We studied cellular phone isolator of gyrator type operating in weak magnetic field below ferromagnetic resonance and derived design equation in order to reduce the insertion loss. Using this design equation and the optimized coupling factor, a small sized Core-Isolator (0.5×1.6×0.4 mm3) for cellular phone terminals has been realized, and the insertion loss of 0.5 dB max and the isolation of 19.8 dB min. have been obtained successfully at 2.57 GHz to 2.62 GHz.
