Multiple suspended cavity filter and design method

Abstract

The application discloses a multiple suspension cavity filter and a design method, and relates to the field of cavity filters, which is used for improving the selectivity and controllability of the transmission zero point of the cavity filter through a simple structure. The filter comprises an input waveguide, an output waveguide, a plurality of intermediate resonant cavities coupled between the input waveguide and the output waveguide, a plurality of left resonant cavities coupled and suspended at a first port of the input waveguide and a plurality of right resonant cavities coupled and suspended at a second port of the output waveguide; and the connection positions of the waveguides or the resonant cavities are coupled and communicated through coupling screws. The filter structure is simple, and the selectivity and controllability of the filter are improved.

Description

Technical Field

[0001] This invention relates to the field of cavity filter technology, and in particular to a multi-suspended cavity filter and its design method. Background Technology

[0002] Filters are key functional components in radio frequency (RF) systems, enabling frequency selection and interference suppression. An ideal filter requires low loss and high selectivity. With the development of modern communication systems, flexible structures, superior performance, and faster design methods have garnered significant attention. Cavity filters, due to their low insertion loss and high power capacity, are widely used in aerospace, military electronics, and civilian communications.

[0003] To improve the performance of cavity filters both inside and outside the passband, cross-coupling or frequency-varying coupling schemes are often employed. For example, Chinese patent document CN121566087A proposes a high-selectivity waveguide filter based on a nonlinear frequency-varying coupling structure. This filter includes three rectangular waveguide resonant cavities, an input waveguide port, and an output waveguide port. A first coupling metal pillar, a first coupling diaphragm, a first coupling metal block, and a first metal baffle between the middle and left resonant cavities together constitute the first set of nonlinear frequency-varying coupling structures. A second coupling metal pillar, a second coupling diaphragm, a second coupling metal block, and a second metal baffle between the second and third rectangular waveguide resonant cavities together constitute the second set of nonlinear frequency-varying coupling structures. These two sets of nonlinear frequency-varying coupling structures are used to couple the three rectangular waveguide resonant cavities, each introducing one reflection zero and two transmission zeros. The filter response is a fifth-order Chebyshev response with four transmission zeros. However, this design adds a structure for frequency-varying coupling to the cavity structure, requiring more parameters to control the transmission zeros, resulting in a complex design. For example, the filter design scheme proposed in "Design of W-band rectangular waveguide filter" (Q Bai et al.) uses a cross-coupling method applied to cavity filters, introducing two transmission zeros on both sides of the passband. However, because the cross-coupling scheme has multiple paths and complex coupling relationships, they can affect each other, and the transmission zeros cannot be controlled flexibly and intuitively.

[0004] Therefore, how to achieve multiple transmission zeros with flexibility and controllability without increasing structural complexity is of great significance and engineering application value for improving the selectivity of cavity filters and meeting the stringent requirements of out-of-band suppression. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-suspended cavity filter and its design method to address all or part of the problems mentioned above, thereby improving the selectivity and controllability of the transmission zero point of the cavity filter through a simple structure.

[0006] The technical solution adopted in this invention is as follows: In a first aspect, this application provides a multi-suspension cavity filter, the filter comprising: Input waveguide; Output waveguide; At least one intermediate resonant cavity is coupled between the input waveguide and the output waveguide; the number of intermediate resonant cavities is matched with the order of the filter coupling matrix and the number of transmission zeros to be introduced. At least one left resonant cavity is coupled and suspended at the first port of the input waveguide, the first port being located at the end away from the output waveguide; at least one right resonant cavity is coupled and suspended at the second port of the output waveguide, the second port being located at the end away from the input waveguide; the number of the left and right resonant cavities corresponds to the number and introduction position of the transmission zeros; the length of the left and right resonant cavities matches the introduction position of the transmission zeros.

[0007] Optionally, the connection points between the input waveguide, output waveguide, intermediate resonant cavity, left resonant cavity, and right resonant cavity are respectively coupled and connected by coupling screws; the lateral setting position of the coupling screw matches the coupling value of the longitudinal position of the coupling screw.

[0008] Optionally, the number of coupling screws is two or three; the two or three coupling screws are arranged in a transverse direction; the spacing between the two or three coupling screws matches the coupling value at the longitudinal position of the coupling screw.

[0009] Optionally, when the K value corresponding to the coupling value is below a set threshold, three coupling screws are used; when the K value corresponding to the coupling value reaches the threshold, two coupling screws are used.

[0010] Optionally, when using two coupling screws, the two coupling screws are arranged symmetrically about the filter axis; when using three coupling screws, the middle coupling screw intersects the filter axis, and the two coupling screws on both sides are arranged symmetrically about the filter axis.

[0011] Optionally, both the input waveguide and the output waveguide are T-type waveguides.

[0012] Optionally, the T-shaped waveguide includes an input / output port, a first port, and a second port; the input / output port, the first port, and the second port constitute a split waveguide.

[0013] Optionally, the first port and the second port are connected back to back along the longitudinal direction, and a bottom boss is formed at the bottom of the connection between the first port and the second port; the input / output port is perpendicular to the longitudinal direction and is connected to the top of the connection between the first port and the second port, forming a top boss.

[0014] Optionally, the input waveguide, output waveguide, intermediate resonant cavity, left resonant cavity, and right resonant cavity form a linearly arranged topology.

[0015] In a second aspect, this application provides a design method for a multi-suspended cavity filter, comprising: Construct the filter coupling matrix; determine the number and location of transmission zeros; Based on the order of the coupling matrix, at least one intermediate resonant cavity is coupled between the input waveguide and the output waveguide. Based on the number and introduction position of the transmission zeros, the number and length of the left and right resonant cavities are determined respectively; the left resonant cavity is coupled and suspended to the first port of the input waveguide, the first port being located at the end away from the output waveguide; the right resonant cavity is coupled and suspended to the second port of the output waveguide, the second port being located at the end away from the input waveguide; wherein, the number of the left and right resonant cavities corresponds to the number and introduction position of the transmission zeros; the length of the left and right resonant cavities matches the introduction position of the transmission zeros.

[0016] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: This application introduces transmission zeros through a suspended resonant cavity structure based on the main transmission path between the input and output waveguides. This structure is simple to implement and design, enhancing the selectivity of the cavity filter. Furthermore, by flexibly controlling the number of each resonant cavity (left and right resonant cavities), the number of transmission zeros can be controlled; and by flexibly controlling the length of each resonant cavity, the location of the transmission zeros can be controlled, thereby improving the controllability of the cavity filter's performance. Attached Figure Description

[0017] The present invention will be described by way of example and with reference to the accompanying drawings, wherein: Figure 1 This is a structural diagram of a multi-suspended cavity filter.

[0018] Figure 2 This is a structural diagram of a T-type waveguide.

[0019] Figure 3 This is a top view of the intermediate resonant cavity.

[0020] Figure 4This is a schematic diagram showing the intermediate resonant cavity connected by two coupling screws.

[0021] Figure 5 It is a graph showing the mapping between the spacing of the two coupling screws and the K value.

[0022] Figure 6 This is a schematic diagram showing the intermediate resonant cavity being connected using three coupling screws.

[0023] Figure 7 It is a graph showing the mapping between the spacing of the three coupling screws and the K value.

[0024] Figure 8 This is a structural diagram of an eighth-order fifth-transmission zero filter in one embodiment.

[0025] Figure 9 yes Figure 8 Performance test graph of the filter.

[0026] In the figure, input waveguide 1; output waveguide 2; left end of input waveguide 3; third coupling screw 4; third resonant cavity 5; second coupling screw 6; second resonant cavity 7; first coupling screw 8; first resonant cavity 9; right end of input waveguide 10; fourth coupling screw 11; fourth resonant cavity 12; fifth coupling screw 13; fifth resonant cavity 14; sixth coupling screw 15; sixth resonant cavity 16; seventh coupling screw 17; seventh resonant cavity 18; eighth coupling screw 19; eighth resonant cavity 20; ninth coupling screw 21; ninth resonant cavity 22; tenth coupling screw 23; tenth resonant cavity 24; eleventh coupling screw 25; left end of output waveguide 26; right end of output waveguide 27; twelfth coupling screw 28; eleventh resonant cavity 29; thirteenth coupling screw 30; twelfth resonant cavity 31; left resonant cavity F1; middle resonant cavity F2; right resonant cavity F3; coupling screw F4; input port 101; first port 102; second port 103; bottom boss 104. Detailed Implementation

[0027] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0028] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0029] Definitions: Longitudinal / Waveguide Longitudinal: This refers to the direction of the main transmission line, the path of the radio frequency signal from the input waveguide to the output waveguide. For a rectangular waveguide, it refers to the length direction of the rectangular waveguide.

[0030] Lateral / Waveguide Lateral: Refers to the direction perpendicular to the longitudinal direction. For a rectangular waveguide, it refers to the width direction of the rectangular waveguide.

[0031] Traditional methods for improving the passband and intra-band performance of cavity filters through cross-coupling or frequency-varying coupling, while introducing transmission zeros to enhance selectivity, suffer from limitations in the number and location of these zeros due to waveguide cavity geometry, increasing design complexity. To address this, this application provides a multi-suspended cavity filter and its design method. The aim is to introduce multiple controllable transmission zeros into the cavity filter through a simple structural design, thereby improving the selectivity and controllability of the cavity filter.

[0032] like Figure 1 As shown, this application embodiment provides a multi-suspended cavity filter, the filter comprising: (1) Input waveguide 1.

[0033] Input waveguide 1 provides an input port for radio frequency signals.

[0034] The input waveguide 1 has three ports, which are responsible for receiving radio frequency signals, connecting to the middle resonant cavity F2, and connecting to the left resonant cavity F1, respectively.

[0035] As an optional implementation, the input waveguide is a T-shaped waveguide. For example... Figure 2 As shown, the T-shaped waveguide includes three ports: input port 101, first port 102, and second port 103. Input port 101 is responsible for receiving radio frequency signals; first port 102 is the port away from the output waveguide and is used to couple and suspend the left resonant cavity F1; second port 103 is the port facing the output waveguide (i.e., the side away from the input waveguide) and is used to couple and connect the middle resonant cavity F2.

[0036] In one optional implementation, the input waveguide has an input port 101, a first port 102, and a second port 103, which are trench power-sharing waveguides. That is, the power / energy of the radio frequency signal input at the input port 101 is evenly distributed to the first port 102 and the second port 103.

[0037] For example, the first port 102 and the second port 103 of the input waveguide are connected back to back along the longitudinal direction (same as the filter axis), and the input port 101 is perpendicularly connected to the connection point of the two. A bottom boss 104 (recessed design) is formed at the bottom of the connection point of the first port 102 and the second port 103; the input port 101 is perpendicular to the longitudinal direction and is connected to the top of the connection point of the first port 102 and the second port 103, forming a top boss.

[0038] In one specific embodiment, input port 101, first port 102, and second port 103 all adopt the standard WR-75 rectangular waveguide dimensions. The top boss 104 is designed with a height of 10 mm, and the bottom boss 104 is designed with a height of 1.935 mm; the width of both the top and bottom bosses 104 is 7.776 mm. According to this embodiment, the cross-sections of other waveguides / resonant cavities also adopt the WR-75 rectangular waveguide dimensions.

[0039] (2) Output waveguide 2.

[0040] Output waveguide 2 provides an output port for the output of radio frequency signals.

[0041] The output waveguide 2 also includes three ports, which are responsible for outputting radio frequency signals, connecting to the middle resonant cavity F2, and connecting to the right resonant cavity F3, respectively.

[0042] Similar to the input waveguide, in one optional implementation, the output waveguide can also be a T-shaped waveguide. Corresponding to the function of the output waveguide, the T-shaped waveguide includes three ports: an output port, a first port 102, and a second port 103. The output port is responsible for outputting the (filtered) radio frequency signal; the first port 102 is the port facing the input waveguide (i.e., away from the output waveguide) and is used to couple the intermediate resonant cavity F2; the second port 103 is the port away from the input waveguide and is used to couple the suspension right resonant cavity F3.

[0043] Except for the difference in names between the output port and the input port 101, the optional structural design of the output waveguide can be completely the same as that of the input waveguide in the above optional embodiments. Therefore, the optional embodiments of the output waveguide will not be described in detail here.

[0044] (3) Intermediate resonant cavity F2.

[0045] An intermediate resonant cavity F2 is coupled between the input and output waveguides. There must be at least one intermediate resonant cavity F2, and its number is matched to the order of the coupling matrix of the filter design and the number of transmission zeros to be introduced. A higher order coupling matrix generally results in better filter performance, but correspondingly, the filter's structural complexity, size, and manufacturing cost will also be higher. Therefore, a comprehensive consideration of both filter performance and structural complexity is usually necessary. For example, assuming a 12th-order coupling matrix is ​​designed and 5 transmission zeros are planned to be introduced, then 7 intermediate resonant cavities F2 need to be sequentially coupled between the input and output waveguides.

[0046] (4) Left resonant cavity F1.

[0047] The left resonant cavities F1 (in sequence) are coupled and suspended at the first port 102 of the input waveguide. They introduce transmission zeros on the left side of the filter passband. The left end of the leftmost resonant cavity F1 is sealed. The number of suspended left resonant cavities F1 determines the number of transmission zeros introduced on the left side of the filter passband. Furthermore, the length L of the left resonant cavity F1 determines the frequency position of the corresponding introduced transmission zero. Therefore, the number of left resonant cavities F1 corresponds to the number of transmission zeros on the left side of the filter passband (the first introduction position relative to the filter passband); the length L of the left resonant cavity F1 matches the frequency of the corresponding transmission zero (the second introduction position relative to the specific frequency). Figure 3 As shown, the resonant frequency of the left resonant cavity F1 can be adjusted by changing its length L. The longer the length L, the lower the resonant frequency, and vice versa. In this way, the number and location (frequency) of the transmission zeros on the left side of the filter's passband can be conveniently and flexibly controlled.

[0048] (5) Right resonant cavity F3.

[0049] The right resonant cavities F3 (in sequence) are coupled and suspended at the second port 103 of the output waveguide. They introduce transmission zeros on the right side of the filter passband. The right end of the rightmost resonant cavity F3 is sealed. The number of suspensions of the right resonant cavities F3 determines the number of transmission zeros introduced on the right side of the filter passband. Furthermore, the length L of the right resonant cavity F3 determines the frequency position of the corresponding introduced transmission zero. Therefore, the number of right resonant cavities F3 corresponds to the number of transmission zeros on the right side of the filter passband (the first introduction position relative to the filter passband); the length L of the right resonant cavity F3 matches the frequency of the corresponding transmission zero (the second introduction position relative to a specific frequency). By adjusting the length L of the right resonant cavity F3, its resonant frequency can be adjusted; the longer the length L, the lower the resonant frequency, and vice versa. In this way, the number and introduction position (frequency) of the transmission zeros on the right side of the filter passband can be conveniently and flexibly controlled.

[0050] In summary, the number of left resonant cavities F1 and right resonant cavities F3 corresponds to the number and introduction position of transmission zeros (left or right side of the filter passband). The number of left resonant cavities F1 determines the number of transmission zeros on the left side of the filter passband, and the number of right resonant cavities F3 determines the number of transmission zeros on the right side of the filter passband. The lengths L of the left and right resonant cavities F1 and F3 are matched to the introduction positions of the transmission zeros. The length L of each left resonant cavity F1 determines the frequency position of each transmission zero on the left side of the filter passband, and the length L of each right resonant cavity F3 determines the frequency position of each transmission zero on the right side of the filter passband.

[0051] For the multi-suspended cavity filter designed in this application, there are no strict requirements on the overall structural shape of the input waveguide, output waveguide, intermediate resonant cavity F2, left resonant cavity F1, and right resonant cavity F3. That is, while maintaining the connection order, the filter can be arranged in a straight line; it can also be in a planar bending form, such as one of the intermediate resonant cavities F2 being "L"-shaped; or it can be in a spatial bending form, such as two (or more) intermediate resonant cavities F2 being "L"-shaped, and the bending directions not being on the same plane. As one relatively simple and easy-to-fabricate implementation, the input waveguide, output waveguide, intermediate resonant cavity F2, left resonant cavity F1, and right resonant cavity F3 are arranged in a straight line topology. In addition, even with a straight line topology, the orientation of the input waveguide and output waveguide (i.e., the orientation of the input / output RF signal ports) can be the same or opposite.

[0052] (6) Coupling screw.

[0053] The coupling screw is a key component for adjusting the coupling value (or K value) of the filter designed in this application.

[0054] The traditional method involves determining the coupling value of the resonant cavity by opening windows on both sides of the cavity's center. However, once the metal cavity is fabricated, its structure is completely fixed and cannot be adjusted later. If fabrication errors cause the coupling value to deviate from the design value, the filter may not be able to achieve its target specifications.

[0055] In this application, the connections between the input waveguide, output waveguide, intermediate resonant cavity F2, left resonant cavity F1, and right resonant cavity F3 are coupled and connected using coupling screws. Using coupling screws instead of opening windows on both sides allows for flexible adjustment of the resonant cavity coupling values ​​laterally. That is, it allows for the batch fabrication of rectangular waveguides (or other types of waveguides) first, followed by adjustment of the coupling values ​​at each longitudinal position using coupling screws. For example, based on the designed coupling matrix, the coupling value / k value at each connection of the intermediate resonant cavity F2 is determined, and then the lateral position of each coupling screw is determined. The lateral position of the coupling screws at the connection between the left resonant cavity F1 and the right resonant cavity F3 is determined using the same principle.

[0056] By using coupling screws (such as screws with a 1mm radius), even after the resonant cavity has been fabricated, the coupling value of the resonant cavity can be adjusted laterally by adjusting the lateral position of the coupling screws. Furthermore, by adjusting the screw-in depth, the coupling value can be precisely and continuously fine-tuned during the debugging phase to compensate for fabrication errors. This not only improves the fabrication efficiency of the resonant cavity but also reduces the precision requirements for its fabrication, while making subsequent debugging feasible and efficient.

[0057] As an optional implementation, for any coupling connection location, such as Figure 3 As shown, there are two or three coupling screws. These two or three coupling screws are arranged laterally (i.e., along the width of the rectangular waveguide). The spacing between the two or three coupling screws matches the coupling value at the longitudinal position of the coupling screw. That is, in this application, as... Figure 3 As shown, the coupling value of the corresponding resonant cavity is adjusted by changing the width W between two or three coupling screws. Experiments show that a wider spacing W results in a larger coupling value, and vice versa. The spacing between the three coupling screws refers to the distance between the two coupling screws at the ends.

[0058] In one specific implementation, three coupling screws are used when the K value corresponding to the coupling value is below a set threshold (e.g., K=0.055 for a WR-75 rectangular waveguide). When the K value corresponding to the coupling value reaches the threshold, two coupling screws are used.

[0059] Furthermore, as a convenient and effective implementation method, using two coupling screws, such as Figure 4 As shown, the two coupling screws are arranged symmetrically about the filter axis, according to... Figure 5 The mapping relationship shown indicates that the spacing W between the two coupling screws should be adjusted to match the required K value. If the corresponding K value cannot be achieved using two coupling screws, then three coupling screws are required, such as... Figure 6As shown, at this point, a second coupling screw is inserted between the two coupling screws. This second coupling screw intersects the axis of the filter and remains in the same position. According to... Figure 7 The mapping curve shown is still matched with the K value by adjusting the original spacing W of the two coupling screws on both sides. After determining the spacing W, the two coupling screws on both sides are arranged symmetrically about the axis of the filter.

[0060] For example, suppose an eighth-order filter with five transmission nodes is designed using the above structure, and its linear topology is as follows: Figure 8 As stated above.

[0061] In this filter, both the input and output waveguides are WR-75 rectangular waveguides. For example... Figure 8 As shown, from left to right, the filter includes: a first resonant cavity 9, a second resonant cavity 7, a third resonant cavity 5, an input waveguide 1, a fourth resonant cavity 12, a fifth resonant cavity 14, a sixth resonant cavity 16, a seventh resonant cavity 18, an eighth resonant cavity 20, a ninth resonant cavity 22, a tenth resonant cavity 24, an output waveguide 2, an eleventh resonant cavity 29, and a twelfth resonant cavity 31. Specifically, the first resonant cavity 9, the second resonant cavity 7, and the third resonant cavity 5 are all left-side resonant cavities (F1), used to introduce three transmission zeros on the left side of the filter's passband; the fourth resonant cavity 12, the fifth resonant cavity 14, the sixth resonant cavity 16, the seventh resonant cavity 18, the eighth resonant cavity 20, the ninth resonant cavity 22, and the tenth resonant cavity 24 are all middle resonant cavities (F2), used for matching with the eighth-order filter; and the eleventh resonant cavity 29 and the twelfth resonant cavity 31 are both right-side resonant cavities (F3), used to introduce two transmission zeros on the right side of the filter's passband. The final performance test diagram of the filter is shown below. Figure 9 As shown.

[0062] The first resonant cavity 9 and the second resonant cavity 7 are coupled together by the first coupling screw 8; the second resonant cavity 7 and the third resonant cavity 5 are coupled together by the second coupling screw 6; the third resonant cavity 5 and the left end 3 of the input waveguide are coupled together by the third coupling screw 4; the fourth resonant cavity 12 and the right end 10 of the input waveguide are coupled together by the fourth coupling screw 11; the fourth resonant cavity 12 and the fifth resonant cavity 14 are coupled together by the fifth coupling screw 13; the fifth resonant cavity 14 and the sixth resonant cavity 16 are coupled together by the sixth coupling screw 15; and the sixth resonant cavity 16 and the seventh resonant cavity 18 are coupled together by the seventh coupling screw 16. The seventh resonant cavity 18 and the eighth resonant cavity 20 are coupled together via screw 17. The eighth resonant cavity 20 and the ninth resonant cavity 22 are coupled together via screw 21. The ninth resonant cavity 22 and the tenth resonant cavity 24 are coupled together via screw 23. The tenth resonant cavity 24 and the left end 26 of the output waveguide are coupled together via screw 25. The eleventh resonant cavity 29 and the right end 27 of the output waveguide are coupled together via screw 28. The eleventh resonant cavity 29 and the twelfth resonant cavity 31 are coupled together via screw 30. The radius of each coupling screw is 1 mm.

[0063] Both input waveguide 1 and output waveguide 2 adopt the following... Figure 2 The T-shaped waveguide structure shown has WR-75 rectangular waveguide dimensions at all three ports. The top boss is 10mm high, the bottom boss 104 is 1.935mm high, and both are 7.776mm wide.

[0064] The radio frequency (RF) signal is input through input waveguide 1, and the energy is evenly distributed to both sides, ultimately outputting through output waveguide 2. On one side of the suspended left resonant cavity F1, when the RF signal resonates in the third resonant cavity 5, the energy cannot be transferred to the output port, thus creating a transmission zero. The same principle applies to the other left resonant cavities F1 (first resonant cavity 9 and second resonant cavity 7) and right resonant cavities F3 (eleventh resonant cavity 29 and twelfth resonant cavity 31). This introduces a total of five transmission zeros. Furthermore, the resonant frequency at each transmission zero can be adjusted by the length L of the corresponding resonant cavity, allowing for relatively independent and flexible control of the transmission zeros.

[0065] Based on the ideas of this application, this application also proposes a design method for a multi-suspended cavity filter, which includes the following multiple stages.

[0066] Phase 1: Construct the filter coupling matrix. Determine the number and location of transmission zeros.

[0067] The construction of the coupling matrix belongs to the early planning stage of the filter. Based on the required performance indicators, the order of the coupling matrix and the coupling value / K value of each order are determined to facilitate the later planning of the number and position of the coupling screws.

[0068] The number of transmission zeros to be introduced and the coupling frequency (frequency point location) of each transmission zero are determined to facilitate the later planning of the number and length of resonant cavities. The order of the (standard) coupling matrix corresponds to the total number of resonant cavities, while the number of resonant cavities on the left and right sides corresponds to the number of transmission zeros. Therefore, the difference between the order of the coupling matrix and the number of transmission zeros determines the number of the middle resonant cavity F2.

[0069] Phase 1 is a routine step in the early planning of the filter. The specific construction method is not part of the design focus of this application, so it will not be described in detail here.

[0070] Phase 2: Based on the order of the coupling matrix, at least one intermediate resonant cavity F2 is coupled between the input waveguide and the output waveguide.

[0071] As mentioned above, once the order of the coupling matrix and the number of transmission zeros (whether located on the left or right side of the filter passband) are determined, the number of intermediate resonant cavities F2 can be determined. A corresponding number of intermediate resonant cavities F2 are then coupled between the input waveguide and the output waveguide.

[0072] Furthermore, the coupling value / K value at each order of the coupling matrix determines the coupling connection parameters at the connection points of each intermediate resonant cavity F2. For example, when coupling screws are used for coupling connection, the number and position (spacing W) of the coupling screws are determined.

[0073] Phase 3: Based on the number and location of transmission zeros, determine the number and length of the left resonant cavity F1 and the right resonant cavity F3, and connect them to the input waveguide and the output waveguide, respectively.

[0074] Specifically, the left resonant cavity F1 is coupled and suspended to the first port 102 of the input waveguide, as mentioned earlier, the first port 102 being located at the end furthest from the output waveguide. The right resonant cavity F3 is coupled and suspended to the second port 103 of the output waveguide, as mentioned earlier, the second port 103 being located at the end furthest from the input waveguide.

[0075] The number of left resonant cavities F1 and right resonant cavities F3 corresponds to the number and introduction position of transmission zeros. This is a constraint on the total number of resonant cavities on both sides. Specifically, the number of left resonant cavities F1 corresponds to (is the same as) the number of transmission zeros introduced on the left side of the filter passband; the number of right resonant cavities F3 corresponds to (is the same as) the number of transmission zeros introduced on the right side of the filter passband.

[0076] Furthermore, the lengths L of the left resonant cavity F1 and the right resonant cavity F3 are matched with the introduction positions of the transmission zeros. Here, the length L of the left resonant cavity F1 or the right resonant cavity F3 is constrained based on the resonant frequency of the transmission zero. The length L of the left resonant cavity F1 or the right resonant cavity F3 directly determines the resonant frequency of its corresponding transmission zero. Based on this relationship, once the resonant frequency of the transmission zero is determined, it is necessary to reverse-engineer the length L of the corresponding left resonant cavity F1 or the right resonant cavity F3.

[0077] In one optional implementation, the coupling connection at the connection points of the aforementioned resonant cavities can be achieved using coupling screws. Taking the coupling connection of the middle resonant cavity F2 as an example, based on the coupling / K values ​​of each order and referring to the historically fitted WK curve (i.e., the mapping curve between the width of the coupling screw and the K value), the number (same as the threshold-based judgment method mentioned earlier) and spacing of the coupling screws are obtained. The coupling screws are then set according to these parameters. For the left resonant cavity F1 or the right resonant cavity F3, the coupling screws can also be set in the same way according to the corresponding coupling / K value requirements.

[0078] This invention is not limited to the specific embodiments described above. The invention extends to any new feature or combination disclosed in this specification, as well as any new method or process step or combination disclosed herein.

Claims

1. A multi-suspension cavity filter, characterized in that, The filter includes: Input waveguide; Output waveguide; At least one intermediate resonant cavity is coupled between the input waveguide and the output waveguide; the number of intermediate resonant cavities is matched with the order of the filter coupling matrix and the number of transmission zeros to be introduced. At least one left resonant cavity is coupled and suspended at the first port of the input waveguide, the first port being located at the end away from the output waveguide; at least one right resonant cavity is coupled and suspended at the second port of the output waveguide, the second port being located at the end away from the input waveguide; the number of the left and right resonant cavities corresponds to the number and introduction position of the transmission zeros; the length of the left and right resonant cavities matches the introduction position of the transmission zeros.

2. The multi-suspended cavity filter as described in claim 1, characterized in that, The connections between the input waveguide, output waveguide, intermediate resonant cavity, left resonant cavity, and right resonant cavity are respectively coupled and connected by coupling screws; the lateral setting position of the coupling screw matches the coupling value of the longitudinal position of the coupling screw.

3. The multi-suspended cavity filter as described in claim 2, characterized in that, The number of coupling screws is two or three; the two or three coupling screws are arranged in a transverse direction; the spacing between the two or three coupling screws matches the coupling value at the longitudinal position of the coupling screw.

4. The multi-suspended cavity filter as described in claim 3, characterized in that, When the K value corresponding to the coupling value is below the set threshold, three coupling screws are used; when the K value corresponding to the coupling value reaches the threshold, two coupling screws are used.

5. The multi-suspended cavity filter as described in claim 3 or 4, characterized in that, When using two coupling screws, the two coupling screws are arranged symmetrically about the filter axis; when using three coupling screws, the middle coupling screw intersects the filter axis, and the two coupling screws on both sides are arranged symmetrically about the filter axis.

6. The multi-suspended cavity filter as described in claim 1, characterized in that, Both the input waveguide and the output waveguide are T-type waveguides.

7. The multi-suspended cavity filter as described in claim 6, characterized in that, The T-shaped waveguide includes an input / output port, a first port, and a second port; the input / output port, the first port, and the second port together form a split waveguide.

8. The multi-suspended cavity filter as described in claim 7, characterized in that, The first port and the second port are connected back to back along the longitudinal direction, and a bottom boss is formed at the bottom of the connection between the first port and the second port; the input / output port is perpendicular to the longitudinal direction and is connected to the top of the connection between the first port and the second port, forming a top boss.

9. The multi-suspended cavity filter as described in claim 6, characterized in that, The input waveguide, output waveguide, intermediate resonant cavity, left resonant cavity, and right resonant cavity form a linearly arranged topology.

10. A design method for a multi-suspended cavity filter, characterized in that, include: Construct the filter coupling matrix; Determine the number and placement of transmission zeros; Based on the order of the coupling matrix, at least one intermediate resonant cavity is coupled between the input waveguide and the output waveguide. Based on the number and introduction position of the transmission zeros, the number and length of the left and right resonant cavities are determined respectively; the left resonant cavity is coupled and suspended to the first port of the input waveguide, the first port being located at the end away from the output waveguide; the right resonant cavity is coupled and suspended to the second port of the output waveguide, the second port being located at the end away from the input waveguide; wherein, the number of the left and right resonant cavities corresponds to the number and introduction position of the transmission zeros; the length of the left and right resonant cavities matches the introduction position of the transmission zeros.

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