Design Of A Microstrip Ferrite Film Circulator

Microwave circulator is widely used in mobile phones, mobile base stations, phased array radar and other civilian and military equipment. The mainstream of the circulator is miniaturization and low cost because of the development of monolithic microwave integrated circuits. Microstrip line has many advantages such as small volume,simple structure, low production cost, short production cycle and so on. So microstrip line has been widely used in hybrid microwave integrated circuits and monolithic microwave integrated circuits. Ferrite film can reduce the size of circulator. But how to maintain the perfect microwave characteristics of the ferrite film circulator is a problem. So a ferrite film circulator which is based on microstrip line is designed in this dissertation.The following work is completed in this dissertation: firstly, a microstrip ferrite film circulator controlled by transversely magnetized field is presented. The substrate is using yttrium iron garnet (YIG) film epitaxially grown on gadolinium gallium garnet (GGG).Secondly, the characteristic parameter of device by analyzing the characteristic of ferrite gyromagnetic material is determined. The transmission equation of ferrite is obtained through the study of the EM wave's propagation characteristic in ferrite. The size of the ferrite used in circulator is designed according to the ferrite characteristic parameter. The characteristic parameter of device by analyzing the characteristic of ferrite gyromagnetic material is determined. Thirdly, the basic working principle of the ferrite thin-film circulator is discussed .and a good impedance matching is achieved between ferrite thin-film ring and 50 ohm microstrip line. The relationship between the microstrip impedance and the substrate dielectric constant with the special structure .The fourth, the performance of the circulator is analyzed with the impact of the relative dielectric constant of the substrate, ferrite thin-film thickness and the saturation magnetic etc. It also achieved the principle of Saturation magnetic moment of ferrite film .In the end, the performance of the microstrip ferrite film circulator in the X-band is given. The result indicates that the circulator in the 8.14GHz has a good microwave performance with isolation is greater than 20dB and insertion loss is less than 1dB.A microstrip ferrite film circulator is designed in this dissertation. Conclusions achieved in this paper can be used in the research of the design of microwave devices.