Design of Tunable Bandpass Filters With Ferrite Sandwich Materials by Using a Piezoelectric Transducer

With their high relative permeability and high permittivity, magneto-dielectric materials show great potential in tunable bandpass filter designs. This paper presents a novel tunable bandpass filter with magneto-dielectric perturbation by using a piezoelectric transducer (PET) on a microstrip hairpin. Compared to traditional dielectric perturbation, the frequency tunability of the bandpass filter with magneto-dielectric is much larger while the insertion loss is not much affected. NiCo-ferrite films were adopted to laminate magneto-dielectric sandwich structure on a commercially available Rogers substrate. Novel bandpass filter designs with self-biased NiCo-ferrite films on one layer to five layers of the sandwich structure were compared and investigated. A maximum frequency shift of 240 MHz with respect to the unperturbed condition has been achieved.