A method of cavity broadband filter plus capacitance coupling

Abstract

The application relates to the field of wideband filters, and discloses a cavity wideband filter capacitive coupling method, which comprises the following steps: a cavity is arranged in a wideband filter, a plurality of resonance columns are arranged in the cavity, the resonance columns are arranged at a predetermined interval to form a resonance mode of the filter; a capacitor sheet is mounted in the cavity, the capacitor sheet spans at least one resonance column, and the capacitor sheet affects energy transmission between the resonance columns through electric field coupling; and both side ends of the capacitor sheet penetrate through the cavity and are grounded to form a transmission zero point. The capacitor sheet is arranged in the cavity wideband filter to form a transmission zero point, improve an out-of-band suppression degree, and enable a 7-order filter to achieve the effect of a 9-order filter. The method not only ensures the same suppression degree, but also significantly reduces the volume of the filter, realizes miniaturized design, and meets the space and weight limitation requirements.

Description

Technical Field

[0001] This invention relates to the field of broadband filters, specifically to a method for adding capacitive coupling to a cavity broadband filter. Background Technology

[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. Capacitive coupling is a common method in filter design, which can be used to adjust the filter's frequency response characteristics, optimize transmission zeros, and improve out-of-band rejection.

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

[0004] Especially in the design of cavity ultrawideband bandpass filters, the large bandwidth requirements make it difficult to effectively control the transmission zeros at the low end of the passband, resulting in difficulties in optimizing out-of-band rejection. The application of traditional capacitive coupling methods in such filters is limited, making it extremely difficult to add zeros at the low end of the passband to improve the filter's rejection.

[0005] Due to the limited size of cavity filters, it is difficult to improve the suppression performance simply by increasing the resonant order. Therefore, existing designs cannot simultaneously meet the requirement of high suppression performance at the low end of the passband within the same bandwidth and size. This technological bottleneck restricts the miniaturization of cavity filters, making them difficult to meet engineering requirements in ultra-wideband applications with high suppression requirements. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this 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 that it cannot meet the requirements for large low-end suppression in the passband under the same bandwidth and volume, as well as the requirements for miniaturization of cavity filters.

[0007] To achieve the above objectives, the present invention provides a method for adding capacitive coupling to a cavity broadband filter, comprising the following steps:

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

[0009] A capacitor sheet is installed inside the cavity, the capacitor sheet spans at least one resonant pillar, and affects the energy transfer between the resonant pillars through electric field coupling;

[0010] The two ends of the capacitor sheet penetrate the cavity and are grounded to form a transmission zero point.

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

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

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

[0014] Preferably, an air gap is provided between the capacitor sheet and the resonant pillar to adjust the capacitive coupling strength.

[0015] Preferably, the capacitor sheet includes: a first branch, a second straight branch, and a third branch;

[0016] Among them, grounding terminal one and grounding terminal two are respectively provided on the far side of branch segment one and branch segment three, which are used to penetrate the cavity and ground.

[0017] Preferably, the distance between the first and third branches spans at least one resonant column.

[0018] Preferably, the first and third branches are parallel to the resonant column, and the second straight branch is perpendicular to or forms an angle with the first and third branches.

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

[0020] Preferably, one side of the card plate is provided with an arc surface, and the cross-section of the contact piece is set to arc shape, and one side of the contact piece is provided with a groove, and the edge of the straight section two contacts the inner wall of the groove.

[0021] Preferably, some of the resonant pillars are cylindrical or columnar.

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

[0023] 1. This invention improves out-of-band rejection by adding capacitors to a cavity broadband filter to create a transmission zero, enabling a 7th-order filter to achieve the effect of a 9th-order filter. This not only ensures the same rejection but also significantly reduces the filter's size, achieving miniaturization and meeting space and weight constraints.

[0024] 2. This invention enhances signal transmission characteristics by employing capacitor-coupled plates, reducing unnecessary energy loss between resonant pillars. Compared to traditional 9th-order filters, this invention significantly reduces insertion loss and improves signal transmission integrity at the same suppression level, making the filter more widely applicable in high-performance wireless communication systems. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the broadband filter section of the present invention;

[0026] Figure 2 This is a schematic diagram of the internal structure of the cavity in this invention;

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

[0028] Figure 4 This is a schematic diagram of the two-segment structure of the present invention;

[0029] Figure 5 This is a schematic diagram of the card plate structure of the present invention;

[0030] Figure 6 This is a schematic diagram of the comparative experimental results in Embodiment 2 of the present invention.

[0031] Among them, 1. cavity; 2. resonant column; 3. capacitor sheet; 31. grounding terminal one; 32. grounding terminal two; 33. branch one; 34. branch two; 35. branch three; 4. clamping plate; 5. contact piece; 6. groove; 7. arc surface. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] To better understand the present invention, the above content will be described in detail below with reference to specific embodiments.

[0034] Example 1: Please refer to the appendix Figure 1 - Appendix Figure 5This invention provides a method for adding capacitive coupling to a cavity broadband filter, comprising the following steps: setting a cavity 1 in a broadband filter, wherein a plurality of resonant pillars 2 are provided in the cavity 1, and the resonant pillars 2 are arranged at a predetermined interval to form the resonant mode of the filter; installing a capacitor 3 inside the cavity 1, the capacitor 3 spanning at least one resonant pillar 2, and influencing the energy transfer between the resonant pillars 2 through electric field coupling; the two ends of the capacitor 3 penetrating the cavity 1 and grounded to form a transmission zero point.

[0035] In this embodiment, a cavity 1 is provided in the broadband filter, and a plurality of resonant pillars 2 are provided inside the cavity 1. The resonant pillars 2 are made of conductive material and are arranged at predetermined intervals and in a specific arrangement to form the resonant mode of the filter, thereby determining the passband and stopband characteristics of the signal. A capacitor 3 is also installed inside the cavity 1, and the capacitor 3 spans at least one resonant pillar 2. It changes the energy transfer characteristics between the resonant pillars 2 through electric field coupling to optimize the frequency response and selectivity of the filter. At the same time, the two ends of the capacitor 3 penetrate the cavity 1 and are grounded to form transmission zeros, which effectively enhances the out-of-band rejection capability, reduces unnecessary parasitic resonances, and enables the filter to achieve better suppression and signal integrity in a wide frequency range.

[0036] The capacitor 3 is made of either a metallic material or a high-dielectric-constant ceramic material, and is used in a cavity 1 broadband filter with a center frequency range of 1–10 GHz and a relative bandwidth greater than 30%. Metallic 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 other high-dielectric-constant ceramic materials with a dielectric constant greater than 50.

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

[0038] Metallic materials have good conductivity and low loss characteristics, making them suitable for high-power and low-loss filtering applications, while high dielectric constant ceramic materials can provide higher capacitance values, improving coupling strength and frequency control capability.

[0039] Metallic materials include copper (Cu), silver (Ag), aluminum (Al), gold (Au), and nickel (Ni). These materials possess excellent conductivity and stability, which can reduce insertion loss and improve filter efficiency. High dielectric constant ceramic materials include lithium niobate (LiNbO3), barium titanate (BaTiO3), lead magnesium niobate (PMN), lead titanate niobate (PTN), alumina (Al2O3), and other high dielectric ceramic materials with a dielectric constant greater than 50. These materials exhibit excellent dielectric properties in high-frequency environments, which can effectively enhance the capacitive coupling effect of the filter and optimize frequency selectivity.

[0040] Please see the appendix Figure 2 - Appendix Figure 4 An air gap is provided between the capacitor sheet 3 and the resonant pillar 2 to adjust the capacitive coupling strength. The capacitor sheet 3 includes: a first branch 33, a second straight branch, and a third branch 35; wherein, the far side of the first branch 33 and the third branch 35 are respectively provided with a first ground terminal 31 and a second ground terminal 32 for passing through the cavity 1 and grounding. The spacing between the first branch 33 and the third branch 35 spans at least one resonant pillar 2. The first branch 33, the third branch 35, and the resonant pillar 2 are parallel to each other, and the second straight branch is perpendicular to the first branch 33 and the third branch 35 or forms an angle with each other.

[0041] In this embodiment, the capacitor sheet 3 is composed of a first branch 33, a second straight branch, and a third branch 35. The first branch 33, the third branch 35, and the resonant pillar 2 are parallel to each other. The far side of the first branch 33 and the third branch 35 are respectively provided with a first ground terminal 31 and a second ground terminal 32. The first ground terminal 31 and the second ground terminal 32 pass through both sides of the cavity 1 and are grounded to the outside, thereby ensuring that the capacitor sheet 3 can effectively form a transmission zero point and improve the suppression degree and signal selectivity of the filter.

[0042] Please see the appendix Figure 5 The cavity 1 contains a retaining plate 4, which is fixedly connected to the inner wall of the broadband filter. A contact piece 5 is fixedly connected to one side of the retaining plate 4, and one side of the contact piece 5 contacts the edge of the straight section 2. One side of the retaining plate 4 has an arc surface 7, and the contact piece 5 has an arc-shaped cross-section. One side of the contact piece 5 has a groove 6, and the edge of the straight section 2 contacts the inner wall of the groove 6. Several resonant pillars 2 are cylindrical or columnar.

[0043] In this embodiment, the clamping plate 4 can support the straight section 2 of the capacitor sheet 3, thereby ensuring the stability of the capacitor sheet 3 inside the cavity 1. The clamping plate 4 can be made of elastic material. When installing the capacitor sheet 3, pressing the capacitor sheet 3 will clamp it into the clamping plate 4. At the same time, one side of the clamping plate 4 is an arc surface 7, which can avoid scratching the straight section 2 of the capacitor sheet 3. One side of the clamping plate 4 is also provided with an arc-shaped contact piece 5. Therefore, after the capacitor sheet 3 is installed, the groove 6 on one side of the arc-shaped contact piece 5 will contact the capacitor sheet 3, thereby clamping the capacitor sheet 3.

[0044] Working principle: This device is based on the principle of capacitive coupling and cavity 1 resonance. In use, multiple resonant pillars 2 are arranged inside the broadband filter of cavity 1 and arranged at a specific interval to form the resonant mode of the filter and determine the signal transmission characteristics.

[0045] By having the capacitor 3 span at least one resonant pillar 2, and with both ends of the capacitor 3 penetrating the cavity 1 and grounded, a transmission zero point is formed, and the energy transfer between the resonant pillars 2 is affected by electric field coupling, thereby optimizing the suppression degree and bandwidth characteristics of the filter.

[0046] Meanwhile, the material of capacitor sheet 3 can be metal or high dielectric constant ceramic to enhance the capacitance effect and improve the coupling ability. At the same time, the clamping plate 4 and contact piece 5 can be used to clamp capacitor sheet 3, thereby fixing capacitor sheet 3 inside the broadband filter of cavity 1.

[0047] Therefore, when the signal is transmitted between the resonant pillars 2, it is coupled by the capacitor sheet 3, forming an optimized frequency response characteristic, which enables the filter to achieve high bandwidth and low loss signal processing capability in the frequency range of 1 to 10 GHz.

[0048] Example 2

[0049] Comparative experiment:

[0050] 1. Experimental Objective

[0051] This study aims to verify whether adding a capacitor with both ends grounded between the 3rd and 5th orders in the cavity broadband filter can create a transmission zero at the low end of the passband and improve the suppression effect. At the same time, it compares the performance differences between the 7th order + capacitor and the 9th order without capacitor to determine whether the filter order can be reduced and the size and performance optimized.

[0052] 2. Sample preparation

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

[0054] 3. Experimental equipment

[0055]

[0056]

[0057] 4. Experimental Testing Procedure

[0058] (1) Connect the test equipment

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

[0060] Perform calibration (use standard parts to calibrate the vector network analyzer and eliminate systematic errors).

[0061] (2) Measuring S-parameters

[0062] Excitation signal settings

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

[0064] Choose an appropriate power level (e.g., 0dBm) as the input signal.

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

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

[0067] Record the filter's passband characteristics, insertion loss, transmission zeros, and suppression.

[0068] Key parameter analysis

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

[0070] Compare the suppression, insertion loss, and passband characteristics of a 7th-order capacitor sheet (Sample 1) and a 9th-order capacitorless sheet (Sample 2).

[0071] Repeated measurements

[0072] Each sample was measured three times, and the average value was taken to ensure data stability.

[0073] 5. Data Recording

[0074] As shown in Table 1:

[0075] 4. Data Recording

[0076] Test Items Sample 1 (7th order + capacitor) Sample 2 (9th-order capacitorless sheet) Number of resonant pillars 7 9 Transmit zero position 1130MHz No obvious zero point Suppression at 1130MHz 50dB <50dB Insertion loss (dB) Low Relatively high Passband range (GHz) 1.2–1.7 1.2–1.7 Filter size Small big Order required to achieve 50dB 7th level 9th level

[0077] Experiment Summary

[0078] By using a 7th-order capacitor scheme, a transmission zero was successfully formed at 1130MHz, achieving a suppression level of 50dB, proving the feasibility of the scheme.

[0079] Reduce filter order to improve performance:

[0080] The 7th-order filter with capacitors achieves the same suppression as a 9th-order filter, but with a smaller size and lower insertion loss.

[0081] If a traditional approach is used, at least a 9th order or higher is required to achieve a suppression level of 50dB.

[0082] Optimize filter design:

[0083] Compared to traditional methods, this approach optimizes filter size, improves signal transmission quality, and reduces cost and insertion loss.

[0084] The addition of capacitors is key, creating a transmission zero at 1130MHz and enhancing out-of-band rejection capability.

[0085] Applicability analysis:

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

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

Claims

1. A method for adding capacitive coupling to a cavity broadband filter, characterized in that, Includes the following steps: A cavity (1) is provided in a broadband filter, and a plurality of resonant pillars (2) are provided in the cavity (1). The resonant pillars (2) are arranged at a predetermined interval to form the resonant mode of the filter. A capacitor sheet (3) is installed inside the cavity (1). The capacitor sheet (3) spans at least one resonant pillar (2) and affects the energy transfer between the resonant pillars (2) through electric field coupling. The two ends of the capacitor sheet (3) penetrate the cavity (1) and are grounded to form a transmission zero point; The capacitor (3) is made of metal or high dielectric constant ceramic material, and the capacitor (3) is applied to a cavity broadband filter with a center frequency range of 1 to 10 GHz and a relative bandwidth of more than 30%. The capacitor sheet (3) includes: a first branch (33), a second straight branch (34), and a third branch (35); Among them, the far side of the first branch (33) and the third branch (35) are respectively provided with grounding terminal one (31) and grounding terminal two (32) for penetrating the cavity (1) and grounding; The distance between the first (33) and the third (35) branch spans at least one resonant column (2); The first branch (33), the third branch (35) and the resonant column (2) are parallel to each other, and the second straight branch (34) is perpendicular to the first branch (33) and the third branch (35) or forms an angle with each other.

2. The method for adding capacitive coupling to a cavity broadband filter according to claim 1, characterized in that, The metallic 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, alumina, and high dielectric ceramic materials with a dielectric constant greater than 50.

3. The method for adding capacitive 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 pillar (2) to adjust the capacitive coupling strength.

4. The method for adding capacitive coupling to a cavity broadband filter according to claim 1, characterized in that, The cavity (1) is provided with a card plate (4), which is fixedly connected to the inner wall of the broadband filter. A contact piece (5) is fixedly connected to one side of the card plate (4), and one side of the contact piece (5) contacts the edge of the straight section (34).

5. The method for adding capacitive coupling to a cavity broadband filter according to claim 4, characterized in that, The card plate (4) has an arc surface (7) on one side, and the contact piece (5) has an arc-shaped cross section. The contact piece (5) has a groove (6) on one side, and the edge of the straight section (34) is in contact with the inner wall of the groove (6).

6. The method for adding capacitive coupling to a cavity broadband filter according to claim 1, characterized in that, Some of the resonant pillars (2) are cylindrical or columnar.

Images