An absorptive tunable bandstop filter

Abstract

The application relates to the technical field of communication, and discloses an absorption type tunable band-stop filter, which comprises a filter circuit, the filter circuit comprises an input port, a first absorption type component, a tunable band-stop filter component, a second absorption type component and an output port which are electrically connected in sequence, the first absorption type component comprises a first A type absorption type coupling component and a first B type absorption type coupling component which are electrically connected in sequence, and the input port, the first A type absorption type coupling component, the first B type absorption type coupling component and the tunable band-stop filter component are electrically connected in sequence. The application solves the problems of the prior art, such as complex structure, large manufacturing difficulty, large tuning difficulty, narrow tuning range and the like.

Description

Technical Field

[0001] This invention relates to the field of communication technology, specifically to an absorption-type tunable bandstop filter. Background Technology

[0002] In order to achieve the segmentation and combination of spectrum resources, communication system front-ends require various high-performance filters. Among them, band-stop filters can shield electromagnetic signals in specific frequency bands and have wide applications in radar countermeasures and communication anti-jamming. After the spectrum signal received from the antenna passes through the band-stop filter, the interference signals that need to be filtered out are significantly attenuated and directly returned to the input. When mixed with the useful signal at the front end, they generate a large amount of interference, deteriorating the system's signal-to-noise ratio and reducing communication quality.

[0003] To address this issue, one approach is to add a ferrite isolator before the band-stop filter. Typical isolators in the 3GHz band are nearly two centimeters long and wide, and use various alloys for magnetic shielding. However, isolators themselves have drawbacks such as large size, heavy weight, and difficulty in integration with other planar circuits, hindering the miniaturization and weight reduction of receiver systems. Another approach is to integrate the isolator and band-stop filter, allowing the filter to simultaneously perform isolation functions. This new type of filter is called an absorptive band-stop filter, also known as a non-reflective filter. It uses a specific resistor network to absorb the desired spectral signal as heat, offering advantages such as small system size, light weight, and low cost.

[0004] Traditional absorptive band-stop filters mainly consist of two structures. Structure one employs the phase cancellation design principle, its basic structure including two filter branches and two power dividers connecting them. This requires a symmetrical transfer function and is rarely used in practical designs. Structure two is implemented using a complementary duplexer, which consists of a low-pass branch and a high-pass branch. The resonant frequencies of the high-pass and low-pass branches connected to the absorption resistor are complementary, thus dissipating unwanted spectral signals across the resistor. However, absorptive filters designed using this technique are relatively complex and bulky. Other typical absorptive filter structures include substrate-integrated waveguide absorptive filters, multilayer metal-coupled absorptive filters, and suspended coplanar waveguide absorptive filters, but they are all difficult to integrate with other planar circuits.

[0005] In recent years, some novel planar absorptive bandstop filters have attracted researchers' interest. A key feature of these filters is the integration of the absorptive network with the resonator, resulting in a significantly smaller size compared to traditional absorptive bandstop filters. Typical design schemes include L-shaped absorptive resonator structures, π-shaped network resonators, hairpin resonators, and resonators with high and low impedance lines. However, these schemes either present significant tuning challenges or have narrow tuning ranges, necessitating further performance improvements. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides an absorption-type tunable bandstop filter, which solves the problems of complex structure, difficult manufacturing, difficult tuning, and narrow tuning range in existing technologies.

[0007] The technical solution adopted by the present invention to solve the above problems is:

[0008] An absorptive tunable bandstop filter includes a filter circuit. The filter circuit includes an input port, a first absorptive component, a tunable bandstop filter component, a second absorptive component, and an output port, which are connected in sequence. The first absorptive component includes a first type A absorptive coupling component and a first type B absorptive coupling component, which are connected in sequence. The input port, the first type A absorptive coupling component, the first type B absorptive coupling component, and the tunable bandstop filter component are connected in sequence.

[0009] As a preferred technical solution, the first type A absorptive coupling component includes a first microstrip line and a second microstrip line arranged in parallel with equal lengths but unequal widths. The second microstrip line is connected to a first grounding resistor and a first grounding metal plate, and the first grounding resistor is electrically connected to the second grounding metal plate. The first type B absorptive coupling component includes a third microstrip line and a fourth microstrip line arranged in parallel with equal lengths but unequal widths. The fourth microstrip line is electrically connected to a second grounding resistor and a third grounding metal plate, and the second grounding resistor is electrically connected to the fourth grounding metal plate. The input port, the first microstrip line, the third microstrip line, and the tunable band-stop filter component are sequentially electrically connected.

[0010] As a preferred technical solution, the second absorption component includes a second type A absorption coupling component and a second type B absorption coupling component, which are electrically connected in sequence. A tunable band-stop filter component, the second type A absorption coupling component, the second type B absorption coupling component, and the output port are also electrically connected in sequence. As another preferred technical solution, the second type A absorption coupling component includes a fifth microstrip line and a sixth microstrip line arranged in parallel with equal lengths but unequal widths. The sixth microstrip line is connected to a third grounding resistor and a fifth grounding metal plate, and the third grounding resistor is electrically connected to the sixth grounding metal plate. The second type B absorption coupling component includes a seventh microstrip line and an eighth microstrip line arranged in parallel with equal lengths but unequal widths. The eighth microstrip line is electrically connected to a fourth grounding resistor and a seventh grounding metal plate, and the fourth grounding resistor is electrically connected to the eighth grounding metal plate. The tunable band-stop filter component, the fifth microstrip line, the sixth microstrip line, and the output port are also electrically connected in sequence.

[0011] As a preferred technical solution, the product of the fundamental mode impedance and the even mode impedance of the first type A absorptive coupling component is less than the square of the characteristic impedance of the filter, and the product of the fundamental mode impedance and the even mode impedance of the second type A absorptive coupling component is less than the square of the characteristic impedance of the filter.

[0012] As a preferred technical solution, the product of the fundamental mode impedance and the even mode impedance of the first type B absorptive coupling component is greater than the square of the characteristic impedance of the filter, and the product of the fundamental mode impedance and the even mode impedance of the second type B absorptive coupling component is greater than the square of the characteristic impedance of the filter.

[0013] As a preferred technical solution, the tunable band-stop filter component includes a central microstrip line and one or more step impedance resonators. The step impedance resonator includes a bottom microstrip line, side microstrip lines connected to both ends of the bottom microstrip line, and a top microstrip line connected to each side microstrip line. It also includes a resonant capacitor, a resonant connecting metal plate, a resonant resistor, and a resonant grounding metal plate. The top microstrip line, resonant capacitor, resonant connecting metal plate, resonant resistor, and resonant grounding metal plate are sequentially electrically connected. The two ends of the central microstrip line are electrically connected to a first absorption component and a second absorption component, respectively. The bottom microstrip line is coupled to the central microstrip line. The capacitance of the resonant capacitor is adjustable.

[0014] As a preferred technical solution, the bottom microstrip line and the side microstrip lines at both ends form a U-shaped structure.

[0015] As a preferred technical solution, the number of tunable bandstop filter components is one or more.

[0016] As a preferred technical solution, multiple tunable bandstop filter components are distributed on one or both sides of the central microstrip line.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The present invention reduces the design difficulty of band-stop filter by using an absorptive component composed of two sets of absorptive coupling lines. The performance of the band-stop filter can be adjusted by simultaneously optimizing the parameters of the coupling lines and the parameters of the resistors connected to the coupling lines in the circuit design software. Any band-stop filter component can be added between the two sets of absorptive coupling lines to construct a new type of absorptive band-stop filter.

[0019] (2) The tunable band-stop filter component of the present invention is tuned by connecting a variable capacitor to an SIR resonator. It has many design parameters and simple filter performance control. The tuning method is simple and the tuning range is large. Together with the absorption component, it broadens the overall tuning range of the absorption filter. Attached Figure Description

[0020] Figure 1This is a circuit diagram of the absorption-type tunable bandstop filter of the present invention.

[0021] Figure 2 This is a more detailed example circuit diagram of the absorption-type tunable bandstop filter of the present invention.

[0022] Figure 3 This is an exploded view of an example of the absorption-type tunable bandstop filter of the present invention;

[0023] Figure 4 This is one of the S-parameter simulation diagrams of the absorption-type tunable bandstop filter of the present invention at typical frequencies;

[0024] Figure 5 This is the second simulation diagram of the S-parameters of the absorption-type tunable bandstop filter of the present invention at typical frequencies;

[0025] Figure 6 This is the third simulation diagram of the S-parameters of the absorption-type tunable bandstop filter of this invention at typical frequencies.

[0026] The attached diagram shows the following component names and their corresponding labels: 1-Input port, 2-First absorptive component, 3-Tunable band-stop filter component, 4-Second absorptive component, 5-Output port, 21-First type A absorptive coupling component, 22-First type B absorptive coupling component, 31-Center microstrip line, 32-Step impedance resonator, 41-Second type A absorptive coupling component, 42-Second type B absorptive coupling component, 211-First microstrip line, 212-Second microstrip line, 213-First grounding resistor, 214-First grounding metal plate, 215-Second grounding metal plate, 221-Third microstrip line, 222-Fourth microstrip line, 2 23-Second grounding resistor, 224-Third grounding metal piece, 225-Fourth grounding metal piece, 321-Bottom microstrip line, 322-Side microstrip line, 323-Top microstrip line, 324-Resonant capacitor, 325-Resonant connection metal piece, 326-Resonant resistor, 327-Resonant grounding metal piece, 411-Fifth microstrip line, 412-Sixth microstrip line, 413-Third grounding resistor, 414-Fifth grounding metal piece, 415-Sixth grounding metal piece, 421-Seventh microstrip line, 422-Eighth microstrip line, 423-Fourth grounding resistor, 424-Seventh grounding metal piece, 425-Eighth grounding metal piece. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0028] It is worth noting that in this invention, "electrically connected" refers to electrical connection. The specific implementation methods include direct contact electrical connection, electrical connection through coupling, electrical connection through wires, electrical connection through connectors, etc. As long as it can transmit electrical signals, it is included in the concept of "electrically connected".

[0029] Example 1

[0030] like Figures 1 to 6 As shown, this invention is mainly applied to mobile communication receivers, radar communication systems, satellite communication receiving systems, and microwave millimeter-wave radiometers.

[0031] The objective of this invention is to propose a novel absorptive tunable bandstop filter. The design in this patent has the advantages of simple structure, convenient cascading of resonant units, simple tuning control, and large tuning range, thereby solving the problems of complex structure, difficult control of filtering characteristics, and large size of resonant units in existing solutions mentioned in the background art description.

[0032] To achieve the above objectives, the band-stop filter circuit mentioned in this invention consists of three parts: a tunable band-stop filter component 3 and an absorptive component connected in series on both sides of the band-stop filter component. Theoretically, any band-stop filter can be connected in series with two absorptive components to form an absorptive band-stop filter, and its characteristic curve is jointly determined by the performance of the absorptive component and the performance of the tunable band-stop filter component.

[0033] Furthermore, the absorptive component consists of two specific absorptive coupling components. Each absorptive coupling component is formed by coupling two microstrip lines of equal length but different widths. A resistor is connected to the left side of the upper microstrip line, and the right side of the upper microstrip line is grounded through a metal via. The left and right sides of the lower microstrip line serve as the input / output ports 5 of the absorptive coupling component, connecting to other components. The product of the fundamental-mode impedance and even-mode impedance of the type A absorptive coupling component is less than the square of the filter's characteristic impedance, while the product of the fundamental-mode impedance and even-mode impedance of the type B absorptive coupling component is greater than the square of the filter's characteristic impedance. The type A and type B absorptive coupling components are connected in series to form the absorptive component.

[0034] Furthermore, the tunable band-stop filter component consists of a microstrip line and tunable band-stop resonators. The left side of the microstrip line is connected to input port 1, and the right side is connected to output port 5. The characteristic impedance of the microstrip line is 50 ohms to match the characteristic impedance of the SMA. The number of tunable band-stop resonators can be one, two, three, or more. Typical layouts fall into two categories: one where all tunable band-stop resonators are distributed on the same side of the microstrip line, and all are coupled to the microstrip line through slots; the second where the resonators are alternately distributed on opposite sides of the microstrip line, and all are coupled to the microstrip line through slots.

[0035] Furthermore, the center frequency of the tunable band-stop resonator is adjusted using a variable capacitor. One end of the variable capacitor is connected to the end of the SIR, and the other end is connected to a voltage source through a bias resistor. By adjusting the capacitance value of the variable capacitor according to its voltage tolerance range, the resonant frequency of the SIR resonator is changed, thereby altering the center frequency of the entire absorptive tunable band-stop filter.

[0036] The technical solution in this embodiment is further refined as follows:

[0037] An absorptive tunable bandstop filter comprises a dielectric substrate, a filter circuit disposed on the dielectric substrate, and a grounding metal plate disposed beneath the dielectric substrate. The filter circuit disposed on the dielectric substrate includes a type A absorptive coupling component, a type B absorptive coupling component, a tunable bandstop filter component 3, an input port 1, and an output port 5.

[0038] Furthermore, the Type A absorptive coupling component consists of a coupling line, a grounding resistor, and a grounding metallized via. The coupling line consists of two closely coupled microstrip lines of equal length but different widths. One microstrip line serves as the input / output interface, while the other microstrip line is connected to the grounding resistor on one side and grounded through the metallized via on the other. The product of the fundamental mode impedance and the even mode impedance of the Type A absorptive coupling component is less than the square of the characteristic impedance of the filter.

[0039] Furthermore, the Type B absorptive coupling component consists of a coupling line, a grounding resistor, and a grounding metallized via. The coupling line consists of two closely coupled microstrip lines of equal length but different widths. One microstrip line serves as the input / output interface, while the other microstrip line is connected to the grounding resistor on one side and grounded through the metallized via on the other. The product of the fundamental mode impedance and the even mode impedance of the Type B absorptive coupling component is greater than the square of the characteristic impedance of the filter.

[0040] Furthermore, the tunable bandstop filter assembly 3 consists of a microstrip line and tunable resonant units. Each tunable resonant unit comprises three folded step impedance resonators (SIRs) of varying widths. The bottom of each folded SIR is coupled to the microstrip line, and the end of the folded SIR is connected to a tunable capacitor. The capacitance of the tunable capacitor is controlled by voltage, thereby adjusting the center frequency of the tunable bandstop filter assembly 3. The number of tunable resonant units can be one, two, three, or more, and they can be distributed on one or both sides of the microstrip line. The characteristic impedance of the microstrip line is 50 ohms.

[0041] Furthermore, the circuit layout from left to right is as follows: input port 1, type A absorbing coupling component, type B absorbing coupling component, tunable bandstop filter component 3, type B absorbing coupling component, type A absorbing coupling component, and output port 5.

[0042] Furthermore, the control unit simultaneously adjusts the capacitor in the resonant unit to achieve tunability of the operating frequency of the absorptive bandstop filter.

[0043] The beneficial effects of this invention are:

[0044] Benefit 1: The absorption component composed of two sets of absorption coupling lines reduces the design difficulty of band-stop filters. The performance of the band-stop filter can be adjusted by simultaneously optimizing the parameters of the coupling lines and the resistors connected to them in the circuit design software. Any band-stop filter component can be added between the two sets of absorption coupling lines to construct a novel absorption band-stop filter.

[0045] Benefit 2: The tunable band-stop filter component is tuned by connecting a variable capacitor to an SIR resonator. It has many design parameters and simple filter performance control. The tuning method is simple and the tuning range is large. Together with the absorption component, it broadens the overall tuning range of the absorption filter.

[0046] Example 2

[0047] like Figures 1 to 6 As shown, as a further optimization of Embodiment 1, this embodiment also includes the following technical features based on Embodiment 1:

[0048] An absorptive tunable bandstop filter includes a filter circuit. The filter circuit includes an input port 1, a first absorptive component 2, a tunable bandstop filter component 3, a second absorptive component 4, and an output port 5, which are connected in sequence. The first absorptive component 2 includes a first type A absorptive coupling component 21 and a first type B absorptive coupling component 22, which are connected in sequence. The input port 1, the first type A absorptive coupling component 21, the first type B absorptive coupling component 22, and the tunable bandstop filter component 3 are connected in sequence.

[0049] As a preferred technical solution, the first type A absorptive coupling component 21 includes a first microstrip line 211 and a second microstrip line 212 arranged in parallel with equal lengths but unequal widths. The second microstrip line 212 is connected to a first grounding resistor 213 and a first grounding metal plate 214. The first grounding resistor 213 is electrically connected to a second grounding metal plate 215. The first type B absorptive coupling component 22 includes a third microstrip line 221 and a fourth microstrip line 222 arranged in parallel with equal lengths but unequal widths. The fourth microstrip line 222 is electrically connected to a second grounding resistor 223 and a third grounding metal plate 224. The second grounding resistor 223 is electrically connected to the fourth grounding metal plate 225. The input port 1, the first microstrip line 211, the third microstrip line 221, and the tunable band-stop filter component 3 are sequentially electrically connected.

[0050] As a preferred technical solution, the second absorption component 4 includes a second type A absorption coupling component 41 and a second type B absorption coupling component 42 that are electrically connected in sequence, a tunable band-stop filter component 3, a second type A absorption coupling component 41, a second type B absorption coupling component 42, and an output port 5 that are electrically connected in sequence.

[0051] As a preferred technical solution, the second type A absorptive coupling component 41 includes a fifth microstrip line 411 and a sixth microstrip line 412 arranged in parallel with equal lengths but unequal widths. The sixth microstrip line 412 is connected to a third grounding resistor 413 and a fifth grounding metal plate 414. The third grounding resistor 413 is electrically connected to the sixth grounding metal plate 415. The second type B absorptive coupling component 42 includes a seventh microstrip line 421 and an eighth microstrip line 422 arranged in parallel with equal lengths but unequal widths. The eighth microstrip line 422 is electrically connected to a fourth grounding resistor 423 and a seventh grounding metal plate 424. The fourth grounding resistor 423 is electrically connected to the eighth grounding metal plate 425. The tunable band-stop filter component 3, the fifth microstrip line 411, the sixth microstrip line 412, and the output port 5 are sequentially electrically connected.

[0052] As a preferred technical solution, the product of the fundamental mode impedance and the even mode impedance of the first type A absorptive coupling component 21 is less than the square of the characteristic impedance of the filter, and the product of the fundamental mode impedance and the even mode impedance of the second type A absorptive coupling component 41 is less than the square of the characteristic impedance of the filter.

[0053] As a preferred technical solution, the product of the fundamental mode impedance and the even mode impedance of the first type B absorptive coupling component 22 is greater than the square of the characteristic impedance of the filter, and the product of the fundamental mode impedance and the even mode impedance of the second type B absorptive coupling component 42 is greater than the square of the characteristic impedance of the filter.

[0054] As a preferred technical solution, the tunable band-stop filter component 3 includes a central microstrip line 31 and one or more step impedance resonators 32. The step impedance resonator 32 includes a bottom microstrip line 321, side microstrip lines 322 connected to both ends of the bottom microstrip line 321, and a top microstrip line 323 connected to each side microstrip line 322. It also includes a resonant capacitor 324, a resonant connecting metal plate 325, a resonant resistor 326, and a resonant grounding metal plate 327. The top microstrip line 323, resonant capacitor 324, resonant connecting metal plate 325, resonant resistor 326, and resonant grounding metal plate 327 are sequentially electrically connected. The two ends of the central microstrip line 31 are electrically connected to the first absorption component 2 and the second absorption component 4, respectively. The bottom microstrip line 321 is coupled to the central microstrip line 31. The capacitance of the resonant capacitor 324 is adjustable.

[0055] As a preferred technical solution, the bottom microstrip line 321 and the side microstrip lines 322 at both ends form a U-shaped structure.

[0056] As a preferred technical solution, the number of tunable bandstop filter components 3 is one or more.

[0057] As a preferred technical solution, multiple tunable bandstop filter components 3 are distributed on one or both sides of the central microstrip line 31.

[0058] Example 3

[0059] like Figures 1 to 6 As shown, as a further optimization of Embodiments 1 and 2, this embodiment also includes the following technical features based on Embodiments 1 and 2:

[0060] In this implementation, the dielectric substrate is Rogers 5880 with a dielectric constant of 2.2 and a thickness of 0.508 mm. The filter circuit is made of copper with a thickness of 2 micrometers, and the grounding circuit is also made of copper with a thickness of 2 micrometers.

[0061] Furthermore, the fundamental-mode impedance of the Type A absorptive coupling component is 24 ohms, and the even-mode impedance is 80 ohms. The square root of their product is less than the characteristic impedance of the filter, which is 50 ohms. The resistor connected to the left side of the Type A absorptive coupling component is 180 ohms, and the right side is grounded through a metal via. The fundamental-mode impedance of the Type B absorptive coupling component is 45 ohms, and the even-mode impedance is 78 ohms. The square root of their product is greater than the characteristic impedance of the filter, which is 50 ohms. The resistor connected to the left side of the Type B absorptive coupling component is 145 ohms, and the right side is grounded through a metal via.

[0062] Furthermore, the initial operating frequency was set at 3 GHz, the microstrip line width was 1.88 mm with a characteristic impedance of 50 ohms, the SIR resonator length was a quarter wavelength, and the initial design length was 18.3 mm. Adjustable capacitors were connected on both sides, and the adjustable capacitors were grounded through a bias circuit to prevent interference signals from adversely affecting the filter. The capacitance value of the adjustable capacitors was controlled by the external power supply.

[0063] Furthermore, this implementation uses three tunable resonant units, two of which are located above the microstrip line and the third is located below the microstrip line. The coupling coefficient of the three resonant units is adjusted through the microstrip line, thereby changing the final S-parameter performance of the filter.

[0064] Furthermore, input port 1 and output port 5 employ a microstrip line structure with a characteristic impedance of 50 ohms. Input port 1 and output port 5 are connected to a type A absorptive coupling component via a transition microstrip line.

[0065] In this implementation, S12 is below -20dB at the center frequency. The stopband bandwidth with S12 below -20dB is approximately 800MHz, and the value of S11 within the stopband is below -10dB. The entire bandstop filter has a tunable range of 2.7-3.3GHz, with a tuning range of 20%.

[0066] As described above, the present invention can be implemented well.

[0067] All features disclosed in all embodiments of this specification, or steps in all methods or processes implied in the disclosure, may be combined and / or extended or replaced in any way, except for mutually exclusive features and / or steps.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Based on the technical essence of the present invention, any simple modifications, equivalent substitutions, and improvements made to the above embodiments within the spirit and principles of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An absorption-type tunable bandstop filter, characterized in that, The filter circuit includes an input port (1), a first absorptive component (2), a tunable bandstop filter component (3), a second absorptive component (4), and an output port (5) that are connected in sequence. The first absorptive component (2) includes a first type A absorptive coupling component (21) and a first type B absorptive coupling component (22) that are connected in sequence. The input port (1), the first type A absorptive coupling component (21), the first type B absorptive coupling component (22), and the tunable bandstop filter component (3) are connected in sequence. The first type A absorptive coupling component (21) includes a first microstrip line (211) and a second microstrip line (212) of equal length but unequal width arranged in parallel. The second microstrip line (212) is connected to a first grounding resistor (213) and a first grounding metal plate (214). The first grounding resistor (213) is electrically connected to a second grounding metal plate (215). The first type B absorptive coupling component (22) includes a third microstrip line (221) and a fourth microstrip line (222) of equal length but unequal width arranged in parallel. The fourth microstrip line (222) is electrically connected to a second grounding resistor (223) and a third grounding metal plate (224). The second grounding resistor (223) is electrically connected to a fourth grounding metal plate (225). The input port (1), the first microstrip line (211), the third microstrip line (221), and the tunable bandstop filter component (3) are electrically connected in sequence. The tunable band-stop filter component (3) includes a central microstrip line (31) and one or more step impedance resonators (32). The step impedance resonator (32) includes a bottom microstrip line (321), side microstrip lines (322) connected to both ends of the bottom microstrip line (321), and a top microstrip line (323) connected to each side microstrip line (322). It also includes a resonant capacitor (324), a resonant connecting metal sheet (325), a resonant resistor (326), and a resonant grounding metal sheet (327). The top microstrip line (323), resonant capacitor (324), resonant connecting metal sheet (325), resonant resistor (326), and resonant grounding metal sheet (327) are connected in sequence. The two ends of the central microstrip line (31) are connected to the first absorption component (2) and the second absorption component (4) respectively. The bottom microstrip line (321) is coupled to the central microstrip line (31). The capacitance of the resonant capacitor (324) is adjustable.

2. The absorptive tunable bandstop filter according to claim 1, characterized in that, The second absorption component (4) includes a second type A absorption coupling component (41), a second type B absorption coupling component (42), a tunable band-stop filter component (3), a second type A absorption coupling component (41), a second type B absorption coupling component (42), and an output port (5) that are connected in sequence.

3. The absorptive tunable bandstop filter according to claim 2, characterized in that, The second type A absorptive coupling component (41) includes a fifth microstrip line (411) and a sixth microstrip line (412) of equal length but unequal width arranged in parallel. The sixth microstrip line (412) is connected to a third grounding resistor (413) and a fifth grounding metal plate (414). The third grounding resistor (413) is electrically connected to the sixth grounding metal plate (415). The second type B absorptive coupling component (42) includes a seventh microstrip line (421) and an eighth microstrip line (422) of equal length but unequal width arranged in parallel. The eighth microstrip line (422) is electrically connected to a fourth grounding resistor (423) and a seventh grounding metal plate (424). The fourth grounding resistor (423) is electrically connected to the eighth grounding metal plate (425). The tunable band-stop filter component (3), the fifth microstrip line (411), the sixth microstrip line (412), and the output port (5) are electrically connected in sequence.

4. An absorption-type tunable bandstop filter according to claim 2, characterized in that, The product of the fundamental mode impedance and the even mode impedance of the first type A absorptive coupling component (21) is less than the square of the characteristic impedance of the filter, and the product of the fundamental mode impedance and the even mode impedance of the second type A absorptive coupling component (41) is less than the square of the characteristic impedance of the filter.

5. An absorptive tunable bandstop filter according to claim 4, characterized in that, The product of the fundamental mode impedance and the even mode impedance of the first type B absorptive coupling component (22) is greater than the square of the characteristic impedance of the filter, and the product of the fundamental mode impedance and the even mode impedance of the second type B absorptive coupling component (42) is greater than the square of the characteristic impedance of the filter.

6. An absorptive tunable bandstop filter according to any one of claims 1-5, characterized in that, The bottom microstrip line (321) and the side microstrip lines (322) at both ends form a U-shaped structure.

7. An absorption-type tunable bandstop filter according to claim 6, characterized in that, The number of tunable bandstop filter components (3) is one or more.

8. An absorption-type tunable bandstop filter according to claim 7, characterized in that, Multiple tunable bandstop filter components (3) are distributed on one or both sides of the central microstrip line (31).

Images