A wideband reflectionless dual-band filter

Abstract

The application discloses a wide-bandwidth non-reflective dual-frequency filter and particularly relates to the technical field of microwave communication, and solves the technical problem of signal reflection outside the working frequency band of the existing dual-frequency filter, and the complex structure, large volume, poor absorption effect and poor high-bandwidth effect of a small amount of non-reflective dual-frequency or multi-frequency filter, and the sacrifice of certain out-of-band suppression performance and insertion loss of the non-reflective dual-frequency filter while pursuing the non-reflective characteristic, especially the poor harmonic suppression in the transition area of the two frequency bands and the high-bandwidth area; the technical scheme is that a pair of quarter-wavelength coupled microstrip lines MCL1 and quarter-wavelength microstrip lines ML2 are connected in series, and three-quarter-wavelength microstrip lines ML1 and microstrip lines ML2 are connected in parallel to form a dual-band pass filter response; the application has the good absorption effect in the whole frequency band and enhances the frequency selectivity of the in-band signal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microwave communication, and particularly relates to a wide-bandwidth non-reflective dual-band filter. BACKGROUND

[0002] In modern wireless communication systems, filters as key passive devices, their performance is directly related to the quality and transmission efficiency of signals. With the continuous development of wireless communication technology, especially the rise of new generation communication technologies such as 5G and 6G, the performance requirements of filters are increasingly improved. The traditional filter usually produces reflection when processing out-of-band signals, which not only may cause signal distortion, but also may cause unnecessary interference in the system. In order to optimize the system performance and reduce signal interference, the academia and industry have begun to widely study non-reflective filters. This kind of filter can absorb out-of-band frequency signals by adding additional absorbing circuits and other ways, thereby significantly reducing reflection and improving the quality of signal transmission. At present, although the research on non-reflective filters has made significant progress, most of the research still focuses on single frequency band, and the stopband and level width are limited. However, with the continuous progress of wireless communication technology, single-band filters have been unable to meet the complex and changing communication needs, and the research on dual-band or even multi-band filters has gradually become a hot spot. On the other hand, wide-bandwidth filters have a wide stopband range, which can effectively suppress unwanted signals or interference in a wide frequency range, helping modern communication systems to flexibly adjust their passband and stopband ranges, optimizing the utilization of spectrum resources, improving the spectral efficiency of communication systems, and enhancing the electromagnetic compatibility of devices and reducing the influence of mutual interference.

[0003] Although some researches have involved dual-band or multi-band filters, there are still many challenges in simultaneously achieving wide-bandwidth and non-reflective performance. First, the design complexity of dual-band filters is much higher than that of single-band filters, which requires precise control of the frequency response of two passbands while ensuring that the stopband has sufficient width and attenuation. Second, achieving the non-reflective characteristic of dual-band filters requires good matching in multiple passband ranges to reduce reflection and return loss. This requires designers to use appropriate matching circuits and structural designs to ensure that the filter can achieve non-reflective or low reflection in multiple wide-bandwidth and out-of-band passbands, which undoubtedly greatly increases the complexity and difficulty of the main circuit and absorbing circuit. In addition, under the condition of ensuring the matching of the complex absorbing circuit and the dual-band main circuit, achieving effective signal suppression in a wide frequency range and obtaining a wide stopband bandwidth further increases the design difficulty of the overall circuit.

[0004] Existing dual-band filters often exhibit reflections outside their operating bands, while the few available non-reflective dual-band or multi-band filters often suffer from complex structures, large size, poor absorption, and poor high-stopband performance. Furthermore, while pursuing non-reflective characteristics, these filters often sacrifice certain out-of-band suppression performance and insertion loss, particularly in the transition region between the two frequency bands and in the high-stopband region, resulting in poor harmonic suppression. Summary of the Invention

[0005] Therefore, the present invention solves the problems in the prior art that dual-band filters usually have reflected signals outside the working band, and a small number of non-reflective dual-band or multi-band filters often have complex structures, large volumes, poor absorption effects, and poor high-stopband effects. In addition, while pursuing non-reflection characteristics, non-reflection dual-band filters often sacrifice certain out-of-band suppression performance and insertion loss, especially in the transition region between the two frequency bands and the high-stopband region, and have poor harmonic suppression. The present invention provides a wide-stopband non-reflective dual-band filter, the circuit of which not only has the characteristics of simple structure, planarization, and easy integration in terms of structure, but also has the advantages of multi-band, full-band non-reflection, and wide stopband. It provides a practical solution for reducing system size, improving the integration of RF components, and improving the overall performance of wireless communication systems.

[0006] The present invention provides a wide-stopband non-reflective dual-frequency filter, comprising a dual-band filter network, wherein both ends of the dual-band filter network are respectively connected to a fan-shaped resonant structure, and one end of the two fan-shaped resonant structures away from the dual-band filter network is respectively connected to an input port and an output port; an absorption network 2 is connected in parallel at the connection between the fan-shaped resonant structure and the dual-band filter network; two groups of absorption networks 1 are connected in parallel inside the dual-band filter network; and the entire dual-band filter circuit with a wide stopband and non-reflective characteristics is completely symmetrically distributed on the left and right sides.

[0007] Furthermore, the dual-band filtering network includes a pair of quarter-wavelength coupled microstrip lines MCL1, a quarter-wavelength microstrip line ML2 and a three-quarter-wavelength microstrip line ML1; one end of the first coupled line MCL1a of the coupled microstrip line MCL1 is open, and the other end is connected to the microstrip line ML2; one end of the second coupled line MCL1b of the two groups of coupled microstrip lines MCL1 is respectively connected to the input port and the output port, and the other end is connected to the absorption network 1.

[0008] Furthermore, the absorption network 1 includes a resistor R2, a quarter-wavelength microstrip line ML3 and a half-wavelength microstrip line ML4 connected in series.

[0009] Furthermore, the second absorption network includes a quarter-wavelength microstrip line ML5, a microstrip line ML6, a microstrip line ML7 and a microstrip line ML8, and a resistor R1; the microstrip line ML5, the resistor R1 and the microstrip line ML7 are connected in series in sequence, and the end of the microstrip line ML7 away from the resistor R1 is grounded; the connection between the microstrip line ML5 and the resistor R1 is connected in parallel to the microstrip line ML6, and the connection between the microstrip line ML7 and the resistor R1 is connected in parallel to the microstrip line ML8.

[0010] Furthermore, the fan-shaped resonant structure includes a first fan-shaped patch pair structure, a third fan-shaped patch pair structure, and a second fan-shaped patch pair structure that are symmetrical in top and bottom. The first fan-shaped patch pair structure and the second fan-shaped patch pair structure are connected at their respective symmetry points. The third fan-shaped patch pair structure is connected via a first microstrip line structure. The first fan-shaped patch pair structure, the second fan-shaped patch pair structure, and the third fan-shaped patch pair structure are connected in series via a second microstrip line structure. The second microstrip line structure is connected to the third microstrip line structure at both ends. The entire structure is completely symmetrical about the horizontal and vertical axes.

[0011] Furthermore, one terminal of the absorption network is open.

[0012] Furthermore, the filter as a whole includes an upper metal structure, a dielectric substrate, and a lower metal grounding structure arranged vertically in the thickness direction.

[0013] Furthermore, the dielectric substrate is made of RO4003C plate with a relative dielectric constant ε r is 3.55, and the thickness H is 1.524mm.

[0014] Furthermore, the thickness of the upper metal structure and the lower metal grounding structure are both 0.017 mm.

[0015] In the above technical solution, the technical effects and advantages provided by the present invention are:

[0016] 1. The present invention provides a wide-stopband, non-reflective dual-band filter. This filter utilizes a pair of quarter-wavelength coupled microstrip lines MCL1 and ML2 in series, and introduces a three-quarter-wavelength microstrip line ML1 and ML2 in parallel. After undergoing lateral signal interference with a half-wavelength electrical length difference, the filter not only forms a stopband at the center frequency but also generates two transmission zeros, thereby constructing a dual-band bandpass filter response with excellent frequency selectivity.

[0017] 2. The present invention provides a wide-stopband non-reflection dual-frequency filter, which adds two complementary absorption networks 1 and 2 to the circuit to form three non-reflection areas in three out-of-band signal areas, ultimately achieving full-band non-reflection characteristics.

[0018] 3. The present invention provides a wide-stopband, non-reflective dual-band filter, in which a complementary absorption network 1 composed of a resistor R2, a microstrip line ML3, and an open-circuit branch ML4 is embedded within the dual-band filter network, so that the reflected signal between the two passbands can be effectively absorbed; moreover, the absorption network 1 can generate a reflection zero point to improve the band-stop characteristics between the two passbands.

[0019] 4. The present invention provides a wide-stopband, non-reflective dual-band filter, in which a complementary absorption network 2 is loaded in parallel at the input / output section of the dual-band filter network N, capable of effectively absorbing reflected signals in the low-frequency and high-frequency band regions of the two passbands; the absorption network 2 is composed of a quarter-wavelength ML5, a resistor R1, and a quarter-wavelength short-circuit branch M7 connected in series, with quarter-wavelength open-circuit branches ML6 and ML4 connected in parallel at both ends of the resistor R1; the absorption network 2 can generate four reflection zeros, which not only achieves good out-of-band signal absorption performance, but also increases the frequency selectivity of the two passbands.

[0020] 5. The present invention provides a wide-stopband non-reflection dual-frequency filter. The proposed fan-shaped resonant structure is composed of three pairs of fan-shaped patch pairs and a high-impedance microstrip line connected in series. The required cutoff frequency can be achieved by adjusting the angle and radius of the fan-shaped load, the length of the load branch, and the distance between the two. While not affecting the non-reflection dual-frequency bandpass filtering characteristics of the main circuit, good high-stopband response is achieved, and the structure is simple, compact, and easy to integrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0022] Figure 1 This is a schematic diagram of the circuit framework of the present invention;

[0023] Figure 2 Schematic diagram of the circuit structure of the present invention;

[0024] Figure 3 Schematic diagram of the fan-shaped resonant structure of the present invention;

[0025] Figure 4 Schematic diagram of the working principle of the present invention for generating a reflectionless filtering response by loading absorption network 1 and absorption network 2, wherein (a) is a schematic diagram of a dual-bandpass filter, (b) is a diagram showing the effect of loading absorption network 1, and (c) is a diagram showing the response curve when both absorption network 1 and absorption network 2 are loaded simultaneously;

[0026] Figure 5Schematic diagram of circuit parameters of the reflectionless dual-band bandpass filter of the present invention;

[0027] Figure 6 This is a schematic diagram of the dimensions of the fan-shaped resonant structure of the present invention;

[0028] Figure 7 This is a schematic diagram of the layout dimensions of the upper metal structure of the wide stopband non-reflective dual-band filter of the present invention;

[0029] Figure 8 This is a schematic diagram of the cross-sectional structure and dimensions of the wide stopband non-reflective dual-frequency filter of the present invention;

[0030] Figure 9 The frequency response curve of the dual-band pass filter with full-band non-reflection function of the present invention;

[0031] Figure 10 This is a comparison diagram of the transmission response before and after the fan-shaped resonant structure of the present invention;

[0032] Figure 11 The figure is a frequency response curve diagram of the dual-band pass filter with full-band reflection-free and wide stopband functions according to the present invention.

[0033] Description of reference numerals:

[0034] 1. Dual-band filtering network; 2. Fan-shaped resonant structure; 3. Absorption network 1; 4. Absorption network 2; 5. Input port; 6. Output port; 10. Upper metal structure; 20. Dielectric substrate; 30. Lower metal grounding structure; 101. First fan-shaped patch pair structure; 102. Second fan-shaped patch pair structure; 103. Third fan-shaped patch pair structure; 104. First microstrip line structure; 105. Second microstrip line structure; 106. Third microstrip line structure. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0036] This embodiment provides a wide stopband non-reflective dual-frequency filter, such as Figure 1As shown. It mainly consists of a dual-band filter network 1, a pair of absorption networks 1-3, a pair of absorption networks 2-4, a pair of fan-shaped resonant structures 2, an input port 5 and an output port 6. The dual-band filter network 1, the pair of absorption networks 1-3 and the pair of absorption networks 2-4 together form a reflectionless dual-band bandpass filter circuit. The two ends of the reflectionless dual-band bandpass filter circuit are respectively connected to a pair of fan-shaped resonant structures 2, and the other ends connected to the fan-shaped resonant structures 2 are respectively connected to the input port 5 and the output port 6 for energy input and output. Specifically, the input port 5 is connected to the fan-shaped resonant structure 2, the dual-band filter network 1, the fan-shaped resonant structure 2 and the output port 6 are connected in series in sequence, the fan-shaped resonant structure 2 is connected in parallel with the absorption network 1-3 at the connection between the fan-shaped resonant structure 2 and the input / output port 6, and two branches are connected in parallel inside the dual-band filter network 1 circuit and connected to the absorption network 1-3. The entire dual-band filter circuit with wide stopband and reflectionless characteristics is completely symmetrically distributed on the left and right sides.

[0037] Figure 2 for Figure 1 Schematic diagram of the structure of the reflectionless dual-band bandpass filter circuit described in . Figure 2 As shown, dual-band filter network 1 consists of a pair of quarter-wavelength coupled microstrip lines MCL1, as well as quarter-wavelength microstrip lines ML2 and three-quarter-wavelength microstrip lines ML1. The left end of the first coupled line MCL1a of coupled microstrip line MCL1 is open-circuited, and the right end is connected to microstrip line ML2. The left end of the second coupled line MCL1b of coupled microstrip line MCL1 is connected to port 1, and the right end of MCL1b is connected to absorption network 1-3. Absorption network 1-3 is composed of resistor R2, quarter-wavelength microstrip line ML3, and half-wavelength microstrip line ML4 connected in series, with the ends of absorption network 1-3 open-circuited. Absorption network 2-4 is connected in parallel at the junction of input port 5 and coupled microstrip line MCL1. Absorption network 2-4 consists of four quarter-wavelength microstrip lines (ML5, ML6, ML7, and ML8) and resistor R1. Microstrip line ML5, resistor R1, and microstrip line ML7 are connected in series, with the other end of microstrip line ML7 grounded. The connection between microstrip line ML5 and resistor R1 is connected in parallel to microstrip line ML6. The connection between microstrip line ML7 and resistor R1 is connected in parallel to microstrip line ML8. Finally, the above structure is mirrored with the vertical center axis of microstrip line ML2 as the symmetry line, forming a completely symmetrical circuit distribution on the left and right sides. Input port 5 is mirrored to form output port 6.

[0038] Figure 3 for Figure 1 Schematic diagram of the fan-shaped resonant structure 2. Figure 3As can be seen in the figure, the fan-shaped resonant structure 2 is mainly composed of three pairs of vertically symmetrical fan-shaped patch pair structures, namely the first fan-shaped patch pair structure 101, the second fan-shaped patch pair structure 102, and the third fan-shaped patch pair structure 103; and three sections of microstrip line structures, namely the first microstrip line structure 104, the second microstrip line structure 105, and the third microstrip line structure 106. The first and second fan-shaped patch pair structures 101 and 102, which are symmetrical in terms of their vertical orientation, are connected at their vertices, and the third fan-shaped patch pair structure 103, which is symmetrical in terms of their vertical orientation, is connected via a section of the first microstrip line structure 104. The three pairs of fan-shaped patch pair structures are horizontally distributed along the horizontal symmetry line and connected in series via the second microstrip line structure 105. The ends of the second microstrip line structure 105 are then connected to the third microstrip line structure 106 to form a complete fan-shaped resonant patch pair structure. The entire structure is completely symmetrical about the horizontal and vertical axes.

[0039] Without a loaded sector-shaped resonant structure 2, a microwave signal is fed into input port 5. After passing through the coupled microstrip line and the half-wavelength coupled microstrip line MCL1 structure, the signal is split into two paths: one path passing through microstrip line ML1, and the other path passing through microstrip line structure ML2. Because the electrical lengths of microstrip lines ML1 and ML2 differ by 180°, high-frequency signals with center frequency f0 cancel out at the convergence point, splitting the bandpass filter response formed by the MWCL1 structure into two, thereby achieving a dual-band filtering effect. Two transmission poles are generated within each passband, and two transmission zeros are generated between the two passbands, ultimately outputting from the output.

[0040] To illustrate the working mechanism of the dual-band reflection-free feature, Figure 4 The working principle of generating non-reflection filtering response by loading absorption network 1 3 and absorption network 2 4 is given. Figure 4 a shows the dual-band bandpass filter response when the absorption network 1 3 and the absorption network 2 4 are not loaded. The effect of loading the absorption network 1 3 is shown in FIG. Figure 4 As shown in Figure 2b, the absorption network 3 is a complementary dual-stopband structure with two transmission zeros located at (2n+1)f0 (n=0, 1, 2…), symmetrical about the center frequency f0. It conducts at the center frequency f0 and outside the upper and lower passbands of the filter, cuts off at the center frequencies of the upper and lower passbands, and generates a reflection zero at f0. Therefore, the reflected signal in the stopband between the two passbands is introduced into the absorption network 3 and dissipated by the resistor R2, forming a reflection-free region in the area between the two passbands. Figure 4c is the response curve when the absorption network 1 3 and the absorption network 2 4 are loaded at the same time. The loaded complementary absorption network 2 4 can generate a complementary wide stopband filter with a center frequency of f0, which can guide the reflected signals of the upper and lower frequency bands of the two passbands into the absorption network 2 4 circuit to be absorbed by the resistor R1, and finally form two reflection-free areas in the upper and lower frequency bands of the two passbands. And by adjusting the impedance of the microstrip line in the absorption network 2 4, four reflection zero points can be generated in the full frequency band, two of which are distributed outside the two passbands, effectively improving the out-of-band absorption level, and the other two are distributed at the filtering edge of the large bandwidth filter generated by the coupled microstrip line MWCL1, that is, the left edge of the lower passband and the right edge of the upper passband, improving the selectivity of signal transmission in the passband. At this point, after passing through the absorption network 1 3 and the absorption network 2 4, the reflected signals in the entire frequency band will be completely absorbed, realizing the full-band reflection-free dual-frequency filtering characteristics. Due to the loading of Figure 3 The fan-shaped resonant structure 2 shown has a low-pass response, so it will not affect the full-band reflectionless dual-band filtering characteristics of the low frequency band, but has a good suppression effect on the harmonics of the high frequency band. Finally, a circuit such as the following is loaded between the reflectionless dual-band bandpass filter circuit and the input / output port. Figure 3 The fan-shaped resonant structure 2 shown can construct a dual-band filter with wide stopband and non-reflection characteristics.

[0041] The following shows the filter completed according to the above working mechanism and related design guidance, and is simulated and verified. Figure 5 This is a schematic diagram of the parameters of the ideal circuit for the reflectionless dual-band bandpass filter involved in the present invention. Its ideal electrical parameters are as follows: θ = 90°, Ze = 113.2Ω, Zo = 59Ω, Z1 = 63.6Ω, Z2 = 64.8Ω, Z3 = 79Ω, Z4 = 47.8Ω, Z5 = 120.7Ω, Z6 = 97.8Ω, Z7 = 34Ω, Z8 = 159Ω, R1 = 68.1Ω, R2 = 127Ω.

[0042] Figure 6 Figure 1 is a schematic diagram of the parameters of the fan-shaped resonant structure. The second microstrip line structure 105 has a length of Lss1 and a width of Ws. The first fan-shaped patch structure 101 has a radius of Ls2 and an angle of β. The third fan-shaped patch structure 103 has an angle of θ and a radius of Ls1. The overlapping length of the third fan-shaped patch structure 103 and the first microstrip line structure 104 is Ws. The first microstrip line structure 104 has a length of Ls4 and a width of WS4. The spacing between the first fan-shaped patch structure 101 and the third fan-shaped patch structure 103 is Lgs12. The width of the third microstrip line structure 106 is W0. The second fan-shaped patch structure 102 is symmetrical to the first fan-shaped patch structure 101.

[0043] Figure 7It is a schematic diagram of the size of the upper metal structure of the wide-bandwidth and reflection-free dual-band filter. The input feed line and the output feed line have a line width of W0 and a length of Lport; the fan-shaped resonant structure 2 is embedded in the port, and the distance from the starting part of the port is IN1; the line width of the coupled microstrip line MCL1 is WCL1, the length is LCL1, and the spacing is S1; the line width of the microstrip line ML1 is W1, and the length is L1; the line width of the microstrip line ML2 is W2, and the length is L2; the line width of the microstrip line ML3 is W3, and the length is L3; the line width of the open-circuit microstrip line ML4 is W4, and the length is L4; the line width of the microstrip line ML5 is W5, and the length is L5; the line width of the microstrip line ML6 is W6, and the length is L6; the line width of the microstrip line ML7 is W7, and the length is L7; the line width of the microstrip line ML8 is W8, and the length is L8; the radius of the metal via is Rvia. The specific structure parameters are as follows: W0=3.38mm, Lport=25mm, IN1=5mm, IN2=1mm, WCL1=1.1mm, S1=0.66mm, LCL1=23.5, W1=2.24mm, L1=19mm, W2=2.16mm, L2=72mm, W3=1.68mm, L3=23mm, W4=3.94mm, L4=43.1mm, W5=0.56mm, L5=22.2mm, W6=0.88mm, L6=24.8mm, W7=6mm, L7=20.2mm, W8=0.17mm, L8=21.8mm, R1=68.1Ω, R2=127Ω; in the fan-shaped resonant structure: WS=0.7mm, β=86°, LS1=4.4mm, Lgs12=6.1mm, θ=48°, LS2=4.1mm, WS4=0.3mm, LS4=1.8mm; LSS1=19mm.

[0044] Figure 8 It is a filter section structure size diagram. As shown in Figure 8 the overall structure of the filter mainly includes an upper metal structure 10, a lower metal ground structure 30, a dielectric substrate 20, and a metalized via structure Via opened on the dielectric substrate 20 in the thickness direction. The dielectric substrate 20 adopts RO4003C plate material, the relative dielectric constant ε r is 3.55, and the thickness H is 1.524mm; the thicknesses of the upper metal structure 10 and the lower metal ground structure 30 are both 0.017mm. The dual-band filter with wide-bandwidth and reflection-free characteristics of other frequency bands can be obtained by scaling in this embodiment.

[0045] Figure 9 It is the frequency response of the reflection-free dual-band bandpass filter obtained by CST MWS three-dimensional simulation software without loading the fan-shaped resonant structure 2. And the formula: absorption rate AR=100×(1-|S 11| 2 -|S 21 | 2 ) obtained the absorption efficiency curve of the absorption network for the signal in the entire frequency band. Figure 9 The center frequencies of the two frequency bands are 1.45 GHz and 2.55 GHz, respectively, corresponding to minimum insertion losses of 1.52 dB and 2.35 dB within the passbands. The reflection coefficient S11 is below -13 dB within the 0-4.75 GHz range, and the return losses within the two passbands are 17.1 dB and 14.3 dB, respectively. The four transmission poles within the bands are located at 1.36 GHz, 1.49 GHz, 2.46 GHz, and 2.65 GHz. Two poles occur at the left edge of the first passband and the right edge of the second passband, at 1.26 GHz and 2.76 GHz, respectively. Combined with the signal absorption efficiency curve, the signal absorption rates at these two points are 92.4% and 98.7%, respectively. Furthermore, absorption network 3 generates two additional reflection zeros at 0.68 GHz and 3.68 GHz. The two transmission zeros between the passbands are located at 1.87 GHz and 2.17 GHz, respectively, with signal suppression better than 39.2 dB. The reflection zero generated by the absorption network 3 is located at 2.25 GHz.

[0046] Figure 10 Comparison diagrams before and after adding the fan-shaped resonant structure to the filter of the present invention. As can be seen from the figure, the reflectionless dual-band filter without the fan-shaped resonant structure 2 generates higher harmonics in the high-frequency band. However, after adding the fan-shaped resonant structure 2, the filter has a significant suppression effect on higher harmonics. In the range of 4.2 GHz to 16 GHz, the signal suppression is above 43.3 dB, ultimately achieving a high level of signal suppression of 6f0.

[0047] Figure 11 The S parameter curve and absorption efficiency curve of the filter of the present invention are shown in FIG. Figure 11 As can be seen from the figure, the center frequencies of the two passbands are 1.45 GHz and 2.55 GHz, respectively, and the minimum insertion losses within the two passbands are 1.77 dB and 2.52 dB, respectively. The reflection coefficient S11 is maintained below -12.2 dB in the 0-4 GHz range, achieving zero reflection across the entire frequency band. Furthermore, the reflected signal absorption rate exceeds 94% in the 0-1.27 GHz, 1.66-2.36 GHz, and 2.7-4 GHz bands.

[0048] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A wide stopband non-reflective dual-frequency filter, characterized in that: The invention comprises a dual-band filter network (1), wherein two ends of the dual-band filter network (1) are respectively connected to fan-shaped resonant structures (2), and one end of the two fan-shaped resonant structures (2) away from the dual-band filter network (1) is respectively connected to an input port (5) and an output port (6); an absorption network 2 (4) is connected in parallel at the connection point between the fan-shaped resonant structure (2) and the dual-band filter network (1); and two groups of absorption network 1 (3) branches are connected in parallel inside the dual-band filter network (1); The dual-band filtering network (1) comprises a pair of quarter-wavelength coupled microstrip lines MCL1, a quarter-wavelength microstrip line ML2 and a three-quarter-wavelength microstrip line ML1; one end of a first coupled line MCL1a of the coupled microstrip line MCL1 is open-circuited, and one end thereof is connected to the microstrip line ML2; one end of a second coupled line MCL1b of the two sets of coupled microstrip lines MCL1 is respectively connected to an input port (5) and an output port (6), and the other end thereof is connected to an absorption network 1 (3); The absorption network 1 (3) comprises a resistor R2, a quarter-wavelength microstrip line ML3 and a half-wavelength microstrip line ML4 connected in series; The absorption network 2 (4) includes a quarter-wavelength microstrip line ML5, a microstrip line ML6, a microstrip line ML7 and a microstrip line ML8, and a resistor R1; the microstrip line ML5, the resistor R1 and the microstrip line ML7 are connected in series in sequence, and the end of the microstrip line ML7 away from the resistor R1 is grounded; the microstrip line ML5 is connected to the resistor R1 at a point where the microstrip line ML6 is connected in parallel, and the microstrip line ML7 is connected to the resistor R1 at a point where the microstrip line ML8 is connected in parallel.

2. The wide stopband non-reflective dual-band filter according to claim 1, wherein: The fan-shaped resonant structure (2) comprises a first fan-shaped patch pair structure (101), a third fan-shaped patch pair structure (103), and a second fan-shaped patch pair structure (102) that are symmetrical in top and bottom; the first fan-shaped patch pair structure (101) and the second fan-shaped patch pair structure (102) are connected at their respective symmetrical points; the third fan-shaped patch pair structure (103) is connected via a first microstrip line structure (104); the first fan-shaped patch pair structure (101), the second fan-shaped patch pair structure (102), and the third fan-shaped patch pair structure (103) are connected in series via a second microstrip line structure (105); and the second microstrip line structure (105) is connected at both ends to a third microstrip line structure (106).

3. The wide stopband non-reflection dual-band filter according to claim 2, characterized in that: The fan-shaped resonant structure (2) is symmetrical in top, bottom, left and right directions.

4. The wide stopband non-reflective dual-band filter according to claim 3, wherein: One (3) terminal of the absorption network is open.

5. The wide stopband non-reflection dual-band filter according to claim 4, characterized in that: The filter as a whole comprises an upper metal structure (10), a dielectric substrate (20), and a lower metal grounding structure (30) arranged vertically in the thickness direction.

6. The wide stopband non-reflective dual-band filter according to claim 5, characterized in that: The dielectric substrate (20) is made of RO4003C plate, with a relative dielectric constant ε r is 3.55, and the thickness H is 1.524mm.

7. The wide stopband non-reflection dual-band filter according to claim 6, characterized in that: The thickness of the upper metal structure (10) and the lower metal grounding structure (30) are both 0.017 mm.

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