High-frequency broadband miniaturized ceramic filter

Abstract

This invention relates to a high-frequency broadband miniaturized ceramic filter, comprising a ceramic substrate with a cascaded fourth-order cross-coupling structure on its front side. The cascaded fourth-order cross-coupling structure includes four quarter-wavelength metal resonators for generating a pair of transmission zeros. A first resonator group is disposed on one side of the cascaded fourth-order cross-coupling structure, and a second resonator group is disposed on the other side. Each of the first and second resonator groups includes at least one quarter-wavelength metal resonator. This invention achieves high suppression performance by introducing a pair of transmission zeros, offering numerous advantages such as miniaturization, high out-of-band suppression, low loss, wide bandwidth, low cost, and ease of manufacturing, making it highly adaptable to high-frequency communication system applications.

Description

Technical Field

[0001] This invention belongs to the field of dielectric filter technology and relates to a high-frequency broadband miniaturized ceramic filter. Background Technology

[0002] With the rapid development of microwave communication technology, the development of microwave filters with advantages such as wide bandwidth, high suppression, high integration, and low cost has gradually become the mainstream demand in the market. Generally, wideband filters have lower stopband suppression compared to narrowband filters. While increasing the filter order can achieve higher suppression performance in wideband filters, increasing the order leads to a larger filter size, which is detrimental to miniaturization requirements. In existing technologies, achieving miniaturization in the design of high-performance microwave filters is difficult, making filter miniaturization a major technical challenge. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a high-frequency broadband miniaturized ceramic filter.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A high-frequency broadband miniaturized ceramic filter includes a ceramic substrate with a front side and a back side opposite to the front side. A cascaded fourth-order cross-coupling structure is disposed on the front side of the ceramic substrate. The cascaded fourth-order cross-coupling structure includes four quarter-wavelength metal resonators for generating a pair of transmission zeros. A first resonator group is disposed on one side of the cascaded fourth-order cross-coupling structure and connected to a first input / output excitation unit. A second resonator group is disposed on the other side of the cascaded fourth-order cross-coupling structure and connected to a second input / output excitation unit. The first and second resonator groups are symmetrically disposed on both sides of the cascaded fourth-order cross-coupling structure, and each of the first and second resonator groups includes at least one quarter-wavelength metal resonator.

[0006] Furthermore, each of the aforementioned quarter-wavelength metal resonators employs a quarter-wavelength impedance step resonator structure.

[0007] Furthermore, each of the quarter-wavelength metal resonators includes a high-impedance stub and a low-impedance stub connected to the high-impedance stub. The end of the high-impedance stub away from the low-impedance stub is short-circuited through a connecting unit to form a short-circuit end, and the end of the low-impedance stub away from the high-impedance stub is open-circuited to form an open-circuit end. Both the high-impedance stub and the low-impedance stub adopt a rectangular structure, and the width of the high-impedance stub is smaller than the width of the low-impedance stub.

[0008] Furthermore, the back side of the ceramic substrate is metallized to form a metal ground plane, and the connection unit is a connection through hole disposed at the short-circuit end of the quarter-wavelength metal resonator. The connection through hole penetrates the front and back sides of the ceramic substrate, and the hole wall of the connection through hole is metallized to form a metal layer connecting the short-circuit end of the quarter-wavelength metal resonator and the metal ground plane.

[0009] Furthermore, the cascaded fourth-order cross-coupled structure includes a third resonator unit, a fourth resonator unit, a fifth resonator unit, and a sixth resonator unit arranged sequentially along the length of the ceramic substrate. Each of these resonator units is a quarter-wavelength metal resonator. The open-circuit terminals of the third and fourth resonator units face opposite directions, forming a magnetic coupling between them. The open-circuit terminals of the fourth and fifth resonator units face the same direction, forming an electrical coupling between them via an interdigital structure. The open-circuit terminals of the fifth and sixth resonator units face opposite directions, forming a magnetic coupling between them. Parasitic coupling, which is magnetic coupling, forms between the third and sixth resonator units, thereby generating a transmission zero at both high and low frequencies.

[0010] Furthermore, the low-impedance stub of the fourth resonator unit has at least one first notch on the side facing the fifth resonator unit, and the low-impedance stub of the fifth resonator unit has a second notch at the position corresponding to each first notch on the side facing the fourth resonator unit. A metal coupling stub is provided in each first notch, with one end of the metal coupling stub located in the first notch and the other end extending outward from the first notch and into the second notch, thereby forming an interdigital structure between the fourth and fifth resonator units.

[0011] Furthermore, the first resonator group includes a first resonator unit and a second resonator unit, and the second resonator group includes a seventh resonator unit and an eighth resonator unit. The first, second, seventh, and eighth resonator units are all quarter-wavelength metal resonators. The first resonator unit is connected to a first input / output excitation unit. The open-circuit terminals of the first and second resonator units face opposite directions, forming a magnetic coupling between them. The open-circuit terminals of the second and third resonator units face opposite directions, forming a magnetic coupling between them. The open-circuit terminals of the seventh and sixth resonator units face opposite directions, forming a magnetic coupling between them. The open-circuit terminals of the eighth and seventh resonator units face opposite directions, forming a magnetic coupling between them. The eighth resonator unit is connected to a second input / output excitation unit.

[0012] Furthermore, the coupling strength between two adjacent quarter-wavelength metal resonators can be adjusted by regulating the spacing between them.

[0013] Furthermore, the ceramic substrate is made of alumina ceramic material.

[0014] Furthermore, the high-frequency broadband miniaturized ceramic filter is a thin-film ceramic filter manufactured using thin-film technology, and the etching process in the fabrication of the thin-film ceramic filter employs dry etching.

[0015] The high-frequency broadband miniaturized ceramic filter of the present invention uses a microstrip filter structure to achieve broadband characteristics and uses alumina with a high dielectric constant as the substrate material. The filter structure is compact and easy to miniaturize. By changing the resonator coupling method, the fourth resonator unit and the fifth resonator unit adopt an interdigital structure to achieve electrical coupling, thereby introducing a pair of transmission zeros to achieve high suppression performance. It can be widely used in high-performance radio frequency microwave communication system components. Attached Figure Description

[0016] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0017] Figure 1 This is a front structural schematic diagram of one embodiment of the high-frequency broadband miniaturized ceramic filter of the present invention.

[0018] Figure 2 This is a schematic diagram of the structure on the back.

[0019] Figure 3 The simulation curve of a filter designed in practice.

[0020] The meanings of the labels in the attached diagram are as follows:

[0021] First resonator unit-1; Second resonator unit-2; Third resonator unit-3; Fourth resonator unit-4; Fifth resonator unit-5; Sixth resonator unit-6; Seventh resonator unit-7; Eighth resonator unit-8; Ceramic substrate-9; High-impedance stub-11; Low-impedance stub-12; First input / output excitation unit-21; Second input / output excitation unit-22; First notch-31; Second notch-32; Metal coupling stub-33; Front side-91; Back side-92. Detailed Implementation

[0022] The following specific examples illustrate the implementation of the present invention. The illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0023] Please see Figure 1 and Figure 2 A preferred embodiment of the high-frequency broadband miniaturized ceramic filter of the present invention includes a ceramic substrate 9, which may be made of alumina ceramic material with a predetermined dielectric constant. The ceramic substrate 9 includes a front side 91 and a back side 92 opposite to the front side 91. The front side 91 of the ceramic substrate 9 is provided with a cascaded fourth-order cross-coupling structure. The cascaded fourth-order cross-coupling structure includes a third resonator unit 3, a fourth resonator unit 4, a fifth resonator unit 5, and a sixth resonator unit 6 arranged sequentially along the length direction of the ceramic substrate 9; the third resonator unit 3, the fourth resonator unit 4, the fifth resonator unit 5, and the sixth resonator unit 6 are all quarter-wavelength metal resonators. The third resonator unit 3 and the sixth resonator unit 6 are symmetrically arranged, and the fourth resonator unit 4 and the fifth resonator unit 5 are symmetrically arranged. The cascaded fourth-order cross-coupling structure is used to generate a pair of transmission zeros to achieve the high suppression requirement of the filter.

[0024] The cascaded fourth-order cross-coupled structure has a first resonator group and a second resonator group symmetrically arranged on both sides. The first resonator group includes a first resonator unit 1 and a second resonator unit 2, both of which are quarter-wavelength metal resonators. The second resonator unit 2 is located on the side of the third resonator unit 3 away from the fourth resonator unit 4, and the first resonator unit 1 is located on the side of the second resonator unit 2 away from the third resonator unit 3. The first resonator unit 1 is connected to a first input / output excitation unit 21. The second resonator group includes a seventh resonator unit 7 and an eighth resonator unit 8, both of which are quarter-wavelength metal resonators. The seventh resonator unit 7 and the second resonator unit 2 are symmetrically arranged, and the eighth resonator unit 8 and the first resonator unit 1 are symmetrically arranged. The eighth resonator unit 8 is connected to a second input / output excitation unit 22, which is symmetrically arranged with the first input / output excitation unit 21. The first input / output excitation unit 21 and the second input / output excitation unit 22 serve as the input and output interfaces of the ceramic filter, respectively. The signal strength fed into the ceramic filter can be adjusted by adjusting the value of the distance L5 between the first input / output excitation unit 21 or the second input / output excitation unit 22 and the edge of the ceramic substrate 9.

[0025] The first resonator unit 1, the second resonator unit 2, the third resonator unit 3, the fourth resonator unit 4, the fifth resonator unit 5, the sixth resonator unit 6, the seventh resonator unit 7, and the eighth resonator unit 8 all employ a quarter-wavelength SIR (Stepped Impedance Resonator) structure. The frequencies of the eight resonator units are determined by their lengths. For example, please refer to [further details omitted]. Figure 1 The frequency of the first resonator unit 1 is determined by its length L1. The quarter-wavelength SIR structure includes a high-impedance stub 11 and a low-impedance stub 12 connected to the high-impedance stub 11. The end of the high-impedance stub 11 away from the low-impedance stub 12 is short-circuited through a connecting unit, thereby forming a short-circuit end; the end of the low-impedance stub 12 away from the high-impedance stub 11 is open-circuited, thereby forming an open-circuit end.

[0026] In this embodiment, a metal ground plane is integrally formed on the back surface 92 of the ceramic substrate 9 through metallization. A connecting via is provided at the short-circuit end of each quarter-wavelength SIR structure (i.e., a quarter-wavelength metal resonator) as a connection unit. The connecting via penetrates both the front surface 91 and the back surface 92 of the ceramic substrate 9, and the wall of the connecting via is metallized to form a metal layer connecting the short-circuit end of the high-impedance stub 11 and the metal ground plane. The metallization process can employ magnetron sputtering, evaporation, electroplating, etc., and the metal layer film system is TiW / Au.

[0027] By short-circuiting the high-impedance stub 11 and opening the low-impedance stub 12, the quarter-wavelength SIR structure can shorten the size of the resonator unit without changing the Q value, thereby achieving filter miniaturization. Both the high-impedance stub 11 and the low-impedance stub 12 adopt a rectangular structure, and the width of the high-impedance stub 11 is smaller than the width of the low-impedance stub 12. The resonant frequency can be adjusted by widening the low-impedance stub 12, thus lowering the frequency. Furthermore, the coupling strength between this resonator unit and adjacent resonator units can be adjusted by changing the width of the low-impedance stub 12.

[0028] In order to better generate a pair of transmission zeros in the cascaded fourth-order cross-coupled structure to achieve high suppression requirements, in this embodiment, the open-circuit terminal of the third resonator unit 3 is oriented opposite to the open-circuit terminal of the fourth resonator unit 4, the open-circuit terminal of the fourth resonator unit 4 is oriented the same as the open-circuit terminal of the fifth resonator unit 5, and the open-circuit terminal of the fifth resonator unit 5 is oriented opposite to the open-circuit terminal of the sixth resonator unit 6. In addition, an interdigital structure is formed between the fourth resonator unit 4 and the fifth resonator unit 5. The specific method for forming the interdigital structure is as follows: two first notches 31 are provided on the side of the low-impedance stub 12 of the fourth resonator unit 4 facing the fifth resonator unit 5. Two second notches 32 are provided on the side of the low-impedance stub 12 of the fifth resonator unit 5 facing the fourth resonator unit 4 at the positions corresponding to the two first notches 31. A metal coupling stub 33 is provided in each of the two first notches 31. One end of the metal coupling stub 33 is located in the first notch 31, and the other end extends outward from the first notch 31 and into the second notch 32, thereby forming an interdigital structure between the fourth resonator unit 4 and the fifth resonator unit 5.

[0029] By adopting the above structure and enhancing the electrical coupling between the fourth resonator unit 4 and the fifth resonator unit 5 through two symmetrical metal coupling branches 33 inserted in the middle, the coupling modes between two adjacent resonator units of the sixth resonator unit 6 in the third resonator unit 3, the fourth resonator unit 4, and the fifth resonator unit 5 are magnetic coupling, electrical coupling, and magnetic coupling, respectively. Parasitic magnetic coupling is generated between the third resonator unit 3 and the sixth resonator unit 6, thereby exciting a limited number of transmission zeros at high and low frequencies and reducing the filter size, thus achieving high suppression performance of miniaturized broadband filters.

[0030] The open-circuit terminals of the first resonator unit 1 and the second resonator unit 2 are oriented opposite to each other, and the open-circuit terminals of the second resonator unit 2 and the third resonator unit 3 are oriented opposite to each other. Magnetic coupling is formed between the first resonator unit 1 and the second resonator unit 2, and between the second resonator unit 2 and the third resonator unit 3. The open-circuit terminal of the seventh resonator unit 7 is oriented opposite to the open-circuit terminal of the sixth resonator unit 6, and the open-circuit terminal of the eighth resonator unit 8 is oriented opposite to the open-circuit terminal of the seventh resonator unit 7. Magnetic coupling is formed between the sixth resonator unit 6 and the seventh resonator unit 7, and between the seventh resonator unit 7 and the eighth resonator unit 8.

[0031] Please continue reading. Figure 1 The interstage magnetic coupling strength between the first resonator unit 1 and the second resonator unit 2 can be adjusted by adjusting the gap g1 between them. Similarly, the interstage magnetic coupling strength between the second resonator unit 2 and the third resonator unit 3 can be adjusted by adjusting the gap g2 between them. Finally, the interstage magnetic coupling strength between the third resonator unit 3 and the fourth resonator unit 4 can be adjusted by adjusting the gap g3 between them. Correspondingly, the interstage magnetic coupling strength between adjacent resonator units in the fifth resonator unit 5, the sixth resonator unit 6, the seventh resonator unit 7, and the eighth resonator unit 8 can be adjusted by adjusting the values ​​of g3_1, g2_1, and g1_1. Furthermore, the electrical coupling strength between the fourth resonator unit 4 and the fifth resonator unit 5 can be adjusted by adjusting the values ​​of W4 and g4. For example, a larger value of W4 results in a larger interstage electrical coupling strength between the fourth resonator unit 4 and the fifth resonator unit 5.

[0032] To accommodate higher frequencies, the high-frequency broadband miniaturized ceramic filter can be a thin-film filter, i.e., fabricated using thin-film technology. Since the length variation of the resonator has a significant impact on the frequency, dry etching can be used in the thin-film filter to ensure accuracy, keeping the precision error within 20μm. Thin-film filters feature high integration, small size, high line precision, excellent component performance, high consistency, good temperature stability, and good frequency characteristics. Compared to cavity filters of the same structure, the volume of a thin-film filter is 1 / 550th that of a cavity filter, and its weight is 1 / 350th that of a cavity filter.

[0033] In this embodiment, filter miniaturization can be achieved by using an interdigital structure with one end open and the other short-circuited in a quarter-wavelength resonator. The length of the resonator unit determines the resonant frequency, and the gap between the resonator units affects the coupling strength and determines the bandwidth of the filter. For example, taking the design of a filter with a center frequency of 17.3 GHz and a bandwidth of 2.7 GHz as an example, the ceramic substrate 9 of this filter uses an alumina ceramic substrate material with a dielectric constant of 9.9. The dimensions of the ceramic substrate 9 are 7 mm × 2.5 mm × 0.254 mm. The pattern on the front side 91 of the ceramic substrate 9 includes two input / output excitation ports and eight resonator units using a quarter-wavelength SIR structure. According to the formula: V = λf, the electrical length of the resonator unit at a frequency of 17.3 GHz is about 17.3 mm. By using an alumina substrate with a dielectric constant of 9.9 and a quarter-wavelength SIR structure, the length of the resonator unit can be reduced to about 3 mm, which is about 6 times smaller than the size of a conventional interdigital dielectric filter. This greatly reduces the size of the thin-film ceramic filter and lowers the manufacturing cost of the thin-film filter. Please refer to the simulation curve of this filter. Figure 3 This filter achieves a -1dB bandwidth in the 15.95GHz to 18.65GHz frequency range, with low-end frequency rejection of 53dB and high-end frequency rejection of 90dB. It exhibits excellent performance characteristics, including wide bandwidth and high rejection. Furthermore, the designed filter demonstrates good consistency, enabling mass production. The ceramic filter in this embodiment offers numerous advantages, including miniaturization, high out-of-band rejection, low loss, wide bandwidth, low cost, and ease of manufacturing, making it highly adaptable to high-frequency communication system applications.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-frequency broadband miniaturized ceramic filter, characterized in that: The system includes a ceramic substrate, which has a front side and a back side opposite to the front side. The front side of the ceramic substrate is provided with a cascaded fourth-order cross-coupling structure. The cascaded fourth-order cross-coupling structure includes four quarter-wavelength metal resonators for generating a pair of transmission zeros. A first resonator group is provided on one side of the cascaded fourth-order cross-coupling structure, and the first resonator group is connected to a first input-output excitation unit. A second resonator group is provided on the other side of the cascaded fourth-order cross-coupled structure, and the second resonator group is connected to a second input-output excitation unit; The first resonator group and the second resonator group are symmetrically arranged on both sides of the cascaded fourth-order cross-coupled structure, and the first resonator group and the second resonator group each include at least one quarter-wavelength metal resonator. Each of the quarter-wavelength metal resonators includes a high-impedance stub and a low-impedance stub connected to the high-impedance stub. The end of the high-impedance stub away from the low-impedance stub is short-circuited through a connecting unit to form a short-circuit end, and the end of the low-impedance stub away from the high-impedance stub is open-circuited to form an open-circuit end. Both the high-impedance stub and the low-impedance stub adopt a rectangular structure, and the width of the high-impedance stub is smaller than the width of the low-impedance stub. The cascaded fourth-order cross-coupled structure includes a third resonator unit, a fourth resonator unit, a fifth resonator unit, and a sixth resonator unit arranged sequentially along the length of the ceramic substrate. Each of the third, fourth, fifth, and sixth resonator units is a quarter-wavelength metal resonator. The open-circuit terminals of the third and fourth resonator units are oriented opposite to those of the fourth resonator unit, and magnetic coupling is formed between the third and fourth resonator units. The open-circuit terminal of the fourth resonator unit and the open-circuit terminal of the fifth resonator unit have the same orientation, and an electrical coupling is formed between the fourth resonator unit and the fifth resonator unit through an interdigital structure. The open-circuit terminal of the fifth resonator unit is oriented in the opposite direction to the open-circuit terminal of the sixth resonator unit, and magnetic coupling is formed between the fifth resonator unit and the sixth resonator unit. Parasitic coupling is formed between the third resonator unit and the sixth resonator unit. The parasitic coupling is magnetic coupling, which generates a transmission zero at both high and low frequencies.

2. The high-frequency broadband miniaturized ceramic filter according to claim 1, characterized in that: Each of the aforementioned quarter-wavelength metal resonators employs a quarter-wavelength impedance step resonator structure.

3. The high-frequency broadband miniaturized ceramic filter according to claim 1, characterized in that: The back side of the ceramic substrate is metallized to form a metal ground plane. The connection unit is a connection through hole disposed at the short-circuit end of the quarter-wavelength metal resonator. The connection through hole penetrates the front and back sides of the ceramic substrate, and the hole wall of the connection through hole is metallized to form a metal layer connecting the short-circuit end of the quarter-wavelength metal resonator and the metal ground plane.

4. The high-frequency broadband miniaturized ceramic filter according to claim 1, characterized in that: The low-impedance stub of the fourth resonator unit has at least one first notch on the side facing the fifth resonator unit. The low-impedance stub of the fifth resonator unit has a second notch at the position corresponding to each first notch on the side facing the fourth resonator unit. A metal coupling stub is provided in each first notch. One end of the metal coupling stub is located in the first notch, and the other end extends outward from the first notch and into the second notch, thereby forming an interdigital structure between the fourth resonator unit and the fifth resonator unit.

5. The high-frequency broadband miniaturized ceramic filter according to claim 4, characterized in that: The first resonator group includes a first resonator unit and a second resonator unit, and the second resonator group includes a seventh resonator unit and an eighth resonator unit. The first resonator unit, the second resonator unit, the seventh resonator unit, and the eighth resonator unit are all quarter-wavelength metal resonators. The first resonator unit is connected to a first input-output excitation unit. The open-circuit terminal of the first resonator unit is oriented opposite to the open-circuit terminal of the second resonator unit, and magnetic coupling is formed between the first resonator unit and the second resonator unit. The open-circuit terminals of the second resonator unit and the third resonator unit are oriented oppositely, and magnetic coupling is formed between the second resonator unit and the third resonator unit. The open-circuit terminal of the seventh resonator unit is oriented opposite to the open-circuit terminal of the sixth resonator unit, and magnetic coupling is formed between the seventh resonator unit and the sixth resonator unit. The open-circuit terminal of the eighth resonator unit is oriented opposite to the open-circuit terminal of the seventh resonator unit, and magnetic coupling is formed between the eighth resonator unit and the seventh resonator unit. The eighth resonator unit is connected to a second input / output excitation unit.

6. The high-frequency broadband miniaturized ceramic filter according to claim 5, characterized in that: The coupling strength between two adjacent quarter-wavelength metal resonators can be adjusted by regulating the spacing between them.

7. The high-frequency broadband miniaturized ceramic filter according to any one of claims 1 to 6, characterized in that: The ceramic substrate is made of alumina ceramic material.

8. The high-frequency broadband miniaturized ceramic filter according to claim 7, characterized in that: The high-frequency broadband miniaturized ceramic filter is a thin-film ceramic filter manufactured using thin-film technology, and the etching process in the fabrication of the thin-film ceramic filter adopts dry etching.

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