Integrated Design And Application Of A Novel Multiplexer

In communication system,the RF-fronit is of the most importance to the system.Meanwhile,as the demand for compact device is higher and higher,more and more devices are designed miniaturized,for a device that can work at multi-frequency band with good performance is focused.Based on this situation,a di/tri/mulitplexer with high isolation and compact size becomes crucial object.In this thesis,the topic is microstrip highisolation multiplexer,and mainly focus the equivalent circuits of coupled microstrip lines in different situations.Besides,the circuit performance of different equivalent circuit will be given.combining with the effect bought by microstrip stubs,the transmission zeros with no effect on the passband are introduced,and the formulas are also given.By making use of these formulas.the sizes of coupled lines of a high-isolation diplexer that works at desired frequencies are calculated,and a high-isolation diplexer is designed.Later,by expanding the microstrip stubs,combining with the method of stepped-impedance,a high-isolation is designed.There are three parts in this thesis.1.The first part goes with a review of different kind of equivalent circuits of coupled lines as the basic microstrip strcture.By expanding an exist equivalent circuit reseaonablly,the equivalent circuit of coupled lines with stub is assumed.The cascade matrix is supposed equal and the realistic form of the equivalent circuit is obtained.The transmission zeros in the presence of equivalent circuit are analysized,including the position formula,the relationship between the length of stub and frequencies in the position.In the end,the first high-isolation diplexer is designed.2.In the second part,the study of this coupled lines goes further deeply.the equivalent circuit of three-port coupled lines is given firstly.The outcome shows three-port coupled lines can be divided into two parts,the first part equals the first order of a filter while the other part is equal to a transmission line,but with matching problem.To solve this problem,the three-port symmetrical coupled lines are designed into three-port asymmetrical coupled lines,of which the equivalent circuit is deduced.The equivalent circuit shows this structure also has the counterpart of the filter first order and the counterpart of a transmission line,but its characteristic impedance is the same with one of the two coupled lines,which provides a feature of adjustification.By making use of this three-port asymmetrical coupled lines,combining with the study in the first part,a diplexer with higher isolaition is designed.3.In the third part,the implication of stepped impedance in resonators is reviewed firstly.Then,conbines with the studies in the first and second part,the stepped impedance is murged with asymmetrical coupled lines.This kind of combination brings an adjustabld second order transmission zeros that can be shifted to a desired position.Based on this combination,a five-port four-channel multiplexer is designed.