Effect of shape anisotropy on stop-band response of Fe and permalloy based tunable microstrip filters

The magnetic/dielectric hybrid transmission line structures provide a new class of microwave/millimeter wave devices, useful for signal processing. Reduction of device dimensions in these magnetic monolithic microwave integrated circuits (M-MMICs) is important from the cost and reliability point of view. Here, we explore the transmission characteristics of Fe and Permalloy based microstrip filters with microstrips of different widths, lengths, and thicknesses. The gyromagnetic resonance occurs at microwave frequencies of up to 12 GHz for Fe and 5 GHz for Permalloy, even in the absence of any dc magnetic field. The resulting absorption yields the stop-band behavior of the device. Our microstrip geometry significantly boosts the operational frequency due to an induced shape-anisotropy. Different geometries induce different demagnetization factors and hence different resonance frequencies. We calculate the frequency-boosting characteristics of the devices due to induced shape-anisotropy and observed a good match to our measurements.