029] 110 - first cavity; 120 - second cavity; 130 - first coupling window; 210 - first connecting portion; 220 - second connecting portion; 230 - bending portion;

[0030] 111-1 / 4 wavelength resonant unit; 121-first coupled resonant unit; 122-second coupled resonant unit; 231-first extension section; 232-second extension section;

[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 DESCRIPTION

[0033] As mentioned in the background, filters are key passive components in wireless communication systems. Their core function is to filter out spurious noise at the transmitter end, ensuring the purity of the transmitted signal. Simultaneously, at the receiver end, they accurately extract the target frequency band signal from the complex electromagnetic signals received by the antenna, suppressing out-of-band interference. The filter's out-of-band suppression capability and frequency selection characteristics directly impact the transmitter's spurious signal suppression performance, the receiver's noise figure optimization, and the overall wireless communication link's anti-interference capability, signal reception sensitivity, and spectrum efficiency.

[0034] Currently, filters can be categorized by their structural form into cavity filters, planar filters (such as microstrip filters and stripline filters), and dielectric filters. Cavity filters, due to their high quality factor, low insertion loss, and high power handling capacity, are widely used in applications such as base stations and radars, which have stringent requirements for signal purity and power handling.

[0035] However, compared to planar filters, the three-dimensional resonant structure of cavity filters makes the distribution of higher-order harmonics more complex. When operating at the fundamental mode frequency, the electromagnetic coupling between the metal cavity walls and the resonant rods can easily excite unintended higher-order mode resonances, resulting in the formation of parasitic passbands at integer or non-integer multiples of the fundamental frequency, which seriously interferes with the suppression of signals outside the target frequency band.

[0036] Related technologies address the parasitic passband issues caused by higher-order harmonics in cavity filters through the following approaches: First, by introducing parallel short-circuit stubs and loading reactive elements into the cavity filter's resonant structure, transmission zeros are created within the target stopband. While this approach can extend the stopband, it offers limited lateral size reduction, and its effectiveness in suppressing higher-order modes relies on complex parameter adjustments.

[0037] The second method is to use multiple resonator units with the same fundamental mode frequency but different high-order mode resonance characteristics to form a filtering network. By precisely controlling the geometric parameters of each resonator, the fundamental frequency resonance points are made to coincide to ensure passband consistency, while the high-order mode resonance frequencies are staggered to avoid the formation of resonant superposition at integer or non-integer multiples of the fundamental frequency. However, in actual applications, the passband consistency may be deteriorated due to processing errors.

[0038] The third method is to electromagnetically couple the outer shell of the cavity filter with an additional structure with frequency selection characteristics to form a "filter-suppression structure" composite system. This method has poor integration and low electromagnetic coupling efficiency.

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

[0040] In view of this, an embodiment of the present application provides 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 passband order, while the two symmetrically distributed coupled resonant units form the second two orders through odd-mode and even-mode resonant modes. This allows for a third-order passband to be formed through the coordinated resonance of multiple resonant units. Compared to a traditional multi-stage cavity cascade structure, one cavity can be eliminated, enabling a miniaturized design.

[0042] In addition, the researchers of this application noticed that the traditional uniform impedance resonance unit has the pain points of being large in size and the harmonic suppression relying on complex parameter adjustment, while the step impedance structure can shorten the electrical length of the resonance unit without reducing the quality factor through impedance mutation. Therefore, the researchers of this application set a 1 / 4 wavelength resonance unit and two coupled resonance units as a step impedance structure, and further realized the miniaturization design by combining the 1 / 4 wavelength step impedance resonance unit with the symmetrically arranged strong coupling step impedance resonance unit. Moreover, through the impedance mutation characteristics of the step impedance structure, the high-order mode resonance frequency is changed to avoid parasitic passband concentration.

[0043] In addition, the design of the stepped impedance structure combined with the symmetrical layout of the coupled resonant units can induce multipath signal inversion, thereby forming multiple transmission zeros within a wide frequency band and jointly suppressing out-of-band interference.

[0044] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0045] Figure 1 This is a schematic diagram of the structure of the cavity filter provided in the embodiment of the present application. Figure 1 As shown, the present 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 intensive high-frequency communication needs. The cavity filter 1 can effectively improve the purity and anti-interference ability of signal processing, 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 spectrum 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 100. In the embodiment of the present application, the housing 100 is described as a rectangular structure. The housing 100 may include a top wall, a bottom wall, a front wall, a rear wall, a left wall, and a right wall. Figure 1 The Z axis is opposite and spaced apart, with the front wall and the rear wall along Figure 1 The Y axis is opposite and spaced apart, with the left and right walls along Figure 1 The X-axis directions are opposite and spaced apart.

[0047] The housing 100 is constructed to form a first cavity 110 and a second cavity 120, and a first coupling window 130 is constructed 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 housing 100 may be recessed inward to form a first partition, and the bottom wall of the housing 100 may be recessed inward to form a second partition. In this embodiment of the present application, the direction from the top wall of the housing 100 toward the bottom wall is defined as the first direction (corresponding to Figure 1 Z-axis direction), the second direction (corresponding to Figure 1 The first cavity 110 and the second cavity 120 are located on either side of the first partition and the second partition, respectively, along the second direction. Furthermore, the first partition and the second partition are opposed to each other and spaced apart along the first direction. Therefore, the space between the first partition and the second partition forms a first coupling window 130.

[0049] In other embodiments, the housing 100 may further include a metal partition (not shown) extending vertically along a first direction and fixedly connected between the top and bottom walls of the housing 100, thereby dividing the interior space of the housing 100 into a first cavity 110 and a second cavity 120 distributed along a second direction. A first coupling window 130 is defined in the metal partition, serving 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 embodiment of the present application does not specifically limit the structural form of the first coupling window 130 .

[0051] Continue to refer to Figure 1 As shown, a quarter wavelength resonant unit 111 is provided in the first cavity 110. The quarter wavelength resonant unit 111 refers to a 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 coaxially arranged first cylinder 1111 and a second cylinder 1112, wherein the bottom end of the first cylinder 1111 is 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 the step impedance characteristic is formed by the sudden change in the diameter of the first cylinder 1111 and the diameter of 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. A gap is provided between the top end of the first cylinder 1111 and 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 coupling resonant unit 121 and a second coupling resonant unit 122 are disposed within the second cavity 120. The first coupling resonant unit 121 and the second coupling resonant unit 122 are symmetrically arranged about the longitudinal center plane of the second cavity 120. In the embodiment of the present application, the longitudinal center plane is parallel to a plane formed by the X-axis and the Z-axis, and the second cavity 120 is symmetrical about the longitudinal center plane along the Y-axis.

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

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

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

[0058] The second resonant portion 1212 includes a first plane 12121, and the fourth resonant portion 1222 includes a second plane 12221. Furthermore, the first plane 12121 and the second plane 12221 are disposed opposite each other along a longitudinal center plane of the second cavity 120, which is perpendicular to the plane in which the first coupling window 130 extends.

[0059] As an embodiment, the first resonating portion 1211 and the third resonating portion 1221 can each be a cylinder with equal diameter. The second resonating portion 1212 is a cylinder extending axially along the first resonating portion 1211, with a cross-section of the cylinder being in the shape of a circular segment. The side surface of the cylinder includes a first arc surface 12122 and a first plane 12121 connected thereto, and the first arc surface 12122 is coaxially arranged with the first resonating portion 1211. The fourth resonating portion 1222 is a cylinder extending axially along the third resonating portion 1221, with a cross-section of the cylinder being in the shape of a circular segment. The side surface of the cylinder includes a second arc surface 12222 and a second plane 12221 connected thereto, and the second arc surface 12222 is coaxially arranged with the third resonating portion 1221.

[0060] The term "segmented shape" refers to the area remaining after a circle is cut by a non-diameter chord, and is enclosed by the chord and the corresponding arc. In this embodiment, the chord in the segmented shape corresponds to the first plane 12121 and the second plane 12221, and the arc in the segmented shape corresponds to the first arc surface 12122 and the second arc surface 12222.

[0061] Thus, by providing the first plane 12121 and the second plane 12221, the effective overlapping area of ​​the first coupling resonant unit 121 and the second coupling resonant unit 122 at the open-circuit end can be significantly increased. According to electromagnetic coupling theory, the fringe electric field effect between parallel conductor surfaces increases with the increase in the area facing each other, thereby increasing the equivalent capacitance between the first coupling resonant unit 121 and the second coupling resonant unit 122. This increase in equivalent capacitance can enhance the electric field coupling strength between the first coupling resonant unit 121 and the second coupling resonant unit 122.

[0062] Compared to uniform impedance resonators, the quarter-wavelength resonant unit 111, first coupled resonant unit 121, and second coupled resonant unit 122 of the present application utilize a stepped impedance resonant structure to establish 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. Furthermore, the stepped impedance structure effectively suppresses higher harmonics by utilizing impedance discontinuities, significantly expanding the stopband width of the cavity filter 1.

[0063] The fundamental mode resonant frequency of the 1 / 4 wavelength resonant unit 111 in the first cavity 110 can constitute a first-order response of the passband. The first coupled resonant unit 121 and the second coupled resonant unit 122 in the second cavity 120 form a strong coupling structure through a symmetrical layout. By utilizing the anti-phase characteristics of the electromagnetic fields of the odd-mode and even-mode resonant modes, two-order independent resonant responses can be excited in the second cavity 120. In this way, the 1 / 4 wavelength resonant unit 111, the first coupled resonant unit 121, and the second coupled resonant unit 122 can complete a third-order passband response in the first cavity 110 and the second cavity 120. Compared with the traditional solution that requires a three-stage cavity cascade structure, the cavity filter 1 of the present application can reduce the volume of one physical cavity, further realizing the miniaturization design of the cavity filter 1.

[0064] Figure 2 This is a top view of the cavity filter provided in the embodiment of the present application. Figure 1 and Figure 2 As shown, the cavity filter 1 further includes a non-resonant node 200 , and the non-resonant node 200 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 bent portion 230. One end of the first connecting portion 210 is connected to the quarter-wavelength resonant unit 111, one end of the second connecting portion 220 is connected to the second coupling resonant unit 122, and the bent portion 230 is connected between the first connecting portion 210 and the second connecting portion 220.

[0066] Through its quarter-wavelength transmission line characteristics, non-resonant node 200 effectively blocks the propagation path of spurious modes induced by capacitive loading, suppresses the interference of spurious resonances on the main passband signal, and significantly improves the passband return loss performance of cavity filter 1. Furthermore, non-resonant node 200 can reconstruct the coupling phase relationship between quarter-wavelength resonant unit 111 and second coupled resonant unit 122 while maintaining efficient transmission of the passband signal, thereby optimizing the impedance matching characteristics of 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, with the first connecting portion 210 perpendicularly connected to the quarter-wavelength resonant unit 111, and the second connecting portion 220 perpendicularly connected to the second coupling resonant unit 122. The bent 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 perpendicularly to the extension direction of the first connecting portion 210 and are spaced apart from each other perpendicularly to the extension direction of the first connecting portion 210. One end 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 the two first extension segments 231 is connected to the second extension segment 232. The second extension segment 232 extends along the extension direction of the first connecting portion 210.

[0069] With this configuration, the bent portion 230 can reduce the axial length of the non-resonant node 200 by folding the transmission line, thereby meeting 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 further includes a coupling boss 300. The coupling boss 300 is disposed between the first coupling resonant unit 121 and the second coupling 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 occurs on the surface of the coupling boss 300, enabling magnetic coupling between the first coupling resonant unit 121 and the second coupling resonant unit 122. The coupling strength increases with increasing boss height. By fine-tuning the height of the coupling boss 300, the coupling coefficient between the first coupling resonant unit 121 and the second coupling resonant unit 122 can be optimized to compensate for frequency offset.

[0071] Continue to refer to Figure 1 and Figure 2 As shown, the cavity filter 1 further includes a first feeding probe 400 and a second feeding probe 500. The first feeding probe 400 extends into the first cavity 110 and connects to the quarter-wavelength resonant unit 111. The second feeding probe 500 extends into the second cavity 120 and connects to the second coupling resonant unit 122. Exemplarily, the first feeding probe 400 and the second feeding probe 500 can be feed probes for a Subminiature version A (SMA) coaxial connector. The first feeding probe 400 and the second feeding probe 500 can effectively reduce signal reflections and ensure efficient energy transmission between the filter's input and output ports.

[0072] Among them, the first feeding probe 400 can serve as the RF input port of the cavity filter 1, and by connecting to the 1 / 4 wavelength resonance unit 111, the external RF signal is input into the first cavity 110 to excite the fundamental mode working mode of the 1 / 4 wavelength resonance unit 111. The second feeding probe 500 serves as the RF output port of the cavity filter 1, and is connected to the second coupling resonance unit 122 to extract the RF signal after cavity filtering processing and complete the signal transmission link. Of course, the second feeding probe 500 can also serve as the RF input port and the first feeding probe 400 can serve as the RF output port. The embodiment of the present application does not impose specific restrictions on this.

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

[0074] Specifically, a removable build unit containing the 3D model data for the cavity filter 1 is placed into the printing apparatus. A material recovery system reciprocates within the build area, depositing the powder material layer by layer. During printing, the printing and melting carriages move synchronously, preheating the powder to the set process temperature. An inkjet nozzle then precisely sprays the flux onto a designated area of ​​the powder bed, achieving selective fusion of the materials. After each layer is printed, the build unit automatically descends by a layer thickness to create space for the next layer of powder to be deposited. This cycle continues until the entire structure is formed. Printing accuracy is controlled within ±0.15mm / 100mm.

[0075] Among them, the powder material can be selected from polylaurolactam (Polyamide 12, referred to as 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 is completed, the following post-processing steps are required: First, the printed cavity filter 1 component is subjected to a cooling process. The operator can fully cool and shape the cavity filter 1 component by placing it naturally or using special cooling equipment. Then, a powder recovery process is carried out to collect the unmelted powder material in the printing chamber into a special storage container to achieve the recycling of the powder material. Next, a surface cleaning process is performed. The residual powder on the surface of the cavity filter 1 component can be completely removed by using sandblasting, air spraying or water flushing. Finally, a metallization process is implemented, including: first, deep cleaning the component with a special degreasing agent, then activating the surface of the component by chemical methods, followed by chemical copper plating, and finally using an electroplating process to form a uniform copper layer with a thickness of 10μm. After treatment with drying equipment, the entire processing flow is completed.

[0077] Thus, the cavity filter 1 of the present application can be manufactured by using 3D printing technology to achieve integrated molding, so that the cavity filter 1 maintains high molding precision. In addition, the printed filter components have both good electromagnetic performance and mechanical properties.

[0078] Figure 3 The S-parameter frequency response curve of the cavity filter 1 provided in the embodiment of the present application. Figure 3 As shown, cavity filter 1 exhibits 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. Return loss within the passband is better than 16 dB, demonstrating excellent impedance matching.

[0079] In addition, the cavity filter 1 also generates four transmission zeros at frequencies of 1.9 GHz, 3.98 GHz, 9.02 GHz, and 10.03 GHz, respectively. Among them, the transmission zero at 1.9 GHz is formed by the phase inversion effect of the multipath signal between the first coupling resonant unit 121 and the second coupling resonant unit 122. The generation of the transmission zero at 3.98 GHz depends on the asymmetric layout characteristics of the first feeding probe 400 and the second feeding probe 500. The transmission zeros at 9.02 GHz and 10.03 GHz originate from the electromagnetic hybrid coupling mechanism between the 1 / 4 wavelength resonant unit 111, the first coupling resonant unit 121, and the second coupling resonant unit 122, as well as the interaction of higher-order resonant modes that are not used for the passband. The synergistic effect of these transmission zeros can significantly expand the stopband suppression range, so that the cavity filter 1 has excellent frequency selectivity while achieving wide stopband characteristics.

[0080] It should be noted that phrases such as "one embodiment," "an embodiment," "exemplary embodiments," and "some embodiments" in this specification may indicate embodiments that may include a particular feature, structure, or characteristic, but not every embodiment necessarily includes that particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, it is within the knowledge of those skilled in the art to implement such feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not.

[0081] Generally speaking, terms should be understood, at least in part, based on the context in which they are used. For example, as used herein, the term "one or more" can be used to describe any feature, structure, or characteristic in the singular sense, or can be used to describe a combination of features, structures, or characteristics in the plural sense, depending at least in part on the context. Similarly, terms such as "a" or "an" can also be understood to convey either singular or plural usage, depending at least in part on the context.

[0082] It should be readily understood that “on,” “above,” and “over” in this application should be interpreted in the broadest manner, such that “on” means not only “directly on something,” but also includes “on something” with intervening features or layers therebetween, and “above” or “over” includes not only the meaning of “above” or “over,” but also includes “above” or “over” with no intervening features or layers therebetween (i.e., directly on something).

[0083] Additionally, spatially relative terms, such as "below," "beneath," "beneath," "above," and the like, may be used herein for ease of description to describe the relationship of one element or feature to other elements or features as depicted in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90° or at other orientations), and the spatially relative descriptors used herein should be interpreted accordingly.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A cavity filter, characterized in that: include: a shell portion, wherein the shell portion is structured to form a first cavity and a second cavity, and a first coupling window is structured to form between the first cavity and the second cavity; A quarter-wavelength resonant unit is provided in the first cavity, and the quarter-wavelength resonant unit includes a first cylinder and a second cylinder arranged coaxially, wherein 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; A first coupling resonance unit and a second coupling resonance unit are provided in the second cavity; 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 part and a fourth resonant part, the top end of the third resonant part is connected to the bottom end of the fourth resonant part, and the impedance of the third resonant part is greater than the impedance of the fourth resonant part; The first coupling resonance unit and the second coupling resonance unit are symmetrically arranged about a longitudinal center plane of the second cavity, and the longitudinal center plane is perpendicular to a plane where an extension direction of the first coupling window is located.

2. The cavity filter according to claim 1, wherein: The top wall of the outer shell is recessed inward to form a first partition, and the bottom wall of the outer shell 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. The 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 shell toward the bottom wall. The first cavity and the second cavity are respectively located on both sides of the first partition and the second partition along a second direction, and the second direction is perpendicular to the first direction.

3. The cavity filter according to claim 1, wherein: The first resonant part and the third resonant part are cylinders with equal diameters.

4. The cavity filter according to claim 3, characterized in that The second resonating portion is a column extending along the axial direction of the first resonating portion, the cross section of the column is a circular segment, the side surface of the column includes a connected arc surface and a first plane, and the arc surface is coaxially arranged with the first resonating portion; The fourth resonating part is a cylinder extending along the axial direction of the third resonating part, the cross section of the cylinder is a circular segment, the side surface of the cylinder includes a connected arc surface and a second plane, and the arc surface is coaxially arranged with the third resonating part; The first plane and the second plane are opposite along a longitudinal center plane of the second cavity.

5. The cavity filter according to claim 1, wherein: 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 in contact with the bottom end of the second cavity respectively, and a gap is provided between the top end of the second resonant part and the top end of the fourth resonant part and the top end of the second cavity respectively.

6. The cavity filter according to claim 1, wherein: Also includes: A first feeding probe and a second feeding probe, wherein the first feeding probe is inserted into the first cavity and connected to the 1 / 4 wavelength resonance unit, and the second feeding probe is inserted into the second cavity and connected to the second coupling resonance unit.

7. The cavity filter according to claim 1, wherein: Also includes: A non-resonant node, wherein the non-resonant node includes a first connecting portion, a second connecting portion and a bending portion, wherein one end of the first connecting portion is connected to the 1 / 4 wavelength resonant unit, one end of the second connecting portion is connected to the second coupling resonant unit, and the bending portion is connected between the first connecting portion and the second connecting portion.

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 portion is vertically connected to the 1 / 4 wavelength resonance unit, and the second connecting portion is vertically connected to the second coupling resonance unit.

9. The cavity filter according to claim 7, characterized in that: The bending portion includes two first extension sections and one second extension section; The two first extension sections 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 the two first extension sections is connected to the first connecting portion and the second connecting portion respectively, and the other end of the two first extension sections is connected to the second extension section; The second extending section extends along an extending direction of the first connecting portion.

10. The cavity filter according to claim 1, wherein: Also includes: A coupling boss is provided between the first coupling resonance unit and the second coupling resonance unit, and a bottom end of the coupling boss is connected to the bottom wall of the second cavity.

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