Research On Characteristics Of Suspended Coplanar Waveguide And Design Of Filter Circuit

With the vigorous development of modern communication systems,people's requirements for communication quality are gradually improved,so each component in the radio frequency transceiver system is facing more severe challenges.As two major frequency selection devices,filters and diplexers play an important role in modern communication systems,which are mainly used to separate RF signals,and their performance directly affects the transmission quality of the entire communication system.At present,most filter circuits such as filters and diplexers use microstrip lines and single-layer structures.Therefore,it is necessary to study new transmission lines and take advantages of multi-layer structures to improve the performance of related devices.Because the suspended coplanar waveguide structure combines the advantages of high Q value and low loss of traditional suspension line with the advantages of easy integration,good electromagnetic shielding performance and good dispersion performance of coplanar waveguide,it has gradually attracted the attention of scholars.In this paper,the conformal transformation method is used to research the characteristics of the suspended coplanar waveguide,a new type of transmission line,and then,the filter circuits are designed based on this structure.Firstly,due to the lack of research on the characteristics of the suspended coplanar waveguide,this paper researches the dielectric constant and characteristic impedance of its ideal structure by conformal transformation method,derives the corresponding closed analytical expressions,verifies them by simulation,and analyzes the main causes of errors in detail.This is of great significance to the computer-aided design and optimization design of microwave integrated circuits.Secondly,two band-pass filters based on the suspended coplanar waveguide structure are proposed.The first band-pass filter is based on the third-order SIR resonator,and uses source-load coupling and coupling between resonators to make transmission zeros on both sides of the pass-band.Equivalent analysis of the circuit structure is carried out by using the even-odd mode analysis method,and the parameters that affect the pass-band performance are analyzed in detail,and the changing laws are given.The second band-pass filter is designed based on the patch resonator.After analyzing the electromagnetic field distribution of the isosceles right-angled triangle,the isosceles right-angled triangle is segmented to form multiple stickers without increasing the size.At the same time,orthogonal feeding is used to disturb the electric field,so that the degenerate modes are coupled and separated from each other,thus forming a pass band.Finally,a diplexer based on the suspended coplanar waveguide structure is proposed.Two groups of open-circuit transmission line resonators and short-circuit transmission line resonators with different sizes are coupled to generate two pass-bands,and an E-type dual-mode resonator is used as a common end resonator,thereby forming a diplexer coupled with multiple resonators.The isolation and out-of-band suppression can be improved by properly assigning the transmission zero of each channel filter to the pass-band of another channel filter.Because the diplexer is formed by coupling multiple resonators,multi-path transmission and mutual coupling between resonators produce other transmission zeros.The interference is suppressed by adjusting additional transmission zeros,and the stop-band suppression of the diplexer is improved.After that,the parameters that affect the performance of the diplexer are analyzed in detail,and their changing laws are given.