Research On Microwave Passive Components Based On Substrate Integrated Coaxial Line

In RF microwave systems,power dividers,couplers,phase shifters and other passive devices are usually designed to achieve power allocation or power combination and phase control functions.Microstrip line is widely used in passive device design because of its simple structure and low cost.However,due to its unshielded structure,crosstalk and scattering problems exist.Substrate Integrated Waveguide(SIW)inherits the advantages of microstrip line,and has the advantages of high Q value and easy processing.However,it can not propagate TEM mode and is not suitable for broadband passive device design.Substrate Integrated Coaxial Line(SICL)inherits the advantages of low loss,low cost and shielding structure of SIW.It is a technology for planarization of coaxial lines.At the same time,the SICL structure can propagate the TEM mode,which is suitable for the design of broadband passive devices,and can be integrated with other planar circuits.Therefore,SICL has great application value.The main work of this paper is as follows:Firstly,the directional coupler of 3d B is designed based on the theory of SICL.The 3d B directional coupler realizes the strong coupling of 3d B based on the common directional coupler and the interdigital coupling line structure.Secondly,based on the research of interdigital coupling line,combined with the principle of three parallel coupling lines,the structure of interdigital coupling line is further studied.It is found that the double interdigitated coupling structure can maintain a strong coupling effect on the premise that the volume of the conventional SICL branch coupler is reduced by more than half.Therefore,a miniaturized SICL branch line coupler is finally designed.Thirdly,based on the SICL technology and the basic principle of the transmission line phase shifter,two improved Schiffman phase shifters are designed.One of them works in the first phase period compared with the traditional Schiffman phase shifter,and it works in the second phase period.It makes the Schiffman phase shifter achieve a 90 degree phase shift and achieves 41.3%relative phase shift bandwidth.Another way is to improve the traditional Schiffman phase shifter’s main line and realize the phase change on the main line by loading ladder shaped open branch line.The volume of the reference line is reduced by bending.In addition,a branch loaded broadband phase shifter operating on the 4-8GHz frequency band is also introduced,which is also called an improved Schiffman phase shifter.The 90 degree phase shift and 50% relative phase shift bandwidth are achieved.The phase shifter has wide bandwidth,small volume and stable phase.It is very suitable for phased array antenna with fixed phase difference.