High Frequency Electromagnetic Properties Of M-type And W-type Ferrites And The Application In Antennas

Nowadays,antennas as an important part of modern communication systems have been developing for miniaturization,high efficiency,and low loss.Among them,microstrip patch antennas have received extensive attention from researchers because of their small size,easy processing and low cost.In the past decades,several proven effective miniaturization approaches have been proposed for the microstrip patch antenna,including crossed slots,inductive shorting pins,and the irregular ground plane etc.Although these techniques are different from the conventional miniaturization methods using high permittivity material as the antenna substrate,they still narrow the effective bandwidth and reduce the antenna efficiency.Relevant reports have proved that the antennas loaded with magnetic materials can achieve miniaturization while maintaining good performance.Magnetic substrate materials,especially ferrite materials,are widely concerned because of their low permittivity,high permeability and excellent impedance matching properties.However,using ferrite materials as microstrip patch antenna substrate materials still has the following two technical challenges:one is that the low cut-off frequency of these materials makes it impractical for using in the GHz band,the other is that high magnetic loss due to domain wall resonance is difficult to suppress.In this work,Ba（CoTi）_xFe_12-2xO₁₉ ferrite ceramics with planar magnetocrystalline anisotropy were selected as the object to solve these problems above,the effects of Co²⁺-Ti⁴⁺substitution on the crystal structure,morphology,static magnetic properties and electromagnetic parameters of Ba Zn_2–xCo_xFe₁₆O₂₇ were studied.And then,its properties were further optimized by doping Bi₂O₃,the effects of Bi₂O₃ content and sintering temperature on its electromagnetic properties were investigated.The experimental results show that the Bi₂O₃-doped M-type ferrites have ultra-high miniaturization factor,ultra-low electromagnetic loss and good impedance matching properties at 100 MHz,it can be used as a potential high-frequency antenna substrate material.In order to increase the application frequency of antenna substrate material to GHz band.The Ba Zn_2–xCo_xFe₁₆O₂₇ ferrites with higher saturation magnetization were selected as the research object,and the effects of Co²⁺substitution,Bi₂O₃ doping,sintering temperature on its electromagnetic properties were explored.The results show that the cut-off frequency of this materials can exceed 10 GHz,and the Bi₂O₃ doping can effectively suppress particle growth during sintering and reduce the magnetic loss caused by domain wall resonance.The simulation results show that the gain of the antenna using this ferrite ceramic as the substrate is almost the same as that of the antenna using the traditional dielectric material FR4 as the substrate,and the return loss and antenna size are significantly reduced.