Topological structure and high-selectivity broadband band-pass filter

Abstract

The utility model discloses a topological structure, comprising a parallel three-line, a first open-circuit branch, a second open-circuit branch, an input port and an output port, one end of the parallel three-line is respectively connected with the input port and the output port, and the other end of the parallel three-line is respectively connected with the first open-circuit branch and the second open-circuit branch. The first open-circuit branch knot and the second open-circuit branch knot are bilaterally symmetrical about the parallel three lines, and the electrical length of the parallel three lines, the electrical length of the first open-circuit branch knot and the electrical length of the second open-circuit branch knot are all 1 / 4 wavelengths corresponding to the center frequency of the band-pass filter based on the topological structure. And the characteristic impedance of the first open-circuit branch knot is equal to that of the second open-circuit branch knot. The utility model further discloses a high-selectivity broadband band-pass filter based on the topological structure, and the high-selectivity broadband band-pass filter has the advantage of high selectivity.

Description

TECHNICAL FIELD

[0001] The utility model relates to filter technical field especially relates to a topology structure and high selectivity wideband band pass filter. BACKGROUND

[0002] With the rapid development of modern wireless communication technology, the contradiction between limited spectrum resources and growing information transmission demand is increasingly intense, various communication systems and communication modes are more and more close to each other even stagger in frequency space, which brings great challenge to the anti-interference ability of each communication system to other system. Under this background, the high selectivity research of wideband filter has very high scientific research and commercial value, and attracts the attention of scholars and engineers. However, the existing wideband band pass filter often has the defect of poor selectivity, which seriously affects its use in modern wireless communication system. SUMMARY

[0003] In view of the above shortcomings of the prior art, the main purpose of the utility model is to provide a topology structure and high selectivity wideband band pass filter, aiming at solving the problem of poor selectivity of the existing wideband band pass filter.

[0004] In order to solve the above technical problem, the utility model adopts the technical scheme that:

[0005] A topology structure, comprising parallel three lines, first open circuit branch, second open circuit branch, input port and output port, one end of the parallel three lines is connected with the input port and the output port respectively, the other end of the parallel three lines is connected with the first open circuit branch and the second open circuit branch respectively, the first open circuit branch and the second open circuit branch are left-right symmetrical about the parallel three lines, the electrical length of the parallel three lines, the electrical length of the first open circuit branch and the electrical length of the second open circuit branch are all quarter wavelength corresponding to the center frequency of the band pass filter based on the topology structure, and the characteristic impedance of the first open circuit branch is equal to that of the second open circuit branch.

[0006] Optionally, the parallel three lines are composed of three parallel transmission lines, the transmission lines have oppositely arranged first ends and second ends, the first ends of the transmission lines on both sides are connected with the input port and the output port one by one respectively, and the second end of the transmission line in the middle is connected with the first open circuit branch and the open circuit branch respectively.

[0007] Optionally, the first open circuit branch and the second open circuit branch are perpendicular to the parallel three lines.

[0008] Optionally, the input port and the output port are left-right symmetrical about the parallel three lines.

[0009] Optionally, the input port and the output port are perpendicular to the parallel three lines.

[0010] A high-selectivity wideband bandpass filter comprising the topology structure.

[0011] Optionally, further comprising a circuit board, the topology structure is arranged on the circuit board, the dielectric constant of the circuit board is 3.38, the dielectric loss is 0.0022, the thickness is 0.813mm, and the size is 11.6mm*11.8mm.

[0012] Optionally, the parallel three lines are composed of three parallel transmission lines, and specific parameters on the circuit board are as follows:

[0013] L T =8.3mm, L T represents the physical length of the transmission line;

[0014] S T =0.1mm, S T represents the spacing between two adjacent transmission lines;

[0015] W T =0.2mm, W T represents the physical width of the transmission line;

[0016] l1=5.3mm, l1 represents the physical length of the first open-circuit branch and the physical length of the second open-circuit branch;

[0017] w1=0.4mm, w1 represents the physical width of the first open-circuit branch and the physical width of the second open-circuit branch.

[0018] The beneficial effects of the utility model lie in: a new topology structure is provided, a wideband bandpass filter can be designed based on the topology structure, and the topology structure has the advantages of high selectivity. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Fig. 1 shows a topology structure schematic diagram of an embodiment of the utility model;

[0020] Figure 2 Fig. 2 shows an equivalent topology structure schematic diagram of the topology structure of the embodiment of the utility model;

[0021] Figure 3 Fig. 3 shows an odd mode form schematic diagram of the equivalent topology structure of the embodiment of the utility model;

[0022] Figure 4 Fig. 4 shows an even mode form schematic diagram of the equivalent topology structure of the embodiment of the utility model;

[0023] Figure 5 Shown is a layout diagram of a highly selective broadband bandpass filter according to an embodiment of the present invention;

[0024] Figure 6 Shown are the S-parameter simulation results of the highly selective broadband bandpass filter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to more clearly understand the technical content, achieved purposes and effects of the present invention, the present invention is described in detail below in conjunction with specific implementation methods and in conjunction with the accompanying drawings. It should be noted that, in the absence of conflict, the implementation methods of the present invention and the features in the implementation methods can be combined with each other. In the following description, many specific details are elaborated in order to fully understand the present invention. The implementation methods described are only part of the implementation methods of the present invention, not all of the implementation methods. Based on the implementation methods in the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] Please refer to Figures 1-4 As shown, the first embodiment of the present utility model is:

[0027] A topology such as Figure 1 As shown, it is a bilaterally symmetrical structure consisting of a parallel three-wire and a pair of open-circuit branches. Specifically, it includes a parallel three-wire, a first open-circuit branch, a second open-circuit branch, an input port, and an output port. The parallel three-wire is composed of three parallel transmission lines, each of which has a first end and a second end that are oppositely arranged. The first ends of the transmission lines on both sides are connected to the input port and the output port respectively, and the second end of the transmission line in the middle is connected to the first open-circuit branch and the open-circuit branch respectively. The first open-circuit branch and the second open-circuit branch, the input port, and the output port are all bilaterally symmetrical about the parallel three-wire. The first open-circuit branch, the second open-circuit branch, the input port, and the output port are all perpendicular to the parallel three-wire. The electrical length of the parallel three-wire, the electrical length of the first open-circuit branch, and the electrical length of the second open-circuit branch are all one-quarter wavelength corresponding to the center frequency of the bandpass filter based on the topological structure, and the characteristic impedance of the first open-circuit branch is equal to the characteristic impedance of the second open-circuit branch.

[0028] In order to analyze the performance of the above topology, Figure 2 The equivalent structure of this topology is given. In the equivalent topology, the odd-mode characteristic impedance of the first parallel line and the odd-mode characteristic impedance of the second parallel line are Z oo The even-mode characteristic impedance of the first parallel line and the even-mode characteristic impedance of the second parallel line are Zoe , the characteristic impedance of the first microstrip line is Z1, and the characteristic impedance of the first open stub and the characteristic impedance of the second open stub are Z2. The electrical length of the first parallel line, the electrical length of the second parallel line, the electrical length of the first microstrip line, the electrical length of the first open stub, and the electrical length of the second open stub are all quarter wavelengths corresponding to the center frequency of the bandpass filter based on the topology.

[0029] Since the equivalent topology is a symmetric structure, its transmission poles can be analyzed by odd and even modes.

[0030] As shown in Figure 3 is the odd mode form of the equivalent topology. When Y ino = 0, it can be concluded that the topology has one odd mode transmission pole. When f0 is the center frequency of the bandpass filter based on the topology, the frequencies corresponding to the two odd mode transmission poles are respectively:

[0031] f op1 = f0

[0032] As shown in Figure 4 is the even mode form of the equivalent topology, wherein the electrical length of the second microstrip line is a quarter wavelength corresponding to the center frequency of the bandpass filter based on the topology, and the characteristic impedance of the second microstrip line is twice the characteristic impedance of the first microstrip line.

[0033] When Y inoL + Y inoR = 0, it can be concluded that the topology has three even mode transmission poles. When f0 is the center frequency of the bandpass filter based on the topology, the frequencies corresponding to the three even mode transmission poles are respectively:

[0034]

[0035] f ep2 = f0

[0036]

[0037] For this topology, the transmission zeros can be calculated by the following method: multiply the ABCD matrices of the cascaded resonators that make up the topology in turn to obtain the ABCD matrix corresponding to the topology; and convert the ABCD matrix of the topology into the corresponding S matrix. When ︱S 21 ︱ = 0, it can be concluded that there are five transmission zeros in the topology, and the frequencies corresponding to the five transmission zeros are respectively:

[0038] f z1 = 0

[0039]

[0040] f z4 =2f0

[0041]

[0042] From the above analysis, it can be seen that the topology of this embodiment has one odd-mode transmission pole, three even-mode transmission poles, and five transmission zeros. oo , Z oe , how the value of Z1 changes, the relative positions of these transmission zeros and poles, that is, f z1 <f z2 <f ep1 <f op1 =f ep2 <f ep3 <f z3 <f z4 <f z5 , which will not change. Therefore, the RF filter designed based on this topology can only be a bandpass filter, with three transmission poles in the passband to ensure passband flatness and five transmission zeros in the stopband to ensure high sideband selectivity and a wide stopband.

[0043] Please refer to Figure 5 and 6 As shown, the second embodiment of the present utility model is:

[0044] A highly selective broadband bandpass filter comprises the topological structure and a circuit board as described in Example 1, wherein the topological structure is provided on the circuit board, and 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 11.6 mm*11.8 mm. Figure 5 Shown is an example of a layout diagram of this embodiment.

[0045] The specific parameters on the circuit board are set as follows:

[0046] L T =8.3mm, L T represents the physical length of the transmission line;

[0047] S T =0.1mm, S T represents the distance between two adjacent transmission lines;

[0048] W T =0.2mm, W T represents the physical width of the transmission line;

[0049] l1=5.3 mm, where l1 represents the physical length of the first open branch and the physical length of the second open branch;

[0050] w1=0.4mm, w1 represents the physical width of the first open-circuit stub and the physical width of the second open-circuit stub.

[0051] The S-parameter simulation results of the high-selectivity wideband bandpass filter of the embodiment are shown in the figure. Figure 6 As can be seen from the figure, the passband bandwidth range with a reflection coefficient less than -10dB is 4.23-7.31GHz, the center frequency of the passband is 5.77GHz, the absolute bandwidth is 3.08GHz, and the relative bandwidth is 53.4%. In addition, there are three transmission poles in the passband range, which are respectively located at 4.56, 5.86 and 7.06GHz. The three transmission poles ensure the characteristics of low insertion loss and high flatness in the passband.

[0052] The stopband range with an isolation degree greater than 20dB is 0-3.31GHz and 8.04-12.00GHz. In the first stopband, there are two transmission zeros, which are respectively located at 0 and 3.02GHz; in the second stopband, there are three transmission zeros, which are respectively located at 8.32GHz, 10.31GHz and 11.52GHz. The five transmission zeros not only determine the high selectivity of the stopband of the filter, but also ensure the high isolation degree in the wide stopband of the filter.

[0053] In summary, the topology structure provided by the embodiment can be used to design a wideband bandpass filter. The high-selectivity wideband bandpass filter designed based on the topology structure has the advantages of high selectivity and high isolation degree while ensuring the characteristics of low insertion loss and high flatness.

[0054] The above description is only an embodiment of the utility model, and does not limit the patent range of the utility model, so any modification, equivalent change and modification made according to the technical essence of the utility model to the above embodiment, which does not deviate from the technical scheme content of the utility model, still belongs to the range of the technical scheme of the utility model.

Claims

1. A topology, characterized in that, The topology structure comprises a parallel three-wire, a first open-circuit branch, a second open-circuit branch, an input port and an output port, one end of the parallel three-wire is connected with the input port and the output port respectively, the other end of the parallel three-wire is connected with the first open-circuit branch and the second open-circuit branch respectively, the first open-circuit branch and the second open-circuit branch are left-right symmetrical about the parallel three-wire, the electrical length of the parallel three-wire, the electrical length of the first open-circuit branch and the electrical length of the second open-circuit branch are all quarter wavelengths corresponding to the center frequency of the band-pass filter based on the topology structure, the characteristic impedance of the first open-circuit branch is equal to the characteristic impedance of the second open-circuit branch.

2. The topology of claim 1, wherein, The parallel three-wire is composed of three parallel transmission lines, the transmission lines have oppositely arranged first ends and second ends, the first ends of the transmission lines on both sides are connected with the input port and the output port one by one respectively, and the second end of the transmission line in the middle is connected with the first open-circuit branch and the open-circuit branch respectively.

3. The topology of claim 1, wherein, The first open-circuit branch and the second open-circuit branch are both perpendicular to the parallel three-wire.

4. The topology of claim 1, wherein, The input port and the output port are left-right symmetrical about the parallel three-wire.

5. The topology of claim 1, wherein, The input port and the output port are both perpendicular to the parallel three-wire.

6. A high selectivity wideband bandpass filter characterized by, The topology structure comprises any one of claims 1-5.

7. The high-selectivity wideband bandpass filter of claim 6, wherein, The topology structure is further arranged on 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 11.6 mm*11.8 mm.

8. The high-selectivity wideband bandpass filter of claim 7, wherein, The parallel three-wire is composed of three parallel transmission lines, and the specific parameters on the circuit board are as follows: L T = 8.3 mm, L T denotes the physical length of the transmission line; S T = 0.1 mm, S T denotes the distance between two adjacent transmission lines; W T = 0.2 mm, W T denotes the physical width of the transmission line; l1=5.3 mm, l1 represents the physical length of the first open-circuit branch and the physical length of the second open-circuit branch; w1=0.4 mm, w1 represents the physical width of the first open-circuit branch and the physical width of the second open-circuit branch.

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