Magnetically tunable micro-strip band-stop filter: Design optimization and characterization

摘要

We investigate ultra-small band-stop filters made with continuous Fe films and with multilayered Fe/Cu films. In ferromagnetic resonance measurements, the continuous Fe(100 nm) film had a larger linewidth, on the order of 200 Oe at 10 GHz, resulting in a device linewidth, which typically was close to 2 GHz in the operational device. In contrast a [Fe(5 nm)/Cu(0.8 nm)]_(20) multilayer structure showed a ferromagnetic resonance linewidth of 50 Oe at 10 GHz and had a device linewdith of about 0.5 GHz. We expect that the breaking of the Fe films by Cu reduces the typical size of crystallites in Fe, thus reducing the linewidth. The filter demonstrates wide tuning range of 10-30 GHz with bias fields up to 4 kOe. This work demonstrates a single notch-filter, which can operate from X- to K-band with a linewidth of 1.8 GHz at 0.07 kOe and 0.33 GHz at 4.0 kOe. The measured minimum insertion loss in each case is ～2.5 dB, with greater than 15 dB return loss in the entire pass-band frequency.