Topological structure and low-pass filter
By employing a symmetrically configured topology and open stubs in the microstrip low-pass filter, the problem of narrow stopband was solved, achieving wide stopband and high selectivity, thus improving the performance of the communication system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-19
- Publication Date
- 2026-03-06
AI Technical Summary
Existing microstrip low-pass filter designs suffer from narrow stopbands, limiting their application in modern wireless communication systems.
A novel topology is adopted, which includes a combination of multiple parallel microstrip lines and open stubs. By using symmetrically arranged open stubs and microstrip lines, symmetrical notch characteristics and selective signal filtering are achieved, enhancing stopband suppression capability. Furthermore, transmission characteristics are optimized through parity-even mode analysis.
It achieves wide stopband characteristics, improves the performance of the communication system, enhances the ability to suppress out-of-band interference signals, and has a compact structure and simple design.
Smart Images
Figure CN223978074U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of filter technology, and in particular to a low-pass filter. Background Technology
[0002] With the advent of the fifth generation of wireless communication, the demand for suppression of spurious signals in adjacent channels and far-end out-of-band communication links is increasing. Therefore, designing compact, high-performance microstrip low-pass filters with steep sidebands and wide stopbands is crucial for improving the performance of communication systems and achieving miniaturization.
[0003] Currently reported microstrip low-pass filter designs mainly include defective ground schemes, step impedance resonator schemes, stub-loaded resonator schemes, and sector resonator schemes. However, low-pass filters designed based on these schemes often suffer from narrow stopbands, which limits their use in modern wireless communication systems. Summary of the Invention
[0004] This application aims to provide a topology that can be used to design low-pass filters to improve the wide stopband performance of low-pass filters.
[0005] In a first aspect, this application proposes a topology including an input terminal and an output terminal. Along a first direction, a second microstrip line and a fifteenth microstrip line are sequentially connected between the input terminal and the output terminal. A first microstrip line and a third microstrip line are connected between the input terminal and the second microstrip line. The first microstrip line is connected to a first open-circuit stub, and the third microstrip line is connected to a second open-circuit stub. Along a second direction, the first open-circuit stub and the second open-circuit stub are located on opposite sides of the second microstrip line. Along the second direction, a fourth microstrip line and a ninth microstrip line are connected between the second microstrip line and the fifteenth microstrip line. Along the first direction, the fourth microstrip line is connected to a fifth microstrip line and a seventh microstrip line. The fifth microstrip line is connected to a sixth microstrip line, and the sixth microstrip line is connected to a third open-circuit stub. The seventh microstrip line is connected to an eighth microstrip line, and the eighth microstrip line is connected to a fourth open-circuit stub. Along the first direction, the ninth microstrip line is connected to the tenth and twelfth microstrip lines, the tenth microstrip line is connected to the eleventh microstrip line, and the eleventh microstrip line is connected to the fifth open-circuit stub. The twelfth microstrip line is connected to the thirteenth microstrip line, and the thirteenth microstrip line is connected to the sixth open-circuit stub. Along the second direction, the third and fifth open-circuit stubs are located on opposite sides of the second microstrip line, and the fourth and sixth open-circuit stubs are located on opposite sides of the fifteenth microstrip line. The output terminal is connected to the fifteenth microstrip line via the fourteenth and sixteenth microstrip lines, the fourteenth microstrip line is connected to the seventh open-circuit stub, and the sixteenth microstrip line is connected to the eighth open-circuit stub. Along the second direction, the seventh and eighth open-circuit stubs are located on opposite sides of the fifteenth microstrip line. The first direction is perpendicular to the second direction.
[0006] The open-circuit stubs can introduce additional resonant frequencies, enabling the selection and control of different signals. This allows the topology to operate at specific frequencies or process signals of specific frequencies. The microstrip line, as a transmission line, can effectively transmit signals. In the above structure, using multiple parallel microstrip lines to transmit signals reduces impedance during signal transmission, increases power capacity, and thus broadens bandwidth to a certain extent. Simultaneously, the symmetrically arranged open-circuit stubs generate symmetrical notch characteristics, forming symmetrical notch points that more effectively suppress out-of-band interference signals. Furthermore, it facilitates impedance balance, enabling better impedance matching at different locations or along different signal paths.
[0007] In some embodiments, the first microstrip line and the third microstrip line are symmetrically arranged about the second microstrip line, and the first open stub and the second open stub are symmetrically arranged about the second microstrip line.
[0008] In some embodiments, the fifth microstrip line and the tenth microstrip line are symmetrically arranged about the second microstrip line, the third open-circuit stub and the fifth open-circuit stub are symmetrically arranged about the second microstrip line, and the sixth microstrip line and the eleventh microstrip line are symmetrically arranged about the second microstrip line.
[0009] In some embodiments, the seventh microstrip line and the twelfth microstrip line are symmetrically arranged about the fifteenth microstrip line, the fourth open-circuit stub and the sixth open-circuit stub are symmetrically arranged about the fifteenth microstrip line, and the eighth microstrip line and the thirteenth microstrip line are symmetrically arranged about the fifteenth microstrip line.
[0010] In some embodiments, the fourteenth microstrip line and the sixteenth microstrip line are symmetrically arranged about the fifteenth microstrip line, and the seventh open-circuit stub and the eighth open-circuit stub are symmetrically arranged about the fifteenth microstrip line.
[0011] In the above structure, the symmetrical topology is conducive to ensuring that the transmission characteristics of the signal are consistent on different paths. The signal is evenly distributed on the symmetrical path for transmission. During the transmission process, the signals on different paths will not generate additional phase differences or amplitude differences. Only when the signal frequency meets specific conditions will constructive interference or destructive interference be achieved at the output end, thereby achieving selective filtering of frequency and improving the ability to select specific frequency signals.
[0012] In some embodiments, along the first direction, the fifth microstrip line and the seventh microstrip line are respectively connected to both sides of the fourth microstrip line, the fifth microstrip line extending towards the input terminal and the seventh microstrip line extending towards the output terminal. Along the first direction, the tenth microstrip line and the twelfth microstrip line are respectively connected to both sides of the ninth microstrip line, the tenth microstrip line extending towards the input terminal and the twelfth microstrip line extending towards the output terminal.
[0013] In some embodiments, the first, second, third, fifth, seventh, tenth, twelfth, fourteenth, fifteenth, and sixteenth microstrip lines are parallel to each other. The third, fourth, fifth, and sixth open-circuit stubs are parallel to each other. The fourth, sixth, eighth, ninth, eleventh, and thirteenth microstrip lines are parallel to each other. The first, second, seventh, and eighth open-circuit stubs are parallel to each other.
[0014] In some embodiments, the wavelength corresponding to the stopband center frequency of the topology is L. The electrical length of the second microstrip line is L2, and the electrical length of the fifteenth microstrip line is L... 15 , The electrical length of the first microstrip line is L1, the electrical length of the first open-circuit stub is K1, the electrical length of the third microstrip line is L3, the electrical length of the second open-circuit stub is K2, and the electrical length of the fourteenth microstrip line is L... 14 The electrical length of the seventh open-circuit stub is K7, and the electrical length of the sixteenth microstrip line is L. 16 The electrical length of the eighth open-circuit stub is K8.
[0015] In some embodiments, the electrical length of the fourth microstrip line is L4, the electrical length of the fifth microstrip line is L5, the electrical length of the sixth microstrip line is L6, and the electrical length of the third open-circuit stub is K3. The electrical length of the seventh microstrip line is L7, the electrical length of the eighth microstrip line is L8, and the electrical length of the fourth open-circuit stub is K4. The electrical length of the ninth microstrip line is L9, and the electrical length of the tenth microstrip line is L. 10 The electrical length of the eleventh microstrip line is L. 11 The electrical length of the fifth open-circuit stub is K5. The electrical length of the twelfth microstrip line is L. 12 The electrical length of the thirteenth microstrip line is L. 13 The electrical length of the sixth open-circuit stub is K6.
[0016] By designing the above topology, the low-pass filter can exhibit wide stopband characteristics, thereby improving its performance in communication processes.
[0017] Secondly, this application also proposes a low-pass filter, including a topology as described in any of the embodiments of the first aspect above.
[0018] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description
[0019] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are not intended to limit the embodiments, and elements having the same reference numerals in the drawings are designated as similar elements.
[0020] Figure 1 This is a topology diagram of some embodiments of this application;
[0021] Figure 2 This is a structural diagram of the odd-mode form of the topology of some embodiments of this application;
[0022] Figure 3 This is a diagram showing the even-mode form of the topology of some embodiments of this application;
[0023] Figure 4 This is a layout diagram of a low-pass filter based on topology design according to some embodiments of this application;
[0024] Figure 5 The diagram shows the S-parameter simulation results of some design examples of embodiments of this application.
[0025] Explanation of reference numerals in the attached figures:
[0026] 1. Input terminal;
[0027] 2. Output terminal;
[0028] 31. First microstrip line; 32. Second microstrip line; 33. Third microstrip line; 34. Fourth microstrip line; 35. Fifth microstrip line; 36. Sixth microstrip line; 37. Seventh microstrip line; 38. Eighth microstrip line; 39. Ninth microstrip line; 310. Tenth microstrip line; 311. Eleventh microstrip line; 312. Twelfth microstrip line; 313. Thirteenth microstrip line; 314. Fourteenth microstrip line; 315. Fifteenth microstrip line; 316. Sixteenth microstrip line; 317. Seventeenth microstrip line; 318. Eighteenth microstrip line;
[0029] 41. First open branch; 42. Second open branch; 43. Third open branch; 44. Fourth open branch; 45. Fifth open branch; 46. Sixth open branch; 47. Seventh open branch; 48. Eighth open branch;
[0030] a. First direction;
[0031] b. Second direction. Detailed Implementation
[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.
[0033] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.
[0034] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.
[0035] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.
[0036] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.
[0037] Firstly, this application provides a topology, please refer to... Figure 1 The topology includes input terminal 1, output terminal 2, first microstrip line 31, second microstrip line 32, third microstrip line 33, fourth microstrip line 34, fifth microstrip line 35, sixth microstrip line 36, seventh microstrip line 37, eighth microstrip line 38, ninth microstrip line 39, tenth microstrip line 310, eleventh microstrip line 311, twelfth microstrip line 312, thirteenth microstrip line 313, fourteenth microstrip line 314, fifteenth microstrip line 315, sixteenth microstrip line 316, first open-circuit stub 41, second open-circuit stub 42, third open-circuit stub 43, fourth open-circuit stub 44, fifth open-circuit stub 45, and sixth open-circuit stub 46.
[0038] Specifically, please refer to Figure 1 Along the first direction a, there is a second microstrip line 32 and a fifteenth microstrip line 315 connected sequentially between the input terminal 1 and the output terminal 2.
[0039] The input terminal 1 is connected to the second microstrip line 32 by a first microstrip line 31 and a third microstrip line 33. The first microstrip line 31 is connected to a first open-circuit stub 41, and the third microstrip line 33 is connected to a second open-circuit stub 42. Along the second direction b, the first open-circuit stub 41 and the second open-circuit stub 42 are located on both sides of the second microstrip line 32.
[0040] Among them, open-circuit stubs can be used to introduce additional resonant frequencies to enable the selection and control of signals of different frequencies, so that the topology can operate at a specific frequency or process signals of a specific frequency. They can also be used to broaden or adjust the bandwidth, interact with other circuit elements, and broaden and adjust the operating bandwidth of the overall topology.
[0041] Along the second direction b, the second microstrip line 32 and the fifteenth microstrip line 315 are connected by the fourth microstrip line 34 and the ninth microstrip line 39. The microstrip line can be used as a microwave transmission line to effectively transmit signals.
[0042] Along the first direction a, the fourth microstrip line 34 is connected to the fifth microstrip line 35 and the seventh microstrip line 37, the fifth microstrip line 35 is connected to the sixth microstrip line 36, the sixth microstrip line 36 is connected to the third open-circuit stub 43; the seventh microstrip line 37 is connected to the eighth microstrip line 38, and the eighth microstrip line 38 is connected to the fourth open-circuit stub 44.
[0043] Along the first direction a, the ninth microstrip line 39 is connected to the tenth microstrip line 310 and the twelfth microstrip line 312. The tenth microstrip line 310 is connected to the eleventh microstrip line 311, and the eleventh microstrip line 311 is connected to the fifth open-circuit stub 45. The twelfth microstrip line 312 is connected to the thirteenth microstrip line 313, and the thirteenth microstrip line 313 is connected to the sixth open-circuit stub 46.
[0044] Along the second direction b, the third open branch 43 and the fifth open branch 45 are located on both sides of the second microstrip line 32, and the fourth open branch 44 and the sixth open branch 46 are located on both sides of the fifteenth microstrip line 315.
[0045] The output terminal 2 is connected to the fifteenth microstrip line 315 by the fourteenth microstrip line 314 and the sixteenth microstrip line 316. The fourteenth microstrip line 314 is connected to the seventh open stub 47, and the sixteenth microstrip line 316 is connected to the eighth open stub 48. Along the second direction b, the seventh open stub 47 and the eighth open stub 48 are located on both sides of the fifteenth microstrip line 315.
[0046] Wherein, the first direction a is perpendicular to the second direction b.
[0047] Based on the above structure, using multiple parallel microstrip lines to transmit signals can reduce the impedance during signal transmission and increase the power capacity of signal transmission, thereby widening the bandwidth to a certain extent. Furthermore, each line is connected to at least one open stub, allowing signals of different modes to be transmitted on the same transmission line, effectively increasing the transmission bandwidth.
[0048] In some embodiments, the first microstrip line 31 and the third microstrip line 33 are symmetrically arranged about the second microstrip line 32, and the first open-circuit stub 41 and the second open-circuit stub 42 are symmetrically arranged about the second microstrip line 32. The symmetrically arranged open-circuit stubs can generate symmetrical notch characteristics, forming symmetrical notch points, and more effectively suppressing out-of-band interference signals. This also facilitates impedance balancing, enabling better impedance balance and matching at different locations or on different signal paths. Furthermore, during the design process, only the parameters of one open-circuit stub need to be designed and optimized; the parameters of the other symmetrical open-circuit stub can be directly determined according to the symmetry principle, reducing the workload and complexity of the design and improving the compactness of the structure.
[0049] In some embodiments, the fifth microstrip line 35 and the tenth microstrip line 310 are symmetrically arranged about the second microstrip line 32, the third open-circuit stub 43 and the fifth open-circuit stub 45 are symmetrically arranged about the second microstrip line 32, and the sixth microstrip line 36 and the eleventh microstrip line 311 are symmetrically arranged about the second microstrip line 32.
[0050] In some embodiments, the seventh microstrip line 37 and the twelfth microstrip line 312 are symmetrically arranged about the fifteenth microstrip line 315, the fourth open-circuit stub 44 and the sixth open-circuit stub 46 are symmetrically arranged about the fifteenth microstrip line 315, and the eighth microstrip line 38 and the thirteenth microstrip line 313 are symmetrically arranged about the fifteenth microstrip line 315.
[0051] In some embodiments, the fourteenth microstrip line 314 and the sixteenth microstrip line 316 are symmetrically arranged about the fifteenth microstrip line 315, and the seventh open-circuit stub 47 and the eighth open-circuit stub 48 are symmetrically arranged about the fifteenth microstrip line 315.
[0052] A symmetrical topology helps ensure consistent signal transmission characteristics across different paths. Signals are evenly distributed across symmetrical paths for transmission, and no additional phase or amplitude differences occur between signals on different paths during transmission. Only when the signal frequency meets specific conditions will constructive or destructive interference occur at the output, thereby enabling selective frequency filtering and improving the ability to select specific frequency signals.
[0053] In some embodiments, along the first direction a, the fifth microstrip line 35 and the seventh microstrip line 37 are respectively connected to both sides of the fourth microstrip line 34, the fifth microstrip line 35 extends toward the input terminal 1, and the seventh microstrip line 37 extends toward the output terminal 2.
[0054] Along the first direction a, the tenth microstrip line 310 and the twelfth microstrip line 312 are respectively connected to the two sides of the ninth microstrip line 39. The tenth microstrip line 310 extends toward the input terminal 1, and the twelfth microstrip line 312 extends toward the output terminal 2.
[0055] In some embodiments, the first microstrip line 31, the second microstrip line 32, the third microstrip line 33, the fifth microstrip line 35, the seventh microstrip line 37, the tenth microstrip line 310, the twelfth microstrip line 312, the fourteenth microstrip line 314, the fifteenth microstrip line 315, and the sixteenth microstrip line 316 are parallel to each other. The third open-circuit stub 43, the fourth open-circuit stub 44, the fifth open-circuit stub 45, and the sixth open-circuit stub 46 are parallel to each other. The fourth microstrip line 34, the sixth microstrip line 36, the eighth microstrip line 38, the ninth microstrip line 39, the eleventh microstrip line 311, and the thirteenth microstrip line 313 are parallel to each other. The first open-circuit stub 41, the second open-circuit stub 42, the seventh open-circuit stub 47, and the eighth open-circuit stub 48 are parallel to each other.
[0056] In some embodiments, the wavelength corresponding to the stopband center frequency of the topology is L. The electrical length of the second microstrip line 32 is L2, and the electrical length of the fifteenth microstrip line 315 is L. 15 The wavelength corresponding to the stopband center frequency is the wavelength corresponding to the center frequency point of the frequency range in which the topology suppresses or blocks the signal. The electrical length of the second microstrip line 32 is equal to the electrical length of the fifteenth microstrip line 315 and is half the wavelength corresponding to the stopband center frequency.
[0057] The electrical length of the first microstrip line 31 is L1, the electrical length of the first open-circuit stub 41 is K1, the electrical length of the third microstrip line 33 is L3, the electrical length of the second open-circuit stub 42 is K2, and the electrical length of the fourteenth microstrip line 314 is L... 14 The electrical length of the seventh open-circuit stub 47 is K7, and the electrical length of the sixteenth microstrip line 316 is L. 16 The electrical length of the eighth open-circuit stub 48 is K8. The sum of the electrical lengths of the first microstrip line 31 and the first open-circuit stub 41, the third microstrip line 33 and the second open-circuit stub 42, the fourteenth microstrip line 314 and the seventh open-circuit stub 47, and the sixteenth microstrip line 316 and the eighth open-circuit stub 48 are equal and are one-quarter of the wavelength corresponding to the stopband center frequency.
[0058] In some embodiments, the electrical length of the fourth microstrip line 34 is L4, the electrical length of the fifth microstrip line 35 is L5, the electrical length of the sixth microstrip line 36 is L6, and the electrical length of the third open-circuit stub 43 is K3. The sum of the electrical lengths of the fourth microstrip line 34, the fifth microstrip line 35, the sixth microstrip line 36, and the third open-circuit stub 43 is half the wavelength corresponding to the stopband center frequency, i.e.
[0059] The electrical length of the seventh microstrip line 37 is L7, the electrical length of the eighth microstrip line 38 is L8, and the electrical length of the fourth open-circuit stub 44 is K4. The sum of the electrical lengths of the fourth microstrip line 34, the seventh microstrip line 37, the eighth microstrip line 38, and the fourth open-circuit stub 44 is half the wavelength corresponding to the stopband center frequency.
[0060] The electrical length of the ninth microstrip line 39 is L9, and the electrical length of the tenth microstrip line 310 is L. 10 The electrical length of the eleventh microstrip line 311 is L. 11 The electrical length of the fifth open-circuit stub 45 is K5. The sum of the electrical lengths of the ninth microstrip line 39, the tenth microstrip line 310, the eleventh microstrip line 311, and the fifth open-circuit stub 45 is half the wavelength corresponding to the stopband center frequency.
[0061] The electrical length of the twelfth microstrip line 312 is L. 12 The electrical length of the thirteenth microstrip line 313 is L. 13 The electrical length of the sixth open-circuit stub 46 is K6. The sum of the electrical lengths of the ninth microstrip line 39, the twelfth microstrip line 312, the thirteenth microstrip line 313, and the sixth open-circuit stub 46 is half the stopband center frequency, i.e.
[0062] The characteristic impedances of each part of the topology may have the following characteristics: the characteristic impedances of the first microstrip line 31, the third microstrip line 33, the fourteenth microstrip line 314, the sixteenth microstrip line 316, the first open-circuit stub 41, the second open-circuit stub 42, the seventh open-circuit stub 47, and the eighth open-circuit stub 48 are equal, and all are Z1; the characteristic impedances of the second microstrip line 32 and the fifteenth microstrip line 315 are equal, and both are Z2; the characteristic impedances of the fourth microstrip line 34 and the ninth microstrip line 315 are equal, and both are Z2; The characteristic impedances of the five microstrip lines 35, 36, 37, 38, 310, 311, 312, 313, 43, 44, 45, and 46 are all equal and 2Z3.
[0063] Based on the above topology analysis, it can be seen that the structure can be equivalent to a symmetrical structure, and its transmission zeros and poles can be analyzed using parity modes.
[0064] Please refer to Figure 2 , Figure 2 This is an odd-mode topology. It includes an input terminal 1, a first microstrip line 31, a second microstrip line 32, a third microstrip line 33, a first open-circuit stub 41, and a second open-circuit stub 42. One end of the second microstrip line 32 is connected to the input terminal 1, and the other end is grounded. Along a first direction a, the first microstrip line 31 and the third microstrip line 33 are connected to each other along a second direction b. The first microstrip line 31 and the third microstrip line 33 are respectively connected to the first open-circuit stub 41 and the second open-circuit stub 42. The first microstrip line 31 and the third microstrip line 33 are symmetrically arranged about the second microstrip line 32, and the first open-circuit stub 41 and the second open-circuit stub 42 are also symmetrically arranged about the second microstrip line 32.
[0065] When Y ino When =∞, it can be concluded that this topology has two odd-mode transmission poles, and their corresponding frequencies are:
[0066] f op1 =0
[0067] f op2 =f0
[0068] Here, f0 is the band-stop center frequency.
[0069] Please refer to Figure 3 , Figure 3It is an even-mode form of the equivalent topology. It includes input terminal 1, first microstrip line 31, second microstrip line 32, third microstrip line 33, fifth microstrip line 35, sixth microstrip line 36, tenth microstrip line 310, eleventh microstrip line 311, seventeenth microstrip line 317, eighteenth microstrip line 318, first open-circuit stub 41, second open-circuit stub 42, third open-circuit stub 43, and fifth open-circuit stub 45. Along the first direction a, input terminal 1 is connected to one end of the second microstrip line 32. The first microstrip line 31 and the third microstrip line 33 are connected between input terminal 1 and the second microstrip line 32, and are symmetrically arranged about the second microstrip line 32. Along the second direction b, the first microstrip line 31 and the third microstrip line 33 are respectively connected to a first open-circuit stub 41 and a second open-circuit stub 42, which are symmetrically arranged about the second microstrip line 32. Along the second direction b, the other end of the second microstrip line 32 is connected to a seventeenth microstrip line 317 and an eighteenth microstrip line 318, which are symmetrically arranged about the second microstrip line 32. The seventeenth microstrip line 317 is sequentially connected to a fifth microstrip line 35, a sixth microstrip line 36, and a third open-circuit stub 43, wherein the fifth microstrip line 35 and the third open-circuit stub 43 are arranged along the first direction a, and the sixth microstrip line 36 is arranged along the second direction b. The eighteenth microstrip line 318 is sequentially connected to the tenth microstrip line 310, the eleventh microstrip line 311, and the fifth open-circuit stub 45. The tenth microstrip line 310 and the fifth open-circuit stub 45 are arranged along a first direction a, and the eleventh microstrip line 311 is arranged along a second direction b. The fifth microstrip line 35 and the tenth microstrip line 310 are symmetrically arranged about the second microstrip line 32. The sixth microstrip line 36 and the eleventh microstrip line 311 are symmetrically arranged about the second microstrip line 32. The third open-circuit stub 43 and the fifth open-circuit stub 45 are symmetrically arranged about the second microstrip line 32.
[0070] Furthermore, the electrical length of the seventeenth microstrip line 317 is equal to the electrical length of the fourth microstrip line 34; the electrical length of the eighteenth microstrip line 318 is equal to the electrical length of the ninth microstrip line 39; the characteristic impedance of the seventeenth microstrip line 317 is twice the characteristic impedance of the fourth microstrip line 34, i.e., 2Z3; the characteristic impedance of the eighteenth microstrip line 318 is twice the characteristic impedance of the ninth microstrip line 39, i.e., 2Z3. When Y ine When =∞, it can be concluded that this topology has an even-mode transmission pole, the corresponding frequency of which is:
[0071]
[0072] For this topology, its transmission zeros can be calculated as follows: multiply the ABCD matrices of the cascaded resonators that make up the topology sequentially to obtain the corresponding ABCD matrix; then transform the ABCD matrix of this topology into the corresponding S matrix. When |S21 When |=0, it can be concluded that this topology has three transmission zeros, and the frequencies corresponding to the three transmission zeros are as follows:
[0073]
[0074] The above analysis shows that this topology has two odd-mode transmission poles, one even-mode transmission pole, and three transmission zeros. Regardless of parameters Z1, Z2, and Z... 34 How the value changes, and the relative positions of these transfer zeros and poles, i.e. It will not change. Furthermore, based on the characteristics of RF filters, when the positions of the transmission zero and transmission pole coincide, only the characteristics of the transmission zero are displayed. Based on this, this topology can be used to design low-pass filters with two transmission poles in the passband to ensure flatness, and three transmission zeros in the stopband to ensure width and height selectivity, wide stopband, and high isolation.
[0075] Secondly, this application provides a low-pass filter designed using the topology structure of any embodiment of the first aspect.
[0076] For ease of understanding, this application provides the following design example. Please refer to... Figure 4 , Figure 4 The image shows the layout of a low-pass filter designed based on the above topology. This low-pass filter is designed on a circuit board with a dielectric loss of 0.0022 and a thickness of 0.813 mm, and the circuit board dimensions are 21.8 mm * 14.0 mm. Figure 4 As shown, one set of typical dimensional parameters is: l 1H =7.3mm, l 1V =1.2mm, l2=8.8mm, l3=6.35mm, l4=6.7mm, l5=3.3mm, l6=1.9mm, w1=0.4mm, w2=0.1mm, w3=0.6mm, w4=0.3mm, w5=0.3mm, w6=0.3mm, s1=0.5mm.
[0077] Please refer to Figure 5 , Figure 5This is a simulation result of the S-parameters for this design example. The filter has an impedance bandwidth ranging from DC (direct current frequency) to 1.26 GHz with a reflection coefficient less than -10 dB, and a maximum in-band loss of 0.488 dB, exhibiting low insertion loss. Its stopband, with isolation greater than 20 dB, extends from 2.18 GHz to 8.918 GHz, demonstrating a wide stopband. The passband has two transmission poles located at 0 and 0.96 GHz to ensure in-band flatness. The stopband has three transmission zeros located at 2.54 GHz, 5.82 GHz, and 8.7 GHz to ensure high selectivity and high isolation. Insertion loss refers to the signal power loss caused by the filter's effect on the signal after insertion into the signal transmission path.
[0078] As can be seen from the above design examples, this topology can be used to design low-pass filters, which have the advantages of compact structure, high selectivity, wide stopband, low insertion loss and simple design.
[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some 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 this application.
Claims
1. A topology, characterized in that, The input end and the output end are connected in sequence with the second microstrip line and the fifteenth microstrip line between them along a first direction; The first microstrip line and the third microstrip line are connected between the input end and the second microstrip line, the first microstrip line is connected with a first open-circuit stub, and the third microstrip line is connected with a second open-circuit stub; Along a second direction, the first open-circuit stub and the second open-circuit stub are respectively located on both sides of the second microstrip line; Along the second direction, the fourth microstrip line and the ninth microstrip line are connected between the second microstrip line and the fifteenth microstrip line; Along the first direction, the fourth microstrip line is connected with the fifth microstrip line and the seventh microstrip line, the fifth microstrip line is connected with the sixth microstrip line, and the sixth microstrip line is connected with a third open-circuit stub; the seventh microstrip line is connected with the eighth microstrip line, and the eighth microstrip line is connected with a fourth open-circuit stub; Along the first direction, the ninth microstrip line is connected with the tenth microstrip line and the twelfth microstrip line, the tenth microstrip line is connected with the eleventh microstrip line, and the eleventh microstrip line is connected with a fifth open-circuit stub; The twelfth microstrip line is connected with the thirteenth microstrip line, and the thirteenth microstrip line is connected with a sixth open-circuit stub; Along the second direction, the third open-circuit stub and the fifth open-circuit stub are respectively located on both sides of the second microstrip line, and the fourth open-circuit stub and the sixth open-circuit stub are respectively located on both sides of the fifteenth microstrip line; The output end and the fifteenth microstrip line are connected with the fourteenth microstrip line and the sixteenth microstrip line, the fourteenth microstrip line is connected with a seventh open-circuit stub, and the sixteenth microstrip line is connected with an eighth open-circuit stub; along the second direction, the seventh open-circuit stub and the eighth open-circuit stub are respectively located on both sides of the fifteenth microstrip line; Wherein, the first direction and the second direction are perpendicular.
2. The topology of claim 1, wherein, The first microstrip line and the third microstrip line are symmetrically arranged about the second microstrip line, and the first open-circuit stub and the second open-circuit stub are symmetrically arranged about the second microstrip line.
3. The topology of claim 1, wherein, The fifth microstrip line and the tenth microstrip line are symmetrically arranged about the second microstrip line, the third open-circuit stub and the fifth open-circuit stub are symmetrically arranged about the second microstrip line, and the sixth microstrip line and the eleventh microstrip line are symmetrically arranged about the second microstrip line.
4. The topology of claim 1, wherein, The seventh microstrip line and the twelfth microstrip line are symmetrically arranged about the fifteenth microstrip line, the fourth open-circuit stub and the sixth open-circuit stub are symmetrically arranged about the fifteenth microstrip line, and the eighth microstrip line and the thirteenth microstrip line are symmetrically arranged about the fifteenth microstrip line.
5. The topology of claim 1, wherein, The fourteenth microstrip line and the sixteenth microstrip line are symmetrically arranged about the fifteenth microstrip line, and the seventh open-circuit stub and the eighth open-circuit stub are symmetrically arranged about the fifteenth microstrip line.
6. The topology of claim 1, wherein, Along the first direction, the fifth microstrip line and the seventh microstrip line are respectively connected on both sides of the fourth microstrip line, the fifth microstrip line extends towards the input end, and the seventh microstrip line extends towards the output end; In the first direction, the tenth microstrip line and the twelfth microstrip line are connected to two sides of the ninth microstrip line respectively, the tenth microstrip line extends towards the input end, and the twelfth microstrip line extends towards the output end.
7. The topology of claim 1, wherein, The first microstrip line, the second microstrip line, the third microstrip line, the fifth microstrip line, the seventh microstrip line, the tenth microstrip line, the twelfth microstrip line, the fourteenth microstrip line, the fifteenth microstrip line and the sixteenth microstrip line are parallel to each other; The third open-circuit stub, the fourth open-circuit stub, the fifth open-circuit stub and the sixth open-circuit stub are parallel to each other; The fourth microstrip line, the sixth microstrip line, the eighth microstrip line, the ninth microstrip line, the eleventh microstrip line and the thirteenth microstrip line are parallel to each other; The first open-circuit stub, the second open-circuit stub, the seventh open-circuit stub and the eighth open-circuit stub are parallel to each other.
8. The topology of claim 7, wherein, The wavelength corresponding to the center frequency of the stopband of the topology structure is L; an electrical length of the second microstrip line is L2, an electrical length of the fifteenth microstrip line is L 15 , an electrical length of the first microstrip line is LI, an electrical length of the first open-circuited stub is KI, an electrical length of the third microstrip line is L3, an electrical length of the second open-circuited stub is K2, an electrical length of the fourteenth microstrip line is L 14 , an electrical length of the seventh open-circuited stub is K7, an electrical length of the sixteenth microstrip line is L 16 , an electrical length of the eighth open-circuited stub is K8, 9. The topology of claim 8, wherein, an electrical length of the fourth microstrip line is L4, an electrical length of the fifth microstrip line is L5, an electrical length of the sixth microstrip line is L6, an electrical length of the third open-circuited stub is K3, an electrical length of the seventh microstrip line is L7, an electrical length of the eighth microstrip line is L8, and an electrical length of the fourth open-circuited stub is K4, an electrical length of the ninth microstrip line is L9, an electrical length of the tenth microstrip line is L 10 , an electrical length of the eleventh microstrip line is L 11 , an electrical length of the fifth open-circuited stub is K5, an electrical length of the twelfth microstrip line is L 12 an electrical length of the thirteenth microstrip line is L 13 an electrical length of the sixth open-circuited stub is K6, 10. A low pass filter characterized by, The topology structure according to any one of claims 1 to 9.