Design Of High Temperature Superconducting Filter Based On Compact Resonator And Analysis Of Its Thermo-mechanical Characteristics

With the acceleration of the commercialization of 5G,the performance requirements of microstrip filters in communication systems are getting higher and higher,and miniaturization and high performance filters have become a new trend in the development of filters.Due to the existence of very low microwave surface resistance on the surface of superconducting thin films,the microstrip filters made by superconducting thin films have the characteristics of small insertion loss,narrow band width and excellent frequency selectivity,which have attracted extensive attention of many scholars.This paper mainly analyzes and studies the miniaturization of the filter structure design and the residual thermal stress existing in the processing of the thin film substrate.The main contents and research results are as follows:(1)In this paper,a spiral stepped impedance resonator structure is proposed,and a sixth-order high-temperature superconducting filter operating between 810 MHz and845MHz is designed by combining the filter coupling coefficient method.The simulation results show that the insertion loss is only 0.08 d B and the return loss is-16 d B.At the same time,to solve the problem of poor frequency selection characteristic of the filter structure,the rectangular degree of the filter is increased from 2.6 to 1.5,and the steepness of the band edge is increased to 7d B/MHz by using the cross-coupling method.In addition,this paper also analyzes the base sensitivity and microstrip line sensitivity of the filter,and discusses the influence rules of base thickness,feeder thickness and mesh precision on the simulation results of the filter.(2)In this paper,based on the second-order SIR resonance design theory,the analytical relationship between different electrical lengths and impedance ratios of SIR structures was obtained,and the specific analytical relationship between the parasitic resonant frequency and impedance ratio of the three-way band was defined.A three-way high-temperature superconducting filter that can work in WiMAX,WiFi frequency band and X-band was designed by using this analytical expression.(3)Based on the thermal stress distribution theory of the lap shear model,the analytical expressions of the internal normal stress,interfacial shear stress and interfacial peel stress of the double layer metal strip with temperature change are given in this paper.The thermal stress distribution of the lapping shear model was verified by comparing the numerical solutions of MATLAB programming and the finite element simulation results of ANSYS software.The relative error between the analytical solution and the finite element solution of the maximum normal stress of the thin film is 9.4% for the Mo-Al thin film when the temperature is 240°C,and 4.6% for the YBCO/Mg O thin film substrate when the temperature is-600°C.The results of finite element simulation and analytical analysis of the two models show that the normal stress and shear stress are the main reasons for the failure of the thin film substrate structure.In conclusion,the research work in this paper has certain reference value for the miniaturization design and engineering application of HTS filter.