Broadband coaxial filter
By designing a coupling loop structure and a multi-turn tapped line tuning structure in the coaxial filter, the shortcomings of existing coaxial filters in a wide bandwidth range are solved, the filter bandwidth is enhanced and the external Q value is tuned, and the debugging process is simplified.
Patent Information
- Application Number
- CN202511720807.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-21
- Publication Date
- 2026-03-06
AI Technical Summary
Existing coaxial filters cannot meet the requirements when a wide bandwidth is needed, and traditional design methods are difficult to implement broadband filters.
The coupling between coaxial filters is enhanced by designing a coupling loop structure, and the external Q value of the filter is changed by a multi-turn tapped line tuning structure to meet different bandwidth requirements.
It achieves enhanced filter bandwidth and tuning of external Q value, meets the bandwidth requirements of different filters, and simplifies the debugging process.
Smart Images
Figure CN121618157A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of filter technology, and specifically relates to a broadband coaxial filter. Background Technology
[0002] Coaxial cavity bandpass filters are widely used in communication, radar, and other systems. They are generally classified into standard coaxial and square cavity coaxial filters based on their cavity structure. Coaxial cavities are characterized by high Q-values and ease of implementation, making them particularly suitable for applications requiring narrow passbands, low in-band insertion loss, and high out-of-band rejection. The traditional design method involves looking up the coupling coefficients between cavities according to response requirements (such as Chebyshev response) in a table, and then using approximate calculation methods to design the corresponding coupling and input / output structures.
[0003] In practical engineering applications, broadband filters are often required. Existing filters adjust the bandwidth by adjusting the layout of the tuning rod and changing the step structure of the resonant rod. However, existing coaxial filters cannot meet the requirements when a wide range of bandwidth is needed. Summary of the Invention
[0004] In view of the above problems, this application proposes a broadband coaxial filter. By designing a coupling loop structure, the coupling between coaxial filters can be enhanced, thereby increasing the filter bandwidth; at the same time, by designing a multi-turn tapped line tuning structure, the external Q value of the filter can be easily changed, thus meeting different filter bandwidth requirements.
[0005] This application provides a broadband coaxial filter, including:
[0006] The shielding cavity is an externally shielded structure, wherein the shielding cavity has a cuboid structure and the top of the shielding cavity includes a detachable top cover plate.
[0007] The shielding cavity is provided with no fewer than three resonant rods, each of which is cylindrical; wherein the second, third, and fourth resonant rods are alternately and in opposite directions arranged on the shielding cavity.
[0008] Each resonant rod has a fixing screw at its bottom, which is used to fix the resonant rod to the shielding cavity.
[0009] The bottoms of the second and fourth resonant rods are respectively fitted with the fifth and sixth polytetrafluoroethylene sheaths.
[0010] Coupler rings are provided alternately between each resonant rod. The top of the coupler ring is welded to the bottom of the coupling tuning screw that passes through the top cover plate. The top cover plate is provided with a locking nut that matches the coupling tuning screw.
[0011] Preferably, the outer wall of the fifth polytetrafluoroethylene sheath is provided with recessed threads and wound with a fifth silver-plated tap copper wire;
[0012] The fifth silver-plated tap copper wire is connected to the filter input connector;
[0013] The fifth silver-plated tap copper wire is tightly wound in multiple turns around the outside of the fifth polytetrafluoroethylene sheath.
[0014] Preferably, the outer wall of the sixth polytetrafluoroethylene sheath is provided with recessed threads and wound with a sixth silver-plated tap copper wire;
[0015] The sixth silver-plated tap copper wire is connected to the filter output connector;
[0016] The sixth silver-plated tap copper wire is tightly wound in multiple turns around the outside of the sixth polytetrafluoroethylene sheath.
[0017] Preferably, the lower branch of the fifth silver-plated tap copper wire is connected to the access terminal of the filter input connector, and the upper branch of the fifth silver-plated tap copper wire is connected to the fixing screw of the filter input connector.
[0018] The fixing screws are fixed to the left side wall of the filter shielding cavity;
[0019] The lower branch of the sixth silver-plated tap copper wire is connected to the output terminal of the filter output connector, and the upper branch of the sixth silver-plated tap copper wire is connected to the fixing screw of the filter output connector.
[0020] The fixing screws are fixed to the right side wall of the filter shielding cavity.
[0021] Preferably, a tapped tuning screw is provided at the bottom of the shielding cavity near the fifth polytetrafluoroethylene sheath, and the bottom of the tapped tuning screw has a spindle-shaped structure; the tapped tuning screw is fixed to the bottom of the filter shielding cavity by a tapped tuning nut.
[0022] A tapped tuning screw is provided at the bottom of the shielding cavity near the sixth polytetrafluoroethylene sheath. The bottom of the tapped tuning screw has a spindle-shaped structure. The tapped tuning screw is fixed to the bottom of the filter shielding cavity by a tapped tuning nut.
[0023] Preferably, the second resonant rod is fixed to the bottom of the shielding cavity by a second fixing screw;
[0024] The top of the second resonant rod is hollow, forming a capacitive loading form with the second frequency tuning screw on the top cover plate; used to tune the resonant frequency of the second resonant rod.
[0025] The second frequency tuning screw is fitted with a second locking nut for locking the second frequency tuning screw.
[0026] Preferably, the fourth resonant rod is fixed to the bottom of the shielding cavity by a fourth fixing screw;
[0027] The top of the fourth resonant rod is hollow, forming a capacitive loading form with the fourth frequency tuning screw on the top cover plate; used to tune the resonant frequency of the fourth resonant rod.
[0028] The fourth frequency tuning screw is fitted with a fourth locking nut for locking the fourth frequency tuning screw.
[0029] Preferably, the third resonant rod is disposed between the second and fourth resonant rods, and the third resonant rod forms an interdigital structure with the second and fourth resonant rods;
[0030] The third resonant rod is fixed to the top of the shielding cavity by the third fixing screw;
[0031] The top of the third resonant rod is hollow, forming a capacitive loading form with the third frequency tuning screw at the bottom of the shielding cavity; used to tune the resonant frequency of the third resonant rod.
[0032] The third frequency tuning screw is fitted with a third locking nut for locking the third frequency tuning screw.
[0033] Preferably, a seventh coupling ring made of silver-plated copper wire is provided between the second resonant rod and the third resonant rod;
[0034] The seventh coupling ring is welded to the bottom of the seventh coupling tuning screw that passes through the top cover plate;
[0035] The top cover plate is equipped with a seventh locking nut that matches the seventh coupling tuning screw.
[0036] Preferably, an eighth coupling ring made of silver-plated copper wire is provided between the third resonant rod and the fourth resonant rod;
[0037] The eighth coupling ring is welded to the bottom of the eighth coupling tuning screw that passes through the top cover plate;
[0038] The top cover plate is equipped with an eighth locking nut that matches the eighth coupling tuning screw.
[0039] The beneficial effects of this application are:
[0040] Based on the above technical solution, the top of the shielding cavity includes a detachable top cover plate; the shielding cavity is provided with no fewer than three resonant rods, each resonant rod being a cylindrical structure; each resonant rod has a fixing screw at its bottom, which fixes the resonant rod to the shielding cavity; the bottoms of the second and fourth resonant rods are respectively fitted with a fifth and a sixth PTFE sheath; coupling rings are arranged alternately between the resonant rods, the top of which is welded to the bottom of a coupling tuning screw passing through the top cover plate, and a locking nut that mates with the coupling tuning screw is provided on the top cover plate. By designing the coupling ring structure, the coupling between coaxial filters can be enhanced, increasing the filter bandwidth. Simultaneously, the number of tap turns can be changed by using the tuning tap screw, thereby changing the external Q value of the filter feed to adapt to different bandwidth requirements of the filter.
[0041] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures pointed out in the description and the accompanying drawings. Attached Figure Description
[0042] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0043] Figure 1 This paper shows a schematic diagram of the main structure of a broadband coaxial filter according to an embodiment of the present application.
[0044] Figure 2 A side view of the resonant rod according to an embodiment of this application is shown;
[0045] Figure 3 A schematic diagram of the tap tuning structure according to an embodiment of this application is shown;
[0046] Figure 4 This paper shows a top view of a broadband coaxial filter according to an embodiment of the present application.
[0047] Figure 5 A schematic diagram of the coupling loop operation according to an embodiment of this application is shown;
[0048] Figure 6 A schematic diagram of the silver-plated tap copper wire feeding according to an embodiment of this application is shown. Detailed Implementation
[0049] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0050] It should be noted that the terms "first," "second," etc., used in this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," "longitudinal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings.
[0051] Existing coaxial filters are particularly suitable for applications with narrow passbands (typically less than 10%), low in-band insertion loss, and high out-of-band rejection. Their traditional design method involves looking up tables based on response requirements (such as Chebyshev response) to calculate the coupling coefficients between cavities, and then using approximate calculation methods to design the corresponding coupling and input / output structures. When the filter bandwidth is greater than 30%, even a simple interdigital filter cannot meet the requirements.
[0052] To address this, this application designs a broadband coaxial filter. By adding a tunable coupling ring between the filter resonant rods, the coupling of the filter resonant rods can be increased. By using multi-turn coupling feed at both ends of the filter in conjunction with tuning screws, different external Q values can be tuned, thereby meeting different bandwidth requirements.
[0053] This application provides a broadband coaxial filter, see [link to relevant documentation]. Figure 1 It includes: an externally shielded shielding cavity A1, wherein the shielding cavity A1 has a cuboid structure and the top of the shielding cavity A1 includes a detachably connected top cover plate A11.
[0054] The shielding cavity A1 is provided with no fewer than three resonant rods, and the resonant rods are cylindrical structures; wherein, the second resonant rod A2, the third resonant rod A3 and the fourth resonant rod A4 are alternately and in opposite directions arranged on the shielding cavity A1;
[0055] Each resonant rod has a fixing screw at its bottom, which is used to fix the resonant rod to the shielding cavity A1.
[0056] The bottoms of the second resonant rod A2 and the fourth resonant rod A4 are respectively fitted with the fifth polytetrafluoroethylene sheath A54 and the sixth polytetrafluoroethylene sheath A64.
[0057] Tapped tuning screws A52 and A62 are provided at the bottom of the shielding cavity near the fifth PTFE sheath A54 and the sixth PTFE sheath A64. Tapped tuning screws A52 and A62 are fixed to the bottom of the filter shielding cavity by tapped tuning nuts A53 and A63.
[0058] Coupler rings are provided alternately between each resonant rod. The top of the coupler ring is welded to the bottom of the coupling tuning screw that passes through the top cover plate A11. The top cover plate A11 is provided with a locking nut that matches the coupling tuning screw.
[0059] Specifically, see Figure 1 , Figure 1 This is a side view of the broadband coaxial filter of this application. The filter is a third-order square-cavity cylindrical rod type, meaning the outer shielding cavity A1 is a cuboid structure, and the interior includes a second resonant rod A2, a third resonant rod A3, and a fourth resonant rod A4. The resonant rods are SIR cylindrical structures, i.e., step impedance resonators (SIR). See [link to relevant documentation]. Figure 2 The resonant rod has a thicker top and lower impedance, and a thinner bottom and higher impedance. The input impedance and admittance are defined as Zi and [missing information - likely a specific characteristic]. Z1 is the short-circuit impedance, and Z2 is the open-circuit impedance. If the discontinuity of the step impedance and the edge capacitance at the open-circuit end are ignored, the input impedance expression is:
[0060]
[0061] set up Then the resonance condition is:
[0062]
[0063] have to:
[0064]
[0065] Therefore, the resonance condition of SIR depends on the short-circuit impedance angle. Open road surface impedance angle and impedance Therefore, in addition to the resonator length, the impedance can also be changed. Adjusting the resonant frequency of the SIR. The coaxial resonator rod is a quarter-wavelength resonator; to change the resonant frequency, the resonator length must be changed. Using an SIR structure allows for a significant reduction in size compared to a quarter-wavelength resonator.
[0066] It should be noted that the number of resonant rods in this application can be set according to the actual situation of the coaxial filter. This application does not specifically limit the number of resonant rods of the coaxial filter, but only uses three resonant rods as an example. These three resonant rods should not be construed as the scope of protection of this application being limited to only three resonant rods.
[0067] In this embodiment, the top cover plate A11 of the shielding cavity A1 is generally detachable. The shielding cavity A1 and the top cover plate A11 are detachably connected, typically using screws for fastening.
[0068] The second resonant rod A2 is fixed to the bottom of the shielding cavity by the second fixing screw A23; the top of the second resonant rod A2 is a hollow structure, which forms a capacitor loading form with the second frequency tuning screw A21 on the top cover plate, and is used to tune the resonant frequency of the second resonant rod A2. After the second frequency tuning screw A21 is tuned, it is locked and fixed by the second locking nut A22.
[0069] In this embodiment, the structure and adjustment method of the fourth resonant rod A4 are the same as those of the second resonant rod A2. The structure and adjustment method of the fourth resonant rod A4 in this specification are based on the second resonant rod A2 as an example, and will not be described again.
[0070] See Figure 1 and Figure 3 The embodiments of this application also include: the outer wall of the fifth polytetrafluoroethylene sheath A54 is provided with a recessed thread and the fifth silver-plated tap copper wire A51 is wound around it;
[0071] The fifth silver-plated tap copper wire A51 is connected to the filter input connector A5;
[0072] The fifth silver-plated tap copper wire A51 is tightly wound in multiple turns around the outside of the fifth polytetrafluoroethylene sheath A54.
[0073] The outer wall of the sixth polytetrafluoroethylene sheath A64 is provided with recessed threads and is wound with the sixth silver-plated tap copper wire A61.
[0074] The sixth silver-plated tap copper wire A61 is connected to the filter output connector A6;
[0075] The sixth silver-plated tap copper wire A61 is tightly wound in multiple turns around the outside of the sixth polytetrafluoroethylene sheath A64.
[0076] The lower branch of the fifth silver-plated tap copper wire A51 is connected to the access terminal A56 of the filter input connector A5, and the upper branch of the fifth silver-plated tap copper wire A51 is connected to the fixing screw A55 of the filter input connector A5.
[0077] Fixing screw A55 is fixed to the left side wall of the filter shielding cavity A1;
[0078] The lower branch of the sixth silver-plated tap copper wire A61 is connected to the output terminal A66 of the filter output connector A6, and the upper branch of the sixth silver-plated tap copper wire A61 is connected to the fixing screw A65 of the filter output connector A6.
[0079] The fixing screw A65 is fixed to the right side wall of the filter shielding cavity A1.
[0080] Specifically, the bottom of the second resonant rod A2 is fitted with a fifth PTFE sheath A54. The inner wall of the fifth PTFE sheath A54 is tightly attached to the second resonant rod A2, and the outer wall is designed with recessed threads. A fifth silver-plated tap copper wire A51 is tightly wound on the recessed threads. One end of the fifth silver-plated tap copper wire A51 is soldered to the solder terminal A56 of the fifth connector A5 at the input end of the filter, and the other end is soldered to the top of the fixing screw A55. The fixing screw A55 is fixed to the side wall of the filter and is near the input connector A5. Next to the fifth PTFE sheath A54, a tap tuning screw A52 is designed. The bottom of the tap tuning screw A52 has a spindle-shaped structure. The spindle-shaped structure at the bottom of the tap tuning screw ensures reliable contact between the thickest part of the spindle and one turn of the multi-turn spiral copper wire.
[0081] See Figure 1 and Figure 3 The embodiments of this application further include: a tapped tuning screw A52 is provided at the bottom of the shielding cavity A1 near the fifth polytetrafluoroethylene sheath A54, the bottom of the tapped tuning screw A52 has a spindle-shaped structure; the tapped tuning screw A52 is fixed to the bottom of the filter shielding cavity A1 by a tapped tuning nut A53;
[0082] A tapped tuning screw A62 is provided at the bottom of the shielding cavity A1 near the sixth polytetrafluoroethylene sheath A64. The bottom of the tapped tuning screw A62 has a spindle-shaped structure. The tapped tuning screw A62 is fixed to the bottom of the filter shielding cavity A1 by a tapped tuning nut A63.
[0083] Specifically, see Figure 3 The tap tuning screw A52 is fixed to the bottom of the filter by the tap tuning nut A53. The spindle-shaped structure of A52 ensures that only one turn of the multi-turn silver-plated tap wire on A54 makes reliable contact with the tap tuning screw. The tap wire above the contact point is connected to the filter, and the tap wire below the contact point is short-circuited and not connected to the filter.
[0084] See Figure 1 The embodiments of this application further include: the second resonant rod A2 is fixed to the bottom of the shielding cavity A1 by the second fixing screw A23;
[0085] The top of the second resonant rod A2 has a hollow structure, which forms a capacitor loading form with the second frequency tuning screw A21 on the top cover plate; it is used to tune the resonant frequency of the second resonant rod A2.
[0086] The second frequency tuning screw A21 is fitted with a second locking nut A22 for locking the second frequency tuning screw A21.
[0087] The fourth resonant rod A4 is fixed to the bottom of the shielding cavity A1 by the fourth fixing screw A43;
[0088] The top of the fourth resonant rod A4 is hollow, forming a capacitive loading form with the fourth frequency tuning screw A41 on the top cover plate; used to tune the resonant frequency of the fourth resonant rod A4.
[0089] The fourth frequency tuning screw A41 is fitted with a fourth locking nut A42 for locking the fourth frequency tuning screw A41. The resonant rod A4 has the same structure as the resonant rod A2 and is fed through the tap line A61.
[0090] See Figure 1 , Figure 4 and Figure 5 The embodiments of this application further include: a third resonant rod A3 is disposed between the second resonant rod A2 and the fourth resonant rod A4, and the third resonant rod A3 forms an interdigital structure with the second resonant rod A2 and the fourth resonant rod A4;
[0091] The third resonant rod A3 is fixed to the top of the shielding cavity A1 by the third fixing screw A33;
[0092] The top of the third resonant rod A3 is hollow, forming a capacitive loading form with the third frequency tuning screw A31 at the bottom of the shielding cavity A1; used to tune the resonant frequency of the third resonant rod A3.
[0093] The third frequency tuning screw A31 is fitted with a third locking nut A32 for locking the third frequency tuning screw A31.
[0094] Specifically, the third resonant rod A3 is installed in the opposite direction to the second resonant rod A2 and the fourth resonant rod A4. It is fixed to the top cover plate A11 by the third fixing screw A33. A third frequency tuning filter A31 is designed at the bottom of the filter.
[0095] The resonant rods A2, A3 and A4 form an interdigital structure. The currents in adjacent resonant rods are in opposite directions, and the magnetic fields generated are superimposed in phase at the interdigital gap, forming a stronger magnetic field coupling.
[0096] See Figure 1 The embodiments of this application also include: a seventh coupling ring A7 made of silver-plated copper wire is provided between the second resonant rod A2 and the third resonant rod A3;
[0097] The seventh coupling ring A7 is welded to the bottom of the seventh coupling tuning screw A71 that passes through the top cover plate A11; adjusting the seventh coupling tuning screw can change the direction of the seventh coupling ring, thereby changing the coupling between the second resonant rod and the third resonant rod to adapt to different bandwidth requirements of the filter.
[0098] The top cover plate A11 is provided with a seventh locking nut A72 that matches the seventh coupling tuning screw A71.
[0099] An eighth coupling ring A8, made of silver-plated copper wire, is provided between the third resonant rod A3 and the fourth resonant rod A4.
[0100] The eighth coupling ring A8 is welded to the bottom of the eighth coupling tuning screw A81 that passes through the top cover plate A11;
[0101] Adjusting the eighth coupling tuning screw can change the direction of the eighth coupling ring, thereby changing the coupling between the third and fourth resonant rods to adapt to different bandwidth requirements of the filter;
[0102] The top cover plate A11 is provided with an eighth locking nut A82 that matches the eighth coupling tuning screw A81.
[0103] Specifically, to further enhance coupling and broaden the operating bandwidth of the filter, this application designs coupling loops A7 and A8 between two adjacent resonant rods.
[0104] Specifically, coupling ring A7 is made of silver-plated copper wire with a diameter of 1mm-2mm. The top center of the coupling ring is soldered to the bottom of coupling tuning screw A71, which is then fixed to the top cover plate A11 of the filter using locking nut A72. Coupling ring A7 significantly enhances the electric and magnetic field coupling between resonant rods A2 and A3. Adjusting coupling tuning screw A71 changes the direction of coupling ring A7, thus altering the coupling magnitude. When the coupling is properly adjusted, locking nut A72 secures coupling ring A7 in place. Coupling rings are generally designed with a uniform structure, and their coupling magnitude is changed by adjusting their direction. Unless individual couplings differ significantly, coupling rings of different sizes can be used to reduce oversensitivity during tuning. The design of coupling ring A8 is similar to that of coupling ring A7 and will not be described further.
[0105] The top view of the filter in this application is shown below. Figure 4 As shown. This application enhances the coupling between coaxial filters and increases the filter bandwidth by designing a coupling loop structure; at the same time, this application designs a multi-turn tapped line tuning structure, which can change the external Q value of the filter, thereby meeting different filter bandwidth requirements and greatly facilitating filter tuning.
[0106] The working principle of the coaxial filter of this application will be explained in detail below with reference to the accompanying drawings.
[0107] According to the basic principles of filters, when designing a coaxial filter, the length of its resonant rod is first designed according to its operating frequency, and its coupling coefficient and external Q value are calculated based on the operating bandwidth. Then, the specific structural parameters of the coaxial filter can be determined with the help of three-dimensional electromagnetic simulation software.
[0108] The resonant rod of a coaxial filter can be equivalent to a quarter-wavelength resonator. Due to the capacitive loading effect at the top, the actual length of the resonant rod will be shorter than a quarter wavelength. If a SIR step impedance resonator is used, such as Figure 2 As shown, its length can be further shortened. The resonant frequency of the resonant rod can be expressed as:
[0109]
[0110] Where L is the inductance and C is the applied capacitance. Given the power supply frequency, it can be seen that changing the length of the resonant rod corresponds to changing the inductance L, and changing the length of the frequency tuning screw at the top of the resonant rod corresponds to changing the loading capacitor C. During the design process, 3D simulation software can be used to design the length of the resonant rod to a suitable size, and the operating frequency of the resonant rod can be fine-tuned using the frequency tuning screw.
[0111] To calculate the external Q value of the filter First, the relative bandwidth of the filter needs to be calculated, as shown in the following formula:
[0112]
[0113] Obtain the external Q value of the filter
[0114]
[0115] Coupling coefficient The calculation formula is as follows:
[0116]
[0117] In the above formula All parameters are derived from the filter prototype and can be obtained by looking up tables or using filter design software. Therefore, it can be concluded that to obtain a larger bandwidth... Requires filter coupling coefficients Increase, external Q value of the filter It gets smaller.
[0118] It should be noted that the bandwidth of a coaxial filter is generally no more than 10%. At the top of the quarter-wavelength resonant rod, the electric field distribution is dominant, while at the bottom, the magnetic field distribution is dominant. If a partition is designed at the bottom of each resonant cavity to separate the two resonant rods, the coupling between the two rods is electric field coupling. If the partition is designed at the top of the resonant cavity, the coupling between the two rods is magnetic field coupling. Therefore, to increase the coupling between the resonant rods, a broadband filter is designed. The original partition is removed, and the installation direction of the resonant rods is reversed, resulting in an interdigital filter design, such as... Figure 1 As shown. In an interdigital filter, the coupling between resonant rods changes from a single electric field coupling or magnetic field coupling to a positive superposition of electric and magnetic field couplings: Interdigital filters can significantly enhance the coupling between resonant rods, and the filter design bandwidth can reach 30%. When a wider bandwidth filter needs to be designed, the resonant rods of the interdigital filter need to be very closely spaced, making the filter difficult to tune or impossible to achieve.
[0119] To address the design problem of broadband filters, this application incorporates a tunable coupling loop between two resonant rods. The coupling loop's wire diameter is typically 1mm-2mm; it should not be too thin to avoid deformation and alteration of the filter characteristics. The coupling loop is fixed to a tunable screw, and rotating the screw changes its direction (i.e., alters the coupling between the two resonant rods). When the coupling loop is in the same plane as the filter's length direction (i.e.,...), the coupling loop... Figure 5 (As shown in the image), the coupling ring is closest to the resonant rod, forming a coupling bridge between the two resonant rods, significantly enhancing the coupling between them. When the plane of the coupling ring is perpendicular to the length direction of the filter (i.e.,...),... Figure 5 (As shown in the 90° rotation position), the coupling ring provides almost no enhancement to the coupling between the resonant rods. Therefore, a robust and reliable coupling ring is designed between the resonant rods, and the coupling of the filter can be adjusted by tuning its top tuning screw.
[0120] This application employs a multi-turn tapped copper wire coupling feeding method. When alternating current is fed into the tapped wire, an alternating magnetic field is generated (see [reference]). Figure 6 The alternating magnetic field interacts with the resonant rod to achieve coupled feeding. The magnitude of the alternating magnetic field can be changed by altering the number of turns in the multi-tapped copper coil, thus achieving different external Q values. .
[0121] This application changes the number of turns of multi-tap copper wire by designing a tap tuning screw, thereby altering the external Q value. ,like Figure 3 As shown. The number of turns in a multi-turn tapped wire and the Q value. There is no direct formulaic relationship. Increasing the number of turns will increase the alternating magnetic field and increase the linkage area with the shaft resonator, leading to an increase in the feed coupling coefficient. In addition, based on the fundamental theory of coupling matrices:
[0122]
[0123] For example, when the tap turns increase from 2 to 4, the feed coupling coefficient... The external Q value could potentially increase from 0.1 to 0.3. Then it drops from 100 to 11.1.
[0124] The above analysis explains the methods and working principles of frequency adjustment, coupling coefficient adjustment between resonant rods, and external Q-value adjustment of the filter in this application.
[0125] The frequency tuning screw, coupling tuning screw, and tapped tuning screw of this application can all be designed with a stepper motor to achieve automatic tuning. Therefore, this application can be applied to tuned filters, for example, to design a tuned filter with a tuning range of... Operating bandwidth maintained Unchanged. The design must first ensure that the frequency tuning range of the resonant rod is supported. The requirements are met, including the coupling between resonant rods and the tap tuning range, all satisfying the operating bandwidth. The requirements are to reasonably select the filter tuning step (i.e., the number of filter tuning times), record the position of each tuning screw (corresponding to the number of tuning turns of the stepper motor) during each tuning, and accurately tune the tuning screws each time by referring to the table during normal operation.
[0126] The number of tap turns can be changed by adjusting the tuning screw of the tuning tap, thereby changing the external Q value of the filter feed to adapt to different bandwidth requirements of the filter.
[0127] The working process of the coaxial filter in this application will be explained below.
[0128] The design and debugging process of the filter in this application is as follows:
[0129] 1) Calculate the filter order, coupling coefficient, and external Q value based on the filter design requirements: frequency, bandwidth, and other specifications;
[0130] 2) Use a 3D electromagnetic simulation to simulate a single-cavity resonator of the filter and check whether the Q value and 3D dimensions of the simulated filter meet the requirements;
[0131] 3) Using a three-dimensional electromagnetic simulation filter with dual-cavity coupling, adjust the size of the coupling loop according to the simulation coupling coefficient, and design the plane of the coupling loop to have a certain angle with the length direction of the filter to ensure that the coupling meets the requirements and avoid insufficient coupling during debugging caused by manufacturing errors;
[0132] 4) Similarly, using 3D simulation software, a multi-turn tap model is established to simulate the external Q value of the filter;
[0133] 5) Finally, perform overall filter modeling and simulation to check whether the performance of the designed filter meets the requirements;
[0134] 6) After processing, the filter can be quickly debugged. For multi-turn tapped copper wire, the tuning screw and locking nut can be fixed with glue, and the filter can then be used.
[0135] The frequency tuning screw, coupling tuning screw, and tap tuning screw of this application can all be designed with a stepper motor to achieve automatic tuning, therefore this application can be applied to numerically controlled tuned filters.
[0136] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. A broadband coaxial filter, characterized by, The external shielding shielding cavity (A1) is a cuboid structure, and the top of the shielding cavity (A1) comprises a top cover plate (A11) provided with detachable connection. The shielding cavity (A1) is provided with not less than three resonance rods, and the resonance rods are cylindrical structures; wherein the second resonance rod (A2), the third resonance rod (A3) and the fourth resonance rod (A4) are alternately and reversely arranged on the shielding cavity (A1); The bottom of each resonance rod is provided with a fixing screw, and the resonance rod is fixed on the shielding cavity (A1) through the fixing screw; The bottom of the second resonance rod (A2) and the fourth resonance rod (A4) is respectively sleeved with the fifth polytetrafluoroethylene sheath (A54) and the sixth polytetrafluoroethylene sheath (A64); The coupling ring is arranged between the resonance rods, and the top of the coupling ring is welded on the bottom of the coupling tuning screw penetrating through the top cover plate (A11), and the top cover plate (A11) is provided with a locking nut matched with the coupling tuning screw.
2. The filter according to claim 1, wherein: The fifth polytetrafluoroethylene sheath (A54) is provided with recessed threads on the outer wall and is wound with the fifth silver-plated tap copper wire (A51); The fifth silver-plated tap copper wire (A51) is connected to the filter input connector (A5); The fifth silver-plated tap copper wire (A51) is tightly wound outside the fifth polytetrafluoroethylene sheath (A54) for multiple turns.
3. The filter according to claim 1, wherein: The sixth polytetrafluoroethylene sheath (A64) is provided with recessed threads on the outer wall and is wound with the sixth silver-plated tap copper wire (A61); The sixth silver-plated tap copper wire (A61) is connected to the filter output connector (A6); The sixth silver-plated tap copper wire (A61) is tightly wound outside the sixth polytetrafluoroethylene sheath (A64) for multiple turns.
4. The filter according to any one of claims 1 to 3, wherein: The lower branch of the fifth silver-plated tap copper wire (A51) is connected to the access terminal (A56) of the filter input connector (A5), and the upper branch of the fifth silver-plated tap copper wire (A51) is connected to the fixing screw (A55) of the filter input connector (A5); The fixing screw (A55) is fixed on the left side wall of the filter shielding cavity (A1); The lower branch of the sixth silver-plated tap copper wire (A61) is connected to the output terminal (A66) of the filter output connector (A6), and the upper branch of the sixth silver-plated tap copper wire (A61) is connected to the fixing screw (A65) of the filter output connector (A6); The fixing screw (A65) is fixed on the right side wall of the filter shielding cavity (A1).
5. The filter according to claim 4, wherein: A tap tuning screw (A52) is arranged on the bottom of the shielding cavity (A1) near the side of the fifth polytetrafluoroethylene sheath (A54), and the bottom of the tap tuning screw (A52) is in a shuttle-shaped structure; the tap tuning screw (A52) is fixed on the bottom of the filter shielding cavity (A1) through a tap tuning nut (A53). A tap tuning screw (A62) is arranged at the bottom of the shielding cavity (A1) near the side of the sixth polytetrafluoroethylene sheath (A64), and the bottom of the tap tuning screw (A62) is in a shuttle-shaped structure; the tap tuning screw (A62) is fixed at the bottom of the filter shielding cavity (A1) through a tap tuning nut (A63).
6. The filter of claim 1, wherein: The second resonant rod (A2) is fixed at the bottom of the shielding cavity (A1) through a second fixing screw (A23); The top end of the second resonant rod (A2) is in a hollow structure, and forms a capacitive loading form with the second frequency tuning screw (A21) on the top end cover plate; The second frequency tuning screw (A21) is matched with a second locking nut (A22) for locking the second frequency tuning screw (A21).
7. The filter of claim 1, wherein: The fourth resonant rod (A4) is fixed at the bottom of the shielding cavity (A1) through a fourth fixing screw (A43); The top end of the fourth resonant rod (A4) is in a hollow structure, and forms a capacitive loading form with the fourth frequency tuning screw (A41) on the top end cover plate; The fourth frequency tuning screw (A41) is matched with a fourth locking nut (A42) for locking the fourth frequency tuning screw (A41).
8. The filter of claim 1, wherein: The third resonant rod (A3) is arranged between the second resonant rod (A2) and the fourth resonant rod (A4), and the third resonant rod (A3) forms an interdigital structure with the second resonant rod (A2) and the fourth resonant rod (A4); The third resonant rod (A3) is fixed at the top of the shielding cavity (A1) through a third fixing screw (A33); The top end of the third resonant rod (A3) is in a hollow structure, and forms a capacitive loading form with the third frequency tuning screw (A31) at the bottom of the shielding cavity (A1); The third frequency tuning screw (A31) is matched with a third locking nut (A32) for locking the third frequency tuning screw (A31).
9. The filter of claim 8, wherein: A seventh coupling ring (A7) made of silver-plated copper wire is arranged between the second resonant rod (A2) and the third resonant rod (A3); The seventh coupling ring (A7) is welded at the bottom of a seventh coupling tuning screw (A71) passing through the top end cover plate (A11); The seventh locking nut (A72) matched with the seventh coupling tuning screw (A71) is arranged on the top end cover plate (A11).
10. The filter of claim 9, wherein: An eighth coupling ring (A8) made of silver-plated copper wire is arranged between the third resonant rod (A3) and the fourth resonant rod (A4); The eighth coupling ring (A8) is welded at the bottom of an eighth coupling tuning screw (A81) passing through the top end cover plate (A11); The eighth locking nut (A82) matched with the eighth coupling tuning screw (A81) is arranged on the top end cover plate (A11).