Adjustable electromagnetic hybrid coupling filter
Technical Field
The invention relates to an electromagnetic hybrid coupling filter, in particular to an adjustable electromagnetic hybrid coupling filter capable of correcting transmission zero positions.
Background
The electromagnetic hybrid coupling technology is a method for improving the out-of-band rejection of a filter by generating a transmission zero point by utilizing the simultaneous electric coupling and magnetic coupling on a coupling path between adjacent resonant cavities. Theoretically, an Nth order filter can have at most N-1 sets of electromagnetic hybrid couplings, producing N-1 transmission zeros, much more than an Nth order filter designed using cross-coupling or source-load coupling techniques.
The frequencies of transmission zeros of the existing electromagnetic hybrid structure are all related to the frequencies of adjacent resonators, and when the passband of the filter is wide, the transmission zeros are difficult to be concentrated near the passband, namely, high out-of-band rejection cannot be realized at the near end of the passband.
Another international patent application, PCT/EP2015/065916a1, discloses a coaxial cavity filter that provides one or more transmission nodes without the need for a bypass connector that provides a direct ohmic connection between non-adjacent conductors by providing inductive cross-coupling between the non-adjacent conductors. However, the above patent still has the following disadvantages: 1. the volume is large; 2. the capacitive coupling and the resonant frequency are both related to the height of the resonant column, and are difficult to tune independently; 3. and the part of the device is sensitive in size and has higher requirement on processing precision.
Another patent application No. CN200810027449.1 discloses a controllable electromagnetic hybrid coupled coaxial cavity filter, which realizes elliptic function filtering characteristics with a coaxial cavity filter having only a main coupling path, but has the following drawbacks: 1. the resonance column needs capacitance loading to reduce frequency and has larger volume; 2. the intermodulation index of the system is deteriorated by adopting the dielectric substrate; 3. the coupling assembly is installed on the top end of the resonance column and is not easy to adjust.
Therefore, a new electromagnetic hybrid coupling filter needs to be researched to solve the technical defects involved in the background art.
Disclosure of Invention
The present invention is directed to overcome the drawbacks of the prior art, and to provide a tunable electromagnetic hybrid coupling filter, which improves the performance of the electromagnetic hybrid coupling filter by adding a coupling compensation structure.
In order to achieve the purpose, the invention provides the following technical scheme: an adjustable electromagnetic hybrid coupling filter comprises a cavity, at least three resonance columns, at least one capacitive coupling structure, at least one inductive coupling structure and a compensation structure, wherein the resonance columns are fixed in the cavity, and the generated resonance frequency is adjustable; a capacitive coupling structure and an inductive coupling structure are arranged between two adjacent resonance columns, and the capacitive coupling quantity of the capacitive coupling structure and the inductive coupling quantity of the inductive coupling structure are adjustable; the two coupling structures exist simultaneously to jointly form an electromagnetic hybrid coupling structure, the compensation structure is connected with the two nonadjacent resonance columns, and capacitive and/or inductive coupling is generated between the nonadjacent resonance columns.
Preferably, the cavity is a closed metal cavity, and includes a top cavity wall and a bottom cavity wall, the resonant column is vertically fixed on the bottom cavity wall of the cavity, and a gap is left between the top end of the resonant column and the top cavity wall of the cavity.
Preferably, a plurality of frequency adjusting screws are fixed on the top cavity wall of the cavity, each frequency adjusting screw corresponds to one resonant column, and the resonant frequency of each resonant column is adjusted through the corresponding frequency adjusting screw.
Preferably, the capacitive coupling structure comprises a first capacitive coupling piece and a capacitive coupling adjusting screw, wherein the first capacitive coupling piece is connected with two adjacent resonance columns and is in insulation connection with the resonance columns; the capacitive coupling adjusting screw is fixed on the top cavity wall of the cavity and is opposite to the first capacitive coupling piece.
Preferably, a first insulator is disposed between the first capacitive coupling element and the resonant column, and the first capacitive coupling element is connected to the resonant column through the first insulator.
Preferably, the first capacitive coupling parts are close to the top end of the resonant column, and two adjacent first capacitive coupling parts are staggered up and down or staggered front and back.
Preferably, the inductive coupling structure includes an inductive coupling conductor and an inductive coupling adjusting screw, the inductive coupling conductor is located at the bottom between two adjacent resonant columns, and the inductive coupling adjusting screw is disposed on the inductive coupling conductor.
Preferably, the compensation structure comprises an inductive compensation structure and/or a capacitive compensation structure, two ends of the inductive compensation structure are connected with the two nonadjacent resonance columns, and the capacitive compensation structure is connected with the two nonadjacent resonance columns in an insulating manner.
Preferably, the capacitive compensation structure comprises a second capacitive coupling piece and a second insulating piece, and at least one end of the second capacitive coupling piece is connected with the resonance column in an insulating mode through the second insulating piece.
Preferably, the first capacitive coupling element is clamped between the gaps of two adjacent resonant columns.
Preferably, the number of the resonance columns bridged by the inductive compensation structure and the capacitive compensation structure is greater than two, and the number of the resonance columns bridged by the inductive compensation structure and the capacitive compensation structure is equal or different.
Preferably, the first and second capacitive couplings may be of sheet metal or block metal construction.
Preferably, the first and second insulating members may be insulating spacers or insulating films.
The invention adds an inductive compensation structure and/or a capacitive compensation structure, and the added compensation structure can adjust the position of the near-end transmission zero point of the passband in a larger range to enable the near-end transmission zero point to be closer to the passband, thereby improving the near-end out-of-band rejection and simultaneously improving the in-band echo and insertion loss indexes. In addition, the invention also has the advantages that the transmission zero point can be adjusted independently of the resonant frequency, the design flexibility is improved, the volume is reduced, the processing cost is reduced, the adjustment allowance is increased, the intermodulation is not influenced, and the like.
Drawings
FIG. 1 is a schematic cross-sectional view of a filter according to the present invention;
FIG. 2 is a schematic perspective view of a filter according to the present invention;
fig. 3 is a graphical illustration of the frequency response of the present invention.
Reference numerals:
1. the resonant cavity comprises a cavity body, 11, a top cavity body wall, 12, a bottom cavity body wall, 2, a resonant column, 3, a frequency adjusting screw, 4, a resonant cavity, 51, a first capacitive coupling piece, 52, a capacitive coupling adjusting screw, 61, an inductive coupling conductor, 62, an inductive coupling adjusting screw, 7, an inductive compensation structure, 8, a second capacitive coupling piece, 81 and a second insulating piece.
Detailed Description
The technical solution of the embodiment of the present invention will be clearly and completely described below with reference to the accompanying drawings of the present invention.
The adjustable electromagnetic hybrid coupling filter disclosed by the invention improves the performances of the electromagnetic hybrid coupling filter, such as out-of-band near-end inhibition, in-band echo and insertion loss indexes, by adding the compensation structure.
As shown in fig. 1, the tunable electromagnetic hybrid coupling filter disclosed in the present invention includes a cavity 1, a resonant column 2, a frequency tuning screw 3, a capacitive coupling structure, an inductive coupling structure, and a compensation structure, wherein the whole cavity 1 in this embodiment is a closed metal cavity including a top cavity wall 11 and a bottom cavity wall 12, and the whole structure of this embodiment is disposed in the cavity 1.
The resonant columns 2 are fixed in the cavity 1, in the embodiment, the resonant columns 2 are vertically fixed on the bottom cavity wall 12 of the cavity at intervals, and a certain gap is reserved between the top end of each resonant column 2 and the top cavity wall 11 of the cavity to provide an installation space for the frequency adjusting screw 3 and/or other components. A group of electromagnetic hybrid coupling structures 4 is formed between two adjacent resonant columns 2, in this embodiment, at least three resonant columns 2 are provided, that is, at least two groups of electromagnetic hybrid coupling structures 4 are formed. The resonance column 2 resonates at a designated frequency, and the level of the resonant frequency is related to the length of the resonance column 2, and the longer the resonance column 2, the lower the resonant frequency.
The frequency tuning screw 3 is used for adjusting the resonance frequency of the resonance column 2 within a certain range. In this embodiment, one end of the frequency adjusting screw 3 is vertically fixed on the top cavity wall 11 of the cavity, and the other end is opposite to the top end of the resonant column 2. The longer the frequency tuning screw 3, the lower the resonance frequency, whereas the shorter the frequency tuning screw 3, the higher the resonance frequency.
The capacitive coupling structure and the inductive coupling structure are arranged between two adjacent resonance columns 2 at the same time, and the capacitive coupling structure and the inductive coupling structure jointly generate electromagnetic hybrid coupling. The electric field of the upper end part of the resonance column 2 is strong and is easy to generate capacitive coupling, and the magnetic field of the lower end part of the resonance column 2 is strong and is easy to generate inductive coupling. The capacitive coupling structure includes a first capacitive coupling element 51 and a capacitive coupling adjusting screw 52, the first capacitive coupling element 51 connects two adjacent resonant columns 2, in this embodiment, the first capacitive coupling element 51 is disposed near the top end of the resonant column 2, and the two adjacent first capacitive coupling elements 51 are disposed in a vertically staggered manner, or disposed in a vertically staggered manner. In specific implementation, the first capacitive coupling element 51 may be implemented by a metal sheet, two ends of the metal sheet are respectively fixed to the side surfaces of two adjacent resonant columns 2, and an insulating gasket is arranged between the first capacitive coupling element 51 and the side surfaces of the resonant columns 2; alternatively, the first capacitive coupling element 51 may be implemented by a metal plate or a metal block, in which the metal plate or the metal block is clamped between two adjacent resonant columns 2, or both ends of the metal plate or the metal block are embedded in the resonant columns 2, in which case the metal plate or the metal block is covered with an insulating layer. The first coupling member 51 may be connected to the resonant column 2 in a conductive manner at one end and to the resonant column 2 in an insulating manner at the other end.
Preferably, a first insulating member (not shown) is provided between the first capacitive coupling element 51 and the resonant column 2, and the first insulating member is used to achieve an insulating connection with the resonant column 2, thereby preventing a dc short circuit therebetween. In practice, the first insulating member may be an insulating spacer or an insulating film. The magnitude of the capacitive coupling amount of the capacitive coupling structure is related to the position and shape of the first capacitive coupling element 51 (e.g., a metal sheet), and the coupling is stronger when the first capacitive coupling element 51 is closer to the top end of the resonant column 2, and the coupling is stronger when the first capacitive coupling element 51 covers a larger area on the resonant column.
The capacitive coupling adjustment screw 52 is used to adjust the capacitive coupling size of the first capacitive coupling element 51 within a certain range. In this embodiment, the capacitive coupling adjusting screw 52 is fixed on the top cavity wall 11 of the cavity and is opposite to the first capacitive coupling element 51, and since the first capacitive coupling element 51 connects the two adjacent resonant columns 2 and the frequency adjusting screw 3 is opposite to the resonant column 2, in this embodiment, a capacitive coupling adjusting screw 52 is disposed between the two adjacent frequency adjusting screws 3. The principle of the frequency tuning screw 3 is the same, the longer the length of the capacitive coupling tuning screw 52 is, the smaller the coupling amount is, and conversely, the shorter the length of the capacitive coupling tuning screw 52 is, the larger the coupling amount is.
The inductive coupling structure comprises an inductive coupling conductor 61 and an inductive coupling adjusting screw 62, the inductive coupling conductor 61 is positioned at the bottom between two adjacent resonant columns 2, and the coupling amount of the inductive coupling structure is larger when the height of the inductive coupling conductor 61 is higher. The inductive coupling adjusting screws 62 are located on the inductive coupling conductors 61, each inductive coupling adjusting screw 62 corresponds to one inductive coupling conductor 61, and the magnitude of the inductive coupling amount can be adjusted within a certain range by adjusting the inductive coupling adjusting screws 62 on the inductive coupling conductors 61. The longer the length of the inductive coupling adjusting screw 62 is, the larger the coupling amount is, and conversely, the shorter the length of the inductive coupling adjusting screw 62 is, the smaller the coupling amount is.
When inductive and capacitive coupling exists between the adjacent resonant columns 2, a transmission zero point is generated near the resonant frequency of the resonant columns, the position of the transmission zero point is related to the magnitude of capacitive and inductive coupling quantities, and the position of the transmission zero point can be controlled within a certain range by respectively adjusting the magnitude of the two coupling quantities.
However, when the transmission zero point is out of the tuning range, the present invention corrects the position of the transmission zero point by the compensation structure. The compensation structure is connected with two nonadjacent resonance columns 2, namely at least three resonance columns 2 are bridged, for example, when three resonance columns 2 are bridged, namely, one end of the compensation structure is connected with the first resonance column, and the other end of the compensation structure is connected with the third resonance column. The compensation structure generates capacitive and/or inductive coupling between the two nonadjacent resonance columns 2, and the capacitive or inductive coupling between the two nonadjacent resonance columns 2 can be generated through the compensation structure, so that compensation of different properties is realized.
Specifically, the compensation structure includes an inductive compensation structure 7 and/or a capacitive compensation structure, that is, the two compensation structures can be used separately or simultaneously, wherein both ends of the inductive compensation structure 7 are directly connected to the resonant column 2, and the larger the distance from the inductive compensation structure 7 to the top of the resonant column 2 is, the smaller the inductive compensation amount is, that is, the distance from the inductive compensation structure 7 to the top of the resonant column 2 can be changed. The capacitive compensation structure comprises a second capacitive coupling part 8 and a second insulating part 81, wherein the second insulating part 81 is arranged between at least one end of the second capacitive coupling part 8 and the resonant column 2 to realize insulating connection, the second insulating part 81 can be arranged at both ends, and the second capacitive coupling part 8 is a metal rod.
Preferably, the second capacitive coupling element 8 is separated from the resonant column 2 by a second insulator 81, and the second insulator 81 provides an insulating connection with the resonant column 2, thereby preventing a dc short circuit therebetween. In practice, the second insulating member 81 may be an insulating spacer or an insulating film. The amount of capacitive compensation of the capacitive compensation structure is related to the area of the second capacitive coupling element 8 overlying the resonant column 2, with greater area of the second capacitive coupling element 8 overlying the resonant column 2 providing greater capacitive compensation. Of course, the compensation structure of the present invention is not limited to that described herein, and other structures of inductive or capacitive compensation are also suitable for use in the present invention, as long as the structures provide capacitive and/or inductive compensation.
In addition, the number of the resonance columns 2 bridged by the inductive compensation structure 7 and the capacitive compensation structure is greater than two, and the number of the resonance columns 2 bridged by the inductive compensation structure 7 and the capacitive compensation structure may be equal to or different from each other, for example, the inductive compensation structure 7 and the capacitive compensation structure may both be bridged by four resonance columns 2, the inductive compensation structure 7 may also be bridged by four resonance columns 2, and the capacitive compensation structure may be bridged by five resonance columns 2, and so on.
Taking the structure shown in fig. 2 as an example, the frequency response of the filter when the compensation structure is not adopted is curve a in fig. 3, and the frequency response curves after the compensation structure is adopted are curves B and C, wherein the compensation degree of the curve C is greater than that of the curve B. It can be seen from fig. 3 that, after the compensation structure is added, the transmission zero frequency at the near end of the passband is increased and is closer to the passband, and the larger the compensation degree is, the larger the transmission zero frequency is increased, and meanwhile, the insertion loss and echo indexes near the edge of the passband are also improved. Therefore, the added compensation structure can adjust the position of the near-end transmission zero point of the passband in a larger range, thereby improving the near-end out-of-band rejection and simultaneously improving the in-band echo and insertion loss indexes.
Therefore, the scope of the present invention should not be limited to the disclosure of the embodiments, but includes various alternatives and modifications without departing from the scope of the present invention, which is defined by the claims of the present patent application.