A dielectric waveguide filter with cross-cavity coupling structure

Abstract

The present invention provides a dielectric waveguide filter with a cross-cavity coupling structure, wherein the dielectric waveguide filter includes at least three resonance units connected in sequence, and a coupling window is provided between each two adjacent resonance units; at least one first coupling blind hole and a second coupling blind hole are provided on at least one pair of non-adjacent first resonance units and second resonance units, respectively, and the first coupling blind hole and the second coupling blind hole are electrically connected to each other, so that the non-adjacent first resonance units and the second resonance units generate cross coupling. Thus, the present invention realizes cross-cavity coupling by introducing a cross-cavity coupling structure between two non-adjacent resonance units, increases the transmission zero point of the dielectric waveguide filter, and thus can further improve the frequency selection characteristics of the dielectric waveguide filter without increasing the volume of the filter, and has the characteristics of simple structure, easy manufacturing and maintenance.

Description

Technical Field

[0001] The present invention relates to a dielectric waveguide filter in the field of communication technology, and in particular to a dielectric waveguide filter with a cross-cavity coupling structure. Background Art

[0002] With the continuous development of modern communication technology, the performance requirements for filters are getting higher and higher. Dielectric waveguide filters have been well applied in miniaturized and highly integrated communication systems due to their small size, high Q value, and low cost. However, with the continuous development of multi-frequency systems, the requirements for the volume and frequency selection characteristics of filters are getting higher and higher. However, in order to achieve the required frequency selection characteristics, the existing dielectric waveguide filters usually greatly increase the volume of the dielectric waveguide filters. Therefore, how to further improve the frequency selection characteristics of the dielectric waveguide filters without increasing the volume of the dielectric waveguide filters is a problem that needs to be solved urgently.

[0003] In summary, the prior art obviously has inconveniences and defects in practical use, so it is necessary to improve it. Summary of the invention

[0004] In view of the above-mentioned defects, an object of the present invention is to provide a dielectric waveguide filter with a cross-cavity coupling structure, which can further improve the frequency selection characteristics of the dielectric waveguide filter without increasing the volume of the filter.

[0005] In order to achieve the above-mentioned object, the present invention provides a dielectric waveguide filter with a cross-cavity coupling structure, wherein the dielectric waveguide filter comprises at least three resonance units connected in sequence, and a coupling window is provided between each two adjacent resonance units; at least one first coupling blind hole and a second coupling blind hole are respectively provided on at least one pair of non-adjacent first resonance units and second resonance units, and the first coupling blind hole and the second coupling blind hole are electrically connected to each other, so that the non-adjacent first resonance units and the second resonance units generate cross coupling.

[0006] According to the dielectric waveguide filter of the present invention, the first coupling blind hole, the second coupling blind hole and at least one circuit board are provided on the side surfaces of the non-adjacent first resonant unit and the second resonant unit; the first coupling blind hole and the second coupling blind hole are respectively provided with a first metal inner core and a second metal inner core; at least one first metal wire is provided on the circuit board, and the first metal wire is respectively connected to the first metal inner core of the first coupling blind hole and the second metal inner core of the second coupling blind hole to realize electrical connection between the first coupling blind hole and the second coupling blind hole; or

[0007] The first coupling blind hole, the second coupling blind hole and at least one second metal wire are provided on the side surfaces of the non-adjacent first resonance unit and the second resonance unit; the first coupling blind hole and the second coupling blind hole are respectively provided with a first metal inner core and a second metal inner core; the second metal wire respectively connects the first metal inner core of the first coupling blind hole and the second metal inner core of the second coupling blind hole to realize electrical connection between the first coupling blind hole and the second coupling blind hole.

[0008] According to the dielectric waveguide filter of the present invention, the circuit board is a three-layer structure, which includes a bottom metal layer, an intermediate dielectric layer and a top metal layer in sequence; at least one first metal wire is etched on the top metal layer, and the first metal wire is electrically connected to the first metal core of the first coupling blind hole and the second metal core of the second coupling blind hole respectively through the metallized through hole on the circuit board; and / or

[0009] The circuit board is a hard circuit board or a flexible circuit board.

[0010] According to the dielectric waveguide filter of the present invention, the first metal line or the second metal line is a suspension line, a microstrip line or a coplanar waveguide; and / or

[0011] The first metal wire or the second metal wire is in a straight line shape, a zigzag line shape or a curved line shape.

[0012] According to the dielectric waveguide filter of the present invention, the first coupling blind hole and the second coupling blind hole are cylindrical, elliptical or prism-shaped.

[0013] According to the dielectric waveguide filter of the present invention, at least one tuning blind hole for tuning the resonance frequency of the resonance unit is provided on the top of each resonance unit; and / or

[0014] The at least three resonance units are arranged in a straight line, a curved line or a folded line.

[0015] According to the dielectric waveguide filter of the present invention, the tuning blind hole is arranged at the center of the top of the resonance unit.

[0016] According to the dielectric waveguide filter of the present invention, a first metal plating layer is attached to the outer surface of the dielectric waveguide filter; the inner walls of the first coupling blind hole and the second coupling blind hole are respectively provided with a second metal plating layer, and the outer edges of the first coupling blind hole and the second coupling blind hole are respectively provided with a circle of a first non-electroplating area and a second non-electroplating area; the first non-electroplating area separates the second metal plating layer of the first coupling blind hole from the first metal plating layer of the dielectric waveguide filter, and the second non-electroplating area separates the second metal plating layer of the second coupling blind hole from the first metal plating layer of the dielectric waveguide filter.

[0017] According to the dielectric waveguide filter of the present invention, the first non-electroplating area and the second non-electroplating area are in the shape of a circular ring or a polygon.

[0018] According to the dielectric waveguide filter of the present invention, the coupling strength between the non-adjacent first resonant unit and the second resonant unit is controlled by the depth of the first coupling blind hole and the second coupling blind hole, and the deeper the depth of the first coupling blind hole and the second coupling blind hole, the greater the coupling strength; and / or

[0019] The magnitude of the coupling strength of the non-adjacent first resonance unit and the second resonance unit is controlled by the positional relationship between the bottom of the first coupling blind hole and the second coupling blind hole and the first resonance unit and the second resonance unit, respectively. When the bottom of the first coupling blind hole and the second coupling blind hole are in the middle position of the first resonance unit and the second resonance unit, the coupling strength is the largest; when the bottom of the first coupling blind hole or the second coupling blind hole is closer to the upper and lower ends of the first resonance unit and the second resonance unit, the coupling strength is weaker.

[0020] The dielectric waveguide filter with a cross-cavity coupling structure of the present invention includes at least three resonance units connected in sequence, and the dielectric waveguide filter is respectively provided with a first coupling blind hole and a second coupling blind hole on at least one pair of non-adjacent first resonance units and second resonance units, and the first coupling blind hole and the second coupling blind hole are electrically connected to each other, so that the non-adjacent first resonance units and the second resonance units generate cross-cavity cross-coupling, and a transmission zero point can be generated near the passband. Preferably, a tuning blind hole for adjusting the resonance frequency is provided on the top of each resonance unit. Thereby, the present invention realizes cross-coupling by introducing a cross-cavity coupling structure between two non-adjacent resonance units, increases the transmission zero point of the dielectric waveguide filter, and can further improve the frequency selection characteristics of the dielectric waveguide filter without increasing the volume of the filter, and has the characteristics of simple structure, easy manufacturing and maintenance. The present invention plays an important role in promoting the development of dielectric waveguide filters in modern miniaturized integrated communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of a preferred structure of a dielectric waveguide filter with a cross-cavity coupling structure according to the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] It should be noted that references to "one embodiment", "embodiment", "example embodiment", etc. in this specification refer to the embodiment described, which may include specific features, structures or characteristics, but not every embodiment must include these specific features, structures or characteristics. In addition, such expressions do not refer to the same embodiment. Furthermore, when describing specific features, structures or characteristics in conjunction with an embodiment, whether or not there is an explicit description, it has been shown that it is within the knowledge of those skilled in the art to combine such features, structures or characteristics into other embodiments.

[0024] In addition, certain words are used in the specification and subsequent claims to refer to specific components or parts. Those with ordinary knowledge in the relevant field should understand that manufacturers can use different nouns or terms to refer to the same component or part. This specification and subsequent claims do not use differences in names as a way to distinguish components or parts, but use differences in the functions of components or parts as the criteria for distinction. "Including" and "including" mentioned throughout the specification and subsequent claims are open-ended terms and should be interpreted as "including but not limited to". In addition, the word "connected" here includes any direct and indirect electrical connection means. Indirect electrical connection means include connection through other devices.

[0025] The dielectric waveguide filter with a cross-cavity coupling structure of the present invention comprises at least three resonance units connected in sequence, wherein the resonance units are connected in an arbitrary topological structure, and a coupling window is provided between each two adjacent resonance units. At least one first coupling blind hole and a second coupling blind hole are provided on at least one pair of non-adjacent first resonance units and second resonance units, respectively, and the first coupling blind hole and the second coupling blind hole are electrically connected to each other, so that the non-adjacent first resonance units and the second resonance units form cross coupling, thereby generating a transmission zero point near the passband, and the frequency selection characteristics of the dielectric waveguide filter can be further improved without increasing the volume of the dielectric waveguide filter.

[0026] Figure 1The preferred structure of the dielectric waveguide filter with a cross-cavity coupling structure of the present invention is shown. The dielectric waveguide filter 100 includes five resonance units 101-105 connected in sequence. In this embodiment, the resonance units 101-105 are arranged in a straight line in sequence. However, the resonance units of the dielectric waveguide filter 100 of the present invention can actually be connected in any topological structure as needed. For example, the resonance units 101-105 can also be arranged in a curve or a broken line in sequence. A coupling window 201-204 is provided between each two adjacent resonance units, and the coupling window 201-204 can be a hollow cavity structure. Specifically, a coupling window 201 is provided between adjacent resonance units 101-102, a coupling window 202 is provided between adjacent resonance units 102-103, a coupling window 203 is provided between adjacent resonance units 103-104, and a coupling window 204 is provided between adjacent resonance units 104-105.

[0027] like Figure 1 In the specific embodiment shown, the dielectric waveguide filter 100 is composed of five resonance units 101-105 and four coupling windows 201-204, and the resonance units 101-105 and the coupling windows 201-204 are arranged in alternating straight lines. It should be noted that the number of resonance units of the dielectric waveguide filter 100 of the present invention is n≥3, and the number of coupling windows is n-1. The specific number of the resonance units is not limited, as long as n≥3 is satisfied, the number of resonance units can be increased or decreased according to actual needs. For example, the dielectric waveguide filter 100 can include three, four, six, seven, eight, nine, ten or more resonance units.

[0028] In order to further improve the frequency selection characteristics of the dielectric waveguide filter, the present invention proposes to introduce a cross-cavity coupling structure between at least one pair of non-adjacent resonant units of the dielectric waveguide filter 100 to achieve cross-cavity cross-coupling. Figure 1 As shown, at least one first coupling blind hole 301 and a second coupling blind hole 302 are preferably provided on the non-adjacent first resonant unit 102 and the second resonant unit 104, respectively, and the first coupling blind hole 301 and the second coupling blind hole 302 are electrically connected to each other. Thus, the non-adjacent first resonant unit 102 and the second resonant unit 104 form cross coupling, and then generate a transmission zero point near the passband, and improve the frequency selection characteristics of the dielectric waveguide filter 100 without increasing the volume of the dielectric waveguide filter 100. The first coupling blind hole 301 and the second coupling blind hole 302 electrically connected to each other in the dielectric waveguide filter 100 of the present invention form a cross-cavity coupling structure, and the cross-cavity coupling structure has the characteristics of simple implementation, easy manufacturing and maintenance, and low cost.

[0029] like Figure 1In the illustrated embodiment, the side surfaces of the non-adjacent first resonant unit 102 and the second resonant unit 104 are provided with a first coupling blind hole 301, a second coupling blind hole 302 and at least one circuit board 501. The first coupling blind hole 301 and the second coupling blind hole 302 are provided with a first metal inner core 401 and a second metal inner core 402, respectively. The circuit board 501 is provided with at least one first metal wire 502, and the two ends of the first metal wire 502 are respectively connected to the first metal inner core 401 of the first coupling blind hole 301 and the second metal inner core 402 of the second coupling blind hole 302. Through the first metal inner core 401 and the second metal inner core 402, the first metal wire 502 on the circuit board 501 is electrically connected to the two coupling blind holes 301-302, so that the non-adjacent resonant units 102 and 104 are cross-coupled.

[0030] Of course, the first coupling blind via 301, the second coupling blind via 302, and the circuit board 501 of the present invention are not limited to being arranged on the sides of non-adjacent resonant units 102 and 104, and can also be arranged on the top, bottom, etc. of non-adjacent resonant units 102 and 104 according to actual needs.

[0031] Figure 1 The first coupling blind hole 301 and the second coupling blind hole 302 are preferably cylindrical. However, the first coupling blind hole 301 and the second coupling blind hole 302 can also be any regular geometric cylinder or irregular geometric cylinder such as an elliptical cylinder or a prism. However, for the convenience of production, the first coupling blind hole 301 and the second coupling blind hole 302 are preferably cylindrical.

[0032] Preferably, the circuit board 501 is a three-layer structure, including a bottom metal layer, an intermediate dielectric layer and a top metal layer (not shown in the figure) in sequence. At least one first metal line 502 may be etched on the top metal layer, and the first metal line 502 is electrically connected to the first metal core 401 of the first coupling blind hole 301 and the second metal core 402 of the second coupling blind hole 302 through the metallized through hole on the circuit board 501. The circuit board 501 may be a hard circuit board or a flexible circuit board. The flexible circuit board may be applicable to the case where the non-adjacent resonant units 102 and 104 are arranged in a non-linear manner such as a curved arrangement or a folded line arrangement.

[0033] It should be noted that the electrical connection method between the first coupling blind via 301 and the second coupling blind via 302 of the present invention is not limited to the method of Figure 1The circuit board 501 and the first metal wire 502 shown in the figure are combined in a manner. In another embodiment of the present invention, the side surfaces of the non-adjacent first resonant unit 102 and the second resonant unit 104 are provided with a first coupling blind hole 301, a second coupling blind hole 302 and at least one second metal wire (not shown in the figure). The first coupling blind hole 301 and the second coupling blind hole 302 are provided with a first metal inner core 401 and a second metal inner core 402 respectively. The second metal wire is connected to the first metal inner core 401 of the first coupling blind hole 301 and the second metal inner core 402 of the second coupling blind hole 302 respectively, so as to realize the electrical connection between the first coupling blind hole 301 and the second coupling blind hole 302. That is, the first coupling blind hole 301 and the second coupling blind hole 302 can be directly electrically connected through the second metal wire without adding the circuit board 501. The non-adjacent resonant units 102 and 104 form cross coupling through the second metal wire and the coupling blind holes 301 and 302, so that the transmission zero point can be increased, and the frequency selection characteristics of the dielectric waveguide filter 100 can be further improved.

[0034] Preferably, the first metal line 502 or the second metal line can be various types such as suspension line, microstrip line or coplanar waveguide, preferably in the form of suspension line. In the present invention, the metal line actually only has the function of electrical connection, so its specific shape is not limited, such as the first metal line 502 or the second metal line can be straight line, broken line or curved line.

[0035] It is worth noting that the dielectric waveguide filter 100 of the present invention is not limited to setting coupling blind holes only on a pair of non-adjacent first resonance units 102 and second resonance units 104. In fact, the dielectric waveguide filter 100 of the present invention can also set coupling blind holes on other two non-adjacent resonance units according to actual needs. For example, coupling blind holes can be set on two non-adjacent resonance units such as resonance unit 101 and resonance unit 103, resonance unit 101 and resonance unit 104, resonance unit 102 and resonance unit 105, respectively, and the coupling blind holes of the two non-adjacent resonance units are electrically connected, so that a cross-cavity coupling structure can be introduced between multiple pairs of non-adjacent resonance units, that is, the dielectric waveguide filter 100 can achieve cross-cavity cross-coupling by setting multiple cross-cavity coupling structures.

[0036] Preferably, at least one tuning blind hole for tuning the resonance frequency of the resonance unit is provided on the top of each resonance unit 101-105. In this embodiment, the tuning blind hole is preferably provided at the center of the top of the resonance unit 101-105, which has a better tuning effect.

[0037] The dielectric material of the dielectric waveguide filter 100 of the present invention is preferably a ceramic material, and other dielectric materials may also be used. Preferably, a first metal coating is attached to the outer surface of the dielectric waveguide filter 100. The inner walls of the first coupling blind hole 301 and the second coupling blind hole 302 are respectively provided with a second metal coating. Preferably, the material of the first metal coating and the second metal coating is preferably silver, and other metal materials such as copper and aluminum may also be used. The outer edges of the first coupling blind hole 301 and the second coupling blind hole 302 are respectively provided with a circle of a first non-electroplating area 310 and a second non-electroplating area 311. The first non-electroplating area 310 is used to separate the second metal coating of the first coupling blind hole 301 from the first metal coating of the dielectric waveguide filter 100, and the second non-electroplating area 311 is used to separate the second metal coating of the second coupling blind hole 302 from the first metal coating of the dielectric waveguide filter 100.

[0038] Figure 1 In the illustrated embodiment, the first non-electroplating area 310 and the second non-electroplating area 311 are preferably in the shape of a circular ring. However, in fact, the first non-electroplating area 310 and the second non-electroplating area 311 may also be in the shape of a polygon or various irregular shapes. The first non-electroplating area 310 and the second non-electroplating area 311 only need to adopt a closed structure of any shape to achieve the effect of separating the first metal plating layer on the surface of the dielectric waveguide filter 100 and the second metal plating layer on the inner wall of the coupling blind holes 301-302.

[0039] It is worth pointing out that although the structure of the dielectric waveguide filter 100 of the present invention is mainly based on Figure 1 However, it is only a partial example of the implementation method of the present invention and is not intended to limit the present invention.

[0040] Preferably, the coupling strength between the non-adjacent first resonant unit 102 and the second resonant unit 104 is controlled by the depth of the first coupling blind hole 301 and the second coupling blind hole 302. That is, the coupling strength between the non-adjacent first resonant unit 102 and the second resonant unit 104 is related to the depth of the first coupling blind hole 301 and the second coupling blind hole 302. The deeper the depth of the first coupling blind hole 301 and the second coupling blind hole 302, the greater the coupling strength.

[0041] More preferably, the magnitude of the coupling strength of the non-adjacent first resonant unit 102 and the second resonant unit 104 is controlled by the positional relationship between the bottom of the first coupling blind hole 301 and the second coupling blind hole 302 and the first resonant unit 102 and the second resonant unit 104, respectively. That is, the coupling strength of the non-adjacent first resonant unit 102 and the second resonant unit 104 is related to the bottom position of the first coupling blind hole 301 and the second coupling blind hole 302. When the bottom of the first coupling blind hole 301 and the second coupling blind hole 302 are in the middle position of the first resonant unit 102 and the second resonant unit 104, the coupling strength is the largest. The closer the bottom of the first coupling blind hole 301 or the second coupling blind hole 302 is to the upper and lower ends of the first resonant unit 102 and the second resonant unit 104, the weaker the coupling strength. When the bottom of the first coupling blind hole 301 or the second coupling blind hole 302 is at the upper and lower ends of the first resonant unit 102 and the second resonant unit 104, the coupling strength is the smallest.

[0042] In summary, the dielectric waveguide filter with a cross-cavity coupling structure of the present invention includes at least three resonance units connected in sequence, and the dielectric waveguide filter is provided with a first coupling blind hole and a second coupling blind hole on at least one pair of non-adjacent first resonance units and second resonance units, respectively, and the first coupling blind hole and the second coupling blind hole are electrically connected to each other, so that the non-adjacent first resonance units and the second resonance units generate cross-cavity cross-coupling, and a transmission zero point can be generated near the passband. Preferably, a tuning blind hole for adjusting the resonance frequency is provided on the top of each resonance unit. Thereby, the present invention realizes cross-coupling by introducing a cross-cavity coupling structure between two non-adjacent resonance units, increases the transmission zero point of the dielectric waveguide filter, and can further improve the frequency selection characteristics of the dielectric waveguide filter without increasing the volume of the filter, and has the characteristics of simple structure, easy manufacturing and maintenance. The present invention plays an important role in promoting the development of dielectric waveguide filters in modern miniaturized integrated communication systems.

[0043] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A dielectric waveguide filter with a cross-cavity coupling structure, characterized in that: The dielectric waveguide filter comprises at least three resonance units connected in sequence, and a coupling window is provided between each two adjacent resonance units; at least one first coupling blind hole and a second coupling blind hole are respectively provided on at least one pair of non-adjacent first resonance units and second resonance units, and the first coupling blind hole and the second coupling blind hole are electrically connected to each other, so that the non-adjacent first resonance units and the second resonance units generate cross coupling; The first coupling blind hole, the second coupling blind hole and at least one circuit board are provided on the side surfaces of the non-adjacent first resonance unit and the second resonance unit; the first coupling blind hole and the second coupling blind hole are respectively provided with a first metal inner core and a second metal inner core; at least one first metal wire is provided on the circuit board, and the first metal wire is respectively connected to the first metal inner core of the first coupling blind hole and the second metal inner core of the second coupling blind hole to realize electrical connection between the first coupling blind hole and the second coupling blind hole; or The first coupling blind hole, the second coupling blind hole and at least one second metal wire are provided on the side surfaces of the non-adjacent first resonance unit and the second resonance unit; the first coupling blind hole and the second coupling blind hole are respectively provided with a first metal inner core and a second metal inner core; the second metal wire is respectively connected to the first metal inner core of the first coupling blind hole and the second metal inner core of the second coupling blind hole, so as to realize electrical connection between the first coupling blind hole and the second coupling blind hole; The outer surface of the dielectric waveguide filter is provided with a first metal plating layer; the inner walls of the first coupling blind hole and the second coupling blind hole are respectively provided with a second metal plating layer, and the outer edges of the first coupling blind hole and the second coupling blind hole are respectively provided with a circle of a first non-electroplating area and a second non-electroplating area; the first non-electroplating area separates the second metal plating layer of the first coupling blind hole from the first metal plating layer of the dielectric waveguide filter, and the second non-electroplating area separates the second metal plating layer of the second coupling blind hole from the first metal plating layer of the dielectric waveguide filter.

2. The dielectric waveguide filter according to claim 1, characterized in that: The circuit board is a three-layer structure, which includes a bottom metal layer, an intermediate dielectric layer and a top metal layer in sequence; at least one first metal line is etched on the top metal layer, and the first metal line is electrically connected to the first metal core of the first coupling blind hole and the second metal core of the second coupling blind hole through the metallized through hole on the circuit board; and / or The circuit board is a hard circuit board or a flexible circuit board.

3. The dielectric waveguide filter according to claim 1, wherein: The first metal line or the second metal line is a suspension line, a microstrip line or a coplanar waveguide; and / or The first metal wire or the second metal wire is in a straight line shape, a zigzag line shape or a curved line shape.

4. The dielectric waveguide filter according to claim 1, wherein: The first coupling blind hole and the second coupling blind hole are cylindrical, elliptical or prism-shaped.

5. The dielectric waveguide filter according to claim 1, wherein: The top of each resonant unit is provided with at least one tuning blind hole for tuning the resonant frequency of the resonant unit; and / or The at least three resonance units are arranged in a straight line, a curved line or a folded line.

6. The dielectric waveguide filter according to claim 5, characterized in that The tuning blind hole is arranged at the center of the top of the resonance unit.

7. The dielectric waveguide filter according to claim 1, wherein: The first non-electroplating area and the second non-electroplating area are in a circular ring shape or a polygonal shape.

8. The dielectric waveguide filter according to any one of claims 1 to 7, characterized in that: The magnitude of the coupling strength between the non-adjacent first resonant unit and the second resonant unit is controlled by the depth of the first coupling blind hole and the second coupling blind hole. The deeper the depth of the first coupling blind hole and the second coupling blind hole, the greater the coupling strength. and / or The magnitude of the coupling strength of the non-adjacent first resonance unit and the second resonance unit is controlled by the positional relationship between the bottom of the first coupling blind hole and the second coupling blind hole and the first resonance unit and the second resonance unit, respectively. When the bottom of the first coupling blind hole and the second coupling blind hole are in the middle position of the first resonance unit and the second resonance unit, the coupling strength is the largest; when the bottom of the first coupling blind hole or the second coupling blind hole is closer to the upper and lower ends of the first resonance unit and the second resonance unit, the coupling strength is weaker.

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