Topological structure of broadband band-pass filter and filter
The topological structure of a broadband bandpass filter addresses the issues of poor selectivity and large size by employing a symmetrical arrangement of microstrip lines and branches, achieving high selectivity and miniaturization for enhanced performance in wireless communication systems.
Patent Information
- Application Number
- CN202420563792.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-03-21
- Publication Date
- 2024-12-20
- Estimated Expiration
- 2034-03-21
AI Technical Summary
Current broadband bandpass filters with dual notch characteristics suffer from poor selectivity and large size, limiting their use in modern wireless communication systems.
A topological structure for a broadband bandpass filter is designed, featuring a specific arrangement of microstrip lines and open-circuit branches with symmetrical connections and impedance settings, including parallel and perpendicular configurations, to enhance selectivity and miniaturization.
The filter achieves high selectivity and miniaturization, with five transmission poles in the passband for flatness, two transmission zeros in the stopband for high selectivity, and two transmission zeros in the passband for notches, ensuring improved performance in modern wireless communication systems.
Smart Images
Figure CN222214435U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of filters, in particular to a topological structure of a broadband bandpass filter and a filter. Background Art
[0002] With the rapid development of modern 5G communication technology, broadband bandpass filters, as one of the key components of wireless communication systems, have attracted more and more attention from scholars and engineers. In this context, filters that can suppress in-band interference and transmit signals at high speed, that is, broadband bandpass filters with notch characteristics, have been developed in large quantities.
[0003] However, most of the current broadband bandpass filters with dual notch characteristics have the defects of poor selectivity and large size, which greatly limits their use in modern wireless communication systems. Utility Model Content
[0004] The main purpose of the utility model is to provide a topological structure of a broadband bandpass filter, aiming to solve the problems of poor selectivity and large size of the existing broadband bandpass filter with double notch characteristics.
[0005] To achieve the above-mentioned purpose, the utility model proposes a topological structure of a broadband bandpass filter, including a fifth microstrip line, one end of the fifth microstrip line is symmetrically connected to one end of a first parallel line and one end of a second parallel line, the other end of the first parallel line is respectively connected to one end of the first microstrip line, an input end, and a third open-circuit branch, the other end of the second parallel line is respectively connected to one end of the third microstrip line, an output end, and a fourth open-circuit branch, the other end of the first microstrip line is connected to one end of the second microstrip line, the other end of the second microstrip line is connected to the first open-circuit branch, the other end of the third microstrip line is connected to one end of the fourth microstrip line, the other end of the fourth microstrip line is connected to the second open-circuit branch, the other end of the fifth microstrip line is symmetrically connected to a sixth microstrip line and an eighth microstrip line, the other end of the sixth microstrip line is connected to one end of the seventh microstrip line, the other end of the seventh microstrip line is connected to the fifth open-circuit branch, the other end of the eighth microstrip line is connected to one end of the ninth microstrip line, and the other end of the ninth microstrip line is connected to the sixth open-circuit branch;
[0006] The first parallel line, the second parallel line, the first microstrip line, the third microstrip line, the sixth microstrip line, the eighth microstrip line, the first open branch, the second open branch, the third open branch, the fourth open branch, the fifth open branch, and the sixth open branch are parallel to each other and are perpendicular to the second microstrip line, the fourth microstrip line, the fifth microstrip line, the seventh microstrip line, and the ninth microstrip line.
[0007] Optionally, the electrical length of the first parallel line and the electrical length of the second parallel line are both a quarter wavelength corresponding to the center frequency of the bandpass filter.
[0008] Optionally, the sum of the electrical length of the fifth microstrip line, the electrical length of the sixth microstrip line, the electrical length of the seventh microstrip line, and the electrical length of the fifth open-circuit branch is half the wavelength corresponding to the center frequency of the bandpass filter;
[0009] The sum of the electrical length of the fifth microstrip line, the electrical length of the eighth microstrip line, the electrical length of the ninth microstrip line, and the electrical length of the sixth open-circuit branch is half the wavelength corresponding to the center frequency of the bandpass filter.
[0010] Optionally, the sum of the electrical length of the first microstrip line, the electrical length of the second microstrip line, and the electrical length of the first open branch is equal to the sum of the electrical length of the third microstrip line, the electrical length of the fourth microstrip line, and the electrical length of the second open branch, and are all one-quarter wavelength corresponding to the first notch center frequency of the bandpass filter, and are greater than one-quarter wavelength corresponding to the center frequency of the bandpass filter.
[0011] Optionally, the electrical length of the third open-circuit branch and the electrical length of the fourth open-circuit branch are both equal to a quarter wavelength corresponding to the second notch center frequency of the bandpass filter, and are both smaller than a quarter wavelength corresponding to the center frequency of the bandpass filter.
[0012] Optionally, the odd-mode characteristic impedance of the first parallel line is equal to the odd-mode characteristic impedance of the second parallel line, and the even-mode characteristic impedance of the first parallel line is equal to the even-mode characteristic impedance of the second parallel line;
[0013] The first parallel lines and the second parallel lines each include two mutually parallel transmission lines.
[0014] Optionally, the characteristic impedance of the first microstrip line, the characteristic impedance of the second microstrip line, the characteristic impedance of the third microstrip line, the characteristic impedance of the fourth microstrip line, the characteristic impedance of the first open-circuit branch, the characteristic impedance of the second open-circuit branch, the characteristic impedance of the third open-circuit branch, and the characteristic impedance of the fourth open-circuit branch are equal;
[0015] The characteristic impedance of the sixth microstrip line, the characteristic impedance of the seventh microstrip line, the characteristic impedance of the eighth microstrip line, the characteristic impedance of the ninth microstrip line, the characteristic impedance of the fifth open branch, and the characteristic impedance of the sixth open branch are equal and are all twice the characteristic impedance of the fifth microstrip line.
[0016] To achieve the above object, the utility model also proposes a filter, including a filter designed by the topological structure described above.
[0017] Optionally, the filter further includes a circuit board, the circuit board has a dielectric constant of 3.38, a dielectric loss of 0.0022, a thickness of 0.813 mm, and a size of 19.2 mm*6.4 mm.
[0018] Optionally, the length of the first parallel line and the length of the second parallel line are both set to l P =7.6mm, the length of the third open branch node and the length of the fourth open branch node are both set to l1=6.4mm, the length of the second microstrip line and the length of the fourth microstrip line are both set to l2=1.0mm, the length of the first open branch node and the length of the second open branch node are both set to l3=2.1mm, the length of the fifth microstrip line is set to l4=2.6mm, the length of the sixth microstrip line and the length of the eighth microstrip line are both set to l5=6.2mm, the length of the seventh microstrip line and the length of the ninth microstrip line are both set to l6=2.0mm, the length of the fifth open branch node and the length of the sixth open branch node are both set to l7=6.0mm, and the spacing between the transmission lines is set to s P =0.1mm, the spacing between the first parallel line and the first microstrip line, the spacing between the first parallel line and the third open branch, the spacing between the second parallel line and the third microstrip line, and the spacing between the second parallel line and the fourth open branch are all s1=0.35mm, and the line width of the transmission line is set to w P =0.1mm, the line width of the first microstrip line, the line width of the second microstrip line, the line width of the third microstrip line, the line width of the fourth microstrip line, the line width of the first open branch node, the line width of the second open branch node, the line width of the third open branch node, and the line width of the fourth open branch node are all set to w1=0.1mm, the line width of the fifth microstrip line is set to w2=0.4mm, the line width of the sixth microstrip line, the line width of the seventh microstrip line, the line width of the eighth microstrip line, the line width of the ninth microstrip line, the line width of the fifth open branch node, and the line width of the sixth open branch node are all set to w3=0.2mm.
[0019] Compared with the prior art, the utility model has the following beneficial effects: the topological structure of the prior filter is improved, including a fifth microstrip line, one end of the fifth microstrip line is symmetrically connected to one end of the first parallel line and one end of the second parallel line, the other end of the first parallel line is respectively connected to one end of the first microstrip line, the input end, and the third open-circuit branch node, the other end of the second parallel line is respectively connected to one end of the third microstrip line, the output end, and the fourth open-circuit branch node, the other end of the first microstrip line is connected to one end of the second microstrip line, the other end of the second microstrip line is connected to the first open-circuit branch node, the other end of the third microstrip line is connected to one end of the fourth microstrip line, the other end of the fourth microstrip line is connected to the second open-circuit branch node, the other end of the fifth microstrip line is symmetrically connected to the sixth microstrip line and the eighth microstrip line, the other end of the sixth microstrip line is connected to one end of the seventh microstrip line, the other end of the seventh microstrip line is connected to the fifth open-circuit branch node, the other end of the eighth microstrip line is connected to one end of the ninth microstrip line, and the other end of the ninth microstrip line is connected to the sixth open-circuit branch node. The filter with double notch characteristics designed based on the topological structure of the utility model has the advantages of high selectivity and miniaturization. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.
[0021] Figure 1 This is a schematic diagram of the topological structure of the filter of the utility model;
[0022] Figure 2 It is an odd-mode diagram of the simplified topological structure of the utility model;
[0023] Figure 3 It is an even-mode diagram of the simplified topological structure of the utility model;
[0024] Figure 4 This is one of the layout diagrams of the filter of the utility model;
[0025] Figure 5 This is the second layout diagram of the filter of the utility model;
[0026] Figure 6 This is a diagram of the S parameter simulation results of the filter of the utility model.
[0027] Description of Figure Numbers:
[0028] 10. Input terminal; 20. First microstrip line; 21. Second microstrip line; 22. Third microstrip line; 23. Fourth microstrip line; 24. Fifth microstrip line; 25. Sixth microstrip line; 26. Seventh microstrip line; 27. Eighth microstrip line; 28. Ninth microstrip line; 30. First open branch; 31. Second open branch; 32. Third open branch; 33. Fourth open branch; 34. Fifth open branch; 35. Sixth open branch; 40. First parallel line; 41. Second parallel line; 50. Output terminal; 401. First left transmission line; 402. Second left transmission line; 411. First right transmission line; 412. Second right transmission line.
[0029] The realization of the purpose, functional features and advantages of the utility model will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION
[0030] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.
[0031] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back...), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.
[0032] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the utility model, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if the meaning of "and / or" appearing in the full text is to include three parallel schemes, taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the utility model.
[0033] An embodiment of the present invention provides a topological structure of a broadband bandpass filter. Figures 1 to 6, including a fifth microstrip line 24, one end of the fifth microstrip line 24 is symmetrically connected to one end of the first parallel line 40 and one end of the second parallel line 41, the other end of the first parallel line 40 is respectively connected to one end of the first microstrip line 20, the input end 10, and the third open branch 32, the other end of the second parallel line 41 is respectively connected to one end of the third microstrip line 22, the output end 50, and the fourth open branch 33, the other end of the first microstrip line 20 is connected to one end of the second microstrip line 21, and the other end of the second microstrip line 21 is connected to the first open branch 30, The other end of the third microstrip line 22 is connected to one end of the fourth microstrip line 23, the other end of the fourth microstrip line 23 is connected to the second open branch 31, the other end of the fifth microstrip line 24 is symmetrically connected to the sixth microstrip line 25 and the eighth microstrip line 27, the other end of the sixth microstrip line 25 is connected to one end of the seventh microstrip line 26, the other end of the seventh microstrip line 26 is connected to the fifth open branch 34, the other end of the eighth microstrip line 27 is connected to one end of the ninth microstrip line 28, and the other end of the ninth microstrip line 28 is connected to the sixth open branch 35;
[0034] The first parallel line 40, the second parallel line 41, the first microstrip line 20, the third microstrip line 22, the sixth microstrip line 25, the eighth microstrip line 27, the first open branch 30, the second open branch 31, the third open branch 32, the fourth open branch 33, the fifth open branch 34, and the sixth open branch 35 are parallel to each other and are perpendicular to the second microstrip line 21, the fourth microstrip line 23, the fifth microstrip line 24, the seventh microstrip line 26, and the ninth microstrip line 28.
[0035] In this embodiment, the topological structure adopts a symmetrical structure setting, and the first parallel line 40 and the second parallel line 41, the first microstrip line 20 and the third microstrip line 22, the second microstrip line 21 and the fourth microstrip line 23, the sixth microstrip line 25 and the eighth microstrip line 27, the seventh microstrip line 26 and the ninth microstrip line 28, the first open branch 30 and the second open branch 31, the third open branch 32 and the fourth open branch 33, the fifth open branch 34 and the sixth open branch 35 are all arranged symmetrically about the fifth microstrip line 24.
[0036] Furthermore, the electrical length of the first parallel line 40 and the electrical length of the second parallel line 41 are both a quarter wavelength corresponding to the center frequency of the bandpass filter.
[0037] Further, the sum of the electrical length of the fifth microstrip line 24, the electrical length of the sixth microstrip line 25, the electrical length of the seventh microstrip line 26, and the electrical length of the fifth open-circuit branch 34 is half the wavelength corresponding to the center frequency of the bandpass filter;
[0038] The sum of the electrical lengths of the fifth microstrip line 24 , the eighth microstrip line 27 , the ninth microstrip line 28 , and the sixth open-circuit branch 35 is half the wavelength corresponding to the center frequency of the bandpass filter.
[0039] Furthermore, the sum of the electrical lengths of the first microstrip line 20, the second microstrip line 21, and the first open branch 30 is equal to the sum of the electrical lengths of the third microstrip line 22, the fourth microstrip line 23, and the second open branch 31, and are all one-quarter wavelength corresponding to the first notch center frequency of the bandpass filter, and are greater than one-quarter wavelength corresponding to the center frequency of the bandpass filter.
[0040] Furthermore, the electrical length of the third open branch 32 and the electrical length of the fourth open branch 33 are both equal to a quarter wavelength corresponding to the second notch center frequency of the bandpass filter, and are both smaller than a quarter wavelength corresponding to the center frequency of the bandpass filter.
[0041] Further, the odd-mode characteristic impedance of the first parallel line 40 is equal to the odd-mode characteristic impedance of the second parallel line 41, and the even-mode characteristic impedance of the first parallel line 40 is equal to the even-mode characteristic impedance of the second parallel line 41; the first parallel line 40 and the second parallel line 41 each include two mutually parallel transmission lines. Specifically, the first parallel line 40 includes a first left transmission line 401 and a second left transmission line 402, and the second parallel line 41 includes a first right transmission line 411 and a second right transmission line 412.
[0042] Furthermore, the characteristic impedance of the first microstrip line 20, the characteristic impedance of the second microstrip line 21, the characteristic impedance of the third microstrip line 22, the characteristic impedance of the fourth microstrip line 23, the characteristic impedance of the first open branch 30, the characteristic impedance of the second open branch 31, the characteristic impedance of the third open branch 32, and the characteristic impedance of the fourth open branch 33 are equal; the characteristic impedance of the sixth microstrip line 25, the characteristic impedance of the seventh microstrip line 26, the characteristic impedance of the eighth microstrip line 27, the characteristic impedance of the ninth microstrip line 28, the characteristic impedance of the fifth open branch 34, and the characteristic impedance of the sixth open branch 35 are equal and are all twice the characteristic impedance of the fifth microstrip line 24.
[0043] In this embodiment, the odd-mode characteristic impedance of the first parallel line 40 and the odd-mode characteristic impedance of the second parallel line 41 are both set to Z oo , the even-mode characteristic impedance of the first parallel line 40 and the even-mode characteristic impedance of the second parallel line 41 are both set to Z oe , the characteristic impedance of the first microstrip line 20, the characteristic impedance of the second microstrip line 21, the characteristic impedance of the third microstrip line 22, the characteristic impedance of the fourth microstrip line 23, the characteristic impedance of the first open branch 30, the characteristic impedance of the second open branch 31, the characteristic impedance of the third open branch 32, and the characteristic impedance of the fourth open branch 33 are all set to Z1, the characteristic impedance of the fifth microstrip line 24 is set to Z2, the characteristic impedance of the sixth microstrip line 25, the characteristic impedance of the seventh microstrip line 26, the characteristic impedance of the eighth microstrip line 27, the characteristic impedance of the ninth microstrip line 28, the characteristic impedance of the fifth open branch 34, and the characteristic impedance of the sixth open branch 35 are all set to 2Z2.
[0044] The topological structure is a bilaterally symmetrical structure, and its transmission poles can be obtained by odd-even mode analysis. To simplify the analysis, it is first assumed that the electrical length of the first microstrip line 20, the electrical length of the third microstrip line 22, the electrical length of the third open-circuit branch 32, and the electrical length of the fourth microstrip line 23 are all equal to a quarter wavelength corresponding to the center frequency of the bandpass filter, and the electrical length of the second microstrip line 21, the electrical length of the fourth microstrip line 23, the electrical length of the first open-circuit branch 30, and the electrical length of the second microstrip line 21 are all zero. Figure 2 is the odd-mode form of the simplified topological structure. ino = 0, it can be concluded that the topology has two transmission poles. When f0 is the center frequency of the bandpass filter, the frequencies corresponding to the two odd-mode transmission poles are:
[0045]
[0046]
[0047] Figure 3 Here, the first parallel line 40 is connected to the sixth microstrip line 25 through the tenth microstrip line shown in the figure, the electrical length of the tenth microstrip line is equal to the electrical length of the fifth microstrip line 24, and the characteristic impedance of the tenth microstrip line is twice the characteristic impedance of the fifth microstrip line 24. ine = 0, it can be concluded that the topology has three even-mode transmission poles. When f0 is the center frequency of the bandpass filter, the frequencies corresponding to the three even-mode transmission poles are:
[0048]
[0049] f ep2 =f0
[0050]
[0051] in,
[0052] α=Z2(Z oe +Z oo )+(Z oe -Z oo ) 2 +Z1Z2
[0053] β=Z2(Z oe +Z oo +2)+4Z oe Z oo +Z1(Z oe +Z oo )
[0054] For this topology, its transmission zero can be calculated by the following method: multiply the ABCD matrix of the cascade resonators that make up the topology in sequence to obtain the ABCD matrix corresponding to the topology; convert the ABCD matrix of the topology into the corresponding S matrix. When |S21| = 0, it can be concluded that this topology has three transmission zeros, and the frequencies corresponding to the three transmission zeros are:
[0055]
[0056] f z2 =f0
[0057]
[0058] The filter based on this topology has two odd-mode transmission poles, three even-mode transmission poles, and three transmission zeros. oo , Z oe , the values of Z1 and Z2, and the relative positions of the transmission zeros and poles, i.e., f z1 <f ep1 <f op1 <f ep2 =f0=f2 <f op2 <f ep3 <f z3 , nothing will change.
[0059] Returning to the topological structure proposed by the present invention, the sum of the electrical length of the first microstrip line 20, the electrical length of the second microstrip line 21, and the electrical length of the first open branch 30 is equal to the sum of the electrical length of the third microstrip line 22, the electrical length of the fourth microstrip line 23, and the electrical length of the second open branch 31, and both are greater than the electrical length of the third open branch 32 and the electrical length of the fourth open branch 33. It can be seen from the basic microwave theory that the transmission zero f2 of the filter designed based on this topological structure will be split into two transmission zeros f z2L and f z2U , while the number of other zero poles remains unchanged. And the center frequency of the first notch is f z2L The relationship between the electrical length θ1 of the first microstrip line 20, the electrical length θ2 of the second microstrip line 21, and the electrical length θ3 of the first open branch 30 can be expressed as:
[0060]
[0061] Where λ is the wavelength of the bandpass filter.
[0062] The center frequency of the second notch is f z2U The relationship between the electrical length θ4 of the second open-circuit branch 31 can be expressed as:
[0063]
[0064] In addition, when the sum of the electrical length of the first microstrip line 20, the electrical length of the second microstrip line 21, and the electrical length of the first open branch 30 and the sum of the electrical length of the third microstrip line 22, the electrical length of the fourth microstrip line 23, and the electrical length of the second open branch 31 are all appropriately greater than a quarter wavelength corresponding to the center frequency of the bandpass filter, and the electrical length of the third open branch 32 and the electrical length of the fourth open branch 33 are both appropriately less than a quarter wavelength corresponding to the center frequency of the bandpass filter, no matter how the parameter Z is changed oo , Z oe , the values of Z1 and Z2, and the relative positions of the transmission zeros and poles, i.e., f z1 <f ep1 <f op1 <f z2L <f ep2 <f z2U <f op2 <f ep3 <f z3 , will not change. Therefore, based on this topology, a broadband bandpass filter with double notch characteristics can be designed, and there are five transmission poles in the passband to ensure flatness, two transmission zeros in the stopband to ensure high selectivity, and two transmission zeros in the passband to form the required notch.
[0065] Another embodiment of the utility model also provides a filter, including a filter designed by the topological structure described above. The filter also includes a circuit board, the circuit board has a dielectric constant of 3.38, a dielectric loss of 0.0022, a thickness of 0.813 mm, and a size of 19.2 mm*6.4 mm.
[0066] Optionally, the length of the first parallel line 40 and the length of the second parallel line 41 are both set to l P =7.6mm, the length of the third open branch 32 and the length of the fourth open branch 33 are both set to l1=6.4mm, the length of the second microstrip line 21 and the length of the fourth microstrip line 23 are both set to l2=1.0mm, the length of the first open branch 30 and the length of the second open branch 31 are both set to l3=2.1mm, the length of the fifth microstrip line 24 is set to l4=2.6mm, the length of the sixth microstrip line 25 and the length of the eighth microstrip line 27 are both set to l5=6.2mm, the length of the seventh microstrip line 26 and the length of the ninth microstrip line 28 are both set to l6=2.0mm, the length of the fifth open branch 34 and the length of the sixth open branch 35 are both set to l7=6.0mm, the spacing between the first left transmission line 401 and the second left transmission line 401, and the spacing between the first right transmission line 411 and the second right transmission line 412 are both set to s P =0.1mm, the spacing between the first parallel line 40 and the first microstrip line 20, the spacing between the first parallel line 40 and the third open branch 32, the spacing between the second parallel line 41 and the third microstrip line 22, and the spacing between the second parallel line 41 and the fourth open branch 33 are all s1=0.35mm, the line width of the first left transmission line 401, the line width of the second left transmission line 402, the line width of the first right transmission line 411, and the line width of the second right transmission line 412 are all set to w P =0.1mm, the line width of the first microstrip line 20, the line width of the second microstrip line 21, the line width of the third microstrip line 22, the line width of the fourth microstrip line 23, the line width of the first open branch node 30, the line width of the second open branch node 31, the line width of the third open branch node 32, and the line width of the fourth open branch node 33 are all set to w1=0.1mm, the line width of the fifth microstrip line 34 is set to w2=0.4mm, the line width of the sixth microstrip line 25, the line width of the seventh microstrip line 26, the line width of the eighth microstrip line 27, the line width of the ninth microstrip line 28, the line width of the fifth open branch node 34, and the line width of the sixth open branch node 35 are all set to w3=0.2mm.
[0067] The S parameter simulation results of the bandpass filter corresponding to the optimized size are as follows: Figure 6 As shown. Figure 6 It can be seen that the impedance bandwidth with a reflection coefficient less than -10dB ranges from 3.967GHz to 8.513GHz, the passband center frequency is 6.24GHz, the absolute bandwidth of the passband is 4.546GHz, and the relative bandwidth of the passband is 72.9%. In addition, there are five transmission poles in the passband, located at 4.101GHz, 4.452GHz, 6.875GHz, 7.975GHz, and 8.448GHz, respectively. These five transmission poles ensure the flatness of the passband of the bandpass filter; there are two transmission zeros in the passband to form a notch, with center frequencies of 5.775GHz and 7.481GHz, respectively, and the isolation at the center frequency is 45.8dB and 56.8dB, respectively, with good isolation; there are two transmission zeros in the stopband, located at 3.275GHz and 8.849GHz, respectively, and these two transmission poles can ensure the high selectivity of the filter.
[0068] It can be seen from the above that the filter with double notch characteristics designed in the topological structure of this embodiment has the advantages of high selectivity and miniaturization.
[0069] The above description is only an optional embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.
Claims
1. A topological structure of a broadband bandpass filter, characterized in that: The invention comprises a fifth microstrip line, wherein one end of the fifth microstrip line is symmetrically connected to one end of the first parallel line and one end of the second parallel line, the other end of the first parallel line is respectively connected to one end of the first microstrip line, an input end, and a third open branch, the other end of the second parallel line is respectively connected to one end of the third microstrip line, an output end, and a fourth open branch, the other end of the first microstrip line is connected to one end of the second microstrip line, the other end of the second microstrip line is connected to the first open branch, the other end of the third microstrip line is connected to one end of the fourth microstrip line, the other end of the fourth microstrip line is connected to the second open branch, the other end of the fifth microstrip line is symmetrically connected to the sixth microstrip line and the eighth microstrip line, the other end of the sixth microstrip line is connected to one end of the seventh microstrip line, the other end of the seventh microstrip line is connected to the fifth open branch, the other end of the eighth microstrip line is connected to one end of the ninth microstrip line, and the other end of the ninth microstrip line is connected to the sixth open branch; The first parallel line, the second parallel line, the first microstrip line, the third microstrip line, the sixth microstrip line, the eighth microstrip line, the first open branch, the second open branch, the third open branch, the fourth open branch, the fifth open branch, and the sixth open branch are parallel to each other and perpendicular to the second microstrip line, the fourth microstrip line, the fifth microstrip line, the seventh microstrip line, and the ninth microstrip line; The first parallel lines and the second parallel lines each include two mutually parallel transmission lines.
2. The topological structure of the broadband bandpass filter according to claim 1, characterized in that: The electrical length of the first parallel line and the electrical length of the second parallel line are both one-quarter wavelength corresponding to the center frequency of the bandpass filter.
3. The topological structure of the broadband bandpass filter according to claim 1, characterized in that: The sum of the electrical length of the fifth microstrip line, the electrical length of the sixth microstrip line, the electrical length of the seventh microstrip line, and the electrical length of the fifth open-circuit branch is half the wavelength corresponding to the center frequency of the bandpass filter; The sum of the electrical length of the fifth microstrip line, the electrical length of the eighth microstrip line, the electrical length of the ninth microstrip line, and the electrical length of the sixth open-circuit branch is half the wavelength corresponding to the center frequency of the bandpass filter.
4. The topological structure of the broadband bandpass filter according to claim 1, characterized in that: The sum of the electrical length of the first microstrip line, the electrical length of the second microstrip line, and the electrical length of the first open branch is equal to the sum of the electrical length of the third microstrip line, the electrical length of the fourth microstrip line, and the electrical length of the second open branch, and are all one-quarter wavelength corresponding to the first notch center frequency of the bandpass filter, and are greater than one-quarter wavelength corresponding to the center frequency of the bandpass filter.
5. The topological structure of the broadband bandpass filter according to claim 1, characterized in that: The electrical length of the third open-circuit branch and the electrical length of the fourth open-circuit branch are both equal to a quarter wavelength corresponding to the second notch center frequency of the bandpass filter, and are both smaller than a quarter wavelength corresponding to the center frequency of the bandpass filter.
6. The topology structure of the broadband bandpass filter according to claim 1, characterized in that: The odd-mode characteristic impedance of the first parallel line is equal to the odd-mode characteristic impedance of the second parallel line, and the even-mode characteristic impedance of the first parallel line is equal to the even-mode characteristic impedance of the second parallel line.
7. The topological structure of the broadband bandpass filter according to claim 1, characterized in that: The characteristic impedance of the first microstrip line, the characteristic impedance of the second microstrip line, the characteristic impedance of the third microstrip line, the characteristic impedance of the fourth microstrip line, the characteristic impedance of the first open branch, the characteristic impedance of the second open branch, the characteristic impedance of the third open branch, and the characteristic impedance of the fourth open branch are equal; The characteristic impedance of the sixth microstrip line, the characteristic impedance of the seventh microstrip line, the characteristic impedance of the eighth microstrip line, the characteristic impedance of the ninth microstrip line, the characteristic impedance of the fifth open branch, and the characteristic impedance of the sixth open branch are equal and are all twice the characteristic impedance of the fifth microstrip line.
8. A filter, characterized in that: A filter comprising a topology structure designed according to any one of claims 1 to 7.
9. The filter according to claim 8, characterized in that The filter also includes a circuit board, the dielectric constant of the circuit board is 3.38, the dielectric loss is 0.0022, the thickness is 0.813 mm, and the size is 19.2 mm*6.4 mm.
10. The filter according to claim 8, characterized in that The length of the first parallel line and the length of the second parallel line are both set to l P =7.6mm, the length of the third open branch node and the length of the fourth open branch node are both set to l1=6.4mm, the length of the second microstrip line and the length of the fourth microstrip line are both set to l2=1.0mm, the length of the first open branch node and the length of the second open branch node are both set to l3=2.1mm, the length of the fifth microstrip line is set to l4=2.6mm, the length of the sixth microstrip line and the length of the eighth microstrip line are both set to l5=6.2mm, the length of the seventh microstrip line and the length of the ninth microstrip line are both set to l6=2.0mm, the length of the fifth open branch node and the length of the sixth open branch node are both set to l7=6.0mm, and the spacing between the transmission lines is set to s P =0.1mm, the spacing between the first parallel line and the first microstrip line, the spacing between the first parallel line and the third open branch, the spacing between the second parallel line and the third microstrip line, and the spacing between the second parallel line and the fourth open branch are all s1=0.35mm, and the line width of the transmission line is set to w P =0.1mm, the line width of the first microstrip line, the line width of the second microstrip line, the line width of the third microstrip line, the line width of the fourth microstrip line, the line width of the first open branch node, the line width of the second open branch node, the line width of the third open branch node, and the line width of the fourth open branch node are all set to w1=0.1mm, the line width of the fifth microstrip line is set to w2=0.4mm, the line width of the sixth microstrip line, the line width of the seventh microstrip line, the line width of the eighth microstrip line, the line width of the ninth microstrip line, the line width of the fifth open branch node, and the line width of the sixth open branch node are all set to w3=0.2mm.