A miniaturized siw bandpass filter with high out-of-band rejection and a design method thereof

Abstract

This invention provides a miniaturized SIW bandpass filter with high out-of-band rejection and its design method. The design method includes: forming a top-layer resonator and a bottom-layer resonator using a three-dimensional structure; determining the center current position of the top-layer and bottom-layer resonators in the operating mode; and etching grooves radially around the center current position, such that the grooves can cut off the current in other modes besides the operating mode along the current direction in the operating mode.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic fields and microwave technology, specifically to a high-frequency filter, and more particularly to a miniaturized SIW bandpass filter with high out-of-band rejection and its design method. Background Technology

[0002] With the rapid development of modern wireless communication technology in defense, civilian and other fields, 5G, and even the upcoming B5G and 6G, are placing increasingly higher technical requirements on key components of wireless communication systems such as filters. Therefore, high-frequency filters with low insertion loss (high Q value), high frequency selectivity, good out-of-band rejection, and miniaturization are currently a hot research topic.

[0003] In existing technologies, traditional microstrip filters are no longer universally applicable to operating frequency bands above 8 GHz due to excessive loss at high frequencies. At higher frequencies, substrate integrated waveguide (SIW) technology is typically used to design filters. While SIW filters offer high Q values ​​and low losses, their unique structure and operating principle make it difficult to introduce a large number of finite transmission zeros (FTZs) in the passband and a wide stopband to improve selectivity and sideband rejection. Even methods that use resonator surface etching to increase the stopband bandwidth and introduce FTZs sacrifice Q values. Therefore, maintaining a high Q value (low loss) while introducing FTZs and achieving wide stopband rejection presents a contradictory technical challenge. Furthermore, the SIW structure itself has a cutoff frequency issue; designing high-order, high-performance filters with a purely planar structure would result in excessively large overall dimensions, failing to meet the requirements of miniaturized systems. Summary of the Invention

[0004] To maintain a high Q value (low loss) while introducing finite frequency transmission zeros and achieving wide stopband suppression, this invention provides a miniaturized SIW bandpass filter with high out-of-band rejection and its design method. This method effectively improves filter performance by maintaining a high Q value, introducing finite frequency transmission zeros, and suppressing high-order harmonics to achieve high out-of-band rejection. Furthermore, the filter's overall structure employs a three-dimensional design, which is more conducive to matching miniaturized systems.

[0005] On one hand, the present invention provides a design method for a miniaturized SIW bandpass filter with high out-of-band rejection, comprising:

[0006] A three-dimensional structure is used to form the top-level resonator and the bottom-level resonator;

[0007] Determine the center current position of the top resonator and the bottom resonator in the operating mode. With the center current position as the center, etch grooves radially so that the grooves can cut the current in other modes besides the operating mode along the current direction in the operating mode.

[0008] On the other hand, the present invention provides a miniaturized SIW bandpass filter with high out-of-band rejection, which is obtained by the above-described design method.

[0009] Further, the filter includes: a top metal layer, a top dielectric substrate, a first intermediate metal layer, a bottom dielectric substrate, and a bottom metal layer stacked sequentially; a top resonator is formed between the top metal layer and the top dielectric substrate; a bottom resonator is formed between the first intermediate metal layer and the bottom dielectric substrate; and the bottom metal layer serves as a ground plane. Two first grooves formed according to a predetermined etching method are provided on both the top metal layer and the bottom metal layer. The predetermined etching method refers to etching the grooves radially with the center current position of the top and bottom resonators in their operating mode as the center.

[0010] Furthermore, an intermediate layer dielectric substrate and a second intermediate metal layer are stacked sequentially between the first intermediate metal layer and the bottom dielectric substrate.

[0011] Correspondingly, a first intermediate resonator and a second intermediate resonator are formed between the first intermediate metal layer and the intermediate layer dielectric substrate, and a bottom resonator is formed between the second intermediate metal layer and the bottom layer dielectric substrate.

[0012] Furthermore, the two first groove lines are each evenly distributed on the top metal layer and the bottom metal layer.

[0013] Furthermore, the groove line is generally in the shape of a cross or in the shape of a rice character.

[0014] Furthermore, both the top-level resonator and the bottom-level resonator operate in the first resonant mode, and both the first intermediate resonator and the second intermediate resonator operate in the second resonant mode.

[0015] Furthermore, the first resonant mode is TE. 102 The second resonant mode is TE. 101 model.

[0016] Furthermore, each of the first intermediate metal layer and the second intermediate metal layer is provided with a second groove line as a coupling path between the top resonator and the first intermediate resonator, and between the second intermediate resonator and the bottom resonator.

[0017] Furthermore, the second groove is a "segment" type groove.

[0018] Furthermore, a first port is provided on the top metal layer, and a second port is provided on the bottom metal layer; one of the first port and the second port serves as an input port, and the other port serves as an output port.

[0019] Furthermore, both the first port and the second port adopt a microstrip line to coplanar waveguide feeding structure.

[0020] Furthermore, the first port and the second port are spatially centrally symmetrically distributed.

[0021] Furthermore, the top resonator and the bottom resonator have the same area, denoted as S1; the first intermediate resonator and the second intermediate resonator have the same area, denoted as S2; where S1 = 2S2.

[0022] The beneficial effects of this invention are:

[0023] 1. In the operating modes of the top and bottom resonators, the current direction diverges outward from the central current, while in other modes, the current direction diverges outward from other central locations. Based on this, this invention employs a design that etchs grooves radially along the central current location in the operating mode onto the top and bottom SIW resonators. The direction of these grooves is precisely along the current direction in the operating modes of the top and bottom resonators, thus not affecting the resonant frequency and Q value in the operating modes. Simultaneously, these grooves can cut off the current in other modes within each SIW resonator, suppressing the effective excitation of other modes. In other words, these grooves only change modes other than the operating mode, without altering the fundamental operating mode. Therefore, the filter of this invention possesses both a high Q value (low loss) and strong wide stopband suppression characteristics, significantly improving the filter's performance.

[0024] 2. This invention also employs a design that etches grooves on the surfaces of each intermediate metal layer. These grooves establish coupling paths between the top / bottom layer resonators and the intermediate layer resonators, while effectively generating parasitic coupling paths, thereby introducing multiple finite-frequency transmission zeros and further enhancing the filter's out-of-band rejection capability. Therefore, the filter designed based on this idea further improves the filter's performance and extremely effectively meets the high-performance development requirements of wireless radio frequency systems.

[0025] 3. This invention employs a combination of SIW resonators and a microstrip line-to-coplanar waveguide feeding structure to design a multi-layered, three-dimensional "box-shaped" substrate integrated waveguide wide-stopband bandpass filter. This design facilitates integration and matching with other wireless RF system devices, while also possessing a high Q value. The SIW structure design provides excellent electromagnetic shielding, stronger anti-interference capabilities, and higher power capacity, making it universally applicable in microwave and millimeter-wave bands. It holds significant application value and promise for 5G and even future B5G and 6G eras.

[0026] 4. This invention employs a multi-layer PCB circuit board structure design, effectively reducing the overall size of the filter and to some extent compensating for the problem of excessively large SIW filter size at lower frequencies. Furthermore, this invention does not require a special dielectric substrate and is universally applicable to millimeter-wave operating frequencies. Therefore, it can meet the needs of miniaturized, low-cost, and high-frequency wireless RF systems, further enhancing its market application prospects and value. Attached Figure Description

[0027] Figure 1 A schematic diagram of radially etched grooves with the center current position of the resonator in the operating mode as the center, provided for an embodiment of the present invention;

[0028] Figure 2 One of the 3D structural schematic diagrams of a miniaturized SIW bandpass filter with high out-of-band rejection provided in an embodiment of the present invention;

[0029] Figure 3 The second 3D structural schematic diagram of a miniaturized SIW bandpass filter with high out-of-band suppression provided in an embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of a two-port circuit coupling topology provided in an embodiment of the present invention;

[0031] Figure 5 A schematic diagram of the top-level resonator provided in an embodiment of the present invention;

[0032] Figure 6 A schematic diagram of the intermediate layer resonator provided in an embodiment of the present invention;

[0033] Figure 7 A schematic diagram of the underlying resonator plane provided in an embodiment of the present invention;

[0034] Figure 8 This is a schematic diagram of the bottom surface of the bottom resonator provided in an embodiment of the present invention;

[0035] Figure 9 The narrowband frequency response curve of the filter provided in the embodiment of the present invention;

[0036] Figure 10 The broadband frequency response curve of the filter provided in the embodiment of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] Example 1

[0039] This invention provides a design method for a miniaturized SIW bandpass filter with high out-of-band rejection, comprising the following steps:

[0040] A three-dimensional structure is used to form the top-level resonator and the bottom-level resonator;

[0041] Determine the center current position of the top resonator and the bottom resonator in the operating mode. With the center current position as the center, etch grooves radially so that the grooves can cut the current in other modes besides the operating mode along the current direction in the operating mode.

[0042] Specifically, in the operating modes of the top and bottom resonators, the current direction is radiating outwards from the central current, while in other modes, the current direction is radiating outwards from other central locations. Based on this, this embodiment employs radial etching of grooves (e.g., cross-shaped, star-shaped, or other patterns) on the top and bottom resonators, with the central current location in the operating mode as the center. Figure 1 As shown, the red dot indicates the location of the central current in the operating mode, and the rest are grooves etched radially. These grooves can cut the current in other modes while moving along the current direction in the operating mode (i.e., with almost no impact on the operating mode), thereby suppressing the effective excitation of other modes and achieving wide stopband characteristics.

[0043] Furthermore, by employing a three-dimensional structure to form the top and bottom resonators, the entire filter can be miniaturized compared to a planar structure.

[0044] Example 2

[0045] Corresponding to the above design method, this embodiment of the invention provides a miniaturized SIW bandpass filter with high out-of-band rejection. In this embodiment, the three-dimensional structure of the top-layer resonator and the bottom-layer resonator can be implemented using existing three-dimensional structures, and is not limited thereto. It should be noted that groove lines are etched on both the top-layer and bottom-layer resonators, and the etching method of the groove lines is as follows: the groove lines are etched radially with the center current position of the top-layer and bottom-layer resonators in the operating mode as the center. For example, the overall groove lines can be in the shape of a cross, a star, or other shapes, such as... Figure 1 As shown.

[0046] Example 3

[0047] Based on the above embodiments, such as Figure 2 The 3D schematic diagram shown illustrates an embodiment of the present invention that provides a miniaturized SIW bandpass filter with high out-of-band rejection using a 5-layer three-dimensional structure. The filter includes: a top metal layer, a top dielectric substrate, a first intermediate metal layer, a bottom dielectric substrate, and a bottom metal layer stacked sequentially. A top resonator is formed between the top metal layer and the top dielectric substrate, and a bottom resonator is formed between the first intermediate metal layer and the bottom dielectric substrate. The bottom metal layer serves as a ground plane (GND). Two first grooves, formed according to a predetermined etching method, are respectively formed on both the top and bottom metal layers. The predetermined etching method refers to etching the grooves radially with the center current position of the top and bottom resonators in their operating mode as the center.

[0048] Specifically, by etching grooves radially with the center current position of the top and bottom resonators in their operating modes as the center, these grooves align precisely with the current direction of the top and bottom resonators in their operating modes, thus not affecting the resonant frequency and Q value in those modes. Simultaneously, these grooves can cut off the current in other modes within each SIW resonator; that is, these grooves only change modes other than the operating mode, without altering the fundamental operating mode. Therefore, the filter of this embodiment possesses both a high Q value (low loss) and strong wide stopband suppression characteristics, significantly improving the filter's performance.

[0049] Furthermore, the embodiments of this invention effectively reduce the overall size of the filter by employing a three-dimensional structure design with a multi-layer PCB circuit board, thus mitigating to some extent the problem of excessively large SIW filter size at lower frequencies. Moreover, this invention does not require a special dielectric substrate and is universally applicable to millimeter-wave operating frequencies. Therefore, it can meet the demands of miniaturized, low-cost, and high-frequency wireless RF systems, further enhancing its market application prospects and value.

[0050] In addition, the filter adopts a SIW structure design, which has excellent electromagnetic shielding, stronger anti-interference ability and higher power capacity. It is universally applicable in microwave and millimeter wave bands and has strong application value and prospects in 5G and even the future B5G and 6G era.

[0051] Preferably, the two first groove lines are each evenly distributed on the top metal layer and the bottom metal layer.

[0052] Preferably, the first groove line is in the shape of a cross, a rice character, or other characters, such as... Figure 1 As shown.

[0053] Example 4

[0054] Based on the above embodiments, such as Figure 3 The 3D schematic diagram shown illustrates an embodiment of the present invention that provides a miniaturized SIW bandpass filter with high out-of-band rejection using a seven-layer three-dimensional structure. The filter has a three-dimensional "box-shaped" structure, comprising: a top metal layer, a top dielectric substrate, a first intermediate metal layer, an intermediate dielectric substrate, a second intermediate metal layer, a bottom dielectric substrate, and a bottom metal layer stacked sequentially. A top resonator is formed between the top metal layer and the top dielectric substrate. A first intermediate resonator and a second intermediate resonator are formed between the first intermediate metal layer and the intermediate dielectric substrate. A bottom resonator is formed between the bottom dielectric substrate and the second intermediate metal layer. The bottom metal layer serves as a ground plane (GND). Two first grooves, formed according to a predetermined etching method, are provided on both the top and bottom metal layers. The predetermined etching method refers to etching the grooves radially with the center current position of the top and bottom resonators in their operating mode as the center.

[0055] It should be noted that the number of intermediate metal layers and intermediate dielectric substrates can be expanded as needed. That is, based on the concept of the embodiments of the present invention, the number of intermediate resonators can be expanded, including third and fourth intermediate resonators, etc.

[0056] Preferably, the two first groove lines are each evenly distributed on the top metal layer and the bottom metal layer.

[0057] Preferably, the first groove line is in the shape of a cross, a rice character, or other characters, such as... Figure 1 As shown.

[0058] Example 5

[0059] Based on the above embodiments, in this embodiment of the invention, both the top-level resonator and the bottom-level resonator operate in the first resonant mode, and both the first intermediate resonator and the second intermediate resonator operate in the second resonant mode. Thus, the entire filter achieves a multi-mode hybrid three-dimensional structure design.

[0060] Preferably, the first resonant mode is TE. 102 The second resonant mode is TE. 101 Mode. Set the second resonant mode to TE. 101 In this design, with the top (or bottom) and middle layers having dielectric substrates and metal layers of the same size, two intermediate resonators are obtained, effectively reducing the overall size.

[0061] It should be noted that all resonators are not limited to the mode in this embodiment. When including the third and fourth intermediate resonators and more intermediate resonators, the resonance mode of the intermediate layer resonators can also be different (for example, the first and second intermediate resonators use the same resonance mode A, the third and fourth intermediate resonators use another resonance mode B, etc.), but the resonance modes of the top and bottom resonators must be the same.

[0062] Example 6

[0063] To further improve the out-of-band rejection capability of the entire filter, based on the above embodiments, the present invention provides that the first intermediate metal layer and the second intermediate metal layer are each provided with a second slot line as a coupling path between the top resonator and the first intermediate resonator, and between the second intermediate resonator and the bottom resonator.

[0064] Specifically, in this embodiment, the slot lines on the intermediate metal layer realize the coupling path between the top / bottom resonators and the intermediate layer resonators, while effectively generating parasitic coupling paths, thereby introducing multiple finite-frequency transmission zeros and further improving the out-of-band rejection capability of the filter. Therefore, the filter in this embodiment can further improve the filter's performance and extremely effectively meet the high-performance development requirements of wireless radio frequency systems.

[0065] Preferably, the grooves disposed on the first intermediate metal layer and the second intermediate metal layer are "segment" type grooves. For example... Figure 6 and Figure 7 As shown.

[0066] Example 7

[0067] Based on the above embodiments, the input and output ports of the entire filter are set on the top resonator and the bottom resonator, specifically: a first port is set on the top metal layer and a second port is set on the bottom metal layer; one of the first port and the second port serves as the input port and the other port serves as the output port.

[0068] Specifically, such as Figure 4 The coupled topology shown explains the coupling relationship and mechanism between the four-layer SIW resonators. In this coupled topology: S represents the input port, L represents the output port, and the two can be interchanged in this example; R1 and R4 represent the operating mode at TE. 102 The top and bottom single-mode SIW resonators (i.e., the top resonator and the bottom resonator); R2 and R3 indicate operation in TE mode. 101 The intermediate layer of the single-mode SIW resonator (i.e., the first intermediate resonator and the second intermediate resonator); solid lines represent direct coupling paths between resonators, and dashed lines represent parasitic coupling (cross-coupling) paths between resonators.

[0069] Preferably, both the first port and the second port employ a microstrip line-to-coplanar waveguide feeding structure. Preferably, the first port and the second port are spatially centrosymmetrically distributed. Figure 5 and Figure 7 As shown.

[0070] Specifically, a multi-layered, three-dimensional "box-shaped" substrate integrated waveguide wide-stopband bandpass filter is designed by combining SIW resonators with a microstrip line to coplanar waveguide feeding structure. The filter designed in this way is easy to integrate and match with other wireless RF system devices. At the same time, it can achieve advantages such as high Q value (low loss), miniaturization, high selectivity and good quasi-elliptic function filtering response curve when operating at higher frequencies.

[0071] Example 8

[0072] Based on the above embodiments, combined with Figure 3 as well as Figures 5 to 7 As shown, metal via arrays are provided on the top dielectric substrate, the middle dielectric substrate, and the bottom dielectric substrate. Different distributions of the metal via arrays can adjust the area of ​​the corresponding resonators, thereby adjusting the resonant frequency of each resonator and thus adjusting the operating frequency band of the filter.

[0073] In this embodiment, the top-layer resonator and the bottom-layer resonator have the same area, denoted as S1; the first intermediate resonator and the second intermediate resonator have the same area, denoted as S2; where S1 = 2S2. As one possible implementation, specifically... Figures 5 to 7In the shown metal via hole array distribution form, when there are dielectric substrates and metal layers with the same parameters in the top layer (or bottom layer) and the middle layer, two intermediate resonators can be achieved. The area size of any one of the intermediate resonators is approximately equal to one-half of the area of the top layer resonator or the bottom layer resonator. It can be understood that more intermediate resonators can be formed by adjusting the distribution form of the metal via hole array as needed, which will not be elaborated here.

[0074] Embodiment 9

[0075] As Figures 5 to 8 shown, in this embodiment, specific settings of some parameters of the filter are given as follows: Four "rice" - shaped coupling slots are evenly distributed on the upper surface of the top - layer single - mode SIW resonator and the lower surface of the bottom - layer single - mode SIW resonator, showing an overall uniform distribution. The "line segment" - shaped etched slot lines are distributed in the middle metal layer to realize the coupling path between the resonators.

[0076] Specifically, the dielectric substrate uses Rogers5880, with a relative dielectric constant of 2.2 and a thickness of 0.508 mm. The filter size L = 33.82 mm, W = 15.98 mm, the diameter of the metal via holes is D = 0.8 mm, the distance between two adjacent metal via holes is 1.2 mm; the width of the feeding microstrip line W 0 = 1.54 mm; the sizes of the "rice" - shaped coupling slot lines are equal, where L 1 = 6.5 mm, L 2 = 4.5 mm; the size of the etched slot line on the surface of the first intermediate resonator is L 3 = 3.4 mm, W 1 = 0.3 mm; the coupling window W 2 between the first intermediate resonator and the second intermediate resonator is 3.64 mm; the size of the etched slot line on the upper surface of the bottom - layer resonator is L 4 = 3.4 mm, W 3 = 0.3 mm, the coupling window size W 4 = 3 mm; the size of the gap of the feeding coplanar waveguide structure is g 1 = 2.5 mm, g 2 = 0.25 mm, g 3 = 1.33 mm.

[0077] Among the four single - mode SIW resonators in this embodiment, the top - layer and bottom - layer resonators operate in the TE 102 mode, and the intermediate - layer resonators operate in the TE 101 mode. The design of the "rice" - shaped etched slot lines on the surfaces of the top - layer and bottom - layer resonators does not affect the TE 102The four single-mode SIW resonators, while differing in size, resonate within the same operating frequency band. The latter operates at TE... 101 The two intermediate layer resonators of the mode operate approximately at TE. 102 Half the size of the top or bottom resonator of the mode.

[0078] Both feed ports are 50 Ω microstrip line to coplanar waveguide feed structures. The two feed lines are connected to two circuits operating at TE. 102 A single-mode SIW resonator is connected, and then excited through a coupling window to operate at TE. 101 Mode resonator.

[0079] Figure 9 The simulation results of frequency scattering parameters in the narrow band range of the bandpass filter in the embodiments of the present invention are presented. The simulation software used is Ansys Electronics Desktop 2021R1. The results show that the filter designed in this invention can obtain a quasi-elliptic function filtering response curve at the fundamental mode. The tested center frequency is 10 GHz, the in-band insertion loss is 0.96 dB, the in-band reflection loss is less than -20 dB, and the 3 dB bandwidth is 290 MHz (relative bandwidth 2.9%).

[0080] Figure 10 The simulation results of the wideband scattering parameters of the bandpass filter in this embodiment of the invention are presented. The simulation software used is Ansys Electronics Desktop 2021R1. The stopband with a suppression level greater than 20 dB extends to approximately 26 GHz, which is 2.6 times the center frequency of the passband. This data directly demonstrates that the bandpass filter designed using this approach can achieve filtering characteristics of high Q value, high selectivity, and high out-of-band rejection capability.

[0081] 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 of the technical features; and these 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 the present invention.

Claims

1. A miniaturized SIW bandpass filter with high out-of-band rejection, characterized in that, The adopted design method includes: Adopting a three-dimensional structure to form a top resonator and a bottom resonator; Determining the central current positions of the top resonator and the bottom resonator in the working mode, taking the central current positions as the centers of circles, and etching slot lines along the radial direction, so that the slot lines can follow the current direction in the working mode and cut off the currents in other modes except the working mode; Correspondingly, the SIW bandpass filter includes: A top metal layer, a top dielectric substrate, a first intermediate metal layer, a bottom dielectric substrate, and a bottom metal layer stacked in sequence. A top resonator is formed between the top metal layer and the top dielectric substrate, a bottom resonator is formed between the first intermediate metal layer and the bottom dielectric substrate, and the bottom metal layer is a ground plane; Two first slot lines formed according to a set etching method are respectively provided on the top metal layer and the bottom metal layer; The set etching method means taking the central current positions of the top resonator and the bottom resonator in the working mode as the centers of circles and etching slot lines along the radial direction; The first slot line is in an overall "rice" shape.

2. The miniaturized SIW bandpass filter with high out-of-band rejection according to claim 1, characterized in that, An intermediate layer dielectric substrate and a second intermediate metal layer are further stacked in sequence between the first intermediate metal layer and the bottom dielectric substrate; Correspondingly, a first intermediate resonator and a second intermediate resonator are formed between the first intermediate metal layer and the intermediate layer dielectric substrate, and the bottom resonator is formed between the second intermediate metal layer and the bottom dielectric substrate.

3. A miniaturized SIW bandpass filter with high out-of-band rejection according to claim 1 or 2, characterized in that, The two first slot lines are respectively uniformly distributed on the top metal layer and the bottom metal layer.

4. A miniaturized SIW bandpass filter with high out-of-band rejection according to claim 2, characterized in that, Both the top resonator and the bottom resonator operate in the first resonance mode, and both the first intermediate resonator and the second intermediate resonator operate in the second resonance mode.

5. A miniaturized SIW bandpass filter with high out-of-band rejection according to claim 4, characterized in that, The first resonant mode is TE 102 The second resonant mode is TE. 101 model.

6. A miniaturized SIW bandpass filter with high out-of-band rejection according to claim 2, characterized in that, Second slot lines are respectively provided on the first intermediate metal layer and the second intermediate metal layer as the coupling paths between the top resonator and the first intermediate resonator and between the second intermediate resonator and the bottom resonator.

7. A miniaturized SIW bandpass filter with high out-of-band rejection according to claim 6, characterized in that, The second slot line is a "line segment" type slot line.

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