Based On The Fcl Microstrip Circulator Design

Circulator is widely used in radio transceivers as one kind of important microwave ferrite devices. In this thesis,the theory and design method of a novel microstrip circulator based on longitudinal magnetized ferrite coupled line (FCL) are presented. Firstly,the introduction to the physics and fundamental of the FCL circulator is provided,such as Faraday rotation and coupled functions. We discussed the different performance of even and odd mode incident at FCL and the influence to the device for different direction of bias H field,which allows one to obtain the scattering matrix of the microstrip FCL. Based on the theory and aided by electromagnetic EDA tools,microstip T-junction and ferrite coupled line(FCL),as the two important components of a there port microstrip FCL circulator were modeled. A new model of wideband T-junction and a three port FCL circulator operating at C band (f0=6.5GHz) were designed and simulated. For the sake of its application at millimeter-wave range,a FCL on the hexagonal ferrite substrate with high anisotropy field is simulated and results showed that it can be self -biased and very wide band may be possible,and also ferrite materials with lower magnetization(4πMs) can be required. The fabricated FCL microstrip circulator was measured using Agilent network analyzer. The measurement results showed a good coherence to the simulation ones and got the design targets with lower 4dB insertion loss, 15dB isolation and less 1.5 VSWR in the frequency range of 5.5GHz～7GHz .We investigate the device's performance with various biased H field and the experiment results confirmed that only a weak biasing field of 8kA/m (about 100Oe) is required.