Combined signal filter

Abstract

The invention provides a combined signal filter, and aims to solve the problems of single function, low integration level and insufficient dynamic adaptation capability of an existing filter, and adopts a three-level layered structure design. The first layer is an LTCC substrate integrated low-pass filter, and suppresses high-frequency harmonic waves through the combination of a spiral inductor and an interdigital capacitor; the second layer is a distributed band-pass filter which adopts an asymmetric resonant cavity structure and inhibits clutters at a Beidou / GPS frequency band (1.56 GHz + / -50 MHz); the third layer is a tunable high-pass filter module, a variable capacitance diode is arranged in the third layer, the cut-off frequency (2.4-5 GHz) can be controlled through external voltage, and the requirement of the 5G frequency band is dynamically met. The inner wall of the asymmetric resonant cavity is coated with a composite dielectric coating, the shielding effectiveness is larger than or equal to 60 dB at 1-6 GHz, and the mode selectivity and stability of the resonant cavity are remarkably improved. According to the invention, 1-6GHz broadband coverage is realized, the harmonic suppression ratio is greater than or equal to 40dBc, the clutter suppression depth is greater than or equal to 60dB, the size is reduced by 50% compared with that of a traditional filter, and the filter is suitable for 5G communication, radar systems and Internet of Things equipment, and has the characteristics of high integration level, high performance and strong dynamic adaptation capability.

Description

Technical Field

[0001] The present invention relates to the technical field of high-frequency electronic circuits, and particularly to a combined signal filter. Background Art

[0002] With the rapid development of modern communication technologies, high-frequency electronic devices are increasingly widely used in fields such as 5G communication, satellite navigation (Beidou / GPS), radar systems, and Internet of Things devices. These devices pose extremely high requirements for the purity and stability of signals. As a key component in signal processing, the performance of filters directly affects the overall performance of the system. However, existing filter technologies have exposed a series of problems that urgently need to be solved when facing complex electromagnetic environments and diverse frequency band requirements.

[0003] 1. Single function

[0004] Traditional filters usually can only suppress a single type of interference. For example, a low-pass filter is mainly used to suppress high-frequency harmonics but cannot handle multi-band clutter; a band-pass filter can only operate within a specific frequency band and it is difficult to meet the requirements of multiple frequency bands simultaneously. Such single-function filters are inadequate in complex communication systems and cannot effectively cope with the superposition of multiple interference signals.

[0005] 2. Insufficient integration

[0006] In practical applications, in order to meet different signal processing requirements, it is often necessary to use multiple filters in combination. However, most existing combined filters adopt the method of stacking discrete components, which results in an overly large volume of the filter. For example, the combination of a cavity filter and a microstrip filter usually requires multiple layers of space, not only increasing the volume and weight of the device but also restricting its application in miniaturized and portable devices. In addition, the connection between discrete components is likely to introduce additional losses and electromagnetic interference, further reducing the performance and reliability of the system.

[0007] 3. Poor dynamic adaptability

[0008] The operating frequency bands and signal characteristics of modern communication systems often change dynamically. For example, the frequency band range of 5G communication technology is relatively wide, and with the development of technology and the expansion of application scenarios, its frequency band requirements are constantly adjusted. Due to their fixed design parameters, traditional filters are difficult to adapt to these changes in real time and cannot meet the requirements of dynamic signal processing. Such static filter designs often require frequent replacement or re-design of filters when facing a rapidly changing communication environment, increasing the maintenance cost and complexity of the system.

[0009] 4. Limited shielding effectiveness

[0010] In high-frequency electronic devices, filters must not only effectively suppress clutter and interference signals, but also have good electromagnetic shielding performance to prevent external electromagnetic interference from affecting internal circuits. However, existing filters are insufficient in shielding effectiveness, especially in high-frequency bands (such as 1-6GHz). For example, although traditional cavity filters have certain shielding capabilities, due to the limitations of their materials and structures, it is difficult to achieve high-efficiency electromagnetic shielding, which affects the purity and stability of the signal.

[0011] In summary, the existing filter technology has obvious deficiencies in terms of functional diversity, integration, dynamic adaptability and shielding effectiveness, and it is difficult to meet the high requirements of modern high-frequency electronic equipment for signal processing. Therefore, the development of a new type of combined signal filter that can solve the above problems at the same time has important practical significance and broad application prospects. Summary of the invention

[0012] The object of the present invention is to provide a combined signal filter to solve the above technical problems.

[0013] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0014] A combined signal filter, characterized by adopting three-level stratification:

[0015] First layer: LTCC substrate integrated low-pass filter, using spiral inductor and interdigital capacitor combination to suppress high-frequency harmonics;

[0016] The second layer: a distributed bandpass filter, connected to the first layer through metallized through-holes, adopts an asymmetric resonant cavity structure to suppress Beidou / GPS frequency band clutter 1.56GHz±50MHz;

[0017] The third layer: tunable high-pass filter module with built-in varactor diode, which controls the cut-off frequency through external voltage, with a range of 2.4-5GHz, and dynamically adapts to 5G frequency band requirements.

[0018] First layer: LTCC substrate integrated low-pass filter

[0019] Spiral inductor parameters: inductance is 10nH, coil diameter is 0.5mm, and number of turns is 5.

[0020] Finger capacitance parameters: capacitance value is 1pF, finger spacing is 50μm, and finger width is 20μm.

[0021] Second layer: Distributed bandpass filter

[0022] Asymmetric resonant cavity dimensions: cavity length is 10 mm, width is 5 mm, and height is 2 mm.

[0023] Resonant frequency design: The center frequency is 1.56 GHz, the bandwidth is 100 MHz, and an asymmetric structure design is adopted to enhance mode selectivity. The third layer: Tunable high-pass filter module

[0024] Varactor diode parameters: The model is a high-frequency varactor diode of a certain brand, and the junction capacitance adjustment range is 0.5 pF - 2 pF.

[0025] External voltage control range: 0V - 10V, corresponding to a cut-off frequency range of 2.4 GHz - 5 GHz.

[0026] This three-level hierarchical combined filter design can effectively suppress clutter, dynamically adapt to various frequency band requirements, and is suitable for complex communication systems.

[0027] As an optimization, the inner wall of the asymmetric resonant cavity is coated with a composite dielectric coating with a thickness of 50 μm to improve the shielding efficiency. The composite dielectric coating can further enhance the mode selectivity of the asymmetric resonant cavity, achieve optimized processing of specific signals, and improve stability.

[0028] As an optimization, the shielding efficiency of the composite dielectric coating is ≥60 dB@1 - 6 GHz and it is prepared from raw materials with the following mass percentages:

[0029] Polyimide resin 40 - 45%

[0030] Barium strontium titanate nanoparticles 25 - 30%

[0031] Silicon carbide nanowires 15 - 20%

[0032] Nickel-zinc ferrite 8 - 10%

[0033] Silane coupling agent 0.015

[0034] Nano graphene sheets 0.5 - 1%

[0035] NMP solvent balance.

[0036] As an optimization, the method for coating the inner wall of the asymmetric resonant cavity with a composite dielectric coating:

[0037] (1) Pretreatment stage

[0038] Perform plasma treatment on barium strontium titanate nanoparticles, silicon carbide nanowires, and nickel-zinc ferrite powder to improve surface activity;

[0039] Nano graphene sheets are ultrasonically exfoliated in isopropanol medium at 40 kHz for 2 h to obtain a monolayer graphene dispersion;

[0040] (2) Slurry preparation

[0041] Under nitrogen protection, dissolve the polyimide resin in NMP solvent with a solid content of 35%, and stir magnetically for 30 min;

[0042] Add a silane coupling agent, barium strontium titanate nanoparticles, silicon carbide nanowires, and nickel-zinc ferrite in sequence, and mix by ball milling;

[0043] Finally, add a monolayer graphene dispersion liquid and perform ultrasonic treatment at 20 kHz for 30 min to form a uniform slurry;

[0044] (3) Coating and curing

[0045] Adopt an electrostatic spraying process: spraying voltage 50 kV, nozzle diameter 0.3 mm, and preheat the substrate to 80 °C;

[0046] Coat in layers, 5 μm for each layer, and cure by interval infrared at 150 °C / 5 min to prevent sagging;

[0047] Finally, perform stepwise curing under N2 atmosphere: 120 °C / 1 h → 200 °C / 2 h → 280 °C / 1 h;

[0048] (4) Post-treatment optimization

[0049] Form a micron-scale periodic structure by laser surface texturing with a period of 50 μm;

[0050] Deposit a 10-nm-thick Al2O3 protective layer by magnetron sputtering to reduce the risk of surface oxidation.

[0051] As a preference, the conditions for plasma treatment in step (1) are: Ar / H2 mixed gas, power 300 W, and 10 min.

[0052] As a preference, in step (2), zirconia balls are used for ball milling and mixing, with a rotation speed of 300 rpm and a time of 4 h.

[0053] The beneficial effects of the present invention are:

[0054] The present invention realizes broadband coverage from 1 to 6 GHz through a three-stage filtering structure, with a harmonic suppression ratio ≥ 40 dBc and a clutter suppression depth ≥ 60 dB, and the performance is improved by 200% compared with a single filter; high integration is achieved: the LTCC process is combined with the cavity embedding technology, and the volume is reduced by 50% compared with the traditional combined filter (preferred size: 15 mm × 10 mm × 3 mm);

[0055] The inner wall of the cavity of the asymmetric resonator is coated with a composite dielectric coating, and through material composition ratio, microstructure design, and process control, the synergistic optimization of high shielding efficiency and resonance mode regulation is realized, which is suitable for the protection of precision resonators in high-frequency electronic devices such as 5G communication and radar systems. Description of the drawings

[0056] Figure 1 Schematic diagram of the three - level hierarchical structure of the combined signal filter of the present invention;

[0057] Figure 2 Process flow chart for preparing the composite dielectric coating of the present invention. Specific embodiments

[0058] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the following combines specific embodiments and drawings to further elaborate the present invention. However, the following embodiments are only the preferred embodiments of the present invention, not all. Based on the embodiments in the implementation manners, other embodiments obtained by those skilled in the art without creative efforts all belong to the protection scope of the present invention.

[0059] The following describes the specific embodiments of the present invention with reference to the drawings.

[0060] Embodiment 1

[0061] As Figure 1 shown, a combined signal filter adopts three - level layering:

[0062] The first layer: LTCC substrate integrated low - pass filter, using a combination of spiral inductor and interdigital capacitor to suppress high - frequency harmonics;

[0063] The second layer: distributed band - pass filter, connected to the first layer through metallized vias, adopting an asymmetric resonator structure to suppress Beidou / GPS band clutter of 1.56 GHz ± 50 MHz;

[0064] The third layer: tunable high - pass filter module, with varactor diodes built - in, and the cut - off frequency is controlled by an external voltage, ranging from 2.4 - 5 GHz, dynamically adapting to the requirements of the 5G band.

[0065] The metallized via process of the LTCC substrate can also adopt 3D printing or laser micromachining technology to improve the accuracy and reliability of inter - layer connection.

[0066] Embodiment 1 integrates a passive filter (low - pass, band - pass layers) and an active tunable module (high - pass layer), taking into account the stability of the passive and the flexibility of the active, and may show stronger anti - interference ability in a complex electromagnetic environment.

[0067] Adopting an LTCC (low - temperature co - fired ceramic) substrate to integrate a low - pass filter, realizing high - frequency harmonic suppression through the combination of a spiral inductor and an interdigital capacitor, meeting the industry's requirements for miniaturization and high integration. At the same time, the vertical stacking design of the three - layer structure reduces space occupation, which is beneficial to the compact layout of complex communication systems (such as 5G base stations, Internet of Things devices).

[0068] The asymmetric resonant cavity bandpass filter of the second layer suppresses clutter in the Beidou / GPS frequency band (1.56 GHz ± 50 MHz), meeting the high-precision filtering requirements of communication systems for specific frequency bands.

[0069] The third layer realizes adjustable cut-off frequency (2.4–5 GHz) through varactor diodes, dynamically adapting to the changes in the 5G frequency band, which is the trend of future intelligent development.

[0070] Embodiment 2

[0071] A combined signal filter adopts three-level layering:

[0072] The first layer: The LTCC substrate integrates a low-pass filter, which uses a combination of spiral inductors and interdigital capacitors to suppress high-frequency harmonics;

[0073] The second layer: A distributed bandpass filter, connected to the first layer through metallized vias, adopts an asymmetric resonant cavity structure to suppress clutter in the Beidou / GPS frequency band of 1.56 GHz ± 50 MHz;

[0074] The third layer: A tunable high-pass filter module, with varactor diodes built-in, controls the cut-off frequency through an external voltage, range: 2.4 - 5 GHz, dynamically adapting to the requirements of the 5G frequency band.

[0075] The inner wall of the asymmetric resonant cavity is coated with a composite dielectric coating with a thickness of 50 μm to improve the shielding efficiency. The composite dielectric coating can further enhance the mode selectivity of the asymmetric resonant cavity, realize the optimized processing of specific signals, and improve stability.

[0076] The composite dielectric coating is prepared from raw materials with the following mass percentages (as shown in Table 1 below):

[0077]

[0078] Table 1

[0079] As Figure 2 shown, the process of preparing the composite dielectric coating and coating the inner wall of the asymmetric resonant cavity with the composite dielectric coating is as follows:

[0080] (1) Pretreatment stage

[0081] Perform plasma treatment on BST, SiC, and nickel-zinc ferrite (Ar / H2 mixed gas, power 300 W, 10 min) to improve surface activity;

[0082] Obtain a monolayer dispersion of nano-graphene sheets through ultrasonic exfoliation (isopropanol medium, 40 kHz, 2 h).

[0083] (2) Slurry preparation

[0084] Under nitrogen protection, dissolve the PI resin in NMP solvent (solid content 35%) and stir magnetically for 30 min;

[0085] Add silane coupling agent, BST, SiC, and ferrite in sequence and mix by ball milling (zirconia balls, rotation speed 300 rpm, 4 h);

[0086] Finally, add graphene dispersion and perform ultrasonic treatment (20 kHz, 30 min) to form a uniform slurry (viscosity 800 - 1200 cP).

[0087] (3) Coating and curing

[0088] Adopt electrostatic spraying process: spraying voltage 50 kV, nozzle diameter 0.3 mm, preheat the substrate to 80 °C;

[0089] Coat in layers (5 μm per layer), and cure by interval infrared (150 °C / 5 min) to prevent sagging;

[0090] Finally, perform stepwise curing: 120 °C / 1 h → 200 °C / 2 h → 280 °C / 1 h (N2 atmosphere).

[0091] (4) Post - treatment optimization

[0092] Perform laser surface texturing (wavelength 1064 nm, pulse energy 50 mJ) to form a micron - scale periodic structure (period 50 μm);

[0093] Deposit a 10 - nm - thick Al2O3 protective layer by magnetron sputtering to reduce the risk of surface oxidation.

[0094] The advantages of the composite dielectric coating in this example are as follows:

[0095] (1) Multi - scale synergistic effect

[0096] BST nanoparticles (50 nm) and SiC nanowires (diameter 200 nm, aspect ratio > 50) form a three - dimensional heterostructure, enhancing broadband absorption through interfacial polarization.

[0097] (2) Gradient impedance design

[0098] The volume ratio of PI / BST decreases gradually from the substrate to the surface (45% → 35%), achieving impedance gradient matching and reducing reflection loss.

[0099] (3) Thermal - mechanical coupling optimization

[0100] The CTE matching degree between NiZn ferrite and PI substrate reaches 95% (ΔCTE < 0.5 ppm / °C), ensuring no cracking under high - temperature conditions.

[0101] Through the material group distribution ratio, microstructure design, and process control, this solution realizes the collaborative optimization of high shielding effectiveness and resonant mode regulation, and is applicable to the protection of precision resonant cavities in high-frequency electronic devices such as 5G communication and radar systems.

[0102] The verification of key performance indicators is shown in Table 2 below.

[0103]

[0104] Table 2

[0105] Electromagnetic shielding effectiveness: Verified by the broadband waveguide method, covering the 1-6 GHz frequency band, meeting the requirement of ≥60 dB and significantly improving the Q value of the resonant cavity.

[0106] Dielectric gradient design: The low dielectric constant (ε_r = 150) on the surface reduces surface reflection, and the high dielectric constant (ε_r = 300) at the bottom enhances mode selectivity.

[0107] Environmental stability: The performance degradation is controllable under extreme temperature (-55~200℃) and humid heat (85℃ / 85%RH) conditions, meeting military standards.

[0108] Multi-performance coordination: Considering the conductive (graphene), dielectric (BST / SiC), and magnetic loss (ferrite) mechanisms, realizing broadband and high-efficiency shielding.

[0109] The electromagnetic performance, environmental adaptability, and reliability of the coating in this embodiment can meet the stringent requirements of asymmetric resonant cavities for high-frequency signal processing and long-term stability.

[0110] Comparison with the prior art:

[0111] 1. Comparison of electromagnetic shielding effectiveness:

[0112] Prior art: The shielding effectiveness of traditional cavity filters in the 1-6 GHz frequency band is 50-55 dB.

[0113] This embodiment: The shielding effectiveness of the composite dielectric coating is 62-68 dB, with an increase of ≥20%.

[0114] 2. Comparison of dielectric constant gradient design:

[0115] Prior art: The dielectric constant of traditional materials is 100-200, without gradient design.

[0116] This embodiment: ε_r = 150 on the surface and ε_r = 300 at the bottom, realizing impedance gradual change matching and reducing reflection loss.

[0117] 3. Comparison of high and low temperature cycle stability:

[0118] Prior art: The shielding effectiveness attenuation ≥5 dB ( 100 cycles).

[0119] In this embodiment: the shielding effectiveness attenuation < 3 dB ( 100 cycles).

[0120] Test methods and standards:

[0121] Electromagnetic shielding effectiveness test: The waveguide method (ASTM D4935) is adopted, and the test frequency band is 1 - 6 GHz.

[0122] Dielectric constant test: The coaxial probe method (Agilent 85072A) is adopted, and the test frequency is 1 GHz.

[0123] High and low temperature cycle test: It is carried out according to Method 503.5 of MIL - STD - 810G, and the test range is The number of cycles is 100 times.

[0124] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art of this industry should understand that the present invention is not limited by the above - mentioned embodiments. The above - mentioned embodiments and the descriptions in the specification are only the 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 all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A combined signal filter, characterized in that: Three-level stratification: First layer: LTCC substrate integrated low-pass filter, using spiral inductor and interdigital capacitor combination to suppress high-frequency harmonics; The second layer: a distributed bandpass filter, connected to the first layer through metallized through-holes, adopts an asymmetric resonant cavity structure to suppress Beidou / GPS frequency band clutter 1.56GHz±50MHz; The third layer: tunable high-pass filter module with built-in varactor diode, which controls the cut-off frequency through external voltage, with a range of 2.4-5GHz, and dynamically adapts to 5G frequency band requirements.

2. The combined signal filter according to claim 1, characterized in that: The inner wall of the asymmetric resonant cavity is covered with a composite dielectric coating with a thickness of 50 μm to improve shielding effectiveness. The composite dielectric coating can further enhance the mode selectivity of the asymmetric resonant cavity, achieve optimized processing of specific signals, and improve stability.

3. The combined signal filter according to claim 2, characterized in that: The composite dielectric coating has a shielding effectiveness of ≥60dB@1-6GHz and is prepared from the following raw materials in the following mass percentages: Polyimide resin 40-45% Barium strontium titanate nanoparticles 25-30% Silicon carbide nanowires 15-20% Nickel zinc ferrite 8-10% Silane coupling agent 0.015 Nanographene sheets 0.5-1% NMP solvent balance.

4. The combined signal filter according to claim 3, characterized in that: Method for coating the inner wall of the asymmetric resonant cavity with a composite dielectric coating: (1) Preprocessing stage Plasma treatment of barium strontium titanate nanoparticles, silicon carbide nanowires, and nickel zinc ferrite powders to increase surface activity; Nanographene sheets were exfoliated in isopropanol medium at 40kHz for 2h to obtain a single-layer graphene dispersion. (2) Slurry preparation Under nitrogen protection, polyimide resin was dissolved in NMP solvent with a solid content of 35% and magnetically stirred for 30 min; Add silane coupling agent, barium strontium titanate nanoparticles, silicon carbide nanowires, and nickel zinc ferrite in sequence, and mix them by ball milling; Finally, the monolayer graphene dispersion was added and ultrasonicated at 20kHz for 30min to form a uniform slurry; (3) Coating and curing The electrostatic spraying process is adopted: the spraying voltage is 50kV, the nozzle diameter is 0.3mm, and the substrate is preheated to 80℃; Layered coating, 5μm per layer, interval infrared curing 150℃ / 5min to prevent sagging; Finally, step curing under N2 atmosphere: 120℃ / 1h→200℃ / 2h→280℃ / 1h; (4) Post-processing optimization Laser surface texturing forms a micrometer-scale periodic structure with a period of 50 μm; A 10 nm thick Al2O3 protective layer is deposited by magnetron sputtering to reduce the risk of surface oxidation.

5. The combined signal filter according to claim 4, characterized in that: The conditions of the plasma treatment in step (1) are: Ar / H2 mixed gas, power 300W, 10min.

6. The combined signal filter according to claim 1, characterized in that: In step (2), the ball milling mixing is performed using zirconium oxide balls at a rotation speed of 300 rpm for 4 hours.

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