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Base Station Filters Overview
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Base Station Filters Overview

  • Categories:News
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  • Time of issue:2019-10-25 17:29
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(Summary description)Filter is the base station RF core device, the filter filters electromagnetic wave signals, allowing only the required signals to pass, the main purpose is to solve the problem of interference between different frequency bands, different forms of wireless communication systems. At present, there are three main types of filters, namely, metal coaxial cavity filters, metal cavity + ceramic dielectric resonator rod filters and ceramic dielectric waveguide filters, the latter two raw materials are involved in ceramic media.

Base Station Filters Overview

(Summary description)Filter is the base station RF core device, the filter filters electromagnetic wave signals, allowing only the required signals to pass, the main purpose is to solve the problem of interference between different frequency bands, different forms of wireless communication systems. At present, there are three main types of filters, namely, metal coaxial cavity filters, metal cavity + ceramic dielectric resonator rod filters and ceramic dielectric waveguide filters, the latter two raw materials are involved in ceramic media.

  • Categories:News
  • Author:
  • Origin:
  • Time of issue:2019-10-25 17:29
  • Views:
Information
What is a filter?
 
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Filter is the base station RF core device, the filter filters electromagnetic wave signals, allowing only the required signal to pass, the main purpose is to solve the interference problem between different frequency bands, different forms of wireless communication systems. At present, there are mainly three types of filters, namely, metal coaxial cavity filters, metal cavity + ceramic medium resonator bar filters and ceramic medium waveguide filters, the latter two raw materials are involved in ceramic medium. 3G/4G era to the metal coaxial cavity filters.

 The application of Massive MIMO technology and active antennas in the 5G era drives the miniaturization and lightweighting of filters, and the filter industry is facing technological upgrading and the evolution of metal cavity to ceramic dielectric filters.

Ceramic dielectric waveguide filter process flow

 ● Adopt high temperature sintering process, the flow is as follows: RF/structure design - dielectric powder manufacturing - spray granulation - press molding - sintering - grinding - metallization -Electrode making -Debugging, etc. Among them, the core manufacturing process mainly consists of four major parts: powder formulation, press molding and sintering, metallization and debugging.

Key Manufacturing Processes for Ceramic Dielectric Waveguide Filters

 
  The technical difficulties in the production of ceramic filters lie in the consistency, the formulation of ceramic powder materials, the automation of production, as well as the yield and efficiency of debugging are the difficulties in the production of filters.
 
1  Powder Preparation: Own formula is one of the competitiveness of the enterprise. Ceramic powder formula is a key factor in determining the performance of the filter, only with a good material formula to obtain the corresponding high Q value of media ceramics, acid and alkali control is unreasonable, impurities and other factors will damage the quality of the powder.
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  Dry compression molding: One of our core competencies is the autonomy of our powder dry compression molding equipment and production process. The dry pressing process involves placing the granulated powder into a mold, where it is eventually rearranged and deformed to form a ceramic blank with a certain strength and shape. The main influencing factors include: the nature of the powder, the choice of binder and lubricant, the design of the mold, the pressing force during the pressing process, the method of pressing, the acceleration speed and the holding time, and so on.
 
 
 
  Sintering: The autonomy of the sintering furnace and the production process is one of the core competencies. Embryo under the action of high temperature, the final formation of hard polycrystalline sintered body with a certain microstructure. The sintering process determines the grain size and density of ceramics, which in turn affects the mechanical strength and polarization of ceramics, and the improvement of the process can significantly affect product performance.
 
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CNC machining: Manufacturers with mature production processes can skip the CNC machining process, significantly increasing production time. CNC machining means the use of CNC numerical control machine tools for grinding, precise dimensional accuracy of the ceramic dielectric body.
  Debugging: Traditional cavity filters are debugged by adjusting the resonance rod, mainly with return loss parameters, insertion loss parameters, out-of-band rejection parameters and so on. Ceramic filter debugging can only be done by grinding. Due to the irreversibility of ceramic grinding, product debugging is a key link that affects product yield and production efficiency.
  Metallization: Chemical plating, spraying, sputtering, screen printing and other processes are used to cover the ceramic dielectric substrate with a silver layer, which is burned in a silver baking oven, and the silver plating can be adjusted using laser equipment.


  Ceramic dielectric filters have advantages in miniaturization, lightweight, low loss, temperature stability, and cost-effectiveness.

 ● Filter usage increases exponentially in the 5G era, placing higher demands on device size, weight, thermal performance, and price. 4GRRU weighs between 13-20kg, and 5GAAU weighs between 38-47kg, resulting in a huge challenge to the load bearing of the ceiling.

 ● Ceramic dielectrics have high quality factor Q, high relative dielectric constant and low loss. According to the propagation characteristics of electromagnetic waves, when an electromagnetic wave enters a medium with a low dielectric constant from a medium with a high dielectric constant, it will be emitted and refracted on the dielectric demarcation surface. When the angle of incidence is greater than or equal to the critical angle, the electromagnetic wave will be fully reflected. The higher the dielectric constant of the medium, the smaller the critical angle, it is easy to form a magnetic wall on the surface of the medium, the electromagnetic field energy is concentrated in the resonant cavity, the radiation loss is small. The loss of the dielectric itself determines the Q value of the resonator, Q=1/tanδ (δ is the loss angle), the higher the Q value, the easier it is to maintain the electromagnetic oscillation.

 ● The relative dielectric constant of the ceramic dielectric can be up to 90 or more, which can greatly reduce the size and mass of the filter without degrading the performance of the filter. The size of the filter is related to the resonant frequency and the relative dielectric constant of the material. The higher the resonant frequency and the higher the relative dielectric constant, the smaller the device size. The geometric ruler of dielectric filter is half of the waveguide wavelength.

 ● Ceramic dielectric materials are lighter and less expensive than metallic materials.
 

 

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