Airborne high-suppression high-power filter and installation method thereof

Abstract

The invention discloses an airborne high-suppression high-power filter and an installation method thereof, and relates to the field of communication. The radio frequency circuit comprises seven inductors which are connected in sequence, and every two adjacent inductors are grounded through a capacitor. The working frequency band is 500MHz, the in-band loss is less than 0.4 dB through circuit design, continuous wave 2000W high power can be borne, the size is small, the weight is light, out-of-band harmonic waves of a high-power transmitter can be filtered, and the electromagnetic compatibility of the system is improved. High suppression is realized by adopting a circuit form of a 13-section Chebyshev LC low-pass filter, and 760MHz out-of-band suppression can reach more than 70dB. Through structural process design and box body laser seal welding, the vibration and low-pressure environment of airborne use can be met. The antenna is suitable for improving the electromagnetic compatibility of an airborne broadband high-power transmitting system.

Description

Technical Field

[0001] The present invention relates to an airborne high-suppression high-power filter in the field of communications, which realizes the function of harmonic filtering of a high-power transmitter, has a wide working frequency band, can withstand large power, has high out-of-band suppression, is small in size and light in weight, has good anti-vibration capability, and can adapt to high-altitude low-pressure environments, meeting the application requirements of airborne broadband high-power transmission systems for improving their own electromagnetic compatibility. Background Art

[0002] With the development of communication technology, the technical level of electronic devices has been continuously improved, with smaller size and stronger functions. The integration of electronic systems has also become higher and higher, and the frequency band coverage has become wider and wider. If different frequency band devices in the system work at the same time, it is necessary for the devices in each frequency band to have good electromagnetic compatibility. When the high-power transmitter in the system is working, the harmonic signal generated is strong, which will affect the normal operation of other frequency band devices. It is necessary to use a high-power filter to filter out the harmonics and improve the electromagnetic compatibility of the system itself.

[0003] There are many ways to classify filters. According to the frequency response, they can be divided into four basic types: low-pass filter, band-pass filter, high-pass filter and band-stop filter. The design method of low-pass filter is the basis. Through appropriate frequency conversion, the low-pass filter design can be transformed into band-pass filter, high-pass filter and band-stop filter. According to the different implementation forms, filters are generally divided into LC filters, dielectric filters, cavity filters, surface acoustic wave filters and microstrip filters.

[0004] Traditional high-inhibition high-power filters require more filter sections for high suppression, and high power requires high withstand voltage, low loss, and good heat dissipation. These requirements will result in a larger filter size. Airborne filters require small size, light weight, good vibration resistance, and adaptability to high-altitude, low-pressure working environments. At present, there is little information on airborne high-inhibition high-power filters. In order to meet the needs of airborne broadband high-power transmission systems to improve their own electromagnetic compatibility, the development of high-inhibition high-power filters that meet the airborne use environment has become a key technology that needs to be urgently solved in current engineering applications. Summary of the invention

[0005] The technical problem to be solved by the present invention is to achieve high suppression through circuit design of a 13-section Chebyshev LC low-pass filter; to increase the power capacity by improving the withstand voltage and heat dissipation capacity and reducing the loss through device design; to improve the withstand voltage of the medium by designing a silicone adhesive coating method, thereby reducing the excess space size of the box body to achieve miniaturization; and to solve the problems of temperature adaptability of the ceramic substrate, high-power air breakdown, high-intensity vibration, high-altitude low-pressure environment, etc. through designing the structure and assembly process.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] An airborne high-rejection high-power filter includes a radio frequency circuit.

[0008] The radio frequency circuit includes seven inductors connected in sequence, and each adjacent inductor is grounded via a capacitor.

[0009] Furthermore, it also includes a box body 28 and a ceramic insulator 24. The ceramic insulator passes through one of the box surfaces of the box body, and its inner end is connected to the radio frequency circuit. A cover plate is provided on the top of the box body, and the top cover is laser-sealed to the box body.

[0010] Furthermore, the capacitor is a single-layer alumina ceramic plate capacitor, and the inductor is a hollow inductor wound with gold-plated copper wire;

[0011] The bottom surface of the box body is provided with a molybdenum copper carrier 27, which is welded to the corresponding position of the bottom surface of the box body 28; the ceramic plate capacitors 21 correspond to the molybdenum copper carriers 27 one by one, and the ceramic plate capacitors 21 are welded to the upper surface of the molybdenum copper carrier 27; the inductor 22 is electrically welded to the corresponding position of the ceramic plate capacitor 21;

[0012] Silicone glue is coated on the inner bottom surface of the box body 28 and the ceramic plate capacitor 21, and the polytetrafluoroethylene support block 25 is fixed to the corresponding position of the box body 28 by screws 26, and the inductor 22 is bonded and fixed to the polytetrafluoroethylene support block 25 using silicone glue.

[0013] Furthermore, the core of the ceramic insulator is a gold-plated Kovar material with a diameter of 2 mm, and the alumina ceramic is processed into an annular column. The core passes through the annular column ceramic and is welded together using gold-tin.

[0014] A method for installing an airborne high-inhibition high-power filter is used to install an airborne high-inhibition high-power filter, specifically comprising the following steps:

[0015] Step 1, the molybdenum copper carrier 27 is soldered to the box body 28;

[0016] Step 2, the ceramic plate capacitor 21 is soldered to the molybdenum copper carrier 27 using solder;

[0017] Step 3, the ceramic insulator 24 is welded to the box body 28 using solder;

[0018] Step 4, electrically welding the inductor 22 to the corresponding positions of the ceramic insulator 24 and the ceramic plate capacitor 21 in the box body 28;

[0019] Step 5: Install the RF socket and conduct debugging test on the vector network analyzer to fine-tune the filter index by adjusting the spacing of the inductor coils; and reserve a certain bandwidth margin during the debugging process;

[0020] Step 6: After debugging is completed, a 3 mm thick silicone adhesive is applied to the inner bottom surface of the box body 28 and the ceramic plate capacitor 21;

[0021] Step 7, after the silicone adhesive is cured, the polytetrafluoroethylene support block 25 is fixed to the corresponding position of the box body 28 using screws 26, and the inductor 22 is bonded and fixed to the polytetrafluoroethylene support block 25 using silicone adhesive;

[0022] Step 8, after the silicone adhesive is completely cured and before the cover plate 23 is installed, use tooling and instruments to perform a gas leakage rate test on the box body 28 to check the welding condition of the ceramic insulator 24;

[0023] Step 9, after the air leakage rate is detected to be normal, the box body 28 and the cover plate 23 are laser sealed;

[0024] Step 10: After the laser sealing is completed, the filter is tested for air leakage rate again. After the test is normal, the filter is qualified.

[0025] The present invention has the following gain effects:

[0026] a) The present invention has high out-of-band suppression through radio frequency circuit design, which facilitates high power implementation of the device.

[0027] b) The present invention improves the power capacity of the filter by solving the voltage resistance and heat dissipation problems of the core high-power devices, and can withstand greater power.

[0028] c) The four structural process designs of the present invention solve the environmental adaptability problems of miniaturization, high power breakdown, high-intensity vibration, high altitude and low air pressure of airborne high-inhibition high-power filters.

[0029] d) The radio frequency interface of the present invention adopts an asymmetric structure layout of ceramic insulators and is designed according to the layout of a power amplifier using a filter, which is conducive to the miniaturization of the upper-level product. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the radio frequency circuit principle of the present invention;

[0031] Figure 2 It is a schematic diagram of the process design of the installation structure of the present invention;

[0032] Figure 3 yes Figure 2 A schematic cross-sectional view of AA;

[0033] Figure 4 It is a transmission loss and return loss test result diagram of the present invention; DETAILED DESCRIPTION

[0034] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0035] A high-suppression high-power filter, characterized in that the filter radio frequency circuit is composed of inductors 01 to 07 and capacitors 08 to 13. Comprehensively considering the requirements of filter frequency, power, volume, use environment and other aspects, a 13-section Chebyshev LC low-pass filter circuit is adopted, with high out-of-band suppression and little difference in device values, which is convenient for high-power device realization and assembly.

[0036] The capacitor is realized by a single-layer alumina ceramic plate capacitor, which has a high dielectric withstand voltage, good heat dissipation capacity, and is suitable for high power. In capacitor design, the metal layer area on the upper and lower sides of the ceramic plate is calculated according to the required capacitance value, and the size of the ceramic plate is increased so that the edge of the upper metal layer pattern is greater than 5mm from the edge of the ceramic plate. The sharp corners of the upper metal pattern are rounded to prevent it from being too close to the ground and the tip from discharging and sparking at high power; the lower layer of the ceramic plate is all metal layer, which is used for welding grounding and high power heat dissipation. The inductor is a hollow inductor wound with gold-plated copper wire, which has low loss, high thermal conductivity, and high power bearing. In inductor design, the diameter of the gold-plated copper wire is 2mm, the winding diameter of the inductor coil is 8mm, and the number of winding turns is calculated according to the required inductance value. The metal wire spacing of the coil is greater than 1mm to prevent sparking between high-power coils. Ceramic insulators are used to replace conventional glass insulators. Compared with glass insulators, the dielectric loss is much smaller and it can withstand higher power. The ceramic insulator is designed with a core made of 2mm diameter Kovar material and gold-plated. The alumina ceramic is processed into a ring-shaped column. The size is calculated based on 50 ohm impedance. The inner and outer surfaces of the ring column are metallized and gold-plated by sputtering process. The core and the ring column are welded with gold-tin to form an insulator.

[0037] The thermal expansion coefficient of alumina is about 6.9ppm / ℃, and the thermal expansion coefficient of aluminum alloy is about 23ppm / ℃. The alumina ceramic plate may break during high-temperature welding or sudden changes in ambient temperature. In order to improve the temperature adaptability of the alumina ceramic plate, a molybdenum-copper carrier with a medium thermal expansion coefficient is added to match the larger difference in thermal expansion coefficients between the ceramic plate and the aluminum alloy box.

[0038] Due to the need for miniaturized design, the space inside the filter box is limited. When working at high power, the electric field strength is very high and close to the air breakdown field strength. Silicone glue with a higher dielectric withstand voltage value is used to coat the ceramic plate to prevent the occurrence of high-power air breakdown.

[0039] In order to cope with high-intensity airborne vibration conditions and prevent high-power inductors from being damaged due to metal fatigue, a polytetrafluoroethylene support block was designed. The dielectric constant of this material is 2.2, which has little effect on the RF circuit indicators. It is bonded to the inductor with silicone glue to avoid metal fatigue damage caused by large swings when the inductor vibrates.

[0040] Low air pressure at high altitude will reduce the air breakdown field strength. To address this problem, the box body is designed in the form of laser sealing, and the RF interface adopts the form of welding ceramic insulators and the box body to ensure good airtightness.

[0041] Reference Figures 1 to 4 , this embodiment includes filter RF circuit design, filter installation structure process design and index test results.

[0042] The filter RF circuit, the RF input end is connected to one end of the inductor 01, the other end of the inductor 01 is connected to the inductor 02 and the capacitor 08, and the other end of the capacitor 08 is grounded; the other end of the inductor 02 is connected to the inductor 03 and the capacitor 09, and the other end of the capacitor 09 is grounded; the other end of the inductor 03 is connected to the inductor 04 and the capacitor 10, and the other end of the capacitor 10 is grounded; the other end of the inductor 04 is connected to the inductor 05 and the capacitor 11, and the other end of the capacitor 11 is grounded; the other end of the inductor 05 is connected to the inductor 06 and the capacitor 12, and the other end of the capacitor 12 is grounded; the other end of the inductor 06 is connected to the inductor 07 and the capacitor 13, and the other end of the capacitor 13 is grounded; the other end of the inductor 07 is connected to the RF output end.

[0043] Filter installation structure process, the molybdenum copper carrier 27 is soldered to the box body 28, the ceramic plate capacitor 21 is soldered to the molybdenum copper carrier 27, and the ceramic insulator 24 is soldered to the box body 28. The inductor 22 is electrically welded to the corresponding positions of the ceramic insulator 24 and the ceramic plate capacitor 21 in the box body 28. After the filter is installed in the RF socket, a debugging test is performed on the vector network analyzer, and the filter indicators are fine-tuned by adjusting the inductor coil spacing. A certain bandwidth needs to be reserved during debugging because the subsequent coating of silicone glue will produce some frequency offsets. After debugging is completed, 3mm thick silicone glue is applied to the bottom surface of the box body 28 and the ceramic plate capacitor 21. After the silicone glue is cured, the polytetrafluoroethylene support block 25 is fixed to the corresponding position of the box body 28 using screws 26, and the inductor 22 is bonded and fixed to the polytetrafluoroethylene support block 25 using silicone glue. After the silicone adhesive is completely cured, the box body 28 is tested for air leakage rate using tools and instruments to check the welding of the ceramic insulator 24. After the air leakage rate test is normal, the box body 28 and the cover plate 23 are laser sealed. After the laser sealing is completed, the filter is tested for air leakage rate again. If the test is normal, the filter is qualified.

[0044] The filter technical index test shows that the in-band loss is less than 0.4dB, the out-of-band suppression from 760MHz to triple frequency is greater than 70dB, and the in-band return loss is also relatively good. After airborne use verification, the power handling and other indicators can meet the requirements.

[0045] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes but is not limited to the contents described in the drawings and the above specific embodiments. Any modification that does not deviate from the functional and structural principles of the present invention will be included in the scope of the claims.

Claims

1. An airborne high-suppression high-power filter, characterized in that: including radio frequency circuits; The radio frequency circuit includes seven inductors connected in sequence, and each adjacent inductor is grounded via a capacitor.

2. The airborne high-suppression high-power filter according to claim 1, characterized in that: It also includes a box body (28) and a ceramic insulator (24), wherein the ceramic insulator penetrates the side wall of the box body and its inner end is connected to the radio frequency circuit; a cover plate is provided on the top of the box body, and the top cover is laser-sealed to the box body.

3. The airborne high-suppression high-power filter according to claim 1, characterized in that: The capacitor is a single-layer alumina ceramic plate capacitor, and the inductor is a hollow inductor wound with gold-plated copper wire; The bottom surface of the box body is provided with a molybdenum copper carrier (27), and the molybdenum copper carrier (27) is welded to a corresponding position of the bottom surface of the box body (28); the ceramic plate capacitor (21) corresponds to the molybdenum copper carrier (27) one by one, and the ceramic plate capacitor (21) is welded to the upper surface of the molybdenum copper carrier (27); and the inductor (22) is then electrically welded to a corresponding position of the ceramic plate capacitor (21); Silicone glue is coated on the inner bottom surface of the box body (28) and the ceramic plate capacitor (21), and a polytetrafluoroethylene support block (25) is fixed to a corresponding position of the box body (28) by means of screws (26), and the inductor (22) is bonded and fixed to the polytetrafluoroethylene support block (25) by means of silicone glue.

4. The airborne high-suppression high-power filter according to claim 2, characterized in that: The ceramic insulator has a core made of gold-plated Kovar material with a diameter of 2 mm, and the alumina ceramic is processed into an annular column. The core passes through the annular column ceramic and is welded together using gold-tin.

5. A method for installing an airborne high-suppression high-power filter, characterized in that: The method for installing an airborne high-suppression high-power filter according to claim 3 specifically comprises the following steps: Step 1, the molybdenum copper carrier (27) is soldered to the box body (28) using solder; Step 2, the ceramic plate capacitor (21) is soldered to the molybdenum copper carrier (27) using solder; Step 3, the ceramic insulator (24) is welded to the box body (28) using solder; Step 4, electrically welding the inductor (22) to the corresponding positions of the ceramic insulator (24) and the ceramic plate capacitor (21) in the box body (28); Step 5: Install the RF socket and conduct debugging test on the vector network analyzer to fine-tune the filter index by adjusting the spacing of the inductor coils; and reserve a certain bandwidth margin during the debugging process; Step 6, after debugging is completed, a 3 mm thick silicone adhesive is coated on the inner bottom surface of the box body (28) and the ceramic plate capacitor (21); Step 7, after the silicone adhesive is cured, the polytetrafluoroethylene support block (25) is fixed to the corresponding position of the box body (28) using screws (26), and the inductor (22) is bonded and fixed to the polytetrafluoroethylene support block (25) using silicone adhesive; Step 8, after the silicone adhesive is completely cured and before the cover plate (23) is installed, a gas leakage rate test is performed on the box body (28) using tooling and instruments to check the welding condition of the ceramic insulator (24); Step 9, after the gas leakage rate is detected to be normal, the box body (28) and the cover plate (23) are laser sealed; Step 10, after the laser sealing is completed, the filter is tested for air leakage rate again, and the filter is qualified after the inspection is normal.

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