Electrically tunable bandpass filtering balun on engineered substrate embedded with patterned Permalloy thin film

An electrically tunable bandpass filtering balun (BPF-Balun) on engineered substrate embedded with patterned Permalloy (Py) thin film is designed and implemented for the first time. The tunability of the BPF-Balun is realized through tuning RF characteristics of the engineered substrate. Embedded with patterned Py thin film which has high and current-dependent permeability, the developed engineered substrate has electrically tunable equivalent permeability. The center frequency of BPF-Balun on engineered substrate thus becomes tunable with different DC current. Patterning of Py film is analyzed and utilized to increase its FMR up to GHz range. The proposed BPF-Balun is fabricated on Rogers 4350 substrate while the engineered substrate is developed separately with high resistivity silicon embedded with patterned Py thin film. Tunable BPF-Balun is implemented through bonding the Rogers 4350 on the top of engineered substrate. The measured results show that the center frequency of the BPF-Balun can be tuned continuously from 1.49GHz to 1.545GHz with applied DC current adjusted from 0mA to 500mA. The measured magnitude imbalance and phase difference of the two balanced outputs are within 0.5dB and 180°± 5° for the whole frequency range. Larger tunability can be achieved with patterned Py thin film with optimized thickness.