Properties of aluminum-substituted YIG with applications in tunable notched UWB antennas

Reconfigurable antennas based on ferrite materials require lower values of saturation magnetization than that of YIG to operate properly below 5 GHz. To this end, we turned to aluminum-substituted YIG. Six Y₃Fe_5-xAl_xO₁₂ samples, with x = 0.0, 0.25, 0.5, 0.7, 0.8 and 0.9, were synthesized with the standard solid state reaction method. Isothermal magnetization measurements at T = 295°K showed ferrimagnetic behaviour with ferromagnetic saturation magnetic moment which diminishes linearly with x. Ferromagnetic resonance measurements revealed that the mixed compounds exhibit approximately half the losses of pure YIG. The YIG-Al compound was then applied in the design of a tunable notched UWB antenna operating in the 1.7-8 GHz range. The ferrite was biased by small permanent magnets. The biased and unbiased states of the YIG-Al block produce isolated stopbands. Moreover, in these stopbands, the notched antenna is not only reflective, but also very inefficient.