High-performance low-pass and dual-passband filter
Through the compact folding coupling line and L-shaped open branch line structural design, combined with LC microstrip transmission line and resonator, the complex problem of existing filter design is solved, and the miniaturization and high performance of high-performance low-pass and dual-pass band filters is achieved, and it is suitable for multi-band communication systems.
Patent Information
- Application Number
- CN202422205088.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-09
- Publication Date
- 2025-07-01
- Estimated Expiration
- 2034-09-09
AI Technical Summary
The existing low-pass and band-pass filters are complex in design, which is difficult to meet the needs of miniaturization and high-performance of modern communication systems, especially in mixers and optical fiber coaxial cable hybrid network systems, which are difficult to achieve effective signal separation and filtering.
Using a compact folding coupling line and L-shaped open-circuit branch line structure, combined with LC microstrip transmission line and resonator, a high-performance low-pass and dual-pass band filter is designed. By cascaded the same resonator and L-shaped branch line, the coupling loop is simplified and the low-pass and dual-pass band characteristics are achieved.
It realizes the miniaturization and high performance of the filter, can achieve higher performance standards in practical applications, has the filtering characteristics of center frequency, passband bandwidth and transmission zero point controllable, improves signal selectivity and isolation, and is suitable for multi-band communication systems.
Smart Images
Figure CN223052356U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of filter design, and more specifically, to a filter with high performance low-pass and dual-passbands. Background Art
[0002] With the rapid update of the communication industry, the coexistence of multi-standard communication systems is the current situation of the communication industry. Modern wireless communication systems require multi-passband filters with small volume, small insertion loss, and high selectivity. In recent years, many multi-passband filters have been designed, but most of these filters focus on the design of multi-passband filters. However, in applications such as mixers and fiber coaxial cable hybrid network support systems, it is necessary to use low-pass filters and band-pass filters. Therefore, in order to separate the intermediate frequency and the local oscillator frequency in the mixer and transmit the microwave signal frequency and the baseband signal on the same coaxial channel, low-pass and band-pass filters are required for filtering.
[0003] To further support communication systems with multiple standards and different frequency points, low-pass multi-band composite filters, as the main components in communication systems, are applied to various research aspects.
[0004] In traditional methods, in order to meet the selection requirements for signals in different frequency bands, generally multiple filters with different frequency bands are used to select signals in the corresponding frequency bands, such as low-pass band-pass filters based on stepped impedance resonators, low-pass band-pass filters based on stepped impedance resonators and defected ground structure (DGS), low-pass band-pass filters based on quasi-lumped element resonators, and low-pass band-pass filters designed based on two hairpin slots etched on the ground plane. These design structures are all particularly complex, with poor manufacturability, and the circuit area does not meet the requirements of miniaturization, which does not conform to the design direction of miniaturization of filters in current communication systems.
[0005] The foregoing description is for the purpose of providing general background information and does not necessarily constitute prior art. Summary of the Utility Model
[0006] The purpose of the utility model is to provide a filter with high performance low-pass and dual-passbands. The overall design of the filter is significantly simplified, effectively improving the overall performance and reliability of the filter, enabling it to meet higher performance standards in practical applications.
[0007] The utility model provides a filter with high performance low-pass and dual-passbands, including a first resonator, an LC microstrip transmission line, and a second resonator; both ends of the LC microstrip transmission line are respectively connected to the first resonator and the second resonator; the first resonator and the second resonator are symmetrically arranged with respect to the middle of the LC microstrip transmission line.
[0008] Further, the first resonator includes a first folded coupled line and a first open stub line. The bottom of the first folded coupled line is connected to the first open stub line. The first folded coupled line is folded in a concave shape, and the first open stub line is in an L shape. The second resonator includes a second folded coupled line and a second open stub line. The bottom of the second folded coupled line is connected to the second open stub line. The first folded coupled line and the second folded coupled line are symmetrically arranged about the middle of the LC microstrip transmission line, and the first open stub line and the second open stub line are symmetrically arranged about the middle of the LC microstrip transmission line.
[0009] With the above technical solution, through the compact and unique layout of the folded coupled line and the L-shaped open stub line structure, the first resonator realizes the characteristics of low-pass and first band-pass. The combination of the first resonator, the LC microstrip transmission line, and the second resonator realizes the low-pass and dual-band-pass characteristics, obtaining resonance frequencies of 1.04 GHz, 1.92 GHz, and 2.9 GHz, and finally forming three ideal passbands. The first resonator and the second resonator are symmetrically arranged about the middle of the LC microstrip transmission line. This method of cascading the same resonators and L-shaped stub lines effectively improves the overall performance and reliability of the filter, enabling it to meet higher performance standards in practical applications.
[0010] Further, the high-performance low-pass and dual-band-pass filter further includes an input port feeder and an output port feeder. The input port feeder is connected to one end of the first resonator far from the LC microstrip transmission line, and the output port feeder is connected to one end of the second resonator far from the LC microstrip transmission line.
[0011] With the above technical solution, the input port feeder and the output port feeder are directly connected to an external high-frequency RF connector by soldering with a soldering iron. This structure can achieve low-pass and dual-band-pass responses and has filtering characteristics with controllable center frequency, passband bandwidth, and transmission zeros. At the same time, the input port feeder and the output port feeder are respectively connected to the first resonator and the second resonator. This two-port resonator structure avoids complex coupling circuits, and the overall design is significantly simplified.
[0012] Further, both the input port feeder and the output port feeder have an impedance of 50 Ω.
[0013] Further, the high-performance low-pass and dual-band-pass filter further includes a dielectric substrate. The first resonator, the LC microstrip transmission line, and the second resonator are disposed on the dielectric substrate.
[0014] Further, the dielectric constant of the dielectric substrate is 10.3, the substrate thickness is 1.35 mm, and the loss tangent is 0.0023.
[0015] Furthermore, a copper plating layer is provided on the surfaces of the first resonator, the LC microstrip transmission line, and the second resonator, and the thickness of the copper plating layer is 35 μm.
[0016] The high-performance low-pass and dual-band filter of the present invention, through a compact and unique folded coupled line and L-shaped stub line structure layout, the first resonator realizes the characteristics of low-pass and the first band-pass, and the combination of the first resonator, the microstrip transmission line, and the second resonator realizes the characteristics of low-pass and dual-band, obtaining resonance frequencies of 1.04 GHz, 1.92 GHz, and 2.9 GHz, and finally forming three ideal passbands; at the same time, this two-port resonator structure avoids complex coupling circuits, and the overall design is significantly simplified; this method of cascading the same resonator and L-shaped stub line effectively improves the overall performance and reliability of the filter, enabling it to reach higher performance standards in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 It is a schematic structural diagram of the high-performance low-pass and dual-band filter provided by the embodiment of the present invention.
[0018] Figure 2 is Figure 1 Another schematic structural diagram of the high-performance low-pass and dual-band filter in
[0019] Figure 3 It is a control diagram of the center frequency of the high-performance low-pass and dual-band filter of the present invention at different folded coupled line gap g1 values.
[0020] Figure 4 It is a control diagram of the center frequency of the high-performance low-pass and dual-band filter of the present invention at different L-shaped band length Ls values.
[0021] Figure 5 It is a control diagram of the passband bandwidth of the high-performance low-pass and dual-band filter of the present invention at different folded coupled line gap g1 values.
[0022] Figure 6 It is a control diagram of the passband bandwidth of the high-performance low-pass and dual-band filter of the present invention at different folded coupled line gap g0 values.
[0023] Figure 7 It is a control diagram of the passband bandwidth of the high-performance low-pass and dual-band filter of the present invention at different L-shaped band length Ls values.
[0024] Figure 8 It is a control diagram of the transmission zero point of the high-performance low-pass and dual-band filter of the present invention at different folded coupled line gap g0 values.
[0025] Figure 9It is a regulation diagram of transmission zeros at different folded coupled line gap g2 values of the high-performance low-pass and dual-band filters of the present utility model.
[0026] Figure 10 It is a regulation diagram of transmission zeros at different folded coupled line gap w1 values of the high-performance low-pass and dual-band filters of the present utility model.
[0027] Figure 11 It is a simulation diagram of the high-performance low-pass and dual-band filters of the present utility model.
[0028] The reference numerals and components involved in the accompanying drawings are shown as follows:
[0029] 100, the first resonator
[0030] 110, the first folded coupled line
[0031] 120, the first open stub line
[0032] 200, the LC microstrip transmission line
[0033] 300, the second resonator
[0034] 310, the second folded coupled line
[0035] 320, the second open stub line
[0036] 400, the input port feeder
[0037] 500, the output port feeder Detailed implementation manners
[0038] The following combines the accompanying drawings and embodiments to further describe in detail the detailed implementation manners of the present utility model. The following embodiments are used to illustrate the present utility model, but not to limit the scope of the present utility model.
[0039] The terms "first", "second", "third", "fourth", etc. in the specification and claims of the present utility model are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence.
[0040] Embodiment 1
[0041] Figure 1 It is a schematic structural diagram of the high-performance low-pass and dual-band filters provided by the embodiment of the present utility model. Figure 2 is Figure 1 Another schematic structural diagram of the high-performance low-pass and dual-band filters in. Please refer to Figure 1 , Figure 2, the high-performance low-pass and dual-band filter provided by the embodiment of the present utility model includes a first resonator 100, an LC microstrip transmission line 200, and a second resonator 300; both ends of the LC microstrip transmission line 200 are respectively connected to the first resonator 100 and the second resonator 300; the first resonator 100 and the second resonator 300 are symmetrically arranged about the middle of the LC microstrip transmission line 200.
[0042] Specifically, the first resonator 100 includes a first folded coupled line 110 and a first open stub line 120. The bottom of the first folded coupled line 110 is connected to the first open stub line 120. The first folded coupled line 110 is folded in a concave shape, and the first open stub line 120 is in an L shape; the second resonator 300 includes a second folded coupled line 310 and a second open stub line 320. The bottom of the second folded coupled line 310 is connected to the second open stub line 320; the first folded coupled line 110 and the second folded coupled line 310 are symmetrically arranged about the middle of the LC microstrip transmission line 200, and the first open stub line 120 and the second open stub line 320 are symmetrically arranged about the middle of the LC microstrip transmission line 200.
[0043] For the high-performance low-pass and dual-band filter of the present utility model, through the compact and unique folded coupled line and L-shaped open stub line structure layout, the first resonator 100 realizes the characteristics of low-pass and the first band-pass. The combination of the first resonator 100, the LC microstrip transmission line 200, and the second resonator 300 realizes the low-pass and dual-band characteristics, obtaining resonance frequencies of 1.04 GHz, 1.92 GHz, and 2.9 GHz, and finally forming three ideal passbands. At the same time, the input port feeder 400 and the output port feeder 500 are respectively connected to the first resonator 100 and the second resonator 300. This two-port resonator structure avoids complex coupling circuits, and the overall design is significantly simplified; the first resonator 100 and the second resonator 300 are symmetrically arranged about the middle of the LC microstrip transmission line 200. This method of cascading the same resonators and L-shaped stub lines effectively improves the overall performance and reliability of the filter, enabling it to meet higher performance standards in practical applications.
[0044] Further referring to Figure 1 , the high-performance low-pass and dual-band filter of the present utility model further includes an input port feeder 400 and an output port feeder 500. The input port feeder 400 is connected to one end of the first resonator 100 far from the LC microstrip transmission line 200, and the output port feeder 500 is connected to one end of the second resonator 300 far from the LC microstrip transmission line 200.
[0045] It should be noted that the input port feeder 400 and the output port feeder 500 are directly connected to the external high-frequency RF connector by soldering with a soldering iron. This structure can achieve low-pass and dual-bandpass responses and has filtering characteristics with controllable center frequency, passband bandwidth, and transmission zeros.
[0046] Furthermore, both the input port feeder 400 and the output port feeder 500 have an impedance of 50Ω; the high-performance low-pass and dual-bandpass filter further includes a dielectric substrate ( 6010LM microwave dielectric substrate, a ceramic-filled polytetrafluoroethylene (PTFE) composite material), and the first resonator 100, the LC microstrip transmission line 200, and the second resonator 300 are disposed on the dielectric substrate; the dielectric constant of the dielectric substrate is 10.3, the substrate thickness is 1.35 mm, and the loss tangent is 0.0023; a copper plating layer with a thickness of 35um is provided on the surface layers of the first resonator 100, the LC microstrip transmission line 200, and the second resonator 300.
[0047] Figure 3 It is a diagram for regulating the center frequency of the high-performance low-pass and dual-bandpass filter of the present invention at different folded coupled line gap g1 values, Figure 4 It is a diagram for regulating the center frequency of the high-performance low-pass and dual-bandpass filter of the present invention at different L-shaped band lengths Ls values, Figure 5 It is a diagram for regulating the passband bandwidth of the high-performance low-pass and dual-bandpass filter of the present invention at different folded coupled line gap g1 values, Figure 6 It is a diagram for regulating the passband bandwidth of the high-performance low-pass and dual-bandpass filter of the present invention at different folded coupled line gap g0 values, Figure 7 It is a diagram for regulating the passband bandwidth of the high-performance low-pass and dual-bandpass filter of the present invention at different L-shaped band lengths Ls values, Figure 8 It is a diagram for regulating the transmission zeros of the high-performance low-pass and dual-bandpass filter of the present invention at different folded coupled line gap g0 values, Figure 9 It is a diagram for regulating the transmission zeros of the high-performance low-pass and dual-bandpass filter of the present invention at different folded coupled line gap g2 values, Figure 10 It is a diagram for regulating the transmission zeros of the high-performance low-pass and dual-bandpass filter of the present invention at different folded coupled line gap w1 values, Figure 11 It is a simulation diagram of the high-performance low-pass and dual-bandpass filter of the present invention.
[0048] As Figure 2As shown, for example, the length of the LC microstrip transmission line 200 of the present utility model is L2; the width is w2, the lengths of the first folded coupling line 110 and the second folded coupling line 310 are L3 + L4 + 2*L5, and the width is w1; the lengths of the first open stub line 120 and the second open stub line 320 are Ls, and the width is w1; the lengths of the input port feeder 400 and the output port feeder 500 are L0, and the width is w0;
[0049] As Figures 3 - 11 shown, Figure 3 、 Figure 4 are the center frequency regulation results of the filter, Figure 5 、 Figure 6 、 Figure 7 are the passband bandwidth regulation results of the filter, Figure 8 、 Figure 9 、 Figure 10 are the transmission zero regulation results of the filter. The response structures of the proposed low-pass filter and dual-bandpass filter are simulated and optimized using the high-frequency simulator (HFSS15.0) software to obtain Figure 11 , Figure 11 where S21 is the insertion loss and S11 is the return loss. The three center frequencies of the designed filter are 1.04, 1.92, and 2.9 GHz respectively, which are applicable to the L and S band mixers.
[0050] It should be noted that, in order to separate the intermediate frequency and the local oscillator frequency in the mixer and to enable the microwave signal frequency and the baseband signal frequency to be transmitted on the same coaxial channel, different signal filtering processes can be simultaneously performed through the low-pass and band-pass filters of the present utility model. In the designed filter, the first passband low-pass filter can separate the digital baseband output intermediate frequency signal of 10 - 1040 MHz, and the second and third passband band-pass filters can separate the local oscillator signals of 1.78 - 2.03 GHz and 2.34 - 3.57 GHZ output by the frequency synthesizer, which has a certain feasibility and meets the design requirements.
[0051] Specifically, in the lumped equivalent circuit model of the filter of the present utility model, in series, the inductor (L1) is attributed to the input and output feeders, the capacitor (C1) and the inductor (L2) are attributed to the parallel resonant circuit formed by the folded coupling lines, and the inductor (L3) is generated by the microstrip transmission line connecting the two resonant units. In parallel, the open L-shaped stub wire acts as a short circuit, realizing the short circuit characteristic at the place where it is placed, so that metal vias are no longer required in the planar circuit, because the open stub line can be equivalent to a shunt, providing a series combination of an inductor (L4) and a capacitor (C2) connected to the ground. The existence of the parasitic capacitor (C3) is due to the coupling between the top structure and the ground plane.
[0052] The design process of the low-pass and dual-band filters of the present utility model is divided into three main steps according to the S scattering parameters and the design structure. The first step: First, a low-pass filter with a cut-off frequency of 1.04 GHz is designed using a folded coupled line based on a series-shunt LC resonance circuit (C1 and L2). At the same time, this structure provides a band-pass response, but the transmission performance is poor. The second step: To improve the band-pass transmission performance, an open-circuit L-shaped stub line is used to add a shunt resonance circuit (L4 and C2), which is a unit composed of series and parallel resonance circuits, but the out-of-band rejection performance does not meet the index requirements. The third step: To improve the out-of-band rejection performance and the number of transmission zeros, two identical and symmetrical resonance units are connected by a microstrip transmission line. Since another pair of resonance circuits is formed and an additional band-pass response is provided, it has a higher number of transmission zeros and good matching characteristics.
[0053] The filter structure of the present utility model generates 7 transmission poles and 4 transmission zeros. The transmission poles are 0.53, 0.99, 1.91, 2.45, 2.71, 3.12, and 3.37 GHz respectively, and the transmission zeros are 1.17, 1.35, 2.21, and 3.78 GHz. The lumped parameter values of the equivalent circuit model are extracted using the circuit simulator ADS: L1 = 5.2 nH, L2 = 4.8 nH, C1 = 0.8 pF, L3 = 8.7 nH, L4 = 11.5 nH, C2 = 0.9 pF, and C3 = 0.63 pF. Among them, the impedance of the folded coupled line part of C1 and L2 is Z2 (Z2 = Zs1 + Zs2 + Zs3, Zs2 = Zs3), the impedance of the shunt resonance circuit of L4 and C2 is Z4, the microstrip transmission line between the two resonance units is Z3, and the impedance of the input / output feeder is Z1. Mathematical theoretical derivation: According to the resonance condition, the denominator of the input impedance is 0, that is, 2Zs1 + 2Zs2 + 2Z4 + Z3 = 0. By extracting the ABCD matrix of the equivalent circuit and using series and parallel LC elements to adjust the transmission zero coefficient (S21) to introduce 4 transmission zeros, S21 = 2 / (A + B / Z0 + CZ0 + D) = 0, where A, B, C, and D are the transmission parameters of the equivalent circuit matrix, and Z0 is the source load impedance of the proposed filter. According to the lumped parameter values of the equivalent circuit model, the corresponding impedance values are obtained respectively.
[0054] Based on the above description, the advantages of the present utility model are as follows:
[0055] 1. The high-performance low-pass and dual-band filter of the present utility model has three center passband frequencies of 1.04, 1.92, and 2.9 GHz respectively, is applicable to L and S band mixers, can separate the intermediate frequency signal output from the digital baseband and the local oscillator signal output from the frequency synthesizer, and has electrical properties where the passband bandwidth, center frequency, and transmission zeros are all controllable. Moreover, it has four transmission zeros, which can improve the selectivity of each passband and the isolation degree between the three passbands. The isolation degree is greater than 20 dB, further enhancing the selectivity of the filter;
[0056] 2. The high-performance low-pass and dual-band filter of the present utility model, due to the use of a one-fifth wavelength folded coupled line and an open-circuit L-shaped stub line structure on a metamaterial (dielectric constant: 10.3) microwave substrate, makes the structure more compact. Its size is only 13.1 mm × 4.8 mm, meeting the requirements of miniaturization engineering. And the signal is transmitted through feeding at both ends, with a 50-ohm impedance match designed to ensure the maximum power transmission of the signal;
[0057] 3. The high-performance low-pass and dual-band filter of the present utility model, the -3 dB relative bandwidths of the two band-pass filters in the designed filter are 13% (1.78 - 2.03 GHz) and 42% (2.34 - 3.57) respectively, the insertion losses are 0.11, 0.6, and 0.2 dB respectively, the return losses are all better than 20 dB, the gain flatness within the passband is small, only 0.5 dB, and the bit error rate after demodulation is low, further improving the signal quality and enhancing the sensitivity of the radio receiver front end;
[0058] 4. The high-performance low-pass and dual-band filter of the present utility model, the simulation results of the filter are consistent with the theoretical analysis, and the stopband suppression degrees are all less than -25 dBc, obviously having a good ability to suppress noise. Therefore, it can be directly applied to applications such as mixers and hybrid fiber-coaxial cable support systems for signal separation and filtering, and has practical value in communication engineering applications;
[0059] 5. The high-performance low-pass and dual-band filter of the present utility model is feasible and provides a good choice for modern multi-band composite communication systems.
[0060] The above is only the specific implementation manner of the present utility model, but the protection scope of the present utility model is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present utility model can easily think of changes or substitutions, which should all be covered within the protection scope of the present utility model. Therefore, the protection scope of the present utility model should be subject to the protection scope of the claimed rights.
Claims
1. A high performance low-pass and dual-passband filter, characterized in that: It comprises a first resonator (100), an LC microstrip transmission line (200) and a second resonator (300); The first resonator (100) and the second resonator (300) are respectively connected to two ends of the LC microstrip transmission line (200); the first resonator (100) and the second resonator (300) are symmetrically arranged with respect to the middle of the LC microstrip transmission line (200).
2. The high performance low-pass and dual-passband filter according to claim 1, characterized in that: The first resonator (100) comprises a first folded coupling line (110) and a first open-circuit branch line (120), The bottom of the first folded coupling line (110) is connected to the first open branch line (120), the first folded coupling line (110) is folded in a concave shape, and the first open branch line (120) is L-shaped; The second resonator (300) comprises a second folded coupling line (310) and a second open branch line (320), wherein the bottom of the second folded coupling line (310) is connected to the second open branch line (320); the first folded coupling line (110) and the second folded coupling line (310) are symmetrically arranged with respect to the middle of the LC microstrip transmission line (200), and the first open branch line (120) and the second open branch line (320) are symmetrically arranged with respect to the middle of the LC microstrip transmission line (200).
3. The high performance low-pass and dual-passband filter according to claim 1, characterized in that: The high-performance low-pass and dual-passband filter further comprises an input port feeder (400) and an output port feeder (500), wherein the input port feeder (400) is connected to an end of the first resonator (100) away from the LC microstrip transmission line (200), and the output port feeder (500) is connected to an end of the second resonator (300) away from the LC microstrip transmission line (200).
4. The high performance low-pass and dual-passband filter according to claim 3, characterized in that: The input port feeder (400) and the output port feeder (500) both have an impedance of 50Ω.
5. The high performance low-pass and dual-passband filter according to claim 1, characterized in that: The high-performance low-pass and dual-passband filter further comprises a dielectric substrate, and the first resonator (100), the LC microstrip transmission line (200) and the second resonator (300) are arranged on the dielectric substrate.
6. The high performance low-pass and dual-passband filter according to claim 5, characterized in that: The dielectric constant of the dielectric substrate is 10.3, the thickness of the substrate is 1.35 mm, and the loss tangent is 0.0023.
7. The high performance low-pass and dual-passband filter according to claim 5, characterized in that: A copper plating layer is provided on the surface of the first resonator (100), the LC microstrip transmission line (200) and the second resonator (300), and the thickness of the copper plating layer is 35 um.