Micro-discharge-resistant microwave filter

Abstract

The invention provides an anti-micro-discharge microwave filter. The filter comprises a top plate, an aluminum film, a blank body, a rubber pad and a body, the body is of a box-shaped structure with an opening in the side face, and a partition plate is arranged in a containing cavity. The rubber mats are arranged in the partition plates; the blank body is arranged on the rubber mat; the aluminum film covers the upper surface of the blank body; the aluminum film, the blank body and the rubber mat are fixed on the body through the top plate; according to the invention, a microwave filter design technology based on a filter blank is provided, the micro-discharge threshold value of the microwave filter is improved by utilizing the high voltage resistance characteristic and the high Q * f value of a microwave dielectric material, no redundant zero cavity is needed on a linear structure, a CT cross coupling structure is realized, and meanwhile, the out-of-band rejection index of the filter is improved; the whole assembly structure is simple, the debugging is simple, and the miniaturization and lightweight design of the microwave filter in the spaceflight load is realized.

Description

Technical Field

[0001] This invention belongs to the field of microwave filters, and specifically relates to an anti-micro-discharge microwave filter. Background Technology

[0002] Micro-discharge effect refers to the secondary electron multiplication effect excited on the surface of a metal or dielectric material under vacuum conditions and accelerated by an applied electric field. Micro-discharge effects are prone to occur in areas with strong electric fields inside high-power microwave filters under vacuum conditions, leading to the failure of high-power microwave components and even the complete failure of the entire payload.

[0003] With the continuous development of satellite payload technology, the requirements for spaceborne filters in terms of miniaturization, lightweight design, high reliability, and resistance to micro-discharge thresholds are becoming increasingly stringent. Currently, traditional cavity filters are limited by size and weight constraints in terms of micro-discharge thresholds, making it difficult to meet the miniaturization and lightweight requirements of aerospace payloads. This invention proposes a filter design method that achieves miniaturization, low weight, and a high micro-discharge threshold, thus meeting the needs of satellite payload technology development.

[0004] Chinese invention patent CN103107388A discloses a "spaceborne L-band micro-discharge high-power multiplexer," which invented a metal cavity multiplexer based on a coaxial cavity structure. Through common cavity coupling technology and resonant rod adjustment technology designed for micro-discharge, the micro-discharge power threshold can reach 500W. Chinese invention patent CN103151585A discloses a "ridge waveguide filter with high micro-discharge threshold and its design method," which invented a ridge waveguide filter that uses a polyetherimide dielectric layer filled inside the filter to achieve a high micro-discharge threshold metal ridge waveguide filter. Chinese invention patent CN112366431A discloses a "coupled structure with double symmetric zeros and a high-suppression dielectric waveguide filter," which employs a U-shaped structure and controls the coupling between the two cavities through a window-opening method. The coupling amount is controlled by adjusting the size of the control window. This U-shaped structure achieves CQ cross-coupling. However, in cases of three-cavity or multi-cavity cross-coupling, achieving CT cross-coupling usually requires additional zero cavities, resulting in irregular filter structures, large dimensions, and difficult manufacturing. Chinese invention patent CN214046157U discloses a "dielectric waveguide filter and its printed circuit board," which discloses a method for connecting the input and output of a dielectric filter to a printed circuit board, using the printed circuit board to achieve connection with external connectors.

[0005] In summary, traditional metal cavity filters use air as the microwave transmission medium. Within a limited volume, the smallest gap size is the weak point for micro-discharge breakdown. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention proposes an anti-micro-discharge microwave filter, which includes: a top plate, an aluminum film, a blank, a rubber pad, and a main body; the main body is a box-shaped structure with side openings, and a partition is provided inside the cavity; the rubber pad is disposed in each partition; the blank is disposed on the rubber pad; the aluminum film covers the upper surface of the blank; the top plate fixes the aluminum film, the blank, and the rubber pad to the main body.

[0007] The beneficial effects of this invention are:

[0008] This invention utilizes the high voltage withstand characteristics and high Q×f value of microwave dielectric materials to improve the micro-discharge threshold of microwave filters. Compared with cavity filters with the same electrical performance indicators, the size is reduced by more than 1 / 3 and the micro-discharge threshold is increased by more than 3dB, realizing the miniaturization, lightweighting and high reliability design of anti-micro-discharge microwave filters in aerospace payloads.

[0009] The filter of this invention adopts a structure of housing, filter blank, and top plate. The filter blank is fixed to the housing body with epoxy resin or epoxy pads. The housing body, filter blank, and top plate are all fixed to the housing body with fasteners. The epoxy resin or epoxy pads ensure the bonding strength between the filter blank and the metal housing, and also buffer the contact between the filter blank and the metal housing, thereby improving the resistance of the anti-micro-discharge microwave filter to mechanical shock and vibration tests. The overall structure is simple, reliable, and easy to assemble.

[0010] The filter of this invention adopts a straight-line structure. The three-cavity cross-coupling CT device is realized through the straight-line coupling slot between non-adjacent resonant cavities. The cross-coupling amount is adjusted by the position and hole depth of the straight-line CT device, thereby realizing the high-end out-of-band transmission zero point of the filter.

[0011] The filter and external connector of this invention are directly soldered through the filter blank connection hole and input / output resonant hole, without the need for additional components such as printed circuit boards, further reducing the size of the filter.

[0012] This invention addresses the problem that the micro-discharge threshold of traditional filters is limited by size and weight, making it difficult to improve in satellite payloads. It proposes a miniaturized, low-weight filter design method with a high micro-discharge threshold, meeting the development needs of miniaturization and lightweight aerospace payloads. Attached Figure Description

[0013] Figure 1 This is an assembly structure diagram of the filter of the present invention;

[0014] Figure 2 This is a schematic diagram of the filter embryo topology of the present invention;

[0015] Figure 3This is a schematic diagram of the linear coupling slot of the cross-coupled CT structure of the filter in this invention;

[0016] Figure 4 This is a schematic diagram of the input and output connection holes of the filter of the present invention;

[0017] Figure 5 This is a schematic diagram of the circuit topology of the example filter of the present invention;

[0018] Figure 6 This is a schematic diagram of the topology of an example filter blank of the present invention;

[0019] Figure 7 This is a graph showing the amplitude-frequency response of an example filter of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention proposes a design method for anti-micro-discharge microwave filters. Utilizing the high withstand voltage and high Q×f value of microwave dielectric materials, the micro-discharge threshold of the microwave filter is improved. No redundant zero-cavity is required in the linear structure, achieving a CT cross-coupling structure and simultaneously improving the filter's out-of-band suppression performance. The overall assembly structure is simple, realizing the miniaturization and lightweight design of microwave filters for aerospace payloads.

[0022] A design method for microwave filters used in aerospace payloads employs the following technical solution: Microwave filters used in aerospace payloads, especially in high-power environments, need to consider the micro-discharge effect. According to aerospace standards, in a vacuum, the filter's micro-discharge threshold must reach at least 6 dB above the actual operating power level, and it must pass a micro-discharge test before it can be used. Improving the filter's micro-discharge threshold within a limited volume is a significant challenge.

[0023] Traditional metal cavity filters use air as the microwave transmission medium. Within a limited volume, the smallest gap size is the weakest point for micro-discharge breakdown. Compared to commonly used metals like aluminum, copper, and other polytetrafluoroethylene (PTFE) materials in microwave filters, microwave dielectric materials possess high voltage resistance. Their secondary electron emission coefficient is half that of aluminum, making it difficult for charged particles to penetrate the medium and generate secondary electron excitation, thus significantly improving the filter's micro-discharge threshold. Simultaneously, microwave dielectric materials exhibit high Q×f values, achieving insertion loss comparable to metal filters.

[0024] The specific implementation steps are as follows: First, based on the technical requirements of the filter, such as insertion loss, bandwidth, and out-of-band rejection, select the optimal number of filter sections and circuit topology. Set transmission zeros at the frequency points where interference needs to be suppressed, and synthesize the coupling matrix to ensure that the electrical performance indicators meet the requirements. Then, obtain the initial theoretical dimensions of the filter resonant cavity, coupling slot, and cross-coupling slot. The resonant cavity and cross-coupling slot can be circular, rectangular, square, etc., with a rectangular shape being preferred. Establish a three-dimensional overall structural model of the filter, and simulate the filter using electromagnetic software such as HFSS and CST. Iteratively optimize the model to obtain the frequency response curve of the filter. Preferably, the return loss of the filter obtained from the three-dimensional model should be greater than 20dB, while other electrical performance indicators can have appropriate margins and are not limited.

[0025] In this embodiment, the electric and magnetic fields of the filter are calculated, and the field data is imported into electromagnetic software such as HFSS and CST to calculate the micro-discharge threshold and discharge particle distribution of the filter. Based on the weak points of the micro-discharge threshold and discharge particle distribution, and by optimizing the resonator geometry to reduce the local electric field concentration area, the filter structure dimensions are corrected, and finally a design that meets the requirements is obtained.

[0026] Based on the selected dielectric material, the filter blank is obtained through processing steps such as die casting, high-temperature sintering, machining, and silver plating.

[0027] The input and output connection hole patterns of the filter blank are laser-engraved. After the connectors are soldered, the external connectors are soldered through the connection holes of the filter blank. The void rate of the filter blank connection holes must be less than 10% to ensure no residual gas is released in a vacuum low-pressure environment, thus ensuring the stability of the filter's power threshold.

[0028] Furthermore, the frequency and coupling amount can be adjusted by grinding the silver plating thickness of the resonant cavity hole, the coupling groove, and the dielectric inside the cross coupling groove.

[0029] Preferably, the grinding and polishing areas are the top of the resonant cavity hole and the top of the cross-coupling slot hole, to ensure that the silver layer is ground as little as possible, to avoid the presence of air layers caused by incomplete silver plating on the outer wall, and to ensure the stability of the filter power threshold.

[0030] Furthermore, after debugging, the filter blank is assembled to the bottom of the housing using epoxy glue or epoxy pads. After curing, the housing body, filter blank, and top plate are fixed to the housing body with fasteners to complete the assembly.

[0031] Preferably, an aluminum film is attached to the opening end of the resonant hole of the filter blank, and an exhaust hole corresponding to the center position of the resonant hole is provided on the aluminum film. This ensures that the residual gas in the resonant hole is discharged in the vacuum low pressure environment, ensuring the stability of the filter power threshold, and also prevents external foreign objects from entering the resonant hole.

[0032] The aforementioned anti-micro-discharge microwave filter is used in the P / L / S frequency band.

[0033] In this embodiment, as Figures 1-6 As shown, the anti-micro-discharge microwave filter includes a housing and a filter blank 3 located within the housing. The housing includes a body 6 and a top plate 1. The body 6 is a box-shaped structure with side openings and a partition is provided inside the cavity. The filter blank 3 is located inside the housing body 6 and is fixed to the housing body 6 with epoxy resin or epoxy pads 5. The housing body 6, the filter blank 3, and the top plate 1 are all fixed to the housing body 6 by fasteners.

[0034] The filter blank 3 is fixed inside the housing body 6 with epoxy glue or epoxy pad 5. The epoxy glue or epoxy pad 5 not only ensures the bonding strength between the filter blank 3 and the metal housing 6, but also provides a buffering effect for the contact between the filter blank 3 and the metal housing 6, thereby improving the resistance of the anti-micro-discharge microwave filter to mechanical shock and vibration tests.

[0035] An aluminum film 2 is attached to the opening end of the resonant hole of the filter blank. The aluminum film 2 has an exhaust hole corresponding to the center position of the resonant hole. This ensures that the residual gas in the resonant hole is discharged in a vacuum low-pressure environment, ensuring the stability of the filter power threshold, and also prevents external foreign objects from entering the resonant hole.

[0036] like Figure 2 As shown, the filter blank has N resonant cavities 31, M coupling slots 32, P cross-coupling slots 33, and two input / output connection holes 34. The N resonant cavities 31, M coupling slots 32, P cross-coupling slots 33, and the connection holes 34 are integrally machined into the filter blank material. The connection holes are used for connection with external connectors. The outer surface of the filter blank material is silver-plated. The relationship between the number of resonant cavities N, the number of coupling slots M, and the number of cross-coupling slots P is: number of coupling slots M ≤ number of resonant cavities N-1, number of cross-coupling slots P ≤ number of resonant cavities N-2. The N resonant cavities 31, M coupling slots 32, and P cross-coupling slots 33 are determined by the coupling matrix obtained by synthesizing the electrical performance indicators of the filter. The order of the filter determines the number of resonant cavities N. The coupling coefficients of adjacent filters determine the number of coupling slots M and the physical dimensions of the coupling slots, such as the width and depth of the coupling slots. The coupling coefficients of non-adjacent filters determine the number of cross-coupling slots P and the physical dimensions of the cross-coupling slots, such as the width, depth, and position of the cross-coupling slots in the overall filter structure.

[0037] In this embodiment, the number of resonant cavities and coupling slots is typically required to be N≥3, M≥1, and P is flexibly set by the out-of-band suppression electrical performance index of the filter and is not limited.

[0038] The N resonant cavities 1, M coupling slots 2 and P cross coupling slots 3 are all blind cavity structures, and their open surfaces are all located on the same side of the filter blank.

[0039] like Figure 3 As shown, the anti-micro-discharge microwave filter, to improve the out-of-band suppression requirement of the filter, has a cross-coupling slot 1 between non-adjacent resonant cavities. The cross-coupling slot 1 introduces a transmission zero, and the coupling strength is controlled by the position and structural dimensions of the cross-coupling slot 1. The number of cross-coupling slots P≥1, and the number P is flexibly selected according to the out-of-band suppression requirement of the filter.

[0040] The filter described herein has N resonant cavities 1, M coupling slots 2, and P cross-coupling slots 3. The N resonant cavities 1 and the P cross-coupling slots 2 are blind cavity structures, integrally formed on the filter blank material. The resonant cavities 1 and the cross-coupling slots 2 are typically circular or square holes, and this invention is not limited thereto.

[0041] like Figure 4 As shown, the filter connection hole 34 is a through hole, and the through section of the hole is plated with a silver layer. The diameter of the connection hole 34 is connected to the inner conductor of the external connector 35, and the outside of the connection hole 34 is provided with an insulating layer for connecting to the outer conductor of the external connector 35. The external connector 35 can be an ASMP connector, an SMA connector, a TNC connector, etc. The structure of the connection hole can be designed according to a specified connector structure, and this invention is not limited thereto.

[0042] The filter blank is characterized in that it is a rectangular or square block structure. The depths of the N resonant cavities can be the same or different depending on the specifications. The spacing between adjacent N resonant cavities can be equal or unequal, depending on the specifications. The N adjacent resonant cavities can be coupled using coupling slots, depending on the specifications. The coupling slots extend through adjacent resonant cavities, and their width and depth are adjusted according to the electrical coupling amount.

[0043] The input / output connection hole directly communicates with the blind hole section of the input / output resonant cavity of the filter blank. The inside of the input / output connection hole is silver-plated.

[0044] The filter blank material is characterized in that it is typically a high-Q microwave dielectric material of the MgTiO3-CaTiO3 system with a dielectric constant ≥10, Q×F ≥45000, low temperature drift coefficient.

[0045] The anti-micro-discharge microwave filter provided by this invention can effectively solve the micro-discharge problem of high-power microwave filters in satellite payloads. It features a simple structure, easy fabrication and debugging, convenient assembly, and high batch production consistency, meeting the requirements of high micro-discharge threshold, miniaturization, and lightweight design for P / L / S band spaceborne filters. The design method described in this invention can be used as a standalone filter or extended to multiplexer design.

[0046] The following is a specific embodiment of the present invention:

[0047] An embodiment of an L-band anti-micro-discharge microwave filter is provided, which is applied to a satellite payload. The operating frequency band is 900MHz~1250MHz, the 1270MHz frequency point suppression is greater than 70dB, and the pulse power level is 60W.

[0048] like Figure 5 As shown, considering the above electrical performance requirements, a 10th-order circuit topology is adopted, and a CT cross-coupling (4) structure is introduced between the resonant cavity (1) and the resonant cavity (3) to introduce an out-of-band suppression zero at the high-end 1270MHz.

[0049] A microwave dielectric material with a relative permittivity of 20, Q×F≥40000, and dielectric loss tangent less than 0.0002 is selected. In this embodiment, the silver plating thickness is required to be greater than 15µm.

[0050] The filter blank is designed with a straight block structure with a height h of 12mm, a sidewall thickness of 12mm, and a length of 74mm.

[0051] The resonant holes are distributed around the central axis of the filter blank. The resonant holes (1), (2), and (3) are arranged in a triangle. The cross coupling groove (4) is parallel to the resonant hole (2). The other two connecting holes (5) are located on the left and right side walls of the filter blank, respectively, and each is connected to one of the resonant holes 1 and 2.

[0052] Ten resonant holes are set at equal intervals. The resonant holes are rectangular structures of 3mm×4mm. Adjacent resonant holes are connected by rectangular coupling grooves with a width of 2mm and a groove depth determined by the coupling coefficient.

[0053] The input / output connection hole (5) has a diameter of Ф0.8mm. The externally welded input / output connector (6) uses an ASMP connector.

[0054] like Figure 1As shown, the housing includes a body 6 and a top plate 1. The body 6 is a box-shaped structure with a side opening and a partition is provided in the cavity. The filter blank 3 is located inside the housing body 6. The filter blank is fixed inside the housing body 6 with epoxy glue or epoxy pad 5. The housing body 6, the filter blank 3 and the top plate 1 are all fixed to the housing body 6 by fasteners.

[0055] The filter blank 3 is fixed inside the housing body 6 with epoxy glue or epoxy pad 5. The epoxy glue or epoxy pad 5 not only ensures the bonding strength between the filter blank 3 and the metal housing 6, but also provides a buffering effect for the contact between the filter blank 3 and the metal housing 6, thereby improving the resistance of the anti-micro-discharge microwave filter to mechanical shock and vibration tests.

[0056] An aluminum film 2 is attached to the opening end of the resonant hole of the filter blank. The aluminum film 2 has an exhaust hole corresponding to the center position of the resonant hole. This ensures that the residual gas in the resonant hole is discharged in a vacuum low-pressure environment, ensuring the stability of the filter power threshold, and also prevents external foreign objects from entering the resonant hole.

[0057] The L-band anti-micro-discharge microwave filter in this embodiment has been verified through micro-discharge testing. The test was conducted in a vacuum chamber to simulate the on-orbit operation of a satellite, with a vacuum level better than 6.65 × 10⁻⁶. -3 Pa, the test temperature was selected at two low and high temperature points: -30℃ and +65℃. Pulse power was applied to the input terminal of the filter, and the pulse frequency was selected at three points: the low end, the high end, and the center frequency of the filter passband. The test pulse power was 480W. The filter did not generate any power, reaching the micro-discharge threshold of 9dB. The product meets the requirements of existing satellite communication technology.

[0058] Compared with existing metal cavity filters of the same specifications and package dimensions, under the same test conditions, existing metal cavity filters exhibit discharge phenomena at a pulse wave power of 200W. In contrast, the filter of this invention improves the anti-micro-discharge threshold level by more than 3dB and reduces the size by more than 3 times. The amplitude-frequency response curve of the filter is shown in the figure. Figure 7 As shown.

[0059] In the description of this invention, it should be understood that the terms "coaxial," "bottom," "one end," "top," "middle," "other end," "upper," "side," "top," "inner," "outer," "front," "center," "both ends," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0060] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A microwave filter for resisting micro-discharge, characterized in that, include: The structure comprises a top plate, an aluminum film, a blank, a rubber pad, and a main body; the main body is a box-shaped structure with an opening on the side, and a partition is provided inside the cavity. The adhesive pads are disposed within each partition; the preform is disposed on the adhesive pads; the aluminum film covers the upper surface of the preform; the aluminum film, the preform, and the adhesive pads are fixed to the main body by the top plate.

2. The anti-micro-discharge microwave filter according to claim 1, characterized in that, The top plate is open on both the left and right sides, and has multiple "I"-shaped through holes evenly arranged on the front and back sides. The bottom of the side of the top plate is provided with inserts to fix the top plate in place. The top surface of the top plate is provided with long through holes to expose part of the aluminum film.

3. The anti-micro-discharge microwave filter according to claim 1, characterized in that, The blank has N resonant cavities, M coupling slots, P cross coupling slots and two input / output connection holes. The N resonant cavities, M coupling slots and P cross coupling slots and connection holes are integrally machined into the filter blank material.

4. The anti-micro-discharge microwave filter according to claim 3, characterized in that, The relationship between the number of resonant cavities N, the number of coupling slots M, and the number of cross-coupling slots P is as follows: the number of coupling slots M ≤ the number of resonant cavities N-1, and the number of cross-coupling slots P ≤ the number of resonant cavities N-2.

5. A microwave filter for resisting micro-discharge according to claim 3, characterized in that, All N resonant cavities, M coupling slots, and P cross-coupling slots are blind cavity structures, and their open surfaces are all located on the same side of the embryo.

6. The anti-micro-discharge microwave filter according to claim 5, characterized in that, Cross-coupling slots introduce transmission zeros, and the coupling strength is controlled by the position and structural dimensions of the cross-coupling slots.

7. The anti-micro-discharge microwave filter according to claim 3, characterized in that, The input and output connection holes are respectively connected to the external conductors of the external connectors.

8. A microwave filter for resisting micro-discharge according to claim 3, characterized in that, The aluminum film is rectangular and has small holes. The aluminum film covers the upper surface of the embryo, so that each small hole corresponds to the top of each resonant cavity of the embryo.

9. A microwave filter for resisting micro-discharge according to claim 1, characterized in that, The gasket is made of epoxy adhesive or epoxy gasket.

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