Design Of Si-based Microstrip Interdigital Bandpass Filters

RF microwave filters are critical for modern wireless communication systems.The design of high performance,small size,low-cost microwave filter is the inevitable requirements for market competition.Microstrip interdigital filter has the characteristics of compact structure,low insertion loss,easy to process,good reliability and consistency,and the silicon substrate has the advantages of high thermal conductivity,high dielectric constant,low cost,mature processing technology and easy to integrate with other semiconductor devices,consistent with the development of today's filters.Therefore,the silicon-based microstrip interdigital filter is studied in this article.An improved method for the grounding hole effect pre-considered of the microstrip interdigital filter is proposed,which can effectively improve the initial design accuracy and reduce the design cycle.Firstly,different traditional methods are used for the initial design of microstrip interdigital filter,and a design procedure for engineering application is given.When traditional methods are used,the initial design result and the specification are quite different,which is due to the parasitic inductance effect of the ground hole of the microstrip interdigital filter,while traditional methods do not consider the influence of the ground hole.Therefore,on the basis of the traditional method,the grounding hole is pre-considered in each step of the initial size design,and a Ka-band filter is used as a case to verify.An ADS-HFSS co-simulation method for microstrip interdigital filter is proposed,which can design the filter quickly and accurately.First,the schematic simulation and layout simulation are carried out with ADS,and the method of schematic-layout co-simulation is given.Then,a three-dimensional electromagnetic field simulation was performed using HFSS.When simulation and optimization,the ADS is fast but the accuracy is low,and the HFSS is enough accuracy but slow.Therefore,a co-simulation method using the rapidity of ADS and the enough accuracy of HFSS is given,and an S-band filter is used as a case to verify.Finally,the thermal behavior simulation analysis of the filter is carried out.Two improved design of tapped-line structure for microstrip interdigital filter are proposed,which can effectively solve the mismatch problem when substrate thickness and center frequency are large.Firstly,the effects of silicon substrate with different resistivity and microstrip lines with different conductivity on the performance of microstrip interdigital filter were experimented.Then,the effects of different grounding hole shapes,numbers and metallization layer thickness on the performance of microstrip interdigital filter were experimented,and their optimum conditions were given.When the substrate thickness and the center frequency are large,the external quality factor of filter with traditional tapped-line structure will not match with the prototype filter,cause the design can not be completed.Therefore,the causes of mismatch are analyzed by simulation,and the solution to the improvement of tapped-line structure is given.Finally,a Ka-band filter is used as a case to verify.Based on microstrip interdigital filter,a broadband diplexer with high isolation is presented.First,the broadband transmission / reception filter is designed,then the T-junction of the connecting filter is designed,and then the diplexer is designed by using different connection modes,in which the serial connected diplexer has the characteristic of high isolation.Finally,the MEMS process of silicon-based microstrip interdigital filter is given.