A coaxial high-power EMI filter based on low-pass filtering technology

Abstract

The application discloses a coaxial high-power EMI filter based on low-pass filtering technology, which comprises an inner conductor and an outer conductor arranged coaxially, and an insulating medium layer filled between the inner conductor and the outer conductor; the inner conductor comprises a center conductor and a plurality of electromagnetic bandgap structures connected with the center conductor and arranged coaxially; the inner conductor, the outer conductor and the medium therebetween form a transmission line, which comprises a high-characteristic-impedance transmission line and a low-characteristic-impedance transmission line; and N segments of high-impedance transmission lines and low-impedance transmission lines forming an impedance conversion low-pass filtering network are arranged at intervals. The application compresses the size of the filter and further improves the filtering performance through coaxial arrangement of the inner and outer conductors, loading of the electromagnetic bandgap structures and filling of the insulating medium, and has the advantages of small size, strong high-frequency anti-interference ability and high-power microwave interference resistance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of filters, and particularly relates to a coaxial high-power EMI filter based on low-pass filtering technology. BACKGROUND

[0002] Commonly used EMI (Electromagnetic Interference) filters are key components in electronic devices for reducing electromagnetic interference. They suppress or reduce high-frequency noise to avoid signal interference, thereby improving the electromagnetic compatibility of the device. The working principle of EMI filters is based on the combination of inductors, capacitors and resistors, which effectively block or absorb unwanted electromagnetic waves through the interaction of these elements. These filters allow frequency signals during normal operation of the device to pass through, while producing a large impedance to high-frequency interference signals. However, existing EMI filters have some limitations, such as passive filters having weak high-frequency anti-interference ability, and active filters being difficult to meet the protection requirements in high-power microwave environments. Future trends in EMI filter development include integrated design, high-frequency high-speed performance optimization, and the application of green and environmentally friendly materials to adapt to a wider range of application environments and more stringent electromagnetic compatibility requirements. SUMMARY

[0003] The purpose of the present application is to provide a coaxial high-power EMI filter based on low-pass filtering technology with small volume, excellent high-frequency anti-interference performance, and strong anti-high-power microwave interference ability.

[0004] Technical solution: The application discloses a coaxial high-power EMI filter based on low-pass filtering technology, which comprises an inner conductor and an outer conductor arranged coaxially, an insulating dielectric layer filled between the inner conductor and the outer conductor, and a plurality of electromagnetic bandgap structures connected to the center conductor and arranged coaxially.

[0005] Optionally, the longitudinal section of the plurality of electromagnetic bandgap structures is in the shape of a mushroom spike, and the structures are arranged in sequence according to the length size.

[0006] Optionally, the inner conductor is added with the coaxial plurality of electromagnetic bandgap structures through metal processing.

[0007] Optionally, the inner conductor and the outer conductor are three-dimensional metal structures, including but not limited to a cylinder, a cube and a cuboid.

[0008] Optionally, the insulating dielectric layer comprises a high dielectric constant medium and an insulating coating coated on the surface of the inner conductor.

[0009] Optionally, the high dielectric constant medium comprises but is not limited to a carbon powder mixed material, a ferrite material and a composite wave-absorbing material.

[0010] Optionally, the insulating coating is a safety thickness high voltage resistant coating, and the material includes but is not limited to PTFE Teflon, electrophoresis and rubber.

[0011] Optionally, the material used by each structure of the EMI filter is passive and pressure-resistant and high-temperature-resistant.

[0012] Optionally, the EMI filter is further connected with a passive filter circuit at one end.

[0013] The equivalent circuit of the filter includes: the center conductor of the inner conductor is divided into several segments by the electromagnetic bandgap structures, each segment is equivalent to an equivalent series inductance of a high impedance transmission line; the electromagnetic bandgap structures are respectively connected with the outer conductor to form several equivalent parallel capacitances of low impedance transmission lines; and the equivalent series inductances and the equivalent parallel capacitances form the equivalent circuit of the filter.

[0014] Advantages: compared with the prior art, the significant technical effects of the present application are: (1) compared with the traditional EMI filter, the present application has the advantages of small size, excellent high-frequency anti-interference and strong anti-high-power microwave interference ability; (2) different from the traditional EMI filter which uses passive devices and active devices for circuit arrangement, the coaxial high-power EMI filter based on low-pass filtering technology is based on the step impedance low-pass filtering principle, and through the filling of the coaxial electromagnetic bandgap structure high-low impedance transmission line and the high dielectric constant medium, the out-of-band suppression performance and the high-power microwave protection performance of the filter are improved; (3) the coaxial electromagnetic bandgap structure high-low impedance transmission line is mainly used to form a low-pass filter equivalent circuit, and the filling of the high dielectric constant medium is mainly used to improve the low-pass filtering performance and reduce the size of the filter; (4) the coaxial high-power EMI filter is mainly used to suppress electromagnetic interference in the frequency band of 300MHz-18GHz and above, and the insertion loss is higher than 120dB, while having good high-power microwave suppression ability. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a structural schematic diagram of the coaxial high-power EMI filter of the present application.

[0016] Figure 2 It is a sectional structure schematic diagram of the coaxial high-power EMI filter of the present application.

[0017] Figure 3 It is a three-dimensional structure schematic diagram of the coaxial high-power EMI filter of the present application.

[0018] Figure 4 It is an equivalent circuit schematic diagram of the coaxial high-power EMI filter of the present application.

[0019] Figure 5 It is an insertion loss simulation curve diagram of the coaxial high-power EMI filter of the present application.

[0020] In the figure: 1 - inner conductor; 2 - outer conductor; 3 - high dielectric constant medium; 4 - insulating coating; 11-14 - electromagnetic bandgap structure. DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0022] The technical solutions provided by the embodiments of the present application will be described in detail below in combination with the drawings.

[0023] The coaxial high-power EMI filter based on low-pass filtering technology provided by the present application comprises an inner conductor 1 and an outer conductor 2 arranged coaxially, and an insulating medium layer filled between the inner conductor 1 and the outer conductor 2. The inner conductor 1 comprises a center conductor and a plurality of electromagnetic bandgap structures connected with the center conductor and arranged coaxially. The plurality of electromagnetic bandgap structures are arranged in sequence according to the length size.

[0024] Referring to Figure 1 , the inner and outer conductors adopt coaxial structure. The inner conductor 1 is added with coaxial bandgap structures 11, 12, 13 and 14 by means of metal processing such as slotted welding. The inner and outer conductors adopt metal materials with high current-carrying capacity such as copper-aluminum alloy to carry large current for input. The inner conductor 1 and the outer conductor 2 are three-dimensional metal structures, including but not limited to cylinder, cube and cuboid.

[0025] Referring to Figure 2 , Figure 2A cross-sectional structure diagram of a coaxial high-power EMI filter based on low-pass filtering technology is provided. The insulating medium layer includes a high dielectric constant medium 3 and an insulating coating 4 coated on the surface of the inner conductor 1. The high dielectric constant medium 3 is filled between the inner conductor 1 and the outer conductor 2, and the insulating coating 4 is coated on the surface of the central conductor of the inner conductor 1 and covers the surfaces of the electromagnetic bandgap structures 11, 12, 13 and 14. The central conductor of the inner conductor 1, the high dielectric constant medium 3 and the outer conductor 2 are high-impedance transmission lines, which can be equivalent to inductance in the low-pass filter equivalent circuit. At the same time, the high dielectric constant medium 3 increases the isolation between the inner and outer conductors and increases the inductance value. The electromagnetic bandgap structures 11, 12, 13 and 14, the high dielectric constant medium 3 and the outer conductor 2 are low-impedance transmission lines, which can be equivalent to capacitance in the low-pass filter equivalent circuit. The side view (i.e. longitudinal section) of the electromagnetic bandgap structure is similar to a mushroom spike shape. The structure increases the contact area between the inner conductor and the high dielectric constant medium, and at the same time reduces the distance between the inner and outer conductors of the low-impedance transmission line part. The three-dimensional structure diagram of the filter is shown in Figure 3 .

[0026] The high dielectric constant medium 3 is filled between the inner conductor 1 and the outer conductor 2. Due to the high loss of high-frequency electromagnetic waves in the high dielectric constant medium during transmission, the medium strengthens the isolation between the inner and outer conductors, and further improves the equivalent inductance and capacitance values in the low-pass filter equivalent circuit.

[0027] Due to the loss of electromagnetic waves in the high dielectric constant medium 3, and the increase of the equivalent inductance and capacitance values in the low-pass filter equivalent circuit caused by the electromagnetic bandgap structure and the medium filling, the high-frequency suppression capability of the filter is significantly enhanced.

[0028] The insulating coating 4 is coated on the surface of the inner conductor 1 to prevent short circuit between the inner and outer conductors caused by direct contact between the inner conductor and the high dielectric constant medium 3.

[0029] The high dielectric constant medium 3 includes but is not limited to carbon powder mixed material, ferrite material and composite wave-absorbing material.

[0030] The insulating coating 4 is a safety thickness high-voltage resistant coating, and the material includes but is not limited to PTFE Teflon, electrophoresis and rubber.

[0031] The materials used in each structure of the EMI filter are passive and pressure and temperature resistant materials. The filter has the characteristics of high power, high voltage resistance, high temperature resistance, strong anti-high power microwave protection capability, etc.

[0032] The EMI filter can also be connected with a passive filter circuit at the front end to further improve the low-frequency anti-interference capability.

[0033] Reference is made to Figure 4 , Figure 4It is a schematic diagram of equivalent circuit of the coaxial high-power EMI filter of the application. L1, L2, L3, L4 and L5 are equivalent series inductances of five high-impedance transmission lines (i.e. five sections of the center conductor of the inner conductor 1 divided by the electromagnetic bandgap structures 11, 12, 13 and 14), and C1, C2, C3 and C4 are equivalent parallel capacitances of four low-impedance transmission lines (i.e. the capacitive structures formed between the electromagnetic bandgap structures 11, 12, 13 and 14 and the outer conductor). The equivalent inductance and capacitance can be calculated from the structural parameters of the inner and outer conductors and the electromagnetic parameters of the high-dielectric-constant medium.

[0034] Referring to Figure 5 , Figure 5 It is an insertion loss simulation curve of the coaxial high-power EMI filter of the application. As can be seen from the curve, the insertion loss is below -140 dB in the frequency band above 300 MHz, reaching the D-level index of the shielding effect of the military shielding body. The current-carrying capacity is greater than 300 A, and the power capacity is greater than 10 kW.

[0035] In summary, the coaxial high-power EMI filter based on the low-pass filtering technology of the application is based on the stepped impedance low-pass filtering technology, and the planar transmission line is designed for high power in three dimensions. The filter size is compressed and the filtering performance is further improved by loading the electromagnetic bandgap structure and innovatively using the high-dielectric-constant medium for filling. The core of the application is to design for high power in three dimensions and fill with high-dielectric-constant medium on the basis of the commonly used low-pass filtering technology. The inner and outer conductors and the medium therebetween constitute a transmission line, including a high-impedance transmission line and a low-impedance transmission line; the N high- and low-impedance transmission lines forming an impedance transformation low-pass filtering network are arranged at intervals. The inner and outer conductors adopt a coaxial structure, which can be designed in shapes including but not limited to cylinder, square and cuboid, etc. according to actual use. The EMI filter designed using the structure has the advantages of simple structure, small size, high insertion loss, strong high-frequency anti-interference ability, strong high-power microwave protection ability, high temperature resistance, high pressure resistance and strong current-carrying capacity.

[0036] The above is a specific embodiment of the application, but the protection scope of the application is not limited thereto, and includes using other low-pass filtering structures for high-dielectric-constant medium filling to enhance high-frequency capability, or using other different shapes or sizes of structures for changes and replacements, which should be covered within the protection scope of the claims of the application.

Claims

1. A coaxial type high power EMI filter based on low pass filtering technique, characterized by, The EMI filter comprises an inner conductor (1) and an outer conductor (2) arranged coaxially, an insulating medium layer filled between the inner conductor (1) and the outer conductor (2), the inner conductor (1) comprises a center conductor and a plurality of electromagnetic bandgap structures connected with the center conductor and arranged coaxially, the longitudinal section of the plurality of electromagnetic bandgap structures is in the shape of mushroom spike, the insulating medium layer comprises a high dielectric constant medium (3) and an insulating coating (4), the high dielectric constant medium (3) is filled between the inner conductor (1) and the outer conductor (2), the insulating coating (4) is a safety-thickness high-voltage-resistant coating, which is coated on the surface of the center conductor of the inner conductor (1) and covers the surface of the plurality of electromagnetic bandgap structures.

2. The low-pass filter technology-based coaxial type high-power EMI filter according to claim 1, characterized by, The plurality of electromagnetic bandgap structures are arranged at intervals according to the size of the length dimension.

3. The low-pass filter technology based coaxial type high power EMI filter according to claim 1, characterized in that, The inner conductor (1) is added with the coaxial plurality of electromagnetic bandgap structures by metal processing.

4. The low-pass filter technology-based coaxial type high-power EMI filter according to claim 1, characterized by, The inner conductor (1) and the outer conductor (2) are three-dimensional metal structures, including but not limited to a cylinder, a cube and a cuboid.

5. The low-pass filter technology based coaxial type high power EMI filter according to claim 1, characterized in that, The high dielectric constant medium (3) includes but is not limited to carbon powder mixed material, ferrite material and composite wave-absorbing material.

6. The low-pass filter technology based coaxial type high power EMI filter according to claim 1, characterized in that, The material of the insulating coating includes but is not limited to PTFE Teflon, electrophoresis and rubber.

7. The low-pass filter technology based coaxial type high power EMI filter according to claim 1, characterized in that, The materials used in each structure of the EMI filter are passive and pressure-resistant and high-temperature-resistant materials.

8. The low-pass filter technology based coaxial type high power EMI filter according to claim 1, characterized in that, The EMI filter is further connected with a passive filter circuit at one end.

9. An equivalent circuit of the coaxial type high power EMI filter based on low pass filtering technique according to any one of claims 1-8, characterized by, The center conductor of the inner conductor (1) is divided into a plurality of segments by the plurality of electromagnetic bandgap structures, each segment is equivalent to an equivalent series inductance of a high-impedance transmission line; the plurality of electromagnetic bandgap structures form a plurality of equivalent parallel capacitances of low-impedance transmission lines with the outer conductor (2) respectively; the plurality of equivalent series inductances and the plurality of equivalent parallel capacitances constitute a filter equivalent circuit.

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