Coaxial high-power EMI (Electro-Magnetic Interference) filter based on low-pass filtering technology

Abstract

The coaxial high-power EMI filter based on the low-pass filtering technology comprises an inner conductor, an outer conductor and an insulating medium layer, the inner conductor and the outer conductor are coaxially arranged, the space between the inner conductor and the outer conductor is filled with the insulating medium layer, and the inner conductor comprises a center conductor and a plurality of electromagnetic band gap structures which are connected with the center conductor and are coaxially arranged; the inner conductor, the outer conductor and the medium between the inner conductor and the outer conductor form a transmission line which comprises a high-characteristic impedance transmission line and a low-characteristic impedance transmission line; and the N sections of high and low impedance transmission lines forming the impedance conversion low-pass filtering network are arranged at intervals. The size of the filter is compressed through coaxial arrangement of the inner conductor and the outer conductor, loading of the electromagnetic band gap structure, filling of the insulating medium and the like, the filtering performance of the filter is further improved, and the filter has the advantages of being small in size, high in high-frequency anti-interference capacity and resistant to high-power microwave interference.

Description

Technical Field

[0001] The invention belongs to the technical field of filters, and in particular relates to a coaxial high-power EMI filter based on low-pass filtering technology. Background Art

[0002] Commonly used EMI (Electromagnetic Interference) filters are key components used in electronic devices to reduce electromagnetic interference. They suppress or reduce high-frequency noise and avoid signal interference, thereby improving the electromagnetic compatibility of the equipment. The working principle of EMI filters is based on the combination of inductance, capacitance and resistance. Through the interaction of these components, they effectively block or absorb unwanted electromagnetic waves. These filters allow the frequency signals of the equipment to pass when it is working normally, while having a greater blocking effect on high-frequency interference signals. However, there are some limitations in existing EMI filters. For example, passive filters have weak anti-interference capabilities at high frequencies, while active filters are difficult to meet the protection requirements in high-power microwave environments. Future development trends of EMI filters include integrated design, high-frequency and 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 of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a coaxial high-power EMI filter based on low-pass filtering technology which has a small size, excellent high-frequency anti-interference and strong anti-high-power microwave interference capability.

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

[0005] Optionally, the longitudinal cross-sections of the plurality of electromagnetic bandgap structures are mushroom-nail shaped and are arranged in sequence and at intervals according to their length dimensions.

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

[0007] Optionally, the inner conductor and the outer conductor are three-dimensional metal structures, including but not limited to cylinders, cubes and cuboids.

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

[0009] Optionally, the high dielectric constant medium includes but is not limited to carbon powder mixed materials, ferrite materials and composite absorbing materials.

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

[0011] Optionally, the materials used in each structure of the EMI filter are passive and pressure-resistant and high-temperature-resistant materials.

[0012] Optionally, one end of the EMI filter is also connected to a passive filtering circuit.

[0013] The equivalent circuit of the filter comprises: a central conductor of an inner conductor is divided into a plurality of sections by a plurality of electromagnetic bandgap structures, each section being equivalent to an equivalent series inductance of a high impedance transmission line; a plurality of electromagnetic bandgap structures respectively forming a plurality of equivalent parallel capacitors of a low impedance transmission line with an outer conductor; and a plurality of equivalent series inductors and equivalent parallel capacitors forming an equivalent circuit of the filter.

[0014] Beneficial effects: Compared with the prior art, the significant technical effects of the present invention are as follows: (1) Compared with the traditional EMI filter, it has the advantages of small size, excellent high-frequency anti-interference, and strong anti-high-power microwave interference capability; (2) Different from the traditional EMI filter using 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 coaxial electromagnetic bandgap structure high and low impedance transmission lines and the filling of high dielectric constant medium, the out-of-band suppression performance and high-power microwave protection performance of the filter are improved; (3) The coaxial electromagnetic bandgap structure high and low impedance transmission lines are mainly used to form a low-pass filtering equivalent circuit, and the filling of the high dielectric constant medium is mainly used to improve the low-pass filtering performance and reduce the filter size; (4) The coaxial high-power EMI filter is mainly used to suppress electromagnetic interference in the 300MHz-18GHz frequency band and above, with an insertion loss higher than 120dB, and at the same time has good high-power microwave suppression capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the structure of the coaxial high-power EMI filter of the present invention;

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

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

[0018] Figure 4 It is a schematic diagram of the equivalent circuit of the coaxial high-power EMI filter of the present invention;

[0019] Figure 5 This is a simulation curve diagram of the insertion loss of the coaxial high-power EMI filter of the present invention;

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

[0021] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0022] The technical solutions provided by various embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0023] The coaxial high-power EMI filter based on low-pass filtering technology described in the present invention includes 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 includes a central conductor and a plurality of electromagnetic bandgap structures connected to the central conductor and coaxially arranged. The plurality of electromagnetic bandgap structures are arranged in sequence according to length sizes.

[0024] See also Figure 1 The inner and outer conductors both adopt a coaxial structure. The inner conductor 1 is added with coaxial bandgap structures 11, 12, 13, and 14 by metal processing methods such as slotting and welding. The inner and outer conductors are made of 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 cylinders, cubes, and cuboids.

[0025] See also Figure 2 , Figure 2The present invention is a cross-sectional structural schematic diagram of a coaxial high-power EMI filter based on low-pass filtering technology. The insulating dielectric layer includes a high dielectric constant dielectric 3 and an insulating coating 4 coated on the surface of the inner conductor 1; the high dielectric constant dielectric 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 surface of the electromagnetic bandgap structure 11, 12, 13, 14; the central conductor of the inner conductor 1 and the high dielectric constant dielectric 3 and the outer conductor 2 are high-impedance transmission lines, which can be equivalent to inductance in the low-pass filtering equivalent circuit, and the isolation between the inner and outer conductors is increased by the high dielectric constant dielectric 3, and the inductance value is increased; the electromagnetic bandgap structure 11, 12, 13, 14 and the high dielectric constant dielectric 3 and the outer conductor 2 are low-impedance transmission lines, which can be equivalent to capacitance in the low-pass filtering equivalent circuit; the side view (i.e., longitudinal section) of the electromagnetic bandgap structure is similar to the shape of a mushroom nail, and the contact area between the inner conductor and the high dielectric constant dielectric is increased by the structure, and the distance between the inner and outer conductors of the low-impedance transmission line is reduced. The schematic diagram of the three-dimensional structure of the filter is as follows Figure 3 shown.

[0026] The high dielectric constant medium 3 is filled between the inner conductor 1 and the outer conductor 2. Since the high-frequency electromagnetic wave itself has a large loss during the transmission process of the high dielectric constant medium, the medium strengthens the isolation between the inner and outer conductors, further improving the equivalent inductance and capacitance values ​​in the low-pass filter equivalent circuit.

[0027] Due to the loss of the electromagnetic wave itself in the high dielectric constant medium 3, and the increase in the equivalent inductance and capacitance values ​​in the low-pass filter equivalent circuit caused by the electromagnetic bandgap structure and dielectric 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 the inner conductor from directly contacting the high dielectric constant medium 3 and causing a short circuit between the inner and outer conductors.

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

[0030] The insulating coating 4 is a high-voltage resistant coating with a safe thickness, and the materials include but are not limited to PTFE Teflon, electrophoresis and rubber.

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

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

[0033] See also Figure 4 , Figure 4The figure is a schematic diagram of the equivalent circuit of the coaxial high-power EMI filter of the present invention. Among them, L1, L2, L3, L4, and L5 are the equivalent series inductances of five sections of high-impedance transmission lines (i.e., the five sections of the central conductor of the inner conductor 1 divided by the electromagnetic bandgap structures 11, 12, 13, and 14), and C1, C2, C3, and C4 are the equivalent parallel capacitances of four sections of low-impedance transmission lines (i.e., the capacitance structure 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] See also Figure 5 , Figure 5 This is the insertion loss simulation curve of the coaxial high-power EMI filter of the present invention. It can be seen from the curve that in the frequency band above 300MHz, the insertion loss is below -140dB, reaching the D-level index of the shielding effect of the military shield. The current carrying capacity is greater than 300A and the power capacity is greater than 10kW.

[0035] In summary, the coaxial high-power EMI filter based on low-pass filtering technology described in the present invention is based on step impedance low-pass filtering technology, and a high-power three-dimensional design is performed on the planar transmission line. By loading the electromagnetic bandgap structure and innovatively using high dielectric constant media for filling, the filter size is compressed and its filtering performance is further improved. The core of the present invention is to perform three-dimensional high-power design based on the commonly used low-pass filtering technology and fill it with high dielectric constant media. The inner and outer conductors and the medium therebetween constitute a transmission line, including a high characteristic impedance transmission line and a low characteristic impedance transmission line; the N sections of high and low impedance transmission lines constituting the impedance transformation low-pass filtering network are arranged at intervals. The inner and outer conductors adopt a coaxial structure, and can be designed to include but not limited to cylindrical, cube and cuboid shapes according to actual use. The EMI filter designed using the structure has a simple structure, small size, high insertion loss, strong high-frequency anti-interference ability, strong high-power microwave protection ability, high temperature resistance, high voltage resistance, and strong current carrying capacity.

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

Claims

1. A coaxial high-power EMI filter based on low-pass filtering technology, characterized in that: It comprises an inner conductor (1) and an outer conductor (2) which are coaxially arranged, and an insulating medium layer (3) filled between the inner conductor (1) and the outer conductor (2); the inner conductor (1) comprises a central conductor and a plurality of electromagnetic bandgap structures which are connected to the central conductor and coaxially arranged.

2. The coaxial high-power EMI filter based on low-pass filtering technology according to claim 1 is characterized in that: The longitudinal sections of the plurality of electromagnetic bandgap structures are mushroom-nail shaped and are arranged in sequence according to their length dimensions.

3. The coaxial high-power EMI filter based on low-pass filtering technology according to claim 1 is characterized in that: The inner conductor (1) is added with a plurality of coaxial electromagnetic band gap structures by metal processing.

4. The coaxial high-power EMI filter based on low-pass filtering technology according to claim 1 is characterized in that: The inner conductor (1) and the outer conductor (2) are three-dimensional metal structures, including but not limited to cylinders, cubes and cuboids.

5. The coaxial high-power EMI filter based on low-pass filtering technology according to claim 1 is characterized in that: The insulating medium layer comprises a high dielectric constant medium (3) and an insulating coating (4) coated on the surface of the inner conductor (1).

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

7. The coaxial high-power EMI filter based on low-pass filtering technology according to claim 5 is characterized in that: The insulating coating (4) is a high-voltage resistant coating with a safe thickness, and the materials include but are not limited to PTFE Teflon, electrophoresis and rubber.

8. The coaxial high-power EMI filter based on low-pass filtering technology according to claim 1 is characterized in that: The materials used in the various structures of the EMI filter are all passive and pressure-resistant and high-temperature-resistant materials.

9. The coaxial high-power EMI filter based on low-pass filtering technology according to claim 1 is characterized in that: One end of the EMI filter is also connected to a passive filtering circuit.

10. An equivalent circuit of a coaxial high-power EMI filter based on low-pass filtering technology according to any one of claims 1 to 9, characterized in that: The central conductor of the inner conductor (1) is divided into a plurality of sections by a plurality of electromagnetic bandgap structures, each section being equivalent to an equivalent series inductance of a high impedance transmission line; the plurality of electromagnetic bandgap structures respectively form a plurality of equivalent parallel capacitors of a low impedance transmission line with the outer conductor (2); and the plurality of equivalent series inductors and equivalent parallel capacitors form a filter equivalent circuit.

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