Tunable stepped impedance resonator bandpass filter using ferroelectric materials

In this paper, a stepped impedance resonator (SIR) bandpass filter using BST thin film as a tunable device has been discussed. For the analysis of relative dielectric constant of BST thin films, the BST interdigital capacitor (IDC) is fabricated with finger's width and gap of 10 mum and 5 mum, respectively, and the capacitance of IDC is 0.951 pF and the relative dielectric constant of BST thin film is 1,097 at 6 GHz. The tunable SIR bandpass filter using BST thin films is designed with coupling section of 22deg and tapped feeding and has been successfully demonstrated with the thickness of BST thin films of 500 mn on the MgO substrate. The center frequency of the tunable SIR bandpass filter is moved from 6.15 GHz to 6.29 GHz at 50 V bias with about 3% bandwidth.