Spur-line based magnetically tunable bandstop filter using partially magnetized ferrite thin films

Abstract

In this letter, a compact spur-line based magnetically tunable bandstop filter in the flip-chip configuration using partially magnetized ferrite thin films is reported. The spur-line bandstop filter is designed to operate at a centre frequency of ∼12.75 GHz and is fabricated on a quartz substrate. Magnetic thin films of cobalt ferrite, cobalt-nickel ferrite, and nickel ferrite are used, which show tunabilities of 5.1%, 6.0%, and 7.5%, respectively, after applying the bias magnetic field ranging from 0 to 300 Oe. The difference in the tunability is attributed to the change in the permeability values of the magnetic thin films after applying the bias magnetic field. The shift in the centre frequency is confirmed by the simulations carried out using CST microwave studio software. This work demonstrates the opportunities to use the partially magnetized ferrite thin films in the presence of a low bias magnetic field for achieving higher tunability in a microwave bandstop filter.