A Multilayer Low-Pass Filter Based on LTCC Technology

Abstract

The present invention relates to the technical field of low-pass filters, and specifically, to a multi-layer low-pass filter based on LTCC technology. This filter is fabricated into a fan-shaped low-pass filter structure by applying the LTCC substrate process, and it includes multi-layer green ceramic sheets, metal conduction bands, and metal vias; among them, the multi-layer green ceramic sheets are stacked and sintered to form a fan-shaped low-pass filter substrate, and metal circuit patterns that affect the radio frequency performance of the filter are printed on the green ceramic sheets according to circuit requirements. The input and output of the module are both microstrip interfaces. The design of the present invention adopts an LTCC multi-layer ceramic dielectric structure. By introducing a vertical interconnection structure, the planar low-pass is improved to a three-dimensional structure. On the premise of ensuring the performance indicators of the filter, the effective combination of performance and size is achieved, making up for the application disadvantages of large size of existing high-performance filters and low performance of small-size filters; its length dimension is small, and it performs excellently in terms of technical indicators. At the same time, it is convenient for system-level integration and is also applicable to traditional microwave hybrid integration processes.

Description

Technical Field

[0001] The present invention relates to the technical field of low-pass filters, and more particularly, to a multilayer low-pass filter based on LTCC technology. Background Art

[0002] With the continuous development of modern communication technologies, there are increasingly high requirements for the volume, weight, and performance of electronic countermeasure equipment and radio frequency instrumentation systems. Especially for various systems used in spaceborne, missile-borne, airborne, and individual soldier applications, such electronic components and parts are rapidly developing towards the direction of being short, small, light, thin, highly reliable, high-performance, and low-cost. The broadband radio frequency circuit part is a core component in electronic countermeasure equipment and radio frequency instrumentation systems. The indicators of the components play a crucial role in the performance of the entire machine. In a broadband radio frequency circuit, a filter is used for signal frequency selection and is one of the key devices affecting the circuit size and performance. Achieving miniaturization and high performance of the filter is one of the most effective ways to achieve miniaturization, high reliability, and high performance of the entire machine.

[0003] Currently, the commonly used planar-structured microwave filters based on thin-film processes are widely used in radio frequency circuits due to their good frequency selection performance, easy processing, easy integration with other active circuit elements, and the ability to be applied in a relatively wide frequency range by using different substrate materials. Among them, using quartz or alumina ceramic materials as the substrate and fabricating metal conduction bands on the substrate surface through thin-film technology can form a high-low impedance frequency selection structure, achieving a passband range up to 60 GHz. And this type of low-pass filter has low loss in the passband, good standing wave in the band, and excellent out-of-band rejection performance.

[0004] In radio frequency circuit modules such as broadband radio frequency circuit modules and frequency agile mixing modules that require frequency selection of multiple radio frequency signals separately, low-pass filters based on planar microstrip high-low impedance line structures are widely used. However, their external dimensions are small in the width dimension and large in the length direction, increasing the difficulty of circuit layout and the overall size of the circuit module, which is the main disadvantage restricting the application of this type of filter. Therefore, improvements need to be made to address this disadvantage.

[0005] Currently, planar microstrip high-low impedance line low-pass filters with conventional structures (such as Figure 1As shown in the figure, it can meet the requirements of the radio frequency circuit part for low loss within the frequency band and suppression outside the frequency band. However, due to the use of the planar microstrip form, the length dimension of the filter in the signal transmission direction is relatively large, which has a negative impact on the overall layout difficulty and module size of the radio frequency circuit module. Currently, other forms such as LC filters and cavity filters all have the defect of larger size compared with the planar microstrip high-low impedance line low-pass filter; the chip-type filter is inferior to the planar microstrip high-low impedance line low-pass filter in terms of in-band loss, out-of-band suppression and other indicators. In view of this, we propose a multi-layer low-pass filter based on LTCC technology.

[0006] Based on the Figure 1 filter structure shown in the figure, this invention is improved according to the LTCC process. The purpose is to, on the basis of meeting the performance requirements of the radio frequency circuit for the filter, through the application of the LTCC substrate process, realize the conversion of the filter structure from planar layout to three-dimensional layout, so that the length dimension of the low-pass filter is greatly reduced. Summary of the Invention

[0007] The purpose of this invention is to provide a multi-layer low-pass filter based on LTCC technology to solve the problems raised in the above background technology.

[0008] To solve the above technical problems, one of the purposes of this invention is to provide a multi-layer low-pass filter based on LTCC technology. This filter is based on the low-pass filter structure of planar microstrip high-low impedance lines and is fabricated into a sector-shaped low-pass filter structure by applying the LTCC substrate process to realize the conversion of the filter structure from planar layout to three-dimensional layout; the sector-shaped low-pass filter structure adopts an LTCC multi-layer ceramic dielectric structure, which includes multi-layer green ceramic dielectric sheets, metal conductive bands, and metal vias; among them, the multi-layer green ceramic sheets are laminated and sintered to form a sector-shaped low-pass filter substrate, and metal circuit patterns that affect the radio frequency performance of the filter are printed on the green ceramic sheets according to circuit requirements, and the input and output of the module are both microstrip interfaces.

[0009] Among them, the sector-shaped low-pass filter structure, as a deformation of the high-low impedance line low-pass filter, is formed by using a sector-shaped planar structure to replace the low-impedance line structure. Thus, by utilizing the three-dimensional layout characteristics of the LTCC substrate, the planar sector-shaped structure can be transformed into a three-dimensional laminated structure, and the length dimension of the filter is greatly reduced.

[0010] As a further improvement of this technical solution, in the sector-shaped low-pass filter structure, the green ceramic dielectric sheet adopts a Ferro-A6S / M material LTCC green ceramic sheet with a dielectric constant of 5.9, and the thickness of each layer of dielectric after sintering is 96μm.

[0011] As a further improvement of this technical solution, the sector low-pass filter structure is designed with twelve dielectric layers and seven conductor layers. The numbers of the seven conductor layers from top to bottom are 3, 5, 7, 9, 11, and 13 in sequence. Among them:

[0012] 3, 7, and 11 are three conductor material layers, which form the resonant structure of the three-dimensional sector low-pass filter and are interconnected by vias.

[0013] 1, 5, 9, and 13 are conductor material layers, which form the corresponding ground plane structure of the resonant structure.

[0014] As a further improvement of this technical solution, the basic process of the LTCC substrate technology includes the following steps:

[0015] S1. Slicing: According to the required production size, the pre-prepared ceramic chip raw materials are sliced into green ceramic chips that meet the requirements.

[0016] S2. Drilling: Use mechanical or laser drilling technology to drill vias (usually with a diameter of 0.1 - 0.2 mm) on the green ceramic chips for interconnecting circuits on different layers.

[0017] S3. Printing: Adopt the screen printing method. First, make the screen, and then adjust the machine for printing. The various printing pastes are in a flowing slurry state.

[0018] S4. Laminating: After all the green ceramic chips are printed, leveled, and dried, perform the lamination operation on each layer of green ceramic chips in sequence according to the basic process.

[0019] S5. Sintering: According to the number of layers of the green ceramic chips and the printing situation of the pastes, set the sintering curve and complete the co-firing of the laminated layers according to the sintering curve.

[0020] S6. Trimming: Laser trimming of the circuit can be selectively performed according to requirements. If there is no such requirement, this step can be omitted.

[0021] S7. Cutting: After sintering, cutting, testing, and inspection can be carried out.

[0022] Among them, in S2, during the drilling stage, die holes and alignment holes also need to be punched. The die holes are used to assist in alignment during lamination, and the alignment holes are used for automatic alignment when printing conductors and dielectrics.

[0023] As a further improvement of this technical solution, in S4, the basic process of lamination includes the following steps:

[0024] S4.1. Machine adjustment: According to the number of layers and size of the green ceramic chips of the required laminated substrate, adjust the parameters of the isostatic press.

[0025] S4.2. Film laying: Lay the bottom film in the isostatic press mold.

[0026] S4.3. Stack the first green ceramic sheet;

[0027] S4.4. Apply the binder;

[0028] S4.5. Stack the second green ceramic sheet;

[0029] S4.6. Repeat steps S4.4 and S4.5 in sequence until the last green ceramic sheet is stacked;

[0030] S4.7. Place the film again: Cover the top film on the last green ceramic sheet;

[0031] S4.8. Isostatic pressing forming: Finally, arrange to ensure that each layer of green ceramic sheets is aligned, and apply uniform pressure in all directions to the mold in an isostatic press to compact and form the substrate.

[0032] As a further improvement of this technical solution, since the LTCC substrate cannot be adjusted after firing, the fan-shaped low-pass filter needs to be accurately simulated and designed before the LTCC process is carried out, that is, use radio frequency simulation software to perform circuit-level design simulation, three-dimensional-level simulation calculation and optimization design on the filter respectively. The specific simulation calculation process includes the following steps:

[0033] First, divide the LTCC multi-layer fan-shaped low-pass filter into three parts: input and output port structure, filter resonance structure, and interlayer vertical interconnection structure; and then perform simulation design on the three parts in sequence, including:

[0034] The first step: Based on the classical microstrip line model, establish the microstrip line transmission model of the input and output ports, calculate the initial width of the microstrip line according to the theoretical calculation formula of the microstrip line, and then optimize its size using radio frequency simulation software;

[0035] The second step: According to the filter prototype, obtain the normalized lumped parameter filter, and then determine the initial dimensions of each part according to the appropriate high and low impedance values and the microstrip line parameters; then, for the obtained fan-shaped low-pass filter structure, use radio frequency simulation software to model the resonance structure of the fan-shaped low-pass filter, and then perform optimization simulation according to the required filter indexes to determine the optimized geometric dimensions of each resonance structure;

[0036] The third step: Use radio frequency simulation software to model the interlayer vertical interconnection structure; first, equivalent the vertical interconnection structure of microstrip line-through hole-strip line to a circuit model; calculate the initial value of the vertical interconnection to establish the interlayer vertical interconnection structure;

[0037] Finally, combining the simulation results of the above three steps, the high-impedance line of the planar sector low-pass filter is converted into a broken line and connected to the next-level sector through a vertical interconnection structure. After two levels of vertical interconnection structures, the seventh-order sector low-pass structure is transformed from a planar structure into a three-layer vertical stacked structure, thereby significantly reducing the filter in the length direction.

[0038] As a further improvement of this technical solution, in the first step, after establishing the microstrip line transmission model of the input and output ports based on the classical microstrip line model, the specific expression for calculating the initial width of the microstrip line according to the theoretical calculation formula of the microstrip line is:

[0039] Taking a 12 GHz low-pass filter as an example, its effective dielectric constant of the microstrip line is:

[0040]

[0041] Then the characteristic impedance of the microstrip line is:

[0042]

[0043]

[0044] Due to the matching requirement, the characteristic impedance is taken as 50 Ω. According to the selected substrate Ferro-A6S / M with a thickness of 0.192 mm, the initial width of the microstrip line can be calculated.

[0045] The second object of the present invention is to provide a simulation design system platform device for a multi-layer sector low-pass filter before LTCC process manufacturing, including a processor, a memory, and a computer program stored in the memory and running on the processor. The processor is used to implement the above steps of accurately simulating and designing the multi-layer low-pass filter based on LTCC technology before LTCC process manufacturing when executing the computer program.

[0046] The third object of the present invention is to provide a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it implements the above steps of accurately simulating and designing the multi-layer low-pass filter based on LTCC technology before LTCC process manufacturing.

[0047] Compared with the prior art, the beneficial effects of the present invention are:

[0048] 1. This multi-layer low-pass filter based on LTCC technology adopts an LTCC multi-layer ceramic dielectric structure, whose physical structure includes multi-layer green ceramic dielectric sheets, metal conduction bands, and vertical interconnection structures, and the input and output of its module are both microstrip interfaces;

[0049] 2. The multi-layer low-pass filter based on LTCC technology, by introducing a vertical interconnection structure, uniquely improves the planar low-pass filter into a three-dimensional low-pass filter structure. On the premise of ensuring the filter performance indicators, the size in the length direction is reduced by more than 1 / 2 compared with the planar microstrip high-low impedance line low-pass filter, achieving an effective combination of performance and size, and making up for the application disadvantages of large size of existing high-performance filters and low performance of small-size filters.

[0050] 3. In the multi-layer low-pass filter based on LTCC technology, the LTCC technology is used to reduce the size of the sector low-pass filter, which has the advantage of small length size, and performs excellently in terms of technical indicators, with all indicators being better than other forms of LTCC low-pass filters. At the same time, it is convenient for system-level integration and is also applicable to traditional microwave hybrid integration processes. Brief Description of the Drawings

[0051] Figure 1 It is a schematic structural diagram of the conventional low-pass filter based on planar microstrip high-low impedance lines in the present invention;

[0052] Figure 2 It is a schematic diagram of the overall structure of the multi-layer sector low-pass filter in the present invention;

[0053] Figure 3 It is a schematic side view structure diagram of the LTCC sector low-pass filter in the present invention;

[0054] Figure 4 It is a schematic top view structure diagram of the LTCC sector low-pass filter in the present invention;

[0055] Figure 5 It is a schematic structural principle diagram of the input / output port microstrip in the present invention;

[0056] Figure 6 It is a schematic structural diagram of the filter resonance structure model in the present invention;

[0057] Figure 7 It is a schematic structural diagram of the equivalent circuit model of the vertical interconnection structure in the present invention;

[0058] Figure 8 It is a schematic side view structure diagram of the on-grid of the interlayer vertical interconnection structure in the present invention;

[0059] Figure 9 It is a schematic top view structure diagram of the interlayer vertical interconnection structure in the present invention;

[0060] Figure 10 It is a schematic structural diagram of an exemplary electronic computer platform device in the present invention. Detailed Embodiments

[0061] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0062] Embodiment 1

[0063] As Figures 1 - 10 shown, this embodiment provides a multilayer low-pass filter based on LTCC technology. This filter is based on the low-pass filter structure of planar microstrip high-low impedance lines and is fabricated into a fan-shaped low-pass filter structure using the LTCC substrate process, realizing the conversion of the filter structure from a planar layout to a three-dimensional layout; the fan-shaped low-pass filter structure adopts an LTCC multilayer ceramic dielectric structure, which includes multiple green ceramic sheet dielectrics, metal conduction bands, and metal vias; among them, multiple green ceramic sheets are laminated and sintered to form a fan-shaped low-pass filter substrate, and metal circuit patterns affecting the radio frequency performance of the filter are printed on the green ceramic sheets according to circuit requirements. The input and output of the module are both microstrip interfaces.

[0064] Among them, the fan-shaped low-pass filter structure, as a deformation of the high-low impedance line low-pass filter, is formed by using a fan-shaped planar structure to replace the low-impedance line structure, thereby utilizing the three-dimensional layout characteristics of the LTCC substrate to transform the planar fan-shaped structure into a three-dimensional laminated structure, and the filter length dimension is greatly reduced.

[0065] Specifically, this embodiment is improved according to the LTCC process based on the Figure 1 shown filter structure. The purpose is to realize the conversion of the filter structure from a planar layout to a three-dimensional layout by applying the LTCC substrate process on the basis of meeting the performance requirements of the radio frequency circuit for the filter, so as to greatly reduce the length dimension of the low-pass filter.

[0066] In this embodiment, in the fan-shaped low-pass filter structure, the green ceramic sheet dielectric uses a Ferro-A6S / M material LTCC green ceramic sheet with a dielectric constant of 5.9, and the thickness of each layer of dielectric after sintering is 96 μm.

[0067] Furthermore, as Figures 2 - 4 shown, the fan-shaped low-pass filter structure is designed with a total of twelve layers of dielectrics and seven layers of conductors. The numbers of the seven layers of conductors are sequentially 3, 5, 7, 9, 11, and 13 from top to bottom; among them:

[0068] 3, 7, and 11 are three layers of conductor material layers, forming the resonant structure of the three-dimensional fan-shaped low-pass filter and interconnected by vias;

[0069] 1, 5, 9, and 13 are conductor material layers, forming the corresponding ground plane structure of the resonant structure.

[0070] In this embodiment, the basic process of the LTCC substrate technology includes the following steps:

[0071] S1. Slicing: According to the required production size, the pre-prepared and formed ceramic chip raw material is sliced into green ceramic chips that meet the requirements.

[0072] S2. Drilling: Through holes (usually with a diameter of 0.1 - 0.2 mm) are drilled on the green ceramic chips by using mechanical or laser drilling technology for interconnecting circuits on different layers.

[0073] S3. Printing: Using the screen printing method, first make the screen, and then adjust the machine for printing. The various pastes used for printing are in the form of flowing slurry.

[0074] S4. Laminating: After all the green ceramic chips are printed, leveled, and dried, the green ceramic chips of each layer are laminated in sequence according to the basic process.

[0075] S5. Sintering: According to the number of layers of the green ceramic chips and the printing situation of the pastes, set the sintering curve, and complete the co-sintering of the laminate according to the sintering curve.

[0076] S6. Resistance trimming: Laser resistance trimming can be selectively performed on the circuit according to requirements. If there is no such requirement, this step can be omitted.

[0077] S7. Cutting: After sintering, cutting, testing, and inspection can be carried out.

[0078] Among them, in S2, during the drilling stage, die holes and alignment holes also need to be punched. The die holes are used to assist in alignment during lamination, and the alignment holes are used for automatic alignment when printing conductors and dielectrics.

[0079] Furthermore, in S4, the basic process of lamination includes the following steps:

[0080] S4.1. Machine adjustment: According to the number of layers and size of the green ceramic chips of the laminate substrate to be produced, adjust the parameters of the isostatic press.

[0081] S4.2. Film laying: Lay the bottom film in the isostatic press mold.

[0082] S4.3. Stack the first layer of green ceramic chips.

[0083] S4.4. Apply the binder.

[0084] S4.5. Stack the second layer of green ceramic chips.

[0085] S4.6. Sequentially repeat steps S4.4 and S4.5 until the last layer of green ceramic chips is stacked.

[0086] S4.7. Film laying again: Cover the top film on the last layer of green ceramic chips.

[0087] S4.8, Isostatic pressing forming: Finally, arrange to ensure that each green ceramic sheet is aligned, and apply uniform pressure in all directions to the mold in an isostatic press to compact and form the substrate.

[0088] As Figures 5 - 9 shown, in this embodiment, since the LTCC substrate cannot be adjusted after firing, the fan-shaped low-pass filter needs to be accurately simulated and designed before the LTCC process is carried out, that is, the radio frequency simulation software is used to perform circuit-level design simulation, three-dimensional-level simulation calculation and optimization design on the filter respectively. The specific simulation calculation process includes the following steps:

[0089] First, divide the LTCC multi-layer fan-shaped low-pass filter into three parts: input and output port structure, filter resonance structure, and interlayer vertical interconnection structure; and then perform simulation design on the three parts in turn, including:

[0090] The first step: Based on the classical microstrip line model, establish the microstrip line transmission model of the input and output ports (refer to Figure 5 ), calculate the initial width of the microstrip line according to the theoretical calculation formula of the microstrip line, and then optimize its size using radio frequency simulation software;

[0091] The second step: According to the filter prototype, obtain the normalized lumped parameter filter, and then determine the initial size of each part according to the appropriate high and low impedance values and the microstrip line parameters; then, for the obtained fan-shaped low-pass filter structure, use radio frequency simulation software to model the resonance structure of the fan-shaped low-pass filter (refer to Figure 6 ), and then perform optimization simulation according to the required filter indexes to determine the optimized geometric size of each resonance structure;

[0092] The third step: Use radio frequency simulation software to model the interlayer vertical interconnection structure; first, equivalent the vertical interconnection structure of microstrip line-through hole-strip line to a circuit model (refer to Figure 7 ); calculate the initial value of the vertical interconnection, so as to establish the interlayer vertical interconnection structure (refer to Figures 8 - 9 );

[0093] Finally: Combine the simulation calculation results of the above three steps, convert the high-impedance line of the planar fan-shaped low-pass filter into a broken line, connect it to the next-level fan through the vertical interconnection structure, and pass through two-level vertical interconnection structures to transform the seventh-order fan-shaped low-pass structure from a plane into a three-layer vertical stacked structure, so as to greatly reduce the filter in the length direction.

[0094] Specifically, in the first step, after establishing the microstrip line transmission model of the input and output ports based on the classical microstrip line model, the specific expression for calculating the initial width of the microstrip line according to the theoretical calculation formula of the microstrip line is:

[0095] Taking a 12 GHz low-pass filter as an example, the effective dielectric constant of its microstrip line is:

[0096]

[0097] Then the characteristic impedance of the microstrip line is:

[0098]

[0099]

[0100] Due to the matching requirement, the characteristic impedance is taken as 50 Ω. According to the selected substrate Ferro-A6S / M with a thickness of 0.192 mm, the initial width of the microstrip line can be calculated.

[0101] Specifically, the LTCC multi-layer sector low-pass filter designed in this embodiment is modeled as Figures 8 - 9 , compared with the structure in Figure 6 , the overall filter area size is reduced from 3 mm * 14 mm to 3 mm * 6.4 mm.

[0102] Furthermore, according to the technical requirements of the LTCC process, especially the influence of the line dimension accuracy, the LTCC-based multi-layer sector low-pass filter can achieve a low-pass filter below 25 GHz, meeting the radio frequency signal filtering and frequency selection functions of broadband radio frequency circuit modules and frequency agile mixer modules and other circuits applied in this frequency band.

[0103] As Figure 10 shown, this embodiment also provides a simulation design system platform device for a multi-layer sector low-pass filter before LTCC process fabrication. The device includes a processor, a memory, and a computer program stored in the memory and running on the processor.

[0104] The processor includes one or more processing cores. The processor is connected to the memory through a bus. The memory is used to store program instructions. When the processor executes the program instructions in the memory, it realizes the steps of accurately simulating and designing the above-mentioned multi-layer low-pass filter based on LTCC technology before LTCC process fabrication.

[0105] Optionally, the memory can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic disk or optical disk.

[0106] In addition, the present invention further provides a computer-readable storage medium storing a computer program, and when the computer program is executed by a processor, the steps of accurately simulating and designing the above-mentioned multi-layer low-pass filter based on LTCC technology before LTCC process fabrication are implemented.

[0107] Optionally, the present invention further provides a computer program product containing instructions, and when it runs on a computer, it causes the computer to execute the steps of accurately simulating and designing the above-mentioned multi-layer low-pass filter based on LTCC technology before LTCC process fabrication in various aspects.

[0108] Those of ordinary skill in the art can understand that the process of implementing all or part of the steps of the above embodiments can be completed by hardware or by a program instructing relevant hardware. The program can be stored in a computer-readable storage medium, and the above-mentioned storage medium can be a read-only memory, a magnetic disk, an optical disk, etc.

[0109] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A multilayer low-pass filter based on LTCC technology, characterized in that: The filter is a low-pass filter structure based on planar microstrip high-low impedance lines, and is fabricated into a sector low-pass filter structure using LTCC substrate technology; the sector low-pass filter structure adopts an LTCC multi-layer ceramic dielectric structure, which includes multiple green ceramic dielectric layers, metal conduction bands, and metal vias; among them, multiple green ceramic layers are stacked and sintered to form a sector low-pass filter substrate, and metal circuit patterns that affect the RF performance of the filter are printed on the green ceramic according to circuit requirements, and the input and output of the module are both microstrip interfaces; In the sector low-pass filter structure, the green ceramic dielectric uses Ferro-A6S / M material LTCC green ceramic with a dielectric constant of 5.9, and the thickness of each dielectric layer after sintering is 96μm; The sector low-pass filter structure is designed with a total of twelve dielectric layers and seven conductors. The numbers of the seven conductors are 1, 3, 5, 7, 9, 11, and 13 from top to bottom in sequence; among them: 3, 7, and 11 are three conductor material layers, which constitute the resonant structure of the three-dimensional sector low-pass filter and are interconnected by vias; 1, 5, 9, and 13 are conductor material layers, which constitute the ground plane structure corresponding to the resonant structure; The basic process of the LTCC substrate technology includes the following steps: S1. Slicing: According to the required production size, the pre-prepared ceramic raw material is sliced into green ceramic slices that meet the requirements; S2. Drilling: Use mechanical or laser drilling technology to drill vias on the green ceramic slices for interconnecting circuits on different layers; S3. Printing: Using the screen printing method, first make the screen, and then adjust the machine for printing. The various slurries for printing are in a flowing mud-like state; S4. Laminating: After all the green ceramic slices are printed, leveled, and dried, perform the lamination operation on each green ceramic slice in sequence according to the basic process; S5. Sintering: According to the number of green ceramic layers and the printing situation of the slurries, set the sintering curve and complete the co-sintering of the stack according to the sintering curve; S6. Resistance trimming: Optionally perform laser resistance trimming on the circuit according to requirements; S7. Cutting: After sintering, cutting, testing, and inspection can be carried out.

2. The multi-layer low-pass filter based on LTCC technology according to claim 1, characterized in that: In S4 above, the basic process of lamination includes the following steps: S4.

1. Machine adjustment: According to the number of green ceramic slices and the size of the laminated substrate required, adjust the parameters of the isostatic press; S4.

2. Film laying: Lay the bottom film in the isostatic pressing mold; S4.

3. Stack the first green ceramic slice; S4.

4. Apply the binder; S4.

5. Stack the second green ceramic slice; S4.

6. Repeat steps S4.4 and S4.5 in sequence until the last green ceramic slice is stacked; S4.

7. Film laying again: Cover the top film on the last green ceramic slice; S4.

8. Isostatic pressing forming: Finally, organize to ensure that each green ceramic slice is aligned, and apply uniform pressure in all directions to the mold in the isostatic press to compact and form the substrate.

3. The multilayer low-pass filter based on LTCC technology according to claim 1, wherein: Before the sector low-pass filter is fabricated using LTCC technology, accurate simulation design is required, that is, use RF simulation software to perform circuit-level design simulation, three-dimensional-level simulation calculation, and optimization design on the filter respectively. The specific simulation calculation process includes the following steps: First, the LTCC multi-layer sector low-pass filter is divided into three parts: the input / output port structure, the filter resonance structure, and the inter-layer vertical interconnection structure; then, simulation designs are carried out on these three parts in sequence, including: Step 1: Based on the classical microstrip line model, establish the microstrip line transmission model of the input / output port. Calculate the initial width of the microstrip line according to the theoretical calculation formula of the microstrip line, and then optimize its size using a radio frequency simulation software. Step 2: According to the filter prototype, obtain the normalized lumped parameter filter. Then, by selecting appropriate high and low impedance values and based on the microstrip line parameters, determine the initial dimensions of each part. After obtaining the sector low-pass filter structure, use the radio frequency simulation software to model the resonance structure of the sector low-pass filter, and then perform optimization simulation according to the required filter specifications to determine the optimized geometric dimensions of each resonance structure. Step 3: Use the radio frequency simulation software to model the inter-layer vertical interconnection structure; first, equivalent the vertical interconnection structure of the microstrip line - via - stripline to a circuit model; calculate the initial value of the vertical interconnection to establish the inter-layer vertical interconnection structure. Finally: Combining the simulation calculation results of the above three steps, convert the high-impedance line of the planar sector low-pass filter into a broken line, connect it to the next-level sector through the vertical interconnection structure, and after two levels of vertical interconnection structures, transform the seventh-order sector low-pass structure from a planar structure to a three-layer vertical stacked structure.

4. The multilayer low-pass filter based on LTCC technology according to claim 3, characterized in that: In the first step, after establishing the microstrip line transmission model of the input / output port based on the classical microstrip line model, the specific expression for calculating the initial width of the microstrip line according to the theoretical calculation formula of the microstrip line is: Taking a 12 GHz low-pass filter as an example, the effective dielectric constant of its microstrip line is: ； Then the characteristic impedance of the microstrip line is: ； ； Due to the matching requirement, take the characteristic impedance as 50 Ω. Based on the selected substrate Ferro-A6S / M with a thickness of 0.192 mm, the initial width of the microstrip line can be calculated.

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