Dual-mode dual-frequency filter based on folded waveguide mode and air slot line mode

Abstract

The invention discloses a dual-mode dual-frequency filter based on a folded waveguide mode and an air slot line mode. Comprising a metal cavity, a first metal resonant plate, a first metal coupling plate, a second metal resonant plate, a second metal coupling plate, a third metal resonant plate, a third metal coupling plate, a fourth metal resonant plate, a first external coupling adjusting metal column and a second external coupling adjusting metal column. The metal cavity is a fan-shaped hollow cavity, and a first metal resonant plate, a first metal coupling plate, a second metal resonant plate, a second metal coupling plate, a third metal resonant plate, a third metal coupling plate and a fourth metal resonant plate are sequentially arranged in the metal cavity; a first external coupling adjusting metal column and a second external coupling adjusting metal column. An irregular etching groove is formed in the middle of the fan-shaped plate to form an air groove line die, the irregular etching groove is formed by connecting and combining a rectangular notch groove and an elliptical groove with the width larger than that of the rectangular groove, and the elliptical groove is located under the rectangular groove.

Description

Technical Field

[0001] The present invention belongs to the technical fields of microwave communication technology and filter technology, and particularly relates to the design of a dual-mode dual-frequency filter based on folded waveguide mode and air slot line mode. Background Art

[0002] Waveguide filters are widely used in the radio frequency front-end equipment of satellite base station communication due to their advantages such as high Q value, low insertion loss, high power capacity, and easy processing. A dual-frequency waveguide filter can output two communication frequency bands, enabling non-interference between different communication standards, thereby reducing the volume, loss, and production cost of the system. However, according to the waveguide filter theory, its resonant frequency is positively correlated with the length, width, and height of the cavity, that is, the lower the frequency, the larger the volume, which is not conducive to the miniaturization design of the communication system. The folded waveguide filter can effectively overcome this defect and can reduce the volume of the filter by 1 / 4 while keeping the resonant frequency and Q value unchanged. Further, the dual-mode folded waveguide filter can reduce the volume by 1 / 2 on this basis and can generate multiple transmission zeros. Therefore, the dual-mode dual-frequency filter based on the dual-mode folded waveguide design has the advantages of small volume, high Q value, and good out-of-band rejection effect.

[0003] In the prior art, the patent authorization number: CN109509950B, and the patent name: An invention patent for a miniaturized dual-frequency waveguide filter, which is a dual-frequency waveguide filter composed of three rectangular cavities. Each rectangular cavity is ridged on the short side and the long side to form a four-ridge waveguide resonator to reduce the frequency and achieve miniaturization. However, its inner cavity size is 209.5mm×56mm×56mm. Considering that the center frequency of its 1st passband is 3.34GHz and the center frequency of its 2nd passband is 3.66GHz, the volume of the filter is still relatively large at this frequency. At the same time, this dual-frequency filter only generates one transmission zero between the two passbands, resulting in poor out-of-band rejection effect.

[0004] The patent application number: CN115642380A, and the patent name: An invention patent for an integrated microwave ceramic waveguide dual-frequency filter, which is a dual-frequency waveguide filter composed of two dielectric waveguide power dividers, two dielectric waveguide filters, and an impedance matching structure, and realizes dual passbands at 2.95GHz and 3.6GHz. However, in order to achieve a pair of zeros outside each passband to improve the frequency selection performance, this filter realizes the CQ coupling structure by introducing multiple rectangular slots and blind holes, resulting in a complex filter structure and difficult adjustment. Summary of the Invention

[0005] The purpose of the present invention is to provide a dual-mode dual-frequency filter based on folded waveguide mode and air slot line mode, which can realize the miniaturization and high Q value of the dual-frequency filter, and at the same time generate multiple transmission zeros with a simple structure to improve the out-of-band rejection performance.

[0006] The present invention adopts the following technical solution: a dual-mode and dual-frequency filter based on folded waveguide mode and air slot line mode, comprising: a first metal resonator plate, a first metal coupling plate, a second metal resonator plate, a second metal coupling plate, a third metal resonator plate, a third metal coupling plate, and a fourth metal resonator plate arranged in sequence within a metal cavity; and further comprising a first external coupling adjustment metal post and a second external coupling adjustment metal post.

[0007] The metal cavity is a fan-shaped hollow cavity. The first metal resonator plate, the second metal resonator plate, the third metal resonator plate, and the fourth metal resonator plate are fan-shaped plates, and there are gaps between the two side edges of the fan-shaped plates and the metal cavity to form electric walls for generating folded waveguide modes. An irregular etching groove is provided in the middle of the fan-shaped plate to form an air slot line mode. The irregular etching groove is composed of a combination of a rectangular etching groove and an elliptical groove with a width greater than that of the rectangular groove, where the elliptical groove is located directly below the rectangular groove.

[0008] The resonant frequency of the folded waveguide is determined by the gap between the two side edges of the fan-shaped metal resonator plate and the fan-shaped metal cavity; the smaller the gap, the lower the frequency.

[0009] The resonant frequency of the air slot line mode is determined by the irregular etching groove in the middle of the fan-shaped metal resonator plate. The narrower the rectangular groove in the irregular etching groove, the lower the frequency; the longer the minor axis and major axis of the elliptical groove, the lower the frequency; and the deeper the etching groove, the lower the frequency.

[0010] By adjusting parameters such as the depth and width of the etching groove, the folded waveguide mode and the air slot line mode can both become the first resonant modes of the dual-mode and dual-frequency filter.

[0011] Further, the first metal resonator plate and the second metal resonator plate are centrosymmetrically distributed with the third metal resonator plate and the fourth metal resonator plate within the metal cavity, that is, all parameters of the first metal resonator plate are exactly the same as those of the fourth metal resonator plate, and all parameters of the second metal resonator plate are exactly the same as those of the third metal resonator plate; the distance between the first resonant metal plate and the second metal resonator plate is the same as the distance between the third resonant metal plate and the fourth metal resonator plate; and the distance between the second metal resonator plate and the center position of the metal cavity is the same as the distance between the third metal resonator plate and the center position of the metal cavity.

[0012] Further, a first metal coupling plate is provided at the center position between the first metal resonator plate and the second metal resonator plate; a second metal coupling plate is provided at the center position between the second metal resonator plate and the third metal coupling plate, which is also the center position of the metal cavity; and a third metal coupling plate is provided at the center position between the third metal resonator plate and the fourth metal resonator plate. Among them, all parameters of the first metal coupling plate are exactly the same as those of the third metal coupling plate.

[0013] The metal coupling plate is a sector plate, and both sides of the sector plate are connected to the sector metal cavity. Rectangular coupling windows are provided on both sides of the upper and bottom of the sector plate. The larger the rectangular coupling window on the upper part, the greater the coupling strength between the air slot line modes, that is, the larger the bandwidth of the air slot line modes; the larger the rectangular coupling windows on both sides of the bottom, the greater the coupling strength between the folded waveguides, that is, the larger the bandwidth of the folded waveguide modes. The distance between the metal resonant plates also affects the coupling strength of each of the two modes. The closer the distance, the greater the coupling strength. By adjusting the magnitude of the coupling strength, independent control of the bandwidths of the two passbands can be achieved.

[0014] The first external coupling adjustment metal post connects the first resonant metal plate and the metal cavity; the second external coupling adjustment metal post connects the fourth metal resonant plate and the metal cavity. The two external coupling adjustment metal posts are symmetrically distributed about the center on both sides of the metal cavity. By adjusting the positions of the external coupling adjustment metal posts, the external coupling value of the dual-mode dual-frequency filter can be controlled, and matching of the external coupling with the folded waveguide mode and the air slot line mode can be achieved, that is, the effect of similar external Q values of the two modes.

[0015] Further, the dual-mode dual-frequency filter based on the folded waveguide mode and the air slot line mode is a centrosymmetric structure. The SMA connectors are centrally distributed on both sides of the dual-mode dual-frequency filter, and the feeding pins are directly connected to the sides of the first resonant metal plate and the fourth metal resonant plate respectively.

[0016] Further, the SMA connectors and the 50Ω characteristic impedance transmission lines connect the dual-mode dual-frequency filter to the external circuit and match it with the external circuit.

[0017] The dual-mode dual-frequency filter of the present invention does not introduce an additional structure, realizes a dual passband, generates four transmission zeros, and the S response curve of the filter with four transmission zeros. Among them, there is one transmission zero on the low-frequency side of the first passband, one transmission zero between the first passband and the second passband, and two output zeros on the high-frequency side of the second passband. The out-of-band rejection effect is greatly improved, and at the same time, the size of the filter is greatly reduced and a high Q value is maintained.

[0018] Beneficial effects: Compared with the existing technologies, the present invention has the following advantages:

[0019] 1. The dual-mode dual-frequency filter provided by the present invention realizes a significant reduction in volume compared with the traditional waveguide dual-frequency filter.

[0020] 2. The dual-mode resonant modes provided by the present invention can make any resonant mode become the fundamental mode through parameter adjustment to form the first passband.

[0021] 3. The dual-mode dual-frequency filter provided by the present invention can achieve relatively independent control of the bandwidths of the two passbands through simple parameter adjustment.

[0022] 4. The dual-mode and dual-frequency filter provided by the present invention can achieve transmission zeros on both the low-frequency side and the high-frequency side of each independent passband, greatly improving the out-of-band rejection effect of each passband. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FIG. is a three-dimensional schematic diagram of a dual-mode and dual-frequency filter based on a folded waveguide mode and an air slot line mode provided by an embodiment of the present invention.

[0024] Figure 2 FIG. is a top view of a dual-mode and dual-frequency filter based on a folded waveguide mode and an air slot line mode provided by an embodiment of the present invention.

[0025] Figure 3 FIG. is a view from perspective A of the first metal resonator plate 4 or a view from perspective B of the fourth metal resonator plate 10 in an embodiment of the present invention.

[0026] Figure 4 FIG. is a dual-mode field diagram of the first metal resonator plate 4 or the fourth metal resonator plate 10 in an embodiment of the present invention.

[0027] Figure 5 FIG. shows the effect of g on the folded waveguide mode frequency in the first metal resonator plate 4 or the fourth metal resonator plate 10 in an embodiment of the present invention. 1 Effect diagram of the influence on the folded waveguide mode frequency

[0028] Figure 6 FIG. shows the effect of w on the air slot line mode frequency in the first metal resonator plate 4 or the fourth metal resonator plate 10 in an embodiment of the present invention. 1 Effect diagram of the influence on the air slot line mode frequency

[0029] Figure 7 FIG. shows the effect of r on the air slot line mode frequency in the first metal resonator plate 4 or the fourth metal resonator plate 10 in an embodiment of the present invention. 1 Effect diagram of the influence on the air slot line mode frequency

[0030] Figure 8 FIG. shows the effect of r on the air slot line mode frequency in the first metal resonator plate 4 or the fourth metal resonator plate 10 in an embodiment of the present invention. 2 Effect diagram of the influence on the air slot line mode frequency

[0031] Figure 9 FIG. shows the effect of h on the air slot line mode frequency in the first metal resonator plate 4 or the fourth metal resonator plate 10 in an embodiment of the present invention. 1 Effect diagram of the influence on the air slot line mode frequency

[0032] Figure 10 FIG. is a view from perspective A of the first metal coupling plate 5 or a view from perspective B of the third metal coupling plate 9 in an embodiment of the present invention.

[0033] Figure 11 FIG. shows cw in the first metal coupling plate 5 in an embodiment of the present invention. 1Effect diagram of the influence on the air slot line mode coupling coefficient k between the first metal resonator plate 4 and the second metal resonator plate 6 2

[0034] Figure 12 In the embodiment of the present invention, Cr in the first metal coupling plate 5 1 Effect diagram of the influence on the folded waveguide mode coupling coefficient k between the first metal resonator plate 4 and the second metal resonator plate 6 1

[0035] Figure 13 A perspective view of the second metal resonator plate 6 from the A perspective or a perspective view of the third metal resonator plate 8 from the B perspective in the embodiment of the present invention.

[0036] Figure 14 Dual-mode field diagram of the second metal resonator plate 6 or the third metal resonator plate 8 in the embodiment of the present invention.

[0037] Figure 15 A perspective view of the second metal coupling plate 7 from the A perspective or a perspective view of the second metal coupling plate 7 from the B perspective in the embodiment of the present invention.

[0038] Figure 16 Simulation S-parameter diagram of the dual-mode dual-frequency filter in the embodiment of the present invention.

[0039] Figure 17 Enlarged view of the passband region of the simulation S-parameters of the dual-mode dual-frequency filter in the embodiment of the present invention. Detailed implementation manners

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the technical solutions of the present invention will be described in detail below in conjunction with the embodiments of the present invention and their accompanying drawings. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0041] Embodiment

[0042] Referring to Figure 1 and Figure 2 , this embodiment discloses a dual-mode dual-frequency filter based on the folded waveguide mode and the air slot line mode. A first metal resonator plate 4, a first metal coupling plate 5, a second metal resonator plate 6, a second metal coupling plate 7, a third metal resonator plate 8, a third metal coupling plate 9, and a fourth metal resonator plate 10 are arranged in sequence in the metal cavity and are fan-shaped plates, and there are gaps between the two sides of the fan-shaped plates and the metal cavity to form electric walls to generate the folded waveguide mode; an irregular etching groove is provided in the middle of the fan-shaped plate to form the air slot line mode, and the irregular etching groove is formed by connecting and combining a rectangular etching groove and an elliptical groove with a width greater than that of the rectangular groove, wherein the elliptical groove is located directly below the rectangular groove.

[0043] ​​The resonant frequency of the air slot waveguide is determined by the irregular etching slot in the middle of the sector-shaped metal resonant plate; the narrower the rectangular slot in the irregular etching slot, the lower the frequency; the longer the minor axis and major axis of the elliptical slot, the lower the frequency; the deeper the etching slot, the lower the frequency.

[0044] Its outer dimensions are R = 28 mm, L = 44 mm, the cavity thickness is 2 mm, and the thickness t of the resonant metal plate and the coupling metal plate is 1 mm. In the embodiment of the present invention, the given structural dimensions are preferred dimensions. Referring to the embodiment of the present invention, modifying the dimensional parameters of each component can further obtain the performance required in practice.

[0045] See Figure 1 , the dual-mode and dual-frequency filter based on the folded waveguide mode and the air slot waveguide mode includes: a metal cavity 1, an SMA connector 2, a first external coupling adjustment metal post 3, a first metal resonant plate 4, a first metal coupling plate 5, a second metal resonant plate 6, a second metal coupling plate 7, a third metal resonant plate 8, a third metal coupling plate 9, a fourth metal resonant plate 10, an SMA connector 11, and a second external coupling adjustment metal post 12. All components are symmetrically distributed about the center line of the metal cavity.

[0046] See Figure 2 , because the dual-mode and dual-frequency filter provided in this embodiment is centrosymmetric, the views from perspective A and perspective B are exactly the same.

[0047] See Figure 3 and Figure 4 , the first metal resonant plate 4 and the fourth metal resonant plate 10 are sector-shaped plates, and there is a gap g 1 = 2.219 mm between the two sides of the sector-shaped plate and the metal cavity 1 to form an electric wall to generate the folded waveguide mode 15. An irregular etching slot is provided in the middle of the sector-shaped plate to form the air slot waveguide mode 16. The irregular etching slot is composed of a combination of a rectangular etching slot 13 and an elliptical slot 14 with a width greater than that of the rectangular slot. The elliptical slot 14 is located directly below the rectangular slot 13. The length h 1 of the rectangular slot 13 is 8.72 mm, the width w 1 is 1.1226 mm, the major axis r 1 of the elliptical slot 14 is 3.5 mm, and r 2 is 3 mm. The feeding pin of the SMA connector 2 is directly connected to the side of the first metal resonant plate 4, and the feeding pin of the SMA connector 11 is directly connected to the side of the fourth metal resonant plate 10. The first external coupling adjustment metal post 3 and the second external coupling adjustment metal post 12 are horizontally connected to the metal cavity 1 and the first metal resonant plate 4, and the metal cavity 1 and the fourth metal resonant plate 10 at the coordinate system (8.5 mm, -1 mm) in the figure.

[0048] See Figure 5The resonant frequency of the folded waveguide mode 15 of the first metal resonator plate 4 and the fourth metal resonator plate 10 is determined by the gap g between the two sides of the fan-shaped metal resonator plate and the fan-shaped metal cavity 1 The smaller the gap, the lower the frequency.

[0049] See Figures 6 - 9 , the resonant frequency of the slot-line mode 16 of the first metal resonator plate 4 and the fourth metal resonator plate 10 is determined by the irregular etching slots in the middle of the fan-shaped metal resonator plate. The narrower the width w 1 of the rectangular slot in the irregular etching slot, the lower the frequency; the longer the major semi-axis r 1 and the minor semi-axis r 2 of the elliptical slot, the lower the frequency; the deeper the etching depth h 1 of the etching slot, the lower the frequency.

[0050] See Figures 5 - 9 , this embodiment is a dual-mode resonance mode. By parameter control, the frequency of either the slot-line mode or the folded waveguide mode can be reduced to become the fundamental mode, and then the first passband is formed through coupling. The other mode with a higher frequency becomes the second mode, and then the second passband is formed through coupling.

[0051] See Figure 10 , the first metal coupling plate 5 and the third metal coupling plate 9 are fan-shaped plates, and the two sides of the fan-shaped plates are connected to the fan-shaped metal cavity. Rectangular coupling windows are provided on both sides of the upper and bottom of the fan-shaped plates. The length cl 1 of the rectangular coupling window 14 in the upper part is 10 mm, and the width cw 1 is 1.4 mm. The length ca 1 of the rectangular coupling window 15 on both sides of the bottom is 9.8 mm, and the width cr 1 is 9.05 mm. The first metal coupling plate 5 is located at the center position between the first metal resonator plate 4 and the second metal resonator plate 6, and the third metal coupling plate 9 is located at the center position between the third metal resonator plate 8 and the fourth metal resonator plate 10.

[0052] See Figure 11 and Figure 12 , taking cw 1 and cr 1 respectively to illustrate the influence on the coupling coefficient k 2 between the slot-line modes and the coupling coefficient k 1 between the folded waveguides. It shows that the larger the rectangular coupling window 17 on the upper part of the first metal coupling plate 5 and the third metal coupling plate 9, the larger the coupling coefficient k 2 between the slot-line modes of the first resonant metal plate 4 and the second metal resonator plate 6, that is, the larger the bandwidth of the slot-line mode; the larger the rectangular coupling window 18 on both sides of the bottom, the larger the coupling coefficient k 1 between the folded waveguides, that is, the larger the bandwidth of the folded waveguide mode.

[0053] See also Figure 13 and 14 The second metal resonance plate 6 and the third metal resonance plate 8 are fan-shaped plates, and a gap g is left between the two sides of the fan-shaped plates and the metal cavity 1. 2 =3.152mm, forming an electric wall to generate a folded waveguide mode 21. An irregular etched groove is provided in the middle of the fan-shaped plate to form an air slot line mode 22, and the irregular etched groove is composed of a rectangular groove 19 and an elliptical groove 20 that is larger than the width of the rectangular groove, wherein the elliptical groove 20 is located directly below the rectangular groove 19, and the length of the rectangular groove 19 is h. 2 =7.59mm, width w 2 =1.079mm, elliptical slot 20 major axis r 3 =3.6mm,r 4 =3mm. The resonant frequency influencing factor g of the folded waveguide mode 21 2 And the resonant frequency influencing factor of the air slot line mode 22 is w 2 、r 3 、r 4 、h 2 The resonant frequency influencing factor g of the folded waveguide mode 15 of the first metal resonant plate 4 and the fourth metal resonant plate 10 is 1 , Factors affecting the resonant frequency of the air slot line mode 16 1 、r 1 、r 2 、h 1 The rules are the same and will not be repeated here.

[0054] See also Figure 15 The second metal coupling plate 7 is a fan-shaped plate, and the two sides of the fan-shaped plate are connected to the fan-shaped metal cavity. A rectangular coupling window is provided on both sides of the upper and lower sides of the fan-shaped plate. The upper rectangular coupling window 18 is cl 2 =12mm, width cw 2 =13.9mm, the rectangular coupling windows on both sides of the bottom are 19 long ca 2 =10mm, width cr 2 =7.95mm, the first metal coupling plate 5 is located at the center of the second metal resonant plate 6 and the third metal resonant plate 8. The larger the upper rectangular coupling window 23 is, the greater the coupling coefficient k between the air slot line modes of the second metal resonant plate 6 and the third metal resonant plate 8 is. 4 The larger the size, the larger the air slot line mode bandwidth; the larger the rectangular coupling windows 24 on both sides of the bottom, the greater the coupling coefficient k between the folded waveguide of the second metal resonant plate 6 and the third metal resonant plate 8. 3 The larger the value is, the larger the folded waveguide mode bandwidth is. The coupling strength k between the air slot line modes of the second metal resonant plate 6 and the third metal resonant plate 8 is 4 Factors affecting cw 2 and cl2 The coupling strength k between the air slot line modes of the first resonant metal plate 4 and the second metal resonant plate 6 2 The influencing factors cw 1 and cl 1 are the same; the coupling coefficient k between the folded waveguide modes of the second metal resonant plate 6 and the third metal resonant plate 8 3 The influencing factors ca 2 and cr 2 are the same as the coupling coefficient k between the folded waveguide modes of the first resonant metal plate 4 and the second metal resonant plate 6 1 The influencing factors ca 1 and cr 1 The pattern is the same and will not be elaborated here.

[0055] Furthermore, the dual-mode dual-band filter based on the folded waveguide mode and the air slot line mode is connected to the external circuit through the SMA connector 2 and the SMA connector 11 and is matched with the external circuit.

[0056] Furthermore, according to general filter knowledge, the coupling strength of the dual-mode dual-band filter based on the folded waveguide mode and the air slot line mode, that is, the passband bandwidth, can also be achieved by controlling the distance between the second resonant metal plate 6 and the third resonant metal plate 8 and between the first metal resonant plate 4 and the second metal resonant plate 6 (central symmetric structure, the distance between the first metal resonant plate 4 and the second metal resonant plate 6 is relative to the distance between the third metal resonant plate 8 and the fourth metal resonant plate 10). In this embodiment, this parameter is reflected as Figure 1 the distance d 1 = 4.08mm, d 2 = 3.65mm.

[0057] Figure 16 、 Figure 17 are the S simulation results of the embodiment of the dual-mode dual-band filter based on the folded waveguide mode and the air slot line mode. In this embodiment, through parameter adjustment, the folded waveguide mode is the fundamental mode and the air slot line mode is the second mode. It can be seen from the simulation results that only 4 metal resonant plates achieve the effect of 8 poles and dual passbands. Among them, one passband is generated by the coupling of 4 folded waveguide modes, with a center frequency of 4.0 GHz and a bandwidth of 150 MHz; the other passband is generated by the coupling of 4 air slot line modes, with a center frequency of 4.75 GHz and a bandwidth of 180 MHz. And no additional structure is introduced, and four transmission zeros (TZ) are achieved. There is one transmission zero on the low-frequency side of the first passband, one transmission zero between the first passband and the second passband, and two output zeros on the high-frequency side of the second passband.

[0058] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A dual-mode dual-frequency filter based on folded waveguide mode and air slot line mode, characterized in that: It includes a metal cavity, a first metal resonance plate, a first metal coupling plate, a second metal resonance plate, a second metal coupling plate, a third metal resonance plate, a third metal coupling plate, a fourth metal resonance plate, a first external coupling adjustment metal column, and a second external coupling adjustment metal column; the metal cavity is a fan-shaped hollow cavity, and the metal cavity is provided with a first metal resonance plate, a first metal coupling plate, a second metal resonance plate, a second metal coupling plate, a third metal resonance plate, a third metal coupling plate, and a fourth metal resonance plate arranged in sequence; a first external coupling adjustment metal column and a second external coupling adjustment metal column.

2. The dual-mode dual-frequency filter according to claim 1, characterized in that: The first metal resonance plate, the second metal resonance plate, the third metal resonance plate and the fourth metal resonance plate are fan-shaped plates, and gaps are left between the two sides of the fan-shaped plates and the fan-shaped metal cavity to form an electric wall to generate a folded waveguide mode; an irregular etched groove is provided in the middle of the fan-shaped plate to form an air slot line mode, and the irregular etched groove is composed of a rectangular groove and an elliptical groove larger than the width of the rectangular groove, wherein the elliptical groove is located directly below the rectangular groove.

3. The dual-mode dual-frequency filter according to claim 1, characterized in that: The metal coupling plate is a fan-shaped plate, and both sides of the fan-shaped plate are connected to the fan-shaped metal cavity, and rectangular coupling windows are provided on both sides of the upper part and the bottom of the fan-shaped plate; the first metal coupling plate is located between the first metal resonant plate and the second metal resonant plate, the second metal coupling plate is located between the second metal resonant plate and the third metal resonant plate, and the third metal coupling plate is located between the third metal resonant plate and the fourth metal resonant plate.

4. The external coupling adjustment metal column according to claim 1, characterized in that: The first external coupling adjustment metal column connects the first resonant metal plate and the metal cavity; the second external coupling adjustment metal column connects the fourth metal resonant plate and the metal cavity; the two external coupling adjustment metal columns are symmetrically distributed on both sides of the metal cavity, and the external coupling value of the dual-mode dual-frequency filter can be controlled by adjusting the position of the external coupling adjustment metal column.

5. The dual-mode dual-frequency filter according to any one of claims 1 to 3, characterized in that: The resonant frequency of the folded waveguide is determined by the gap between the two sides of the fan-shaped metal resonant plate and the fan-shaped metal cavity; the smaller the gap, the lower the frequency.

6. The dual-mode dual-frequency filter according to any one of claims 1 to 3, characterized in that: The resonant frequency of the air slot line mode is determined by the irregular etched slot in the middle of the fan-shaped metal resonant plate; the narrower the rectangular slot in the irregular etched slot, the lower the frequency; the longer the short semi-axis and the long semi-axis of the elliptical slot, the lower the frequency; the deeper the etched slot, the lower the frequency.

7. The dual-mode dual-frequency filter according to claims 5 and 6, characterized in that: The folded waveguide mode and the air slot line mode can change the depth and width of the etching groove by adjusting parameters, so that the folded waveguide mode and the air slot line mode can both become the first resonant mode of the dual-mode dual-frequency filter.

8. The dual-mode dual-frequency filter according to claims 1-7, characterized in that: The coupling strength of the folded waveguide can be determined by the distance between the two rectangular coupling windows at the bottom of the metal coupling plate and the metal resonant plate. The closer the distance, the greater the coupling strength; the larger the two rectangular coupling windows at the bottom, the greater the coupling strength. The coupling strength of the air slot line mode can be determined by the distance between the rectangular coupling window at the top of the metal coupling plate and the metal resonant plate. The closer the distance, the greater the coupling strength; the larger the rectangular coupling window at the top, the greater the coupling strength.

9. The dual-mode dual-frequency filter according to claims 1-8, characterized in that: The folded waveguide mode and the air slot line mode can achieve relatively independent control of the dual-mode frequency and coupling strength by adjusting the corresponding parameters respectively.

10. The dual-mode dual-frequency filter according to claims 1-9, characterized in that: A dual passband, four transmission zero point S-curve response is achieved; there is a transmission zero point on the low frequency side of the first passband, there is a transmission zero point between the first passband and the second passband, and there are two output zero points on the high frequency side of the second passband.

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