A microstrip-Y-junction circulator with ferrite thin film was designed and its transmission characteristics were analyzed by the 3D finite-element method. The circulator consists of a dielectric substrate with a cylindrical GND, a dielectric layer with a low dielectric constant, a ferrite thin film, a silver transmission line, and a ground plane. The thickness of the ferrite thin film is set at 5 μm. The cylindrical GND is located in the proximity of the center of Y-junction to obtain a large gyro-magnetic effect efficiently. A 15-μm-thick dielectric layer with a dielectric constant of 4 is inserted between the ferrite thin film and the cylindrical GND to decrease the loss resulting from the transmission line, and to obtain a wide permissible range for misalignment between the GND and Y-junction. The results show non-reciprocal transmission characteristics at approximately 5.9 GHz with an insertion loss of 1.6 dB and an isolation of 23 dB.
