Filter structures and filters

Abstract

The present invention provides a filtering structure and a filter, which relates to the field of filters, including an input feeding port, an output feeding port, a first branch and a resonant cavity; the resonant cavity includes a first resonant cavity and a second resonant cavity, the input feeding port is connected to the output feeding port through the first branch; the end of the first branch connected to the input feeding port is connected to the first resonant cavity; the end of the first branch connected to the output feeding port is connected to the second resonant cavity; the first resonant cavity and the second resonant cavity adopt a slow wave structure; the first resonant cavity and the second resonant cavity are electrically coupled; the first resonant cavity and the second resonant cavity generate the second harmonic of the first resonant frequency and the second resonant frequency respectively. The filtering structure and the filter have the advantages of wide stopband, high suppression, low difference loss, small size, low cost, easy processing, etc., which alleviates the problems of high cost, poor filter design performance and large volume in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of filters used in the communication field, and in particular to a filtering structure and a filter. Background Art

[0002] With the rapid development of wireless communication technology, higher and higher requirements are placed on wireless communication equipment. Filters are widely used in communication and signal processing. In the field of filters, the designed filters must not only meet the electrical performance requirements, but also develop in the direction of small size as much as possible.

[0003] At present, although filters used in wireless communication systems are packaged and integrated to a certain extent, the size of filters designed by traditional methods is generally large, which cannot meet the development needs of modern wireless communication systems for miniaturization, low cost, and low loss of filters. Due to the limitations of processing technology and limited product area, it is difficult to truly achieve miniaturization in filter design. The design of low-cost, miniaturized and high-performance filters is still an important challenge in wireless communication systems. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a filtering structure and a filter to alleviate the technical problem of large size existing in the prior art.

[0005] In order to achieve the above purpose, the technical solution adopted by the embodiment of the present invention is as follows:

[0006] In a first aspect, the present invention provides a filtering structure, the filtering structure comprising an input feeding port, an output feeding port, a first branch and a resonant cavity;

[0007] The resonant cavity comprises a first resonant cavity and a second resonant cavity, the input end feeding port is connected to the output end feeding port through the first branch; one end of the first branch connected to the input end feeding port is connected to the first resonant cavity; one end of the first branch connected to the output end feeding port is connected to the second resonant cavity;

[0008] The first resonant cavity and the second resonant cavity both adopt a slow-wave structure;

[0009] The coupling mode between the first resonant cavity and the second resonant cavity is electrical coupling;

[0010] The first resonant cavity is configured to generate a second harmonic of a first resonant frequency, and the second resonant cavity is configured to generate a second harmonic of a second resonant frequency, wherein the first resonant frequency is less than the second resonant frequency.

[0011] In combination with the first aspect, an embodiment of the present invention provides a first possible implementation of the first aspect, wherein the filtering structure is of a “П” type.

[0012] In combination with the first aspect, an embodiment of the present invention provides a second possible implementation of the first aspect, wherein a “T”-shaped structural unit is formed between the first resonant cavity and the second resonant cavity.

[0013] In combination with the first aspect, an embodiment of the present invention provides a third possible implementation manner of the first aspect, wherein the first resonant cavity includes a first connecting portion, a second connecting portion, and a third connecting portion, the first connecting portion includes a first vertical line portion and a first horizontal line portion connected to each other, the first vertical line portion connects an end of the first branch connected to the input end feeding port; the first vertical line portion and the first horizontal line portion are perpendicular to each other to form an "L" shape;

[0014] The second connecting portion includes a second vertical line portion and a second horizontal line portion connected to each other, and the second vertical line portion and the second horizontal line portion are perpendicular to each other to form a type;

[0015] The first horizontal line portion is perpendicular to the second vertical line portion, and the first horizontal line portion is connected to an end portion of the second vertical line portion;

[0016] The length of the second vertical line portion is shorter than the length of the first vertical line portion; the length of the second horizontal line portion is shorter than the length of the first horizontal line portion;

[0017] The third connection portion is in the shape of a letter "I", and is parallel to the first horizontal line portion and the second horizontal line portion; one end of the third connection portion is connected to the first vertical line portion, and the other end of the third connection portion is not connected to the second vertical line portion, and the third connection portion is located between the first horizontal line portion and the second horizontal line portion;

[0018] The area enclosed by the first branch, the first connecting portion, the second connecting portion and the third connecting portion forms an "S"-shaped structural unit.

[0019] In combination with the first aspect, the embodiment of the present invention provides a fourth possible implementation manner of the first aspect, wherein the second resonant cavity includes a fourth connecting portion, a fifth connecting portion and a sixth connecting portion, the fourth connecting portion includes a fourth vertical line portion and a fourth horizontal line portion connected to each other, and the fourth vertical line portion and the fourth horizontal line portion are perpendicular to each other to form Type; the fourth vertical line portion is connected to one end of the first branch connected to the output feeding port;

[0020] The sixth connecting portion includes a sixth vertical line portion and a sixth horizontal line portion connected to each other, and the sixth vertical line portion and the sixth horizontal line portion are perpendicular to each other to form type;

[0021] The fourth horizontal line portion is perpendicular to the sixth vertical line portion, and the fourth horizontal line portion is connected to an end of the sixth vertical line portion;

[0022] The length of the sixth vertical line portion is shorter than the length of the fourth vertical line portion; the length of the sixth horizontal line portion is shorter than the length of the fourth horizontal line portion;

[0023] The fifth connecting portion is in the shape of a letter "|", and is parallel to the fourth vertical line portion and the sixth vertical line portion; one end of the fifth connecting portion is connected to the sixth horizontal line portion, and the other end of the fifth connecting portion is not connected to the fourth horizontal line portion, and the fifth connecting portion is located between the fourth vertical line portion and the sixth vertical line portion;

[0024] The area enclosed by the fourth connecting portion, the fifth connecting portion and the sixth connecting portion forms a "U"-shaped structural unit.

[0025] In combination with the first aspect, the embodiment of the present invention provides a fifth possible implementation of the first aspect, wherein the microstrip line impedance of the first branch is 77 ohms.

[0026] In combination with the first aspect, the embodiment of the present invention provides a sixth possible implementation of the first aspect, wherein the input feeding port and the output feeding port adopt a conical structure.

[0027] In a second aspect, an embodiment of the present invention further provides a filter, comprising a substrate and the filtering structure as described above, wherein the filtering structure is formed on the substrate.

[0028] In combination with the second aspect, an embodiment of the present invention provides a first possible implementation of the second aspect, wherein the substrate is a PCB board; the substrate is a FR-4 fiberboard.

[0029] In combination with the second aspect, an embodiment of the present invention provides a second possible implementation of the second aspect, wherein the substrate is rectangular, and two rows of metal through holes parallel to the two long sides of the substrate are arranged on the substrate, and the filtering structure is located between the two parallel rows of metal through holes.

[0030] The embodiments of the present invention bring the following beneficial effects: the filter structure and filter provided by the embodiments of the present invention, wherein the filter structure comprises an input feeding port, an output feeding port, a first branch and a resonant cavity; the resonant cavity comprises a first resonant cavity and a second resonant cavity, the input feeding port is connected to the output feeding port through the first branch; the end of the first branch connected to the input feeding port is connected to the first resonant cavity; the end of the first branch connected to the output feeding port is connected to the second resonant cavity; the first resonant cavity and the second resonant cavity both adopt a slow-wave structure; the coupling mode between the first resonant cavity and the second resonant cavity is electrical coupling; the first resonant cavity is configured to generate the second harmonic of the first resonant frequency, and the second resonant cavity is configured to generate the second harmonic of the second resonant frequency, and the first resonant frequency is less than the second resonant frequency. The technical solution provided by the embodiments of the present invention reduces the length of the resonant cavity by designing each resonant cavity as a slow-wave structure, and the internal coupling and electrical coupling between each resonant cavity are used, which is conducive to the miniaturization of the device and the higher out-of-band suppression capability; while the size is greatly reduced relative to the traditional filter, a wider relative bandwidth is also obtained. The filtering structure and filter have the advantages of wide stopband, high suppression, low differential loss, small size, low cost, easy processing, etc., and can alleviate the problems of high cost, poor filter design performance and large size caused by designing filters in limited product space and discrete components in the prior art.

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 A schematic diagram of a filtering structure provided by an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of the structure of a filter provided by an embodiment of the present invention;

[0035] Figure 3 A schematic diagram of the back side of a filter provided by an embodiment of the present invention;

[0036] Figure 4A three-dimensional structure diagram of a filter provided for an example implementation of the present invention;

[0037] Figure 5 A schematic structural diagram of a capacitive gap coupled microstrip SIR resonator provided by an embodiment of the present invention;

[0038] Figure 6 An equivalent circuit diagram of a filter provided by an embodiment of the present invention;

[0039] Figure 7 An equivalent circuit diagram of a resonant cavity provided by an embodiment of the present invention;

[0040] Figure 8 A schematic diagram of S-parameter simulation results of a filter provided for an example implementation of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0042] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0044] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0045] In addition, the terms "horizontal", "vertical", "overhanging" and the like do not mean that the components are required to be absolutely horizontal or overhanging, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0046] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0047] With the development of wireless high-fidelity (Wi-Fi) communication technology and wireless communication technology, filters have been widely used in the process of communication and signal processing. The RF front-end design has higher and higher requirements for signal selectivity and in-band and out-of-band, especially the design of filters, which requires high performance, miniaturization, low cost, effective filtering of various useless signals and spurious signals, and reducing signal interference between communication channels.

[0048] In recent years, compared with other fields, WIFI communication technology has developed rapidly, and there are more and more spectrum resources in product design. The higher the frequency, the stronger the interference, the greater the harmonics and high-order spurious power generated, which makes the design of RF filters difficult. Therefore, higher requirements are put forward for filters: such as wide stopband, good in-band amplitude-frequency characteristics, high out-of-band suppression, and low cost.

[0049] At present, filters designed with discrete components are widely used in radio frequency circuits. However, in order to obtain higher out-of-band suppression characteristics, the order of the filter needs to be increased. As the order increases, the cost also increases. There are also more and more application designs of microstrip filters. Among them, the interdigitated form, parallel coupling, and hairpin type have relatively flat amplitude-frequency characteristics within the band, but occupy a large space. The elliptical structure has higher selectivity outside the band, but is not suitable for higher frequency designs. Based on this, an embodiment of the present invention proposes a filtering structure and a filter. Compared with filters and various microstrip filters designed with discrete components in the existing scheme, the filtering structure and the filter scheme can achieve low insertion loss within the band, good selectivity, high out-of-band suppression, and low cost, and can solve the size design difficulties in a limited product area, alleviating the current communication product RF front-end channel selectivity and the high cost of filters composed of discrete devices used, as well as the design defects caused by various microstrip filter structures and performances. In addition, for the RF front-end design of WIFI products, the finished products are gradually miniaturized and integrated. Various high-speed interfaces, such as DDR3, PCIE, USB3.0, PHY, SGMII, PGMII, SFP, etc. and the communication spectrum of various public networks, the local oscillator frequency and high-order harmonics of the RF chip itself are easily radiated through space and interfere with each other, resulting in nonlinearity in the RF front-end. Therefore, the filter designed in the RF front-end requires wide stopband, high suppression, low loss, small size and low cost. The new filtering structure and filter solution can be applied to WIFI products to solve the current design ideas of WIFI RF front-end, simplify RF design, improve system anti-interference and design problems, solve the coexistence problems and interference of rich product spectrum, and improve the communication quality of the whole system.

[0050] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0051] Figure 1 A schematic diagram of a filtering structure provided by an embodiment of the present invention is shown.

[0052] Reference Figure 1 , the filtering structure includes an input feeding port P1, an output feeding port P2, a first branch 101 and a resonant cavity;

[0053] The resonant cavity comprises a first resonant cavity 10 and a second resonant cavity 20, the input end feeding port P1 is connected to the output end feeding port P2 through the first branch 101; the end of the first branch 101 connected to the input end feeding port P1 is connected to the first resonant cavity 10; the end of the first branch 101 connected to the output end feeding port P2 is connected to the second resonant cavity 20;

[0054] Wherein, the first resonant cavity 10 and the second resonant cavity 20 both adopt a slow-wave structure;

[0055] It should be noted that the above slow wave structure may be, for example, a spiral structure or a meander structure. Figure 1 A slow-wave structure is only shown as an example.

[0056] The coupling mode between the first resonant cavity 10 and the second resonant cavity 20 is electrical coupling;

[0057] Specifically, the structure adopted by the first resonant cavity 10 is capacitive gap coupling and the structure adopted by the second resonant cavity 20 is microstrip open loop internal coupling. The coupling structure between the first resonant cavity and the second resonant cavity is electromagnetic coupling, which has good passband and high suppression of out-of-band selectivity.

[0058] The first resonant cavity is configured to generate a second harmonic of a first resonant frequency, and the second resonant cavity is configured to generate a second harmonic of a second resonant frequency, wherein the first resonant frequency is less than the second resonant frequency.

[0059] For example, the first resonant frequency mentioned above refers to the lower frequency limit of the filter, and the second resonant frequency mentioned above is the upper frequency limit of the filter.

[0060] In this embodiment, the input feeding port P1 of the filtering structure is connected to the first resonant cavity and one end of the first branch (the left end in the figure); the output feeding port P2 is connected to the second resonant cavity and the other end of the first branch (the right end in the figure).

[0061] The resonant frequency generated by the first resonant cavity is f L The second harmonic, f L is the lower limit frequency of the filter; the resonant frequency generated by the second resonant cavity is f H The second harmonic, f H is the upper frequency limit of the filter.

[0062] In an optional embodiment, the first resonant cavity 10 includes a first connecting portion 103, a second connecting portion 105 and a third connecting portion 104, wherein the first connecting portion connects one end of the first branch connected to the input feeding port; the first connecting portion is L-shaped; the first connecting portion 103 includes a first vertical line portion 1031 and a first horizontal line portion 1032 connected to each other, the first vertical line portion 1031 connects one end of the first branch 101 connected to the input feeding port P1; the first vertical line portion 1031 and the first horizontal line portion 1032 are perpendicular to each other to form an "L" shape;

[0063] The second connecting portion 105 includes a second vertical line portion 1051 and a second horizontal line portion 1052 connected to each other. The second vertical line portion 1051 and the second horizontal line portion 1052 are perpendicular to each other. type;

[0064] The first horizontal line portion 1032 is perpendicular to the second vertical line portion 1051 , and the first horizontal line portion 1032 is connected to the end of the second vertical line portion 1051 ;

[0065] The length of the second vertical line portion 1051 is shorter than the length of the first vertical line portion 1031 ; the length of the second horizontal line portion 1052 is shorter than the length of the first horizontal line portion 1032 ;

[0066] The third connection portion 104 is in the shape of an "I", and the third connection portion is parallel to the first horizontal line portion 1032 and the second horizontal line portion 1052; one end of the third connection portion 104 is connected to the first vertical line portion 1031, and the other end of the third connection portion 104 is not connected to the second vertical line portion 1051, that is, there is a gap between the third connection portion and the second vertical line portion; the third connection portion 104 is located between the first horizontal line portion 1032 and the second horizontal line portion 1052; the first horizontal line portion, the second horizontal line portion, and the third connection portion are parallel to the first branch.

[0067] The area enclosed by the first branch 101 , the first connecting portion 103 , the second connecting portion 105 and the third connecting portion 104 forms an “S”-shaped structural unit 201 .

[0068] In this embodiment, the above-mentioned first resonant cavity is a capacitive gap coupling type gradient arm resonator structure (first connecting part 103, second connecting part 104 and third connecting part 105). The first resonant cavity is an inductor-capacitor resonator composed of multiple arms, which is a cascaded multi-stage topology structure. The first resonant cavity is a slow-wave structure, and the slow-wave structure is composed of a cascade of inductors and capacitors.

[0069] Specifically, the first resonant cavity realizes loading capacitance and slow wave effect through coupling at the arm end. The first resonant cavity is a slow wave structure, which is composed of a cascade of microstrip lines equivalent to inductance and capacitance. The slow wave structure can obtain inductance by reducing the line width, and can obtain capacitance by increasing the line width, so the length of the half-wavelength resonator can be reduced. In addition, since the loading capacitance effect can move the spurious response frequency from integer harmonic times of the fundamental wave to higher harmonics, the stopband bandwidth is expanded wider.

[0070] In an optional embodiment, the second resonant cavity includes a fourth connecting portion 102, a fifth connecting portion 107 and a sixth connecting portion 106, the fourth connecting portion 102 includes a fourth vertical line portion 1021 and a fourth horizontal line portion 1022 connected to each other, and the fourth vertical line portion 1021 and the fourth horizontal line portion 1022 are perpendicular to each other to form a The fourth vertical line portion 1021 is connected to one end of the first branch 101 connected to the output feeding port P2;

[0071] The sixth connection portion 106 includes a sixth vertical line portion 1061 and a sixth horizontal line portion 1062 connected to each other. The sixth vertical line portion 1061 and the sixth horizontal line portion 1062 are perpendicular to each other. type;

[0072] The fourth horizontal line portion 1022 is perpendicular to the sixth vertical line portion 1061 , and the fourth horizontal line portion 1022 is connected to an end of the sixth vertical line portion 1061 ;

[0073] The length of the sixth vertical line portion 1061 is shorter than the length of the fourth vertical line portion 1021 ; the length of the sixth horizontal line portion 1062 is shorter than the length of the fourth horizontal line portion 1022 ;

[0074] The fifth connection portion 107 is in the shape of a letter "|". The fifth connection portion 107 is parallel to the fourth vertical line portion 1021 and the sixth vertical line portion 1061. One end of the fifth connection portion 107 is connected to the sixth horizontal line portion 1062, and the other end of the fifth connection portion 107 is not connected to the fourth horizontal line portion 1022, that is, there is a gap between the fifth connection portion 107 and the fourth horizontal line portion 1022. The length of the fifth connection portion 107 is less than the sixth vertical line portion 1061, and the fifth connection portion 107 is located between the fourth vertical line portion 1021 and the sixth vertical line portion 1061.

[0075] The area enclosed by the fourth connecting portion, the fifth connecting portion and the sixth connecting portion forms a “U”-shaped structural unit 202 .

[0076] In this embodiment, similarly, the above-mentioned second resonant cavity is a microstrip open ring internal coupling mode gradient arm resonator structure (the fourth connecting part 102, the fifth connecting part 107 and the sixth connecting part 106), and the second resonant cavity is an inductor and capacitor resonator composed of multiple arms, which is a cascaded multi-stage topology structure. The second resonant cavity is a slow-wave structure, and the slow-wave structure is composed of a cascade of inductors and capacitors.

[0077] Specifically, the second resonant cavity adopts a low impedance coupling structure, a loading capacitor formed between the open ends of the open loop, and a slow wave effect. The second resonant cavity is a slow wave structure, and the slow wave structure is composed of a cascade of microstrip lines equivalent to inductance and capacitance. The slow wave structure can obtain inductance by reducing the line width, and increase the line width to obtain capacitance, so the length of the half-wavelength resonator can be reduced. By adjusting the microstrip open loop loading capacitance, the stopband pole frequency changes with its change.

[0078] In an optional embodiment, the filtering structure is of a "П" type.

[0079] In an optional embodiment, in the filtering structure, the first resonant cavity and the second resonant cavity are internally coupled, and a "T"-shaped structural unit is formed between the first resonant cavity and the second resonant cavity.

[0080] In an optional implementation, the microstrip line impedance of the first branch is 77 ohms.

[0081] In an optional implementation, the input feeding port and the output feeding port have a conical structure.

[0082] In this embodiment, the input feeding port P1 and the output feeding port P2 adopt a tapered gradient line structure instead of a quarter-wavelength impedance transformation line, which reduces the circuit area compared to using a longer quarter-wavelength impedance transformation line.

[0083] In an optional embodiment, the overall size of the filter structure is only 1.4 mm×3 mm, which is a 60% reduction in size compared to traditional filters, while achieving a wider relative bandwidth.

[0084] The filtering structure provided by the embodiment of the present invention can be applied to a low-pass filter, and has the advantages of wide stopband, high suppression, low differential loss, small size, low cost, and convenient processing. Each resonant cavity of the filtering structure adopts a slow-wave structure and internal coupling and capacitor gap coupling modes, thereby reducing the length, achieving miniaturization, and having a higher out-of-band suppression capability. The resonant cavity is a capacitor gap coupling mode based on a tapered arm resonator and a microstrip open loop internal coupling mode structure, and is composed of multiple arms to form an inductor capacitor resonator, which is a cascaded multi-segment topology structure. Each resonant cavity is a slow-wave structure composed of an inductor capacitor cascade. Inductance can be obtained by reducing the line width, and capacitance can be obtained by increasing the line width, thereby reducing the length of the half-wavelength resonator. The filtering technology alleviates the high cost caused by designing filters in limited product space and discrete components, the poor design performance of various types of current microstrip filters, and the large volume. Technical problems, more importantly, can simplify the design of the RF front end of WIFI, improve the anti-interference ability and the communication quality of the whole system.

[0085] Figure 2FIG. 4 shows a schematic diagram of the structure of a filter provided by an embodiment of the present invention. Figure 3 A schematic diagram of the back side of a filter provided for an example implementation of the present invention; Figure 4 A schematic diagram of a three-dimensional structure of a filter provided for an example implementation of the present invention.

[0086] Reference Figure 2 , Figure 3 and Figure 4 The filter comprises a substrate 30 and the above-mentioned filtering structure, wherein the filtering structure is formed on the substrate.

[0087] In an optional implementation manner, the substrate 30 is a PCB board; the substrate 30 is a FR-4 fiberboard.

[0088] In this embodiment, the plate medium of the substrate 30 is selected from conventional FR-4 ordinary Tg130 glass fiber KB-6160, whose relative dielectric constant εr=4.5 and dielectric loss is 0.022.

[0089] Specifically, the filter structure is arranged on the first surface of the substrate 30, and the second surface of the substrate is provided with a ground terminal; the filter can be obtained by etching the filter structure on the first surface of the substrate;

[0090] In this embodiment, the input feeding port P1, the output feeding port P2, the first resonant cavity, the second resonant cavity, the first branch 101, the T-shaped structure unit, the U-shaped structure unit, and the S-shaped structure unit are all formed on the first surface of the substrate, and the ground end is set on the second surface of the substrate as a reference.

[0091] On the first side of the PCB board, a pattern is formed by etching. Figure 1 The filter structure shown forms a ground terminal on the second side of the PCB board as a reference. The grounding requirement is simple and the manufacturing process is easy. The overall size of the actual filter is only 1.4×3mm.

[0092] In an optional embodiment, the substrate 30 is rectangular, and two rows of metal through holes 50 parallel to two long sides of the substrate are arranged on the substrate, and the filtering structure is located between the two parallel rows of metal through holes.

[0093] Specifically, this embodiment provides a filter design case for WiFi 5.8G, the frequency is 5180~5850MHz, see Figure 2The filter is a miniaturized high-suppression coupled cavity filter, comprising an input feeding port P1, an output feeding port P2, a first branch 101, a first resonant cavity 10 and a second resonant cavity 20, wherein the first resonant cavity 10 comprises a first connecting portion 103, a second connecting portion 105, and a third connecting portion 104, wherein the first connecting portion 103 comprises a first vertical line portion 1031 and a first horizontal line portion 1032 connected to each other, and the second connecting portion 105 comprises a second vertical line portion 1051 and a second horizontal line portion 1052 connected to each other. The second horizontal line portion 1052; the second resonant cavity 20 includes a fourth connecting portion 102, a fifth connecting portion 107, and a sixth connecting portion 106, the fourth connecting portion 102 includes a fourth vertical line portion 1021 and a fourth horizontal line portion 1022 connected to each other; the sixth connecting portion 106 includes a sixth vertical line portion 1061 and a sixth horizontal line portion 1062 connected to each other; in the filter, a coupling structure mode "T" type structural unit 203, a "U" type structural unit 202, and an "S" type structural unit 201 are formed.

[0094] The input feeding port P1 is located at the connection between one end of the first branch 101 and the first resonant cavity 10, and the input feeding port P1 and the first resonant cavity 10 (specifically, the first vertical line portion of the first resonant cavity) form a Type structure.

[0095] The output feeding port P2 is located at the connection between the other end of the first branch 101 and the second resonant cavity 20, and the output feeding port P2 and the second resonant cavity 20 (specifically, the fourth vertical line portion of the second resonant cavity) form The structure of the filter composed of each combination is in the shape of "П". Since the resonant cavity is not expanded in one direction, the volume is reduced.

[0096] The first resonant cavity 10 is composed of a first connecting portion 103, a second connecting portion 105, and a third connecting portion 104 branching tapered arms. The second connecting portion 105, the third connecting portion 104 are connected to the first connecting portion 103 to form an "S"-shaped structural unit 201, namely an S-shaped coupled resonant cavity.

[0097] The second resonant cavity is composed of the fourth connecting part 102, the fifth connecting part 107, and the sixth connecting part 106 branching gradual branch arms. The fourth connecting part 102, the fifth connecting part 107 and the sixth connecting part 106 are connected to form a "U"-shaped structural unit 202, that is, a U-shaped coupled resonant cavity.

[0098] In this embodiment, the first resonant cavity is a step impedance resonator (SIR), which is an open-circuit branch-loaded low-pass filter structure with a capacitive gap-coupled resonant cavity, and has a harmonic suppression function. The low-pass filter controls the impedance ratio of the SIR and the center frequency position of the second-order harmonic passband, thereby indirectly achieving the purpose of suppressing the second-order harmonic.

[0099] Specifically, the open branch loaded low pass filter is at a quarter wavelength f L A transmission zero is generated at the frequency, and at even multiples of f L A transmission zero will also be generated at (2N). In order to prevent the transmission zero of the even-multiple frequency from falling in the passband, SIR capacitor gap coupling is used here. By adjusting the impedance ratio of the SIR resonator, the position of the center frequency of the second-order harmonic passband of the filter can be adjusted. This structure can shift the transmission zero of the even-multiple frequency to a higher frequency, which has the advantage of suppressing harmonics.

[0100] Figure 5 The structure diagram of a capacitive gap coupled microstrip SIR resonator provided by an embodiment of the present invention is shown. The SIR resonator structure is symmetrical, the characteristic impedances in the middle and at both ends are Z1 and Z2 respectively, and the electrical lengths are 2θ1 and θ2 respectively. R =2(θ1+θ2), impedance ratio K=Z2 / Z1. When the SIR resonator terminal is open, its input admittance is:

[0101]

[0102] When θ1=θ2=θ, the equal SIR resonator equation is simplified to

[0103]

[0104] According to electromagnetic field theory, when Y in = 0, SIR meets the resonance condition, so K = tan 2 θ, that is, tanθ=K 1 / 2 . Assume the center frequency of the harmonic response is F SN (where n = 1, 2, 3, ...) The corresponding electrical length is θsn, tanθ s1 =∞,tan 2 θ s2 -K=0,tanθ s3 =0, the minimum electrical length of the second-order parasitic passband is π / 2, so f s1 / f0=θ s1 / θ0=π / 2tan -1 K 1 / 2It can be seen that different impedance ratios of the SIR resonator will make the position of its second-order harmonic center frequency different. Therefore, the center frequency of the second-order harmonic passband can be controlled by adjusting the SIR impedance ratio. For example, when the SIR resonator impedance ratio K = 1 / 2, the center frequency of the second-order harmonic passband is 2.55f L Place.

[0105] In this embodiment, the second resonant cavity is a low-pass filter with SIR coupled inside the microstrip open loop, which is similar to an elliptic function filter. It adopts a low-impedance coupling structure. The loading capacitor technology formed by the coupling effect of the open end of the open loop can reduce the electrical length of the resonator, reduce the circuit size and widen the stopband. By adjusting the microstrip loop coupling gap and changing the loading capacitor, the resonant frequency of the microstrip open loop changes with the change of the loop, and the center frequency of the parasitic passband can be moved to solve the periodic frequency response of the transmission line without affecting the passband characteristics. The transmission zero point is obtained at a finite frequency through a quarter-wavelength open line, and the resulting resonant frequency is f H Its lumped parameter equivalent circuit can be found in Figure 6 As shown, L5 can be replaced by a high impedance line, the equivalent capacitor C4 formed by coupling, and the series resonator L4C2 is replaced by a quarter-wavelength open line. The resulting circuit generates a transmission pole 2f at the resonance of L4C2. H .

[0106] It should be noted that the selectivity of the transmission pole is related to the coupling effect. Generally, the smaller the coupling gap, the better the selectivity and the wider the stopband.

[0107] In this embodiment, the structure of the resonant cavity of the filter is capacitor gap coupling and microstrip open loop internal coupling (its equivalent circuit refers to Figure 7 As shown in the figure, the "T"-shaped unit electromagnetic coupling is formed through two resonant cavities, so that the filter has good passband and high suppression band selectivity. The "T"-shaped structural unit has low passband rejection and single-pole resonance characteristics. A single T-shaped structural unit can be equivalent to a band-stop filter with L3 and C3 in parallel. The filter is simulated by EM, as shown in the figure below. Figure 8 As shown, the transmission coefficient S can be obtained 21 , the transmission coefficient S obtained by EM electromagnetic simulation 21 Can be extracted:

[0108]

[0109]

[0110] Where ωc is the 3dB cutoff frequency, ω0 is the resonant frequency, and Z0 is the characteristic impedance of the filter.

[0111] In this equivalent model, the main characteristic of the thin wire above the "horizontal" gap of the "T"-shaped structural unit is the inductance L3 in the equivalent circuit, and the main characteristic of the "vertical" gap of the "T"-shaped structural unit is the capacitance C3 in the equivalent circuit. As the length of the "horizontal" gap of the "T"-shaped structural unit increases, the inductance value L3 increases, and the resonant frequency decreases; the length of the "vertical" gap of the "T"-shaped structural unit increases, which is equivalent to the increase of the capacitance value C3 in the equivalent circuit, resulting in a decrease in the resonant frequency; the width of the "vertical" gap in the "T"-shaped structural unit increases, the capacitance value decreases, and the resonant frequency increases.

[0112] In order to test the performance of the filter, the filter input feed port P1 and output feed port P2 are respectively connected to an external load with an impedance of 50 ohms. Figure 6 shown. Figure 8 The S-parameter simulation diagram of the filter is shown. Figure 8 In the figure, the horizontal axis represents the signal frequency of the filter, the vertical axis of each curve represents different amplitudes, and each m point on the curve is a frequency test point. Figure 8 S(1,1)) and S22 (corresponding to Figure 8 S(2,2)) in the filter respectively represents the parameters of the impedance matching performance of the input feeding port P1 and the output feeding port P2 of the filter; S21 (corresponding to Figure 8 S(2,1)) in the figure represents the forward transmission curve of the filter. It can be seen that the filter has low insertion loss in the passband, high suppression, wide stopband, low cost and small size.

[0113] The filter provided by the embodiment of the present invention is a miniaturized high-suppression coupled cavity filter, comprising an input feeding port, an output feeding port, a first resonant cavity, a second resonant cavity, and a first branch, wherein one end of the first branch connected to the input feeding port is connected to the first resonant cavity; one end of the first branch connected to the output feeding port is connected to the second resonant cavity, thereby applying coupled cavity technology within a limited product space to reduce the order and size of the microstrip filter; in addition, in order to solve the interference of high-order harmonics generated by nonlinear devices of receivers and transmitters when out-of-band signals reach the receiver, the filter has a wider stopband and a larger stopband attenuation, thereby simplifying the design of the front-end radio frequency system and improving the system communication quality of wireless products.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A filtering structure, characterized in that: The filtering structure comprises an input feeding port, an output feeding port, a first branch and a resonant cavity; The resonant cavity comprises a first resonant cavity and a second resonant cavity, the input end feeding port is connected to the output end feeding port through the first branch; one end of the first branch connected to the input end feeding port is connected to the first resonant cavity; one end of the first branch connected to the output end feeding port is connected to the second resonant cavity; The first resonant cavity and the second resonant cavity both adopt a slow-wave structure; The structure of the first resonant cavity is capacitive gap coupling, and the structure of the second resonant cavity is microstrip open loop internal coupling; The coupling mode between the first resonant cavity and the second resonant cavity is electrical coupling; The first resonant cavity is configured to generate a second harmonic of a first resonant frequency, and the second resonant cavity is configured to generate a second harmonic of a second resonant frequency, wherein the first resonant frequency is less than the second resonant frequency.

2. The filtering structure according to claim 1, characterized in that: The filtering structure is in the shape of "П".

3. The filtering structure according to claim 1, characterized in that: A "T"-shaped structural unit is formed between the first resonant cavity and the second resonant cavity.

4. The filtering structure according to claim 1, characterized in that: The first resonant cavity comprises a first connecting portion, a second connecting portion and a third connecting portion, the first connecting portion comprises a first vertical line portion and a first horizontal line portion connected to each other, the first vertical line portion connects one end of the first branch connected to the input end feeding port; the first vertical line portion and the first horizontal line portion are perpendicular to each other to form an "L" shape; The second connecting portion includes a second vertical line portion and a second horizontal line portion connected to each other, and the second vertical line portion and the second horizontal line portion are perpendicular to each other to form a type; The first horizontal line portion is perpendicular to the second vertical line portion, and the first horizontal line portion is connected to an end portion of the second vertical line portion; The length of the second vertical line portion is shorter than the length of the first vertical line portion; the length of the second horizontal line portion is shorter than the length of the first horizontal line portion; The third connection portion is in the shape of a letter "I", and is parallel to the first horizontal line portion and the second horizontal line portion; one end of the third connection portion is connected to the first vertical line portion, and the other end of the third connection portion is not connected to the second vertical line portion, and the third connection portion is located between the first horizontal line portion and the second horizontal line portion; The area enclosed by the first branch, the first connecting portion, the second connecting portion and the third connecting portion forms an "S"-shaped structural unit.

5. The filtering structure according to claim 1, characterized in that: The second resonant cavity includes a fourth connecting portion, a fifth connecting portion and a sixth connecting portion, wherein the fourth connecting portion includes a fourth vertical line portion and a fourth horizontal line portion connected to each other, and the fourth vertical line portion and the fourth horizontal line portion are perpendicular to each other to form Type; the fourth vertical line portion is connected to one end of the first branch connected to the output feeding port; The sixth connecting portion includes a sixth vertical line portion and a sixth horizontal line portion connected to each other, and the sixth vertical line portion and the sixth horizontal line portion are perpendicular to each other to form type; The fourth horizontal line portion is perpendicular to the sixth vertical line portion, and the fourth horizontal line portion is connected to an end of the sixth vertical line portion; The length of the sixth vertical line portion is shorter than the length of the fourth vertical line portion; the length of the sixth horizontal line portion is shorter than the length of the fourth horizontal line portion; The fifth connecting portion is The fifth connecting portion is parallel to the fourth vertical line portion and the sixth vertical line portion; one end of the fifth connecting portion is connected to the sixth horizontal line portion, and the other end of the fifth connecting portion is not connected to the fourth horizontal line portion, and the fifth connecting portion is located between the fourth vertical line portion and the sixth vertical line portion; The area enclosed by the fourth connecting portion, the fifth connecting portion and the sixth connecting portion forms a "U"-shaped structural unit.

6. The filtering structure according to claim 1, characterized in that: The microstrip line impedance of the first branch is 77 ohms.

7. The filtering structure according to claim 1, characterized in that: The input feeding port and the output feeding port adopt a conical structure.

8. A filter, characterized in that: The invention comprises a substrate and a filtering structure as claimed in any one of claims 1 to 7, wherein the filtering structure is formed on the substrate.

9. The filter according to claim 8, characterized in that The substrate is a PCB board; the substrate is selected from FR-4 fiberboard.

10. The filter according to claim 8, characterized in that The substrate is rectangular, and two rows of metal through holes parallel to two long sides of the substrate are arranged on the substrate. The filter structure is located between the two parallel rows of metal through holes.

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