A filter and a communication device

Abstract

The embodiment of the present application relates to the technical field of communication, and discloses a filter, the filter comprises a third microstrip line, one end of the third microstrip line is connected with one end of a first parallel line, one end of a second parallel line and one end of a third parallel line, and the other end of the third microstrip line is connected with one end of a third open-circuit branch; the other end of the first parallel line is connected with an input end and one end of a first microstrip line, and the other end of the first microstrip line is connected with one end of a first open-circuit branch; the other end of the second parallel line is connected with an output end and one end of a second microstrip line, and the other end of the second microstrip line is connected with one end of a second open-circuit branch; and the other end of the third parallel line is grounded. Through the above mode, the wide double-passband filter has the characteristics of good selectivity, compact structure, high isolation, small insertion loss, small passband center frequency ratio and the like.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to the technical field of communication, in particular to a filter and a communication device. BACKGROUND

[0002] With the rapid development of modern wireless communication technology, the radio frequency receiving front end needs to be compatible with different communication systems and provide more abundant services to meet the growing demand of people for digital application. Under this background, the research on miniaturization and high selectivity of microstrip wide dual-passband filter with low cost, low profile, light weight and easy integration has very high scientific research and commercial value.

[0003] In the implementation of the embodiment of the present application, the inventor found that: the currently reported microstrip wide dual-passband filter has defects such as poor selectivity, non-compact structure, poor isolation, large insertion loss, and seriously limits its use in modern wireless communication systems. SUMMARY

[0004] The technical problem solved by the embodiment of the present application is to provide a filter which can have the characteristics of wide dual-passband, good selectivity, compact structure, high isolation, small insertion loss, and small passband center frequency ratio at the same time.

[0005] To solve the above technical problems, one technical scheme adopted by the embodiment of the present application is to provide a filter, comprising a third microstrip line, one end of the third microstrip line is connected with one end of a first parallel line, one end of a second parallel line and one end of a third parallel line, the other end of the third microstrip line is connected with one end of a third open stub, one end of a first microstrip line is connected with one end of the first parallel line and an input terminal, the other end of the first microstrip line is connected with one end of a first open stub, one end of a second microstrip line is connected with one end of the second parallel line and an output terminal, the other end of the second microstrip line is connected with one end of a second open stub, and the other end of the third parallel line is grounded.

[0006] Optionally, the first microstrip line, the second microstrip line, the first parallel line, the second parallel line and the third open stub are placed in parallel, and are placed vertically with the third microstrip line, the third parallel line, the first open stub and the second open stub.

[0007] Optionally, the input terminal and the output terminal are symmetrically arranged about the third parallel line, the first parallel line and the second parallel line are symmetrically arranged about the third parallel line, the first microstrip line and the second microstrip line are symmetrically arranged about the third parallel line, and the first open stub and the second open stub are symmetrically arranged about the third parallel line.

[0008] Optionally, the first parallel line is composed of a first transmission line and a second transmission line; the second parallel line is composed of a third transmission line and a fourth transmission line; the third parallel line is composed of a fifth transmission line and a sixth transmission line; one end of the first transmission line is connected to an input terminal, one end of the second transmission line is connected to one end of the fourth transmission line, one end of the fifth transmission line and one end of a third microstrip line, one end of the third transmission line is connected to an output terminal, and one end of the sixth transmission line is connected to ground; the first transmission line, the second transmission line, the third transmission line and the fourth transmission line are parallel to each other and perpendicular to the fifth transmission line and the sixth transmission line.

[0009] Optionally, the electrical length of the first parallel line, the electrical length of the second parallel line and the electrical length of the third parallel line are all one quarter of the wavelength corresponding to the center frequency of the stop band between the two pass bands of the filter.

[0010] Optionally, the sum of the electrical length of the first microstrip line and the electrical length of the first open stub is one quarter of the wavelength corresponding to the first transmission zero point in the stop band between the two pass bands of the filter, and the sum of the electrical length of the second microstrip line and the electrical length of the second open stub is one quarter of the wavelength corresponding to the first transmission zero point in the stop band between the two pass bands of the filter.

[0011] Optionally, the sum of the electrical length of the third microstrip line and the electrical length of the third open stub is one quarter of the wavelength corresponding to the second transmission zero point in the stop band between the two pass bands of the 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] Optionally, the characteristic impedance of the first microstrip line, the characteristic impedance of the second microstrip line, the characteristic impedance of the first open stub and the characteristic impedance of the second open stub are equal.

[0014] To solve the above technical problems, another technical solution adopted by the embodiments of the present application is to provide a communication device comprising any of the above filters.

[0015] The embodiment of the present application provides a filter, which comprises a third microstrip line, one end of the third microstrip line is connected with one end of a first parallel line, one end of a second parallel line and one end of a third parallel line, and the other end of the third microstrip line is connected with one end of a third open stub; the other end of the first parallel line is connected with an input end and one end of a first microstrip line, and the other end of the first microstrip line is connected with one end of a first open stub; the other end of the second parallel line is connected with an output end and one end of a second microstrip line, and the other end of the second microstrip line is connected with one end of a second open stub; and the other end of the third parallel line is grounded. Through the above arrangement, a wide dual-passband filter with good selectivity, compact structure, high isolation, small insertion loss and small ratio of passband center frequency can be formed. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the drawings needed to be used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference signs. In the drawings, each element or part is not necessarily drawn according to the actual proportion.

[0017] Figure 1 is a topological structure of the filter of the embodiment of the present application;

[0018] Figure 2 is a layout of the filter of the embodiment of the present application;

[0019] Figure 3 is a topological structure of the odd mode form of the filter of the embodiment of the present application;

[0020] Figure 4 is a topological structure of the even mode form of the filter of the embodiment of the present application;

[0021] Figure 5 is another layout of the filter of the embodiment of the present application;

[0022] Figure 6 is a simulation result parameter diagram of the filter of the embodiment of the present application.

[0023] The reference signs in the specific embodiments are as follows: 100, filter; 10, input end; 20, first microstrip line; 21, second microstrip line; 22, third microstrip line; 30, first open stub; 31, second open stub; 32, third open stub; 40, first parallel line; 41, second parallel line; 42, third parallel line; 401, first transmission line; 402, second transmission line; 411, third transmission line; 412, fourth transmission line; 421, fifth transmission line; 422, sixth transmission line; 50, output end. Specific embodiments

[0024] For the purpose of promoting the understanding of the present application, the present application will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. It needs to be noted that when an element is described as "fixed to" another element, it can be directly on the other element or one or more intermediate elements can be present therebetween. When an element is described as "connected to" another element, it can be directly connected to the other element or one or more intermediate elements can be present therebetween. The terms "upper", "lower", "inner", "outer", "vertical", "horizontal", and the like used in the present specification indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are merely used for the purpose of facilitating the description of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", and the like are merely used for the purpose of description and cannot be understood as indicating or implying relative importance.

[0025] Unless otherwise defined, all technical and scientific terms used in the present specification have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used in the present specification includes any and all combinations of one or more of the related listed items.

[0026] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict.

[0027] Please refer to Figure 1 and Figure 2 , the filter 100 includes a third microstrip line 22, one end of the third microstrip line 22 is connected to one end of the first parallel line 40, one end of the second parallel line 41, and one end of the third parallel line 42, the other end of the third microstrip line 22 is connected to one end of the third open stub 32; the other end of the first parallel line 40 is connected to the input end 10 and one end of the first microstrip line 20, the other end of the first microstrip line 20 is connected to one end of the first open stub 30; the other end of the second parallel line 41 is connected to the output end 50 and one end of the second microstrip line 21, the other end of the second microstrip line 21 is connected to one end of the second open stub 31; the other end of the third parallel line 42 is grounded. Through the above arrangement, a wide double-passband filter 100 with good selectivity, compact structure, high isolation, small insertion loss, and small passband center frequency ratio can be formed.

[0028] In the embodiment, the first microstrip line 20, the second microstrip line 21, the first parallel line 40, the second parallel line 41 and the third open stub 32 are parallel, and are perpendicular to the third microstrip line 22, the third parallel line 42, the first open stub 30 and the second open stub 31; the input terminal 10 and the output terminal 50 are symmetrically arranged about the third parallel line 42, the first parallel line 40 and the second parallel line 41 are symmetrically arranged about the third parallel line 42, the first microstrip line 20 and the second microstrip line 21 are symmetrically arranged about the third parallel line 42, and the first open stub 30 and the second open stub 31 are symmetrically arranged about the third parallel line 42.

[0029] Please refer to Figure 2 , the first parallel line 40 is composed of a first transmission line 401 and a second transmission line 402; the second parallel line 41 is composed of a third transmission line 411 and a fourth transmission line 412; the third parallel line 42 is composed of a fifth transmission line 421 and a sixth transmission line 422; one end of the first transmission line 401 is connected to the input terminal 10, one end of the second transmission line 402 is connected to one end of the fourth transmission line 412, one end of the fifth transmission line 421 and one end of the third microstrip line 22, one end of the third transmission line 411 is connected to the output terminal 50, and one end of the sixth transmission line 422 is grounded; the first transmission line 401, the second transmission line 402, the third transmission line 411 and the fourth transmission line 412 are parallel to each other and perpendicular to the fifth transmission line 421 and the sixth transmission line 422. The electrical length of the first parallel line 40, the electrical length of the second parallel line 41 and the electrical length of the third parallel line 42 are all one-quarter wavelength of the center frequency of the stop band between the two pass bands of the filter 100. The sum of the electrical length of the first microstrip line 20 and the electrical length of the first open stub 30 is one-quarter wavelength of the frequency corresponding to the first transmission zero point in the stop band between the two pass bands of the filter 100, and the sum of the electrical length of the second microstrip line 21 and the electrical length of the second open stub 31 is one-quarter wavelength of the frequency corresponding to the first transmission zero point in the stop band between the two pass bands of the filter 100. The sum of the electrical length of the third microstrip line 22 and the electrical length of the third open stub 32 is one-quarter wavelength of the frequency corresponding to the second transmission zero point in the stop band between the two pass bands of the filter 100. 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 characteristic impedance of the first microstrip line 20, the characteristic impedance of the second microstrip line 21, the characteristic impedance of the first open stub 30 and the characteristic impedance of the second open stub 31 are equal.

[0030] In the embodiments of the present application, the electrical length of the first parallel line 40, the electrical length of the second parallel line 41 and the electrical length of the third parallel line 42 are all represented by θ, which is a quarter of the wavelength corresponding to the center frequency of the stop band between the two pass bands of the filter 100; the sum of the electrical length of the first microstrip line 20 and the electrical length of the first open stub 30 and the sum of the electrical length of the second microstrip line 21 and the electrical length of the second open stub 31 are all represented by θ1; the electrical length of the third microstrip line 22 and the electrical length of the third open stub 32 are represented by θ2; 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 represented by ; 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 represented by ; the odd mode impedance of the third parallel line 42 is represented by ; the even mode impedance of the third parallel line 42 is represented by ; the characteristic impedance of the first microstrip line 20, the characteristic impedance of the second microstrip line 21, the characteristic impedance of the first open stub 30 and the characteristic impedance of the second open stub 31 are all represented by Z1; the characteristic impedance of the third microstrip line 22 and the characteristic impedance of the third open stub 32 are represented by Z2.

[0031] Since the filter 100 can be equivalent to a symmetrical structure, the transmission poles thereof can be obtained by means of odd-even mode analysis. In order to simplify the analysis, θ1 and θ2 are set to be equal to θ. Considering that θ is a quarter of the wavelength corresponding to the center frequency of the stop band between the two pass bands of the filter 100, the topology structure of the odd mode form of the filter 100 is as follows. Figure 3

[0032] When Y ino = ∞, the filter 100 has two odd mode transmission poles, and the frequencies corresponding to the two odd mode transmission poles are respectively:

[0033]

[0034]

[0035] wherein f0 is the center frequency of the stop band between the two pass bands of the filter 100.

[0036] Please refer to Figure 4 , Figure 4 for the topology structure of the even mode form of the filter 100. When Y ine = 0, the filter 100 has four even mode transmission poles, and the frequencies corresponding to the four even mode transmission poles are respectively:

[0037]

[0038] ​

[0039]

[0040]

[0041] wherein

[0042]

[0043]

[0044]

[0045] Here, f0is the center frequency of the stopband between the two passbands of the filter 100.

[0046] In the present application, the transmission zero of the filter 100 can be calculated by the following method: multiply the ABCD matrix of the cascaded resonator constituting the topology structure in turn to obtain the ABCD matrix corresponding to the topology structure; convert the ABCD matrix of the topology structure into the corresponding S matrix. When IS 21 When I = 0, it can be concluded that the topology structure has three transmission zeros, and the frequencies corresponding to the three transmission zeros are respectively:

[0047]

[0048] f z2 = f0

[0049]

[0050] wherein f0is the center frequency of the stopband between the two passbands of the filter 100.

[0051] From the above analysis, it can be known that when θ1and θ2are equal to θ, the filter 100 has two odd-mode transmission poles, four even-mode transmission poles and three transmission zeros. And for any parameters and The relative positions of the transmission poles and the transmission zeros can only satisfy the following relationship: f z1 < f ep1 < f op1 < f ep2 < f z2 = f0< f op2 < f ep3 < f ep4 < f z3Therefore, the filter 100 is a dual-passband filter 100, each passband has three transmission poles to ensure the flatness of the passband, and each passband has one transmission zero point below the first passband edge and above the fourth passband edge to ensure high selectivity; and one transmission zero point between the second passband edge and the third passband edge to form a narrow stop band. Obviously, since there is only one transmission zero point between the second passband edge and the third passband edge, the selectivity at the second passband edge and the third passband edge is not high. To improve the selectivity at this place, a transmission zero point needs to be added in the stop band between the two passbands.

[0052] In the embodiment of the present application, when the parameters and are determined values, appropriately adjusting the values of the electrical lengths θ1 and θ2 will not change the bandwidth and the center frequency of the filter 100, but only change the number and position of the transmission zero points in the stop band between the two passbands. When the values of θ1 and θ2 are not equal, the number of transmission zero points in the stop band between the two passbands is 2. Assuming that θ2 < θ1 and λ is a wavelength corresponding to the center frequency of the stop band between the two passbands, the first transmission zero point at the stop band between the two passbands corresponds to a frequency f 2L and the second transmission zero point corresponds to a frequency f 2H The relationship between the frequency f

[0053]

[0054]

[0055] Since appropriately changing the values of the electrical lengths θ1 and θ2 will not change the bandwidth and the center frequency of the filter 100, but only change the number and position of the transmission zero points in the stop band between the two passbands, the parameters and are not changed, the relative positions of the transmission zero points f z1 < f ep1 < f op1 < f ep2 < f 2L < f 2H < f op2 < f ep3 < f ep4 < f z3 are not changed, so when the values of θ1 and θ2 are not equal, a dual-passband filter 100 can be designed, and each passband has three transmission poles to ensure the flatness, and the stop band has four transmission zero points to ensure high selectivity and high isolation.

[0056] Please refer to Figure 5In some embodiments, the filter 100 is designed on a circuit board with dielectric loss of 0.0022 and thickness of 0.813 mm, and the size of the circuit board is 19.9 mm*12.6 mm. The length of the first parallel line 40 and the length of the second parallel line 41 are denoted by l H , and take the value of 8.1 mm; the interval distance between the first transmission line 401 and the second transmission line 402 and the interval distance between the third transmission line 411 and the fourth transmission line 412 are denoted by s H , and take the value of 0.1 mm; the width of the first transmission line 401, the width of the second transmission line 402, the width of the third transmission line 411, and the width of the fourth transmission line 412 are denoted by w H , and take the value of 0.1 mm; the length of the third parallel line 42 is denoted by l V , and takes the value of 7.9 mm; the interval distance between the fifth transmission line 421 and the sixth transmission line 422 is denoted by s V , and takes the value of 0.1 mm; the width of the fifth transmission line 421 and the width of the sixth transmission line 422 are denoted by w V , and take the value of 0.1 mm; the length of the first microstrip line 20 and the length of the second microstrip line 21 are denoted by l1, and take the value of 6.2 mm; the length of the first open-circuit stub 30 and the length of the second open-circuit stub 31 are denoted by l2, and take the value of 2.2 mm; the length of the third microstrip line 22 is denoted by l3, and takes the value of 1.9 mm; the length of the third open-circuit stub 32 is denoted by l4, and takes the value of 6.1 mm; the width of the first microstrip line 20, the width of the second microstrip line 21, the width of the first open-circuit stub 30, and the width of the second open-circuit stub 31 are denoted by w1, and take the value of 0.4 mm; the width of the third microstrip line 22 and the width of the third open-circuit stub 32 are denoted by w2, and take the value of 0.1 mm.

[0057] For the above designed filter 100, the S parameter simulation result is as shown in Figure 6From the figure, it can be seen that in the first passband, the impedance bandwidth range with reflection coefficient less than -10dB is 4.43 to 5.63GHz, the center frequency of the passband is 5.03GHz, the absolute bandwidth of the passband is 1.2GHz, and the relative bandwidth of the passband is 23.9%; in the second passband, the impedance bandwidth range with reflection coefficient less than -10dB is 6.86 to 7.92GHz, the center frequency of the passband is 7.39GHz, the absolute bandwidth of the passband is 1.06GHz, and the relative bandwidth of the passband is 14.3%. From the bandwidth simulation of the two passbands, it can be seen that the filter 100 is a wide dual-passband filter 100. In the first passband, the maximum insertion loss is 0.78dB; in the second passband, the maximum insertion loss is 0.89dB. Therefore, it can be seen that the filter 100 has a low insertion loss characteristic. In addition, there are three transmission poles in the first passband, respectively at 4.52, 4.99, and 5.58GHz; there are also two transmission poles in the second passband, respectively at 7.04, 7.31, and 7.82GHz. The six transmission poles can ensure the flatness in the passband.

[0058] In the stopband between the two passbands, the stopband bandwidth range with isolation greater than 15dB is 5.692 to 6.368GHz, the center frequency of the stopband is 6.03GHz, the absolute bandwidth of the stopband is 0.676GHz, and the relative bandwidth of the stopband is 11.2%.

[0059] There are also four transmission zeros in the stopband, respectively at 4.22, 5.99, 6.38, and 8.16GHz. The four transmission zeros not only ensure the high selectivity of the wide dual-passband filter 100, but also ensure the high isolation of the stopband.

[0060] From the comprehensive simulation results, it can be seen that for the dual-passband filter 100 with the first passband relative bandwidth of 23.9% and the second passband relative bandwidth of 14.3%, the center frequency ratio of the two passbands is only 1.47, which has the characteristic of small center frequency ratio of passbands.

[0061] The embodiment of the present application provides a filter 100, which comprises a third microstrip line 22, one end of the third microstrip line 22 being connected with one end of a first parallel line 40, one end of a second parallel line 41 and one end of a third parallel line 42, the other end of the third microstrip line 22 being connected with one end of a third open stub 32; the other end of the first parallel line 40 being connected with an input end 10 and one end of a first microstrip line 20, the other end of the first microstrip line 20 being connected with one end of a first open stub 30; the other end of the second parallel line 41 being connected with an output end 50 and one end of a second microstrip line 21, the other end of the second microstrip line 21 being connected with one end of a second open stub 31; and the other end of the third parallel line 42 being grounded. Through the above arrangement, a wide dual-passband filter 100 with good selectivity, small size, high isolation, small insertion loss and small ratio of passband center frequency can be formed.

[0062] The present application also provides a communication device embodiment, which is described above in the filter 100 embodiment and will not be repeated here.

[0063] The above description is only the embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation using the content of the present application specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A filter, characterized by, The third microstrip line has one end connected with one end of the first parallel line, one end of the second parallel line and one end of the third parallel line, and the other end connected with one end of the third open stub; one end of the first parallel line is connected with the input end and one end of the first microstrip line, and the other end of the first microstrip line is connected with one end of the first open stub; one end of the second parallel line is connected with the output end and one end of the second microstrip line, and the other end of the second microstrip line is connected with one end of the second open stub; the other end of the third parallel line is grounded; The first microstrip line, the second microstrip line, the first parallel line, the second parallel line and the third open stub are parallel, and are perpendicular to the third microstrip line, the third parallel line, the first open stub and the second open stub; The first parallel line is composed of a first transmission line and a second transmission line; the second parallel line is composed of a third transmission line and a fourth transmission line; the third parallel line is composed of a fifth transmission line and a sixth transmission line; one end of the first transmission line is connected with the input end, one end of the second transmission line is connected with one end of the fourth transmission line, one end of the fifth transmission line and one end of the third microstrip line, one end of the third transmission line is connected with the output end, and one end of the sixth transmission line is grounded; the first transmission line, the second transmission line, the third transmission line and the fourth transmission line are parallel to each other and are perpendicular to the fifth transmission line and the sixth transmission line.

2. The filter according to claim 1, wherein the input end and the output end are symmetrically arranged about the third parallel line, the first parallel line and the second parallel line are symmetrically arranged about the third parallel line, the first microstrip line and the second microstrip line are symmetrically arranged about the third parallel line, and the first open stub and the second open stub are symmetrically arranged about the third parallel line.

3. The filter according to claim 1, wherein the electric length of the first parallel line, the electric length of the second parallel line and the electric length of the third parallel line are all one quarter of the wavelength corresponding to the center frequency of the stop band between the two pass bands of the filter.

4. The filter according to claim 1, wherein the sum of the electric length of the first microstrip line and the electric length of the first open stub is one quarter of the wavelength corresponding to the first transmission zero point in the stop band between the two pass bands of the filter, and the sum of the electric length of the second microstrip line and the electric length of the second open stub is one quarter of the wavelength corresponding to the first transmission zero point in the stop band between the two pass bands of the filter.

5. The filter according to claim 1, wherein the sum of the electric length of the third microstrip line and the electric length of the third open stub is one quarter of the wavelength corresponding to the second transmission zero point in the stop band between the two pass bands of the filter.

6. The filter according to claim 1, wherein 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 filter according to claim 1, wherein The characteristic impedance of the first microstrip line, the characteristic impedance of the second microstrip line, the characteristic impedance of the first open stub, and the characteristic impedance of the second open stub are equal.

8. A communication device, characterized by A filter comprising a filter according to any one of claims 1 to 7.

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