Research On Miniaturization Technology Of Microwave Filters For 5G Communication System

With the application of large-scale MIMO antenna in 5G communication system,the filters applied in front-end of base station will increase greatly.This requires higher requirements for miniaturization and integration of filters.Traditional coaxial cavity comb-line filters widely used in base station of mobile communication system is too large and difficult to be integrated.It is hard to meet the new requirements of new generation communication system.In this paper,starting from polynomial representation for S parameters of filter,the extraction of generalized Chebyshev polynomials and the basic theory of coupled matrix are introduced.Different kinds of resonators,equivalent coupling circuits and coupling structures are studied and compared.By using electromagnetic simulation tools,some filters operating in 3.3~6GHz frequency range for 5G are synthesized and designed.Network analyzer and other testing equipments are used to verify the performance of the filters.The main work completed in this paper is shown as follows:1)The basic theory of microwave filter is introduced.The process of solving the coupling matrix by Generalized Chebyshev polynomial is deduced in detail.The principle of elimination of coupling matrix is also introduced,and an actual example is provided.2)The classification and characteristics of different microwave resonators are introduced.The measurement methods of resonant frequency and unload quality factor of the resonator are introduced in detail.The coupling mode and the coupling coefficient extraction are further described.The measurement of external resonator's quality factor is deduced in detail.These provides theoretical basis for the following research.3)The characteristics of the half-wavelength transmission line cascaded reactance component are analyzed in detail.Coupling characteristics of two coupling structures are obtained.The optimal impedance of transmission line for keeping these characteristics is obtained.By using these characteristics,two microstrip hairpin filters are designed.In these microstrip filters,a number of transmission zeros are realized and cross-coupling from source to load is achieved.The theoretical calculation is in good agreement with the experimental results.The parasitic cross coupling is reduced while the cross coupling is realized4)An embedded cavity filter is designed,and the test results are in good agreement with the theoretical calculation.Embedded cavity filter has the advantages of small insertion loss,easy adjustment,convenient system integration and large scale production.