Topological structure of high-performance low-pass filter and filter

Abstract

The high-performance low-pass filter topological structure comprises a second microstrip line and a seventh microstrip line which are connected in sequence, the second microstrip line is connected with an input end, and the seventh microstrip line is connected with an output end; a first microstrip line and a third microstrip line are symmetrically connected between the second microstrip line and the input end, the first microstrip line is connected with a first open-circuit branch knot, and the third microstrip line is connected with a second open-circuit branch knot; a fourth microstrip line and a fifth microstrip line are symmetrically connected between the second microstrip line and the seventh microstrip line, the fourth microstrip line is symmetrically connected with a third open-circuit branch knot and a fourth open-circuit branch knot, and the fifth microstrip line is symmetrically connected with a fifth open-circuit branch knot and a sixth open-circuit branch knot; a sixth microstrip line and an eighth microstrip line are symmetrically connected between the seventh microstrip line and the output end, the sixth microstrip line is connected with a seventh open-circuit branch knot, and the eighth microstrip line is connected with an eighth open-circuit branch knot; according to the low-pass filter, the defects of poor selectivity, narrow stop band and complex design process of a low-pass filter design scheme are overcome.

Description

Technical Field

[0001] The utility model relates to the technical field of filters, in particular to a high-performance low-pass filter topology structure and a filter. Background Art

[0002] With the advent of the fifth-generation wireless communication era, the requirements for adjacent-channel and out-of-band spurious suppression in radio frequency communication links are increasing day by day. Therefore, designing a high-performance microstrip low-pass filter with steep sidebands and a wide stopband is crucial for improving the performance of communication systems.

[0003] Existing microstrip low-pass filter design schemes mainly include defective schemes, stepped-impedance resonator schemes, stub-loaded resonator schemes, fan-shaped resonator schemes, etc. However, the low-pass filters designed based on the above schemes often have defects such as poor selectivity, narrow stopbands, and complex design processes, which will greatly limit their use in modern wireless communication systems. Summary of the Utility Model

[0004] The main purpose of the utility model is to provide a high-performance low-pass filter topology structure and a filter, aiming to solve the defects of poor selectivity, narrow stopbands, and complex design processes existing in existing low-pass filter design schemes.

[0005] To achieve the above object, the utility model proposes a high-performance low-pass filter topology structure, including a second microstrip line and a seventh microstrip line connected in sequence along a first direction. The other end of the second microstrip line is connected to an input end, and the other end of the seventh microstrip line is connected to an output end;

[0006] A first microstrip line and a third microstrip line are symmetrically connected between the second microstrip line and the input end. The other end of the first microstrip line is connected to a first open stub, and the other end of the third microstrip line is connected to a second open stub;

[0007] A fourth microstrip line and a fifth microstrip line are symmetrically connected between the second microstrip line and the seventh microstrip line. The other end of the fourth microstrip line is symmetrically connected to a third open stub and a fourth open stub, and the other end of the fifth microstrip line is symmetrically connected to a fifth open stub and a sixth open stub;

[0008] A sixth microstrip line and an eighth microstrip line are symmetrically connected between the seventh microstrip line and the output end. The other end of the sixth microstrip line is connected to a seventh open stub, and the other end of the eighth microstrip line is connected to an eighth open stub;

[0009] The first microstrip line, the third microstrip line, the sixth microstrip line, the eighth microstrip line, the third open stub, the fourth open stub, the fifth open stub, and the sixth open stub are all arranged along a first direction. The fourth microstrip line, the fifth microstrip line, the first open stub, the second open stub, the seventh open stub, and the eighth open stub are all arranged along a second direction. The first direction is perpendicular to the second direction.

[0010] Optionally, the first microstrip line and the sixth microstrip line, the second microstrip line and the seventh microstrip line, the third microstrip line and the eighth microstrip line, the first open stub and the seventh open stub, the second open stub and the eighth open stub, and the fifth open stub and the sixth open stub are symmetrically arranged with respect to the second direction;

[0011] The first microstrip line and the third microstrip line, the fourth microstrip line and the fifth microstrip line, the sixth microstrip line and the eighth microstrip line, the first open stub and the second open stub, the seventh open stub and the eighth open stub, the third open stub and the fifth open stub, and the fourth open stub and the sixth open stub are symmetrically arranged with respect to the first direction.

[0012] Optionally, the electrical lengths of the fourth microstrip line, the fifth microstrip line, the third open stub, the fourth open stub, the fifth open stub, and the sixth open stub are equal, and each is a quarter wavelength corresponding to the center frequency of the stopband of the filter.

[0013] Optionally, the sum of the electrical length of the first microstrip line and the electrical length of the first open stub, the sum of the electrical length of the third microstrip line and the electrical length of the second open stub, the sum of the electrical length of the sixth microstrip line and the electrical length of the seventh open stub, and the sum of the electrical length of the eighth microstrip line and the electrical length of the eighth open stub are equal, and each is a quarter wavelength corresponding to the center frequency of the stopband of the filter.

[0014] Optionally, the characteristic impedances of the first microstrip line, the third microstrip line, the sixth microstrip line, the eighth microstrip line, the first open stub, the second open stub, the seventh open stub, and the eighth open stub are equal.

[0015] Optionally, the characteristic impedances of the second microstrip line and the seventh microstrip line are equal.

[0016] Optionally, the characteristic impedances of the fourth microstrip line and the fifth microstrip line are equal.

[0017] Optionally, the characteristic impedances of the third open stub, the fourth open stub, the fifth open stub, and the sixth open stub are equal.

[0018] To achieve the above object, the present utility model further provides a filter, which includes any one of the above-mentioned topological structures.

[0019] Optionally, the filter further 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 22 mm * 19.8 mm;

[0020] The line lengths of the first microstrip line, the third microstrip line, the sixth microstrip line and the eighth microstrip line are all set to l 1H = 7.4 mm, and the line widths are all set to w1 = 0.5 mm;

[0021] The line lengths of the first open stub, the second open stub, the seventh open stub and the eighth open stub are all set to l 1V = 1.65 mm, and the line widths are all set to w1 = 0.5 mm;

[0022] The line lengths of the second microstrip line and the seventh microstrip line are both set to l2 = 8.9 mm, and the line widths are all set to w2 = 0.1 mm; the distances between the second microstrip line and the first microstrip line and the third microstrip line, and the distances between the seventh microstrip line and the sixth microstrip line and the eighth microstrip line are all set to s1 = 0.4 mm;

[0023] The line lengths of the fourth microstrip line and the fifth microstrip line are both set to l3 = 9.35 mm, and the line widths are all set to w3 = 0.6 mm;

[0024] The line lengths of the third open stub, the fourth open stub, the fifth open stub and the sixth open stub are all set to l4 = 9 mm, and the line widths are all set to w4 = 0.4 mm.

[0025] The beneficial effects of the present utility model are as follows: It improves the topological structure of the existing low-pass filter. The topological structure includes a second microstrip line and a seventh microstrip line connected in sequence. The second microstrip line is connected to an input end, and the seventh microstrip line is connected to an output end; a first microstrip line and a third microstrip line are symmetrically connected between the second microstrip line and the input end. The first microstrip line is connected to a first open stub, and the third microstrip line is connected to a second open stub; a fourth microstrip line and a fifth microstrip line are symmetrically connected between the second microstrip line and the seventh microstrip line. The fourth microstrip line is symmetrically connected to a third open stub and a fourth open stub, and the fifth microstrip line is symmetrically connected to a fifth open stub and a sixth open stub; a sixth microstrip line and an eighth microstrip line are symmetrically connected between the seventh microstrip line and the output end. The sixth microstrip line is connected to a seventh open stub, and the eighth microstrip line is connected to an eighth open stub;

[0026] The filter based on this topology has two odd-mode transmission poles, one even-mode transmission pole, and three transmission zeros. Moreover, no matter how the characteristic impedance values of its respective branches are changed, the relative positions of the transmission poles and zeros will not change. Therefore, a low-pass filter can be designed based on this topology, with two transmission poles in the passband to ensure flatness, and three transmission zeros in the stopband to ensure wide and high selectivity, a wide stopband, and high isolation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0028] Figure 1 Schematic diagram of the topology structure of the filter of the present invention;

[0029] Figure 2 Odd-mode form diagram of the topology structure of the present invention;

[0030] Figure 3 Even-mode form diagram of the topology structure of the present invention;

[0031] Figure 4 Layout layout of the filter of the present invention;

[0032] Figure 5 S-parameter simulation result diagram of the filter of the present invention;

[0033] The realization, functional features, and advantages of the object of the present invention will be further described in conjunction with the embodiments with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] It should be noted that if there are directional indications (such as up, down, left, right, front, back...) involved in the embodiments of the present invention, the directional indications are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly.

[0036] In addition, if the embodiments of the present utility model involve descriptions such as "first", "second", etc., the descriptions of "first", "second", etc. are only for descriptive purposes and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the meaning of "and / or" appearing throughout the text is that it includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, or solution B, or the solution where A and B are satisfied simultaneously. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present utility model.

[0037] An embodiment of the present utility model provides a high-performance low-pass filter topology structure. Refer to Figure 1 , which includes a second microstrip line and a seventh microstrip line connected in sequence along a first direction. The other end of the second microstrip line is connected to an input end, and the other end of the seventh microstrip line is connected to an output end;

[0038] A first microstrip line and a third microstrip line are symmetrically connected between the second microstrip line and the input end. The other end of the first microstrip line is connected to a first open stub, and the other end of the third microstrip line is connected to a second open stub;

[0039] A fourth microstrip line and a fifth microstrip line are symmetrically connected between the second microstrip line and the seventh microstrip line. The other end of the fourth microstrip line is symmetrically connected to a third open stub and a fourth open stub, and the other end of the fifth microstrip line is symmetrically connected to a fifth open stub and a sixth open stub;

[0040] A sixth microstrip line and an eighth microstrip line are symmetrically connected between the seventh microstrip line and the output end. The other end of the sixth microstrip line is connected to a seventh open stub, and the other end of the eighth microstrip line is connected to an eighth open stub;

[0041] The first microstrip line, the third microstrip line, the sixth microstrip line, the eighth microstrip line, the third open stub, the fourth open stub, the fifth open stub, and the sixth open stub are all arranged along the first direction. The fourth microstrip line, the fifth microstrip line, the first open stub, the second open stub, the seventh open stub, and the eighth open stub are all arranged along a second direction, and the first direction is perpendicular to the second direction.

[0042] This embodiment improves the topological structure of the existing filter, which is composed of eight open stubs and eight microstrip lines. Among them, the first microstrip line and the sixth microstrip line, the second microstrip line and the seventh microstrip line, the third microstrip line and the eighth microstrip line, the first open stub and the seventh open stub, the second open stub and the eighth open stub, the fifth open stub and the sixth open stub are symmetrically arranged with respect to the second direction;

[0043] The first microstrip line and the third microstrip line, the fourth microstrip line and the fifth microstrip line, the sixth microstrip line and the eighth microstrip line, the first open stub and the second open stub, the seventh open stub and the eighth open stub, the third open stub and the fifth open stub, the fourth open stub and the sixth open stub are symmetrically arranged with respect to the first direction.

[0044] Furthermore, the electrical lengths of the fourth microstrip line, the fifth microstrip line, the third open stub, the fourth open stub, the fifth open stub, and the sixth open stub are equal, and each is a quarter wavelength corresponding to the center frequency of the stopband of the filter.

[0045] Furthermore, the sum of the electrical length of the first microstrip line and the electrical length of the first open stub, the sum of the electrical length of the third microstrip line and the electrical length of the second open stub, the sum of the electrical length of the sixth microstrip line and the electrical length of the seventh open stub, the sum of the electrical length of the eighth microstrip line and the electrical length of the eighth open stub are equal, and each is a quarter wavelength corresponding to the center frequency of the stopband of the filter.

[0046] Furthermore, the characteristic impedances of the first microstrip line, the third microstrip line, the sixth microstrip line, the eighth microstrip line, the first open stub, the second open stub, the seventh open stub, and the eighth open stub are equal. In this embodiment, the characteristic impedances of the first microstrip line, the third microstrip line, the sixth microstrip line, the eighth microstrip line, the first open stub, the second open stub, the seventh open stub, and the eighth open stub are denoted as Z1.

[0047] Furthermore, the characteristic impedances of the second microstrip line and the seventh microstrip line are equal. In this embodiment, the characteristic impedances of the second microstrip line and the seventh microstrip line are denoted as Z2.

[0048] Furthermore, the characteristic impedances of the fourth microstrip line and the fifth microstrip line are equal. In this embodiment, the characteristic impedances of the fourth microstrip line and the fifth microstrip line are denoted as Z3.

[0049] Further, the characteristic impedances of the third open stub, the fourth open stub, the fifth open stub, and the sixth open stub are equal. In this embodiment, the characteristic impedances of the third open stub, the fourth open stub, the fifth open stub, and the sixth open stub are denoted as Z4.

[0050] For this topology, its transmission zeros and poles can be analyzed using the even - odd mode method. Specifically, Figure 2 is the odd - mode form diagram of the topology:

[0051] When Y ino = ∞, it can be obtained that this topology has two odd - mode transmission poles, and the corresponding frequencies are respectively:

[0052] f op1 = 0

[0053] f op2 = f0

[0054] Here, f0 is the center frequency of the band - stop filter.

[0055] Figure 3 is the even - mode form diagram of the topology:

[0056] Here, the electrical lengths of the ninth microstrip line and the tenth microstrip line are both one - quarter wavelength corresponding to the center frequency of the stopband; the characteristic impedances of the ninth microstrip line and the tenth microstrip line are both twice the characteristic impedances of the fourth microstrip line and the fifth microstrip line, that is, 2Z3. When Y ine = ∞, it can be obtained that this topology has one even - mode transmission pole, and the corresponding frequency is:

[0057]

[0058] For this topology, its transmission zeros can be calculated by the following method: Multiply the ABCD matrices of the cascaded resonators that make up the topology in sequence to obtain the ABCD matrix corresponding to this topology; convert the ABCD matrix of this topology into the corresponding S matrix. When |S 21 | = 0, it can be obtained that this topology has three transmission zeros, and the frequencies corresponding to the three transmission zeros are respectively:

[0059]

[0060] f z2 = f0

[0061]

[0062] From the above analysis, it can be seen that this topological structure has two odd-mode transmission poles, one even-mode transmission pole, and three transmission zeros. And regardless of how the values of parameters Z1, Z2, Z3, and Z4 change, the relative positions of these transmission zeros and poles, that is, f op1 <f ep1 <f z1 <f op2 = f0 = f z2 <f z3 , will not change. In addition, according to the characteristics of the RF filter, when the positions of the transmission zero and the transmission pole coincide, only the characteristics of the transmission zero are shown. Therefore, the RF filter designed based on this topological structure can only be a low-pass filter, and there are two transmission poles in the passband to ensure flatness, and three transmission zeros in the stopband to ensure wide and high selectivity, wide stopband, and high isolation.

[0063] The present invention also provides a filter, including the topological structure described in any one of the above.

[0064] Further, the filter further 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 22 mm * 19.8 mm;

[0065] Reference Figure 4 , the line lengths of the first microstrip line, the third microstrip line, the sixth microstrip line, and the eighth microstrip line are all set to l 1H = 7.4 mm, and the line widths are all set to w1 = 0.5 mm;

[0066] The line lengths of the first open-circuit stub, the second open-circuit stub, the seventh open-circuit stub, and the eighth open-circuit stub are all set to l 1V = 1.65 mm, and the line widths are all set to w1 = 0.5 mm;

[0067] The line lengths of the second microstrip line and the seventh microstrip line are both set to l2 = 8.9 mm, and the line widths are both set to w2 = 0.1 mm; the distances between the second microstrip line and the first microstrip line and the third microstrip line, and the distances between the seventh microstrip line and the sixth microstrip line and the eighth microstrip line are all set to s1 = 0.4 mm;

[0068] The line lengths of the fourth microstrip line and the fifth microstrip line are both set to l3 = 9.35 mm, and the line widths are both set to w3 = 0.6 mm;

[0069] The line lengths of the third open-circuit stub, the fourth open-circuit stub, the fifth open-circuit stub, and the sixth open-circuit stub are all set to l4 = 9 mm, and the line widths are all set to w4 = 0.4 mm.

[0070] Figure 5This is the S-parameter simulation result diagram of the filter in this embodiment. The impedance bandwidth range where the reflection coefficient of this filter is less than -10 dB is from DC to 1.212 GHz, and the maximum in-band loss is 0.49 dB, having the advantage of low insertion loss; the stopband with isolation greater than 20 dB ranges from 2.062 GHz to 9 GHz, having the advantage of a wide stopband; there are two transmission poles in the passband, located at 0 and 0.899 GHz respectively, to ensure flatness in the band; there are three transmission zeros in the stopband, located at 2.36 GHz, 5.52 GHz, and 8.76 GHz respectively, to ensure high selectivity and high isolation.

[0071] Therefore, the topological structure of this embodiment can be designed as a low-pass filter with reconfigurable bandwidth, having the advantages of high selectivity, wide stopband, low insertion loss, and simple design.

[0072] The above are only optional embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made under the inventive concept of the present invention by using the content of the specification and drawings of the present invention, or any direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A high performance low pass filter topology structure, characterized in that: It includes a second microstrip line and a seventh microstrip line connected in sequence along a first direction, the other end of the second microstrip line is connected to an input end, and the other end of the seventh microstrip line is connected to an output end; A first microstrip line and a third microstrip line are symmetrically connected between the second microstrip line and the input end, the other end of the first microstrip line is connected to a first open branch, and the other end of the third microstrip line is connected to a second open branch; The fourth microstrip line and the fifth microstrip line are symmetrically connected between the second microstrip line and the seventh microstrip line, the other end of the fourth microstrip line is symmetrically connected to the third open branch node and the fourth open branch node, and the other end of the fifth microstrip line is symmetrically connected to the fifth open branch node and the sixth open branch node; The sixth microstrip line and the eighth microstrip line are symmetrically connected between the seventh microstrip line and the output end, the other end of the sixth microstrip line is connected to the seventh open-circuit branch node, and the other end of the eighth microstrip line is connected to the eighth open-circuit branch node; The first microstrip line, the third microstrip line, the sixth microstrip line, the eighth microstrip line, the third open branch node, the fourth open branch node, the fifth open branch node and the sixth open branch node are all arranged along the first direction, and the fourth microstrip line, the fifth microstrip line, the first open branch node, the second open branch node, the seventh open branch node and the eighth open branch node are all arranged along the second direction, and the first direction is perpendicular to the second direction.

2. The high performance low pass filter topology structure according to claim 1, characterized in that: The first microstrip line and the sixth microstrip line, the second microstrip line and the seventh microstrip line, the third microstrip line and the eighth microstrip line, the first open branch and the seventh open branch, the second open branch and the eighth open branch, and the fifth open branch and the sixth open branch are all arranged symmetrically about the second direction; The first microstrip line and the third microstrip line, the fourth microstrip line and the fifth microstrip line, the sixth microstrip line and the eighth microstrip line, the first open branch and the second open branch, the seventh open branch and the eighth open branch, the third open branch and the fifth open branch, and the fourth open branch and the sixth open branch are all arranged symmetrically about the first direction.

3. The high performance low pass filter topology structure according to claim 1, characterized in that: The electrical length of the fourth microstrip line, the electrical length of the fifth microstrip line, the electrical length of the third open branch, the electrical length of the fourth open branch, the electrical length of the fifth open branch, and the electrical length of the sixth open branch are equal and are all one-quarter wavelength corresponding to the center frequency of the filter stopband.

4. The high performance low pass filter topology structure according to claim 3, characterized in that: The sum of the electrical length of the first microstrip line and the electrical length of the first open branch, the sum of the electrical length of the third microstrip line and the electrical length of the second open branch, the sum of the electrical length of the sixth microstrip line and the electrical length of the seventh open branch, and the sum of the electrical length of the eighth microstrip line and the electrical length of the eighth open branch are equal, and are all one-quarter wavelength corresponding to the center frequency of the filter stopband.

5. The high performance low pass filter topology structure according to claim 1, characterized in that: The characteristic impedance of the first microstrip line, the characteristic impedance of the third microstrip line, the characteristic impedance of the sixth microstrip line, the characteristic impedance of the eighth microstrip line, the characteristic impedance of the first open branch, the characteristic impedance of the second open branch, the characteristic impedance of the seventh open branch and the characteristic impedance of the eighth open branch are equal.

6. The high performance low pass filter topology structure according to claim 5, characterized in that: The characteristic impedance of the second microstrip line is equal to the characteristic impedance of the seventh microstrip line.

7. The high performance low pass filter topology structure according to claim 6, characterized in that: The characteristic impedance of the fourth microstrip line is equal to the characteristic impedance of the fifth microstrip line.

8. The high performance low pass filter topology structure according to claim 1, characterized in that: The characteristic impedance of the third open-circuit branch, the characteristic impedance of the fourth open-circuit branch, the characteristic impedance of the fifth open-circuit branch and the characteristic impedance of the sixth open-circuit branch are equal.

9. A filter, characterized in that: It comprises the topological structure described in any one of claims 1 to 8.

10. The filter according to claim 9, characterized in that The filter further comprises 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 22 mm*19.8 mm; The lengths of the first microstrip line, the third microstrip line, the sixth microstrip line and the eighth microstrip line are all set to l 1H =7.4mm, the line width is set to w1=0.5mm; The line lengths of the first open branch, the second open branch, the seventh open branch and the eighth open branch are all set to l 1V =1.65mm, the line width is set to w1=0.5mm; The line lengths of the second microstrip line and the seventh microstrip line are both set to l2=8.9 mm, and the line widths are both set to w2=0.1 mm; the spacing between the second microstrip line and the first microstrip line and the third microstrip line, and the spacing between the seventh microstrip line and the sixth microstrip line and the eighth microstrip line are both set to s1=0.4 mm; The line lengths of the fourth microstrip line and the fifth microstrip line are both set to l3=9.35mm, and the line widths are both set to w3=0.6mm; The line lengths of the third open branch, the fourth open branch, the fifth open branch and the sixth open branch are all set to l4=9 mm, and the line widths are all set to w4=0.4 mm.

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