Magnetically Tunable Resonant Phase Shifters for UHF Band

This paper presents a new type of magnetically tunable phase shifter. The shifter has the structure of microstrip bandpass filter on a substrate containing magnetic material whose magnetic permeability is controlled by magnetic field due to ferromagnetic resonance. The phase shifter's operation is based on the fact that phase shift in a bandpass filter changes with tuning of its central frequency. Two types of devices were designed and fabricated for the UHF band. One of them has a five-layer NiFe film as an active medium and demonstrates a figure of merit of 40 degrees/dB achieved already at 20 Oe of the controlling magnetic field in 10% of the relative operational bandwidth. The second device with YIG ferrite as an active medium gave 360 degrees tunable phase shift in 5% operational bandwidth that corresponds to the figure of merit of 150 degrees/dB (3.1 degrees/dB.Oe).