Folding type broadband band-pass filter

Abstract

The invention provides a folding type broadband band-pass filter. The folding type broadband band-pass filter comprises a dielectric substrate which serves as an installation base, an input port is connected with a feed source, an output port is connected with a load, a first parallel coupling line is connected with the end, away from the feed source, of the input port, and a second parallel coupling line is connected with the end, away from the load, of the output port. The open-circuit branch is loaded in the middle of the third parallel coupling line and passes through the first parallel coupling line and the second parallel coupling line to form a T-shaped branch resonator; the open-circuit branch, the first high-low impedance resonator and the second high-low impedance resonator are all bent by a specific angle, and the open-circuit branch, the first high-low impedance resonator and the second high-low impedance resonator do not interfere with each other. By means of the folded microstrip line layout, a traditional linear stepped impedance resonator and an open-circuit branch knot are rearranged in a bending and folding mode, the electrical length of the resonator and the open-circuit branch knot is kept unchanged, the occupied area is reduced, and therefore the miniaturization design of the filter is achieved.

Description

Technical Field

[0001] This invention relates to the field of radio frequency communication device technology, and more specifically, to a folded wideband bandpass filter. Background Technology

[0002] Filters, as key components in radio frequency (RF) front-end circuits, are widely used in wireless communication, radar detection, satellite navigation, and ultra-wideband (UWB) systems. Their main function is to selectively allow signals within their operating frequency band while suppressing out-of-band interference signals, thereby improving the system's channel selectivity, anti-interference characteristics, and communication quality. With the rapid development of 5G, UWB, and IoT technologies, filters are evolving towards wider bandwidth, miniaturization, and higher selectivity.

[0003] Currently, common microstrip bandpass filter structures mainly include parallel coupled-line filters, open-loop resonator filters, and traditional λ / 2 or λ / 4 resonator filters. These filters have certain advantages in achieving conventional bandwidth (such as 10%~20% relative bandwidth), but they have the following shortcomings in ultra-wideband scenarios: (1) Limited passband bandwidth: The bandwidth is limited by the coupling structure, making it difficult to achieve extremely wide bandwidth. (2) Insufficient selectivity: Traditional filters have a limited number of transmission zeros, and the transition bands on both sides of the passband are relatively wide, making it impossible to effectively suppress interference signals in adjacent frequency bands. (3) Poor stopband suppression performance: Conventional structures have parasitic passbands or out-of-band leakage in frequency bands far from the passband, resulting in insufficient stopband suppression and affecting the overall system performance. (4) Large circuit size: Filters based on traditional λ / 2 resonators require long transmission lines, occupying a large circuit area in high-frequency applications, which is not conducive to miniaturization and integration.

[0004] To address these issues, researchers have proposed a bandpass filter based on a stepped impedance resonator (SIR). By alternating between high and low impedance segments, the SIR can adjust the resonant frequency and bandwidth while maintaining a small circuit size, thus achieving a certain degree of broadband. However, existing SIR filters still have the following shortcomings: (1) Limited number of zeros: A single SIR structure can usually only introduce 1 to 2 transmission zeros at the edge of the passband, which is difficult to meet the requirements of high selectivity applications; (2) General out-of-band suppression effect: Although it can broaden the passband, strong out-of-band interference may still occur in the stopband; (3) Insufficient design flexibility: The ratio of different impedance segments is often fixed, lacking precise control over the passband shape and zero position.

[0005] Therefore, existing filter designs struggle to simultaneously meet the requirements of ultra-wideband characteristics, multiple transmission zeros, high selectivity, and miniaturization. In next-generation RF communication systems, there is an urgent need for an improved filter structure that can achieve ultra-wideband characteristics in a smaller size and introduce multiple transmission zeros at the upper and lower edges of the passband to significantly improve stopband rejection and selectivity. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a folded wideband bandpass filter.

[0007] A folded broadband bandpass filter according to the present invention includes a dielectric substrate, an input port, an output port, a first parallel coupling line, a second parallel coupling line, a third parallel coupling line, an open-circuit stub, a first high- and low-impedance resonator, and a second high- and low-impedance resonator. The dielectric substrate serves as a mounting base. The input port is connected to a feed source, and the output port is connected to a load. The first and second parallel coupling lines are symmetrically placed, with the first parallel coupling line connected to the input port away from the feed source and the second parallel coupling line connected to the output port away from the load. The third parallel coupling line is placed on... The first and second parallel coupling lines are below each other and open at both ends; the open-circuit stub is loaded in the middle of the third parallel coupling line with open ends and passes through the first and second parallel coupling lines, forming a T-shaped stub resonator; the first high- and low-impedance resonator is loaded above the input port away from the feed end, and the second high- and low-impedance resonator is loaded above the output port away from the load end; the open-circuit stub, the first high- and low-impedance resonator, and the second high- and low-impedance resonator are all bent at a specific angle, and the open-circuit stub, the first high- and low-impedance resonator, and the second high- and low-impedance resonator do not interfere with each other.

[0008] Preferably, both the input port and the output port are microstrip lines with a characteristic impedance of 50Ω.

[0009] Preferably, the dielectric substrate is a printed circuit board.

[0010] Preferably, the characteristic impedance range of the high-impedance transmission line segment of both the first high-impedance resonator and the second high-impedance resonator is 80 to 120 Ω, and the characteristic impedance range of the low-impedance transmission line segment is 20 to 60 Ω.

[0011] Preferably, the electrical lengths of the high-impedance segment and the low-impedance segment of both the first high- and low-impedance resonators are 0.5 to 2.

[0012] Preferably, the characteristic impedance ratio of the high impedance segment to the low impedance segment of both the first high-low impedance resonator and the second high-low impedance resonator is 2 to 5.

[0013] Preferably, the first high- and low-impedance resonators and the second high- and low-impedance resonators are arranged symmetrically or alternately to generate multiple transmission zeros on both sides of the passband.

[0014] Preferably, the open branch is folded 90° to the right or left at the end of the branch.

[0015] Preferably, both the first high-low impedance resonator and the second high-low impedance resonator are bent inward at 90° at the low impedance transmission line.

[0016] Preferably, the filter employs a folded structure for use in miniaturized RF front-ends.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses a folded microstrip line layout to rearrange the traditional linear stepped impedance resonator and open-circuit stubs by bending and folding, so that the electrical length of the resonator and open-circuit stubs remains unchanged and the occupied area is reduced, thereby realizing the miniaturization design of the filter.

[0018] 2. By introducing multiple high- and low-impedance stubs into the folded structure and combining them with a reasonable coupling layout, the filter of this invention can form multiple transmission zeros at the passband edge and out-of-band region, significantly improving out-of-band rejection capability and frequency selectivity. 3. The present invention has good impedance regulation capability through the stepped impedance resonator structure. After folding, the impedance matching can be further optimized, enabling the filter of the present invention to achieve a wider bandwidth.

[0019] 4. The present invention effectively reduces the radiation loss and parasitic effects of microstrip lines through the folded structure. At the same time, by rationally designing the impedance ratio and length ratio between the stepped impedance resonator, open stubs and parallel coupling lines, the filter of the present invention maintains low insertion loss and flat transmission characteristics in the passband range. Attached Figure Description

[0020] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a three-dimensional schematic diagram illustrating the structure of the folded wideband bandpass filter of this invention. Figure 2 This is a planar schematic diagram illustrating the structure of the folded wideband bandpass filter, which is the main feature of this invention. Figure 3 This is a schematic diagram illustrating the dimensions of the folded wideband bandpass filter structure, which is the main feature of this invention. Figure 4 This is a circuit diagram illustrating the testing of a folded wideband bandpass filter structure, which is the main feature of this invention. Figure 5 This invention primarily demonstrates the S21 curve of the simulation and experimental testing of the folded wideband bandpass filter structure. Figure 6 The S11 curve is used to illustrate the simulation and experimental testing of the folded wideband bandpass filter structure, which is the main feature of this invention.

[0021] The figure shows: 1. Input port; 2. Output port; 3. Third parallel coupling line; 4. First parallel coupling line; 5. Second parallel coupling line; 6. Open circuit stub; 7. First high- and low impedance resonator; 8. Second high- and low impedance resonator; 9. Dielectric substrate. Detailed Implementation

[0022] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0023] like Figures 1 to 6 As shown, a folded wideband bandpass filter provided by the present invention includes a dielectric substrate 9, an input port 1, an output port 2, a first parallel coupling line 4, a second parallel coupling line 5, a third parallel coupling line 3, an open-circuit stub 6, a first high- and low-impedance resonator 7, and a second high- and low-impedance resonator 8.

[0024] The dielectric substrate 9 serves as the mounting base. Input port 1 is connected to the feed source, and output port 2 is connected to the load. The first parallel coupling line 4 and the second parallel coupling line 5 are placed symmetrically, with the first parallel coupling line 4 connected to the input port 1 away from the feed source and the second parallel coupling line 5 connected to the output port 2 away from the load. Input port 1 and output port 2 are placed symmetrically.

[0025] The third parallel coupling line 3 is placed below the first parallel coupling line 4 and the second parallel coupling line 5, and is open at both ends; the open-circuit stub 6 is loaded in the middle of the third parallel coupling line 3 which is open at both ends, and passes through the first parallel coupling line 4 and the second parallel coupling line 5, forming a T-shaped stub resonator.

[0026] The first high-low impedance resonator 7 is loaded above the input port 1 away from the feed end, and the second high-low impedance resonator 8 is loaded above the output port 2 away from the load end. The open-circuit stub 6, the first high-low impedance resonator 7, and the second high-low impedance resonator 8 are all bent at specific angles, and the three components do not interfere with each other.

[0027] It should be further noted that both input port 1 and output port 2 are microstrip lines with a characteristic impedance of 50Ω. The dielectric substrate 9 is a printed circuit board.

[0028] It should be further explained that the open-circuit stub 6 is folded 90° to the right or left at the end of the stub, resulting in a significant reduction in physical size. Both the first high-low impedance resonator 7 and the second high-low impedance resonator 8 are bent inwards by 90° at the low-impedance transmission line. The first high-low impedance resonator 7 and the second high-low impedance resonator 8 are centrally located opposite each other. This folded structure allows the microstrip lines to be compactly arranged on the dielectric substrate 9, improving the miniaturization and integrability of the filter.

[0029] It should be further explained that the characteristic impedance range of the high-impedance transmission segment of both the first high-low impedance resonator 7 and the second high-low impedance resonator 8 is 80 to 120 Ω, with 106 Ω selected in a preferred embodiment. The characteristic impedance range of the low-impedance transmission segment is 20 to 60 Ω, with 50 Ω selected in a preferred embodiment. The electrical length of the high-impedance segment to the low-impedance segment of both the first high-low impedance resonator 7 and the second high-low impedance resonator 8 is 0.5 to 2, with 1.05 selected in a preferred embodiment. The characteristic impedance ratio of the high-impedance segment to the low-impedance segment of both the first high-low impedance resonator 7 and the second high-low impedance resonator 8 is 2 to 5, with 4.8 selected in a preferred embodiment. The first high-low impedance resonator 7 and the second high-low impedance resonator 8 are arranged symmetrically or alternately to generate multiple transmission zeros on both sides of the passband. Through the above arrangement, the first high-low impedance resonator 7 and the second high-low impedance resonator 8 can form multiple transmission zeros in a wide bandwidth, improving out-of-band rejection capability.

[0030] It should be emphasized that the filter of this application adopts a folded structure to achieve miniaturization design, and has a compact structure for application in miniaturized RF front-ends.

[0031] This application proposes a feasible implementation method using a Jiangsu Wangling TFA300 dielectric substrate 9 with a dielectric constant ε_r = 3, a loss tangent tanδ = 0.0013, and a thickness h = 0.508 mm. Both sides of the dielectric substrate 9 are coated with 35 μm thick copper foil. This dielectric substrate 9 has low dielectric loss, which is beneficial for achieving lower insertion loss. The overall size of the filter circuit board is 36 mm × 22 mm. The parameters of each part in this embodiment are as follows: Figure 3 As shown.

[0032] The structure was simulated using the electromagnetic simulation software ANSYS HFSS. The simulation results show that the filter achieves ultra-wideband transmission in the range of 4.2~8.2GHz, with a 3dB bandwidth of 64.5%, an insertion loss of less than 1dB in the passband, a return loss better than 15dB, and forms multiple transmission zeros at the upper and lower edges of the passband and in the out-of-band region far from the passband. The out-of-band rejection is greater than 50dB.

[0033] according to Figure 4 The filter in this embodiment of the invention was fabricated and tested. The S21 curves from simulation and experimental tests are shown below. Figure 5 As shown, the S11 curve is as follows Figure 6 As shown in the figure. Experiments show that the bandwidth of this filter is as follows: S21 = -68.49dB at 2.4GHz, S21 = -1.04dB at 4.8GHz, and S21 = -1.31dB at 7.2GHz. The 3dB bandwidth is 64%, the in-passband insertion loss is less than 1.5dB, the return loss is better than 10dB, and the out-of-band rejection is greater than 40dB, which is in good agreement with the simulation results.

[0034] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0035] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A folded wideband bandpass filter, characterized in that, It includes a dielectric substrate (9), an input port (1), an output port (2), a first parallel coupling line (4), a second parallel coupling line (5), a third parallel coupling line (3), an open-circuit stub (6), a first high-low impedance resonator (7), and a second high-low impedance resonator (8); The dielectric substrate (9) serves as the mounting base. The input port (1) is connected to the feed source, and the output port (2) is connected to the load. The first parallel coupling line (4) and the second parallel coupling line (5) are placed symmetrically. The first parallel coupling line (4) is connected to the input port (1) away from the feed source end, and the second parallel coupling line (5) is connected to the output port (2) away from the load end. The third parallel coupling line (3) is placed below the first parallel coupling line (4) and the second parallel coupling line (5), and is open at both ends; The open-circuit stub (6) is loaded in the middle of the third parallel coupling line (3) which is open at both ends, and passes through the first parallel coupling line (4) and the second parallel coupling line (5) to form a T-shaped stub resonator. The first high-low impedance resonator (7) is loaded above the input port (1) away from the feed end, and the second high-low impedance resonator (8) is loaded above the output port (2) away from the load end; The open-circuit stub (6), the first high-low impedance resonator (7), and the second high-low impedance resonator (8) are all bent at a specific angle, and the open-circuit stub (6), the first high-low impedance resonator (7), and the second high-low impedance resonator (8) do not interfere with each other.

2. The folded wideband bandpass filter as described in claim 1, characterized in that, Both the input port (1) and the output port (2) are microstrip lines with a characteristic impedance of 50Ω.

3. The folded wideband bandpass filter as described in claim 1, characterized in that, The dielectric substrate (9) is a printed circuit board.

4. The folded wideband bandpass filter as described in claim 1, characterized in that, The characteristic impedance range of the high impedance transmission line segment of the first high-low impedance resonator (7) and the second high-low impedance resonator (8) is 80 to 120Ω, and the characteristic impedance range of the low impedance transmission line segment is 20 to 60Ω.

5. The folded wideband bandpass filter as described in claim 1, characterized in that, The electrical lengths of the high impedance segment and the low impedance segment of the first high-low impedance resonator (7) and the second high-low impedance resonator (8) are 0.5 to 2.

6. The folded wideband bandpass filter as described in claim 1, characterized in that, The characteristic impedance ratio of the high impedance segment to the low impedance segment of the first high-low impedance resonator (7) and the second high-low impedance resonator (8) is 2 to 5.

7. The folded wideband bandpass filter as described in claim 1, characterized in that, The first high-low impedance resonator (7) and the second high-low impedance resonator (8) are arranged symmetrically or alternately to generate multiple transmission zeros on both sides of the passband.

8. The folded wideband bandpass filter as described in claim 1, characterized in that, The open branch (6) is folded 90° to the right or left at the end of the branch.

9. The folded wideband bandpass filter as described in claim 1, characterized in that, The first high-low impedance resonator (7) and the second high-low impedance resonator (8) are both bent inward at 90° at the low impedance transmission line.

10. The folded wideband bandpass filter as described in claim 1, characterized in that, The filter employs a folded structure for use in miniaturized RF front-ends.

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