Electrically Tunable Bandpass Filter With Patterned Permalloy Thin-Film-Enabled Engineered Substrate

An electrically tunable bandpass filter based on an engineered substrate embedded with patterned permalloy (Py) thin film has been designed, implemented, and characterized. The bandpass filter is designed with metamaterial resonators to achieve a compact size; the designed filter is fabricated on a multilayered engineered substrate, which is composed of a layer of liquid crystal polymer, a layer of patterned Py thin film, and silicon substrate. The tunability of center frequency for the designed bandpass filter is dependent on the radio frequency (RF) characteristics of the implemented engineered substrate. The equivalent permeability of the Py thin film embedded in the engineering substrate is electrically tunable with the dc current, which thus provides high and tunable inductance densities for the split-ring resonators in the designed filter; the center frequency of the implemented bandpass filter is thus electrically tunable. The measured results show that the center frequency of the designed bandpass filter shifts from 2.37 to 2.45 GHz continuously when the applied tuning dc current is changed from 0 to 500 mA. The introduced unique concept of the engineered substrate provides design feasibility of filters with continuous frequency tunability, and the implementation of the engineered substrate enabled with the patterned Py thin film is suitable for the cost-effective fabrication of the arbitrary tunable RF devices.