AbstractA small size circulator with a coplanar waveguide structure was designed and its transmission characteristics were analyzed using a high frequency electromagnetic simulation based on 3D FEM. The circulator consisted of a YIG ferrite substrate and a transmission line and a ground. When a YIG ferrite substrate with a saturation magnetization of 90 mT was used and a magnetic bias field of 64 kA/m was applied, the circulator operates at 6.98 GHz with an insertion loss |S21| of 1.06 dB, an isolation |S31| of 32.90 dB, a return loss |S11| of 29.89 dB, and a bandwidth (at 20 dB) of 43 MHz. The nonreciprocal transmission characteristics are achieved skillfully utilizing the wavy non‐uniform distribution of microwave. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)