Design Of Microstrip Filter With Tunable Center Frequency And Bandwidth

With the rapid development of mobile communication industry,wireless communication has met a constant change in recent years.As a critical filtering device in the wireless communication system,the microwave filter faces a greater challenge.With the spectrum resources increasingly crowded,spectrum technologies,such as frequency-hopping and multi-pass bands,have been widely used,meanwhile the corresponding applications of these technologies are closely related to microwave filters.At the same time,these novel technologies also represent excellence and high standards in the field of the design of current filter.The electrically tunable filter is emerging at the proper time and conditions.The emergence of electrically tunable filter settles the problem of multi-channels,reduces the volume of the whole communication system correspondingly and further promotes the implementation of miniaturization and low cost of wireless communication system development.Therefore,the design method of electrically tunable filter with excellent performance is still the research focus and nodus of the domestic and overseas researchers.In the past decade,the electrically tunable filter and related design methods have entered a new stage of rapid development.However,the realized electrically tunable filter does not meet the actual application requirements in terms of structure and performance.In this paper,a compact electrically tunable filter with independently frequencies and bandwidths is designed based on the electromagnetic simulation software HFSS.At the same time,two balanced electrically tunable filters have been designed in this paper.Due to the commonmode(CM)suppression characteristics,balanced devices can transfer the differential signals successfully and improve the signal-to-noise ratio of the wireless communication system.Therefore,the balanced(differential)electrically tunable filter conforms to the future development demands.The main contents of this thesis are as follows: First of all,this thesis introduces the relevant research backgrounds and significances.At the same time,the early electrically tunable filters domestic and abroad have been reviewed and detailed analysis and summary,thus determining the research direction of this thesis.Next,the relevant design index,filter synthesis methods and common microwave filter resonance units are introduced.The theory of stepped-impedance resonator and slotline theory have been introduced emphatically,which establish a foundation for the following designs of balanced electrically tunable filters.Then,a compact electrically tunable filter with independently frequencies and bandwidths and the relevant analysis of design theory are presented.The measured results show a good agreement with simulation ones,which further demonstrates the validity of the design method.Through the theoretical analysis of folded S-shaped slotline resonator,complementary split-ring resonators(CSRRs)and balanced(differential)input port,two balanced electrically tunable filters,which based on folded S-shaped slotline resonator and CSRRs respectively,are designed in this thesis.Meanwhile,the corresponding prototype circuits are fabricated and measured,and the agreement between simulation and measurement results verify the correctness and feasibility of the design theory.Finally,the prospects of the research direction of this thesis are expatiated,which indicates the direction of further research.