Cavity broadband filter and capacitor coupling method

Abstract

The invention relates to the field of broadband filters, and discloses a cavity broadband filter and capacitor coupling method, which comprises the following steps that a cavity is arranged in a broadband filter, a plurality of resonant columns are arranged in the cavity, and the resonant columns are arranged at preset intervals to form a resonant mode of the filter; a capacitor sheet is installed in the cavity, the capacitor sheet spans at least one resonant column, and energy transmission between the resonant columns is influenced through electric field coupling; and the end parts of the two sides of the capacitor sheet penetrate through the cavity and are grounded to form a transmission zero point. According to the invention, the capacitor sheets are additionally arranged in the cavity broadband filter, so that a transmission zero point is formed, the out-of-band rejection degree is improved, and a 7-order filter can achieve the effect of a 9-order filter. Therefore, the same suppression degree is ensured, the size of the filter is obviously reduced, the miniaturization design is realized, and the limitation requirements of space and weight are met.

Description

Technical Field

[0001] The present invention relates to the field of broadband filters, and particularly to a method for adding capacitive coupling to a cavity broadband filter. Background Art

[0002] Cavity bandpass filters are widely used in wireless communication, radar, and radio frequency systems. Their main function is to select signals within a specific frequency range and effectively suppress out-of-band interference. In filter design, capacitive coupling is a common method that can be used to adjust the frequency response characteristics of the filter, optimize transmission zeros, and improve out-of-band suppression.

[0003] However, currently, the capacitive coupling of mainstream cavity bandpass filters is mainly applicable to the case where the relative bandwidth is within 30%. When the relative bandwidth exceeds 30%, the implementation of capacitive coupling becomes extremely difficult and even difficult to effectively apply.

[0004] Especially in the design of cavity ultra-wideband bandpass filters, due to the large bandwidth requirement, it is difficult to effectively control the transmission zeros at the lower end of the passband, resulting in difficulty in optimizing the out-of-band suppression. The application of traditional capacitive coupling methods in such filters is limited, making it extremely difficult to increase zeros at the lower end of the passband to improve the suppression of the filter.

[0005] Due to the limited volume of the cavity filter, it is difficult to improve the suppression by simply increasing the number of resonant orders. Therefore, the existing designs cannot meet the requirement of high suppression at the lower end of the passband under the same bandwidth and the same volume. This technical bottleneck restricts the miniaturization development of cavity filters, making it difficult to meet the engineering requirements in ultra-wideband applications with high suppression requirements. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the present invention provides a method for adding capacitive coupling to a cavity broadband filter, which solves the problems that capacitive coupling is difficult to implement in existing ultra-wideband cavity bandpass filters, and cannot meet the requirement of large suppression at the lower end of the passband under the same bandwidth and the same volume, and cannot meet the miniaturization requirement of cavity filters.

[0007] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for adding capacitive coupling to a cavity broadband filter, comprising the following steps:

[0008] A cavity is provided in the broadband filter, and a plurality of resonant posts are provided in the cavity. The resonant posts are arranged at a predetermined interval to form the resonant mode of the filter;

[0009] A capacitor plate is installed inside the cavity. The capacitor plate straddles at least one resonant post and affects the energy transmission between the resonant posts through electric field coupling;

[0010] Both end portions of the capacitor plate penetrate through the cavity and are grounded to form a transmission zero point.

[0011] Preferably, the material of the capacitor plate is set as a metal material or a high-dielectric-constant ceramic material, and the capacitor plate is applied to a cavity broadband filter with a center frequency range of 1 - 10 GHz and a relative bandwidth greater than 30%.

[0012] Preferably, the metal material includes: copper, silver, aluminum, gold, and nickel;

[0013] The high-dielectric-constant ceramic material includes: lithium niobate, barium titanate, lead magnesium niobate, lead niobate titanate, alumina, and high-dielectric ceramics with a dielectric constant greater than 50.

[0014] Preferably, an air gap is provided between the capacitor plate and the resonant post for adjusting the capacitance coupling strength.

[0015] Preferably, the capacitor plate includes: branch section one, straight section two, and branch section three;

[0016] Among them, a ground terminal one and a ground terminal two are respectively provided on the far sides of branch section one and branch section three for penetrating through the cavity and being grounded.

[0017] Preferably, the distance between branch section one and branch section three spans at least one resonant post.

[0018] Preferably, branch section one, branch section three, and the resonant post are parallel to each other, and straight section two is perpendicular to or forms an inclination angle with branch section one and branch section three.

[0019] Preferably, a clamping plate is provided inside the cavity, the clamping plate is fixedly connected to the inner wall of the broadband filter, a contact piece is fixedly connected to one side of the clamping plate, and one side of the contact piece is in contact with the edge portion of straight section two.

[0020] Preferably, one side of the clamping plate is provided with a curved surface, the cross section of the contact piece is set as an arc, a groove is provided on one side of the contact piece, and the edge portion of straight section two is in contact with the inner wall of the groove.

[0021] Preferably, several of the resonant posts are cylindrical or columnar.

[0022] The present invention provides a method for adding capacitance coupling to a cavity broadband filter. It has the following beneficial effects:

[0023] 1. By adding a capacitor plate in the cavity broadband filter, the present invention forms a transmission zero point, improves the out-of-band suppression degree, so that a 7-order filter can achieve the effect of a 9-order filter. This not only ensures the same suppression degree but also significantly reduces the volume of the filter, realizes miniaturized design, and meets the requirements of space and weight limitations.

[0024] 2. The present invention enhances the signal transmission characteristics through the coupling of capacitor plates, reducing the unnecessary energy loss between the resonant columns. Compared with the traditional 9th-order filter, under the same suppression level, the present invention significantly reduces the insertion loss and improves the integrity of signal transmission, making the filter have a broader application prospect in high-performance wireless communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of a partial structure of the broadband filter of the present invention;

[0026] Figure 2 It is a schematic diagram of the internal structure of the cavity of the present invention;

[0027] Figure 3 It is a schematic diagram of the capacitor plate structure of the present invention;

[0028] Figure 4 It is a schematic diagram of the structure of the second branch section of the present invention;

[0029] Figure 5 It is a schematic diagram of the partial structure of the card board of the present invention;

[0030] Figure 6 It is a schematic diagram of the data of the comparative experiment results in Embodiment 2 of the present invention.

[0031] Among them, 1. Cavity; 2. Resonant column; 3. Capacitor plate; 31. First grounding end; 32. Second grounding end; 33. First branch section; 34. Second branch section; 35. Third branch section; 4. Card board; 5. Contact piece; 6. Groove; 7. Arc surface. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the specification of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] For a better understanding of the present invention, the above content will be described in detail below in conjunction with specific embodiments.

[0034] Embodiment 1: Please refer to the attached Figure 1 - attached Figure 5, an embodiment of the present invention provides a method for adding capacitive coupling to a cavity broadband filter, including the following steps: setting a cavity 1 in the broadband filter, where several resonant posts 2 are arranged in the cavity 1, and the resonant posts 2 are arranged at a predetermined spacing to form the resonant mode of the filter; installing a capacitor plate 3 inside the cavity 1, the capacitor plate 3 straddles at least one resonant post 2, and affects the energy transmission between the resonant posts 2 through electric field coupling; both end portions of the capacitor plate 3 penetrate through the cavity 1 and are grounded to form a transmission zero point.

[0035] In this embodiment, a cavity 1 is set in the broadband filter, and several resonant posts 2 are arranged in the cavity 1. Among them, the resonant posts 2 are made of conductive materials and are arranged at a predetermined spacing and a specific arrangement to form the resonant mode of the filter, thereby determining the passband and stopband characteristics of the signal; and a capacitor plate 3 is also installed inside the cavity 1, and the capacitor plate 3 straddles at least one resonant post 2, and changes the energy transmission characteristics between the resonant posts 2 through electric field coupling to optimize the frequency response and selectivity of the filter. At the same time, both end portions of the capacitor plate 3 penetrate through the cavity 1 and are grounded to form a transmission zero point, effectively enhancing the out-of-band rejection ability, reducing unnecessary parasitic resonances, and enabling the filter to achieve better suppression and signal integrity in a wide frequency band range.

[0036] The material of the capacitor plate 3 is set as a metal material or a high-dielectric-constant ceramic material, and the capacitor plate 3 is applied to a cavity 1 broadband filter with a center frequency range of 1 - 10 GHz and a relative bandwidth greater than 30%. Metal materials include: copper, silver, aluminum, gold, and nickel; high-dielectric-constant ceramic materials include: lithium niobate, barium titanate, lead magnesium niobate, lead titanate niobate, alumina, and high-dielectric ceramics with a dielectric constant greater than 50.

[0037] In this embodiment, the material of the capacitor plate 3 can be selected as a metal material or a high-dielectric-constant ceramic material to meet the requirements of high-frequency broadband filtering, where:

[0038] Metal materials have good electrical conductivity and low-loss characteristics, and are suitable for high-power and low-loss filtering applications, while high-dielectric-constant ceramic materials can provide higher capacitance values, improve the coupling strength and frequency regulation ability;

[0039] Metal materials include: copper (Cu), silver (Ag), aluminum (Al), gold (Au), and nickel (Ni), and these materials have excellent electrical conductivity and stability, which can reduce the insertion loss and improve the filter efficiency; high-dielectric-constant ceramic materials include: lithium niobate (LiNbO 3 ), barium titanate (BaTiO 3 ), lead magnesium niobate (PMN), lead titanate niobate (PTN), alumina (Al2O 3), and other high-dielectric ceramic materials with a dielectric constant greater than 50. These materials have excellent dielectric properties in high-frequency environments, can effectively enhance the capacitive coupling effect of the filter, and optimize the frequency selection characteristics.

[0040] Please refer to the appendix Figure 2 - appendix Figure 4 , an air gap is provided between the capacitor plate 3 and the resonant column 2 for adjusting the capacitive coupling strength. The capacitor plate 3 includes: a first branch segment 33, a second straight segment, and a third branch segment 35; wherein, a first grounding end 31 and a second grounding end 32 are respectively provided on the far sides of the first branch segment 33 and the third branch segment 35 for passing through the cavity 1 and grounding. The distance between the first branch segment 33 and the third branch segment 35 spans at least one resonant column 2. The first branch segment 33, the third branch segment 35, and the resonant column 2 are parallel to each other, and the second straight segment is perpendicular to or forms an inclination angle with the first branch segment 33 and the third branch segment 35.

[0041] In this embodiment, the capacitor plate 3 is composed of a first branch segment 33, a second straight segment, and a third branch segment 35. Among them, the first branch segment 33, the third branch segment 35, and the resonant column 2 are parallel to each other, and a first grounding end 31 and a second grounding end 32 are respectively provided on the far sides of the first branch segment 33 and the third branch segment 35, and the first grounding end 31 and the second grounding end 32 respectively pass through both sides of the cavity 1 and are grounded to the outside, so as to ensure that the capacitor plate 3 can effectively form a transmission zero point and improve the suppression degree and signal selectivity of the filter.

[0042] Please refer to the appendix Figure 5 , a clamping plate 4 is provided inside the cavity 1. The clamping plate 4 is fixedly connected to the inner wall of the broadband filter. A contact piece 5 is fixedly connected to one side of the clamping plate 4, and one side of the contact piece 5 is in contact with the edge of the second straight segment. An arc surface 7 is provided on one side of the clamping plate 4, and the cross section of the contact piece 5 is set to be arc-shaped, and a groove 6 is provided on one side of the contact piece 5, and the edge of the second straight segment is in contact with the inner wall of the groove 6. Several resonant columns 2 are cylindrical or columnar.

[0043] In this embodiment, the clamping plate 4 can be used to support the second straight segment of the capacitor plate 3, thereby ensuring the stability of the capacitor plate 3 inside the cavity 1. The clamping plate 4 can be made of an elastic material. When installing the capacitor plate 3, the capacitor plate 3 can be clamped in the clamping plate 4 by pressing the capacitor plate 3. At the same time, one side of the clamping plate 4 is an arc surface 7, so that the second straight segment of the capacitor plate 3 can be avoided from being scratched. In addition, an arc-shaped contact piece 5 is provided on one side of the clamping plate 4. Therefore, when the installation of the capacitor plate 3 is completed, the groove 6 on one side of the arc-shaped contact piece 5 will contact the capacitor plate 3, and then the capacitor plate 3 will be clamped.

[0044] Working principle: This device is based on the principles of capacitive coupling and cavity 1 resonance. When in use, by arranging a plurality of resonant columns 2 inside the broadband filter of the cavity 1 and arranging them at a specific spacing, the resonant mode of the filter is formed, and the transmission characteristics of the signal are determined;

[0045] By making the capacitor plate 3 span at least one resonant post 2, and the two end portions of the capacitor plate 3 penetrate through the cavity 1 and are grounded, a transmission zero point is formed, and the energy transmission between the resonant posts 2 is affected by electric field coupling, thereby optimizing the suppression degree and bandwidth characteristics of the filter;

[0046] Meanwhile, the material of the capacitor plate 3 can be selected as metal or high-dielectric constant ceramic to enhance the capacitance effect and improve the coupling ability. At the same time, the capacitor plate 3 can be clamped by the clamping plate 4 and the contact piece 5, so that the capacitor plate 3 is fixed in the cavity 1 broadband filter;

[0047] Therefore, when the signal is transmitted between the resonant posts 2, it is affected by the coupling action of the capacitor plate 3 to form an optimized frequency response characteristic, so that the filter can achieve high-bandwidth and low-loss signal processing capabilities in the frequency range of 1 to 10 GHz.

[0048] Embodiment 2

[0049] Comparative experiment:

[0050] 1. Experimental purpose

[0051] Verify whether a capacitor plate grounded at both ends can form a transmission zero point at the low end of the passband and improve the suppression effect in the broadband filter of this cavity. At the same time, compare the performance differences between the two structures of 7th order + capacitor plate and 9th order without capacitor plate to determine whether the filter order can be reduced and the size and performance can be optimized.

[0052] 2. Sample preparation

[0053] Sample 1: (Embodiment 1, 7th order cavity broadband filter + capacitor plate), Sample 2: (Comparative Example 1, 9th order cavity broadband filter, without capacitor plate).

[0054] 3. Experimental equipment

[0055]

[0056]

[0057] 4. Experimental test procedure

[0058] (1) Connect the test equipment

[0059] Use an SMA RF coaxial cable to connect the input end of the filter to the RF signal source and the output end to the vector network analyzer (VNA).

[0060] Calibrate (use a standard component to calibrate the vector network analyzer to eliminate system errors).

[0061] (2) Measure the S parameters

[0062] Incentive Signal Setting

[0063] Set the frequency range of the signal source to 0.5 GHz - 2.5 GHz.

[0064] Select an appropriate power level (such as 0 dBm) as the input signal.

[0065] Collect S21 (insertion loss) and S11 (reflection coefficient).

[0066] Measure S21 (transmission coefficient) and S11 (reflection coefficient) on a vector network analyzer (VNA).

[0067] Record the passband characteristics, insertion loss, transmission zeros, and rejection ratio of the filter.

[0068] Key Parameter Analysis

[0069] Pay attention to the transmission zero at 1130 MHz and its rejection ratio.

[0070] Compare the rejection ratio, insertion loss, and passband characteristics of the 7th - order + capacitor chip (sample one) and the 9th - order without capacitor chip (sample two).

[0071] Repeated Measurements

[0072] Measure each sample 3 times and take the average to ensure data stability.

[0073] 5. Data Recording

[0074] As shown in Table 1:

[0075] 4. Data Recording

[0076] Test item Sample 1 (7th order + capacitor chip) Sample 2 (9th order without capacitor chip) Number of resonator columns 7 9 Transmission zero position 1130 MHz No obvious zero Suppression ratio at 1130 MHz 50 dB <50dB Insertion loss (dB) Low Relatively high Passband range (GHz) 1.2–1.7 1.2–1.7 Filter size Small Large Order required to achieve 50 dB 7th order 9th order

[0077] Experimental Summary

[0078] Through the 7th - order + capacitor chip solution, a transmission zero is successfully formed at 1130 MHz, and a rejection ratio of 50 dB is achieved, proving the feasibility of this solution.

[0079] Reduce the filter order and improve performance:

[0080] The 7th - order + capacitor chip solution achieves the same rejection ratio as a 9th - order filter, but with a smaller size and lower insertion loss.

[0081] If the traditional solution is adopted, at least 9th - order or higher is required to achieve a rejection ratio of 50 dB.

[0082] Optimize the filter design:

[0083] Compared with the traditional solution, this method optimizes the filter volume, improves the signal transmission quality, and reduces costs and insertion loss at the same time.

[0084] The addition of the capacitor chip is crucial, forming a transmission zero at 1130 MHz and enhancing the out-of-band rejection ability.

[0085] Applicability analysis:

[0086] This method is applicable to the design of broadband cavity filters, especially suitable for wireless communication systems that require high rejection, low insertion loss, and compact size.

[0087] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for adding capacitance coupling to a cavity broadband filter, characterized in that: The following steps are involved: A cavity (1) is arranged in a broadband filter, a plurality of resonant columns (2) are arranged in the cavity (1), and the resonant columns (2) are arranged at a predetermined interval to form a resonant mode of the filter; A capacitor sheet (3) is installed inside the cavity (1), wherein the capacitor sheet (3) spans over at least one resonant column (2) and affects energy transmission between the resonant columns (2) through electric field coupling; The two side ends of the capacitor sheet (3) penetrate the cavity (1) and are grounded to form a transmission zero point.

2. The method for adding capacitance coupling to a cavity broadband filter according to claim 1, characterized in that: The material of the capacitor sheet (3) is set to be a metal material or a high dielectric constant ceramic material, and the capacitor sheet (3) is applied to a cavity broadband filter with a center frequency range of 1 to 10 GHz and a relative bandwidth greater than 30%.

3. The method for adding capacitance coupling to a cavity broadband filter according to claim 2, characterized in that: The metal materials include: copper, silver, aluminum, gold and nickel; The high dielectric constant ceramic materials include: lithium niobate, barium titanate, lead magnesium niobate, lead titanate niobate, aluminum oxide, and high dielectric constant ceramic materials with a dielectric constant greater than 50.

4. The method for adding capacitance coupling to a cavity broadband filter according to claim 1, characterized in that: An air gap is provided between the capacitor sheet (3) and the resonant column (2) for adjusting the capacitance coupling strength.

5. The method for adding capacitance coupling to a cavity broadband filter according to claim 1, characterized in that: The capacitor sheet (3) comprises: a branch segment 1 (33), a straight segment 2 (34) and a branch segment 3 (35); Wherein, a grounding terminal 1 (31) and a grounding terminal 2 (32) are respectively arranged on the far sides of the branch segment 1 (33) and the branch segment 3 (35), which are used to penetrate the cavity (1) and be grounded.

6. The method for adding capacitance coupling to a cavity broadband filter according to claim 5, characterized in that: The distance between the branch segment 1 (33) and the branch segment 3 (35) at least spans one resonant column (2).

7. The method for adding capacitance coupling to a cavity broadband filter according to claim 6, characterized in that: The branch section 1 (33), the branch section 3 (35) and the resonant column (2) are parallel to each other, and the straight section 2 (34) and the branch section 1 (33) and the branch section 3 (35) are perpendicular to each other or form an inclination angle.

8. The method for adding capacitance coupling to a cavity broadband filter according to claim 3, characterized in that: A card plate (4) is provided inside the cavity (1), the card plate (4) is fixedly connected to the inner wall of the broadband filter, one side of the card plate (4) is fixedly connected to a contact sheet (5), and one side of the contact sheet (5) is in contact with the edge of the second straight segment (34).

9. The method for adding capacitance coupling to a cavity broadband filter according to claim 8, characterized in that: One side of the clamping plate (4) is provided with an arc surface (7), the cross section of the contact piece (5) is arranged to be arc-shaped, and one side of the contact piece (5) is provided with a groove (6), and the edge of the second straight section (34) is in contact with the inner wall of the groove (6).

10. The method for adding capacitance coupling to a cavity broadband filter according to claim 1, characterized in that: A plurality of the resonant columns (2) are cylindrical or columnar.

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