Flexible microwave filter based on substrate integrated waveguide
By employing a substrate-integrated waveguide and a distributed DGS structure, the problem of unstable performance of flexible microwave filters under deformation was solved, achieving stable performance under large bending conditions and small-volume application in the low-frequency band.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING UNIV OF POSTS & TELECOMM
- Filing Date
- 2023-11-30
- Publication Date
- 2026-07-07
AI Technical Summary
Existing flexible microwave filters are unstable in performance when deformed, especially with severe frequency shift under large deformation, and SIW filters occupy a large volume in the low frequency band.
A flexible microwave filter structure based on substrate integrated waveguide is adopted, including half-mode substrate integrated waveguide (HMSIW) and distributed DGS structure. By reducing the filter size and optimizing the coupling window and interdigital DGS structure, the performance is kept stable.
By maintaining stable performance under significant bending, reducing frequency shift, and occupying a small volume in the low-frequency band, the high-efficiency performance of the flexible filter is maintained.
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Figure CN117810659B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of microwave filter technology, and in particular to a flexible microwave filter based on a substrate integrated waveguide. Background Technology
[0002] With the rapid development of flexible electronics technology, it is now widely used in various fields. Research on flexible circuits has also gradually expanded from flexible materials to multiple directions such as flexible circuit structures and flexible device fabrication. In the microwave radio frequency field, the design of flexible devices has gradually received more attention, and flexible microwave filters based on flexible substrates have gradually become one of the research hotspots.
[0003] Initially, flexible microwave filters were mainly created by transplanting traditional microwave filter structures onto flexible substrates. These filters are highly sensitive to deformation, often exhibiting significant performance changes such as frequency shift and passband degradation upon deformation. To address this issue, researchers have proposed various solutions, including modifying the filter structure, etching defect ground structures (DGS) on the back of the filter, and developing novel flexible substrate materials. These methods can reduce the deformation sensitivity of traditional microwave filters, enabling them to maintain stable performance even in flexible environments, thus achieving the flexibility of traditional microwave filters.
[0004] SIW filters have advantages over traditional microwave filters, such as low loss, high selectivity and ease of fabrication. However, SIW filters still occupy a large volume in the lower frequency band, and how to maintain their stable performance under large deformation is one of the problems to be solved. Summary of the Invention
[0005] In view of this, the purpose of this application is to propose a flexible microwave filter based on a substrate integrated waveguide to solve or partially solve the above problems.
[0006] To achieve the above objectives, this application provides a flexible microwave filter based on a substrate integrated waveguide, comprising:
[0007] A first metal layer, a dielectric substrate, a second metal layer, and a metallized via array are stacked sequentially from top to bottom. The first metal layer has a first microstrip line feed and a second microstrip line feed. The metallized via array penetrates the dielectric substrate and, together with the first and second metal layers, forms an HMSIW resonant cavity. The first metal layer also has a first DGS coupling window, a second DGS coupling window, and a third DGS coupling window. The second metal layer has a first annular coupling window, a second annular coupling window, and a third annular coupling window. The first annular coupling window is located near the second annular coupling window. A first interdigitated DGS structure is provided on one side, a second interdigitated DGS structure is provided on the side of the second annular coupling window close to the first annular coupling window, a third interdigitated DGS structure is provided on the side of the second annular coupling window close to the third annular coupling window, and a fourth interdigitated DGS structure is provided on the side of the third annular coupling window close to the second annular coupling window; the first interdigitated DGS structure corresponds to the second interdigitated DGS structure, and the third interdigitated DGS structure corresponds to the fourth interdigitated DGS structure; the second metal layer is also etched with a first spliced DGS coupling window and a second spliced DGS coupling window.
[0008] In one possible implementation, the metallized via array is located at the side edge of the dielectric substrate away from the first microstrip line feed and the second microstrip line feed, and is parallel to the first microstrip line feed and the second microstrip line feed.
[0009] In one possible implementation, the second DGS coupling window is located at a predetermined distance below the center of the HMSIW resonant cavity, the first DGS coupling window and the third DGS coupling window are located on both sides of the second DGS coupling window, and the distance between the first DGS coupling window and the second DGS coupling window is equal to the distance between the third DGS coupling window and the second DGS coupling window.
[0010] In one possible implementation, the first microstrip line feed is located on one side of the resonant cavity, and the second microstrip line feed is located on the other side of the resonant cavity.
[0011] In one possible implementation, the projection of the center of the first DGS coupling window onto the second metal layer coincides with the projection of the center of the first annular coupling window onto the second metal layer, the projection of the center of the second DGS coupling window onto the second metal layer coincides with the projection of the center of the second annular coupling window onto the second metal layer, and the projection of the center of the third DGS coupling window onto the second metal layer coincides with the projection of the center of the third annular coupling window onto the second metal layer.
[0012] In one possible implementation, the first and second spliced DGS coupling windows are located on opposite sides of the second metal layer. Both the first and second spliced DGS coupling windows are formed by splicing two identical semi-circular DGS coupling windows, and the splicing lines of the semi-circular DGS coupling windows are parallel to the arrangement direction of the metallized via array. The projection of the first microstrip line feed line onto the second metal layer coincides with the splicing line of the first spliced DGS coupling window; the projection of the second microstrip line feed line onto the second metal layer coincides with the splicing line of the second spliced DGS coupling window.
[0013] In one possible implementation, the first DGS coupling window and the third DGS coupling window have the same size, and the second DGS coupling window has a larger size than the first DGS coupling window and the third DGS coupling window.
[0014] In one possible implementation, the first annular coupling window and the third annular coupling window are the same size, and the second annular coupling window is larger than the size of the first annular coupling window and the third annular coupling window.
[0015] As can be seen from the above, the flexible microwave filter based on substrate integrated waveguide provided in this application includes, in terms of structure, a first metal layer, a dielectric substrate, a second metal layer, and a metallized via array stacked sequentially from top to bottom. A first microstrip line feed and a second microstrip line feed are disposed on the first metal layer. The metallized via array penetrates the dielectric substrate and, together with the first and second metal layers, forms an HMSIW resonant cavity. The first metal layer also has a first DGS coupling window, a second DGS coupling window, and a third DGS coupling window. The second metal layer has a first annular coupling window, a second annular coupling window, and a third annular coupling window. The coupling windows have the following configurations: a first annular coupling window has a first interdigitated DGS structure on the side closest to the second annular coupling window; a second annular coupling window has a second interdigitated DGS structure on the side closest to the first annular coupling window; a third interdigitated DGS structure on the side closest to the third annular coupling window; and a fourth interdigitated DGS structure on the side closest to the second annular coupling window. The first interdigitated DGS structure corresponds to the second interdigitated DGS structure, and the third interdigitated DGS structure corresponds to the fourth interdigitated DGS structure. The second metal layer also has a first spliced DGS coupling window and a second spliced DGS coupling window etched into it. To reduce the size of the SIW filter, this application employs a half-mode substrate integrated waveguide (HMSIW) structure. The HMSIW is equivalent to half the size of a complete SIW resonant cavity. One side of the HMSIW is the same metallized via array as the SIW resonant cavity, and the other side is a flat opening surface. This reduces the physical size of the flexible filter, allowing it to occupy only a small physical volume when operating in the low-frequency band. The introduction of a distributed DMS structure can mitigate the performance changes caused by bending of the DGS structure, thereby reducing the frequency shift of the filter in the bending state. This allows the flexible filter to maintain stable performance even under a large degree of bending, and the performance in the flat state and the bending state remains basically consistent. Attached Figure Description
[0016] To more clearly illustrate the technical solutions in 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 only for this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 This is a schematic diagram of the exploded structure of a flexible microwave filter based on a substrate integrated waveguide, provided in an embodiment of this application.
[0018] Figure 2 A top view of the first metal layer provided in an embodiment of this application.
[0019] Figure 3A top view of the second metal layer provided in an embodiment of this application.
[0020] Figure 4 This is a schematic diagram of the simulation results of the flexible microwave filter provided in the embodiment of this application in a flat state.
[0021] Figure 5 A schematic diagram showing the simulation results of the flexible microwave filter provided in the embodiments of this application in a flat state and a bent state.
[0022] In the figure: 1. First metal layer; 3. Dielectric substrate; 2. Second metal layer; 4. Metallized via array; 5. First microstrip line feed line; 6. Second microstrip line feed line; 7. HMSIW resonant cavity; 8. First DGS coupling window; 9. Second DGS coupling window; 10. Third DGS coupling window; 11. Third annular coupling window; 12. First interdigitated DGS structure; 13. Second interdigitated DGS structure; 14. Third interdigitated DGS structure; 15. Fourth interdigitated DGS structure; 16. First spliced DGS coupling window; 17. Second spliced DGS coupling window; 18. Semicircular DGS coupling window; 19. Detailed Implementation
[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.
[0024] It should be noted that, unless otherwise defined, the technical or scientific terms used in this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.
[0025] As described in the background section, SIW structures were initially used as transmission lines. This structure uses two rows of metal via arrays to simulate an electric metal wall, suppressing electromagnetic wave radiation and ensuring that electromagnetic waves can only propagate within a specific space. SIW structures are easy to integrate, inexpensive, and improve system reliability, thus they are widely used in microwave device design.
[0026] In developing this application, the applicant discovered that the physical size of the filter is relatively large, and this drawback becomes more pronounced as the operating frequency decreases, as the size of the SIW resonant cavity increases. Furthermore, existing filters have limited tolerance for bending and thus limited flexibility. Therefore, to address the issue of traditional flexible SIW filters being too large and unable to maintain stable performance under significant bending, this application proposes a flexible microwave filter based on a substrate integrated waveguide.
[0027] The DGS (Defected Ground Structure) structure is created by etching defect patterns on the ground plane of the circuit substrate to change the distribution of the effective dielectric constant of the circuit substrate material, thereby changing the distributed inductance and distributed capacitance of the microstrip line. This allows the microstrip line with the DGS structure to exhibit band-stop characteristics and slow wave characteristics.
[0028] The technical solution of this application will be further described in detail below through specific embodiments.
[0029] refer to Figure 1 This is an exploded view of the flexible microwave filter based on a substrate integrated waveguide provided in an embodiment of this application.
[0030] As shown in the figure, the flexible microwave filter based on a substrate integrated waveguide provided in this application includes:
[0031] The following layers are stacked sequentially from top to bottom: a first metal layer, a dielectric substrate, a second metal layer, and a metallized via array. A first microstrip line feed and a second microstrip line feed are disposed on the first metal layer. The metallized via array penetrates the dielectric substrate and, together with the first and second metal layers, forms an HMSIW resonant cavity. The first metal layer also has a first DGS coupling window, a second DGS coupling window, and a third DGS coupling window. The second metal layer has a first annular coupling window, a second annular coupling window, and a third annular coupling window, with the first annular coupling window located close to the second annular coupling window. A first interdigitated DGS structure is provided on one side of the second annular coupling window, a second interdigitated DGS structure is provided on the side of the second annular coupling window close to the first annular coupling window, a third interdigitated DGS structure is provided on the side of the second annular coupling window close to the third annular coupling window, and a fourth interdigitated DGS structure is provided on the side of the third annular coupling window close to the second annular coupling window; the first interdigitated DGS structure corresponds to the second interdigitated DGS structure, and the third interdigitated DGS structure corresponds to the fourth interdigitated DGS structure; the second metal layer is also etched with a first spliced DGS coupling window and a second spliced DGS coupling.
[0032] As an optional embodiment, the dielectric substrate is a single-layer flexible dielectric board, and conductive metal layers are deposited on both the upper and lower surfaces of the dielectric board. The metallized via array is composed of a plurality of metallized vias arranged in combination. The diameter of each metallized via in the metallized via array is preferably 0.6 mm, and the distance between each metallized via is preferably 1 mm.
[0033] It should be noted that the diameter of the metallized via and the spacing between each metallized via can be flexibly set according to actual needs. The above-mentioned diameter of the metallized via and the distance between each metallized via are preferred embodiments of this application.
[0034] It should be noted that, in order to reduce the size of the filter, this invention employs a half-mode substrate integrated waveguide (HMSIW) structure. The HMSIW is equivalent to half the size of a complete SIW resonant cavity. One side of the HMSIW is the same metallized via array as the SIW resonant cavity, while the other side is a flat opening. Since the opening of the HMSIW can be considered equivalent to an ideal magnetic wall, the HMSIW resonant cavity can maintain the field distribution characteristics of the SIW filter while reducing its volume by nearly 50%. Therefore, the HMSIW resonant cavity in this application is only half the size of a traditional SIW resonant cavity.
[0035] As an optional embodiment, the metallized via array is located on the side edge of the dielectric substrate away from the first microstrip line feed and the second microstrip line feed, and is parallel to the first microstrip line feed and the second microstrip line feed.
[0036] In practice, the metallized via array is located at the upper edge of the HMSIW resonant cavity, penetrating the dielectric substrate and the upper and lower surface metal layers.
[0037] As an optional embodiment, the first microstrip line feed is located on one side of the HMSIW resonant cavity, and the second microstrip line feed is located on the other side of the HMSIW resonant cavity. Preferably, both the first and second microstrip line feeds are powered by 50-ohm microstrip lines.
[0038] As an optional embodiment, the second DGS coupling window is located at a predetermined distance below the center of the HMSIW resonant cavity, and the first DGS coupling window and the third DGS coupling window are located on both sides of the second DGS coupling window. The distance between the first DGS coupling window and the second DGS coupling window is equal to the distance between the third DGS coupling window and the second DGS coupling window.
[0039] In specific implementation, the projection of the center of the first DGS coupling window onto the second metal layer coincides with the projection of the center of the first annular coupling window onto the second metal layer, the projection of the center of the second DGS coupling window onto the second metal layer coincides with the projection of the center of the second annular coupling window onto the second metal layer, and the projection of the center of the third DGS coupling window onto the second metal layer coincides with the projection of the center of the third annular coupling window onto the second metal layer.
[0040] refer to Figure 2 This is a top view of the first metal layer provided in an embodiment of this application.
[0041] As shown in the figure, L siw H is the length of the HMSIW resonant cavity. siw L represents the width of the HMSIW resonant cavity. The HMSIW resonant cavity exhibits high-pass characteristics, and its cutoff frequency is related to the width and length of the HMSIW resonant cavity. Therefore, by adjusting L... siw and H siw The passband range of the HMSIW resonant cavity can be controlled.
[0042] In this embodiment of the application, the length L of the HMSIW resonant cavity siw It is 11mm long and has a width of H. siw The thickness is 6mm, and the flexible dielectric board uses a 0.05mm thick polyimide (PI) sheet with a dielectric constant of 3.2.
[0043] It should be noted that the length and width of the resonant cavity can be flexibly set according to actual needs. The above dimensions are the resonant cavity dimensions of the preferred embodiment of this application. The material and dimensions of the flexible dielectric plate can also be flexibly set according to actual needs.
[0044] As an optional embodiment, the first DGS coupling window and the third DGS coupling window have the same size, and the second DGS coupling window has a larger size than the first DGS coupling window and the third DGS coupling window.
[0045] As an optional embodiment, the first annular coupling window and the third annular coupling window have the same size, and the second annular coupling window has a larger size than the first annular coupling window and the third annular coupling window.
[0046] In practical implementation, this application combines the high-pass characteristics of the SIW resonant cavity and the low-pass characteristics of the DGS structure to achieve the bandpass effect of the SIW filter.
[0047] refer to Figure 3 This is a top view of the second metal layer provided in an embodiment of this application.
[0048] In this embodiment, the HMSIW resonant cavity has high-pass characteristics, which can be achieved by adjusting the length L of the HMSIW resonant cavity. siwand width H siw The high-pass cutoff frequency of the flexible microwave filter can be controlled. The first, second, and third annular coupling windows etched into the second metal layer have low-pass characteristics. In this application, the first and third annular coupling windows are of identical size and symmetrically distributed around the second annular coupling window. By adjusting the radius of the three annular DGS structures, the low-pass cutoff frequency of the flexible microwave filter can be controlled. To improve the filter's in-band performance and reduce losses, a first interdigitated DGS structure is added between the first and second annular coupling windows, and a second interdigitated DGS structure is added between the second and third annular coupling windows.
[0049] The interdigital DGS structure is characterized by N resonant units arranged in an alternating pattern to form an interdigital line structure. If N is odd, the metal microstrip structure is symmetrical about the centerline axis of the central resonant unit; if N is even, the metal microstrip structure is symmetrical about the centerline axis of the gap between the two central resonant units.
[0050] As an optional embodiment, the first and second spliced DGS coupling windows are located on both sides of the second metal layer. Both the first and second spliced DGS coupling windows are formed by splicing two semi-circular DGS coupling windows of the same shape. The splicing line of the semi-circular DGS coupling windows is parallel to the arrangement direction of the metallized via array. The projection of the first microstrip line feed line on the second metal layer coincides with the splicing line of the first spliced DGS coupling window. The projection of the second microstrip line feed line on the second metal layer coincides with the splicing line of the second spliced DGS coupling window.
[0051] In practical implementation, traditional SIW filters typically experience significant frequency shifts when bent. To mitigate this frequency shift, this application introduces a distributed DMS structure and a semi-circular DGS structure. The distributed DMS structure consists of a first DGS coupling window, a second DGS coupling window, and a third DGS coupling window, positioned directly above the first, second, and third annular coupling windows, respectively. The introduction of the distributed DMS structure reduces the performance changes caused by bending of the DGS structure, thereby reducing the frequency shift of the SIW filter under bending conditions. Simultaneously, a first spliced DGS coupling window and a second spliced DGS coupling window are also introduced directly below the first and second microstrip line feeds on both sides to reduce the electrical length changes of the transmission lines under bending conditions, similarly achieving the effect of reducing frequency shift.
[0052] In the embodiments of this application, both the first spliced DGS coupling window and the second spliced DGS coupling window are obtained by splicing two semi-circular DGS coupling windows. The splicing point of the two semi-circular DGS coupling windows is not completely joined, and the reserved seam width can coincide with the projection of the first microstrip line feeder and the second microstrip line feeder.
[0053] refer to Figure 4 This is a schematic diagram of the simulation results of the flexible microwave filter provided in the embodiment of this application in a flat state.
[0054] Its center frequency is 5.3 GHz, the in-band insertion loss is about -1.2 dB, and the return loss is below -20 dB, exhibiting obvious bandpass characteristics.
[0055] refer to Figure 5 This is a schematic diagram comparing the simulation results of the flexible microwave filter in the flat and bent states provided in the embodiments of this application.
[0056] Let θ be the angle at which the filter bends horizontally. Figure 5 The simulation results show a comparison of the filter under flat conditions and bending angles of θ = 90° and θ = 180°. It can be seen that the filter's performance is well consistent under both flat and bending conditions, with frequency shifts within 0.09 GHz, maintaining stable performance under different conditions.
[0057] As can be seen from the above, the flexible microwave filter based on substrate integrated waveguide provided in this application includes, in terms of structure, a first metal layer, a dielectric substrate, a second metal layer, and a metallized via array stacked sequentially from top to bottom. A first microstrip line feed and a second microstrip line feed are disposed on the first metal layer. The metallized via array penetrates the dielectric substrate and, together with the first and second metal layers, forms an HMSIW resonant cavity. The first metal layer also has a first DGS coupling window, a second DGS coupling window, and a third DGS coupling window. The second metal layer has a first annular coupling window, a second annular coupling window, and a third annular coupling window. The coupling window has a first interdigitated DGS structure on the side of the first annular coupling window near the second annular coupling window, a second interdigitated DGS structure on the side of the second annular coupling window near the first annular coupling window, a third interdigitated DGS structure on the side of the second annular coupling window near the third annular coupling window, and a fourth interdigitated DGS structure on the side of the third annular coupling window near the second annular coupling window; the first interdigitated DGS structure corresponds to the second interdigitated DGS structure, and the third interdigitated DGS structure corresponds to the fourth interdigitated DGS structure; the second metal layer is also etched with a first spliced DGS coupling window and a second spliced DGS coupling window.
[0058] To reduce the size of the SIW filter, this application employs a half-mode substrate integrated waveguide (HMSIW) structure. The HMSIW is equivalent to half the size of a complete SIW resonant cavity. One side of the HMSIW is the same metallized via array as the SIW resonant cavity, while the other side is a flat opening. This reduces the physical size of the flexible filter, allowing it to occupy only a small physical volume when operating in the low-frequency range. The introduction of the distributed DMS structure can mitigate the performance changes caused by bending of the DGS structure, thereby reducing the frequency shift of the filter in the bending state. This allows the flexible filter to maintain stable performance even under significant bending, with performance remaining essentially consistent between the flat and bent states.
[0059] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this application (including the claims) is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this application as described above, which are not provided in the details for the sake of brevity.
[0060] Additionally, to simplify the description and discussion, and to avoid obscuring the embodiments of this application, the well-known power / ground connections to integrated circuit (IC) chips and other components may or may not be shown in the provided drawings. Furthermore, the apparatus may be shown in block diagram form to avoid obscuring the embodiments of this application, and this also takes into account the fact that the details of the implementation of these block diagram apparatuses are highly dependent on the platform on which the embodiments of this application will be implemented (i.e., these details should be fully understood by those skilled in the art). While specific details (e.g., circuits) have been set forth to describe exemplary embodiments of this application, it will be apparent to those skilled in the art that the embodiments of this application can be implemented without these specific details or with variations thereof. Therefore, these descriptions should be considered illustrative rather than restrictive.
[0061] Although this application has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. For example, other memory architectures (e.g., dynamic RAM (DRAM)) may be used with the embodiments discussed.
[0062] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.
Claims
1. A flexible microwave filter based on a substrate integrated waveguide, characterized in that, include: The following layers are stacked sequentially from top to bottom: a first metal layer, a dielectric substrate, a second metal layer, and a metallized via array. The first metal layer has a first microstrip line feed line and a second microstrip line feed line. The metallized via array penetrates the dielectric substrate and together with the first metal layer and the second metal layer, forms an HMSIW resonant cavity. The first metal layer also has a first DGS coupling window, a second DGS coupling window, and a third DGS coupling window. The second metal layer is provided with a first annular coupling window, a second annular coupling window, and a third annular coupling window. A first interdigitated DGS structure is provided on the side of the first annular coupling window near the second annular coupling window. A second interdigitated DGS structure is provided on the side of the second annular coupling window near the first annular coupling window. A third interdigitated DGS structure is provided on the side of the second annular coupling window near the third annular coupling window. A fourth interdigitated DGS structure is provided on the side of the third annular coupling window near the second annular coupling window. The first interdigitated DGS structure corresponds to the second interdigitated DGS structure, and the third interdigitated DGS structure corresponds to the fourth interdigitated DGS structure. The second metal layer is also etched with a first spliced DGS coupling window and a second spliced DGS coupling window.
2. The flexible microwave filter based on a substrate integrated waveguide according to claim 1, characterized in that, The metallized via array is located on the side edge of the dielectric substrate away from the first microstrip line feed and the second microstrip line feed, and is parallel to the first microstrip line feed and the second microstrip line feed.
3. The flexible microwave filter based on a substrate integrated waveguide according to claim 1, characterized in that, The second DGS coupling window is located at a predetermined distance below the center of the HMSIW resonant cavity. The first DGS coupling window and the third DGS coupling window are located on both sides of the second DGS coupling window. The distance between the first DGS coupling window and the second DGS coupling window is equal to the distance between the third DGS coupling window and the second DGS coupling window.
4. The flexible microwave filter based on a substrate integrated waveguide according to claim 1, characterized in that, The first microstrip line feed is located on one side of the resonant cavity, and the second microstrip line feed is located on the other side of the resonant cavity.
5. The flexible microwave filter based on a substrate integrated waveguide according to claim 1, characterized in that, The projection of the center of the first DGS coupling window onto the second metal layer coincides with the projection of the center of the first annular coupling window onto the second metal layer; the projection of the center of the second DGS coupling window onto the second metal layer coincides with the projection of the center of the second annular coupling window onto the second metal layer; and the projection of the center of the third DGS coupling window onto the second metal layer coincides with the projection of the center of the third annular coupling window onto the second metal layer.
6. The flexible microwave filter based on a substrate integrated waveguide according to claim 1, characterized in that, The first and second spliced DGS coupling windows are located on both sides of the second metal layer. Both the first and second spliced DGS coupling windows are spliced together by two semi-circular DGS coupling windows of the same shape. The splicing line of the semi-circular DGS coupling windows is parallel to the arrangement direction of the metallized via array. The projection of the first microstrip line feed line onto the second metal layer coincides with the splicing line of the first spliced DGS coupling window; The projection of the second microstrip line feed line onto the second metal layer coincides with the splicing line of the second spliced DGS coupling window.
7. The flexible microwave filter based on a substrate integrated waveguide according to claim 1, characterized in that, The first DGS coupling window and the third DGS coupling window have the same size, and the second DGS coupling window has a larger size than the first DGS coupling window and the third DGS coupling window.
8. The flexible microwave filter based on a substrate integrated waveguide according to claim 1, characterized in that, The first annular coupling window and the third annular coupling window have the same size, and the second annular coupling window has a larger size than the first annular coupling window and the third annular coupling window.