CN112072242A - Filter structure and filter - Google Patents
Filter structure and filter Download PDFInfo
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- CN112072242A CN112072242A CN202011108030.6A CN202011108030A CN112072242A CN 112072242 A CN112072242 A CN 112072242A CN 202011108030 A CN202011108030 A CN 202011108030A CN 112072242 A CN112072242 A CN 112072242A
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- H01P1/20—Frequency-selective devices, e.g. filters
- H01P1/212—Frequency-selective devices, e.g. filters suppressing or attenuating harmonic frequencies
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- H—ELECTRICITY
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Abstract
The invention provides a filtering structure and a filter, which relate to the field of filters and comprise an input end feed port, an output end feed port, a first branch and a resonant cavity; the resonant cavity comprises a first resonant cavity and a second resonant cavity, and the input end feed port is connected with the output end feed port through a first branch; one end of the first branch circuit, which is connected with the input end feed port, is connected with the first resonant cavity; one end of the first branch circuit, which is connected with the output end feed port, is connected with the second resonant cavity; the first resonant cavity and the second resonant cavity adopt slow wave structures; the first resonant cavity and the second resonant cavity are electrically coupled; the first resonant cavity and the second resonant cavity respectively generate second harmonics of the first resonant frequency and the second resonant frequency. The filter structure and the filter have the advantages of wide stop band, high suppression degree, low differential loss, small size, low cost, easiness in processing and the like, and the problems of high cost, poor filter design performance and large size in the prior art are solved.
Description
Technical Field
The invention relates to the technical field of filters used in the field of communication, in particular to a filtering structure and a filter.
Background
With the rapid development of wireless communication technology, higher and higher requirements are put on wireless communication equipment. The filter is widely applied in communication and signal processing processes, and in the field of filters, the designed filter is required to be developed towards a small size as far as possible besides meeting the electrical performance.
At present, although a filter for a wireless communication system is packaged and integrated to a certain extent, a filter designed by a traditional method is generally large in size, and the development requirements of miniaturization, low cost and low loss of the filter of a modern wireless communication system cannot be met. Due to the limitation of the processing technology and the limited product area, it is difficult to actually realize the miniaturization of the filter in design. Low cost, compact, and well-behaved filter design remains a significant challenge in wireless communication systems.
Disclosure of Invention
In view of the above, the present invention provides a filter structure and a filter to alleviate the problem of large size in the prior art.
In order to achieve the above purpose, the embodiment of the present invention adopts the following technical solutions:
in a first aspect, the present invention provides a filtering structure, where the filtering structure includes an input feed port, an output feed port, a first branch, and a resonant cavity;
the resonant cavity comprises a first resonant cavity and a second resonant cavity, and the input end feed port is connected with the output end feed port through the first branch; one end of the first branch circuit connected with the input end feed port is connected with the first resonant cavity; one end of the first branch circuit, which is connected with the output end feed port, is connected with the second resonant cavity;
the first resonant cavity and the second resonant cavity both adopt slow wave structures;
the first resonant cavity and the second resonant cavity are coupled electrically;
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, the first resonant frequency being less than the second resonant frequency.
With reference to the first aspect, this embodiment of the present invention provides a first possible implementation manner of the first aspect, wherein the filtering structure is in a "ii" shape.
With reference to the first aspect, an embodiment of the present invention provides a second possible implementation manner of the first aspect, where a "T" type structural unit is formed between the first resonant cavity and the second resonant cavity.
With reference to the first aspect, an embodiment of the present invention provides a third possible implementation manner of the first aspect, where the first resonant cavity includes a first connection portion, a second connection portion, and a third connection portion, the first connection portion includes a first vertical line portion and a first horizontal line portion that are connected, and the first vertical line portion is connected to one end of the first branch that is connected to the input-end feed port; the first vertical line part and the first transverse line part are perpendicular to each other to form an L shape;
the second connecting part comprises a second vertical line part and a second transverse line part which are connected, and the second vertical line part and the second transverse line part are formed perpendicularly to each other
Molding;
the first transverse line part is vertical to the second vertical line part, and the end part of the first transverse line part is connected with the end part of the second vertical line part;
the length of the second vertical line portion is less than the length of the first vertical line portion; the length of the second crossline portion is less than the length of the first crossline portion;
the third connecting part is in a straight shape and is parallel to the first transverse line part and the second transverse line part; one end of the third connecting part is connected with the first vertical line part, the other end of the third connecting part is not connected with the second vertical line part, and the third connecting part is positioned between the first transverse line part and the second transverse line part;
and an S-shaped structural unit is formed in the area enclosed by the first branch, the first connecting part, the second connecting part and the third connecting part.
With reference to the first aspect, an embodiment of the present invention provides a fourth possible implementation manner of the first aspect, where the second resonant cavity includes a fourth connection portion, a fifth connection portion, and a sixth connection portion, the fourth connection portion includes a fourth vertical line portion and a fourth horizontal line portion that are connected to each other, and the fourth vertical line portion and the fourth horizontal line portion are formed perpendicular to each other
Molding; the fourth vertical line part is connected with one end of the first branch circuit connected with the output end feed port;
the sixth connecting part comprises a sixth vertical line part and a sixth transverse line part which are connected, and the sixth vertical line part and the sixth transverse line part are formed perpendicularly to each other
Molding;
the fourth transverse line part is vertical to the sixth vertical line part, and the fourth transverse line part is connected with the end part of the sixth vertical line part;
a length of the sixth riser portion is less than a length of the fourth riser portion; the length of the sixth crossline portion is less than the length of the fourth crossline portion;
the fifth connecting part is in a shape of a Chinese character 'i', and the fifth connecting part is parallel to the fourth vertical line part and the sixth vertical line part; one end of the fifth connecting part is connected with the sixth transverse line part, the other end of the fifth connecting part is not connected with the fourth transverse line part, and the fifth connecting part is positioned between the fourth vertical line part and the sixth vertical line part;
the area enclosed by the fourth connecting part, the fifth connecting part and the sixth connecting part forms a U-shaped structural unit.
With reference to the first aspect, an embodiment of the present invention provides a fifth possible implementation manner of the first aspect, where the microstrip line impedance of the first branch is 77 ohms.
With reference to the first aspect, an embodiment of the present invention provides a sixth possible implementation manner of the first aspect, where the input end feed port and the output end feed port adopt a tapered structure.
In a second aspect, an embodiment of the present invention further provides a filter, including a substrate and the filter structure as described above, where the filter structure is formed on the substrate.
With reference to the second aspect, an embodiment of the present invention provides a first possible implementation manner of the second aspect, wherein the substrate is a PCB; the substrate is made of FR-4 fiberboard.
With reference to the second aspect, an embodiment of the present invention provides a second possible implementation manner of the second aspect, where the substrate is rectangular, two rows of metal vias parallel to two long sides of the substrate are arranged on the substrate, and the filter structure is located between the two parallel rows of metal vias.
The embodiment of the invention has the following beneficial effects: the filtering structure and the filter provided by the embodiment of the invention comprise an input end feed port, an output end feed port, a first branch and a resonant cavity; the resonant cavity comprises a first resonant cavity and a second resonant cavity, and the input end feed port is connected with the output end feed port through the first branch; one end of the first branch circuit connected with the input end feed port is connected with the first resonant cavity; one end of the first branch circuit, which is connected with the output end feed port, is connected with the second resonant cavity; the first resonant cavity and the second resonant cavity both adopt slow wave structures; the first resonant cavity and the second resonant cavity are coupled electrically; 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, the first resonant frequency being less than the second resonant frequency. According to the technical scheme provided by the embodiment of the invention, each resonant cavity is designed into a slow wave structure, and the resonant cavities are internally coupled and electrically coupled, so that the length of the resonant cavity is reduced, the miniaturization of equipment is facilitated, and the out-of-band inhibition capability is higher; while the size is greatly reduced relative to the conventional filter, a wider relative bandwidth is obtained. The filter structure and the filter have the advantages of wide stop band, high suppression degree, low differential loss, small size, low cost, easy processing and the like, and can solve the problems of high cost, poor filter design performance and large volume caused by designing the filter in limited product space and discrete components in the prior art.
In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a schematic diagram of a filter structure according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a filter according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a back side of a filter according to an embodiment of the present invention;
fig. 4 is a schematic three-dimensional structure diagram of a filter according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of a capacitive gap-coupled microstrip SIR resonator according to an embodiment of the present invention;
fig. 6 is an equivalent circuit diagram of a filter according to an embodiment of the present invention;
FIG. 7 is an equivalent circuit diagram of a resonant cavity according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a simulation result of S parameter of a filter according to an embodiment of the present invention.
Detailed Description
In order to make the objects, 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 with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings or the orientations or positional relationships that the products of the present invention are conventionally placed in use, and are only used for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," "third," and the like are used solely to distinguish one from another and are not to be construed as indicating or implying relative importance.
Furthermore, the terms "horizontal", "vertical", "overhang" and the like do not imply that the components are required to be absolutely horizontal or overhang, but may be slightly inclined. For example, "horizontal" merely means that the direction is more horizontal than "vertical" and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.
In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly and may, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
With the development of Wireless Fidelity (Wi-Fi) communication technology and Wireless communication technology, filters are widely applied in communication and signal processing processes, the requirements of radio frequency front end design on signal selectivity and in-band and out-band are higher and higher, and especially the design of filters puts forward higher requirements: such as high performance, miniaturization, low cost, effectively filtering various useless signals and stray signals, and reducing signal interference among communication channels.
In recent years, compared with other fields, the WIFI communication technology is rapidly developed, more and more spectrum resources exist in product design, the higher the frequency is, the stronger the interference is, the larger the generated harmonic and high-order stray power are, and the design difficulty of the radio frequency filter is brought, so that higher requirements are put forward on the filter: for example, wide stop band, good in-band amplitude-frequency characteristics, high out-of-band rejection and low cost.
At present, a filter is designed by adopting discrete components, the filter is widely applied to a radio frequency circuit, but the filter obtains higher out-of-band rejection characteristics, the order of the filter needs to be increased, the cost is increased due to the increase of the order, and microstrip filters are more and more applied and designed, wherein the interdigital mode, the parallel coupling and the hairpin type have flatter amplitude-frequency characteristics in band but occupy large space, and the out-of-band of the ellipse-like structure has higher selectivity but is not suitable for the design of higher frequency; based on this, the embodiment of the present invention provides a filtering structure and a filter, and compared with a filter and various microstrip filters designed by using discrete components in the existing scheme, the filtering structure and the filter scheme can achieve low insertion loss in band, good selectivity, high out-of-band rejection degree, low cost, and can also achieve the solution of size design difficulty on the limited product area, and alleviate the defects of the existing communication product that the selectivity of the radio frequency front end channel and the filter formed by the used discrete devices are high in cost and the design is caused by the structure and performance of various microstrip filters. In addition, for the design of the radio frequency front end of a WIFI product, the finished product is gradually miniaturized and integrated, various high-speed interfaces, such as DDR3, PCIE, USB3.0, PHY, SGMII, PGMII, SFP, etc., and communication frequency spectrums of each public network, local oscillation frequency and high-order harmonic of a radio frequency chip themselves are easily radiated and interfered with each other through space, resulting in nonlinearity of the radio frequency front end, therefore, a filter designed by the radio frequency front end requires a wide stop band, a high suppression degree, a low differential loss, a small size and a low cost.
Some embodiments of the invention are described in detail below with reference to the accompanying drawings. The embodiments described below and the features of the embodiments can be combined with each other without conflict.
Fig. 1 shows a schematic diagram of a filtering structure provided in an embodiment of the present invention.
Referring to fig. 1, the filtering structure includes an input feed port P1, an output feed port P2, a first branch 101, and a resonant cavity;
the resonant cavities comprise a first resonant cavity 10 and a second resonant cavity 20, and the input end feed port P1 is connected with the output end feed port P2 through the first branch 101; one end of the first branch 101 connected to the input end feed port P1 is connected to the first resonant cavity 10; one end of the first branch 101 connected to the output end feed port P2 is connected to the second resonant cavity 20;
wherein, the first resonant cavity 10 and the second resonant cavity 20 both adopt slow wave structures;
it should be noted that the slow-wave structure may be a spiral line structure or a meander line structure, and fig. 1 shows only an exemplary slow-wave structure.
The coupling mode between the first resonant cavity 10 and the second resonant cavity 20 is electric coupling;
specifically, the first resonant cavity 10 is structured in a capacitive gap coupling manner, the second resonant cavity 20 is structured in a microstrip open-loop inner coupling manner, and the first resonant cavity and the second resonant cavity are coupled in an electromagnetic coupling manner, so that the microstrip open-loop inner coupling structure has a good passband and a high suppression out-of-band selectivity.
The first resonant cavity is configured to generate a second harmonic of the first resonant frequency and the second resonant cavity is configured to generate a second harmonic of the second resonant frequency, the first resonant frequency being less than the second resonant frequency.
For example, the first resonant frequency is a lower limit frequency of the filter, and the second resonant frequency is an upper limit frequency of the filter.
In this embodiment, the input feed port P1 of the filtering structure is connected to the first resonant cavity and one end (left end in the figure) of the first branch; and the output end feeding port P2 is connected with the second resonant cavity and the other end (the right end in the figure) of the first branch.
The first resonant cavity generates a resonant frequency fLSecond harmonic of (f)LIs the lower limit frequency point of the filter; the second resonant cavity generates a resonant frequency fHSecond harmonic of (f)HIs the upper limit frequency point of the filter.
In an alternative embodiment, the first resonant cavity 10 includes a first connection portion 103, a second connection portion 105, and a third connection portion 104, where the first connection portion connects one end of the first branch connected to the input feed port; the first connecting part is L-shaped; the first connection portion 103 includes a first vertical line portion 1031 and a first horizontal line portion 1032 connected to each other, and the first vertical line portion 1031 connects one end of the first branch 101 connected to the input end feed port P1; the first vertical line part 1031 and the first horizontal line part 1032 are perpendicular to each other to form an "L" shape;
the second connecting portion 105 includes a second vertical line portion 1051 and a second horizontal line portion 1052 connected to each other, and the second vertical line portion 1051 and the second horizontal line portion 1052 are formed perpendicular to each other
Molding;
the first transverse line part 1032 is perpendicular to the second vertical line part 1051, and the first transverse line part 1032 is connected with the end part of the second vertical line part 1051;
the length of the second vertical line portion 1051 is less than the length of the first vertical line portion 1031; the length of the second transverse line 1052 is less than the length of the first transverse line 1032;
the third connecting portion 104 is in a line shape, and the third connecting portion is parallel to the first horizontal line portion 1032 and the second horizontal line portion 1052; one end of the third connecting portion 104 is connected to the first vertical line portion 1031, and the other end of the third connecting portion 104 is not connected to the second vertical line portion 1051, that is, there is a gap between the third connecting portion and the second vertical line portion; the third connecting portion 104 is located between the first horizontal line portion 1032 and the second horizontal line portion 1052; the first horizontal line part, the second horizontal line part and the third connecting part are parallel to the first branch.
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.
In this embodiment, the first resonant cavity is a capacitance-gap coupling type graded arm resonator structure (the first connection portion 103, the second connection portion 104, and the third connection portion 105), the first resonant cavity is an inductance-capacitance resonator formed by multiple arms, and is a cascade multi-section topology structure, the first resonant cavity is a slow-wave structure, and the slow-wave structure is formed by inductance-capacitance cascade.
Specifically, the first resonant cavity is coupled through a support arm end to realize capacitance loading and a slow wave effect, the first resonant cavity is of a slow wave structure, the slow wave structure is formed by cascading microstrip lines which are equivalent to inductance and capacitance, the slow wave structure can obtain the inductance by reducing the line width, and can obtain the capacitance by increasing the line width, so that the length of the half-wavelength resonator can be reduced. In addition, the loaded capacitance effect can shift the stray response frequency from integral harmonic times of the fundamental wave to higher harmonic, so that the bandwidth of the stop band is expanded more widely.
In an alternative 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 which are connected, and the fourth vertical line portion 1021 and the fourth horizontal line portion 1022 are perpendicular to each other to form the fourth vertical line portion 1021 and the fourth horizontal line portion 1022
Molding; the fourth vertical line portion 1021 is connected to one end of the first branch 101 connected to the output end feed port P2;
the sixth connecting portion 106 includes a sixth vertical line portion 1061 and a sixth horizontal line portion 1062 connected to each other, and the sixth vertical line portion 1061 and the sixth horizontal line portion 1062 are perpendicular to each other to form
Molding;
the fourth horizontal line part 1022 is perpendicular to the sixth vertical line part 1061, and the fourth horizontal line part 1022 is connected to an end of the sixth vertical line part 1061;
the length of the sixth vertical line part 1061 is less than the length of the fourth vertical line part 1021; the length of the sixth transverse line part 1062 is less than that of the fourth transverse line part 1022;
the fifth connecting portion 107 is in a shape of a character |, and the fifth connecting portion 107 is parallel to the fourth vertical line portion 1021 and the sixth vertical line portion 1061; one end of the fifth connecting portion 107 is connected to the sixth horizontal line portion 1062, and the other end of the fifth connecting portion 107 is not connected to the fourth horizontal line portion 1022, that is, a gap exists between the fifth connecting portion 107 and the fourth horizontal line portion 1022, the length of the fifth connecting portion 107 is smaller than that of the sixth vertical line portion 1061, and the fifth connecting portion 107 is located between the fourth vertical line portion 1021 and the sixth vertical line portion 1061;
the area enclosed by the fourth connecting part, the fifth connecting part and the sixth connecting part forms a U-shaped structural unit 202.
In this embodiment, similarly, the second resonant cavity is a microstrip open-loop internal coupling mode tapered arm resonator structure (the fourth connection portion 102, the fifth connection portion 107, and the sixth connection portion 106), the second resonant cavity is an inductor-capacitor resonator formed by multiple arms and is a cascaded multi-stage topology structure, the second resonant cavity is a slow-wave structure, and the slow-wave structure is formed by inductor-capacitor cascading.
Specifically, the second resonant cavity adopts a low-impedance coupling structure, a loading capacitor and a slow wave effect are formed between open ends of the open loop, the second resonant cavity is of a slow wave structure, the slow wave structure is formed by cascading microstrip lines which are equivalent to an inductor and a capacitor, the inductor can be obtained by reducing the line width of the slow wave structure, the capacitor can be obtained by increasing the line width, and therefore the length of the half-wavelength resonator can be reduced. The frequency of the stop band pole is changed along with the change of the capacitance loaded by the microstrip open loop.
In an alternative embodiment, the filtering structure is of the "pi" type.
In an alternative embodiment, the filter structure has an internal coupling between the first resonant cavity and the second resonant cavity, and a "T" shaped structural unit is formed between the first resonant cavity and the second resonant cavity.
In an alternative embodiment, the microstrip line impedance of the first branch is 77 ohms.
In an alternative embodiment, the input and output feed ports are tapered.
In this embodiment, the input feed port P1 and the output feed port P2 have a tapered-gradient structure, and do not use a quarter-wavelength impedance transformation line, which reduces the circuit area compared to a longer quarter-wavelength impedance transformation line.
In an alternative embodiment, the overall size of the filter structure is only 1.4mm x 3mm, which is a 60% reduction in size compared to conventional filters, while obtaining a wider relative bandwidth.
The filtering structure provided by the embodiment of the invention can be applied to a low-pass filter, and has the advantages of wide stop band, high suppression degree, low differential loss, small size, low cost, convenience in processing and the like. Each resonant cavity of the filtering structure adopts a slow wave structure and an internal coupling and capacitance gap coupling mode, thereby reducing the length, realizing miniaturization and higher out-of-band inhibition capability, the resonant cavity is a structure based on a capacitance gap coupling mode of a gradually-changed arm resonator and an internal coupling mode of a micro-strip open-circuit ring, an inductance-capacitance resonator is formed by a plurality of arms and is a cascade multi-section topological structure, each resonant cavity is a slow-wave structure formed by inductance-capacitance cascade connection, inductance is obtained by reducing the line width, and capacitance is obtained by increasing the line width, so that the length of the half-wavelength resonator can be reduced, the filtering technology relieves the technical problems of high cost caused by designing the filter in limited product space and discrete components, poor design performance and large volume of various microstrip filters at present, and more importantly, the design of the radio frequency front end of WIFI can be simplified, and the interference resistance and the communication quality of the whole system are improved.
Fig. 2 is a schematic structural diagram of a filter according to an embodiment of the present invention, and fig. 3 is a schematic back side diagram of a filter according to an embodiment of the present invention; fig. 4 is a schematic three-dimensional structure diagram of a filter according to an embodiment of the present invention.
With reference to fig. 2,3 and 4, the filter comprises a substrate 30 and the above-mentioned filter structure, which is formed on said substrate.
In an alternative embodiment, the substrate 30 is a PCB; the substrate 30 is made of FR-4 fiberboard.
In this embodiment, the board medium of the substrate 30 is made of FR-4 ordinary Tg130 glass fiber KB-6160, which has a relative dielectric constant r of 4.5 and a dielectric loss of 0.022.
Specifically, the filter structure is disposed on a first surface of the substrate 30, and a ground terminal is disposed on a second surface of the substrate; the filter can be obtained by etching the filter structure on the first surface of the substrate;
in this embodiment, the input feed port P1, the output feed port P2, the first resonant cavity, the second resonant cavity, the first branch 101, the T-shaped structural unit, the U-shaped structural unit, and the S-shaped structural unit are all formed on the first surface of the substrate, and the ground terminal is disposed on the second surface of the substrate as a reference.
The filtering structure shown in fig. 1 is formed on the first surface of the PCB by etching, and the grounding end is formed on the second surface of the PCB as a reference, so that the grounding requirement is simple and the process is easy to manufacture, and the overall size of the filter is only 1.4 × 3 mm.
In an alternative embodiment, the substrate 30 is rectangular, two rows of metal vias 50 are arranged on the substrate parallel to two long sides of the substrate, and the filter structure is located between the two parallel rows of metal vias.
Specifically, this embodiment provides a design case of a WiFi 5.8G filter, the frequency is 5180-5850 MHz, see fig. 2, the filter is a miniaturized high-rejection coupled cavity filter, and includes an input feed port P1, an output feed port P2, a first branch 101, a first resonant cavity 10 and a second resonant cavity 20, where the first resonant cavity 10 includes a first connection portion 103, a second connection portion 105, and a third connection portion 104, the first connection portion 103 includes a first vertical line portion 1031 and a first horizontal line portion 1032 that are connected, and the second connection portion 105 includes a second vertical line portion 1051 and a second horizontal line portion 1052 that are connected; 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 which are connected; the sixth connecting portion 106 includes a sixth vertical line portion 1061 and a sixth horizontal line portion 1062 connected to each other; in this filter, a coupling structure type "T" configuration unit 203, "U" configuration unit 202, "S" configuration unit 201 are formed.
Input terminalThe feeding port P1 is located at a connection between one end of the first branch 101 and the first resonant cavity 10, and the input end feeding port P1 and the first resonant cavity 10 (specifically, the first vertical line portion of the first resonant cavity) form a
And (4) a mold structure.
The output end 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 end feeding port P2 and the second resonant cavity 20 (specifically, the fourth vertical line part of the second resonant cavity) form a
The structure shape of each combined filter is of a 'II' shape, and the volume is reduced because the resonant cavity is not unfolded in one direction.
The first resonant cavity 10 is composed of a first connection portion 103, a second connection portion 105, and a third connection portion 104, and the second connection portion 105 and the third connection portion 104 are connected to the first connection portion 103 to form an S-shaped structure unit 201, i.e., an S-shaped coupling resonant cavity.
The second resonant cavity is composed of a fourth connecting part 102, a fifth connecting part 107 and a sixth connecting part 106, and 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, namely a U-shaped coupling resonant cavity.
In this embodiment, the first resonant cavity is a Step Impedance Resonator (SIR), which is a low-pass filter structure with open stub loading of a capacitive gap coupled resonant cavity, and has a function of suppressing harmonics. The low-pass filter indirectly achieves the purpose of inhibiting second-order harmonic waves by controlling the impedance ratio of SIR and the central frequency position of a second-order harmonic wave pass band.
Specifically, the low-pass filter loaded with open-circuit branches is at a quarter wavelength fLGenerating a transmission zero at the frequency, at even frequency multiplication fLA transmission zero point is also generated at the position (2N), and in order to avoid the transmission zero point of even frequency multiplication falling in a pass band, S is adoptedThe position of the central frequency of the second harmonic pass band of the filter can be adjusted by adjusting the impedance ratio of the SIR resonator through IR capacitance gap coupling. The structure can shift the even frequency multiplication transmission zero point to higher frequency offset, and has the advantage of harmonic suppression.
FIG. 5 is a schematic diagram of a capacitive gap-coupled microstrip SIR resonator according to an embodiment of the present invention, where the SIR resonator has a symmetrical structure and characteristic impedances Z at the middle and both ends1And Z2Each having an electrical length of 2 theta1And theta2，θR＝2(θ1+θ2) Impedance ratio K ═ Z2/Z1. The input admittance of the SIR resonator when the terminal is open is as follows:
when theta 1 is equal to theta 2, the equal SIR resonator formula is simplified to be
According to the electromagnetic field theory as YinWhen 0, the SIR satisfies the resonance condition so that K is tan2Theta, i.e. tan theta-K1/2. Let the harmonic response center frequency be FSN(where n is 1,2,3, …) corresponds to an electrical length θ sn, tan θs1＝∞，tan2θs2-K＝0，tanθs3The electrical length of the second order parasitic passband is at a minimum of pi/2, so there is fs1/f0＝θs1/θ0＝π/2tan-1K1/2It can be seen that different impedance ratios of the SIR resonators will cause the second order harmonic center frequencies to be located differently, and therefore the center frequency of the second order harmonic passband can be controlled by adjusting the impedance ratio of the SIR. For example, when SIR resonator impedance ratio K is 1/2, the center frequency of the second order harmonic passband is 2.55fLTo (3).
In this embodiment, the second resonant cavity is a low-pass filter with an SIR coupled inside the open-loop microstripSimilar to an elliptic function filter, the electric length of the resonator can be reduced, the circuit size can be reduced, and the stop band can be widened by adopting a low-impedance coupling structure and a loading capacitance technology formed by the coupling effect of the open end of the open loop. By adjusting the coupling gap of the microstrip ring and changing the loading capacitance, the resonance frequency of the microstrip open-circuit ring changes along with the change of the ring, the center frequency of the parasitic passband can be moved, the periodic frequency response of the transmission line is solved, and the characteristic of the passband is not influenced. Obtaining transmission zero at finite frequency by means of quarter-wave open circuit, resulting in resonant frequency fH. Lumped parameter equivalent circuit referring to fig. 6, L5 can be replaced by a high impedance line, the equivalent capacitance C4 formed by coupling, and the series resonator L4C2 is replaced by a quarter-wave open line. The resulting circuit produces a transmission pole 2f at the L4C2 resonanceH。
It should be noted that the selectivity of the transmission pole is related to the coupling effect, and generally, the coupling gap is reduced, the better the selectivity is, and the wider the stop band is.
In this embodiment, in the filter, the resonant cavities are configured in a capacitive gap coupling manner and a microstrip open-loop internal coupling manner (an equivalent circuit thereof is shown in fig. 7), and a "T" type unit electromagnetic coupling manner is formed by 2 resonant cavities, so that the filter has a better passband and a high suppression out-of-band selectivity. The T-shaped structural unit has low-pass band-stop and single-pole resonance characteristics, wherein a single T-shaped structural unit can be equivalent to a band-stop filter with L3 and C3 connected in parallel, EM (electromagnetic simulation) is carried out on the filter, and as shown in figure 8, a transmission coefficient S can be obtained21Transmission coefficient S obtained by EM electromagnetic simulation21Can extract:
where ω c is the 3dB cutoff frequency, ω 0 is the resonance frequency, and Z0 is the characteristic impedance of the filter.
In the equivalent model, the main characteristic of the thin wire above the slot of the T-shaped structural unit is inductance L3 in the equivalent circuit, and the main characteristic of the slot of the T-shaped structural unit is capacitance C3 in the equivalent circuit. The length of a transverse gap of the T-shaped structural unit is increased, the inductance value L3 is increased, and the resonant frequency is reduced; the length of a vertical gap of the T-shaped structural unit is increased, which is equivalent to the increase of a capacitance value C3 in an equivalent circuit, so that the resonant frequency is reduced; the width of a vertical gap in the T-shaped structural unit is increased, the capacitance is reduced, and the resonant frequency is increased.
To test the performance of the filter, the input feed port P1 and the output feed port P2 of the filter were used to externally connect a load with an impedance of 50 ohms, respectively, as shown in fig. 6. Fig. 8 shows an S-parameter simulation diagram of the filter. In fig. 8, the horizontal axes each represent the signal frequency of the filter, the vertical axes of the respective curves represent different amplitudes, and the m points on the curves are frequency test points. S11 (corresponding to S (1,1) in fig. 8) and S22 (corresponding to S (2,2) in fig. 8) respectively represent parameters of the input feed port P1 and output feed port P2 impedance matching performance of the filter; s21 (corresponding to S (2,1) in fig. 8) represents the forward transmission curve of the filter. Therefore, the filter has the characteristics of low insertion loss in a pass band, high suppression degree, wider stop band, low cost, small size and the like.
The filter provided by the embodiment of the invention is a miniaturized high-suppression coupled cavity filter, and comprises an input end feed port, an output end feed port, a first resonant cavity, a second resonant cavity, a first branch, and a second branch, wherein one end of the first branch, which is connected with the input end feed port, is connected with the first resonant cavity; one end of the first branch circuit, which is connected with the output end feed port, is connected with the second resonant cavity, so that the order and the size of the microstrip filter are reduced by applying a coupled cavity technology in a limited product space; in addition, in order to solve the interference of high-order harmonics generated when an out-of-band signal reaches nonlinear devices of a receiver and a transmitter, the filter has a wider stop band and larger stop band attenuation, so that the design of a front-end radio frequency system is simplified, and the system communication quality of a wireless product is improved.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A filtering structure is characterized by comprising an input end feed port, an output end feed port, a first branch and a resonant cavity;
the resonant cavity comprises a first resonant cavity and a second resonant cavity, and the input end feed port is connected with the output end feed port through the first branch; one end of the first branch circuit connected with the input end feed port is connected with the first resonant cavity; one end of the first branch circuit, which is connected with the output end feed port, is connected with the second resonant cavity;
the first resonant cavity and the second resonant cavity both adopt slow wave structures;
the first resonant cavity and the second resonant cavity are coupled electrically;
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, the first resonant frequency being less than the second resonant frequency.
2. The filtering structure according to claim 1, characterized in that said filtering structure is of the "pi" type.
3. The filtering structure according to claim 1, wherein 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, wherein the first resonant cavity comprises a first connection portion, a second connection portion and a third connection portion, the first connection portion comprises a first vertical line portion and a first horizontal line portion which are connected, and the first vertical line portion is connected with one end of the first branch circuit connected with the input end feed port; the first vertical line part and the first transverse line part are perpendicular to each other to form an L shape;
the second connecting part comprises a second vertical line part and a second transverse line part which are connected, and the second vertical line part and the second transverse line part are formed perpendicularly to each other
Molding;
the first transverse line part is vertical to the second vertical line part, and the end part of the first transverse line part is connected with the end part of the second vertical line part;
the length of the second vertical line portion is less than the length of the first vertical line portion; the length of the second crossline portion is less than the length of the first crossline portion;
the third connecting part is in a straight shape and is parallel to the first transverse line part and the second transverse line part; one end of the third connecting part is connected with the first vertical line part, the other end of the third connecting part is not connected with the second vertical line part, and the third connecting part is positioned between the first transverse line part and the second transverse line part;
and an S-shaped structural unit is formed in the area enclosed by the first branch, the first connecting part, the second connecting part and the third connecting part.
5. The filtering structure according to claim 1, wherein the second resonant cavity comprises a fourth connecting portion, a fifth connecting portion and a sixth connecting portion, the fourth connecting portion comprises a fourth vertical line portion and a fourth horizontal line portion which are connected, and the fourth vertical line portion and the fourth horizontal line portion are formed perpendicularly to each other
Molding; the fourth vertical line part is connected with one end of the first branch circuit connected with the output end feed port;
the sixth connecting part comprises a sixth vertical line part and a sixth transverse line part which are connected, and the sixth vertical line part and the sixth transverse line part are formed perpendicularly to each other
Molding;
the fourth transverse line part is vertical to the sixth vertical line part, and the fourth transverse line part is connected with the end part of the sixth vertical line part;
a length of the sixth riser portion is less than a length of the fourth riser portion; the length of the sixth crossline portion is less than the length of the fourth crossline portion;
the fifth connecting part is in a shape of a Chinese character 'i', and the fifth connecting part is parallel to the fourth vertical line part and the sixth vertical line part; one end of the fifth connecting part is connected with the sixth transverse line part, the other end of the fifth connecting part is not connected with the fourth transverse line part, and the fifth connecting part is positioned between the fourth vertical line part and the sixth vertical line part;
the area enclosed by the fourth connecting part, the fifth connecting part and the sixth connecting part forms a U-shaped structural unit.
6. The filtering structure according to claim 1, wherein the microstrip line impedance of the first branch is 77 ohms.
7. The filtering structure according to claim 1, characterized in that said input and output feed ports are tapered.
8. A filter comprising a substrate and a filter structure according to any of claims 1-7, the filter structure being formed on the substrate.
9. The filter of claim 8, wherein the substrate is a PCB board; the substrate is made of FR-4 fiberboard.
10. The filter according to claim 8, wherein the substrate is rectangular, two rows of metal vias are arranged on the substrate parallel to two long sides of the substrate, and the filter structure is located between the two parallel rows of metal vias.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113161740A (en) * | 2021-03-03 | 2021-07-23 | 佛山市粤海信通讯有限公司 | Isolation circuit structure of calibration port and RAE port |
| WO2022141439A1 (en) * | 2020-12-31 | 2022-07-07 | 华为技术有限公司 | Filter, feed network, and antenna |
| CN116706479A (en) * | 2023-07-10 | 2023-09-05 | 中科芯集成电路有限公司 | High near-end suppression low-pass filter |
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| CN107425250A (en) * | 2017-05-03 | 2017-12-01 | 华南理工大学 | A kind of plane Wide stop bands double frequency filter |
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| WO2012162972A1 (en) * | 2011-05-27 | 2012-12-06 | 华南理工大学 | Balanced radio frequency electrically tunable band-pass filter with constant absolute bandwidth |
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