A coaxial cavity filter with high out-of-band suppression

Abstract

A coaxial cavity filter with high out-of-band suppression consists of a lower cavity, a cover, five resonators, a first spring, a second spring, an SMA-to-microstrip connector, a resonant column, and two matching stages. The SMA-to-microstrip connector consists of a jack, three insulators, a shell, and a compression sleeve. The signal is input to the filter through the SMA-to-microstrip connector at the P1 port, and the filter then sends the processed signal to the SMA-to-microstrip connector at the P2 port through coupling, thereby realizing the frequency selection function. The cross-coupling between the resonant cavities, that is, there is a coupling window between resonator 1 and resonator 4, and an out-of-band zero point is generated through the raised coupling structure, thereby achieving a high out-of-band suppression index of the coaxial filter. The structural processing and assembly proposed in the patent of this invention are relatively simple, and the power capacity of the filter is effectively improved. The device has a compact structure, is stable and reliable, has excellent wide temperature range working performance, and can withstand mechanical tests such as impact and vibration.

Description

Technical Field

[0001] The invention relates to a coaxial cavity filter with high out-of-band suppression, belonging to the technical field of microwave passive devices. Background Art

[0002] Microwave filters are crucial passive components in microwave RF circuit systems. Their primary function is frequency selection, allowing signals of desired frequencies to pass while suppressing signals of undesired frequencies. They are widely used in military radar, missile-borne, and satellite-borne systems. Cavity filters are particularly popular in microwave systems due to their high power handling capacity, high Q factor, low insertion loss, wide applicable frequency range, and excellent heat dissipation. Coaxial cavity filters are widely used due to their compact structure, small size, mature processing and debugging optimization methods, and high reliability.

[0003] Today's microwave frequency bands are relatively crowded, and the scarcity of spectrum resources has led to very short frequency separations between communication systems. This places increasingly stringent demands on the isolation of microwave RF circuit systems. This translates to filters requiring steep sideband roll-offs for high selectivity and strong suppression to suppress harmonics and reduce interference. Existing coaxial cavity filters typically utilize coupling windows between resonant cavities or inter-cavity coupling probe structures to achieve zeros on either side of the filter's passband, meeting out-of-band suppression requirements. However, these structures are complex to manufacture and assemble, and when the coupling strength is high, the distance between the coupling probe structure and the resonator is small, making them unable to meet the filter's power requirements. Summary of the Invention

[0004] The technical problem solved by the present invention is: to overcome the shortcomings of the existing technology and provide a coaxial cavity filter with high out-of-band suppression. The signal is input to the filter through the SMA-to-microstrip connector coupling at the P1 port, and the filter then sends the processed signal to the SMA-to-microstrip connector at the P2 port through coupling, thereby realizing the frequency selection function.

[0005] The technical solution of the present invention is: a coaxial cavity filter with high out-of-band suppression, comprising a lower cavity, a cover plate, a plurality of resonators, a first spring, a second spring, an SMA to microstrip connector, a resonant column, a plurality of matching stages, an adjustment screw and an adjustment nut; the length of the first spring is less than the length of the second spring;

[0006] The lower cavity and the cover plate are fastened by screws and fixed with glue to enhance stability and form a cavity;

[0007] The adjusting screw and the adjusting nut are assembled and installed at the corresponding thread position of the cover plate, and glue is applied between the adjusting screw and the adjusting nut and between the adjusting nut and the cover plate to fix them;

[0008] The resonator is fastened to the resonant column by a resonator fastening screw, and glue is applied between the resonator fastening screw and the internal thread to fix it;

[0009] The SMA to microstrip connector is installed on the side of the lower cavity by screws, spring washers, and small washers, and glue is applied to the connection between the screw nut and the SMA to microstrip connector to fix it;

[0010] One end of the first elastic piece is fastened to the first matching platform, and the other end is welded to the P1 port jack;

[0011] One end of the second elastic piece is fastened to the second matching platform, and the other end is welded to the P2 port jack;

[0012] The matching platform and the resonant column are an integrated structure, and cooperate with the first elastic piece and the second elastic piece to couple the P1 port to the resonator or couple the microwave signal of the resonator to the P2 port.

[0013] Furthermore, the number of resonators is four, including a first resonator, a second resonator, a third resonator, and a fourth resonator; wherein, the fourth resonator has a raised coupling structure extending from the edge of the disk based on the disk, the raised coupling structure passes through the coupling window between the first resonator and the fourth resonator and points to the first resonator, and the symmetry axis of the raised coupling structure passes through the center of the disk of the fourth resonator.

[0014] Furthermore, the protruding coupling structure is in a rectangular parallelepiped shape, and its thickness is consistent with that of the fourth resonator disk.

[0015] Furthermore, the length, width and installation angle of the protruding coupling structure are determined according to the coupling strength.

[0016] Furthermore, the SMA to microstrip connector includes a jack, a first insulator, a second insulator, a third insulator, a housing and a compression sleeve;

[0017] The socket is cylindrical, with a slot at one end and a solid cylindrical head at the other end;

[0018] The second insulator is inserted into the jack slot;

[0019] The third insulator is located on one side of the slot of the jack;

[0020] The first insulator is located on one side of the solid cylindrical head of the socket;

[0021] The compression sleeve is located outside the first insulator;

[0022] The shell is located at the outermost side of the SMA to microstrip connector, and the pressing sleeve is fitted with the end surface of the shell.

[0023] Furthermore, the jack has a slot structure and a knurled structure for assembly, positioning and fixing.

[0024] Furthermore, the assembly between the pressing sleeve and the housing adopts interference fit.

[0025] Furthermore, there is a metal ridge structure between the resonant columns, which increases the inter-cavity coupling on the one hand and increases the overall mechanical stability of the device on the other hand.

[0026] Furthermore, the first elastic piece and the second elastic piece are both in a 90° right-angle shape, with through holes left at both ends.

[0027] Furthermore, the depth of the adjusting screw is adjustable.

[0028] The advantages of the present invention compared with the prior art are:

[0029] Resonators are used in irregular cavities to generate resonance functions for microwave signals, effectively reducing the volume of the filter and making the filter structure compact; appropriate coupling structures are adopted between cavities to achieve the target bandwidth of the filter; cross-coupling between the resonant cavities, that is, there is a coupling window between the first resonator and the fourth resonator, and an out-of-band zero point is generated through the raised coupling structure, achieving a high out-of-band suppression index of the filter, and this structure is beneficial to improving the power capacity of the filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A coaxial cavity filter with high out-of-band suppression provided by the present invention;

[0031] Figure 2 A diagram showing the lower cavity structure of a coaxial cavity filter with high out-of-band suppression provided by the present invention;

[0032] Figure 3 A cross-sectional view of an SMA to microstrip connector for a coaxial cavity filter with high out-of-band suppression provided by the present invention;

[0033] Figure 4 A schematic diagram of the jack structure of a coaxial cavity filter with high out-of-band suppression provided by the present invention;

[0034] Figure 5 A schematic structural diagram of a first spring piece and a second spring piece of a coaxial cavity filter with high out-of-band suppression provided by the present invention;

[0035] Figure 6 This is a schematic structural diagram of a resonator 4 of a coaxial cavity filter with high out-of-band suppression provided by the present invention. DETAILED DESCRIPTION

[0036] In order to better understand the above technical solution, the technical solution of the present application is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical solution of the present application, rather than limitations on the technical solution of the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other.

[0037] The following is a further detailed description of a coaxial cavity filter with high out-of-band suppression provided by an embodiment of the present application in conjunction with the accompanying drawings. The specific implementation method may include (eg Figures 1 to 6 The device comprises a lower cavity 1, a cover plate 2, a first resonator 3, a second resonator 4, a third resonator 5, a fourth resonator 6, a fifth resonator 7, a first spring 8, a second spring 9, an SMA-to-microstrip connector 10, a resonant column 11, a first matching platform 12, a second matching platform 13, an adjustment screw 14, and an adjustment nut 15. The lower cavity 1 and cover plate 2 are fastened together with screws 16 and secured with glue to enhance stability, forming a cavity 17. The length of the first spring is less than that of the second spring.

[0038] Specifically, the SMA to microstrip connector 10 consists of a jack 20, a first insulator 21, a second insulator 22, a third insulator 23, a shell 24 and a compression sleeve 25. The jack 20 is cylindrical, with a slot at one end and a solid cylindrical head at the other end. In order to assemble, position and fix, the jack 20 has a slot structure and a knurled structure with a smaller diameter. The P1 port jack 201 and the P2 port jack 202 have the same structure and are respectively assembled at the two ports of the coaxial cavity filter. The second insulator 22 is completely inserted into the slot of the jack 20, the third insulator 23 is located on the slot side of the jack 20, the first insulator 21 is located on the solid cylindrical head side of the jack 20, the compression sleeve 25 is located on the periphery of the first insulator 21, and the shell 24 is located on the outermost side of the SMA to microstrip connector 10. The end faces of the compression sleeve 25 and the shell 24 are completely fitted together. The SMA to microstrip connector 10 is installed on the side of the lower cavity 1 by means of screws 26 , spring washers 27 and small washers 28 . The jack 20 is inserted into the cavity 17 , and glue is applied to the connection between the screw 26 and the nut of the SMA to microstrip connector 10 to fix it.

[0039] The first, second, third, fourth, and fifth resonators 3, 4, 5, 6, and 7 are fastened to the resonant column 11 via resonator fastening screws 18. Glue is applied between the resonator fastening screws 18 and the internal threads to enhance the reliability of the resonator installation. Resonant columns 111-115 are located below the first, second, and fifth resonators 3-7, respectively, and have identical structures. The fourth resonator 6, based on a circular disc, has a raised coupling structure 19 extending from its edge. The axis of symmetry of the raised coupling structure 19 passes through the center of the disc. The raised coupling structure 19 is rectangular and has a thickness that matches the thickness of the disc of the fourth resonator 6. The length, width, and mounting angle of the raised coupling structure 19 are determined based on the coupling strength. The raised coupling structure 19 points toward the first resonator 3 through the coupling window between the first and fourth resonators 3, 6. Appropriately adjusting the spacing between the edge of the raised coupling structure 19, the coupling window, and the first resonator allows for high out-of-band suppression while also improving the filter's microdischarge margin compared to conventional coupled probe structures. There is a metal ridge 29 structure between the resonant columns 11, which increases the inter-cavity coupling on the one hand and the overall mechanical stability of the device on the other hand.

[0040] The first spring clip 8 is 90° right-angled, with through holes at both ends. One end is fastened to the first matching platform 12, and the other end is welded to the P1 port jack 201. The second spring clip 9 is 90° right-angled, with through holes at both ends. One end is fastened to the second matching platform 13, and the other end is welded to the P2 port jack 202. The assembly structure of the first spring clip 8 and the second spring clip 9 is stable, achieving a height transition between the P1 port jack 201 and the first matching platform 12, the P2 port jack 202, and the second matching platform 13, thereby achieving a specific input and output coupling strength. To prevent the jack 20 from rotating and causing stress on the welds between the jack 20 and the first spring clip 8 and the second spring clip 9, a knurled structure is provided on the jack 20 to increase friction with the first insulator 21.

[0041] Assemble the adjusting screw 14 and the adjusting nut 15 and install them at the corresponding threaded position of the cover plate 2. Adjusting the depth of the adjusting screw 14 can adjust the resonant frequency and coupling bandwidth. Apply glue between the adjusting screw 14 and the adjusting nut 15 and between the adjusting nut 15 and the cover plate 2 to fix them.

[0042] In the solution provided in the embodiment of the present application, in order to meet the requirements of the rapidly developing radar, communication and satellite navigation technologies for miniaturization, low insertion loss, good in-band response and high out-of-band suppression and other characteristics of the filter, the patent of the present invention proposes a high-reliability, high-suppression coaxial cavity filter, which is characterized by: comprising a lower cavity 1, a cover plate 2, a first resonator 3, a second resonator 4, a third resonator 5, a fourth resonator 6, a fifth resonator 7, a first spring 8, a second spring 9, an SMA to microstrip connector 10, a resonant column 11, a first matching platform 12, a second matching platform 13, an adjusting screw 14 and an adjusting nut 15, as shown Figure 1 As shown. Lower cavity 1 and cover plate 2 are fastened together with screws 16 and glued together to enhance stability, forming cavity 17. Cavity 17 has an irregular shape, making the overall device compact and smaller. Metal ridges 29 are provided between resonant columns 11 to enhance inter-cavity coupling and increase the mechanical stability of the overall device structure. Lower cavity 1 is provided with mounting ears, which increase the mounting surface area, facilitate heat dissipation, and improve the filter's power capacity.

[0043] The SMA to microstrip connector 10 consists of a jack 20, a first insulator 21, a second insulator 22, a third insulator 23, a shell 24 and a sleeve 25. The jack 20 is cylindrical, with a slot at one end and a solid cylindrical head at the other end. For assembly positioning and fixation, the jack 20 has a slot structure and a knurled structure with a smaller diameter. The P1 port jack 201 and the P2 port jack 202 have the same structure and are respectively assembled at the two ports of the coaxial cavity filter. The second insulator 22 is completely inserted into the slot of the jack 20, the third insulator 23 is located on the slot side of the jack 20, the first insulator 21 is located on the solid cylindrical head side of the jack 20, the sleeve 25 is located on the periphery of the first insulator 21, and the shell 24 is located at the outermost side of the SMA to microstrip connector 10. The end faces of the sleeve 25 and the shell 24 are completely fitted together, and the assembly between the sleeve 25 and the shell 24 adopts an interference fit to ensure reliability. The SMA to microstrip connector 10 is installed on the side of the lower cavity 1 by means of screws 26 , spring washers 27 and small washers 28 . The jack 20 is inserted into the cavity 17 , and glue is applied to the connection between the screw 26 and the nut of the SMA to microstrip connector 10 to fix it.

[0044] The first, second, third, fourth, and fifth resonators 3, 4, 5, 6, and 7 are fastened to the resonant column 11 via resonator fastening screws 18. Glue is applied between the resonator fastening screws 18 and the internal threads to enhance the reliability of the resonator installation. Resonant columns 111-115 are located below the first, second, and third resonators 3-7, respectively, and have the same structure. Among them, there is a coupling window between the first resonator 3 and the fourth resonator 6. On the basis of the disk, the fourth resonator 6 has a protruding coupling structure 19 extending from the edge. The symmetry axis of the protruding coupling structure 19 passes through the center of the disk. The protruding coupling structure 19 is in the shape of a rectangular parallelepiped and has a thickness consistent with the thickness of the disk of the fourth resonator 6. The length, width and installation angle of the protruding coupling structure 19 are determined according to the coupling strength. The protruding coupling structure 19 passes through the coupling window between the first resonator 3 and the fourth resonator 6 and points to the first resonator 3. The spacing between the edge of the protruding coupling structure 19 and the coupling window and the first resonator 3 is appropriately adjusted. Compared with the conventional coupling probe structure, this structure enables a zero point to be generated on the left and right sides of the filter passband, thereby achieving a high out-of-band suppression index and at the same time being more beneficial to improving the micro-discharge margin of the filter.

[0045] The first spring clip 8 is 90° right-angled, with through holes at both ends. One end is fastened to the first matching platform 12, and the other end is welded to the P1 port jack 201. The second spring clip 9 is 90° right-angled, with through holes at both ends. One end is fastened to the second matching platform 13, and the other end is welded to the P2 port jack 202. The assembly structure of the first spring clip 8 and the second spring clip 9 is stable, achieving a height transition between the P1 port jack 201 and the first matching platform 12, the P2 port jack 202, and the second matching platform 13, thereby achieving a specific input and output coupling strength. To prevent the jack 20 from rotating and causing stress on the welds between the jack 20 and the first spring clip 8 and the second spring clip 9, a knurled structure is provided on the jack 20 to increase friction with the first insulator 21.

[0046] Assemble the adjusting screw 14 and the adjusting nut 15 and install them at the corresponding thread position of the cover plate 2. Adjusting the depth of the adjusting screw 14 can adjust the resonant frequency and coupling bandwidth. Apply glue between the adjusting screw 14 and the adjusting nut 15 and between the adjusting nut 15 and the cover plate 2 to fix them.

[0047] Analysis using high-frequency electromagnetic field simulation software reveals that the signal is coupled to the filter via the SMA-to-microstrip connector 101 at the P1 port, and the filter then transmits the processed signal to the SMA-to-microstrip connector 102 at the P2 port through coupling, thereby achieving frequency selection. Resonators 3-7 within the irregular cavity 17 resonate the microwave signal. A suitable coupling structure is employed between the cavities to achieve the filter's target bandwidth, and adjustment screws 14 are used to fine-tune the frequency and coupling bandwidth, effectively reducing the filter's size and making it compact and smaller. Furthermore, the cross-coupling between the resonant cavities, namely the coupling window provided between the first resonator 3 and the fourth resonator 6, generates an out-of-band zero through a raised coupling structure 19, achieving high out-of-band suppression. This structure also contributes to improving the filter's power capacity.

[0048] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0049] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

[0050] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A coaxial cavity filter with high out-of-band suppression, characterized in that: It includes a lower cavity, a cover plate, a plurality of resonators, a first spring piece, a second spring piece, an SMA to microstrip connector, a resonant column, a plurality of matching platforms, an adjusting screw and an adjusting nut; the length of the first spring piece is less than the length of the second spring piece; The lower cavity and the cover plate are fastened by screws and fixed with glue to enhance stability and form a cavity; The adjusting screw and the adjusting nut are assembled and installed at the corresponding thread position of the cover plate, and glue is applied between the adjusting screw and the adjusting nut and between the adjusting nut and the cover plate to fix them; The resonator is fastened to the resonant column by a resonator fastening screw, and glue is applied between the resonator fastening screw and the internal thread to fix it; The SMA to microstrip connector is installed on the side of the lower cavity by screws, spring washers, and small washers, and glue is applied to the connection between the screw nut and the SMA to microstrip connector to fix it; The matching platform and the resonant column are integrated into a structure, and cooperate with the first spring piece and the second spring piece to couple the microwave signal of the P1 port to the resonator or couple the microwave signal of the resonator to the P2 port; The matching platform includes a first matching platform and a second matching platform; One end of the first elastic piece is fastened to the first matching platform, and the other end is welded to the P1 port jack; One end of the second elastic piece is fastened to the second matching platform, and the other end is welded to the P2 port jack; There are four resonators, including a first resonator, a second resonator, a third resonator, and a fourth resonator; wherein, the fourth resonator has a protruding coupling structure extending from the edge of the disk, the protruding coupling structure passes through the coupling window between the first resonator and the fourth resonator and points to the first resonator, and the symmetry axis of the protruding coupling structure passes through the center of the disk of the fourth resonator.

2. The coaxial cavity filter with high out-of-band suppression according to claim 1, characterized in that: The protruding coupling structure is in a rectangular parallelepiped shape, and its thickness is consistent with that of the fourth resonator disk.

3. The coaxial cavity filter with high out-of-band suppression according to claim 1, characterized in that: The length, width and installation angle of the protruding coupling structure are determined according to the coupling strength.

4. The coaxial cavity filter with high out-of-band suppression according to claim 1, characterized in that: The SMA to microstrip connector includes a jack, a first insulator, a second insulator, a third insulator, a shell and a compression sleeve; The socket is cylindrical, with a slot at one end and a solid cylindrical head at the other end; The second insulator is inserted into the jack slot; The third insulator is located on one side of the slot of the jack; The first insulator is located on one side of the solid cylindrical head of the socket; The compression sleeve is located outside the first insulator; The shell is located at the outermost side of the SMA to microstrip connector, and the pressing sleeve is fitted with the end surface of the shell.

5. The coaxial cavity filter with high out-of-band suppression according to claim 4, characterized in that: The jack is provided with a slot structure and a knurled structure for assembly, positioning and fixing.

6. The coaxial cavity filter with high out-of-band suppression according to claim 4, characterized in that: The assembly between the press sleeve and the shell adopts interference fit.

7. The coaxial cavity filter with high out-of-band suppression according to claim 1, characterized in that: There is a metal ridge structure between the resonant columns, which increases the inter-cavity coupling on the one hand and the overall mechanical stability of the device on the other hand.

8. The coaxial cavity filter with high out-of-band suppression according to claim 1, characterized in that: The first spring piece and the second spring piece are both in a 90° right angle shape, with through holes at both ends.

9. The coaxial cavity filter with high out-of-band suppression according to claim 1, characterized in that: The depth of the adjusting screw is adjustable.

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