A wide-band quasi-elliptic SIW filter with opposite side feed

Abstract

The application is suitable for the technical field of microwave passive devices, and provides a wide-band quasi-elliptic SIW filter with opposite surface feed, which comprises a dielectric layer, an upper metal layer arranged on the upper surface of the dielectric layer, a lower metal layer arranged on the lower surface of the dielectric layer, and a metallized via array; the metallized via array, the upper metal layer and the lower metal layer jointly enclose a plurality of SIW resonant cavities; the SIW filter is provided with an input port and an output port, the input port is arranged on the upper metal layer, and the output port is arranged on the lower metal layer; the input port and the output port are respectively located on the opposite surfaces of the dielectric layer and are spatially isolated through the dielectric layer to suppress source-load parasitic coupling; under the premise of not changing the main structure of the filter, the application eliminates the additional transmission zero point caused by parasitic coupling, makes the frequency response more pure and controllable, and meanwhile maintains the wide-band characteristics and compact structure.

Description

Technical Field

[0001] This invention relates to the field of microwave passive device technology, specifically a wide-stopband quasi-elliptic SIW filter with opposite-side feeding. Background Technology

[0002] Substrate integrated waveguides (SIWs) combine the advantages of low loss and high power capacity of metallic waveguides with the small size and ease of integration of microstrip circuits, making them one of the mainstream implementations of filters in the microwave and millimeter-wave bands. Quasi-elliptic filters, with transmission zeros on both sides of the passband, possess excellent frequency selectivity and are widely used in RF systems with high out-of-band suppression requirements.

[0003] A wide-stopband quasi-elliptic SIW filter structure is presented, employing a four-stage cascaded SIW resonator architecture. Adjacent resonators are coupled along the main path via coupling windows. Simultaneously, a slotted cross-coupling structure is placed between the first and last resonators, forming a cross-coupling path and generating a pair of transmission zeros on both sides of the passband, thus achieving a quasi-elliptic filtering response. By rationally designing the port and coupling window positions and utilizing the field distribution characteristics of different modes, this filter can effectively suppress TE (transmission distortion). 102 With TE 201 Higher-order modes are used to achieve wide stopband characteristics.

[0004] However, the input and output ports of the aforementioned filter are both located on the same metal layer of the dielectric substrate, and their physical spacing is relatively close. In a real electromagnetic environment, unintended parasitic coupling paths, i.e., source-load parasitic coupling, will form between the two ports through spatial radiation. This parasitic coupling will cause the filter to generate additional transmission zeros, resulting in a deviation of the frequency response from the theoretical design, deterioration of stopband rejection performance, and reduced controllability and performance stability of the filter design. Therefore, to address the above situation, there is an urgent need to provide a wide-stopband quasi-elliptic SIW filter with opposite-side feeding to overcome the shortcomings in current practical applications. Summary of the Invention

[0005] The purpose of this invention is to provide a wide-stopband quasi-elliptic SIW filter with opposite feed, which effectively solves the problems mentioned in the background art.

[0006] This invention is implemented as follows: a wide-stopband quasi-elliptic SIW filter with opposite-side feeding includes a dielectric layer, an upper metal layer disposed on the upper surface of the dielectric layer, a lower metal layer disposed on the lower surface of the dielectric layer, and a metallized via array penetrating the dielectric layer and connecting the upper metal layer and the lower metal layer; the metallized via array, the upper metal layer, and the lower metal layer together enclose multiple SIW resonant cavities, and the multiple SIW resonant cavities are cascaded sequentially through coupling windows and are provided with a cross-coupling structure to achieve a quasi-elliptic response; The SIW filter has an input port and an output port, with the input port located on the upper metal layer and the output port located on the lower metal layer. The input port and the output port are located on opposite sides of the dielectric layer, and are spatially isolated by the dielectric layer to suppress source-load parasitic coupling.

[0007] As a further aspect of the present invention: the dielectric layer is a Rogers RT / duroid 5880 dielectric substrate.

[0008] As a further aspect of the present invention: the plurality of SIW resonant cavities include a first resonant cavity, a second resonant cavity, a third resonant cavity and a fourth resonant cavity, and coupling windows are respectively provided between the first resonant cavity and the second resonant cavity, between the second resonant cavity and the third resonant cavity, and between the third resonant cavity and the fourth resonant cavity, so that the four resonant cavities are cascaded in sequence to form a main coupling path.

[0009] As a further aspect of the present invention: the cross-coupling structure is an S-shaped slot disposed between the first resonant cavity and the fourth resonant cavity, and the signal is directly coupled from the first resonant cavity to the fourth resonant cavity through the S-shaped slot to form an electrical coupling path.

[0010] As a further aspect of the present invention: the main operating mode of the SIW filter is TE. 101 model.

[0011] As a further aspect of the present invention: the higher-order mode TE within the stopband range of the SIW filter 102 and TE 201 It is suppressed.

[0012] As a further aspect of the present invention: the main coupling path is a magnetic coupling path, the cross coupling structure is an electrical coupling path, and the main coupling path and the cross coupling structure work together to form a transmission zero on each side of the passband.

[0013] As a further aspect of the present invention: the S-shaped groove is disposed on the upper metal layer.

[0014] As a further aspect of the present invention, the relative permittivity of the dielectric layer is 2.2.

[0015] As a further aspect of the present invention: the thickness of the dielectric layer is 0.508 mm, and the loss tangent is 0.0009.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: No changes to the original filter structure are required: This invention only optimizes the layout of the feed port, setting the input port and output port on different metal layers respectively. There is no need to modify the SIW resonant cavity, cross-coupling structure and operating mode. It has the characteristics of simple design, easy implementation and convenient engineering application.

[0017] Effective suppression of source-load coupling: By using a separate upper and lower layer feeding method, the electromagnetic isolation between the input and output ports is increased, parasitic coupling paths are weakened, additional transmission zeros caused by source-load coupling are eliminated, and the controllability of the filter's frequency response is improved. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of a wide-stopband quasi-elliptic SIW filter with opposite-side feeding, provided by the present invention.

[0020] Figure 2 This is a comparison chart of insertion losses for different feed filters.

[0021] Figure 3 This is a schematic diagram of an existing wide-stopband quasi-elliptic SIW filter structure.

[0022] Figure 4 This is a coupling topology diagram of an existing wide-stopband quasi-elliptic SIW filter.

[0023] Figure 5 This is a schematic diagram of the working principle of an existing wide-stopband quasi-elliptic SIW filter.

[0024] Figure 6 This is a diagram of the conventional microstrip operating mode of an existing wide-stopband quasi-elliptic SIW filter.

[0025] Figure 7 This is a parasitic mode diagram of a conventional microstrip for an existing wide-stopband quasi-elliptic SIW filter.

[0026] Figure 8 For existing wide-stopband quasi-elliptic SIW filters, TE 102 Suppression map of the pattern.

[0027] Figure 9 For existing wide-stopband quasi-elliptic SIW filters, TE 201 Suppression map of the pattern.

[0028] Figure 10 Comparison of simulated S-parameters for existing wide-stopband quasi-elliptic SIW filters.

[0029] In the attached diagram: 1-upper metal layer, 2-input port, 3-electrical coupling path, 4-dielectric layer, 5-output port, 6-lower metal layer, 7-magnetic coupling path. Detailed Implementation

[0030] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The present invention will be further explained below with reference to specific embodiments.

[0032] Please see Figure 1 and Figure 2 This invention provides a wide-stopband quasi-elliptic SIW filter with opposite-side feeding, comprising a dielectric layer 4, an upper metal layer 1 disposed on the upper surface of the dielectric layer 4, a lower metal layer 6 disposed on the lower surface of the dielectric layer 4, and a metallized via array penetrating the dielectric layer 4 and connecting the upper metal layer 1 and the lower metal layer 6. The metallized via array, together with the upper metal layer 1 and the lower metal layer 6, enclose multiple SIW resonant cavities, including a first resonant cavity, a second resonant cavity, a third resonant cavity, and a fourth resonant cavity. Coupling windows are respectively provided between adjacent resonant cavities. Specifically, coupling windows are respectively provided between the first resonant cavity and the second resonant cavity, between the second resonant cavity and the third resonant cavity, and between the third resonant cavity and the fourth resonant cavity, so that the four resonant cavities are cascaded sequentially to form the main coupling path.

[0033] A cross-coupling structure, namely electrical coupling path 3, is provided between the first resonant cavity and the fourth resonant cavity. Specifically, it is an S-shaped slot disposed on the upper metal layer 1. Through this S-shaped slot, the signal can be directly coupled from the first resonant cavity to the fourth resonant cavity, forming electrical coupling path 3. The main coupling path (magnetic coupling path 7) and the cross-coupling path (electrical coupling path 3) coexist and interact, generating transmission zeros on both sides of the passband, thereby achieving quasi-elliptic response characteristics.

[0034] The key improvement of this invention lies in the following: the input port 2 is disposed on the upper metal layer 1 for inputting radio frequency signals; the output port 5 is disposed on the lower metal layer 6 for outputting radio frequency signals. The input port 2 and the output port 5 are located on opposite sides (i.e., front and back sides) of the dielectric layer 4, and are physically isolated from each other by the dielectric layer 4. This spatial separation significantly weakens the direct parasitic coupling path between the ports, not only further improving the stopband suppression capability, but also completely eliminating the source-load parasitic coupling effect.

[0035] In this embodiment, dielectric layer 4 is made of Rogers RT / duroid 5880 high-frequency substrate with a thickness of 0.508 mm, a relative permittivity of 2.2, and a loss tangent of 0.0009. The filter body adopts a SIW resonant cavity structure, forming an equivalent rectangular waveguide sidewall through a metallized via array, and achieving a quasi-elliptic response using a cross-coupling structure.

[0036] The filter's main operating mode is TE. 101 Mode. For higher-order modes TE 102 and TE 201 By rationally designing the port and coupling window positions, this is effectively suppressed, thus achieving wide stopband characteristics. Specifically, TE 102 The mode is difficult to effectively excite at the input port, or although it is excited, it cannot be effectively transmitted to the subsequent resonant cavity because the coupling window is located in a region with weak field strength; TE 201 Although the mode can be excited by the input port, the intermediate coupling windows are all located in the region where the field strength is relatively weak, TE 201 The mode cannot be effectively coupled to the subsequent resonant cavity and is also suppressed.

[0037] This invention optimizes only the layout of the feed port, placing the input and output ports on the upper and lower metal layers respectively, without requiring any modifications to the SIW resonant cavity, cross-coupling path, operating mode, or overall topology. This design approach retains all the core structural parameters of the original filter, thus avoiding additional design complexity or fabrication difficulties. It has good engineering compatibility, is easily migrated and applied to existing SIW filter solutions, and significantly reduces redesign and debugging costs.

[0038] By employing a top-to-bottom non-plane feeding method, spatial isolation is achieved by introducing a dielectric layer between the input and output terminals, significantly enhancing the electromagnetic isolation between the two ports and effectively cutting off parasitic coupling paths that bypass the main coupling channel. This measure completely eliminates additional transmission zeros caused by source-load coupling, avoids stopband degradation and passband response distortion due to parasitic effects, and makes the filter's frequency response cleaner and more controllable. It is particularly beneficial for achieving wide stopband characteristics with high roll-off and deep stopband suppression.

[0039] refer to Figure 2 The results clearly show that the wide stopband characteristics are retained, and the additional transmission zeros TZ3 and TZ4 caused by parasitic coupling from the source load have completely disappeared. This indicates that the undesired coupling paths between the input and output ports were successfully suppressed through optimized port layout. The transmission zeros in the filter are only generated by the expected coupling structure, making the overall frequency response more stable and improving the controllability of the design.

[0040] In the prior art (reference) Figures 3-10 ): The filter mainly operates at TE. 101 In this mode, its working principle is as follows: Figure 5 As shown, there are two signal coupling paths in the entire structure.

[0041] The first path is the main coupling path, TE. 101 The mode is transmitted sequentially between the resonant cavities R1, R2, R3 and R4 through the coupling window, and finally output from the output port.

[0042] The second path is the cross-coupling path, where the signal is directly coupled from R1 to R4 through the S-shaped slot on the surface, and then output from the output port.

[0043] Since these two paths exist simultaneously and interact with each other, they form a cross-coupled structure, which ultimately generates a transmission zero on each side of the passband, further improving the selectivity of the filter and realizing quasi-elliptic characteristics.

[0044] Conventional microstrip port design such as Figure 6 The ports shown are designed on both sides of the cavity, and their main operating mode is TE. 101 However, it cannot achieve wide stopband characteristics. For example... Figure 7 The higher-order mode TE shown 102 Coupling can proceed normally through ports and coupling windows and cannot be suppressed.

[0045] The achievement of wide stopband characteristics in existing filters mainly relies on the rational design of port positions and coupling window positions, such as... Figure 8 and Figure 9 As shown. For TE 201 In terms of mode, although it can be excited by the input port, the intermediate coupling windows are all located in the region where the field strength is relatively weak, therefore TE 201 The mode cannot be effectively coupled to the subsequent resonant cavity and will also be suppressed.

[0046] Ultimately, by utilizing the field distribution characteristics of different modes and designing the port positions, high-order mode TE was achieved. 102 and TE 201Effective suppression was achieved, thus obtaining a hybrid coupled quasi-elliptic SIW filter with wide stopband characteristics.

[0047] like Figure 10 As shown in the comparison results, by changing the port position, the existing wide-stopband quasi-elliptic SIW filter achieves wide-stopband characteristics, i.e., TE. 102 and TE 201 It is suppressed. However, in addition to the two normally generated transmission zeros TZ1 and TZ2 on both sides of the passband, the filter also produces two additional transmission zeros, TZ3 and TZ4.

[0048] According to traditional cross-coupling theory, a single cross-coupling path typically generates only one pair of transmission zeros. However, the presence of four transmission zeros in this structure indicates the possible existence of additional, unintended coupling paths within the filter. The input and output terminals may be too close together, potentially leading to additional direct source-load coupling via spatial radiation.

[0049] The purpose of this invention is to provide a wide-stopband quasi-elliptic SIW filter with opposite feed to solve the problems of strong source-load parasitic coupling and insufficient out-of-band suppression performance in existing wide-stopband quasi-elliptic SIW filters.

[0050] The filter effectively suppresses TE through a reasonable layout of ports and coupling paths. 102 Model and TE 201 This design strategy, based on mode selection and suppression, provides a simple and effective technical path for realizing wide-stopband, high-performance substrate integrated waveguide (SIW) filters.

[0051] However, the input and output ports of this filter are located on the same metal plane, and the physical distance between them is small. In a real electromagnetic environment, this inevitably creates a parasitic coupling path, introducing parasitic coupling effects between the source and the load. This non-ideal coupling path bypasses the designed main coupling and cross-coupling structures, allowing some signal energy to be transmitted directly from the input to the output without passing through the intended coupling path, thus having an additional impact on the filter's frequency response.

[0052] To address the source-load parasitic coupling problem caused by excessively close port spacing, this invention departs from the traditional design approach of placing input and output ports on the same metal layer. Instead, it employs a layout with upper and lower metal layers, meaning the ports are located on opposite sides of the filter. This spatial physical isolation significantly weakens the direct coupling path between ports, thereby further enhancing stopband rejection and completely eliminating source-load parasitic coupling. It is worth noting that this improvement does not alter the overall filter structure; it is achieved simply by adjusting the feeding method (changing from same-side feeding to opposite-side feeding). Ultimately, while maintaining the original compact structure, excellent performance is achieved, including a flat passband, wide stopband response, and effective suppression of higher-order modes.

[0053] Unlike existing technologies, this invention maintains the original resonant cavity structure, coupling window structure, and operating mode, only improving the input and output feeding structure. The input port is located on the upper surface metal layer of the dielectric substrate, and the output port is located on the lower surface metal layer of the dielectric substrate, with the two ports spatially separated by different metal layers. Because the input and output ports are located on different metal layers, the direct electromagnetic coupling path between the source and load is significantly weakened, thereby effectively suppressing source-load coupling.

[0054] Electromagnetic simulation analysis shows that, compared with the traditional same-layer feeding structure, the present invention can eliminate the additional transmission zeros caused by source-load coupling, making the filter frequency response closer to the theoretical design result.

[0055] In summary, the commercial application scenarios of this invention are as follows: The opposite-face-fed, wide-stopband quasi-elliptic SIW filter proposed in this invention features high selectivity, strong wide-stopband suppression capability, and compact structure. It can be widely used in microwave and millimeter-wave systems with high RF performance requirements, and its main application scenarios include: Satellite communication systems use radio frequency front-end filtering modules for onboard and ground stations to achieve high rejection ratio signal frequency selection, thereby improving link stability and anti-interference capabilities.

[0056] Radar systems (military / civilian): Transceiver channel filtering units used in phased array radar, imaging radar and other systems to improve the dynamic range of the system and reduce out-of-band spurious interference.

[0057] 5G / 6G millimeter-wave communication system: suitable for base station RF front-end and millimeter-wave transceiver modules, achieving low-loss and high-isolation signal selection function in high-frequency bands.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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 or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wide-stopband quasi-elliptic SIW filter with opposite-side feeding, comprising a dielectric layer (4), an upper metal layer (1) disposed on the upper surface of the dielectric layer (4), a lower metal layer (6) disposed on the lower surface of the dielectric layer (4), and a metallized via array penetrating the dielectric layer (4) and connecting the upper metal layer (1) and the lower metal layer (6); the metallized via array, the upper metal layer (1), and the lower metal layer (6) together enclose a plurality of SIW resonant cavities, the plurality of SIW resonant cavities being cascaded sequentially through coupling windows and provided with a cross-coupling structure to achieve a quasi-elliptic response; characterized in that: The SIW filter is provided with an input port (2) and an output port (5). The input port (2) is located on the upper metal layer (1), and the output port (5) is located on the lower metal layer (6). The input port (2) and the output port (5) are located on opposite sides of the dielectric layer (4) and are spatially isolated through the dielectric layer (4) to suppress source-load parasitic coupling.

2. The wide-stopband quasi-elliptic SIW filter with opposite feed as described in claim 1, characterized in that, The dielectric layer (4) is a Rogers RT / duroid 5880 dielectric substrate.

3. The wide-stopband quasi-elliptic SIW filter with opposite feed as described in claim 1, characterized in that, The multiple SIW resonant cavities include a first resonant cavity, a second resonant cavity, a third resonant cavity, and a fourth resonant cavity. Coupling windows are respectively provided between the first resonant cavity and the second resonant cavity, between the second resonant cavity and the third resonant cavity, and between the third resonant cavity and the fourth resonant cavity, so that the four resonant cavities are cascaded in sequence to form a main coupling path.

4. The wide-stopband quasi-elliptic SIW filter with opposite feed as described in claim 3, characterized in that, The cross-coupling structure is an S-shaped slot between the first resonant cavity and the fourth resonant cavity. The signal is directly coupled from the first resonant cavity to the fourth resonant cavity through the S-shaped slot, forming an electrical coupling path (3).

5. The wide-stopband quasi-elliptic SIW filter with opposite feed as described in claim 1, characterized in that, The main operating mode of the SIW filter is TE. 101 model.

6. The wide-stopband quasi-elliptic SIW filter with opposite feed as described in claim 5, characterized in that, The higher-order TE mode within the stopband range of the SIW filter 102 and TE 201 It is suppressed.

7. The wide-stopband quasi-elliptic SIW filter with opposite feed as described in claim 3, characterized in that, The main coupling path is a magnetic coupling path (7), and the cross coupling structure is an electrical coupling path (3). The main coupling path and the cross coupling structure work together to form a transmission zero on each side of the passband.

8. The wide-stopband quasi-elliptic SIW filter with opposite feed as described in claim 4, characterized in that, The S-shaped groove is provided on the upper metal layer (1).

9. The wide-stopband quasi-elliptic SIW filter with opposite feed as described in claim 1, characterized in that, The relative permittivity of the dielectric layer (4) is 2.

2.

10. The wide-stopband quasi-elliptic SIW filter with opposite feed as described in claim 1, characterized in that, The dielectric layer (4) has a thickness of 0.508 mm and a loss tangent of 0.0009.

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