Four-order filter based on half-mode resonator

Abstract

The invention belongs to the technical field of microwave circuits, and particularly provides a four-order filter based on a half-mode resonator, so as to realize the performance characteristics of small size, high selectivity and high out-of-band rejection. The invention comprises a port coupling structure, namely an input coaxial port and an output coaxial port; the filter cavity structure is a cavity body; the windowing coupling structure comprises a long-side windowing coupling through hole and a short-side windowing coupling through hole; and the tuning structures comprise a first tuning structure, a second tuning structure, a third tuning structure and a fourth tuning structure. According to the invention, the virtual magnetic wall is established by using the high dielectric constant of the cavity, so that the dielectric waveguide resonators working in a half mode are realized, and the four resonators are used to form the four-order band-pass filter. Due to the novel design thought, compared with a traditional four-order band-pass filter, the size of the four-order band-pass filter is reduced by about 50%. The invention can be used in communication systems and millimeter wave related applications.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave circuits, and specifically provides a fourth-order filter based on a half-mode resonator. Background Art

[0002] In modern communication systems and RF front-end equipment, with the development of 5G communication technology and the popularization of multi-band communication, the requirements for selective signal transmission and noise suppression are becoming increasingly higher, so the performance requirements for filters are also constantly increasing. Not only high selectivity and out-of-band suppression are required, but also compact size and easy integration are required to adapt to increasingly complex multi-band communication systems and compact equipment design. Although traditional bandpass filters can meet basic signal processing needs, when faced with higher frequency and larger bandwidth applications, they are usually limited by factors such as power and loss, resulting in a large size, which makes it difficult to meet the needs of modern communication systems for miniaturization and high integration.

[0003] Therefore, how to reduce the size of the filter without sacrificing performance, especially selectivity and out-of-band suppression, has become a research focus. Summary of the invention

[0004] The object of the present invention is to provide a fourth-order filter based on a half-mode resonator, which can maintain high selectivity and high out-of-band suppression while achieving a small volume.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] The present invention is mainly composed of a port coupling structure, a filter cavity structure, a window coupling structure and a tuning structure. The port coupling structure is composed of two major parts, which are mainly divided into an input coaxial port and an output coaxial port, and is connected to the outside through a coaxial line to realize the input and selective output of signals. The filter cavity structure is in the shape of a cube as a whole. In order to prevent the edge current from affecting the field distribution of the entire cavity, the edge edges are rounded and chamfered. The entire cavity is silver-plated except for two cut surfaces, so that the silver-plated part is equivalent to an electric wall, and the unsilver-plated part can be equivalent to a virtual magnetic wall, thereby effectively reducing the overall filter volume. The window coupling structure is mainly composed of a long-side window coupling through hole and a short-side window coupling through hole. At the same time, the surface of the through hole is also silver-plated, which is also equivalent to an equivalent electric wall, thereby effectively cutting the electric field distribution inside the cavity. The tuning structure is mainly composed of four blind holes on the back, which are equivalent to four resonators. The four resonators use the window coupling structure and the silver plating of the cavity itself to cut the direction of the electric field inside the cavity, thereby realizing cross-coupling between the four resonators. This can improve the out-of-band suppression capability of the filter and solve the problem of decreased out-of-band suppression capability of traditional filters after being reduced in size.

[0007] How to eliminate the performance degradation caused by the reduction of the filter volume is a major difficulty of the present invention. The tuning structure composed of four blind holes can be divided into a first tuning structure, a second tuning structure, a third tuning structure and a fourth tuning structure according to the distribution position. The first tuning structure is located on the back of the input port, the second tuning structure and the first tuning structure are symmetrically distributed on the same side of the long side, the fourth tuning structure is located on the back of the output port, and the third tuning structure and the fourth tuning structure are also symmetrically distributed on the same side of the long side. The window coupling structure is effectively used to block the direction of the electric field in the filter cavity, thereby realizing the coupling between the first tuning structure and the second tuning structure and the third tuning structure and the fourth tuning structure through lateral magnetic coupling. At the same time, the second tuning structure and the third tuning structure are connected by back magnetic coupling. This cross-coupling design can significantly improve the passband flatness of the filter, and improve the out-of-band suppression performance and selectivity of the filter.

[0008] The innovation of the present invention lies in:

[0009] 1. By selecting materials with high dielectric constants and combining them with surface silver plating, a virtual magnetic wall is introduced to achieve a half-mode propagation mode. While ensuring the stability of the electromagnetic field distribution in the filter cavity, the cavity volume is reduced by half, achieving the small size of the filter and making it easy to integrate in the current communication system.

[0010] Second, by introducing a windowed coupling structure and combining it with a back-facing blind hole, cross-coupling between tuning structures is achieved, thereby significantly improving the passband flatness of the filter, and achieving the characteristics of high out-of-band suppression performance and high selectivity of the filter, realizing the application characteristics of the current communication system that has extremely high requirements for signal quality. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The overall view of the fourth-order filter based on the half-mode resonator of the present invention; Figure 2 It is a schematic diagram of the port coupling structure and the filter cavity structure of the present invention; Figure 3 It is a schematic diagram of the window coupling structure of the present invention; Figure 4 It is a schematic diagram of the tuning structure of the present invention; Figure 5 It is a front view of the overall structure of the fourth-order filter based on the half-mode resonator of the present invention; Figure 6 A top view of the overall structure of a fourth-order filter based on a half-mode resonator of the present invention; Figure 7 A side view of the overall structure of a fourth-order filter based on a half-mode resonator of the present invention; Figure 8The return loss (S11) within the working passband range of the fourth-order filter based on the half-mode resonator of the present invention; Fig. 9 is the insertion loss (S12) within the working passband range of the fourth-order filter based on the half-mode resonator of the present invention; Fig.10 It is an overall comparison of the return loss (S11) and the insertion loss (S12) within the working passband range of the fourth-order filter based on the half-mode resonator of the present invention; Specific implementation plan

[0011] In order to make the objectives, technical solutions and innovative points of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0012] Figure 1 This is the overall structure of the present invention. The structure of the present invention is mainly divided into four parts, wherein 1 is a port coupling structure, 2 is a filter cavity structure, 3 is a window coupling structure, and 4 is a tuning structure.

[0013] Figure 2 It is a schematic diagram of the external connection mechanism and the filter cavity structure of the present invention, wherein 101 is the input coaxial port, 102 is the output coaxial port, 201 and 202 are sections of the cavity surface that are not silver-plated, which is equivalent to adding two ideal magnetic walls to the cavity section, and other silver-plated planes can be regarded as equivalent electric walls, thereby introducing a half-mode working state.

[0014] Figure 3 It is a schematic diagram of the window coupling structure of the present invention, 301 is a long-side window coupling through hole, 302 is a short-side window coupling through hole, and the two through holes realize the isolation of the electric field inside the cavity.

[0015] Figure 4 It is a schematic diagram of the tuning structure of the present invention, 401 is the first tuning structure, which is on the back of the input coaxial port 101. 402 is the second tuning structure, which is symmetrically distributed on the long side of the cavity with respect to the first tuning structure. 403 is the third tuning structure, which is symmetrically distributed on the short side of the cavity with respect to the second tuning structure. 404 is the fourth tuning structure, which is on the back of the output coaxial port, the fourth tuning structure is symmetrically distributed on the long side of the cavity with respect to the third tuning structure, and the fourth tuning structure is symmetrically distributed on the short side of the cavity with respect to the first tuning structure. In addition to the different positions, the sizes of the four tuning structures are adjusted according to the specific operating frequency range of the filter. The first resonant structure and the second resonant structure, as well as the third resonant structure and the fourth resonant structure, achieve lateral magnetic coupling by means of a window coupling structure, and the second resonant structure and the third resonant structure achieve back magnetic coupling by means of a window coupling structure.

[0016] In order to show the layout and size of each structure of the present invention in detail, Figure 5This is the front view of the overall structure. Figure 6 It is a top view of the overall structure and Figure 7 It is a side view of the overall structure. The overall cavity dimensions are l1 = 36.7mm in length, w1 = 18.2mm in width, and h1 = 6mm in height. The input coaxial port and output coaxial port dimensions of the cavity port coupling structure are the same, with the coaxial inner core dimension R2 = 0.65mm, the coaxial outer core dimension R3 = 1.495mm, and the dimension of the inner core inserted into the cavity h3 = 3.23mm. The windowed coupling structure has a long side windowed coupling through hole with a short distance from the cavity edge of l2 = 1.7mm and a long distance from the cavity edge of l3 = 7.8mm. The long side windowed coupling through hole has a length of l4 = 27.2mm and a width of w3 = 2mm. The short side windowed coupling through hole has a distance from the cavity edge of w4 = 2.3mm and w5 = 2.3mm on both sides, and a short side windowed coupling through hole with a length of l5 = 13.6mm and a width of w2 = 1.5mm. The tuning structure is made by blind hole drilling on the back of the cavity. The blind hole can be regarded as a cylinder. The drilling radius is R1 = 1.5mm and the drilling depth is h2 = 1.8mm. The four blind holes are used as four tuning structures to adjust the specific operating frequency of the filter. At the same time, in order to prevent the edge current from affecting the field distribution of the entire cavity, the edge edges are chamfered smoothly, and the chamfer of the entire cavity is 0.2mm.

[0017] Figure 8 The small-size fourth-order bandpass filter based on half-mode dielectric waveguide resonator has an operating passband range of 2.505GHz-2.665GHz, an in-band return loss of less than -22dB, and a filter length of only 0.32λ, a width of only 0.16λ, and a height of only 0.05λ at the operating frequency, which is smaller in size than traditional design methods.

[0018] Fig. 9 The insertion loss of a small-size fourth-order bandpass filter based on a half-mode dielectric waveguide resonator within the working passband range is demonstrated, and the insertion loss is only 1.6dB within the working range of 2.505GHz-2.665GHz.

[0019] Fig.10 The overall performance diagram of the in-band return loss and insertion loss of a small-sized fourth-order bandpass filter based on a half-mode dielectric waveguide resonator in the operating range of 2.505GHz-2.665GHz is shown. It can be intuitively seen that the fourth-order bandpass filter has the characteristics of compact size and high out-of-band suppression.

[0020] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A fourth-order filter based on a half-mode resonator, comprising a port coupling structure, a filter cavity structure, a window coupling structure and a tuning structure, characterized in that: The port coupling structure comprises an input coaxial port (101) for signal input and an output coaxial port (102) for signal output, which are located at the top of the overall structure; the filter cavity structure comprises a cavity (2) embedded with the input coaxial port and the output coaxial port and surface-silvered, and cut surfaces (201) and (202) that are not silver-plated; the window coupling structure comprises a long-side window coupling through hole (301) etched on the cavity, and a short-side window coupling through hole (302) etched on the cavity and intersecting with the long-side window coupling through hole; the tuning structure comprises a first tuning structure (401) located at the bottom of the overall structure and close to the input coaxial port, a second tuning structure (402) symmetrically distributed on the same side of the long side of the first tuning structure, a third tuning structure (403) symmetrically distributed on the same side of the short side of the second tuning structure, and a fourth tuning structure (404) close to the output coaxial port.

2. The port coupling structure of a fourth-order filter based on a half-mode resonator according to claim 1, characterized in that: The input coaxial port (101) and the output coaxial port (102) are located at the top of the overall structure, and can be connected to the outside through a coaxial line to realize signal input and output. The overall inner core is inserted into the cavity structure by 3.23 mm.

3. The filter cavity structure of a fourth-order filter based on a half-mode resonator according to claim 1, characterized in that: The cavity (2) itself is in the shape of a cube, with an overall size of 36.7 mm×18.2 mm×6 mm, and is chamfered at the edges. Its relative dielectric constant is 20.3, relative magnetic permeability is 1, and loss tangent is 0.0005.

4. The window coupling structure of a fourth-order filter based on a half-mode resonator according to claim 1, characterized in that: The window coupling structure mainly includes two parts, one is a long side window coupling through hole (301), and the other is a short side window coupling through hole (302); the long side window coupling through hole has an opening length of 27.2 mm and a width of 2 mm, and the short side window coupling through hole has an opening length of 13.6 mm and a width of 1.5 mm. The edges of the slot through holes also need to be chamfered and rounded.

5. The tuning structure of a small-size fourth-order bandpass filter based on a half-mode dielectric waveguide resonator according to claim 1, characterized in that: The tuning structures are all located on the back of the overall structure. In addition to the different positions, the overall size and opening depth of the four tuning structures can be adjusted accordingly with the operating frequency. The four tuning structures themselves are cylindrical in shape with a radius of 1.5mm and an opening depth of 1.7mm.

6. The filter cavity structure of a fourth-order filter based on a half-mode resonator according to claim 1 or claim 3, characterized in that: In addition to chamfering and rounding the edges of the filter cavity structure surface, the entire outer surface needs to be silver-plated, but silver plating is not required on the section planes (201) and (202). In this case, the section plane is equivalent to a virtual magnetic wall, thereby achieving a half-mold working state of the overall structure.

7. A tuning structure of a fourth-order filter based on a half-mode resonator according to claim 1 or claim 5, characterized in that: The blind holes are all located on the back side of the overall structure, that is, the other side of the port coupling structure; the first tuning structure (401) and the second tuning structure (402) are symmetrically distributed about the long side of the filter cavity, the second tuning structure and the third tuning structure (403) are symmetrically distributed about the short side of the filter cavity, and the third tuning structure and the fourth tuning structure (404) are symmetrically distributed about the long side of the filter cavity. The overall size and opening depth of the four tuning structures are consistent, and they are symmetrically distributed compared to the back side of the cavity, thereby forming a fourth-order bandpass filter.

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