Topological structure of high-selectivity band-pass filter and filter

Abstract

The topological structure comprises a first microstrip line, a first end of the first microstrip line is symmetrically connected with one end of a first parallel three-line and one end of a second parallel three-line, and the other end of the first parallel three-line is connected with an input port. The second end of the first microstrip line is connected with the negative electrode end of a variable capacitance diode, the positive electrode end of the variable capacitance diode is symmetrically connected with one end of a second microstrip line and one end of a third microstrip line, and the other end of the second microstrip line is connected with one end of a first open-circuit branch knot. The other end of the third microstrip line is connected with one end of a second open-circuit branch knot. The band-pass filter overcomes the defects that an existing band-pass filter cannot give consideration to high selectivity, the first pass band edge is independently and continuously adjustable, and the tuning range is wide.

Description

Technical Field

[0001] The utility model relates to the technical field of filters, in particular to a topological structure of a high-selectivity bandpass filter. Background Art

[0002] With the rapid development of modern 5G communication technology, the miniaturization of multifunctional communication systems has become an inevitable development trend. However, the reality is that the RF filters currently widely used in multifunctional communication systems have the characteristics of being non-adjustable and having fixed functions. In order to realize the multifunctionality of the communication system, a large number of RF filters with different indicators need to be arranged inside the system, which will undoubtedly increase the complexity and volume of the communication system. If the RF filter has adjustable characteristics, so that the same filter can flexibly meet different indicators, it will help to simplify the design of the wireless communication system and greatly reduce its volume and weight.

[0003] In addition, in order to fully utilize spectrum resources, high selectivity is required in each microwave communication system. However, the existing bandpass filters cannot take into account high selectivity, continuous adjustment of the first passband edge, and wide tuning range. Utility Model Content

[0004] The main purpose of the utility model is to provide a topological structure of a high-selectivity bandpass filter, aiming to solve the problem that the existing bandpass filter cannot have both high selectivity, independent and continuous adjustment of the first passband edge, and a wide tuning range.

[0005] To achieve the above-mentioned purpose, the utility model proposes a topological structure of a highly selective bandpass filter, comprising a first microstrip line, wherein a first end of the first microstrip line is symmetrically connected to one end of a first parallel three-line and one end of a second parallel three-line, the other end of the first parallel three-line is connected to an input port, the other end of the second parallel three-line is connected to an output port, the second end of the first microstrip line is connected to a negative terminal of a varactor diode, the positive terminal of the varactor diode is symmetrically connected to one end of the second microstrip line and one end of a third microstrip line, the other end of the second microstrip line is connected to one end of a first open-circuit branch, and the other end of the third microstrip line is connected to one end of a second open-circuit branch;

[0006] The first open branch and the second open branch are symmetrical about the first microstrip line, the first parallel three lines, the second parallel three lines, the second microstrip line and the third microstrip line extend along a first direction, the first microstrip line, the first open branch and the second open branch extend along a second direction, and the first direction is perpendicular to the second direction.

[0007] Optionally, the first end of the first microstrip line is connected to a second radio frequency blocking inductor, and the second radio frequency blocking inductor is connected to a DC ground;

[0008] The other end of the first open-circuit branch or the second open-circuit branch is connected to a first radio frequency blocking inductor, the first radio frequency blocking inductor is connected to a protection resistor, and the protection resistor is connected to a direct current power supply.

[0009] Optionally, when the capacitance of the varactor diode is infinite, the electrical length of the first three parallel lines and the electrical length of the second three parallel lines are both one-quarter wavelength corresponding to the center frequency of the bandpass filter.

[0010] Optionally, when the capacitance of the varactor diode is infinite, the electrical length of the first microstrip line is one eighth of the wavelength corresponding to the center frequency of the bandpass filter.

[0011] Optionally, when the capacitance of the varactor diode is infinite, the sum of the electrical length of the second microstrip line and the electrical length of the first open-circuit branch is three-eighths of the wavelength corresponding to the center frequency of the bandpass filter;

[0012] When the capacitance of the varactor diode is infinite, the sum of the electrical length of the third microstrip line and the electrical length of the second open-circuit branch is three-eighths of the wavelength corresponding to the center frequency of the bandpass filter.

[0013] Optionally, the characteristic impedance of the second microstrip line, the characteristic impedance of the third microstrip line, the characteristic impedance of the first open-circuit branch, and the characteristic impedance of the second open-circuit branch are equal and are all twice the characteristic impedance of the first microstrip line.

[0014] Optionally, the first three parallel lines and the second three parallel lines respectively include three transmission lines that are arranged in parallel and at equal intervals.

[0015] To achieve the above object, the utility model also proposes a filter, including a filter designed with any of the above-mentioned topological structures.

[0016] Optionally, the filter further includes a circuit board, the circuit board has a dielectric loss of 0.0022, a thickness of 0.813 mm, and a size of 22.0 mm*10.9 mm.

[0017] Optionally, the lengths of the first parallel three lines and the second parallel three lines are both set to l=8.8mm, the spacing between adjacent transmission lines is set to s=0.2mm, the width of the transmission line is set to w=0.1mm, the length of the first microstrip line is set to l=4.6mm, the sum of the lengths of the second microstrip line and the third microstrip line is set to l=19.4mm, the lengths of the first open branch node and the second open branch node are both set to l=4.2mm, the width of the first microstrip line is set to w=0.6mm, the widths of the second microstrip line and the third microstrip line are both set to w=0.3mm, and the widths of the first open branch node and the second open branch node are both set to w=0.3mm.

[0018] Compared with the prior art, the utility model has the following beneficial effects: the topological structure of the existing filter is improved, including a first microstrip line, the first end of the first microstrip line is symmetrically connected to one end of the first parallel three lines and one end of the second parallel three lines, the other end of the first parallel three lines is connected to the input port, the other end of the second parallel three lines is connected to the output port, the second end of the first microstrip line is connected to the negative end of the varactor diode, the positive end of the varactor diode is symmetrically connected to one end of the second microstrip line and one end of the third microstrip line, the other end of the second microstrip line is connected to one end of the first open-circuit branch, and the other end of the third microstrip line is connected to one end of the second open-circuit branch; the first open-circuit branch and the second open-circuit branch are symmetrical about the first microstrip line, the first parallel three lines, the second parallel three lines, the second microstrip line and the third microstrip line extend along the first direction, the first microstrip line, the first open-circuit branch and the second open-circuit branch extend along the second direction, and the first direction is perpendicular to the second direction. The filter designed based on the topological structure of the utility model takes into account the advantages of high selectivity, continuous adjustment of the first passband edge, and wide tuning range. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0020] Figure 1 This is a schematic diagram of the topological structure of the filter of the utility model;

[0021] Figure 2 This is one of the layout diagrams of the filter based on the topological structure of the utility model;

[0022] Figure 3 This is the second layout diagram of the filter based on the topological structure of the utility model;

[0023] Figure 4 This is the S parameter diagram of the utility model filter when the capacitance of the varactor diode is 0.6pF;

[0024] Figure 5 This is the S parameter diagram of the utility model filter when the capacitance of the varactor diode is 38pF;

[0025] Figure 6 IS is the filter parameter of the utility model 21 I vs. different varactor diode values.

[0026] Description of Figure Numbers:

[0027] 10. Input port; 20. First three parallel lines; 21. Second three parallel lines; 30. First microstrip line; 31. Second microstrip line; 32. Third microstrip line; 40. First open-circuit branch; 41. Second open-circuit branch; 50. Output port; 60. First solder pad; 61. First RF blocking inductor; 62. Protection resistor; 70. Second solder pad; 80. DC ground; 81. Second RF blocking inductor; 90. Varactor diode; 201. First left transmission line; 202. Second left transmission line; 203. Third left transmission line; 211. First right transmission line; 212. Second right transmission line; 213. Third right transmission line.

[0028] The realization of the purpose, functional features and advantages of the utility model will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0030] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back...), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0031] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the utility model, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if the meaning of "and / or" appearing in the full text is to include three parallel schemes, taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the utility model.

[0032] An embodiment of the present invention provides a topological structure of a highly selective bandpass filter. Figures 1 to 3 , comprising a first microstrip line 30, wherein a first end of the first microstrip line 30 is symmetrically connected to one end of a first parallel three-line 20 and one end of a second parallel three-line 21, the other end of the first parallel three-line 20 is connected to an input port 10, and the other end of the second parallel three-line 21 is connected to an output port 50, the second end of the first microstrip line 30 is connected to a negative terminal of a varactor diode 90, the positive terminal of the varactor diode 90 is symmetrically connected to one end of a second microstrip line 31 and one end of a third microstrip line 32, the other end of the second microstrip line 31 is connected to one end of a first open-circuit branch 40, and the other end of the third microstrip line 32 is connected to one end of a second open-circuit branch 41;

[0033] The first open branch 40 and the second open branch 41 are symmetrical about the first microstrip line 30, the first parallel three lines 20, the second parallel three lines 21, the second microstrip line 31 and the third microstrip line 32 extend along a first direction, the first microstrip line 30, the first open branch 40 and the second open branch 41 extend along a second direction, and the first direction is perpendicular to the second direction.

[0034] This embodiment improves the topological structure of the existing filter, which consists of three microstrip lines, two parallel three-wires, two open-circuit branches and a varactor diode 90. The first parallel three-wire 20 and the second parallel three-wire 21, the second microstrip line 31 and the third microstrip line 32, the first open-circuit branch 40 and the second open-circuit branch 41 are symmetrical about the first microstrip line 30, respectively. The first parallel three-wire 20, the second parallel three-wire 21, the second microstrip line 31, and the third microstrip line 32 are parallel to each other and are perpendicular to the first microstrip line 30, the first open-circuit branch 40, and the second open branch 41.

[0035] The first end of the first microstrip line 30 is connected to one end of the second RF blocking inductor 81, and the other end of the second RF blocking inductor 81 is connected to a DC ground 80; the other end of the first open-circuit branch 40 or the second open-circuit branch 41 is connected to a first RF blocking inductor 61, and the first RF blocking inductor 61 is connected to a protective resistor 62, and the protective resistor 62 is connected to a DC power supply. The first microstrip line 30 is connected to the DC ground 80 through the second RF blocking inductor 81 to form a DC loop, and the DC power supply is used to provide a DC voltage acting on the varactor diode 90. Specifically, the first RF blocking inductor 61 is connected to the protective resistor 62 through a first pad 60, and the protective resistor 62 is directly connected to the DC power supply through a second pad 70.

[0036] Furthermore, when the capacitance of the varactor diode 90 is infinite, the electrical length of the first three parallel wires 20 and the electrical length of the second three parallel wires 21 are both one-quarter wavelength corresponding to the center frequency of the bandpass filter.

[0037] Furthermore, when the capacitance of the varactor diode 90 is infinite, the electrical length of the first microstrip line 30 is one eighth of the wavelength corresponding to the center frequency of the bandpass filter.

[0038] Furthermore, when the capacitance of the varactor diode 90 is infinite, the sum of the electrical length of the second microstrip line 31 and the electrical length of the first open branch node 40 is three-eighths of the wavelength corresponding to the center frequency of the bandpass filter; when the capacitance of the varactor diode 90 is infinite, the sum of the electrical length of the third microstrip line 32 and the electrical length of the second open branch node 41 is three-eighths of the wavelength corresponding to the center frequency of the bandpass filter.

[0039] Furthermore, the characteristic impedance of the second microstrip line 31 , the characteristic impedance of the third microstrip line 32 , the characteristic impedance of the first open-circuit branch 40 , and the characteristic impedance of the second open-circuit branch 41 are equal and are all twice the characteristic impedance of the first microstrip line 30 .

[0040] Further, the first parallel three lines 20 and the second parallel three lines 21 respectively include three transmission lines arranged in parallel and at equal intervals. Specifically, the first parallel three lines 20 include a first left transmission line 201, a second left transmission line 202, and a third left transmission line 203, and the second parallel three lines 21 include a first right transmission line 211, a second right transmission line 212, and a third right transmission line 213.

[0041] It is known from common microwave knowledge that by proportionally changing the physical length of the first parallel three-wire 20 and the physical length l of the second parallel three-wire 21, the physical length l of the first microstrip line 30, the sum of the physical length l of the second microstrip line 31 and the physical length l of the third microstrip line 32, the physical length l of the first open-circuit branch 40 and the physical length l of the second open-circuit branch 41, the operating frequency of the bandpass filter can be inversely linearly changed. In the present utility model, in order to ensure that the filter designed based on this topological structure takes into account the advantages of high selectivity, the first passband edge being independently and continuously adjustable, and the wide tuning range, the filter design parameters of this embodiment include the capacitance of the varactor diode 90. The filter characteristics designed based on the topological structure of this embodiment will be described in detail in the filter of another embodiment.

[0042] Another embodiment of the utility model also provides a filter, including a filter with any of the above-mentioned topological structure designs. The filter also includes a circuit board, the dielectric loss of the circuit board is 0.0022, the thickness is 0.813mm, and the size is 22.0mm*10.9mm.

[0043] For further information, see Figure 3 , the lengths of the first parallel three lines 20 and the second parallel three lines 21 are both set to l=8.8mm, the spacing between adjacent transmission lines is set to s=0.2mm, the width of the transmission line is set to w=0.1mm, the length of the first microstrip line 30 is set to l=4.6mm, the sum of the lengths of the second microstrip line 31 and the third microstrip line 32 is set to l=19.4mm, the lengths of the first open branch 40 and the second open branch 41 are both set to l=4.2mm, the width of the first microstrip line 30 is set to w=0.6mm, the widths of the second microstrip line 31 and the third microstrip line 32 are both set to w=0.3mm, and the widths of the first open branch 40 and the second open branch 41 are both set to w=0.3mm.

[0044] It should be noted that, in the previous embodiment, the design parameters affecting the filter performance include the capacitance of the varactor diode 90. Therefore, in this embodiment, the influence of the capacitance of the varactor diode 90 on the filter performance will be described in detail;

[0045] See also Figure 4 , Figure 4The S parameter simulation results of the bandpass filter are given when the capacitance of the varactor diode is 0.6pF. The impedance bandwidth of the filter with a reflection coefficient less than -10dB ranges from 5.451GHz to 7.453GHz, the center frequency of the passband is 6.452GHz, the absolute bandwidth of the passband is 2.002GHz, and the relative bandwidth of the passband is 31%. In the passband, there are two transmission poles, located at 6.389GHz and 7.301GHz, which ensure the flatness of the passband; there are two transmission zeros in the stopband, located at 4.102GHz and 8.139GHz, which ensure the high selectivity of the filter.

[0046] See also Figure 5 , Figure 5 The S parameter simulation results of the bandpass filter are given when the capacitance of the varactor diode is 90 and the value is 38pF. The impedance bandwidth of the filter with a reflection coefficient less than -10dB ranges from 3.376GHz to 7.428GHz, the passband center frequency is 5.402GHz, the absolute bandwidth of the passband is 4.052GHz, and the relative bandwidth of the passband is 75%. In the passband, there are five transmission poles, located at 3.502GHz, 4.219GHz, 6.081GHz, 6.357GHz and 7.283GHz, respectively. These five transmission poles ensure the flatness of the passband; there are two transmission zeros in the stopband, located at 2.577GHz and 7.98GHz, respectively, which can ensure the high selectivity of the filter.

[0047] See also Figure 6 , the IS parameter of the bandpass filter is given for different capacitance values ​​of the varactor diode 90 21 I simulation results. Figure 6 It can be seen that as the capacitance of the varactor diode 90 increases, its first passband edge moves downward, and its second passband edge remains unchanged. Therefore, it has the characteristic that the first passband edge can be adjusted separately.

[0048] Depend on Figure 4 and Figure 5 It can be seen that the bandpass filter designed based on this topological structure can increase its relative bandwidth from 31% to 75% when the capacitance of the varactor diode 90 increases from 0.6pF to 38pF, and has the characteristic of high selectivity in each state. Therefore, it has the advantages of high selectivity and wide bandwidth tuning range.

[0049] The above description is only an optional embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A highly selective bandpass filter topology, It is characterized in that The invention comprises a first microstrip line, wherein a first end of the first microstrip line is symmetrically connected to one end of a first parallel three-line and one end of a second parallel three-line, the other end of the first parallel three-line is connected to an input port, the other end of the second parallel three-line is connected to an output port, the second end of the first microstrip line is connected to a negative terminal of a varactor diode, the positive terminal of the varactor diode is symmetrically connected to one end of a second microstrip line and one end of a third microstrip line, the other end of the second microstrip line is connected to one end of a first open-circuit branch node, and the other end of the third microstrip line is connected to one end of a second open-circuit branch node; The first open branch and the second open branch are symmetrical about the first microstrip line, the first parallel three lines, the second parallel three lines, the second microstrip line and the third microstrip line extend along a first direction, the first microstrip line, the first open branch and the second open branch extend along a second direction, and the first direction is perpendicular to the second direction.

2. The topology of the highly selective bandpass filter according to claim 1, It is characterized in that The first end of the first microstrip line is connected to one end of the second radio frequency blocking inductor, and the other end of the second radio frequency blocking inductor is connected to a DC ground; The other end of the first open-circuit branch or the second open-circuit branch is connected to a first radio frequency blocking inductor, the first radio frequency blocking inductor is connected to a protection resistor, and the protection resistor is connected to a direct current power supply.

3. The topology of the highly selective bandpass filter according to claim 1, It is characterized in that When the capacitance of the varactor diode is infinite, the electrical length of the first three parallel lines and the electrical length of the second three parallel lines are both one-quarter wavelength corresponding to the center frequency of the bandpass filter.

4. The topology of the highly selective bandpass filter according to claim 1, It is characterized in that When the capacitance of the varactor diode is infinite, the electrical length of the first microstrip line is one eighth of the wavelength corresponding to the center frequency of the bandpass filter.

5. The topology of the highly selective bandpass filter according to claim 1, It is characterized in that When the capacitance of the varactor diode is infinite, the sum of the electrical length of the second microstrip line and the electrical length of the first open-circuit branch is three-eighths of the wavelength corresponding to the center frequency of the bandpass filter; When the capacitance of the varactor diode is infinite, the sum of the electrical length of the third microstrip line and the electrical length of the second open-circuit branch is three-eighths of the wavelength corresponding to the center frequency of the bandpass filter.

6. The topology of the highly selective bandpass filter according to claim 1, It is characterized in that The characteristic impedance of the second microstrip line, the characteristic impedance of the third microstrip line, the characteristic impedance of the first open-circuit branch, and the characteristic impedance of the second open-circuit branch are equal and are all twice the characteristic impedance of the first microstrip line.

7. The topology of the highly selective bandpass filter according to claim 1, It is characterized in that The first parallel three lines and the second parallel three lines respectively include three transmission lines arranged in parallel and at equal intervals.

8. A filter, It is characterized in that A filter comprising a topology structure designed according to any one of claims 1 to 7.

9. The filter according to claim 8, It is characterized in that The filter also includes a circuit board, the dielectric loss of the circuit board is 0.0022, the thickness is 0.813 mm, and the size is 22.0 mm*10.9 mm.

10. The filter according to claim 8, It is characterized in that The lengths of the first parallel three lines and the second parallel three lines are both set to l=8.8mm, the spacing between adjacent transmission lines is set to s=0.2mm, the width of the transmission line is set to w=0.1mm, the length of the first microstrip line is set to l=4.6mm, the sum of the lengths of the second microstrip line and the third microstrip line is set to l=19.4mm, the lengths of the first open branch node and the second open branch node are both set to l=4.2mm, the width of the first microstrip line is set to w=0.6mm, the widths of the second microstrip line and the third microstrip line are both set to w=0.3mm, and the widths of the first open branch node and the second open branch node are both set to w=0.3mm.

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