An adjustable attenuated balanced filter

Abstract

The application discloses a balanced filter with adjustable attenuation, which realizes the function of adjustable attenuation of the balanced filter, reduces the device size on the basis of not affecting the performance, improves the integration of the device, and has the advantages of simple structure, high economy and high practicability. The balanced filter comprises a dielectric substrate and a graphene nanometer plate. The upper surface of the dielectric substrate is symmetrically provided with microstrip feed line structures on both sides, and the microstrip feed line structures are provided with a microstrip resonance structure. One side of the microstrip resonance structure close to the central axis of the dielectric substrate is connected to one side of the graphene nanometer plate, and the other side of the graphene nanometer plate is connected to a metal sheet. The lower surface of the dielectric substrate is provided with a metal ground plate.

Description

Technical Field

[0001] This invention belongs to the field of filter technology, specifically relating to a balanced filter with adjustable attenuation. Background Technology

[0002] As a frequency-selective device, a filter allows useful signals to pass through with near-zero attenuation while suppressing unwanted signals and noise interference signals outside the operating frequency band, reducing signal interference between communication channels, and thus ensuring the normal operation of communication equipment. It plays a crucial role in modern wireless communication systems. Compared to traditional two-port filters, balanced filters, as a two-wire transmission structure, have better common-mode rejection capabilities and can achieve better noise interference immunity, thereby improving the signal-to-noise ratio and sensitivity of the communication system, and playing an important role in the field of wireless communication.

[0003] Graphene is a two-dimensional thin film composed of carbon atoms connected by sp2 hybridization and arranged in a two-dimensional honeycomb lattice structure. Graphene's unique arrangement and electronic hybridization give it exceptionally superior electrical, optical, thermal, and mechanical properties. Graphene exhibits tunable surface sheet resistance in the microwave band; its surface impedance can be altered by adjusting the applied bias voltage. This characteristic makes graphene widely used in tunable microwave devices and circuits.

[0004] Currently, traditional designs for adjustable attenuation balanced filters require cascading the balanced filter and the adjustable attenuator, resulting in a large size that is not conducive to miniaturization. Moreover, traditional adjustable attenuators achieve their functionality through resistive attenuation networks or controllable replacement of resistors in the transmission network (such as PIN diodes) and the introduction of active thermistors, leading to high overall circuit complexity, complex design schemes, and uncontrollable costs.

[0005] While designing the balanced filter, an adjustable attenuation function was introduced based on the adjustable sheet resistance of graphene nanoplates in the microwave band, completing the design of a balanced filter with adjustable attenuation and further improving the integration of the device. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides an adjustable attenuation balanced filter, which realizes the adjustable attenuation function of the balanced filter, while reducing the device size without affecting performance, improving the device integration, and has a simple structure, strong economy and practicality.

[0007] This invention is achieved through the following technical solution:

[0008] A balanced filter with adjustable attenuation includes a dielectric substrate and a graphene nanoplate.

[0009] The dielectric substrate has microstrip feed structures symmetrically arranged on both sides of its upper surface, and a microstrip resonant structure is arranged between the microstrip feed structures. The side of the microstrip resonant structure closest to the central axis of the dielectric substrate is connected to one side of the graphene nanoplate, and the other side of the graphene nanoplate is connected to a metal sheet. A metal ground plane is arranged on the lower surface of the dielectric substrate.

[0010] Preferably, the microstrip feed structure employs two U-shaped microstrip lines that are axially symmetrical about the central axis of the dielectric substrate and have openings facing away from each other.

[0011] Preferably, the microstrip resonant structure includes two first resonators, two second resonators, and two third resonators that are mirror-symmetrical about the central axis of the dielectric substrate, and the first resonators, second resonators, and third resonators are arranged sequentially along the central axis of the dielectric substrate.

[0012] Preferably, the first resonator, the second resonator, and the third resonator are capacitively coupled through a coupling gap and inductively coupled through a connecting line.

[0013] Preferably, the first resonator, the second resonator, and the third resonator are all quarter-wavelength stepped impedance resonators.

[0014] Preferably, the quarter-wavelength stepped impedance resonator includes a low-impedance line G2, a high-impedance line G1, and a square-hole grounded transmission line G0 connected in sequence.

[0015] Preferably, the graphene nanoplatelet comprises two first graphene nanoplatelets, two second graphene nanoplatelets, and two third graphene nanoplatelets that are mirror-symmetrical about the central axis of the dielectric substrate, and the first, second, and third graphene nanoplatelets are arranged sequentially along the central axis of the dielectric substrate.

[0016] Preferably, a rectangular slot line symmetrical about the central axis of the dielectric substrate is etched on the metal floor. A first solder joint and a second solder joint are provided inside the rectangular slot line, and a third solder joint is provided on the metal floor outside the rectangular slot line. The second solder joint is connected to the power line, the third solder joint is connected to the ground line, and the first solder joint is electrically connected to the metal sheet through a through hole to provide a bias voltage to the metal sheet.

[0017] Preferably, the through hole is circular.

[0018] Preferably, the metal sheet is axially symmetrical about the central axis of the dielectric substrate.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] This invention provides an adjustable attenuation balanced filter. Compared to existing adjustable attenuation balanced filters, which require cascading a balanced filter and an adjustable attenuator to achieve adjustable attenuation, this invention utilizes the characteristic that graphene nanosheets primarily exhibit resistance in the microwave band, and that their surface impedance can change with applied voltage. A graphene nanoplate with adjustable conductivity, small size, and low initial sheet resistance is loaded onto the open-circuit terminal of a microstrip resonant structure. In this case, the graphene nanoplate is equivalent to a variable resistor connected in series with the microstrip resonant structure, resulting in a non-zero real part of the resonator's input impedance. Changing the bias voltage on the graphene nanoplate changes the resistance of the variable resistor, thus achieving adjustable attenuation of the balanced filter. The adjustable attenuation balanced filter of this invention reduces size and improves system integration without affecting performance. Furthermore, it offers advantages in terms of ease of integration, high flexibility, and a wide adjustable frequency range. Its structure is simple and reasonable, cost-effective, and easy to implement, fully utilizing the excellent electrical properties of graphene. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the adjustable attenuation balanced filter of the present invention;

[0022] Figure 2 This is a schematic diagram of the upper surface structure of the dielectric substrate of the present invention;

[0023] Figure 3 This is a diagram showing the dimensions of the various structures on the upper surface of the dielectric substrate of the present invention;

[0024] Figure 4 This is a schematic diagram of the quarter-wavelength stepped impedance resonator structure of the present invention;

[0025] Figure 5 This is a schematic diagram of the lower surface structure of the dielectric substrate of the present invention;

[0026] Figure 6 These are simulation and measured S-parameter diagrams of differential mode return loss in embodiments of the present invention;

[0027] Figure 7 These are simulation and measured graphs of the differential insertion loss S-parameters in embodiments of the present invention;

[0028] Figure 8 These are simulation and measured diagrams of the common-mode return loss S-parameters in embodiments of the present invention;

[0029] Figure 9 These are simulation and measured graphs of the common-mode insertion loss S-parameters in embodiments of the present invention.

[0030] In the figure: dielectric substrate 1, microstrip feed structure 2, input feed structure 21, output feed structure 22, microstrip resonant structure 3, first resonator 31, second resonator 32, third resonator 33, first coupling gap 41, second coupling gap 42, first connecting line 51, second connecting line 52, metal ground plane 6, first solder joint 61, second solder joint 62, third solder joint 63, graphene nanoplate 7, first graphene nanoplate 71, second graphene nanoplate 72, third graphene nanoplate 73, metal sheet 8. Detailed Implementation

[0031] The principles and features of the present invention will be further described in detail below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clearly illustrate the purpose of the embodiments of the present invention.

[0032] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or it can be in a centered component. When a component is said to be "connected to" another component, it can be directly connected to the other component or it may also be in a centered component. When a component is said to be "set to" another component, it can be directly set on the other component or it may also be in a centered component.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] This invention provides a balanced filter with adjustable attenuation, such as... Figure 1 As shown, it includes a dielectric substrate 1, a microstrip feed structure 2, a microstrip resonant structure 3, a metal ground plane 6, a graphene nanoplate 7, and a metal sheet 8.

[0035] The upper surface of the dielectric substrate 1 is printed with a microstrip feed structure 2, a microstrip resonant structure 3 and a metal sheet 8. The microstrip feed structure 2 consists of two U-shaped microstrip lines that are symmetrical about the axis A-A' and have opposite openings, which are used to realize the feeding characteristics.

[0036] Among them, such as Figure 1 As shown, the axis A-A' is the central axis of the dielectric substrate 1 along the direction from one side of the U-shaped microstrip line to the other side of the U-shaped microstrip line.

[0037] like Figure 2As shown, a microstrip resonant structure 3 is provided between the two U-shaped microstrip lines. The microstrip resonant structure 3 includes two first resonators 31, two second resonators 32, and two third resonators 33 that are mirror-symmetrical about the axis A-A'. The first resonators 31, the second resonators 32, and the third resonators 33 are arranged vertically along the axis A-A' and are all quarter-wavelength stepped impedance resonators.

[0038] like Figure 4 As shown, the quarter-wavelength stepped impedance resonator is formed by connecting a high-impedance line G1, a low-impedance line G2, and a square-hole grounded transmission line G0. The different resonators (i.e., the first resonator 31, the second resonator 32, and the third resonator 33) of the microstrip resonant structure 3 achieve capacitive coupling through the first coupling gap 41 and the second coupling gap 42 between the low-impedance lines G2, and achieve inductive coupling through the first connecting line 51 and the second connecting line 52 between the high-impedance lines G1.

[0039] like Figure 5 As shown, a metal ground plane 6 is printed on the lower surface of the dielectric substrate. A rectangular slot line 60 symmetrical about the axis A-A' is etched on the metal ground plane. A first solder joint 61 and a second solder joint 62 are provided in the rectangular slot line 60, and a third solder joint 63 is provided on the metal ground plane outside the rectangular slot line 60. The second solder joint 62 is connected to the power line, and the third solder joint 63 is connected to the ground line. A bias voltage is applied to the metal sheet 8 through the through hole of the dielectric substrate 1 directly above the first solder joint 61. The metal sheet 8 is symmetrical about the axis A-A', and its two sides parallel to the axis A-A' are connected to the graphene nanoplate 7, so that the bias voltage is applied to the graphene nanoplate 7.

[0040] like Figure 2 As shown, the graphene nanoplate 7 is disposed on the upper surface of the dielectric substrate 1, including two first graphene nanoplates 71, two second graphene nanoplates 72, and two third graphene nanoplates 73 that are mirror-symmetrical about the axis A-A'. The sides of the first graphene nanoplates 71, the second graphene nanoplates 72, and the third graphene nanoplates 73 away from the axis A-A' are respectively connected to the first resonator 31, the second resonator 32, and the third resonator 33, and the sides closer to the axis A-A' are all connected to the metal sheet 8.

[0041] This invention designs an adjustable attenuation balanced filter. Compared to existing adjustable attenuation balanced filters, which require cascading a balanced filter and an adjustable attenuator to achieve adjustable attenuation, this invention utilizes the characteristic that graphene nanosheets primarily exhibit resistance in the microwave band, and that their surface impedance can change with applied voltage. A graphene nanoplate 7, with adjustable conductivity, small size, and low initial sheet resistance, is loaded onto the open-circuit terminal of a microstrip resonant structure 3. In this case, the graphene nanoplate 7 is equivalent to a variable resistor connected in series with the microstrip resonant structure 3, resulting in a non-zero real part of the resonator's input impedance. When the bias voltage on the graphene nanoplate 7 is changed, the resistance value of the variable resistor changes accordingly, achieving adjustable attenuation of the balanced filter. The adjustable attenuation balanced filter of this invention reduces size and improves system integration without affecting performance. Furthermore, it offers advantages in terms of ease of integration, high flexibility, and a wide adjustable frequency range. Its structure is simple and reasonable, cost-effective, and easy to implement, fully utilizing the excellent electrical properties of graphene.

[0042] Example

[0043] This embodiment provides a balanced filter with adjustable attenuation based on graphene nanosheets, whose input and output ports are soldered with SMA connectors for connection to test or practical devices.

[0044] refer to Figure 1 The diagram shows a balanced filter with adjustable attenuation based on graphene nanoplates according to this embodiment, including a dielectric substrate 1, a microstrip feed structure 2, a microstrip resonant structure 3, a metal ground plane 6, a graphene nanoplate 7, and a metal sheet 8.

[0045] The dielectric substrate 1 is made of Rogers 4350 material with a relative permittivity of 3.66, a loss factor of 0.009, and a thickness of 0.508 mm.

[0046] The structure of the upper surface of the dielectric substrate 1 is as follows: Figure 2 and Figure 3 As shown, a microstrip feed structure 2, a microstrip resonant structure 3, and a metal sheet 8 are printed on the upper surface of the dielectric substrate 1. The microstrip feed structure 2 includes an input feed structure 21 and an output feed structure 22. The input feed structure 21 and the output feed structure 22 are two U-shaped microstrip lines that are symmetrical about the axis A-A' and have opposite openings. The U-shaped microstrip line consists of a microstrip base that is perpendicular to the axis A-A' and two microstrip arms that are parallel to the axis A-A'.

[0047] There is a microstrip resonant structure 3 between the input feed structure 21 and the output feed structure 22; the microstrip resonant structure 3 includes two first resonators 31, two second resonators 32, and two third resonators 33 that are mirror-symmetrical about the axis A-A'; the first resonators 31, the second resonators 32, and the third resonators 33 are arranged vertically along the axis A-A' and are all quarter-wavelength stepped impedance resonators.

[0048] The structure of the quarter-wavelength stepped impedance resonator is as follows: Figure 4 As shown, it is composed of a square perforated grounding transmission line G0, a straight high-impedance microstrip line G1, and a straight low-impedance microstrip line G2 connected together. The square perforated grounding transmission line G0 has a through hole drilled in the dielectric substrate 1 directly below it to achieve grounding. The end of the straight high-impedance microstrip line G1 away from the axis A-A' is connected to the square perforated grounding transmission line G0, serving as the short-circuit end of the quarter-wavelength stepped impedance resonator, where the magnetic field dominates. The end closer to the axis A-A' is connected to the straight low-impedance transmission line G2. The end of the straight low-impedance transmission line G2 closer to the axis A-A' serves as the open-circuit end of the quarter-wavelength stepped impedance resonator and is connected to the graphene nanoplate 7, where the electric field dominates.

[0049] The linear low-impedance transmission lines G2 of the first resonator 31 and the second resonator 32 are separated by a first coupling gap 41 to achieve capacitive coupling between the first resonator 31 and the second resonator 32; the linear low-impedance transmission lines G2 of the second resonator 32 and the third resonator 33 are separated by a second coupling gap 42 to achieve capacitive coupling between the second resonator 32 and the third resonator 33.

[0050] The straight high-impedance transmission lines G1 of the first resonator 31 and the second resonator 32 are connected by a first connecting line 51 parallel to the axis A-A' to achieve inductive coupling between the first resonator 31 and the second resonator 32; the straight high-impedance transmission lines G1 of the second resonator 32 and the third resonator 33 are connected by a second connecting line 52 parallel to the axis A-A' to achieve inductive coupling between the second resonator 32 and the third resonator 33.

[0051] The structure of the lower surface of the dielectric substrate 1 is as follows: Figure 5As shown, a metal ground plane 6 is printed on the lower surface of the dielectric substrate 1. A rectangular slot line 60, symmetrical about the axis A-A', is etched on the metal ground plane 6. A first solder joint 61 and a second solder joint 62 are provided on the rectangular slot line 60, and the line connecting the two is parallel to the axis A-A' and connected via an inductor. A third solder joint 63 is located on the metal ground plane 6 outside the rectangular slot line 60. The line connecting the third solder joint 63 and the second solder joint 62 is perpendicular to the axis A-A' and connected via a capacitor. The second solder joint 62 is used to connect a power line, and the third solder joint 63 is used to connect a ground line. A bias is applied to the metal sheet 8 through a through-hole in the dielectric substrate 1 directly above the first solder joint 61. A bias voltage is applied; the metal sheet 8 is symmetrical about axis A-A', and its two sides parallel to axis A-A' are connected to the graphene nanoplate 7, applying a bias voltage to the graphene nanoplate 7; the graphene nanoplate 7 includes two first graphene nanoplates 71, two second graphene nanoplates 72, and two third graphene nanoplates 73 that are mirror-symmetrical about axis A-A'; the ends of the first graphene nanoplates 71, second graphene nanoplates 72, and graphene nanoplates 73 away from axis A-A' are respectively connected to the open terminals of the first resonator 31, second resonator 32, and third resonator 33, and the ends closer to axis A-A' are connected to the metal sheet 8.

[0052] The working principle of this invention is as follows:

[0053] Because the structure of this invention is horizontally symmetrical, when the differential mode and common mode are operating, the symmetry plane A-A' of the balanced filter with adjustable attenuation is equivalent to an ideal electric wall and a magnetic wall, respectively.

[0054] When operating in differential mode, the plane of symmetry A-A' is equivalent to an ideal electric wall, i.e., a short-circuit state. At this time, the imaginary impedance of the equivalent standard coupling line of the differential mode circuit is:

[0055]

[0056] When the electrical length θ = π / 2, the imaginary impedance of the equivalent standard coupled line of the differential-mode circuit is:

[0057]

[0058] According to transmission line theory, the balanced quarter-wavelength coupled line of a differential-mode circuit will appear as a bandpass coupled line.

[0059] When operating in common mode, the plane of symmetry A-A' is equivalent to an ideal magnetic wall, i.e., an open circuit. The imaginary impedance of the equivalent standard coupled line in the common-mode circuit is equal to 0 or jX over the entire frequency range. L This indicates that the balanced coupling line of the common-mode circuit behaves as a fully resistive coupling line and can achieve wide stopband characteristics.

[0060] The coupling between adjacent quarter-wavelength stepped impedance resonators is a hybrid coupling. Electrical coupling is achieved through the first coupling slot 41 and the second coupling slot 42 between low-impedance transmission lines G2, while magnetic coupling is achieved through the first connecting line 51 and the second connecting line 52 between high-impedance transmission lines G1. In differential mode operation, a zero is generated on the left side of the passband when electrical coupling dominates in the hybrid coupling, and a zero is generated on the right side of the passband when magnetic coupling dominates in the hybrid coupling.

[0061] Graphene nanosheets are small-volume, resistance-tunable materials characterized by adjustable conductivity, small size, and low initial sheet resistance. In this design, the graphene nanoplate is equivalent to a variable resistor, connected in series with a microstrip quarter-step impedance resonator. This results in a non-zero real part of the resonator's input impedance. When the bias voltage on the graphene nanoplate 7 is changed, the resistance of the variable resistor changes accordingly, thus achieving adjustable attenuation of the balanced filter.

[0062] In this embodiment, the design parameters of the balanced filter with adjustable attenuation based on graphene nanoplatelets are shown in the following table and Figure 3 As shown, the overall area is 28.5×42.1mm.

[0063] Parameter table (unit: mm)

[0064]

[0065] The technical effects of this invention will be further explained below in conjunction with simulation experiments and test results:

[0066] The simulation experiment used the electromagnetic simulation software HFSS_19.0. The differential-mode response of the invention was simulated in the 2.5-3.1 GHz range, and the common-mode response was simulated in the 0.5-6 GHz range. Simulation curves of return loss S11 and insertion loss S21 were obtained. The simulation results of the differential-mode return loss are shown in the appendix. Figure 6 The simulation results for differential-mode insertion loss are attached. Figure 7 Simulation results for common-mode return loss are attached. Figure 8 The simulation results for common-mode insertion loss are shown in the appendix. Figure 9 .

[0067] In this embodiment, a vector network analyzer N5230A was used to conduct two measurement experiments on the present invention.

[0068] The resistance was tested using the DC method. A DC bias voltage was applied to the graphene nanoplate 7 to achieve impedance regulation. When the bias voltage increased from 0V to 4V, the resistance of the graphene nanoplate decreased from 200Ω to about 20Ω, and the impedance regulation range was close to 10 times.

[0069] Experiment 1 tested the differential mode return loss of the present invention when different bias voltages were applied to the graphene nanoplate 7. Sum and difference mode insertion loss The experimental results of differential mode return loss measurement are attached. Figure 6 The experimental results of differential mode insertion loss measurement are attached. Figure 7 .

[0070] Experiment 2 tested the common-mode return loss of the present invention when different bias voltages were applied to the graphene nanoplate 7. and common-mode insertion loss The experimental results of common-mode return loss measurement are attached. Figure 8 The experimental results of common-mode insertion loss measurement are attached. Figure 9 .

[0071] Figures 6-9 In the graph, the horizontal axis represents frequency in GHz, and the vertical axis represents the simulated and measured S-parameters in dB; the dashed line represents the measured result curve, and the solid line represents the simulated result curve.

[0072] Analysis of simulation and experimental results:

[0073] From the appendix Figure 6 and attached Figure 7 As can be seen, the operating center frequency of this differential filter is 2.7 GHz for differential-mode signals. When the graphene nanoplatelet 7 is not loaded at the open-circuit end of the resonator, the minimum insertion loss within the passband is... The differential mode return loss is 1.6dB across the entire passband. Greater than 20dB. When graphene nanoplate 7 is applied to the open-circuit terminal of the resonator and the bias voltage on graphene nanoplate 7 is adjusted from 4V to 2.7V, the sheet resistance of graphene nanoplate 7 increases from 20Ω to 80Ω, and the insertion loss in the passband increases. The differential mode return loss increases with the increase of the sheet resistance of the graphene nanoplate, gradually increasing from 4.5 dB to 10.5 dB; The resistance increases with the increase of the sheet resistance of the graphene nanoplate, but is still less than -15dB.

[0074] From the appendix Figure 6 and attached Figure 7 As can be seen, for common-mode signals, when the graphene nanoplatelet 7 is not loaded at the open end of the resonator, the common-mode return loss in the frequency range of 0-6GHz is... Common-mode insertion loss greater than -0.5dB Greater than 45dB. When graphene nanoplate 7 is applied to the open-circuit terminal of the resonator and the bias voltage of graphene nanoplate 7 is adjusted from 4V to 2.7V, the sheet resistance of graphene nanoplate 7 increases from 20Ω to 80Ω. In the frequency range of 0-6GHz, the common-mode return loss... The common-mode insertion loss decreases with increasing sheet resistance of graphene nanoplatelets, with a maximum change of 0.4 dB; The differential mode insertion loss increases with the increase of the sheet resistance of the graphene nanoplate, with a maximum change of 2.3 dB. This proves that when the graphene nanoplate 7 is loaded at the open end of the resonator, the differential mode insertion loss can be controlled by adjusting its bias voltage to change the sheet resistance of the graphene nanoplate 7, without affecting the common mode suppression.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A balanced filter with adjustable attenuation, characterized in that, It includes a dielectric substrate (1) and graphene nanoplates (7); Among them, microstrip feed structures (2) are symmetrically arranged on both sides of the upper surface of the dielectric substrate (1), and microstrip resonant structures (3) are arranged between the microstrip feed structures (2). The side of the microstrip resonant structure (3) close to the central axis of the dielectric substrate (1) is connected to one side of the graphene nanoplate (7), and the other side of the graphene nanoplate (7) is connected to a metal sheet (8). A metal ground plate (6) is arranged on the lower surface of the dielectric substrate (1). The microstrip resonant structure (3) includes two first resonators (31), two second resonators (32) and two third resonators (33) that are mirror-symmetrical about the central axis of the dielectric substrate (1). The first resonators (31), the second resonators (32) and the third resonators (33) are arranged sequentially along the central axis of the dielectric substrate (1). The graphene nanoplate (7) includes two first graphene nanoplates (71), two second graphene nanoplates (72) and two third graphene nanoplates (73) that are mirror-symmetrical about the central axis of the dielectric substrate (1). The first graphene nanoplates (71), the second graphene nanoplates (72) and the third graphene nanoplates (73) are arranged sequentially along the central axis of the dielectric substrate (1).

2. The adjustable attenuation balanced filter according to claim 1, characterized in that, The microstrip feed structure (2) uses two U-shaped microstrip lines that are symmetrical about the central axis of the dielectric substrate (1) and have opposite openings.

3. The adjustable attenuation balanced filter according to claim 1, characterized in that, The first resonator (31), the second resonator (32) and the third resonator (33) are capacitively coupled through coupling gaps and inductively coupled through connecting lines.

4. The adjustable attenuation balanced filter according to claim 1, characterized in that, The first resonator (31), the second resonator (32) and the third resonator (33) are all quarter-wavelength stepped impedance resonators.

5. A balanced filter with adjustable attenuation according to claim 4, characterized in that, The quarter-wavelength stepped impedance resonator includes a low-impedance line G2, a high-impedance line G1, and a square-hole grounded transmission line G0 connected in sequence.

6. A balanced filter with adjustable attenuation according to claim 1, characterized in that, The metal floor (6) is etched with a rectangular slot line (60) that is symmetrical about the central axis of the dielectric substrate (1). A first solder joint (61) and a second solder joint (62) are provided in the rectangular slot line. A third solder joint (63) is provided on the metal floor (6) outside the rectangular slot line (60). The second solder joint (62) is connected to the power line, and the third solder joint (63) is connected to the ground line. The first solder joint (61) is electrically connected to the metal sheet (8) through a through hole to provide a bias voltage to the metal sheet (8).

7. A balanced filter with adjustable attenuation according to claim 6, characterized in that, The through hole is circular.

8. A balanced filter with adjustable attenuation according to claim 1, characterized in that, The metal sheet (8) is axially symmetrical about the central axis of the dielectric substrate (1).

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