CN110739510A - dielectric waveguide filter with cross-cavity coupling structure - Google Patents

Abstract

The present invention provides a dielectric waveguide filter with a cross-cavity coupling structure. The dielectric waveguide filter includes at least three resonance units connected in sequence, and a coupling is provided between every two adjacent resonance units. a window; at least one first blind coupling hole and a second blind coupling hole are respectively provided on at least one pair of non-adjacent first resonating unit and second resonating unit, and the first blind coupling hole and the second blind coupling hole are The blind coupling holes are electrically connected to each other, so that the non-adjacent first resonance unit and the second resonance unit generate cross-coupling. Thereby, the present invention realizes cross-cavity coupling by introducing a cross-cavity coupling structure between two non-adjacent resonant units, and increases the transmission zero point of the dielectric waveguide filter, so that the volume of the filter can not be increased without increasing the volume of the filter. The frequency selection characteristic of the dielectric waveguide filter is further improved, and the structure is simple to realize and easy to manufacture and maintain.

Description

A dielectric waveguide filter with a cross-cavity coupling structure

technical field

The invention relates to a dielectric waveguide filter in the field of communication technology, in particular to a dielectric waveguide filter with a cross-cavity coupling structure.

Background technique

With the continuous development of modern communication technology, the requirements for filter performance indicators are also getting higher and higher. Due to its small size, high Q value and low cost, dielectric waveguide filters have been well used in miniaturized and highly integrated communication systems. However, with the continuous development of multi-frequency systems, the requirements for the volume and frequency selection characteristics of the filter are also higher and higher. However, in order to achieve the required frequency selection characteristic of the existing dielectric waveguide filter, the volume of the dielectric waveguide filter is usually greatly increased. Therefore, how to further improve the frequency selection characteristics of the dielectric waveguide filter without increasing the volume of the dielectric waveguide filter is an urgent problem to be solved at present.

To sum up, the prior art obviously has inconvenience and defects in practical use, so it is necessary to improve it.

SUMMARY OF THE INVENTION

In view of the above-mentioned defects, the purpose 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.

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

According to the dielectric waveguide filter of the present invention, the first blind coupling hole, the second blind coupling hole and at least one blind coupling hole are disposed on the sides of the non-adjacent first resonating unit and the second resonating unit. a circuit board; a first metal inner core and a second metal inner core are respectively arranged inside the first blind coupling hole and the second blind coupling hole; at least one first metal wire is arranged on the circuit board, so The first metal wire is respectively connected to the first metal inner core of the first blind coupling hole and the second metal inner core of the second blind coupling hole, so as to realize the first blind coupling hole and the second metal inner core of the second blind coupling hole. the electrical connection between the second blind coupling vias; or

The first blind coupling hole, the second blind coupling hole and at least one second metal wire are provided on the sides of the non-adjacent first resonating unit and the second resonating unit; the first blind coupling hole The inside of the hole and the second blind coupling 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 and the second metal inner core of the first coupling blind hole. The second metal inner core of the second blind coupling hole is used to realize the electrical connection between the first blind coupling hole and the second blind coupling hole.

According to the dielectric waveguide filter of the present invention, the circuit board has a three-layer structure, including a bottom metal layer, an intermediate dielectric layer and a top metal layer in sequence; at least one of the first metal lines is etched on the top metal layer. , the first metal line is respectively connected with the first metal core of the first coupling blind hole and the second metal inner core of the second coupling blind hole through the metallized through hole on the circuit board. core for electrical connection; and/or

The circuit board is a rigid circuit board or a flexible circuit board.

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

The first metal wire or the second metal wire is straight, folded or curved.

According to the dielectric waveguide filter of the present invention, the first blind coupling hole and the second blind coupling hole are cylindrical, elliptical or prismatic.

According to the dielectric waveguide filter of the present invention, 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 curve arrangement or a broken line arrangement.

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

According to the dielectric waveguide filter of the present invention, the outer surface of the dielectric waveguide filter is provided with a first metal coating; the inner walls of the first blind coupling hole and the second blind coupling hole are respectively provided with a second metal layer and the outer edges of the first coupling blind hole and the second coupling blind hole are respectively provided with a circle of first non-plating area and second non-plating area; the first non-plating area connects the first coupling The second metal coating of the blind hole is separated from the first metal coating of the dielectric waveguide filter, and the second non-plated area separates the second metal coating of the second coupling blind hole from the dielectric waveguide filter of the first metal plating separated.

According to the dielectric waveguide filter of the present invention, the first electroless area and the second electroless area are circular or polygonal.

According to the dielectric waveguide filter of the present invention, the coupling strength of the non-adjacent first resonance unit and the second resonance unit is determined by the difference between the first blind coupling hole and the second blind coupling hole. depth control, the deeper the depth of the first blind coupling hole and the second blind coupling hole, the greater the coupling strength; and/or

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

The dielectric waveguide filter with the 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 at least a pair of non-adjacent first resonance units and second resonance units. The first coupling blind hole and the second coupling blind hole, and the first coupling blind hole and the second coupling blind hole are electrically connected to each other, so that the non-adjacent first resonant unit and the second resonator unit cross the cavity coupling and can produce a transmission zero near the passband. Preferably, the top of each resonance unit is provided with a tuning blind hole for adjusting the resonance frequency. Thereby, the present invention realizes cross-coupling by introducing a cross-cavity coupling structure between two non-adjacent resonant units, and increases the transmission zero point of the dielectric waveguide filter, so that the volume of the filter can be further improved without increasing the volume of the filter. The frequency selection characteristic of the dielectric waveguide filter is improved, and the realization structure is simple, and the manufacture and maintenance are convenient. The invention plays an important role in promoting the development of the dielectric waveguide filter in the modern miniaturized integrated communication system.

Description of drawings

FIG. 1 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 ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

It should be noted that references in this specification to "one embodiment", "an embodiment", "example embodiment", etc., mean that the described embodiment may include specific features, structures or characteristics, but not every Embodiments must contain these specific features, structures or characteristics. Furthermore, such expressions are not referring to the same embodiment. Further, when a particular feature, structure or characteristic is described in conjunction with an embodiment, whether or not explicitly described, it has been shown that it is within the knowledge of those skilled in the art to incorporate such feature, structure or characteristic into other embodiments .

In addition, certain terms are used in the description and the following claims to refer to specific components or components, and it should be understood by those of ordinary skill in the art that manufacturers may use different terms or terms to refer to the same component or component. This specification and the following claims do not use the difference in name as a way of distinguishing components or parts, but use the difference in function of the components or parts as a criterion for distinguishing. References to "including" and "comprising" throughout the specification and subsequent claims are open-ended terms and should be interpreted as "including but not limited to". Otherwise, the term "connected" herein includes any direct and indirect means of electrical connection. Indirect electrical connection means include connection through other means.

The dielectric waveguide filter with the cross-cavity coupling structure of the present invention includes at least three resonance units connected in sequence, the resonance units are connected in an arbitrary topology, and a coupling window is provided between every two adjacent resonance units. At least one first blind coupling hole and one second blind coupling hole are respectively provided on at least one pair of non-adjacent first resonance unit and second resonance unit, and the first blind coupling hole and the second blind coupling hole are mutually The electrical connection makes the non-adjacent first resonant unit and the second resonant unit form cross-coupling, thereby generating a transmission zero point near the passband, which can further improve the dielectric waveguide filter without increasing the volume of the dielectric waveguide filter. frequency selection characteristics of the converter.

FIG. 1 shows the preferred structure of the dielectric waveguide filter with the cross-cavity coupling structure of the present invention. The dielectric waveguide filter 100 includes five resonance units 101 to 105 connected in sequence. In this embodiment, the resonance units 101 to 105 are sequentially arranged in a straight line. However, the resonant units of the dielectric waveguide filter 100 of the present invention can actually be connected in any topology as required. For example, the resonant units 101 to 105 can also be arranged in a curved line or a broken line. A coupling window 201-204 is respectively provided between two adjacent resonance units, and the coupling windows 201-204 may be hollow cavity structures. Specifically, coupling windows 201 are provided between adjacent resonance units 101-102, coupling windows 202 are provided between adjacent resonance units 102-103, and coupling windows are provided between adjacent resonance units 103-104 203, a coupling window 204 is provided between adjacent resonant units 104-105.

In the specific embodiment shown in FIG. 1 , 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 alternately arranged in a straight line . 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 the resonance units can be arbitrarily increased or decreased according to actual needs. For example, the dielectric waveguide filter 100 may include three, four, six, seven, eight, nine, ten or more resonant units.

In order to further improve the frequency selection characteristic of the dielectric waveguide filter, the present invention proposes to introduce a cross-cavity coupling structure between at least a pair of non-adjacent two resonant units of the dielectric waveguide filter 100 to realize cross-cavity cross-coupling. As shown in FIG. 1 , preferably at least one blind coupling hole 301 and blind coupling hole 302 are respectively provided on the non-adjacent first resonance unit 102 and the second resonance unit 104 , and the first blind coupling hole 301 and the second blind coupling via 302 are electrically connected to each other. Therefore, the non-adjacent first resonance unit 102 and the second resonance unit 104 form cross-coupling, thereby generating a transmission zero near the passband, and without increasing the volume of the dielectric waveguide filter 100, the dielectric waveguide filter can be improved. 100 frequency selection characteristics. The first blind coupling hole 301 and the second blind coupling 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 .

In the embodiment shown in FIG. 1 , a first blind coupling hole 301 , a second blind coupling hole 302 and at least one circuit board 501 are provided on the sides of the non-adjacent first resonance unit 102 and the second resonance unit 104 . A first metal inner core 401 and a second metal inner core 402 are respectively provided inside the first blind coupling hole 301 and the second blind coupling hole 302 . The circuit board 501 is provided with at least one first metal wire 502 , two ends of the first metal wire 502 are respectively connected to the first metal core 401 of the first blind coupling hole 301 and the second metal core 402 of the second blind coupling hole 302 402. 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 blind coupling holes 301-302, so that the non-adjacent resonant units are electrically connected. 102 and 104 create cross-coupling.

Of course, the first blind coupling hole 301 , the second blind coupling hole 302 , and the circuit board 501 of the present invention are not limited to being arranged on the side surfaces of the non-adjacent resonating units 102 and 104 , and may also be arranged on the non-adjacent resonating units according to actual needs. 102 and 104 top, bottom, etc.

In FIG. 1 , the first blind coupling hole 301 and the second blind coupling hole 302 are preferably cylindrical. However, the first blind coupling hole 301 and the second blind coupling hole 302 may also be any regular geometric cylindrical shape or irregular geometric cylindrical shape such as an elliptical cylinder or a prism. However, for the convenience of production, the first blind coupling hole 301 and the second blind coupling hole 302 are preferably cylindrical.

Preferably, the circuit board 501 has a three-layer structure, which sequentially includes a bottom metal layer, an intermediate dielectric layer and a top metal layer (not shown in the figure). At least one first metal line 502 may be etched on the top metal layer, and the first metal line 502 is respectively connected with the first metal core 401 and the first metal core 401 of the first coupling blind hole 301 through the metallized through hole on the circuit board 501 . The second metal cores 402 of the two coupling blind vias 302 are electrically connected. The circuit board 501 may be a rigid circuit board or a flexible circuit board. The flexible circuit board can be applied to the case where the non-adjacent resonant units 102 and 104 are arranged in a non-linear arrangement such as a curved arrangement or a broken line arrangement.

It should be noted that the electrical connection between the first blind coupling hole 301 and the second blind coupling hole 302 of the present invention is not limited to the combination of the circuit board 501 and the first metal wire 502 as shown in FIG. 1 . In another embodiment of the present invention, a first blind coupling hole 301, a second blind coupling hole 302 and at least one second metal line are provided on the sides of the non-adjacent first resonant unit 102 and the second resonator unit 104 (Fig. not shown). A first metal inner core 401 and a second metal inner core 402 are respectively provided inside the first blind coupling hole 301 and the second blind coupling hole 302 . The second metal lines are respectively connected to the first metal core 401 of the first blind coupling via 301 and the second metal core 402 of the second blind coupling via 302 to realize the blind coupling via 301 and the blind blind coupling second Electrical connections between 302. That is, the first blind coupling hole 301 and the second blind coupling hole 302 can be directly electrically connected through the second metal wire without adding a circuit board 501 . The non-adjacent resonant units 102 and 104 form cross-coupling through the second metal line and the coupling blind holes 301 and 302 , so that the transmission zero point can be increased, and the frequency selection characteristic of the dielectric waveguide filter 100 can be further improved.

Preferably, the first metal wire 502 or the second metal wire may be of various types such as suspension wire, microstrip line or coplanar waveguide, and preferably in the form of suspension wire. In the present invention, the metal wire actually only has the function of electrical connection, so its specific shape is not limited.

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

Preferably, at least one tuning blind hole for tuning the resonance frequency of the resonance unit is provided at the top of each resonance unit 101-105. In this embodiment, the tuning blind hole is preferably arranged at the center of the top of the resonance units 101-105, and the tuning effect is better.

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

In the embodiment shown in FIG. 1 , the first electroless plating area 310 and the second electroless plating area 311 are preferably circular rings. But in fact, the first non-plating area 310 and the second non-plating area 311 may also adopt polygonal shapes or various irregular shapes. The first non-plating area 310 and the second non-plating area 311 only need to adopt a closed structure of any shape, which can serve as the first metal coating layer on the surface of the dielectric waveguide filter 100 and the second metal coupling the inner walls of the blind holes 301-302. The effect of plating separation.

It is worth noting that although the structure of the dielectric waveguide filter 100 of the present invention is mainly described according to FIG. 1 , it is only a partial example of the implementation method of the present invention, and is not intended to limit the present invention.

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

More preferably, the magnitude of the coupling strength of the non-adjacent first resonance unit 102 and the second resonance unit 104 is determined by the size of the coupling strength between the bottoms of the first blind coupling hole 301 and the second blind coupling hole 302 and the first resonance unit 102 and the second blind coupling hole 302 respectively. The positional relationship of the two resonance units 104 is controlled. That is, the coupling strength of the non-adjacent first resonance unit 102 and the second resonance unit 104 is related to the bottom positions of the first blind coupling hole 301 and the second blind coupling hole 302 , and the first blind coupling hole 301 and the second blind coupling hole 301 When the bottom of 302 is at the middle position of the first resonance unit 102 and the second resonance unit 104, the coupling strength is the maximum. When the bottom of the first blind coupling hole 301 or the second blind coupling hole 302 is closer to the upper and lower ends of the first resonance unit 102 and the second resonance unit 104, the coupling strength is weaker. When the bottom of the first blind coupling hole 301 or the second blind coupling hole 302 is at the upper and lower ends of the first resonance unit 102 and the second resonance unit 104, the coupling strength is the smallest.

To sum up, the dielectric waveguide filter with the cross-cavity coupling structure of the present invention includes at least three resonance units connected in sequence, and the dielectric waveguide filter has at least a pair of non-adjacent first resonance units and second resonance units. The unit is provided with a first blind coupling hole and a second blind coupling hole respectively, and the first blind coupling hole and the second blind coupling hole are electrically connected to each other, so that the non-adjacent first resonance unit and the second resonance unit Cross-coupling across the cavity is created and a transmission zero can be created near the passband. Preferably, the top of each resonance unit is provided with a tuning blind hole for adjusting the resonance frequency. Thereby, the present invention realizes cross-coupling by introducing a cross-cavity coupling structure between two non-adjacent resonant units, and increases the transmission zero point of the dielectric waveguide filter, so that the volume of the filter can be further improved without increasing the volume of the filter. The frequency selection characteristic of the dielectric waveguide filter is improved, and the realization structure is simple, and the manufacture and maintenance are convenient. The invention plays an important role in promoting the development of the dielectric waveguide filter in the modern miniaturized integrated communication system.

Of course, the present invention can also have other various embodiments, without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding Changes and deformations should belong to the protection scope of the appended claims of the present invention.

Claims (10)

1. The dielectric waveguide filter with the cavity-crossing coupling structure is characterized by comprising at least three resonance units which are connected in sequence, coupling windows are arranged between every two adjacent resonance units, at least coupling blind holes and at least second coupling blind holes are arranged on the th resonance unit and the second resonance unit which are not adjacent to each other of at least pairs of resonance units, and the th coupling blind hole and the second coupling blind hole are electrically connected with each other, so that the th resonance unit and the second resonance unit which are not adjacent to each other generate cross coupling.
2. 2. The dielectric waveguide filter of claim 1, wherein the side surfaces of the th resonant unit and the second resonant unit which are not adjacent to each other are provided with the th coupling blind hole, the second coupling blind hole and at least 0 circuit boards, the th coupling blind hole and the second coupling blind hole are respectively provided with a th metal inner core and a second metal inner core, the circuit boards are provided with at least th metal wires, and the th metal wires are respectively connected with the th metal inner core of the th coupling blind hole and the second metal inner core of the second coupling blind hole to realize the electrical connection between the th coupling blind hole and the second coupling blind hole, or

   The lateral surfaces of the th resonance unit and the second resonance unit which are not adjacent to each other are provided with the coupling blind hole, the second coupling blind hole and at least second metal wires, th metal inner cores and second metal inner cores are respectively arranged in the coupling blind hole and the second coupling blind hole, and the second metal wires are respectively connected with the th metal inner core of the coupling blind hole and the second metal inner core of the second coupling blind hole, so that the coupling blind hole and the second coupling blind hole are electrically connected.
3. 3. The dielectric waveguide filter of claim 2, wherein the circuit board has a three-layer structure comprising a bottom metal layer, a middle dielectric layer and a top metal layer, at least of the metal lines are etched on the top metal layer, the metal lines are electrically connected with the metal core of the coupling blind via and the second metal core of the second coupling blind via through-metallization vias on the circuit board, and/or

   The circuit board is a hard circuit board or a flexible circuit board.
4. 4. The dielectric waveguide filter of claim 2, wherein the th metal line or the second metal line is a suspended line, a microstrip line or a coplanar waveguide, and/or

   The th metal wire or the second metal wire is in a straight line shape, a fold line shape or a curve shape.
5. 5. The dielectric waveguide filter of claim 1, wherein the th and second coupling blind holes are cylindrical, elliptic cylindrical, or prismatic.
6. 6. A dielectric waveguide filter according to claim 1, wherein the top of each of the resonator elements is provided with at least tuning blind holes for tuning the resonant frequency of the resonator element, and/or

   The at least three resonance units are arranged in a straight line, a curve line or a broken line.
7. 7. A dielectric waveguide filter according to claim 6, wherein the tuning blind hole is provided at the center of the top of the resonator unit.
8. 8. The dielectric waveguide filter of claim 1 wherein th metallization is attached to the outer surface of the dielectric waveguide filter, wherein the st and second coupling blind vias have second metallization on their inner walls, and wherein circles of th and second electroless regions are provided on the outer edges of the st and second coupling blind vias, respectively, wherein the th electroless region separates the second metallization of the st coupling blind via from the th metallization of the dielectric waveguide filter, and the second electroless region separates the second metallization of the second coupling blind via from the th metallization of the dielectric waveguide filter.
9. 9. The dielectric waveguide filter of claim 8 wherein the th electroless plated region and the second electroless plated region are circular or polygonal.
10. 10. The dielectric waveguide filter of any of claims 1-9, wherein the coupling strength of the non-adjacent th and second resonant cells is controlled by the depths of the th and second coupling blind holes, the coupling strength is larger the deeper the th and second coupling blind holes are, and/or

    The size of the coupling strength of the th resonance unit and the second resonance unit which are not adjacent to each other is controlled by the position relationship between the bottoms of the th coupling blind hole and the second coupling blind hole and the th resonance unit and the second resonance unit respectively, the coupling strength is maximum when the bottoms of the th coupling blind hole and the second coupling blind hole are at the middle position of the th resonance unit and the second resonance unit, and the coupling strength is weaker when the bottoms of the th coupling blind hole or the second coupling blind hole are closer to the upper end position and the lower end position of the th resonance unit and the second resonance unit.