A low pass filter and a communication device

Abstract

The application relates to the technical field of filters, in particular to a low-pass filter and a communication device, which comprise a substrate and a topological structure, the topological structure is arranged on the substrate, and the topological structure comprises an input end, an output end, a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line, a fifth microstrip line, a sixth microstrip line, a seventh microstrip line, an eighth microstrip line, a first open-circuit stub, a second open-circuit stub, a third open-circuit stub, a fourth open-circuit stub and a fifth open-circuit stub, one end of the first microstrip line and one end of the first open-circuit stub are both connected to the input end, a first end of the second microstrip line and a first end of the third microstrip line are both connected to the output end, a second end of the first microstrip line, a second end of the second microstrip line and a first end of the eighth microstrip line are all connected to a first end of the seventh microstrip line. In the above manner, the design process of the low-pass filter can be simplified under the requirements of high selectivity, wide stopband, low insertion loss and miniaturization.

Description

Technical Field

[0001] This invention relates to the field of filter technology, and in particular to a low-pass filter and a communication device. Background Technology

[0002] With the rapid development of wireless communication technology, we are gradually ushering in the fifth generation of wireless communication. The amount of data transmission and the coverage will grow explosively. Communication equipment is becoming smaller and smaller. The demand for RF communication links to suppress spurious emissions from adjacent channels and far-end out-of-band signals is increasing. As a result, filters that can improve the performance of communication systems are gradually being designed to be miniaturized, have steep sidebands, and wide stopbands.

[0003] However, in the process of realizing this invention, the inventors discovered that currently available microstrip low-pass filters, in order to achieve high selectivity, wide stopband, low insertion loss, and miniaturization, mainly employ design schemes such as defective ground schemes, step impedance resonator schemes, stub-loaded resonator schemes, and sector resonator schemes. Most low-pass filters designed based on these schemes suffer from complex design processes. For example, a defective ground low-pass filter 1, such as... Figure 1-2 As shown, the defective ground low-pass filter 1 includes a dielectric substrate 2, a microstrip structure 3, a ground plane 4, and a defective ground structure 5. The microstrip structure 3 is disposed on one side of the dielectric substrate 2, and the ground plane 4 is disposed on the other side of the dielectric substrate 2. The defective ground structure 5 is a defect pattern of a certain shape etched on the ground plane 4. In order to achieve high selectivity and wide stopband, the design of the microstrip structure 3 is often too complex, which can easily increase the filter size and insertion loss. Etching the defective ground structure 5 on the ground plane 4 can improve the stopband and selectivity of the filter, thereby simplifying the structure of the microstrip structure 3. However, in order to obtain better performance, the design of the defective ground structure 5 will also tend to be more complex. Etching the defective ground structure 5 on the ground plane 4 also increases the complexity of the filter design. In addition, since the design of the defective ground structure 5 needs to be based on the design of the microstrip structure 3, when the filter parameters are designed, when the microstrip structure 3 needs to be adjusted, the defective ground structure 5 also needs to be adjusted accordingly. Moreover, if the layout and shape of the microstrip structure 3 are too complicated, it will also make the filter design parameters difficult to design. Therefore, the design process of the defective ground low-pass filter 1 is relatively complex. Similar problems exist with the step impedance resonator scheme, the stub-loaded resonator scheme, and the sector resonator scheme. The example of the low-pass filter 1 with the above defects will not be described here. Summary of the Invention

[0004] In view of the above problems, embodiments of the present invention provide a low-pass filter and a communication device that overcome or at least partially solve the above problems.

[0005] According to one aspect of the present invention, a low-pass filter is provided, including a substrate and a topology. The topology is disposed on the substrate. The topology includes an input terminal, an output terminal, a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line, a fifth microstrip line, a sixth microstrip line, a seventh microstrip line, an eighth microstrip line, a first open-circuit stub, a second open-circuit stub, a third open-circuit stub, a fourth open-circuit stub, and a fifth open-circuit stub. A first end of the first microstrip line and a first end of the first open-circuit stub are both connected to the input terminal, and a first end of the second microstrip line and a first end of the third microstrip line are both connected to the output terminal. The second end of the first microstrip line, the second end of the second microstrip line, and the first end of the eighth microstrip line are all connected to the first end of the seventh microstrip line. The second end of the eighth microstrip line is connected to one end of the fifth open-circuit stub. The second end of the third microstrip line is connected to the first end of the fourth microstrip line. The second end of the fourth microstrip line is connected to one end of the second open-circuit stub. The first ends of the fifth microstrip line and the sixth microstrip line are both connected to the two sides of the second end of the seventh microstrip line. The second end of the fifth microstrip line is connected to one end of the third open-circuit stub. The second end of the sixth microstrip line is connected to one end of the fourth open-circuit stub.

[0006] In some embodiments, the seventh and eighth microstrip lines are on the same straight line, with the straight line as the axis, the first and second microstrip lines are symmetrically arranged, the input and output terminals are symmetrically arranged, the fifth and sixth microstrip lines are symmetrically arranged, and the third and fourth open-circuit stubs are symmetrically arranged, which is beneficial to simplifying the design of the low-pass filter.

[0007] In some embodiments, the first microstrip line and the fifth microstrip line are both perpendicular to the seventh microstrip line, the first open-circuit stub is parallel to the first microstrip line, the third open-circuit stub is perpendicular to the fifth microstrip line, the fifth open-circuit stub is perpendicular to the eighth microstrip line, the third microstrip line is parallel to the second microstrip line, the fourth microstrip line is perpendicular to the third microstrip line, and the second open-circuit stub is perpendicular to the fourth microstrip line. This is beneficial to improving the performance of the low-pass filter.

[0008] In some embodiments, the low-pass filter satisfies the following conditions: the characteristic impedances of the first microstrip line, the second microstrip line, the third microstrip line, the fourth microstrip line, the eighth microstrip line, the first open-circuit stub, the second open-circuit stub, and the fifth open-circuit stub are all Z1; the characteristic impedance of the seventh microstrip line is Z2; and the characteristic impedances of the fifth microstrip line, the sixth microstrip line, the third open-circuit stub, and the fourth open-circuit stub are all 2*Z2. This simplifies the design of the low-pass filter.

[0009] In some embodiments, the wavelength corresponding to the stopband center frequency of the low-pass filter is λ, and the electrical lengths of both the first and second microstrip lines are λ / 4. This facilitates the simplified design of the low-pass filter.

[0010] In some embodiments, the low-pass filter satisfies:

[0011]

[0012] The θ 1L This is the electrical length of the first open-circuit stub. This improves the performance of the low-pass filter.

[0013] In some embodiments, the low-pass filter satisfies:

[0014]

[0015] The θ 1R θ1 is the electrical length of the third microstrip line, θ2 is the electrical length of the fourth microstrip line, and θ3 is the electrical length of the second open-circuit stub. This improves the performance of the low-pass filter.

[0016] In some embodiments, the low-pass filter satisfies the following conditions: the electrical length of the seventh microstrip line is θ4, the electrical lengths of the third open-circuit stub and the fourth open-circuit stub are both θ5, and the electrical lengths of the fifth microstrip line and the sixth microstrip line are both λ / 2 - θ4 - θ5. This improves the performance of the low-pass filter.

[0017] In some embodiments, the low-pass filter satisfies the following conditions: the electrical length of the eighth microstrip line is θ6, and the electrical length of the fifth open-circuit stub is λ / 4 - θ6. This is beneficial for improving the performance of the low-pass filter.

[0018] According to one aspect of the present invention, a communication device is provided, including the low-pass filter described above.

[0019] The beneficial effects of this invention are as follows: Unlike the prior art, this invention provides a low-pass filter comprising a substrate and a topology. The topology includes an input terminal, an output terminal, a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line, a fifth microstrip line, a sixth microstrip line, a seventh microstrip line, an eighth microstrip line, a first open-circuit stub, a second open-circuit stub, a third open-circuit stub, a fourth open-circuit stub, and a fifth open-circuit stub. This topology simplifies the layout of the low-pass filter. Through symmetrical arrangement and the interrelationship between design parameters, the design of the low-pass filter parameters can be simplified. Thus, while meeting the requirements of high selectivity, wide stopband, low insertion loss, and miniaturization, the design process of the low-pass filter can be simplified. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0021] Figure 1 This is a 3D diagram of a defective low-pass filter in existing technology;

[0022] Figure 2 This is a stereoscopic view of a flawed low-pass filter in existing technology from another perspective;

[0023] Figure 3 This is a schematic diagram of the topology of a low-pass filter provided in an embodiment of the present invention;

[0024] Figure 4 This is a layout diagram of a low-pass filter provided in an embodiment of the present invention;

[0025] Figure 5 This is provided by the embodiment of the present invention when θ 1L =θ 1R The equivalent symmetric structure of the topology when =λ / 4 and θ2 = θ3 = 0;

[0026] Figure 6 This is provided in the embodiments of the present invention. Figure 5 A schematic diagram of an odd-mode form in the equivalent symmetric structure of the topological structure;

[0027] Figure 7 This is provided in the embodiments of the present invention. Figure 5 A schematic diagram of an even-mode form in the equivalent symmetric structure of the topological structure;

[0028] Figure 8 This is a simulation result diagram of the S-parameters of the low-pass filter provided in an embodiment of the present invention.

[0029] The reference numerals in the detailed embodiments are as follows:

[0030] 1000, Low-pass filter;

[0031] 100. Topology; 200. Substrate;

[0032] 10. First microstrip line; 11. Second microstrip line; 12. Third microstrip line; 13. Fourth microstrip line; 14. Fifth microstrip line; 15. Sixth microstrip line; 16. Seventh microstrip line; 17. Eighth microstrip line; 18. First open-circuit stub; 19. Second open-circuit stub; 20. Third open-circuit stub; 21. Fourth open-circuit stub; 22. Fifth open-circuit stub; 23. Input terminal; 24. Output terminal; 25. Sixth open-circuit stub;

[0033] 1. Defective ground low-pass filter; 2. Dielectric board; 3. Microstrip structure; 4. Ground plane; 5. Defective ground structure. Detailed Implementation

[0034] To facilitate understanding of the present invention, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is described as being "fixed to" another element, it can be directly on the other element, or one or more intermediate elements may exist between them. When an element is described as being "connected to" another element, it can be directly connected to the other element, or one or more intermediate elements may exist between them. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this specification are for illustrative purposes only.

[0035] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0036] Please see Figure 3 and Figure 4 The low-pass filter 1000 includes a substrate 200 (not shown) and a topology 100. The topology 100 is disposed on the substrate 200, and the substrate 200 serves as a carrier for the topology 100. It is understood that the material of the substrate 200 can be selected according to requirements. For example, the material of the substrate 200 is a polymer material with a metal ground layer.

[0037] For the above-described topology 100, the topology 100 includes an input terminal 23, an output terminal 24, a first microstrip line 10, a second microstrip line 11, a third microstrip line 12, a fourth microstrip line 13, a fifth microstrip line 14, a sixth microstrip line 15, a seventh microstrip line 16, an eighth microstrip line 17, a first open-circuit stub 18, a second open-circuit stub 19, a third open-circuit stub 20, a fourth open-circuit stub 21, and a fifth open-circuit stub 22. The first end of the first microstrip line 10 and one end of the first open-circuit stub 18 are both connected to the input terminal 23, and the first ends of the second microstrip line 11 and the third microstrip line 12 are both connected to the output terminal 24. The second end of the first microstrip line 10... The second end of the second microstrip line 11 and the first end of the eighth microstrip line 17 are all connected to the first end of the seventh microstrip line 16. The second end of the eighth microstrip line 17 is connected to one end of the fifth open stub 22. The second end of the third microstrip line 12 is connected to the first end of the fourth microstrip line 13. The second end of the fourth microstrip line 13 is connected to one end of the second open stub 19. The first ends of the fifth microstrip line 14 and the sixth microstrip line 15 are both connected to the two sides of the second end of the seventh microstrip line 16. The second end of the fifth microstrip line 14 is connected to one end of the third open stub 20. The second end of the sixth microstrip line 15 is connected to one end of the fourth open stub 21. The seventh microstrip line 16 and the eighth microstrip line 17 are on the same straight line. With this straight line as the axis, the first microstrip line 10 and the second microstrip line 11 are symmetrically arranged. The input terminal 23 and the output terminal 24 are symmetrically arranged. The fifth microstrip line 14 and the sixth microstrip line 15 are symmetrically arranged. The third open-circuit stub 20 and the fourth open-circuit stub 21 are symmetrically arranged, which facilitates the simplified design of the low-pass filter 1000. The first microstrip line 10 and the fifth microstrip line 14 are both perpendicular to the seventh microstrip line 16. The first open-circuit stub 18 is parallel to the first microstrip line 10. The third open-circuit stub 20 is perpendicular to the fifth microstrip line 14. The fifth open-circuit stub 22 is perpendicular to the eighth microstrip line 17. The third microstrip line 12 is parallel to the second microstrip line 11. The fourth microstrip line 13 is perpendicular to the third microstrip line 12. The second open-circuit stub 19 is perpendicular to the fourth microstrip line 13. This arrangement helps improve the performance of the low-pass filter 1000.

[0038] In some embodiments, preset parameters Z1, Z2, λ, θ 1L θ 1R θ2, θ3, θ4, θ5, and θ6, the low-pass filter 1000 satisfies the following conditions:

[0039] (1) The characteristic impedances of the first microstrip line 10, the second microstrip line 11, the third microstrip line 12, the fourth microstrip line 13, the eighth microstrip line 17, the first open-circuit stub 18, the second open-circuit stub 19, and the fifth open-circuit stub 22 are all Z1. The characteristic impedance of the seventh microstrip line 16 is Z2. The characteristic impedances of the fifth microstrip line 14, the sixth microstrip line 15, the third open-circuit stub 20, and the fourth open-circuit stub 21 are all 2*Z2. This facilitates the simplified design of the low-pass filter 1000.

[0040] (2) The wavelength corresponding to the stopband center frequency of the low-pass filter 1000 is λ, and the electrical lengths of the first microstrip line 10 and the second microstrip line 11 are both λ / 4. This facilitates the simplified design of the low-pass filter 1000. (3)

[0042]

[0043] The θ 1L Here, π represents the electrical length of the first open-circuit stub 18, and arctan represents the arctangent function. This facilitates the simplified design of the low-pass filter 1000. (4)

[0045]

[0046] The θ 1R The electrical length of the third microstrip line 12, θ2 is the electrical length of the fourth microstrip line 13, and θ3 is the electrical length of the second open-circuit stub 19. This facilitates the simplified design of the low-pass filter 1000.

[0047] (5) The electrical length of the seventh microstrip line 16 is θ4, the electrical lengths of the third open-circuit stub 20 and the fourth open-circuit stub 21 are both θ5, and the electrical lengths of the fifth microstrip line 14 and the sixth microstrip line 15 are both λ / 2-θ4-θ5. This facilitates the simplified design of the low-pass filter 1000.

[0048] (6) The electrical length of the eighth microstrip line 17 is θ6, and the electrical length of the fifth open stub 22 is λ / 4-θ6. This facilitates the simplified design of the low-pass filter 1000.

[0049] To demonstrate that the topology 100 can be used to design the low-pass filter 1000, the following analysis is provided in this embodiment of the invention:

[0050] (1) Figure 5 This is provided by the embodiment of the present invention when θ1L =θ 1R For the equivalent symmetric structure of topology 100 when λ / 4 and θ2 = θ3 = 0, please refer to [reference needed]. Figure 5 When θ 1L =θ 1R When = λ / 4 and θ2 = θ3 = 0, the third microstrip line 12, the fourth microstrip line 13, and the second open-circuit stub 19 are equivalent to the sixth open-circuit stub 25. The topology 100 can be equivalent to a symmetrical structure, and its transmission poles can be analyzed using odd and even modes.

[0051] (2) Figure 6 This is provided in the embodiments of the present invention. Figure 5 A schematic diagram of an odd-mode form in the equivalent symmetric structure of topology 100 is shown below. Figure 6 When the odd mode admittance Y ino When f = ∞, it can be concluded that the topology 100 has two odd-mode transmission poles. When f0 is the center frequency of the wide stopband of the low-pass filter 1000, the frequency corresponding to its odd-mode transmission pole is f. op1 =0 and f op2 =f0.

[0052] (3) Figure 7 This is provided in the embodiments of the present invention. Figure 5 Please refer to the schematic diagram of an even mode in the equivalent symmetric structure of topology 100. Figure 7 When the even-mode admittance Y ine When =∞, it can be concluded that the topology 100 has three even-mode transmission poles, and the frequencies corresponding to the even-mode transmission poles are as follows:

[0053]

[0054]

[0055]

[0056] For the topology 100, its transmission zeros can be calculated using the following method: Multiply the ABCD matrices of the cascaded resonators constituting the topology 100 sequentially to obtain the ABCD matrix corresponding to the topology 100; then convert the ABCD matrix of the topology 100 into the corresponding S matrix. When |S 21 When |=0, it can be concluded that the topology 100 has three transmission zeros, namely: and

[0057] From the above analysis, it can be seen that the topology 100 has two odd-mode transmission poles, three even-mode transmission poles, and three transmission zeros. Regardless of how the values ​​of parameters Z1 and Z2 change, the relative positions of these transmission poles and zeros, i.e., f... op1 <f ep1 <f z1 <f ep2 <f oep2 =f z2 <f ep3 <f z3 The value will not change. If you want to design a high-performance low-pass filter 100 using the aforementioned topology 100, you must introduce two additional transmission zeros f. z4 and f z5 And the following relationship exists: f z4 =f ep2 f z5 =f ep3 Thus, based on 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 displayed. This is achieved by introducing two transmission zeros f. z4 and f z5 This eliminates the transmission poles in the stopband, thus obtaining the desired low-passband filter. Furthermore, the low-pass filter 1000 has two transmission poles to ensure its flatness and five transmission zeros within the stopband to ensure high selectivity, high isolation, and a wide stopband. Transmission zero f z5 Introduced by the first open-circuit stub 18, therefore, the electrical length of the first open-circuit stub 18 must be [value missing].

[0058]

[0059] Transmission zero point f z4 Introduced by the third microstrip line 12, the fourth microstrip line 13, and the second open-circuit stub 19, the sum of the electrical lengths of the third microstrip line 12, the fourth microstrip line 13, and the second open-circuit stub 19 must be:

[0060]

[0061] To achieve a wider stopband, higher stopband isolation, and lower passband reflection coefficient, the low-pass filter 1000 designed based on the aforementioned topology 100 should, under realistic conditions, maximize Z1 and minimize Z2. It should be noted that the maximum value of Z1 is limited by parameters such as the dielectric constant and thickness of the substrate 200, as well as the etching precision of the substrate 200; the minimum value of Z2 is limited by parameters such as the dielectric constant and thickness of the substrate 200, and the stopband center frequency of the low-pass filter 1000.

[0062] In some embodiments, the low-pass filter 1000 is designed on a substrate 200 with a dielectric constant of 3.38, a dielectric loss of 0.0022, and a thickness of 0.813 mm. The substrate 200 has dimensions of 33.0 mm * 12.0 mm. It is understood that the dielectric constant, dielectric loss, thickness, and dimensions of the substrate 200 are not limited to the above values ​​and can be adjusted according to requirements. Assume: L1 is the physical length of the first microstrip line 10, L2 is the physical length of the first open stub 18, L3 is the physical length of the fourth microstrip line 13, L4 is the physical length of the second open stub 19, L5 is the physical length of the seventh microstrip line 16, L6 is the physical length of the fifth microstrip line 14, L7 is the physical length of the third open stub 20, L8 is the physical length of the eighth microstrip line 17, L9 is the physical length of the fifth open stub 22, W1 is the physical width of the first microstrip line 10, W2 is the physical width of the third microstrip line 12, W3 is the physical width of the seventh microstrip line 16, W4 is the physical width of the fifth microstrip line 14, W5 is the physical width of the third open stub 20, and W6 is the physical width of the eighth microstrip line 17.

[0063] In some embodiments, the design parameters of the low-pass filter 1000 satisfy: W1 = W2 = W6, W3 = 2W4 = 2W5, and the first open stub 18 and the third microstrip line 12 are symmetrically arranged with the straight line containing the seventh microstrip line 16 and the eighth microstrip line 17 as the axis. This facilitates the simplified design of the low-pass filter 1000.

[0064] As is known from microwave basics, synchronously and equally changing the values ​​of L1, L2, L3, L4, L5, L6, L7, L8, and L9 can inversely and linearly adjust the operating frequency range of the low-pass filter 1000; there are only two parameters that affect the performance of the low-pass filter 1000, namely W1 and W3.

[0065] In some typical embodiments, one set of optimized dimensional parameters is: L1 = 12.9 mm, L2 = 11.3 mm, L3 = 2.3 mm, L4 = 2.4 mm, L5 = 3.2 mm, L6 = 12.6 mm, L7 = 5.2 mm, L8 = 1.2 mm, L9 = 12.7 mm, W1 = W2 = W6 = 0.1 mm, W3 = 2W4 = 2W5 = 3.2 mm. The simulation results of the low-pass filter 1000 designed with the above parameters are as follows: Figure 8 As shown, by Figure 8It is known that its passband, with a reflection coefficient less than -10dB, ranges from 0GHz to 0.705GHz, and its maximum insertion loss within the passband is 0.479dB, exhibiting low insertion loss characteristics. Within the passband, there are two transmission poles located at 0GHz and 0.491GHz, ensuring flatness within the passband. Its stopband, with isolation greater than 20dB, ranges from 1.466GHz to 6.000GHz, and contains five transmission zeros at 1.389GHz, 3.062GHz, 3.714GHz, 4.288GHz, and 5.782GHz. These five transmission zeros not only guarantee the high selectivity of the low-pass filter 1000 but also ensure high isolation across the wide stopband. Furthermore, its passband edge steepness is 71dB / GHz, demonstrating excellent selectivity, and the ratio of its maximum stopband frequency to its maximum passband frequency is 8.5, exhibiting wide stopband characteristics. It is understood that the parameters L1, L2, L3, L4, L5, L6, L7, L8, L9, W1, W2, W3, W4, W5, and W6 are not limited to the values ​​mentioned above and can be adjusted according to requirements.

[0066] In this embodiment of the invention, the topology 100 includes an input terminal 23, an output terminal 24, a first microstrip line 10, a second microstrip line 11, a third microstrip line 12, a fourth microstrip line 13, a fifth microstrip line 14, a sixth microstrip line 15, a seventh microstrip line 16, an eighth microstrip line 17, a first open-circuit stub 18, a second open-circuit stub 19, a third open-circuit stub 20, a fourth open-circuit stub 21, and a fifth open-circuit stub 22. The topology 100 simplifies the layout of the low-pass filter 1000. Through symmetrical arrangement and the interrelationship between design parameters, the design of the low-pass filter 1000 parameters can be simplified. Thus, while meeting the requirements of high selectivity, wide stopband, low insertion loss, and miniaturization, the design process of the low-pass filter 1000 can be simplified.

[0067] The present invention also provides an embodiment of a communication device, the communication device including the low-pass filter 1000 described above. For the functions and structure of the communication device, please refer to the above embodiments, which will not be repeated here.

[0068] It should be noted that while the preferred embodiments of the present invention are given in the specification and accompanying drawings, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are not intended to impose additional limitations on the content of the present invention; their purpose is to provide a more thorough and comprehensive understanding of the disclosure of the present invention. Furthermore, the above-described technical features can be combined with each other to form various embodiments not listed above, all of which are considered to be within the scope of the present invention specification. Moreover, those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A low-pass filter, characterized by The low-pass filter comprises: a substrate; a topology structure arranged on the substrate, the topology structure comprising an input end, an output end, a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line, a fifth microstrip line, a sixth microstrip line, a seventh microstrip line, an eighth microstrip line, a first open stub, a second open stub, a third open stub, a fourth open stub and a fifth open stub; wherein a first end of the first microstrip line and one end of the first open stub are both connected to the input end, a first end of the second microstrip line and a first end of the third microstrip line are both connected to the output end, a second end of the first microstrip line, a second end of the second microstrip line and a first end of the eighth microstrip line are all connected to a first end of the seventh microstrip line, a second end of the eighth microstrip line is connected to one end of the fifth open stub, a second end of the third microstrip line is connected to a first end of the fourth microstrip line, a second end of the fourth microstrip line is connected to one end of the second open stub, a first end of the fifth microstrip line and a first end of the sixth microstrip line are both connected to two sides of a second end of the seventh microstrip line, a second end of the fifth microstrip line is connected to one end of the third open stub, and a second end of the sixth microstrip line is connected to one end of the fourth open stub; the seventh microstrip line and the eighth microstrip line are on the same straight line, the first microstrip line and the second microstrip line are symmetrically arranged, the input end and the output end are symmetrically arranged, the fifth microstrip line and the sixth microstrip line are symmetrically arranged, and the third open stub and the fourth open stub are symmetrically arranged; The low pass filter satisfies: characteristic impedances of the first microstrip line, the second microstrip line, the third microstrip line, the fourth microstrip line, the eighth microstrip line, the first open-circuit stub, the second open-circuit stub and the fifth open-circuit stub are Z 1, and a characteristic impedance of the seventh microstrip line is Z 2, characteristic impedances of the fifth microstrip line, the sixth microstrip line, the third open-circuit stub and the fourth open-circuit stub are Z 2.

2. The low-pass filter according to claim 1, wherein: the first microstrip line and the fifth microstrip line are both perpendicular to the seventh microstrip line, the first open stub is parallel to the first microstrip line, the third open stub is perpendicular to the fifth microstrip line, the fifth open stub is perpendicular to the eighth microstrip line, the third microstrip line is parallel to the second microstrip line, the fourth microstrip line is perpendicular to the third microstrip line, and the second open stub is perpendicular to the fourth microstrip line.

3. The low-pass filter according to claim 1, wherein: a wavelength corresponding to a center frequency of a stop band of the low-pass filter is λ, and an electrical length of the first microstrip line and the second microstrip line is λ / 4.

4. The low-pass filter of claim 3, wherein, the low-pass filter satisfies: The θ 1L The electrical length of the first open stub.

5. The low-pass filter of claim 3, wherein, the low-pass filter satisfies: The θ 1R is the electrical length of a third microstrip line, the θ 2 is the electrical length of a fourth microstrip line, the the low-pass filter satisfies: 3 is the electrical length of a second open stub.

6. The low-pass filter of claim 3, wherein, θ an electrical length of the seventh microstrip line is θ 4, an electrical length of the third open-circuited stub and an electrical length of the fourth open-circuited stub are both θ 5, an electrical length of the fifth microstrip line and an electrical length of the sixth microstrip line are both λ / 2 the low-pass filter satisfies: 4- θ 5.

7. The low-pass filter of claim 3, wherein, θ an electrical length of the eighth microstrip line is a low-pass filter as claimed in any one of claims 1-7. 6, an electrical length of the fifth open stub is λ / 4 ​ 6.

8. A communication device, characterized by ​

Images