A fourth-order filter based on a half-mode resonator

Abstract

This invention belongs to the field of microwave circuit technology, specifically providing a fourth-order filter based on a half-mode resonator to achieve performance characteristics of small size, high selectivity, and high out-of-band suppression. The invention includes: a port coupling structure, namely an input coaxial port and an output coaxial port; a filter cavity structure, namely the cavity itself; a window coupling structure, namely a long-side window coupling via and a short-side window coupling via; and a tuning structure, namely a first tuning structure, a second tuning structure, a third tuning structure, and a fourth tuning structure. This invention utilizes the high dielectric constant of the cavity itself to create a virtual magnetic wall, thereby realizing a half-mode operating dielectric waveguide resonator, and then uses four resonators to form a fourth-order bandpass filter. Due to its novel design concept, this invention reduces the size by approximately 50% compared to traditional fourth-order bandpass filters. This invention can be used in communication systems and millimeter-wave related applications.

Description

Technical Field

[0001] This invention belongs to the field of microwave circuit technology, specifically providing a fourth-order filter based on a half-mode resonator. Background Technology

[0002] In modern communication systems and RF front-end equipment, with the development of 5G communication technology and the widespread adoption of multi-band communication, the requirements for selective signal transmission and noise suppression are becoming increasingly stringent. Consequently, the performance requirements for filters are constantly rising, demanding not only high selectivity and out-of-band suppression but also compact size and ease of integration to adapt to increasingly complex multi-band communication systems and compact equipment designs. While traditional bandpass filters can meet basic signal processing needs, they are often limited by power and loss factors when facing higher frequency and wider bandwidth applications, resulting in larger sizes that fail to meet the miniaturization and high integration requirements of modern communication systems.

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

[0004] The objective of this invention is to provide a fourth-order filter based on a half-mode resonator that maintains high selectivity and high out-of-band rejection while achieving a small size.

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

[0006] This invention mainly consists of a port coupling structure, a filter cavity structure, a windowed coupling structure, and a tuning structure. The port coupling structure comprises two main parts: an input coaxial port and an output coaxial port, connected externally via coaxial lines to achieve signal input and selective output. The filter cavity structure is cubic in shape. To prevent edge currents from affecting the overall field distribution of the cavity, the edges are rounded. The entire cavity, except for two cross-sections, is silver-plated, making the silver-plated parts equivalent to electric walls and the unplated parts equivalent to virtual magnetic walls, thus effectively reducing the overall filter volume. The windowed coupling structure mainly consists of long-side and short-side windowed coupling vias, both also silver-plated, similarly acting as equivalent electric walls, effectively cutting through the electric field distribution inside the cavity. The tuning structure is mainly composed of four blind holes on the back. The four blind holes are equivalent to four resonators. The electric field inside the cavity is cut off by the window coupling structure and the silver plating of the cavity itself, thereby realizing the cross coupling between the four resonators. This can improve the out-of-band rejection capability of the filter and solve the problem of the decrease in out-of-band rejection capability after the traditional filter is reduced in size.

[0007] A major challenge of this invention is eliminating the performance degradation caused by the reduction in filter size. The tuning structure, composed of four blind vias, can be categorized into a first tuning structure, a second tuning structure, a third tuning structure, and a fourth tuning structure based on their distribution. 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 and fourth tuning structures are also symmetrically distributed on the same side of the long side. The windowed coupling structure effectively blocks the electric field within the filter cavity, thus achieving lateral magnetic coupling between the first and second tuning structures, as well as between the third and fourth tuning structures. Simultaneously, the second and third tuning structures are connected via back magnetic coupling. This cross-coupling design significantly improves the passband flatness of the filter and enhances its out-of-band rejection performance and selectivity.

[0008] The innovation of this invention lies in:

[0009] First, by selecting materials with high dielectric constant and combining them with silver plating on the surface, a virtual magnetic wall is introduced, realizing a half-mode propagation mode. While ensuring the stability of the electromagnetic field distribution inside the filter cavity, the cavity volume is reduced by half, achieving the small size characteristic of this filter, which is easy to integrate into current communication systems.

[0010] Second, by introducing a windowed coupling structure and combining it with a back-facing blind aperture, cross-coupling between the tuning structures is achieved, which significantly improves the passband flatness of the filter and realizes the characteristics of high out-of-band rejection performance and high selectivity of this filter, thus meeting the application characteristics of current communication systems with extremely high signal quality requirements. Attached Figure Description

[0011] Figure 1 This is an overall view of the fourth-order filter based on a half-mode resonator according to the present invention;

[0012] Figure 2 This is a schematic diagram of the port coupling structure and filter cavity structure of the present invention;

[0013] Figure 3 This is a schematic diagram of the window coupling structure of the present invention;

[0014] Figure 4 This is a schematic diagram of the tuning structure of the present invention;

[0015] Figure 5 This is a front view of the overall structure of the fourth-order filter based on a half-mode resonator according to the present invention;

[0016] Figure 6 This is a top view of the overall structure of the fourth-order filter based on a half-mode resonator according to the present invention;

[0017] Figure 7 This is a side view of the overall structure of the fourth-order filter based on a half-mode resonator according to the present invention;

[0018] Figure 8 The return loss (S11) within the working passband of the fourth-order filter based on a half-mode resonator of the present invention;

[0019] Figure 9 The insertion loss (S12) within the operating passband of the fourth-order filter based on a half-mode resonator of the present invention;

[0020] Figure 10 A comparison of the return loss (S11) and insertion loss (S12) within the working passband of the fourth-order filter based on a half-mode resonator of the present invention; Detailed Implementation Plan

[0021] To make the objectives, technical solutions, and innovations of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and examples.

[0022] Figure 1 This is the overall structure of the present invention. The structure of the present invention is mainly divided into four parts, of which 1 is the port coupling structure, 2 is the filter cavity structure, 3 is the window coupling structure, and 4 is the tuning structure.

[0023] Figure 2 This is a schematic diagram of the external connection mechanism and filter cavity structure of the present invention. 101 is the input coaxial port, 102 is the output coaxial port, and 201 and 202 are the unplated surfaces of the cavity, which is equivalent to adding two ideal magnetic walls to the cavity surfaces. The other silver-plated planes can be regarded as equivalent electric walls, thereby introducing a half-mode working state.

[0024] Figure 3 This is a schematic diagram of the windowed coupling structure of the present invention. 301 is a long-side windowed coupling through hole, and 302 is a short-side windowed coupling through hole. The two through holes realize the isolation of the electric field inside the cavity.

[0025] Figure 4This is a schematic diagram of the tuning structure of the present invention. 401 is the first tuning structure, located on the back side of the input coaxial port 101. 402 is the second tuning structure, symmetrically distributed about the long side of the cavity with respect to the first tuning structure. 403 is the third tuning structure, symmetrically distributed about the short side of the cavity with respect to the second tuning structure. 404 is the fourth tuning structure, located on the back side of the output coaxial port. The fourth tuning structure is symmetrically distributed about the long side of the cavity with respect to the third tuning structure, and also symmetrically distributed about the short side of the cavity with respect to the first tuning structure. The dimensions of the four tuning structures, except for their different positions, 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 through a windowed coupling structure. The second resonant structure and the third resonant structure achieve back-to-back magnetic coupling through the same windowed coupling structure.

[0026] To illustrate in detail the layout and dimensions of the various structures of this invention, Figure 5 This is a front view of the overall structure. Figure 6 It is a top view of the overall structure and Figure 7 This is a side view of the overall structure. The dimensions of the overall cavity are: length l1 = 36.7 mm, width w1 = 18.2 mm, and height h1 = 6 mm. The input and output coaxial ports of the cavity port coupling structure have the same dimensions. The inner coaxial core has a dimension of R2 = 0.65 mm, the outer coaxial core has a dimension of R3 = 1.495 mm, and the inner core is inserted into the cavity with a dimension of h3 = 3.23 mm. In the windowed coupling structure, the distance from the shortest part of the long-side windowed coupling through-hole to the cavity edge is l2 = 1.7 mm, and the distance from the longest part is l3 = 7.8 mm. The length of the long-side windowed coupling through-hole is l4 = 27.2 mm, and the width is w3 = 2 mm. The distances from the two sides of the short-side windowed coupling through-hole to the cavity edge are w4 = 2.3 mm and w5 = 2.3 mm, respectively. The length of the short-side windowed coupling through-hole is l5 = 13.6 mm, and the width is w2 = 1.5 mm. The tuning structure consists of blind holes drilled on the back of the cavity. Each blind hole can be considered a cylinder with a drilling radius of R1 = 1.5 mm and a drilling depth of h2 = 1.8 mm. These four blind holes serve as four tuning structures, allowing adjustment of the filter's specific operating frequency. Simultaneously, to prevent edge currents from affecting the overall field distribution of the cavity, the edges are rounded and chamfered, with the entire cavity having a chamfer of 0.2 mm.

[0027] Figure 8 A small-sized fourth-order bandpass filter based on a half-mode dielectric waveguide resonator was demonstrated, with an operating passband range of 2.505 GHz to 2.665 GHz and an in-band return loss of less than -22 dB. At the operating frequency, the filter's dimensions are only 0.32λ in length, 0.16λ in width, and 0.05λ in height, which is significantly smaller than traditional design methods.

[0028] Figure 9 The insertion loss of a small-sized fourth-order bandpass filter based on a half-mode dielectric waveguide resonator is demonstrated in the operating passband, with an insertion loss of only 1.6 dB in the operating range of 2.505 GHz to 2.665 GHz.

[0029] Figure 10 The diagram shows the overall performance of a small-sized fourth-order bandpass filter based on a half-mode dielectric waveguide resonator in the 2.505 GHz-2.665 GHz operating range, including its in-band return loss and insertion loss. It can be seen that the fourth-order bandpass filter has the characteristics of compact size and high out-of-band suppression.

[0030] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can 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 those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should 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 windowed coupling structure, and a tuning structure, characterized in that: The port coupling structure includes an input coaxial port (101) for signal input located at the top of the overall structure and an output coaxial port (102) for signal output; the filter cavity structure includes a cavity (2) embedded with the input coaxial port and the output coaxial port and silver-plated, a cross-section (201) not silver-plated and close to the output coaxial port, and a cross-section (202) not silver-plated and close to the input coaxial port; the window coupling structure includes a long-side window coupling via (301) etched on the cavity and a short-side window coupling via (302) etched on the cavity and intersecting with the long-side window coupling via; the tuning structure includes 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 as 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 fourth-order filter based on a half-mode resonator according to claim 1, characterized in that: The input coaxial port (101) and output coaxial port (102) are located at the top of the overall structure. They are connected to the outside through coaxial lines to realize signal input and output. The overall inner core is inserted into the cavity structure by 3.23mm.

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

4. A fourth-order filter based on a half-mode resonator according to claim 1, characterized in that: The window coupling structure comprises two main parts: a long-side window coupling through-hole (301) and a short-side window coupling through-hole (302). The long-side window coupling through-hole has a length of 27.2 mm and a width of 2 mm, while the short-side window coupling through-hole has a length of 13.6 mm and a width of 1.5 mm. The edges of both the long-side and short-side window coupling through-holes need to be chamfered and rounded.

5. A fourth-order filter based on a half-mode resonator according to claim 1, characterized in that: The tuning structures are all located on the back of the overall structure. Apart from their different positions, the overall size and opening depth of the four tuning structures can be adjusted according to the operating frequency. The four tuning structures themselves are cylindrical blind holes with a radius of 1.5mm and an opening depth of 1.7mm.

6. A fourth-order filter based on a half-mode resonator according to claim 1 or claim 3, characterized in that: In addition to rounding the edges, the surface of the filter cavity structure also needs to be silver-plated. However, silver plating is not required on the cut surfaces (201) and (202). The cut surface (201) is located on the side of the cavity near the output coaxial port, and the cut surface (202) is located on the side of the cavity near the input coaxial port. At this time, the plane of the cut surface is equivalent to a virtual magnetic wall, thereby realizing the half-mode working state of the overall structure.

7. A fourth-order filter based on a half-mode resonator according to claim 1 or claim 5, characterized in that: The tuning structures are all blind-hole shaped and located on the back 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 aperture depth of the four tuning structures are consistent, and they are symmetrically distributed relative to the back of the cavity, thus forming a fourth-order bandpass filter.

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