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


A compact spur-line based magnetically tunable bandstop filter with different ferrite thin films viz. cobalt ferrite (CFO), cobalt-nickel ferrite (CNFO) and nickel ferrite (NFO) in the flip-chip configuration has been fabricated. The spur-line bandstop filter has been designed to operate at centre frequency ~12.75 GHz and ferrite thin films are used in partially magnetized state, deposited on the quartz substrate. After applying the bias magnetic field from 0 to 300 Oe, the bandstop filter showed tunability of 5.1%, 6.0% and 7.5% with CFO, CNFO and NFO thin films respectively. The difference in the tunability is attributed to the change in the permeability values of the magnetic thin films after applying bias magnetic field. The bandstop filter structure has also been designed (simulated) using CST microwave studio software and the experimentally observed change in the centre frequency for different ferrite thin films has been confirmed. The present work demonstrates the opportunities to use the partially magnetized ferrite thin films in the presence of low bias magnetic field for achieving higher tunability in a microwave bandstop filter.

Contact details: 

Prof. Neeraj Khare

Department of Physics