The Research Of M-type Barium Ferrite And Its Application On Self-biased Circulators

The development of electronic information technology is along with the continued expansion of the electromagnetic spectrum. The development of microwave communication technology requires the devices to be smaller, lighter and more integrated. M-type barium ferrite has a high saturation magnetization, large coercivity and large remanence ratio. The magnetic anisotropy field and saturation magnetization can be effectively adjusted by doping ions or other methods. As a result, it is potential for millimeter wave applications and devices.In this thesis, we studied the effect of ions substitution(Co2+Zr4+, Co2+Ti4+, Zn2+Zr4+), designed single Y junction circulators based on the doped M-type barium ferrite, and discussed the effect of magnetic crystal anisotropy fields and remanent magnetization on the self-biased circulators. XRD shows that a single phase could be found in Co-Ti, Co-Zr and Zn-Zr substitutions for iron in BaM ferrites. However mutiple phases were found in Co-Zr doped M-type barium ferrites when x > 0.6. The position of the diffraction peak was slightly shifted. This was due to a difference of the radius between the substitution ion and iron, which caused lattice distortion. SEM images indicates that Co-Ti doped M-type barium ferrites have large grain size and higher density than the other two doped BaM prepared in the same conditions. Co-Ti ion doping help sintering densification. Saturation magnetization is very different in these doping experiments. Increasing Co-Zr ion doping lead to increase saturation magnetization to 58.5emu/g firstly, which then decreased to 48.7emu/g. The saturation magnetization decreased with the Co-Ti ion doping, which was opposite for Zn-Zr doped BaM. Saturation magnetization variation was due to the substitution of iron ions in the unit cell of BaM. Co ions tend to occupy 4f2 and 4f1 sites, Zr ions not only occupy 4f2 but also occupy 12k; Ti ions preferentially occupy the 2b; Zn ion and Zr ion enter 4f2 and 2b.Different subsition sites of these ions cause changes in net magenetic moment of the unit cell, thereby causing different trends of saturation magnetization as doping increase. These experiments show decreased magnetic anisotropy and coercivity.Based on the circulator junction field analysis, first and second annular conditions was derived, and electronmagnetic simulation software HFSS was used to design two single Y junction circulators that each worked in 12-18 GHz and 20-28 GHz. Ferrite substrate materials with saturation magnetization of 2600 guass and 4000 guass were used in the circulators. Simulation results shows that the insertion loss is less than 3dB, and return loss and isolation loss are both higher than 20 dB in circulators.Magnetic anisotropy field changes the κ/μ ratio in the self-biased circulators. And the performance of circulators become worse when remanence ratio is very low.