CN216903276U - Coaxial low-pass filter - Google Patents
Coaxial low-pass filter Download PDFInfo
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- CN216903276U CN216903276U CN202122888272.8U CN202122888272U CN216903276U CN 216903276 U CN216903276 U CN 216903276U CN 202122888272 U CN202122888272 U CN 202122888272U CN 216903276 U CN216903276 U CN 216903276U
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Abstract
The utility model is suitable for the technical field of communication, and provides a coaxial low-pass filter which comprises a coaxial inner core, wherein the coaxial inner core comprises a low-impedance section and a high-impedance section which are connected in series at intervals in a thick-thin crossing manner, at least one high-impedance section is set as a winding inductor, blind grooves are formed in the low-impedance section on two adjacent sides of the winding inductor, and two ends of the winding inductor are respectively connected to the two blind grooves. Therefore, at least one transmission zero point can be formed above the cut-off frequency of the coaxial low-pass filter, the high-frequency suppression performance is improved, and the total length of the coaxial low-pass filter can be reduced.
Description
Technical Field
The utility model relates to the technical field of communication, in particular to a coaxial low-pass filter.
Background
With the rapid development of wireless communication technology, radio frequency spectrum resources are increasingly tense, and higher requirements are put forward on the high-frequency harmonic suppression performance of a communication base station duplexer.
The coaxial impedance step low-pass filter is commonly called a 'sugarcoated haw string' low-pass filter, and equivalent parallel capacitors and series inductors are respectively realized by matching metal coaxial inner cores and coaxial outer walls which are alternately cascaded in thickness, so that the coaxial impedance step low-pass filter is widely applied due to the advantages of low loss, large power capacity, simple structure, easiness in integration with a metal filter or a duplexer and the like.
The coaxial low-pass filters in the prior art are generally divided into two types, the difference is that the cross section of the low-impedance section is circular or square, and if the cross section of the low-impedance section is circular, the cross section is generally referred to as circular low-pass in the industry. If the cross section of the low-impedance section is square, the low-impedance section is generally referred to as square low-pass in the industry, wherein the circular low-pass is applicable to the application scenario in which the coaxial outer wall is a circular hole or a square groove, but the high-frequency rejection performance is affected to a certain extent because the fit clearance between the coaxial outer wall of the square groove and the low-impedance section of the circular low-pass is large. And the square low pass is designed for the application scene of the coaxial outer wall specially used for the square groove, and the performance is improved compared with the performance of the round low pass with the coaxial outer wall of the same length as the square groove and the round low pass with the coaxial outer wall as the round hole. FIG. 1A shows a decomposition structure and a schematic cross-sectional structure of a circular low-pass in the prior art; and FIG. 1B shows a decomposition structure and a schematic cross-sectional structure of a square low-pass in the prior art. In fig. 1A and 1B, the coaxial inner core 210 is generally a metal lathed part, the outer surface of which is reduced by silver plating or copper plating to reduce losses; the insulating sleeve 220 is used to separate the coaxial inner core from the coaxial outer wall, avoiding short circuits; impedance matching sections 211 at the ends of the coaxial inner core cooperate with the coaxial outer wall to achieve the desired input and output impedance (e.g., 50 ohms, 75 ohms, etc.). The low impedance section 212 of the coaxial inner core is thick in diameter and is matched with the coaxial outer wall to realize equivalent parallel capacitance; the high impedance section 213 of the coaxial inner core has a smaller diameter and is matched with the coaxial outer wall to realize equivalent series inductance; the high-impedance section and the low-impedance section are alternately cascaded, so that the functions of equivalent low-pass filtering and high-frequency suppression are realized, the more the cascaded orders are, the higher the rectangular coefficient of the low-pass is, and the better the suppression performance of the high-frequency is.
The frequency response curve of the existing coaxial low-pass filter above the cut-off frequency is smooth, and the transmission zero point cannot be increased to improve the high-frequency rejection performance. If the higher harmonic of the system is closer to the low-pass cut-off frequency, the low-pass suppression performance is limited, and the suppression performance can only be improved by increasing the low-pass order or the difference of high-low step impedance, so that the length or volume of the low-pass is increased, and the miniaturization design of the whole machine is not facilitated.
In summary, the conventional structure has disadvantages and drawbacks in practical use, so that improvement is needed.
SUMMERY OF THE UTILITY MODEL
In view of the above-mentioned drawbacks, an object of the present invention is to provide a coaxial low-pass filter, which can form at least one transmission zero above a cut-off frequency of the coaxial low-pass filter, improve high-frequency rejection performance, and reduce the total length of the coaxial low-pass filter.
In order to achieve the above object, the present invention provides a coaxial low-pass filter, which includes a coaxial inner core, where the coaxial inner core includes a low impedance section and a high impedance section that are connected in series at intervals in a thick-thin cross manner, at least one of the high impedance sections is configured as a winding inductor, blind grooves are formed in the low impedance sections on two adjacent sides of the winding inductor, and two ends of the winding inductor are connected to the two blind grooves, respectively.
According to the coaxial low-pass filter, the centers of the bottoms of the two blind grooves are respectively provided with a first blind hole, and two ends of the coil inductor are respectively connected to the two first blind holes.
According to the coaxial low-pass filter, two ends of the coil inductor are respectively welded to the two first blind holes.
According to the coaxial low-pass filter, only one high-impedance section is set as the winding inductor;
the coil inductor and the other high-impedance sections on the coaxial inner core are integrally formed;
the low impedance sections on the coaxial inner core are provided with through holes except the low impedance sections at two ends, and the low impedance sections at two ends are provided with second blind holes;
the high-impedance section at two ends of the winding inductor penetrates through the through hole and is connected with the second blind hole.
According to the coaxial low-pass filter, the high-impedance section is connected with the through hole and the second blind hole in a welding mode.
According to the coaxial low-pass filter, the low-impedance section is in a square shape or a cylindrical shape.
According to the coaxial low-pass filter, the coaxial low-pass filter further comprises an insulating sleeve, the insulating sleeve is sleeved on the outer side of the coaxial inner core, and the insulating sleeve is square.
According to the coaxial low-pass filter, impedance matching sections are further arranged at the two ends of the coaxial inner core.
The embodiment of the utility model provides a coaxial low-pass filter, which comprises a coaxial inner core, wherein the coaxial inner core comprises a low-impedance section and a high-impedance section which are connected in series at intervals in a thick-thin crossing manner, at least one high-impedance section is set as a winding inductor, blind grooves are respectively arranged on the low-impedance sections at two adjacent sides of the winding inductor, and two ends of the winding inductor are respectively connected to the two blind grooves. The coil inductor realizes the function of series inductance, and greatly shortens the space length of the high-impedance section, thereby drawing the mutual distance between low-impedance sections (inner core sections with thicker diameters) at two sides of the coil inductor; optionally, the length of the low impedance section on two adjacent sides of the winding inductor may be increased appropriately, and a blind slot is formed on the side of the low impedance section close to the winding inductor to increase an inductor avoiding space. Through the measures, a series capacitor is additionally arranged between the two low-impedance sections, so that at least a transmission zero point is formed above the low-pass cut-off frequency, and the high-frequency rejection performance of the coaxial low-pass filter is improved.
Drawings
FIG. 1A is a schematic diagram of a decomposition structure and a cross-sectional structure of a circular low-pass provided by the prior art;
FIG. 1B is a schematic diagram of a decomposition structure and a cross-sectional structure of a square low-pass provided by the prior art;
fig. 2 is a schematic structural view of a coaxial inner core according to an embodiment of the present invention;
fig. 3 is an exploded view of a coaxial inner core according to an embodiment of the present invention;
fig. 4 is a schematic perspective structural diagram of a coaxial low-pass filter according to an embodiment of the present invention;
FIG. 5 is a cross-sectional view of a coaxial low pass filter provided in accordance with an embodiment of the present invention;
fig. 6 is an exploded schematic diagram of a coaxial low-pass filter according to an embodiment of the present invention;
fig. 7 is a second exploded schematic diagram of a coaxial low-pass filter according to an embodiment of the present invention;
fig. 8 is an equivalent circuit diagram of a coaxial low-pass filter according to an embodiment of the present invention;
fig. 9 is a schematic diagram comparing the frequency response of the coaxial low-pass filter provided by an embodiment of the utility model with that of the coaxial low-pass filter of the prior art.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the utility model and are not intended to limit the utility model.
Referring to fig. 2 to 9, in a first embodiment of the present invention, a coaxial low-pass filter 100 is provided, which includes a coaxial inner core 10, where the coaxial inner core 10 includes a thick low-impedance section 11 and a thin high-impedance section 12 connected in series at intervals, at least one high-impedance section 12 is provided as a winding inductor 20, blind slots 13 are formed on the low-impedance sections 11 on two adjacent sides of the winding inductor 20, and two ends of the winding inductor 20 are respectively connected to the two blind slots 13.
In this embodiment, the coaxial low-pass filter 100 has a simple structure, and can be applied to the application scenario of the coaxial low-pass filter 100, such as the coaxial outer wall of a circular hole or the coaxial outer wall of a grooved square. Since the space length of the coil inductor 20 is greatly shortened compared with the high impedance section in the prior art, the total length of the coaxial low-pass filter 100 is shorter than that of the coaxial low-pass filter in the prior art, which is beneficial to reducing the overall size of the radio frequency front-end filter/duplexer and realizing the miniaturization of the radio frequency overall. And because the space length is greatly shortened by adopting the coil inductor 20, the mutual distance between the low impedance sections 11 at the two sides of the coil inductor 20 is shortened, and a blind slot 13 (the blind slot is not a through slot) is arranged on the low impedance section 11 close to the coil inductor 20 side to increase the inductor avoiding space, through the above measures, a series capacitor is added between the two low impedance sections 11, so that at least a transmission zero point is formed above the low-pass cut-off frequency, and the high-frequency suppression performance of the coaxial low-pass filter 100 is improved. Alternatively, the lengths of the low impedance sections 11 on the adjacent two sides of the winding inductor 20 may be increased appropriately to obtain a design space of the blind slot 13. Referring to fig. 2, which shows an equivalent circuit diagram of the coaxial inner core 10 of the 7-stage coaxial low-pass filter 100 of the embodiment and referring to fig. 8, which shows the coaxial low-pass filter 100 of the 7-stage coaxial low-pass filter 100, the coaxial inner core 10 of the 7-stage coaxial low-pass filter 100 includes four low-impedance sections 11 and three high-impedance sections 12. The difference from the prior art is that one winding inductor 20 replaces the high-impedance section of the second section to generate the equivalent series inductor L2, the distance between two adjacent low-impedance sections 11 of the inductor is greatly reduced, and a blind slot 13 is added on one side of the low-impedance section 11 close to the winding inductor 20 to enlarge the inductor back-off space. After the two low impedance sections 11 are close to each other, in addition to the equivalent parallel capacitors C2 and C3 generated by the original coaxial outer wall, a series capacitor C5 is additionally generated between the two low impedance sections, so that a transmission zero is generated at a high-frequency part above the low-pass cut-off frequency, and the high-frequency rejection performance of the low-pass filter is improved. By adjusting the distance d between the low impedance segments 11 on two adjacent sides of the winding inductor 20, the size of the series capacitor C5 can be changed, thereby realizing the control of the transmission zero position. When the distance d is reduced, C5 is increased, and the transmission zero frequency is reduced; as the separation d increases, C5 decreases and the transmission zero frequency increases. The total length of the 7 th order coaxial low pass filter 100 in this embodiment is 37.5mm, whereas the total length of the prior art is typically 45 mm. On the basis that the total length is shortened by 17%, thanks to the introduction of the transmission zero point, the high-frequency rejection performance at the 4000-8000 MHz frequency band is greatly improved, and the rejection performance at the 4000MHz frequency band is improved from 50dB to 80dB (see the comparison between the S21_ traditional square low pass and the S21_ novel square low pass in fig. 9).
Referring to fig. 6, as an alternative embodiment, the centers of the bottoms of the two blind slots 13 are respectively provided with a first blind hole 14, and two ends of the winding inductor 20 are respectively connected to the two first blind holes 14. Specifically, two ends of the coil inductor 20 are soldered to the two first blind holes 14 (the blind holes are not through holes).
In this embodiment, for the convenience of assembly, the first blind holes 14 are respectively opened at the bottom centers of the two blind slots 13, and two ends of the winding inductor 20 are respectively connected to the two first blind holes 14. Alternatively, if the high-impedance segment 12 is not replaced by the winding inductor 20, the high-impedance segment 12 and the adjacent low-impedance segment 11 may be integrally formed. During assembly, the winding inductor 20 and the low impedance sections 11 on two adjacent sides can be aligned and assembled through an external tool, two ends of the winding inductor 20 are respectively assembled into the first blind holes 14, and then the winding inductor can be pre-coated with solder paste and welded in a furnace integrally. Of course, other equivalent combinations of assembly are possible.
Referring to fig. 7, as an alternative embodiment, only one of the high-impedance segments 12 is provided as a winding inductor 20; the coil inductor 20 is integrally formed with the other high-impedance sections 12 on the coaxial inner core 10; the low impedance sections 11 on the coaxial inner core 10 are provided with through holes 15 except the low impedance sections 11 at two ends, and the low impedance sections 11 at two ends are provided with second blind holes 16; the high-impedance section 12 at both ends of the coil inductor 20 extends through the through hole 15 and is connected to the second blind hole 16. Specifically, the high-impedance section 12 is connected to the through hole 15 and the second blind hole 16 by welding.
In this embodiment, if only one of the high-impedance segments 12 is provided as the coil inductor 20, the coil inductor 20 is integrally formed with the other high-impedance segments 12 on the coaxial inner core 10 for easy assembly; during assembly, all parts are aligned and assembled through an external tool, and finally, the parts are pre-coated with solder paste and integrally welded in a furnace. Of course, the combination assembly can be carried out in other equivalent manners.
As an alternative embodiment, the low impedance segment 11 is square or cylindrical, i.e. the cross-section of the low impedance segment 11 is square or circular.
As an alternative embodiment, the coaxial low-pass filter 100 further includes an insulating sleeve 30, the insulating sleeve 30 is sleeved outside the coaxial inner core 10, and the insulating sleeve 30 is in a square shape. Of course, the insulating sleeve 30 may also have a cylindrical shape. The insulating sleeve 30 prevents the coaxial inner core 10 and the coaxial outer wall from being short-circuited.
As an alternative embodiment, the two ends of the coaxial inner core 10 are further provided with impedance matching sections 17, which cooperate with the coaxial outer wall of the coaxial low-pass filter 100 to achieve the required input and output impedance, and reduce the insertion loss.
In summary, in an embodiment of the present invention, a coaxial low-pass filter is provided, which includes a coaxial inner core, where the coaxial inner core includes a low impedance section and a high impedance section that are connected in series at intervals in a thick-thin cross manner, at least one of the high impedance sections is configured as a winding inductor, blind slots are formed in the low impedance section on two adjacent sides of the winding inductor, and two ends of the winding inductor are connected to the two blind slots, respectively. The coil inductor realizes the function of series inductance, and greatly shortens the space length of the high-impedance section, thereby drawing the mutual distance between low-impedance sections (inner core sections with thicker diameters) at two sides of the coil inductor; optionally, the length of the low impedance section on two adjacent sides of the winding inductor may be increased appropriately, and a blind slot is formed on the side of the low impedance section close to the winding inductor to increase an inductor avoiding space. Through the measures, a series capacitor is additionally arranged between two low-impedance sections, so that at least a transmission zero point is formed above the low-pass cut-off frequency, and the high-frequency rejection performance of the coaxial low-pass filter is improved.
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it should be understood that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit and scope of the utility model as defined in the appended claims.
Claims (8)
1. A coaxial low-pass filter comprises a coaxial inner core, wherein the coaxial inner core comprises a low-impedance section and a high-impedance section which are connected in series at intervals in a thick-thin crossing manner, and is characterized in that at least one high-impedance section is provided as a winding inductor, blind grooves are formed in the low-impedance sections on two adjacent sides of the winding inductor, and two ends of the winding inductor are respectively connected to the two blind grooves.
2. The coaxial low-pass filter according to claim 1, wherein the centers of the bottoms of the two blind slots are respectively provided with a first blind hole, and two ends of the coil inductor are respectively connected to the two first blind holes.
3. The coaxial low-pass filter according to claim 2, wherein two ends of the coil inductor are soldered to the two first blind holes, respectively.
4. The coaxial low pass filter according to claim 1, characterized in that only one of the high impedance segments is provided as the winding inductance;
the coil inductor and the other high-impedance sections on the coaxial inner core are integrally formed;
the low impedance sections on the coaxial inner core are provided with through holes except the low impedance sections at two ends, and the low impedance sections at two ends are provided with second blind holes;
the high-impedance section at two ends of the winding inductor penetrates through the through hole and is connected with the second blind hole.
5. The coaxial low pass filter of claim 4, wherein the high impedance section is solder connected to the through hole and the second blind hole.
6. A coaxial low pass filter according to claim 1 wherein the low impedance section is square or cylindrical.
7. The coaxial low pass filter according to claim 1, further comprising an insulating sleeve disposed outside the coaxial inner core, wherein the insulating sleeve has a square shape.
8. The coaxial low pass filter of claim 1, wherein the coaxial inner core is further provided with an impedance matching section at both ends.
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| CN202122888272.8U CN216903276U (en) | 2021-11-19 | 2021-11-19 | Coaxial low-pass filter |
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| CN202122888272.8U CN216903276U (en) | 2021-11-19 | 2021-11-19 | Coaxial low-pass filter |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114142194A (en) * | 2021-11-19 | 2022-03-04 | 摩比天线技术（深圳）有限公司 | Coaxial low-pass filter |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114142194A (en) * | 2021-11-19 | 2022-03-04 | 摩比天线技术（深圳）有限公司 | Coaxial low-pass filter |
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