Research And Design Of Ka-band SIW Magic T Structure

Magic T is a typical four-port device with H-T and E-T branches.As a commonly used microwave / millimeter wave passive device,magic T has the advantages of large power capacity as well as low insertion loss.Meanwhile,due to well quality of the port characteristics of waveguide magic T,it is widely used in microwave integrated systems,guided weapons and electronic warfare equipment.Besides,the guided wave structure is essential in the microwave communication system.Basically,guided wave structure was developed from a single type to various structures,three-dimensional structure to planar integration.High integration and performance have attracted public research focus on waveguide structures.The traditional waveguide structure was classified into rectangular waveguide and microstrip line.However,volume of rectangular waveguide is not suitable for integration;the microstrip line has a small enough volume while low power capacity.The planar as well as no-planar guided wave structures have been comprehensively studied that relevant experts proposed substrate integrated waveguide(SIW).SIW has the volume of microstrip line and performance of rectangular waveguide,which was greatly developed in recent years.The present thesis studies,firstly,the basic structure and mechanism of SIW and designs the matching structure of SIW and microstrip line simultaneously.Since the ideal magic T is a reciprocal,passive,and lossless four-port device,its performance can be studied with the S-parameter matrix of a four-port device.Therefore,this thesis illustrates the properties of a four-port network with reciprocal and lossless nature.In order to achieve matching,the diaphragm can be placed in a waveguide.The diaphragm could be divided into inductive and capacitive one.The principle of the matched diaphragm is described in this thesis.For H-T and E-T joint,the port reflection would be giant without matching components,thus a certain matching method is necessary.One method is to add inductive matching metal columns,however,the radius and position are relatively difficult to determine.In this thesis,based on the characteristic impedance of the transmission line,a method based on lumped element matching in order to determine the radius and position of the inductively-matched metal columns is developed,which could easily determine the former two parameters of the inductive metal columns.In addition,sharp wedge-shaped matching and matching diaphragm can broaden the working bandwidth of H-T joint.Due to the high similarity between SIW and rectangular waveguide,the wedge-shaped matching method is utilized to design a H-T branch of the sharp wedge-shaped and matching diaphragm of SIW magic T.Due to the large height of the E-T branch of traditional Magic T,in order to be conducive to integration,the E-T branch is realized by capacitive coupling and matching diaphragm in this thesis.By simulation,the best value of the coupling capacitor and matching diaphragm position and size are determined.Designed magic T has better performance at frequency of 28.2GHz-30.5GHz.