Diamond-based multi-frequency radio frequency filter

Abstract

The invention discloses a multi-frequency radio frequency filter based on diamond, and relates to the technical field of microwave communication. The filter comprises a diamond dielectric substrate, a pair of bent interdigital stepped impedance resonators arranged on the substrate and two sections of open-circuit branches loaded at low impedance sections of the resonators, and a 50-ohm microstrip line is adopted for feeding. By optimizing structural parameters, the filter forms three passbands, and four depth transmission zero points are generated at 4.23 GHz, 7.55 GHz, 10.84 GHz and 16.38 GHz by using open circuit branches, so that high-selectivity filtering and strong out-of-band rejection are realized. The high thermal conductivity and low dielectric loss of the diamond substrate significantly improve the heat dissipation performance, the power capacity and the quality factor of the device, and the SiO2 protection layer enhances the environmental reliability. The antenna is compact in structure, and is suitable for 5.8 GHz ISM, X-band satellite communication and Ku-band radar systems.

Description

Technical Field

[0001] This invention relates to the field of radio, and more specifically to a diamond-based multi-frequency radio frequency filter. Background Technology

[0002] With the rapid development of modern wireless communication systems, especially in future mobile communications (5G / B5G), satellite communications, radar systems, and the Internet of Things, the demand for high-performance, miniaturized, and highly reliable filters in radio frequency (RF) front-ends is becoming increasingly urgent. Multi-band bandpass filters, capable of handling multiple operating frequency bands simultaneously within a single device, are key components for achieving device integration and multifunctionality, effectively reducing system size, complexity, and cost. Therefore, developing multi-band filters with high selectivity, low insertion loss, compact structure, and excellent heat dissipation performance has become a key focus and challenge in the current microwave device field.

[0003] Traditional multiband filter designs are mostly based on cascading multiple single-frequency filters or using multiple resonant cavities for coupling. While these methods can achieve multi-frequency functionality, they generally suffer from complex structures, large overall size, and difficulties in port matching, making it difficult to meet the miniaturization requirements of modern communication equipment. To reduce size, researchers have proposed various resonator designs based on microstrip structures, such as stepped impedance resonators (SIR) and stub-loaded resonators (SLR). SIR can excite multiple resonant modes on a single resonator by changing the impedance ratio of different sections of the transmission line, thus forming a multi-frequency response. SLR, on the other hand, introduces additional resonances or transmission zeros by loading open-circuit or short-circuit stubs onto the resonator to improve frequency selectivity. However, these single techniques often have trade-offs: for example, while traditional SIR designs help with miniaturization, their passband isolation and out-of-band rejection performance are usually insufficient; and while using stub loading alone can improve selectivity, it may sacrifice insertion loss or increase design complexity.

[0004] In recent years, synergistically optimizing performance by combining different resonator structures has become a mainstream research direction. For example, using an interdigital coupling structure can enhance the coupling strength between resonators, facilitating wider bandwidth or more compact layouts. However, existing multi-frequency filter designs based on interdigital structures still face challenges in accurately controlling multiple passband positions and bandwidths, as well as independently generating controllable transmission zeros. Most designs struggle to achieve high selectivity and deep stopband suppression simultaneously across three or more frequency bands, and are prone to generating unwanted spurious responses between passbands.

[0005] On the other hand, the performance of filters is fundamentally limited by the dielectric substrate material used. Currently, commercial filters widely use polymer-based composite dielectric substrates such as the Rogers series. Although the processing technology of these materials is mature, their physical properties have inherent limitations: First, in the microwave high-frequency band (especially the millimeter-wave band), their dielectric loss (usually characterized by the loss tangent Df) is relatively high, which directly leads to a limited filter quality factor (Q value), increased insertion loss, and decreased overall efficiency. Second, their thermal conductivity is generally low (usually below 1 W / (m·K)). In high-power applications, the heat generated by the filter itself cannot be dissipated quickly, causing the device temperature to rise, resulting in performance drift (such as center frequency shift, increased insertion loss), and in severe cases, even damage to the device, limiting its reliable application in high-power systems such as radar and satellite communications.

[0006] To address the aforementioned issues, the applicant proposes a diamond-based multi-frequency radio frequency filter. Summary of the Invention

[0007] The purpose of this invention is to provide a diamond-based multi-frequency radio frequency filter to solve the problems in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a diamond-based multi-frequency radio frequency filter, comprising:

[0009] The dielectric substrate is made of diamond, has a dielectric constant of 5.68, and a thickness of 0.3 mm.

[0010] Two bent interdigitated stepped impedance resonators are disposed on the upper surface of the dielectric substrate, and two open-circuit stubs are loaded on the low impedance transmission line of each resonator.

[0011] The zero-degree feed structure includes an input feed line and an output feed line, with a feed line impedance of 50Ω;

[0012] The filter structure parameters satisfy:

[0013] L0=1.7mm, L1=4.25mm, L2=5.1mm, L3=1.8mm, L4=1mm, L5=0.75mm, L6=3.075mm, L7=0.3mm; W0=0.444mm, W1=0.35mm, W2=0.25mm, W3=1mm, W4=0.15mm;

[0014] The filter has three passbands with center frequencies of 5.65 GHz, 8.245 GHz, and 12.19 GHz, respectively.

[0015] Optionally, the lower surface of the dielectric substrate is provided with a metal ground plane, and the upper surface is provided with a SiO2 protective layer, with the copper resonant structure embedded in the SiO2 layer.

[0016] Optionally, the two bent interdigitated stepped impedance resonators are symmetrical in structure and arranged symmetrically about the central axis of the filter.

[0017] Optionally, the three passband performances of the filter satisfy:

[0018] 5.65GHz passband: return loss ≤ -31.7dB, -3dB relative bandwidth is 2.1%;

[0019] 8.245GHz passband: return loss ≤ -16.6dB, -3dB relative bandwidth is 0.4%;

[0020] 12.19GHz passband: return loss ≤ -25.3dB, -3dB relative bandwidth is 1.3%.

[0021] 5. The multi-frequency radio frequency filter according to claim 1, characterized in that four transmission zeros are formed on both sides of the passband, located at 4.23GHz, 7.55GHz, 10.84GHz and 16.38GHz respectively, with corresponding attenuation values ​​not less than -59.8dB, -50.3dB, -47.4dB and -68.1dB respectively.

[0022] Optionally, the filter is applicable to at least one of the following frequency bands:

[0023] 5.8GHz ISM band;

[0024] X-band satellite communication frequency band;

[0025] Ku-band radar system frequency band.

[0026] Optionally, the thermal conductivity of the diamond substrate is not less than 1000 W / (m·K), and the dielectric loss tangent is not higher than 0.0005.

[0027] Beneficial effects: 1. Achieving high-performance multi-frequency integration and excellent frequency selectivity

[0028] This invention achieves three high-performance passbands with center frequencies of 5.65 GHz, 8.245 GHz, and 12.19 GHz in a compact device through a composite structure of an interdigital stepped impedance resonator and an open-circuit stub. Through structural optimization, four transmission zeros (4.23 GHz, 7.55 GHz, 10.84 GHz, and 16.38 GHz) are precisely formed on both sides of the passband, with a maximum out-of-band attenuation of -68.1 dB, achieving steep out-of-band rejection and excellent frequency selectivity.

[0029] II. Significantly reduce device size

[0030] By employing a bent stepped impedance resonator structure combined with a high-dielectric-constant diamond substrate, the physical size of the resonator is effectively compressed. The interdigital layout enhances the coupling efficiency between resonators, achieving a significant reduction in planar size while maintaining excellent electrical performance, facilitating integration into modern RF front-end modules.

[0031] III. Improving High-Frequency Performance and Power Capacity

[0032] The extremely low dielectric loss characteristics of the diamond substrate (loss tangent ≤ 0.0005) significantly reduce dielectric loss, resulting in a higher unloaded quality factor for the filter, with return losses in all three passbands exceeding -16.6 dB (optimally reaching -31.7 dB). The ultra-high thermal conductivity of diamond (≥1000 W / (m·K)) provides excellent heat dissipation capabilities, rapidly dissipating heat generated during high-power operation, effectively preventing performance degradation, and significantly improving power capacity and long-term stability.

[0033] IV. Enhancing Environmental Reliability

[0034] The SiO2 protective layer on the surface of the copper resonant structure can optimize the performance of the millimeter-wave band and effectively prevent conductor oxidation and environmental pollution, significantly improving the long-term reliability of the device in complex environments. Attached Figure Description

[0035] Figure 1 A schematic diagram of a diamond-based three-band radio frequency filter provided in this application embodiment;

[0036] Figure 2 This is a diamond-based process substrate diagram of a diamond-based tri-band radio frequency filter provided in an embodiment of this application;

[0037] Figure 3 This is a front view of a diamond-based tri-band radio frequency filter provided in an embodiment of this application;

[0038] Figure 4 This is a simulation S-parameter diagram of a diamond-based three-band radio frequency filter provided in an embodiment of this application. Detailed Implementation

[0039] The preferred embodiments of the present invention are described below with reference to the accompanying drawings to make the technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0040] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, the thickness of some components has been appropriately exaggerated in the drawings.

[0041] This invention provides a diamond-based multi-frequency radio frequency filter, aiming to solve the problems of large size, limited out-of-band rejection, poor heat dissipation, and limited quality factor (Q value) in high-frequency bands of existing multi-band filters. The core of this invention lies in the innovative use of diamond as the dielectric substrate material, combined with a specially optimized bent interdigital stepped impedance resonator structure, which incorporates open-circuit stubs in the low-impedance section. This synergistic design of a "high-performance substrate material" and a "refined circuit topology" enables the filter to simultaneously form high-performance passbands at three center frequencies: 5.65 GHz, 8.245 GHz, and 12.19 GHz, and generate multiple deep transmission zeros on both sides of the passband, thereby achieving a compact size, excellent frequency selectivity, low insertion loss, and excellent thermal management capabilities. This filter is particularly suitable for demanding wireless communication scenarios, such as IoT devices requiring compatibility with the 5.8 GHz ISM band, satellite communication terminals operating in the X-band, and radar detection systems applied in the Ku-band.

[0042] The specific structure, material selection, design method, and performance of the present invention will be described in detail below with reference to the accompanying drawings. First, refer to... Figure 1This figure illustrates a top-level structural planar diagram of a preferred embodiment of the present invention. As shown, the main structure of the filter is printed on the upper surface of a dielectric substrate, with a centrally symmetrical layout, which is beneficial for the balance of excitation modes and the consistency of fabrication. The structure mainly includes two microstrip feed lines serving as signal input and output ports, a pair of stepped impedance resonators that are cross-coupled to form an interdigital structure, and two open-circuit stubs loaded at specific locations on the resonators. The input and output feed lines adopt a standard 50-ohm microstrip line design to ensure good impedance matching with other RF components in the system (such as amplifiers, mixers, or antennas), minimizing signal reflection at the ports. The specific width W0 of the feed line is determined by the dielectric constant and thickness of the selected substrate material (diamond), which can be accurately calculated using electromagnetic simulation software. In this embodiment, to achieve a characteristic impedance of 50 ohms, the feed line width W0 is designed to be 0.444 mm. The feeder length L0 is 1.7 mm. This length mainly serves the overall layout of the filter and the physical connection requirements with external connectors (such as SMA connectors). Its impact on the performance within the filter passband is relatively minor, but it needs to be taken into account in the simulation to obtain an accurate full-band response.

[0043] One of the most critical features of this invention is the pair of bent interdigital stepped impedance resonators (SIRs). A stepped impedance resonator is a multimode resonant unit constructed by connecting transmission line segments with different characteristic impedances in series; its resonant characteristics are determined by the impedance ratio and electrical length of each segment. Compared to traditional uniform impedance resonators, SIRs offer additional design freedom, enabling the generation of multiple resonant modes at a specified frequency more easily, and helping to shorten the physical length of the resonator, thus facilitating miniaturization. In this design, each SIR is not a simple straight or U-shaped structure, but rather cleverly bent. Figure 1 As can be clearly seen, the main body of each resonator is composed of multiple broken line segments. These bends effectively "fold" the long electrical path into a limited planar region, thereby significantly reducing the length of the filter without compromising electrical performance. The two SIRs are not arranged parallel to each other, but rather interlock in an interdigital manner. This interdigital coupling structure is a strong coupling mechanism; the coupling area between the two resonators is no longer limited to narrow gaps at the ends or sides, but extends the interaction area through tooth-like interlacing. This brings several benefits: firstly, it enables a stronger coupling coefficient within a given physical spacing, which is crucial for achieving the required passband bandwidth; secondly, interdigital coupling has a significant impact on the transmission zero position in the filter's frequency response, providing an effective means to precisely control the zeros to optimize out-of-band rejection; and thirdly, this structure itself also contributes to a more compact layout.

[0044] Furthermore, two open-circuit stubs are loaded at specific locations on each stepped impedance resonator—specifically, on its low-impedance transmission line segment. An open-circuit stub is essentially a transmission line with an open-circuit termination; when its length is approximately a quarter wavelength, it exhibits high impedance characteristics near its resonant frequency, similar to a short circuit, thus significantly affecting the main transmission line path it connects to. The core objectives of loading these two open-circuit stubs in this invention are as follows: First, they introduce additional resonant modes, which, combined with the multimode characteristics of the SIR itself, precisely locate and shape the three target passbands, playing a crucial role, especially in the formation and modulation of the second (8.245 GHz) and third (12.19 GHz) passbands; second, the loading of the open-circuit stubs is the direct and primary cause of the four deep transmission zeros of this filter. These transmission nulls originate from the destructive interference of the signal path. The length and loading position of the stubs are carefully optimized so that the nulls appear precisely at the frequency points where enhanced suppression is needed (4.23GHz, 7.55GHz, 10.84GHz, 16.38GHz), thereby constructing steep stopband barriers between and at high distances on both sides of the passband. Third, the loading of the stubs also provides additional design parameters, allowing for a more flexible balance of the mutual influence between frequency bands when adjusting the passband performance.

[0045] The following is a detailed explanation. Figure 1The key dimensional parameters shown are determined through iterative optimization using electromagnetic field simulation software (such as CST Microwave Studio or HFSS), and together they determine the final frequency response of the filter. L1 (4.25 mm) and L2 (5.1 mm) primarily define the physical lengths of two key impedance segments in the main body of the stepped impedance resonator, which play a fundamental role in determining the center frequencies of the three passbands. L3 (1.8 mm) is a key dimension of the resonator's bend section and also contributes to determining the overall electrical length of the resonator. L4 (1 mm) and L5 (0.75 mm) correspond to the lengths of the two open-circuit stubs themselves, and these two parameters are most sensitive to the frequency positions of the second and third passbands and the positions of adjacent transmission zeros. L6 (3.075 mm) is the length of another transmission line segment in the resonator, which works in conjunction with L1, L2, etc. L7 (0.3 mm) represents the gap width between the toothed portions of the two resonators within the interdigital coupling region. This dimension directly controls the coupling strength between the two resonators; even a small change can significantly affect the passband bandwidth and the depth of the transmission zeros, making it a highly sensitive parameter in the optimization process. Regarding width parameters, W1 (0.35 mm) and W2 (0.25 mm) represent the dimensions of two adjacent transmission line segments of different widths in the SIR. Their ratio constitutes the impedance ratio of the SIR, one of the core factors controlling the multimode resonant frequency distribution. W3 (1 mm) is the width of a relatively wide transmission line segment in the SIR, typically corresponding to a low-impedance segment. W4 (0.15 mm) is the width of the loaded open stub itself, affecting the characteristic impedance of the stub. All these length (L) and width (W) parameters together constitute a complex but precise parameter space. Through system simulation optimization, a set of specific values ​​is ultimately locked to simultaneously satisfy the requirements for three passband frequencies, bandwidth, insertion loss, and the location and depth of four transmission zeros.

[0046] Turn now Figure 2This figure schematically illustrates the layered structure cross-section of the diamond-based substrate used in this invention. This is another fundamental innovation that distinguishes this invention from most traditional microstrip filters. From bottom to top, the structure includes: a bottom metal ground plane, a middle diamond dielectric substrate, and an top composite structure containing copper patch circuitry and a silicon dioxide (SiO2) protective layer. The metal ground plane is typically made of a high-conductivity material such as gold or copper, and is attached to the lower surface of the diamond substrate through electroplating or deposition processes, providing a complete ground reference plane for the microstrip line and forming a standard microstrip line transmission structure. The dielectric substrate material selected in this invention is not the common FR-4, Rogers RO4003C, or Al2O3 ceramic, but single-crystal or polycrystalline diamond. The advantages of diamond in this application are revolutionary. First, in the microwave RF field, the loss characteristics of the material are characterized by the loss tangent (tanδ). The tanδ of commercial high-frequency PCB materials is typically in the range of 0.001 to 0.004, while high-quality diamond can have a tanδ as low as 10^-5 (e.g., 0.0001 or lower). Such low dielectric loss means that very little energy is converted into heat when electromagnetic waves propagate in diamond, directly translating into an extremely high unloaded quality factor (Qu). For resonators, a high Qu value means lower passband insertion loss and a sharper resonance curve, which is the physical basis for achieving high-performance filters. The filter in this invention exhibits excellent return loss performance (≤-16.6dB, optimally reaching -31.7dB) in all three passbands, primarily due to the ultra-low loss characteristics of the diamond substrate.

[0047] Secondly, diamond possesses unparalleled thermal conductivity, reaching 1000-2000 W / (m·K) at room temperature, which is 4-5 times that of copper and hundreds to thousands of times that of conventional RF substrate materials (such as the Rogers series, with a thermal conductivity of approximately 0.5-1.5 W / (m·K)). In RF filters, especially in high-power applications, conductor losses (mainly generated by current in the microstrip line) and limited dielectric losses generate heat. If this heat cannot be dissipated in time, it will cause the device temperature to rise. This temperature rise causes a slight change in the material's dielectric constant (typically with a negative temperature coefficient), resulting in a drift in the filter's center frequency. Simultaneously, the conductor resistance increases with temperature, further increasing insertion loss, creating a positive feedback loop of performance degradation, which can lead to device failure in severe cases. Using diamond as a substrate is equivalent to installing an extremely efficient "heat sink" for the filter chip. The heat generated during operation can be rapidly diffused laterally through the diamond substrate and conducted away (e.g., through the package or heat sink), thereby keeping the chip's temperature rise at an extremely low level. This ensures the long-term frequency stability and reliability of the filter under high-temperature environments or high-power continuous wave operating conditions, making it ideal for applications with extremely demanding thermal management requirements, such as satellite payloads and radar transmitter front-ends.

[0048] Furthermore, diamond possesses high hardness, chemical inertness, and good mechanical stability, providing robust support as a substrate. In this embodiment, the dielectric constant (ε_r) of the diamond substrate is chosen to be 5.68, and the thickness (h) is selected to be 0.3 mm. This dielectric constant is higher than that of many common microwave substrates (such as Rogers RO4350B with ε_r≈3.48). A higher dielectric constant facilitates further reduction of the waveguide wavelength, thereby achieving a smaller circuit size at the same operating frequency. The 0.3 mm thickness is a trade-off, ensuring sufficient mechanical strength for handling and packaging while avoiding the problems of increased microstrip line radiation loss and potential excitation of higher-order modes caused by an excessively thick substrate.

[0049] exist Figure 2 In the structure shown, a copper patch circuit for a filter is fabricated on the upper surface of the diamond substrate (i.e., Figure 1(All microstrip patterns shown). Copper is a commonly used low-resistivity metal, suitable for fabricating high-performance transmission lines. However, at millimeter-wave frequencies and even higher frequencies, the skin effect causes current to concentrate on the conductor surface, and the surface roughness of the conductor significantly increases the equivalent resistance, thereby increasing conductor losses. Furthermore, copper is easily oxidized in air, forming copper oxide or cuprous oxide. These oxides have poor conductivity, increasing contact resistance and losses, and reducing long-term reliability. To address these issues, this invention covers the copper surface-mount circuit with a silicon dioxide (SiO2) protective layer. This SiO2 layer plays several important roles: First, it completely encapsulates the copper conductor, isolating it from air and thoroughly preventing oxidation and environmental pollution, greatly improving the long-term storage and operational reliability of the device; Second, the SiO2 layer fills the microscopic depressions on the copper surface, providing a relatively smoother interface and reducing surface scattering losses during electromagnetic wave propagation, which is particularly beneficial in high-frequency bands (such as the Ku band and above); Third, in some sophisticated designs, this dielectric capping layer can fine-tune the effective dielectric constant of the microstrip line or play a certain role in impedance transformation, although its main function in this design is protection and passivation.

[0050] Figure 3 A front-view dimensioned diagram of the filter structure is provided, which can be used to more intuitively compare it with... Figure 1 The dimensional parameters in the diagram correspond to each other, making it easier to understand the geometric relationships between the parts. All key dimensions, such as L0 to L7 and W0 to W4, as well as the locations of the input / output ports, are clearly marked in the diagram.

[0051] After completing the structural design and material selection, full-wave electromagnetic simulation is needed to verify and optimize the performance. Figure 4 The figure shows the S-parameter results obtained from simulations of the above embodiments using CST Microwave Studio software. The figure includes two curves: S11 (return loss) and S21 (insertion loss), with the horizontal axis representing frequency (GHz) and the vertical axis representing amplitude (dB). The S21 curve clearly shows three distinct passbands, whose center frequencies perfectly match the design target, located at 5.65 GHz, 8.245 GHz, and 12.19 GHz, respectively. Each passband exhibits a good bandpass shape. By reading the -3 dB point, the relative bandwidths of each passband can be obtained: the first passband (5.65 GHz) is approximately 2.1%, the second passband (8.245 GHz) is approximately 0.4%, and the third passband (12.19 GHz) is approximately 1.3%. These bandwidth characteristics are well-suited to the requirements of the target application scenario; for example, the narrowband characteristics of the second passband perfectly meet the signal purity requirements of satellite communication channels.

[0052] Even more striking is the steep drop of the S21 curve to deep valleys on both sides of the passband, which correspond to transmission zeros. As shown in the figure, S21 reaches extremely low levels at four frequency points: 4.23 GHz, 7.55 GHz, 10.84 GHz, and 16.38 GHz, with simulated values ​​of -59.8 dB, -50.3 dB, -47.4 dB, and -68.1 dB, respectively. These deep zeros create near-vertical band edges, clearly separating the passband from the stopband, giving the filter extremely high frequency selectivity and strong out-of-band rejection capabilities. For example, between the 5.65 GHz and 8.245 GHz passbands, the -50.3 dB zero at 7.55 GHz provides extremely strong isolation, effectively preventing crosstalk between the two operating frequency bands. Meanwhile, the S11 curve drops to very low levels in each passband, with the lowest points reaching -31.7dB, -16.6dB, and -25.3dB respectively. This indicates that the input port achieves good impedance matching in the passband, with very little signal reflection, and most of the power can be transmitted through the filter.

[0053] The manufacturing process of this invention can be summarized as follows: First, a diamond wafer or substrate with a dielectric constant of 5.68, a thickness of 0.3 mm, and a polished surface is prepared. A metal layer several micrometers thick (such as a titanium / gold or chromium / gold laminate, with titanium or chromium as an adhesion layer) is deposited on the lower surface of the diamond using processes such as magnetron sputtering or electron beam evaporation to form a ground plane. Then, a copper layer several micrometers thick is formed on the upper surface of the diamond using thin-film processes (such as sputtering or electroplating). Next, photolithography and etching processes (such as wet etching or dry etching) are used to determine the desired surface thickness. Figure 1 and Figure 3 The design pattern is used to etch the copper layer into the required microstrip lines, resonators, and stub patterns. Subsequently, a silicon dioxide thin film is uniformly grown on the etched copper circuit surface using chemical vapor deposition (CVD) or plasma-enhanced chemical vapor deposition (PECVD) to form a protective layer. Finally, dicing, testing, and packaging yield the complete filter device. Packaging can employ a metal cavity package, where the diamond chip is bonded to the housing base, and the filter's input and output feed lines are connected to the RF pins (such as coplanar waveguides or microstrip lines) on the housing via gold wire bonding. The housing cover seals the surface to provide electromagnetic shielding and environmental protection.

[0054] In summary, this invention provides a diamond-based multi-frequency radio frequency filter. By employing diamond, with its high dielectric constant, ultra-low loss, and ultra-high thermal conductivity, as the substrate material, it fundamentally improves the device's quality factor, power capacity, and thermal stability. Through the design of a bent interdigital stepped impedance resonator combined with open-circuit stub loading, a compact structure achieves tri-band operation and multiple controllable transmission zeros, resulting in high selectivity, low insertion loss, and excellent out-of-band rejection. This invention provides a key filter solution for next-generation high-performance, highly integrated, and highly reliable wireless communication systems. Any reasonable changes or equivalent substitutions based on the concept of this invention in structural parameters, material parameters (such as using diamond with different dielectric constants or thicknesses, or using other high-performance wide-bandgap semiconductor materials such as aluminum nitride), or process details, as long as they achieve a similar multi-frequency high-selectivity filtering function and utilize the advantages of a high thermal conductivity, low-loss substrate, should be considered to fall within the protection scope of the claims of this invention.

[0055] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0056] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A diamond-based multi-frequency radio frequency filter, characterized in that, include: The dielectric substrate is made of diamond, has a dielectric constant of 5.68, and a thickness of 0.3 mm. Two bent interdigitated stepped impedance resonators are disposed on the upper surface of the dielectric substrate, and two open-circuit stubs are loaded on the low impedance transmission line of each resonator. The zero-degree feed structure includes an input feed line and an output feed line, with a feed line impedance of 50Ω; The filter structure parameters satisfy: L0=1.7mm, L1=4.25mm, L2=5.1mm, L3=1.8mm, L4=1mm, L5=0.75mm, L6=3.075mm, L7=0.3mm; W0=0.444mm, W1=0.35mm, W2=0.25mm, W3=1mm, W4=0.15mm; The filter has three passbands with center frequencies of 5.65 GHz, 8.245 GHz, and 12.19 GHz, respectively.

2. The multi-frequency radio frequency filter according to claim 1, characterized in that, The dielectric substrate has a metal ground plane on its lower surface and a SiO2 protective layer on its upper surface, with the copper resonant structure embedded in the SiO2 layer.

3. The multi-frequency radio frequency filter according to claim 1, characterized in that, The two bent interdigitated stepped impedance resonators are symmetrical in structure and arranged symmetrically about the central axis of the filter.

4. The multi-frequency radio frequency filter according to claim 1, characterized in that, The three passband performances of the filter satisfy: 5.65GHz passband: return loss ≤ -31.7dB, -3dB relative bandwidth is 2.1%; 8.245GHz passband: return loss ≤ -16.6dB, -3dB relative bandwidth is 0.4%; 12.19GHz passband: return loss ≤ -25.3dB, -3dB relative bandwidth is 1.3%.

5. The multi-frequency radio frequency filter according to claim 1, characterized in that, Four transmission zeros are formed on both sides of the passband, located at 4.23GHz, 7.55GHz, 10.84GHz and 16.38GHz respectively, with corresponding attenuation values ​​of no less than -59.8dB, -50.3dB, -47.4dB and -68.1dB respectively.

6. The multi-frequency radio frequency filter according to claim 1, characterized in that, The filter is applicable to at least one of the following frequency bands: 5.8GHz ISM band; X-band satellite communication frequency band; Ku-band radar system frequency band.

7. The multi-frequency radio frequency filter according to claim 1, characterized in that, The thermal conductivity of the diamond substrate is not less than 1000 W / (m·K), and the dielectric loss tangent is not higher than 0.0005.

Images