| In recent years,mobile communication has stepped from 4G to 5G,which puts forward higher requirements for the performance and size of the filter.The development direction of commercial filters is miniaturization,low cost and high integration.Compared with the widely used SAW,FBAR and LTCC filters,the filters designed and manufactured with LC lumped elements have the advantages of low cost and short production cycle,and have market demand in some small batch customization systems.Based on the theoretical knowledge of filter.The commercial LC components will be used to design and manufacture RF filter in this thesis.filter is made by the strategy of real-time measurement and feedback adjustment.The specific contents of this thesis are as follows:(1)The LC filter is designed with capacitive and inductive elements in the frequency band near1.0 GHz.In this frequency band,the influence of circuit parasitic parameters and other factors cannot be ignored,and the electrical properties of components will change with the change of frequency.There is a large deviation between the actual response of the physical filter and the ideal simulation results.The S-parameters need to be adjusted by repeatedly replacing the components.To solve this problem,the air core inductor with high Q value is selected to replace the traditional chip SMT inductor.The operating frequency and bandwidth of the filter can be corrected by tuning the coil.The layout design of an elliptic function bandpass LC filter with a center frequency of 1.2GHz and a bandwidth of 240 mhz is completed.According to the selected SMT elements,the filter is made by assembling and tuning the inductor.(2)A vertical mounting design of components based on PCB circuit is proposed,so that the components can still play a role in the state of welding perpendicular to PCB.By arranging inductors and capacitors in three-dimensional space and mounting them vertically,and using components of the same specification,the filter circuit area is reduced by 50% and the integration degree is improved.The physical test results of the filter show that this method can achieve the expected performance index.(3)A four port fifth order low reflection filter is designed and fabricated.The structure consists of two high pass and low pass branches.The normalized element values are given by theoretical calculation.The filter circuit is realized by using LC element.The filter is measured and compared with the simulation model. |
