Z-shaped four-order small band-pass filter based on quarter mode

Abstract

The invention belongs to the technical field of microwave circuits, and particularly provides a Z-shaped four-order small band-pass filter based on a quarter mode, so as to realize the performance characteristics of small size, light weight and high out-of-band rejection of the band-pass filter. The invention comprises a port coupling structure, namely an input coaxial port and an output coaxial port; the embedded tuning structure comprises a first tuning blind hole, a second tuning blind hole, a third tuning blind hole and a fourth tuning blind hole; a U-shaped windowing coupling structure; the through holes are positive symmetric short windowing through holes and oblique symmetric long windowing through holes; the Z-shaped filter cavity structure is a cavity with a silver-plated surface. According to the four-order band-pass filter, the high-dielectric-constant material is combined with partial surface silver plating of the cavity, so that a virtual magnetic wall is formed on the non-silver-plated surface to realize a quarter-mode working mode, and tuning and windowing coupling structures are combined to form the four-order band-pass filter. Due to the novel design thought, compared with a traditional full-mode band-pass filter, the full-mode band-pass filter has the advantages that the size and the weight are reduced by about 75%. The invention can be used in communication systems and millimeter wave related applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave circuits, and specifically provides a quarter-mode Z-shaped fourth-order miniaturized bandpass filter. Background Art

[0002] With the expansion of 5G communication to millimeter-wave frequency bands and the increasing demand for multi-band collaborative operation, as well as the development of future 6G, the overall communication system will have higher and higher requirements for the selective transmission of signals and noise suppression. Moreover, for different application environments and scenarios, the requirements for filters not only need high selectivity and out-of-band rejection, but also require a compact volume, easy integration, and multi-form display to meet the increasingly complex multi-band communication system and compact device design. Although traditional dielectric resonator filters occupy an important position in related applications such as base stations due to their low-loss characteristics, in the face of modern high-frequency communication and future communication applications, it is very likely that they will become unusable due to volume and shape limitations. Therefore, how to reduce the volume of the filter and expand the shape selection of the filter without sacrificing performance, especially selectivity and out-of-band rejection, has become the research focus. Summary of the Invention

[0003] The object of the present invention is to provide a quarter-mode fourth-order miniaturized bandpass filter in the shape of a Z, which still maintains the required high selectivity and high out-of-band rejection while achieving a small volume.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] The present invention mainly consists of four major structures: a port coupling structure, an embedded tuning structure, a U-shaped window coupling structure, and a Z-shaped filter cavity structure. The port coupling structure is composed of two major parts, namely an input coaxial port and an output coaxial port. The two ports complete the input and selective output of signals by inserting the coaxial inner core into the cavity. The embedded tuning structure is mainly realized in the form of blind holes on the back, with chamfers made at the edges of the blind holes. The four blind holes are equivalent to four resonant units, thus realizing the performance of a fourth-order filter. The U-shaped window coupling structure is mainly composed of a symmetric short window through-hole and an asymmetric long window through-hole, and a total of four U-shaped window through-holes are included. The U-shaped window coupling structure can effectively cut the electric field distribution inside the cavity. Combining with the embedded tuning structure, it can effectively control the electric field direction inside the cavity, thereby improving the out-of-band rejection ability of the overall filter. The Z-shaped filter cavity structure is overall in the shape of a Z, and its material is selected as a ceramic material with a high dielectric constant. The above-mentioned port coupling structure, embedded tuning structure, and U-shaped window coupling structure are loaded on it. Its surface is selectively silver-plated. The silver-plated parts are mainly the surfaces of the four U-shaped window through-holes, the long surfaces connected by the two symmetric short window through-holes, the upper surface of the Z-shaped filter cavity, and the lower surface of the Z-shaped filter cavity including the blind holes. Through such selective silver-plating treatment, the silver-plated parts are equivalent to electric walls, and combined with the high dielectric constant of the cavity itself, the un-silver-plated parts are equivalent to virtual magnetic walls during operation, thereby realizing the operating form of a quarter-mode. This reduces the overall volume and weight by approximately 75% compared to the full-mode operating state.

[0006] How to achieve the reduction of the filter volume and the performance degradation caused by the selection of unconventional shapes is a major difficulty in the present invention. Among them, the four embedded tuning blind hole structures are divided into the first tuning blind hole, the second tuning blind hole, the third tuning blind hole, and the fourth tuning blind hole according to the layout and resonance sequence. The first tuning blind hole is located on the back of the input coaxial port and is coupled and excited through an embedded probe. The second tuning blind hole is connected to the first tuning blind hole through an asymmetric long window U-shaped through-hole and appears horizontally connected in the top view. The third tuning blind hole is vertically connected to the second tuning blind hole, with a symmetric U-shaped short window through-hole in the middle. The fourth tuning blind hole is on the back of the output coaxial port and is horizontally connected to the third tuning blind hole through an asymmetric long window U-shaped through-hole. The cavity-to-cavity coupling is realized by relying on the U-shaped window through-hole structure between each tuning unit. At the same time, combined with the quarter-mode operating form realized by introducing virtual magnetic walls, the passband flatness is significantly improved while maintaining the reduction of the overall volume and weight of the filter, and excellent out-of-band rejection performance and selectivity are maintained.

[0007] The innovation of the present invention lies in:

[0008] 1. By selecting materials with high dielectric constant and combining them with surface selective silver plating treatment, a virtual magnetic wall is introduced to achieve the quarter-mode propagation mode, reducing the cavity volume to approximately one-fourth of that in the full-mode, realizing the characteristic of small volume and facilitating integration in communication systems.

[0009] 2. By introducing a U-shaped window coupling structure combined with an embedded tuning structure, while maintaining the reduction of the overall volume and weight of the filter, the passband flatness of the filter is significantly improved, and the characteristics of high out-of-band rejection performance and high selectivity are achieved, meeting the requirements of current and future communication systems for signal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is the overall view of the quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter of the present invention;

[0011] Figure 2 is the schematic diagram of the port coupling structure of the quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter of the present invention;

[0012] Figure 3 is the schematic diagram of the embedded tuning structure of the quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter of the present invention;

[0013] Figure 4 is the schematic diagram of the U-shaped window coupling structure of the quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter of the present invention;

[0014] Figure 5 is the schematic diagram of the Z-shaped filter cavity structure of the quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter of the present invention;

[0015] Figure 6 is the front view of the overall structure of the quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter of the present invention;

[0016] Figure 7 is the top view of the overall structure of the quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter of the present invention;

[0017] Figure 8 is the side view of the overall structure of the quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter of the present invention;

[0018] Figure 9 is the overall comparison of the return loss (S11) and insertion loss (S12) within the working passband of the quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0019] To make the objectives, technical solutions, and innovative points of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0020] Figure 1 This is the overall structure of the present invention. The structure of the present invention is mainly divided into four major parts, where 1 is the port coupling structure, 2 is the embedded tuning structure, 3 is the U-shaped window coupling structure, and 4 is the Z-shaped filter cavity structure.

[0021] Figure 2 This is a schematic diagram of the port coupling structure of the present invention, where 101 is the input coaxial port and 102 is the output coaxial port. Figure 3 This is a schematic diagram of the embedded tuning structure of the present invention, where 201 is the first tuning blind hole, 202 is the second tuning blind hole, 203 is the third tuning blind hole, and 204 is the fourth tuning blind hole. Figure 4 This is a schematic diagram of the U-shaped window coupling structure of the present invention, where 301 is the symmetric short window through hole and 302 is the skew-symmetric long window through hole. Figure 5 This is the Z-shaped filter cavity structure of the present invention, where 401 is the cavity itself with chamfered edges and loaded with the embedded tuning structure and the U-shaped window coupling structure. The cavity is made of a ceramic material with a dielectric constant of 20.3, a relative magnetic permeability of 1, and a loss tangent of 0.0005. 402 is the silver-plated surface on the upper part of the cavity, 403 is the silver-plated surface on the lower part of the cavity, and 404 is the silver-plated surface on the side of the cavity. Among them, the embedded tuning structures are all located on the back of the overall structure, and the four tuning structures are all embedded blind holes. The first tuning blind hole is located on the back of the input coaxial port. The first tuning blind hole and the second tuning blind hole are coupled to each other through the skew-symmetric long window through hole. The two are Figure 7 shown as horizontally linearly connected in the top view shown, and the third tuning blind hole and the second horizontal blind hole are Figure 7 shown as vertically connected in the top view shown, and there is a symmetric short window through hole between the third tuning blind hole and the second tuning blind hole. The fourth tuning blind hole and the third tuning blind hole are horizontally linearly connected, and the two are coupled through the skew-symmetric long window through hole. The silver-plated surface on the lower part of the cavity, including the tuning blind holes, is silver-plated. The silver-plated surface on the side of the cavity is mainly the surface of the four U-shaped window through holes and the long surface connected by the two symmetric short window through holes. By silver-plating the surface, an ideal electric wall is formed so that the unplated surface is equivalent to a virtual magnetic wall, thereby exciting the propagation mode of the quarter-mode.

[0022] In order to detail the layout and dimensions of each structure of the present invention, Figure 6 This is the front view of the overall structure, Figure 7 This is the top view of the overall structure, Figure 8It is a side view of the overall structure. The overall cavity presents a Z shape. The total length W5 of the cavity is 30 mm, the total width l1 is 20 mm, the total height h2 is 9 mm, the height h1 of the cavity itself is 6 mm, the unilateral length of the cavity is W1 = 20.3 mm, and the unilateral width l2 is 9.25 mm. The outward height h4 of the coaxial input port and output port is 2 mm, the total height of the coaxial port is h3 = 4.5 mm, the inserted inner core height h6 is 2.5 mm, and the inserted inner core diameter R2 is 1.5 mm. The opening length l4 of the obliquely symmetric long open window U-shaped through hole is 2.5 mm, and the opening width W2 is 2 mm. The opening length W4 of the symmetric short open window U-shaped through hole is 1.6 mm, and the opening width l3 is 1.9 mm. The opening position of the obliquely symmetric long open window through hole is at the middle position of the side, and the opening position of the symmetric short open window through hole is at the center position of the width. The tuning blind holes are all located at the back position. The four blind holes can be regarded as cylinders, with a drilling diameter R1 = 2.4 mm and a drilling depth h5 = 1.5 mm. The four tuning blind holes are all embedded blind holes, and the overall size and opening depth of the blind holes can be adjusted accordingly with the change of the working frequency. At the same time, to prevent the edge current from affecting the field distribution of the overall cavity, a smooth chamfering treatment is carried out at the edge edges, and the chamfering treatment of the entire cavity is 0.15 mm.

[0023] Figure 9 It shows a schematic diagram of the overall performance of the in-band return loss and insertion loss of a quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter within its working passband. Its working passband range is 2.495 GHz - 2.685 GHz, the in-band return loss is lower than -20 dB, and the in-band insertion loss is only 1.55 dB. At the working frequency, the filter size length is about 0.26λ, the width is about 0.18λ, and the height of the cavity itself is about 0.05λ. It has the characteristic of small volume compared with the traditional design method. At the same time, its performance schematic diagram also shows that the fourth-order bandpass filter has the characteristic of high out-of-band rejection.

[0024] The above embodiments merely illustrate the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter, comprising a port coupling structure, an embedded tuning structure, a U-shaped window coupling structure, and a Z-shaped filter cavity structure, characterized in that: The port coupling structure includes an input coaxial port (101) for signal input and an output coaxial port (102) for signal output, which are located at the uppermost part of the overall structure; the embedded tuning structure includes a first tuning blind hole (201) located at the lowermost part of the overall structure and close to the input coaxial port, a second tuning blind hole (202) that is horizontally linearly connected to the first tuning blind hole in the plane, a third tuning blind hole (203) that is vertically linearly connected to the second tuning blind hole in the plane, and a fourth tuning blind hole (204) that is horizontally linearly connected to the third tuning blind hole in the plane and close to the output coaxial port; the U-shaped window coupling structure includes a positive symmetric short window through hole (301) that separates the second tuning blind hole and the third tuning blind hole and both present a U shape, and an oblique symmetric long window through hole (302) that separates the first tuning blind hole and the second tuning blind hole and the third tuning blind hole and the fourth tuning blind hole respectively and presents a U shape; the Z-shaped filter cavity structure includes a cavity (401) that is overall presented with chamfered edges and loaded with an embedded tuning structure and a U-shaped window coupling structure, a silver-plated surface (402) on the upper part of the cavity, a silver-plated surface (403) on the lower part of the cavity, and a silver-plated surface (404) on the side of the cavity.

2. The port coupling structure of a quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter according to claim 1, characterized in that: The input coaxial port (101) and the output coaxial port (102) are located at the uppermost part of the overall structure, and their coaxial inner cores are inserted into the cavity itself, with an insertion length of 2.5 mm, and the signal input and output are realized by inserting the inner cores.

3. The embedded tuning structure of a quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter according to claim 1, characterized in that: The embedded tuning structures are all located on the back of the overall structure, that is, at the opposite side of the port coupling structure. The four tuning structures are all embedded blind holes, and the overall size and the opening depth of the blind holes can be adjusted accordingly with the change of the operating frequency. The four blind holes are cylindrical in shape with the same overall size and opening depth. The opening radius of the four blind holes is 1.2 mm, and the opening depth is 1.5 mm.

4. The U-shaped window coupling structure of a quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter according to claim 1, characterized in that: The U-shaped window coupling structure mainly includes two parts, one is a positive symmetric short window through hole (301), and the other is an oblique symmetric long window through hole (302). The two window through holes altogether include four U-shaped window through holes. Among them, the two positive symmetric U-shaped short window through holes have the same size. The U-shaped length of the short window through hole is 1.6 mm and the width is 1.9 mm. The two oblique symmetric U-shaped long window through holes also have the same size. The U-shaped length of the long window through hole is 2.5 mm and the width is 2 mm.

5. The Z-shaped filter cavity structure of a quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter according to claim 1, characterized in that: In the Z-shaped filter cavity structure, the cavity (401) is Z-shaped, and an embedded tuning structure, a port coupling structure, and a U-shaped window coupling structure are loaded on the cavity. The surface of the cavity is also silver-plated to form an electric wall. The silver-plated surfaces are the upper silver-plated surface (402) loaded with the port coupling structure, the lower silver-plated surface (403) loaded with the embedded tuning structure, and the side silver-plated surface (404) loaded with the U-shaped window coupling structure. The dielectric constant of the cavity is 20.3, the relative magnetic permeability is 1, and the overall dimensions are: 30mm * 20mm * 9mm.

6. The embedded tuning structure of a quarter-mode-based Z-shaped fourth-order miniaturized bandpass filter according to claim 1, characterized in that: The plane where the embedded tuning structure is distributed is the plane obtained when looking from the port coupling structure, that is, the top view. The positions where the horizontally straight lines are connected are the positions of the obliquely symmetric long window through holes (302) in the horizontal direction, and the positions of the symmetric short window through holes (301) are in the vertical direction.

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