Study Of Suspended Substrate Stripline Filters And Multiplexers

With the continuous progress of science and technology,wireless communication technology has also been vigorous development,especially in the microwave and millimeter wave fileds.Due to the growing demand for numerous high performance engineering application,practical design theory has been presented in some works.Furthermore,the quality of communication is the vital target in the wireless communication application,filters and multiplexers which are ultilized to frequency selection is essential part in wireless communication chain.In recent years,wireless communication device with high performance and miniaturization quality has increasingly in demand,therefore much attention has been drawn to the physical implementation of the miniaturized filters and multiplexers with low loss and high selectivity.Suspended stripline(SSL)structure is a novel transmission line medium proposed in the 1980 s,which can be regarded as a special stripline structure and thereby it has very significant low loss compared with microstrip line structure as its unique physical structure and unlike the conventional metal coaxial and waveguide structure,superiority and innovation of the suspended stripline structure include easy to achieve miniaturization and integrate.Moreover,the general structure of an SSL consists of a thin substrate suspended in the center of an air-filled metal cavity,therefore the SSL structure has low temperature drift and high power capability characteristics.Hence,in-depth study in filter and multiplexer utilized by SSL structure is a great prospect and significant significance.In this paper,the background of filter and multiplexer research is discribed,and the progress of the filter and multiplexer research is studied and thereby,the trend of filter development in communication applications is analyzed.Then,the progress and development direction of the SSL filter research are studied and analyzed in detail.Afterwards,based on the theory of generalized Chebyshev function filter and general coupling matrix synthesis methods,the design of the SSL bandpass filter,the diplexer and the quadplexer is implemented.In general,the work of this paper mainly includes the following aspects:1.The theory of generalized Chebyshev filter is studied.The most important characteristic of the designed filter with the generalized Chebyshev function as the approximation function is that cross-coupling can be introduced to optimize the transmission characteristics of the filter.In this paper,the synthesis of the characteristic polynomial is deduced,and then the initial coupling matrix of the filter is synthesized.Then,the synthesis matrix of the custom topology is realized by the rotation elimination method,which is provided theoretical basis of the coupling matrix synthesis for the filter with cross coupling.2.The transmission line characteristics of the SSL structure are analyzed,and the method of utilizing SSL structure to realize the lumped element is studied.On the basis of this,two types of six-pole bandpass filters with cross-coupling are designed based on these transmission line characteristics and the physical realization method of lumped elements.In this design,a novel resonantor unit physical implementation is used,which is smaller and has lower losses than the conventional single layer SSL resonantor structure,and also facilitates cross-coupling,which ultimately realize the designed filter with high performance of miniaturization,low loss and good selectivity.3.WCDMA diplexer is designed by using SSL structure.The diplexer is based on the design concept of the frequency selective duplexer,The coupling matrix of the diplexer is synthesized by MATLAB.And then the physical model to be built and then measure it.Finally,we get a duplexer having a good performance in the structure of miniaturization,in the low loss and high isolation.4.The UHF passband adjacent quadplexer was designed by using the SSL structure.The four-processor is designed using a full-wave-circuit hybrid optimization method.The coupling network adopts the multi-head line network structure,and each channel filter adopts a "T" type connector to connect with it.At the same time,the design of the multiplexer is proposed to construct a novel structure of the resonantor of the SSL,which is a kind of structure of the resonant unit which is folded in space,which can be further reduced the size of the resonant unit on the basis of guaranteeing the high unloaded Q value.