A high-selectivity triple-passband filter based on triple-mode hairpin resonator

Abstract

This invention relates to the field of microwave passive device technology, and in particular to a high-selectivity three-passband filter based on a three-mode hairpin ring resonator. The filter includes a dielectric substrate with two mirror-symmetrical hairpin ring resonators printed on its surface, electromagnetically coupled through a coupling gap. Each resonator consists of an upper conductor segment, a lower conductor segment, a first connecting conductor segment, and a second connecting conductor segment forming a ring body, with a folded loading stub connected at the bottom. The ring body generates odd-mode and even-mode resonances, and the folded loading stub introduces a third resonant mode, enabling the filter to form three independent passbands. The outer side of the resonator is coupled to the input and output microstrip feed lines through an outer conductor segment. This invention uses dual resonators to couple between adjacent passbands and the high-frequency stopband to form transmission zeros, significantly improving the passband edge roll-off rate and inter-band isolation. It has advantages such as compact structure, low loss, high selectivity, and ease of planar integration.

Description

Technical Field

[0001] This invention relates to the field of microwave passive device technology, and in particular to a highly selective three-passband filter based on a three-mode hairpin ring resonator. Background Technology

[0002] Microwave bandpass filters are key components in radio frequency (RF) front-ends for achieving spectrum selection and suppressing out-of-band interference. With the rapid development of wireless communication, satellite communication, radar detection, and multi-standard fusion systems, single operating frequency bands are no longer sufficient to meet system requirements, leading to widespread interest in multi-passband filters capable of operating simultaneously in multiple discrete frequency bands. Compared to cascading multiple single-passband filters, three-passband filters can reduce the number of front-end stages, shorten signal paths, and improve system integration.

[0003] Existing three-passband filters often employ combinations of multiple resonators of different types, parallel / cascaded multiple single-band filters, or complex multi-coupling networks to construct the three passbands separately. While these approaches can achieve multi-frequency operation, they often suffer from problems such as complex structures, numerous design parameters, large area, increased passband insertion loss, difficulty in independently controlling the frequency ratio and bandwidth of the three passbands, and difficulty in coordinating the coupling relationships between the three passbands. Especially when it is necessary to obtain both low insertion loss and steep skirt at higher frequencies, traditional structures often require increasing the order or introducing additional cross-coupling, further increasing the design complexity.

[0004] Multimode resonator technology provides an effective approach to the miniaturization design of three-passband filters. If a single physical resonator can excite multiple usable resonant modes, multiple passbands can be constructed with a reduced number of resonators. The center frequency and bandwidth of each passband can be adjusted through mode splitting, stub loading, and coupling control. Existing research shows that using symmetrically loaded resonators or multimode stub loading structures can improve selectivity and create multiple transmission zeros while maintaining a compact structure. Summary of the Invention

[0005] To address the technical problems of existing three-passband filters, such as large size, high loss, insufficient inter-band isolation, difficulty in independent control of the passband, and limited selectivity, this invention provides a high-selectivity three-passband filter based on a three-mode hairpin ring resonator.

[0006] Therefore, the present invention provides the following technical solution:

[0007] A high-selectivity three-pass band filter based on a three-mode hairpin ring resonator includes a dielectric substrate with an input port and an output port. Two hairpin ring resonators are printed on the surface of the dielectric substrate. Each hairpin ring resonator includes an upper conductor segment, a lower conductor segment, a first connecting conductor segment, and a second connecting conductor segment. There are two upper conductor segments, located at both ends of the first connecting conductor segment, and the lower ends of the two upper conductor segments are connected to both ends of the first connecting conductor segment. The lower ends of the two upper conductor segments are connected to the upper ends of the corresponding lower conductor segments, and the upper ends of the two lower conductor segments are connected to the corresponding ends of the first connecting conductor segment. The lower ends of the two lower conductor segments are connected to both ends of the second connecting conductor segment. The second connecting conductor segment connects to a folded loading stub. The hairpin ring resonator and the folded loading stub together constitute a three-mode hairpin ring resonator. The upper conductor segment, lower conductor segment, first connecting conductor segment, and second connecting conductor segment form a hairpin ring body. The hairpin ring body resonates to form two resonant frequency points: odd mode and even mode. The folded loading stub introduces a third resonant frequency point on the basis of the ring body. The three resonant frequency points are respectively extended to form a passband. Two hairpin ring resonators are arranged in a mirror-symmetrical manner with the coupling gap between them. The two hairpin ring resonators achieve electromagnetic coupling through the coupling gap, making the three passbands independent of each other, thus forming the three-passband filtering characteristics of the filter. The two hairpin ring resonators have an inner conductor segment electromagnetically coupled to the inner side of their mutually distant upper conductor segments, and an outer conductor segment electromagnetically coupled to the outer side. The upper ends of the inner conductor segment and the outer conductor segment electromagnetically coupled to the same upper conductor segment are connected by a third connecting conductor segment. One of the outer conductor segments is coupled to the input port via the input microstrip feed line, and the other outer conductor segment is coupled to the output port via the output microstrip feed line.

[0008] Furthermore, the three passbands serve the 5.62GHz-5.75GHz band, the 7.58GHz-7.80GHz band, and the 10.15GHz-10.51GHz band, respectively.

[0009] Furthermore, the lengths of the upper conductor segment L3, the lower conductor segment L6, the folded loading stub L7, and the second connecting conductor segment L8 determine the even mode frequency; the lengths of the upper conductor segment L3 and the first connecting conductor segment L4 determine the odd mode frequency; and the lengths of the upper conductor segment L3, the first connecting conductor segment L4, the lower conductor segment L6, and the folded loading stub L7 determine the higher-order mode frequencies of the even mode.

[0010] Furthermore, after the two hairpin ring resonators are electromagnetically coupled through a coupling gap, several transmission zeros are formed between adjacent passbands and in the high-frequency stopband region.

[0011] Advantages and positive effects of the present invention: Compared with existing technologies, this invention utilizes a combination of the tri-mode characteristics of a single resonator and the coupling mechanism of a dual resonator to obtain three independent working passbands with fewer structural units. It has the advantages of compact structure, easy integration, low passband loss, high inter-band isolation, and good selectivity.

[0012] A single hairpin ring resonator can provide three usable resonant modes by connecting folded loading stubs. With the symmetrical coupling arrangement of two hairpin ring resonators, a three-pass band response can be achieved without significantly increasing the area. This is more conducive to miniaturization than the scheme of splicing multiple single-mode resonators.

[0013] The three passbands can each serve different frequency band applications. According to... Figure 6 The simulation results show that the first passband is located in the 5.62GHz-5.75GHz frequency band and can be used for 5.8GHz WLAN / ISM links; the second passband is located in the 7.58GHz-7.80GHz frequency band and can be used for X-band satellite telemetry and control and satellite communication front-ends; the third passband is located in the 10.15GHz-10.51GHz frequency band and can be used for X-band radar, remote sensing and imaging systems, and has strong applicability to multiple scenarios.

[0014] Figure 6 The return loss S11 of the first passband is -16.31dB and the insertion loss S21 is -0.29dB; the return loss S11 of the second passband is -12.13dB and the insertion loss S21 is -0.37dB; and the return loss S11 of the third passband is -14.91dB and the insertion loss S21 is -0.217dB. Therefore, this invention maintains low transmission loss and good port matching across all three operating passbands.

[0015] Through electromagnetic coupling between hairpin ring resonators and synergistic effects between different modes, the filter forms multiple transmission zeros between the three passbands and on the high-frequency stopband side, which can significantly improve passband edge roll-off, suppress signal leakage in non-target frequency bands, and thus improve frequency selectivity and inter-band isolation.

[0016] By adjusting the length of the main resonant path and the length of the loaded stub, the center frequency, relative spacing, and stopband characteristics of the three passbands can be refined and optimized, facilitating parameter reconstruction for different application requirements. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This invention provides a schematic diagram of the overall structure of a high-selectivity three-pass band filter based on a three-mode hairpin ring resonator.

[0019] Figure 2 This invention provides a schematic diagram of the geometric structure of a single hairpin ring resonator for a high-selectivity three-pass band filter based on a three-mode hairpin ring resonator.

[0020] Figure 3 for Figure 2 When the length of the upper conductor segment L3 = 6.2 mm, the length of the second connecting conductor segment L8 = 2 mm, and the length of the lower conductor segment L6 = 4.3 mm, the simulated resonant frequency of the three-mode hairpin ring resonator is changed by altering the length L7 of the folded loading stub.

[0021] Figure 4 The present invention provides a high-selectivity three-passband filter based on a three-mode hairpin ring resonator, and an even-mode equivalent circuit of the three-mode hairpin ring resonator.

[0022] Figure 5 This invention provides a high-selectivity three-passband filter based on a three-mode hairpin ring resonator, and an odd-mode equivalent circuit of the three-mode hairpin ring resonator.

[0023] Figure 6 for Figure 2 The simulation response curves of the three-mode hairpin ring resonator in this embodiment of the invention are as follows: the upper conductor segment length L3 = 6.2 mm, the first connecting conductor segment length L4 = the second connecting conductor segment length L8 = 2 mm, the lower conductor segment length L6 = 4.3 mm, and the conductor segment width W1 = 0.2 mm. The length of the folded loading branch L7 and the outer conductor segment length L5 = 10.76 mm are changed.

[0024] Figure 7 The following are the S-parameter simulation results of a high-selectivity three-passband filter based on a three-mode hairpin ring resonator according to the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0026] This invention provides a high-selectivity three-passband filter based on a three-mode hairpin ring resonator, such as... Figure 1-2 As shown, the device includes a dielectric substrate with an input port (Port1) and an output port (Port2) on it. Two hairpin ring resonators are printed on the surface of the substrate. Each hairpin ring resonator includes an upper conductor segment, a lower conductor segment, a first connecting conductor segment, and a second connecting conductor segment. There are two upper conductor segments, located at both ends of the first connecting conductor segment, with the lower ends of the two upper conductor segments connected to both ends of the first connecting conductor segment. The lower ends of the two upper conductor segments are connected to the upper ends of their respective lower conductor segments, and the upper ends of the two lower conductor segments are connected to the corresponding ends of the first connecting conductor segment. The lower ends of the two lower conductor segments are connected to both ends of the second connecting conductor segment. The second connecting conductor segment connects to a folded loading stub. The hairpin ring resonator, together with the folded loading stub, constitutes a three-mode hairpin ring resonator.

[0027] The upper conductor segment, the lower conductor segment, the first connecting conductor segment, and the second connecting conductor segment form a hairpin ring body. The ring body resonates to form two resonant frequencies: odd mode and even mode. The folded loading stub introduces a third resonant frequency on the basis of the ring body. The three resonant frequencies are extended to form a passband.

[0028] Two hairpin ring resonators are coupled through a coupling gap g1, and are arranged mirror-symmetrically around the coupling gap. The two hairpin ring resonators are electromagnetically coupled through the coupling gap, making the three passbands independent and forming the three-passband filtering characteristics of the filter. The three passbands serve the 5.62GHz-5.75GHz, 7.58GHz-7.80GHz, and 10.15GHz-10.51GHz frequency bands, respectively.

[0029] The two hairpin ring resonators have an inner conductor segment electromagnetically coupled to the inner side of their mutually distant upper conductor segments, and an outer conductor segment electromagnetically coupled to the outer side. The upper ends of the inner conductor segment and the outer conductor segment electromagnetically coupled to the same upper conductor segment are connected by a third connecting conductor segment.

[0030] One of the outer conductor segments is coupled to the input port via the input microstrip feed line, and the other outer conductor segment is coupled to the output port via the output microstrip feed line.

[0031] like Figure 1 , 2 As shown, the length of the third connecting conductor segment is L1, the length of the inner conductor segment is L2, the length of the upper conductor segment is L3, the length of the first connecting conductor segment is L4, the length of the outer conductor segment is L5, the length of the lower conductor segment is L6, the length of the folded loading branch is L7, the length of the second connecting conductor segment is L8, and the line width is W1.

[0032] Where L3, L6, L7, and L8 determine the even-mode frequency f01; L3 and L4 determine the odd-mode frequency fi; L3, L4, L6, and L7 determine the higher-order mode frequencies f02 of the even-mode; the calculation formula is as follows:

[0033]

[0034]

[0035] In the formula, c is the speed of light in a vacuum, and εeff is the effective dielectric constant of the substrate.

[0036] Compared to ordinary dual-mode hairpin resonators, the hairpin ring resonator structure of this application expands the number of modes by loading stubs, which is beneficial for realizing three-band in a single structure.

[0037] Two hairpin ring resonators are electromagnetically coupled through a coupling gap, forming several transmission zeros between adjacent passbands and in the high-frequency stopband region to improve passband roll-off and interband isolation. This is achieved through the inherent interference path of the hairpin ring resonators and the feed method, giving the filter multiple passbands, low loss, and high selectivity.

[0038] The hairpin ring resonator's symmetry plane can be analyzed using the odd-even mode method. The resonator body forms odd-mode and even-mode resonances, while the lower folded loading stub further introduces a third usable resonant mode. These three modes collectively support the three-band response. By adjusting structural parameters such as L1-L8 and g1, the resonant frequency positions, mode spacing, and coupling strength between the three modes can be changed.

[0039] Example The design and optimization were carried out using Sonnet electromagnetic simulation software. An RT5880 substrate with a relative permittivity of approximately 9.8 and a thickness of approximately 0.508 mm was selected to balance miniaturization and low loss performance.

[0040] like Figure 1As shown, the filter in this embodiment consists of an input port Port1, an output port Port2, and a pair of mirror-symmetric hairpin ring resonators located between the two ports. The two resonators are coupled to each other through a central gap g1. The input and output microstrip feed lines are arranged on the left and right outer sides, respectively, forming electromagnetic coupling with the corresponding hairpin ring resonators. The entire structure is basically symmetrical about the central axis of the central gap g1, which is beneficial for mode analysis, parameter extraction, and layout optimization.

[0041] A set of optimized parameters is as follows: L1=0.53mm, L2=2.95mm, L3=6.2mm, L4=2mm, L5=5.77mm, L6=4.3mm, L7=10.73mm, W1=0.2mm, g1=0.09mm. By configuring these geometric dimensions, the three resonant modes can be distributed within the target operating frequency band while maintaining a compact structure.

[0042] like Figure 4-5 As shown, the hairpin ring resonator can be analyzed using the even-odd mode method. Taking the resonator's symmetry plane as a reference, the even-mode and odd-mode equivalent circuits correspond to different electromagnetic boundary conditions. Through comprehensive analysis of the main resonant path and the loaded stubs, it can be concluded that the first two modes are mainly contributed by the odd and even modes, while the third mode is formed by the combined effect of the loaded stubs and the main loop. This analytical method helps explain the mechanism by which variations in geometric parameters affect the three passband positions.

[0043] Figure 6 The correlation response curves of the three-mode hairpin ring resonator are presented, showing that a single resonator can provide three usable resonance peaks within the target frequency band, while simultaneously forming transmission zeros in the resonance interval that are beneficial for improving selectivity. These results demonstrate that the structure of this invention not only meets the requirements of three-mode design but also possesses good stopband suppression potential.

[0044] Figure 6 This demonstrates that a single hairpin ring resonator can form three usable resonant modes and generate transmission zeros in adjacent resonant intervals that are beneficial for improving selectivity, thus providing a foundation for the design of subsequent three-passband filters.

[0045] Depend on Figure 6 As can be seen, the filter forms three distinct passbands: the first passband has an S11 of -16.31 dB and an S21 of -0.29 dB; the second passband has an S11 of -12.13 dB and an S21 of -0.37 dB; and the third passband has an S11 of -14.91 dB and an S21 of -0.217 dB. All three passbands exhibit low insertion loss and good return loss, indicating that the filter has excellent in-band transmission performance.

[0046] Combination Figure 7Further observation reveals a significant stopband dip and steep edge transitions among the three passbands, indicating that the transmission zeros formed by mode coupling and structural coupling play a crucial role in enhancing filter selectivity. Specifically, the first passband is suitable for 5.8GHz WLAN / ISM links, the second passband for X-band satellite communication / telemetry links near 8GHz, and the third passband for X-band radar, remote sensing, or imaging links near 10GHz.

[0047] Figure 7 This indicates that three distinct passbands are formed after coupling with dual resonators, and all three passbands have low insertion loss and good return loss, verifying the effectiveness of the structure of the present invention in a three-passband filtering scenario.

[0048] In summary, the high-selectivity three-passband filter based on a three-mode hairpin ring resonator proposed in this embodiment achieves the coordinated design of three working passbands with relatively low structural complexity. It combines low loss, high selectivity, good matching, and adaptability to multi-frequency applications, making it suitable for multi-frequency communication and detection front-end systems.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-selectivity three-passband filter based on a three-mode hairpin ring resonator, characterized in that, The device includes a dielectric substrate with an input port and an output port. Two hairpin ring resonators are printed on the surface of the dielectric substrate. Each hairpin ring resonator includes an upper conductor segment, a lower conductor segment, a first connecting conductor segment, and a second connecting conductor segment. There are two upper conductor segments, located at both ends of the first connecting conductor segment, and the lower ends of the two upper conductor segments are connected to both ends of the first connecting conductor segment. The lower ends of the two upper conductor segments are connected to the upper ends of the corresponding lower conductor segments, and the upper ends of the two lower conductor segments are connected to the corresponding ends of the first connecting conductor segment. The lower ends of the two lower conductor segments are connected to both ends of the second connecting conductor segment. The second connecting conductor segment connects to a folded loading stub. The upper conductor segment, lower conductor segment, first connecting conductor segment, and second connecting conductor segment form a hairpin ring body. The hairpin ring body resonates to form two resonant frequency points: odd mode and even mode. The folded loading stub introduces a third resonant frequency point on the basis of the ring body. The three resonant frequency points are respectively extended to form a passband. Two hairpin ring resonators are arranged in a mirror-symmetrical manner with the coupling gap between them. The two hairpin ring resonators achieve electromagnetic coupling through the coupling gap, making the three passbands independent of each other, thus forming the three-passband filtering characteristics of the filter. The two hairpin ring resonators have an inner conductor segment electromagnetically coupled to the inner side of their mutually distant upper conductor segments, and an outer conductor segment electromagnetically coupled to the outer side. The upper ends of the inner conductor segment and the outer conductor segment electromagnetically coupled to the same upper conductor segment are connected by a third connecting conductor segment. One of the outer conductor segments is coupled to the input port via the input microstrip feed line, and the other outer conductor segment is coupled to the output port via the output microstrip feed line.

2. The high-selectivity triple-passband filter based on triple-mode hairpin resonator according to claim 1, characterized in that, The three passbands serve the 5.62GHz-5.75GHz, 7.58GHz-7.80GHz, and 10.15GHz-10.51GHz frequency bands, respectively.

3. The high-selectivity triple-passband filter based on triple-mode hairpin resonator according to claim 1, characterized in that, The lengths of the upper conductor segment L3, lower conductor segment L6, folded loading stub L7, and second connecting conductor segment L8 determine the even-mode frequency; the lengths of the upper conductor segment L3 and first connecting conductor segment L4 determine the odd-mode frequency. The lengths of the upper conductor segment L3, the first connecting conductor segment L4, the lower conductor segment L6, and the folded loading stub L7 determine the higher-order modes of the even mode.

4. The high-selectivity triple-passband filter based on triple-mode hairpin resonator according to claim 1, characterized in that, After the two hairpin ring resonators are electromagnetically coupled through a coupling gap, several transmission zeros are formed between adjacent passbands and in the high-frequency stopband region.

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