Microwave Transmission Line Transition Structure And Its Application In Antenna

With the rapid development of contemporary wireless communication and radar systems,higher requirements for antennas are raised,including gain,bandwidth and volume.As a critical component of an antenna system,transmission line has an important impact on antenna performance.There are often circumstances that more than one kind of transmission line is applied in a single microwave system,which makes the requirements for transition structure between transmission lines more stringent,especially on its insertion loss and bandwidth.In this paper,literature reviews on several typical microwave transition structures as well as further research on their innovative applications are presented.Firstly,the research background and significance of microwave transmission line transition structure are introduced.Secondly,the principle of transmission line theory is briefly introduced.Detailed descriptions of transmission characteristics of microstrip line,stripline and substrate integrated waveguide(SIW)are also given in this section.Then,four kinds of transition structures of microwave transmission line are proposed,and two of them are applied to the actual antenna design.The impedance bandwidth of the microstrip Yagi-Uda antenna decreases when the number of the directors increases.In order to enhance the directivity of the microstrip Yagi-Uda antenna and reduce the influence of the directors on the impedance bandwidth,a vertical transition structure of microstrip line to microstrip line is proposed.Furthermore,a power divider based on the vertical transition structure is designed and applied to form an antenna array with two microstrip Yagi-Uda antennas without director.By applying the vertical transition structure,the directivity and impedance bandwidth of the antenna are enhanced,thus realizing the design of an antenna with high-gain and broadband characteristics.Broadside-coupled suspended microstrip-line(BCSML)is a kind of microwave transmission line with the advantages of high quality factor and low loss,whereas the application of broadside-coupled suspended microstrip-line is limited in microwave system due to the multilayer dielectric structure.For more comprehensive application in microwave systems,three kinds of transition structures are proposed in this section,i.e.,the transition from BCSML to stripline,double-sided parallel stripline and SIW.Furthermore,an application illustration is presented by integrating the transition structure with a double-sided parallel stripline monopulse antenna.The proposed antenna system is characterized by broadband,low insertion loss,high gain and electronic beam-scanning capability.