Miniaturized Antennas and Planar Bandpass Filters With Self-Biased NiCo-Ferrite Films

Miniaturized microwave devices are realized by using magnetodielectric substrate comprising thin magnetic films that exhibit both high permittivity and high permeability at gigahertz frequency. We have fabricated and tested miniature circular patch antennas and hairpin bandpass filters with the alumina and Rogers substrate loaded with self-biased NiCo-ferrite films that exhibit excellent uniformity and low loss at frequencies exceeding 1.5 GHz. The measured results of magnetic hairpin bandpass filters have improved the central resonant frequency shift from 1.55 to 1.44 GHz, and a large resonant frequency tunability of about 23%-34% of the - 3-dB bandwidth was achieved. For the circular patch antenna, we observed an improvement of 0.8 dB in gain and a large resonance frequency tunability of 100%-320% of the antenna -10-dB bandwidth.