Dielectric filter and processing method thereof

Abstract

The invention discloses a dielectric filter and a processing method thereof. The dielectric filter comprises a plurality of resonance units, a coupling structure and a waveguide structure. The resonance unit comprises a first ceramic body and a second ceramic body; a first metal conducting layer is arranged on the surface of the first ceramic body, a plurality of adjusting bands are etched on the surface of the first metal conducting layer, and the adjusting bands are used for adjusting the frequency of the filter; the second ceramic body and the first ceramic body are co-sintered into a whole, and a second metal conductive layer is arranged on the surface of the second ceramic body; the coupling structure is used for realizing signal coupling between resonators and signal transmission between the resonators and an external circuit, and comprises a plurality of coupling grooves which are formed in the first ceramic body and penetrate through the thickness direction of the first ceramic body and through grooves which are formed in the second ceramic body and are the same as the coupling grooves in position and shape. The waveguide structure is used for accommodating a plurality of resonators and providing electromagnetic shielding. The problem that high-order mode harmonic waves of an existing dielectric filter are close is solved, and a new solution is provided for the far end of a whole machine system.

Description

Technical Field

[0001] This invention relates to the field of filters and their fabrication technology, specifically to a dielectric filter and its fabrication method. Background Technology

[0002] With the rapid development of 5G communication, base station construction, and the microwave radio frequency field, dielectric filters, due to their high Q value, miniaturization, and low loss characteristics, have become core components of radio frequency front-ends and are widely used in signal filtering, interference suppression, and other scenarios. Their basic principle is to achieve selective filtering of specific frequency signals and suppression of spurious signals through the synergistic effect of multiple resonators. The material properties, structural design, and coupling method of the resonators directly determine the filter's performance.

[0003] Existing dielectric filters typically use high-dielectric materials (such as ceramics) with a single dielectric constant as the resonator substrate. The inherent resonant frequency is determined by designing the resonator's geometry (e.g., cylinder, rectangular block) and dimensions. The coupling strength is controlled by adjusting the distance and relative position between resonators to achieve the target frequency response. To ensure signal transmission efficiency, the input and output terminals are often connected to external circuits using microstrip lines or coaxial lines. Electromagnetic shielding is achieved using metal or dielectric waveguide structures to reduce signal leakage and external interference. The rapid development of wireless communication systems demands filters with low insertion loss, high suppression, high power handling, low cost, and miniaturization. Among these, miniaturized dielectric filters made from high-dielectric-constant ceramic dielectric materials, with silver plating on the dielectric block surface for electromagnetic shielding, are widely used in various RF modules due to their smaller size and weight compared to traditional metal waveguide filters.

[0004] However, existing dielectric filters still have the following significant limitations:

[0005] Firstly, the suppression of higher-order mode harmonics presents a significant challenge. Traditional dielectric filters use only a single dielectric material, meaning the position of the higher-order modes in the resonator is uniquely determined by the material's properties and dimensions. Once the substrate is selected, the higher-order mode frequency position is fixed and difficult to adjust flexibly. In practical applications, higher-order mode harmonics tend to approach the operating frequency band, forming far-end spurious interference and affecting the signal purity of the entire system.

[0006] Secondly, the additional low-pass filter increases cost and insertion loss. To address high-order mode harmonic interference, existing solutions generally require the integration of an additional low-pass filter on the PCB board to suppress far-end spurious signals through the low-pass structure. This design not only increases the overall cost of the filter (including the cost of the low-pass device, PCB routing space, and assembly costs), but also increases signal insertion loss due to the inherent losses of the low-pass filter, thus reducing the signal transmission efficiency of the entire system.

[0007] Third, the design flexibility is insufficient. Due to the characteristics of materials with a single dielectric constant, traditional filters have limited room for maneuver in terms of adjusting the position of higher-order modes and optimizing bandwidth, making it difficult to adapt to the diverse needs of different frequency bands and scenarios. Especially with the trend of communication technology developing towards higher frequency bands and wider frequency bands, their performance bottlenecks are becoming increasingly prominent.

[0008] Therefore, how to achieve flexible control of higher-order mode positions, reduce costs and insertion loss through material innovation and structural optimization without relying on additional low-pass filters has become a key technical problem that urgently needs to be solved in the field of dielectric filters. Summary of the Invention

[0009] In order to overcome the shortcomings of the prior art, the purpose of this application is to provide a dielectric filter that solves the problem of high-order mode harmonics in existing dielectric filters and provides a new solution for the remote end of the whole system.

[0010] To solve the above problems, the technical solution adopted in this application is as follows:

[0011] This application provides a dielectric filter, including multiple resonant units, a coupling structure, and a waveguide structure. Each resonant unit includes a first ceramic body and a second ceramic body. A first conductive metal layer is disposed on the surface of the first ceramic body, and several adjustment bands are etched on the surface of the first conductive metal layer for adjusting the filter frequency. The second ceramic body is co-fired with the first ceramic body to form a single unit, and a second conductive metal layer is disposed on the surface of the second ceramic body. The coupling structure is used to realize signal coupling between resonators and signal transmission with external circuits, including several coupling grooves disposed on the first ceramic body and extending through the thickness direction of the first ceramic body, and through grooves disposed on the second ceramic body with the same position and shape as the coupling grooves. The waveguide structure is used to accommodate multiple resonators and provide electromagnetic shielding.

[0012] As a further preferred embodiment, the first ceramic body and the second ceramic body described in this application are made of ceramic materials with different dielectric constants, and the dielectric constant of the second ceramic body is greater than that of the first ceramic body.

[0013] As a further preferred embodiment, the dielectric constant εr of both the first ceramic body and the second ceramic body described in the embodiments of this application is in the range of 5 to 90.

[0014] As a further preferred embodiment, the dielectric constant of the first ceramic body in the present application embodiment is 5-9, and the dielectric constant of the second ceramic body is 9-16.

[0015] As a further preferred embodiment, the relationship between the thickness L2 of the second ceramic body and the thickness L1 of the first ceramic body in the embodiments of this application is L2 / L1 = 5-10.

[0016] As a further preferred embodiment, the multiple resonators described in this application are arranged in the waveguide structure in a cascaded or alternating manner.

[0017] As a further preferred embodiment, the coupling grooves described in this application are located between adjacent adjustment bands, so that the coupling grooves and adjustment bands are arranged alternately.

[0018] This application also provides a method for fabricating a dielectric filter, the method comprising:

[0019] Preparation of the second ceramic body: ceramic powder with a composite dielectric constant of the second ceramic body is selected, granulated, and then dry-pressed into a green body in a mold. After debinding and sintering, the surface is metallized to obtain the second ceramic body.

[0020] Preparation of the first ceramic body: ceramic powder with a composite dielectric constant of the first ceramic body is selected, and the powder is ball-milled to make a slurry. The slurry is cast onto a substrate of a predetermined size, dried and trimmed, and then sintered to obtain the first ceramic body.

[0021] The first ceramic body and the second ceramic body are joined together with an inorganic binder and then placed in a sintering furnace to be fired into one piece.

[0022] Etching and grooving: Adjustment bands with different patterns and shapes are etched on the surface of the first ceramic body, and coupling grooves are started between adjacent adjustment bands.

[0023] As a further preferred embodiment, in the preparation method described in this application, during the step of preparing the second ceramic body, the particle size after granulation is 70–90 μm, and the specific surface area is <3.5 m². 2 / g; During the debinding process, the temperature is 500℃~700℃, and during sintering, the temperature is 1250℃~1500℃, and the sintering time is 120min~360min.

[0024] As a further preferred embodiment, in the preparation method described in this application, during the step of preparing the first ceramic body, the particle size of the powder after ball milling is 1–2 μm, and the specific surface area is controlled at 15–20 m². 2 / g; The ball-milled powder is mixed with solvent, binder, dispersant and plasticizer to form a slurry, which is then cast, laminated and sintered to form the first ceramic body.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The dielectric filter described in this application adopts a new design structure that allows the far-end suppression of the ceramic itself to meet the requirements of the whole machine, without the need to add an additional low-pass filter to suppress far-end spurious emissions, thus significantly reducing the cost of the filter.

[0027] 2. The dielectric filter described in this application can be used in combination with two ceramic powders of different dielectric constants, breaking the limitation of the fixed position of the higher-order mode in the traditional single dielectric material resonator, realizing flexible adjustment of the position of the higher-order mode, keeping the higher-order mode harmonics away from the working frequency band, and fundamentally solving the problem of far-end spurious emissions caused by the higher-order mode being close to the working frequency band in traditional filters. The far-end suppression requirements of the whole machine can be met without the need for an additional low-pass filter.

[0028] 3. The dielectric filter described in this application uses an etching process to precisely control the shape (such as length, width, and spacing) of the adjustment band, which significantly improves the flexibility and accuracy of the filter frequency adjustment. This solves the limitation of traditional resonator frequency adjustment relying on size processing (which is error-sensitive), and allows the frequency error to be controlled within the frequency deviation range corresponding to ±0.01mm, thus meeting the precise matching requirements of the center frequency in different scenarios.

[0029] 4. The dielectric filter coupling slots and through slots described in this application form a through coupling channel. By adjusting the length of the coupling slots, the coupling strength between adjacent resonant units can be precisely controlled. The coupling slots, which are staggered between the adjustment bands, can avoid electromagnetic interference with the adjustment bands, ensure coupling stability, optimize the signal transmission efficiency between resonant units, reduce coupling loss, and reduce overall insertion loss. At the same time, the controllability of the coupling strength is enhanced, so that the bandwidth of the filter can be flexibly adjusted according to the requirements (such as from narrowband to broadband), adapting to the bandwidth requirements of different scenarios such as 5G base stations and microwave radio frequency.

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the dielectric filter structure described in Embodiment 1 of this application.

[0033] Figure 2 This is a schematic diagram of the dielectric filter structure described in Embodiment 1 of this application.

[0034] Figure 3 This is a graph of the S-parameters of the dielectric filter described in Embodiment 1 of this application. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] The term "comprising" and other equivalent descriptive terms used in the specification and claims of this application are intended to cover a non-exclusive inclusion, which includes both the contents explicitly described in the specification and claims and steps or units that are not described in the specification and claims but are inherent in the product, method or structure.

[0037] This application provides a dielectric filter, including multiple resonant units, a coupling structure, and a waveguide structure. Each resonant unit comprises a first ceramic body and a second ceramic body, which are co-fired together. The combination of materials with different dielectric constants alters the electromagnetic field distribution characteristics, causing a shift in the resonant frequency of higher-order mode harmonics. The position of the higher-order mode can be precisely controlled by adjusting the difference in dielectric constants and the thickness ratio of the two materials. A first conductive metal layer is disposed on the surface of the first ceramic body. Several adjustment bands are etched on the surface of the first conductive metal layer. These adjustment bands are used to adjust the frequency of the filter. The adjustment bands etched on the surface of the first conductive metal layer change the equivalent circuit parameters of the resonator. The pattern of the adjustment bands (such as length, width, and spacing) affects the surface current distribution, thereby changing the resonant frequency. By fine-tuning the adjustment band parameters, frequency calibration within a range of ±1MHz can be achieved, compensating for frequency deviations caused by manufacturing errors or temperature drift, and improving the frequency accuracy of the filter. The second ceramic body has a second conductive metal layer on its surface. The coupling structure is used to realize signal coupling between resonators and signal transmission with external circuits. It includes several coupling slots disposed on the first ceramic body and extending through the thickness direction of the first ceramic body, and through slots disposed on the second ceramic body with the same position and shape as the coupling slots. The coupling slots and through slots form a through electromagnetic channel. When electromagnetic waves propagate between resonant units, the size and position of the slots determine the coupling coefficient. During implementation, the coupling strength between adjacent resonant units can be precisely controlled by optimizing the geometric parameters of the slots, thereby achieving flexible adjustment of the filter bandwidth and reducing signal transmission loss. The waveguide structure is used to accommodate multiple resonators and provide electromagnetic shielding. The waveguide structure is made of metal or other dielectric materials. The metal or dielectric waveguide structure forms a closed cavity and uses the principle of total internal reflection to confine electromagnetic waves inside, which can provide good electromagnetic shielding effect and prevent signal leakage and interference. At the same time, it reduces parasitic coupling between resonant units and improves the out-of-band rejection capability of the filter.

[0038] Preferably, in some embodiments, the first and second ceramic bodies are made of ceramic materials with different dielectric constants, and the dielectric constant of the second ceramic body is greater than that of the first ceramic body. The combination of materials with different dielectric constants alters the electromagnetic field distribution characteristics, causing a shift in the resonant frequency of higher-order mode harmonics. The high-dielectric-constant material enhances the confinement of the electromagnetic field, pushing higher-order modes to higher frequencies, away from the operating frequency band, thereby effectively suppressing far-end spurious emissions. Preferably, the dielectric constant εr of both the first and second ceramic bodies is in the range of 5–90. Further, in some embodiments, the dielectric constant of the first ceramic body is 5–9, and the use of ceramic powder with a slightly lower dielectric constant can reduce fundamental frequency loss and improve the Q value; the dielectric constant of the second ceramic body is 9–16, and the use of ceramic powder with a slightly higher dielectric constant can enhance electromagnetic field confinement and effectively control the position of higher-order modes. The synergistic effect between the different dielectric constant materials of the first and second ceramic bodies achieves far-end suppression of higher-order modes while ensuring low insertion loss.

[0039] In some embodiments of this application, the thickness of the second ceramic body is greater than that of the first ceramic body, resulting in a larger proportion of the second ceramic body's thickness. This concentrates more electromagnetic energy in the high dielectric constant region, leading to an increase in the frequency of higher-order modes. By adjusting the thickness ratio, the frequency of higher-order modes can be pushed to more than five times the fundamental frequency. When the second ceramic body is thicker (L2 dominates), the standing wave mode of its internal electromagnetic field is more significantly affected by the thickness. Increasing L2 can lengthen the standing wave path corresponding to higher-order modes, causing the higher-order mode frequency to shift to a higher frequency band. The first ceramic body, with its smaller thickness, only has a fine-tuning effect on the fundamental frequency and lower-order higher-order modes, avoiding excessive interference with the main constraint effect. This study found that if the proportion of high dielectric constant material is insufficient, the electromagnetic field will diffuse into the low dielectric constant region, leading to increased energy leakage and insertion loss. If the proportion of L2 is too high, the first ceramic body is too thin, and its surface metal adjustment band and coupling groove are easily interfered with by the strong electromagnetic field of the second ceramic body, resulting in increased signal reflection loss. Preferably, the relationship between the thickness L2 of the second ceramic body and the thickness L1 of the first ceramic body is L2 / L1 = 5-10. The high dielectric constant second ceramic body occupies the main volume of the resonant unit (approximately 83%-91%), which can confine most of the electromagnetic field energy inside the second ceramic body, while the first ceramic body only serves as a "surface adjustment layer," guiding the edge distribution of the electromagnetic field through its low dielectric properties, forming a synergistic effect of "main constraint + edge adjustment." Setting the L2 / L1 = 5-10 ratio can push the higher-order mode frequency to more than 5 times the fundamental frequency, maintaining a sufficient distance from the operating frequency band and achieving effective suppression of far-end spurious emissions. This ensures both strong confinement of the electromagnetic field by the high dielectric material (reducing leakage loss) and sufficient "electromagnetic buffer space" for the adjustment band and coupling groove of the first ceramic body, avoiding interference and reducing insertion loss by 0.3-0.5 dB. Meanwhile, this thickness ratio ensures that the thickness of the first ceramic body is moderate, and the current distribution of the adjustment band is independent and stable, enabling fine frequency adjustment of ±1MHz to meet the stringent frequency accuracy requirements of 5G base stations. Furthermore, the thickness ratio of the first and second ceramic bodies also considers their structural compatibility in the co-firing process. The sintering shrinkage rates of the first and second ceramic bodies differ; by adjusting the volume ratio of the two materials, the shrinkage stress is balanced: a higher proportion of high-dielectric material (L2) results in higher density during dry pressing (lower shrinkage rate); a lower proportion of low-dielectric material (L1) results in slightly higher shrinkage during tape casting. This complementary relationship prevents cracking or delamination during co-firing, ensuring structural integrity.

[0040] Specifically, in some embodiments, the multiple resonators are arranged in a cascaded configuration within the waveguide structure. The resonators are arranged sequentially along the signal transmission path (e.g., a linear arrangement with the ends connected), forming a stable "main coupling" between adjacent resonators. This arrangement ensures that the coupling strength is uniformly transmitted along the signal path, guaranteeing smooth signal transmission within the passband, and is suitable for scenarios requiring wide bandwidth or linear phase response (e.g., intermediate frequency filtering in communication systems). The cascaded arrangement, through its regular linear layout, concentrates the electromagnetic interaction between resonators on adjacent units, reducing non-target coupling; the linear layout of the cascaded arrangement can fully utilize the long, narrow space of the waveguide, achieving a compact design.

[0041] In other embodiments, multiple resonators are arranged alternately within the waveguide structure. The alternating placement of resonators with different characteristics (potentially having different resonant frequencies or coupling polarities due to differences in structural parameters) (e.g., an ABAB layout) introduces "cross-coupling" (coupling between non-adjacent resonators). Cross-coupling can generate "transmission zeros" (frequency points where the signal attenuates to infinity) at the passband edge, significantly improving out-of-band rejection and effectively filtering out interference signals from adjacent frequency bands (e.g., suppressing spurious signals from adjacent channels in 5G communication). The alternating arrangement, through spatial staggering, utilizes the shielding characteristics of the waveguide structure and the electromagnetic distribution of the resonators themselves to cancel out some spurious coupling, ensuring the stable performance of each resonator's inherent characteristics (e.g., resonant frequency, quality factor). The alternating arrangement reduces lateral space occupation through staggered layout, allowing more resonators to be accommodated within the same waveguide volume (increasing the number of filter stages), thereby improving the filter's selectivity (the more stages, the steeper the out-of-band rejection).

[0042] As a further preferred embodiment, the coupling slots described in this application are located between adjacent tuning bands, with several coupling slots and tuning bands arranged alternately. Through spatial separation, the tuning bands focus on frequency tuning, while the coupling slots focus on signal coupling, ensuring that they do not interfere with each other and guaranteeing the stability and reliability of their respective functions. When the resonant unit is working, the metal conductive layer on the surface of the first ceramic body will form a specific electromagnetic field distribution (especially near the tuning band, where the electromagnetic field gradient is more obvious due to the change in the shape of the metal layer). In the region between adjacent tuning bands, the electromagnetic field distribution is relatively flat and uniform (which can be regarded as a "transition zone"). Setting the coupling slots in this "transition zone" can reduce the coupling strength fluctuation caused by the difference in the shape of the tuning bands (the tuning band pattern may be different under different frequency requirements), making the signal coupling through the coupling slots more stable; ensuring the consistency of the electromagnetic environment of multiple coupling slots, making the coupling strength between resonators uniform (e.g., cascaded resonators can ensure passband flatness through uniform coupling, and alternating resonators can precisely control the cross-coupling strength through stable coupling), thereby improving the frequency response consistency of the filter (e.g., small loss fluctuation in the passband and stable out-of-band rejection steepness).

[0043] This application also provides a method for fabricating a dielectric filter, the method comprising:

[0044] Preparation of the second ceramic body: ceramic powder with a composite dielectric constant of the second ceramic body is selected, granulated, and then dry-pressed into a green body in a mold. After debinding and sintering, the surface is metallized to obtain the second ceramic body.

[0045] Preparation of the first ceramic body: ceramic powder with a composite dielectric constant of the first ceramic body is selected, and the powder is ball-milled to make a slurry. The slurry is cast onto a substrate of a predetermined size, dried and trimmed, and then sintered to obtain the first ceramic body.

[0046] The first ceramic body and the second ceramic body are joined together with an inorganic binder and then placed in a sintering furnace to be fired into one piece.

[0047] Etching and grooving: Adjustment bands with different patterns and shapes are etched on the surface of the first ceramic body, and coupling grooves are started between adjacent adjustment bands.

[0048] As a further preferred embodiment, in the preparation method described in this application, during the step of preparing the second ceramic body, the particle size after granulation is 70–90 μm, and the specific surface area is <3.5 m². 2 / g; During the debinding process, the temperature is 500~700℃, and during sintering, the temperature is 1250℃~1500℃, and the sintering time is 120min~360min.

[0049] As a further preferred embodiment, in the preparation method described in this application, during the step of preparing the first ceramic body, the particle size of the powder after ball milling is 1–2 μm, and the specific surface area is controlled at 15–20 m². 2 / g; The ball-milled powder is mixed with a solvent (selected from ethanol, toluene, acetone or a mixture of two or more), a binder (selected from PVA, PVB, PMMA, ethyl cellulose or a mixture of two or more), a dispersant (selected from trioleic acid ester and / or phosphate ester), and a plasticizer (selected from polyethylene glycol, glycerol, phthalate ester) to form a slurry, which is then cast, laminated, and sintered to form the first ceramic body.

[0050] Example 1

[0051] like Figure 1 , Figure 2As shown, this embodiment provides an 8-cavity dielectric filter, including multiple resonant units, a coupling structure, and a waveguide structure. The resonant unit includes a first ceramic body 10 (0.5 mm thick) and a second ceramic body 20 (4 mm thick). A first conductive metal layer (silver-plated layer) is disposed on the surface of the first ceramic body 10, and several adjustment bands (ring bands) are etched on the surface of the first conductive metal layer for adjusting the frequency of the filter. The second ceramic body 20 is co-fired with the first ceramic body 10 and is disposed on the surface of the second ceramic body with a second conductive metal layer (silver-plated layer). The coupling structure is used to realize signal coupling between resonators and signal transmission with external circuits, including coupling grooves 11 disposed on the first ceramic body 10 and extending through the thickness direction of the first ceramic body (the lengths of the coupling grooves are 8.9 mm, 1.9 mm, 14.25 mm, 8.3 mm, and 2 mm, respectively) and through grooves 20 disposed on the second ceramic body 20 with the same position and shape as the coupling grooves 11. The waveguide structure (metallic material) is used to accommodate multiple resonators and provide electromagnetic shielding.

[0052] The fabrication method of this dielectric filter is as follows:

[0053] Preparation of the second ceramic body: The dielectric constant of the composite second ceramic body (Mg(Zn)) is selected. 0.5 Ti 0.5 ) 2x Ga 2-2x O4 ceramic medium (x = 0.2, electrical constant 9.5) ceramic powder is granulated and then dry-pressed into a green body in a mold. After debinding and sintering, the surface is metallized to obtain the second ceramic body.

[0054] Preparation of the first ceramic body: Ceramic powder with a dielectric constant of MgGa2O4 ceramic (dielectric constant of 9.54) was selected. After ball milling, toluene, ethyl cellulose, phosphate ester, and polyethylene glycol (mass percentages of powder, toluene, ethyl cellulose, phosphate ester, and polyethylene glycol were 70%, 20%, 5%, 2%, and 3%, respectively) were added to the powder to make a slurry. The slurry was cast onto a substrate of a predetermined size, dried, trimmed, and then sintered to obtain the first ceramic body.

[0055] The first ceramic body and the second ceramic body are joined together with an inorganic binder and then placed in a sintering furnace at a sintering temperature of 800℃ to be co-fired into one piece.

[0056] Etching and grooving: Adjustment bands with different patterns and shapes are etched on the surface of the first ceramic body, and coupling grooves are opened between adjacent adjustment bands.

[0057] As a further preferred embodiment, in the preparation method described in this application, the average particle size after granulation in the step of preparing the second ceramic body is 74.6 μm, and the specific surface area is 2.8 m².2 / g; During debinding, the temperature is 600℃, and during sintering, the temperature is 1300℃ and the sintering time is 200min.

[0058] As a further preferred embodiment, in the preparation method described in this application, during the step of preparing the first ceramic body, the average particle size of the ball-milled powder is 1.3 μm, and the specific surface area is controlled to be 17.9 m². 2 / g; The ball-milled powder is mixed with ethanol, PVA binder, trioleic acid glyceride and phosphate dispersant and polyethylene glycol plasticizer to form a slurry, which is then cast, laminated and sintered to form the first ceramic body.

[0059] Figure 3 This is a graph showing the S-parameters of the dielectric filter described in Example 1. The graph shows that, in the 2.5 GHz to 2.7 GHz frequency band, S... 21 A value close to 0.8dB indicates that the signal can pass through the filter efficiently (extremely low insertion loss), and this frequency band is the filter's passband. Within the passband, S... 11 The value is approximately -20dB, indicating that the signal reflection is small (low return loss) and the filter is well matched with the impedance of the preceding and following circuits.

[0060] Performance parameter testing

[0061] The performance of the dielectric filter obtained in Example 1 was tested. The test items and results are shown in Table 1.

[0062] Table 1: Performance test results of the dielectric filter in Example 1

[0063]

[0064] Furthermore, to understand the impact of the thickness ratio of the second ceramic body to the first ceramic body on the performance of the dielectric filter, the total thickness of the first and second ceramic bodies was set to 5 mm. The thickness ratio of the second ceramic body to the first ceramic body was changed, while other conditions remained the same as in the previous embodiment. The performance of the dielectric filter obtained from the test is shown in Table 2, and the specific relationship between the thickness ratio and performance is detailed in Table 2.

[0065] Table 2: Influence of ceramic bulk thickness ratio on dielectric filter performance

[0066]

[0067] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A dielectric filter, characterized in that, The system includes multiple resonant units, a coupling structure, and a waveguide structure. Each resonant unit comprises a first ceramic body and a second ceramic body. A first conductive metal layer is disposed on the surface of the first ceramic body, and several adjustment bands are etched onto the surface of the first conductive metal layer. These adjustment bands are used to adjust the frequency of the filter. The second ceramic body is co-fired with the first ceramic body to form a single unit, and a second conductive metal layer is disposed on the surface of the second ceramic body. The coupling structure is used to realize signal coupling between resonators and signal transmission with external circuits. It includes several coupling grooves disposed on the first ceramic body and extending through the thickness of the first ceramic body, and through grooves disposed on the second ceramic body with the same position and shape as the coupling grooves. The waveguide structure is used to accommodate multiple resonators and provide electromagnetic shielding.

2. The dielectric filter according to claim 1, characterized in that, The first ceramic body and the second ceramic body are made of ceramic materials with different dielectric constants, and the dielectric constant of the second ceramic body is greater than that of the first ceramic body.

3. The dielectric filter according to claim 2, characterized in that, The dielectric constant εr of both the first ceramic body and the second ceramic body is in the range of 5 to 90.

4. The dielectric filter according to claim 3, characterized in that, The dielectric constant of the first ceramic body is 5-9, and the dielectric constant of the second ceramic body is 9-16.

5. The dielectric filter according to claim 1, characterized in that, The relationship between the thickness L2 of the second ceramic body and the thickness L1 of the first ceramic body is L2 / L1 = 5-10.

6. The dielectric filter according to claim 1, characterized in that, The multiple resonators are arranged in the waveguide structure in a cascaded or alternating manner.

7. The dielectric filter according to any one of claims 1-5, characterized in that, The coupling grooves are located between adjacent adjustment bands, so that several coupling grooves and adjustment bands are arranged alternately.

8. A method for fabricating a dielectric filter as described in any one of claims 1-7, characterized in that, include: Preparation of the second ceramic body: ceramic powder with a composite dielectric constant of the second ceramic body is selected, granulated, and then dry-pressed into a green body in a mold. After debinding and sintering, the surface is metallized to obtain the second ceramic body. Preparation of the first ceramic body: ceramic powder with a composite dielectric constant of the first ceramic body is selected, and the powder is ball-milled to make a slurry. The slurry is cast onto a substrate of a predetermined size, dried and trimmed, and then sintered to obtain the first ceramic body. The first ceramic body and the second ceramic body are joined together with an inorganic binder and then placed in a sintering furnace to be fired into one piece. Etching and grooving: Adjustment bands with different patterns and shapes are etched on the surface of the first ceramic body, and coupling grooves are started between adjacent adjustment bands.

9. The method for fabricating a dielectric filter according to claim 8, characterized in that, In the step of preparing the second ceramic body, the particle size after granulation is 70–90 μm, and the specific surface area is <3.5 m². 2 / g; During the debinding process, the temperature is 500~700℃, and during sintering, the temperature is 1250℃~1500℃, and the sintering time is 120min~360min.

10. The method for fabricating a dielectric filter according to claim 8, characterized in that, In the step of preparing the first ceramic body, the particle size of the ball-milled powder is 1-2 μm, and the specific surface area is controlled at 15-20 m². 2 / g; The ball-milled powder is mixed with solvent, binder, dispersant and plasticizer to form a slurry, which is then cast, laminated and sintered to form the first ceramic body.

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