Enhanced microwave ferromagnetic resonance absorption and bandwidth using a microstrip meander line with step-impedance low-pass filter in a yttrium iron garnet–gallium arsenide layer structure

Abstract

Simulations of the step-impedance low-pass filter (LPF) in gallium arsenide (GaAs) substrate show that, in contrast to a 50Ω microstrip, the magnetic fields of the propagating microwaves are heavily concentrated in its inductive elements. The concentrated local magnetic fields facilitate enhanced coupling into an yttrium iron garnet/gadolinium gallium garnet layer over the GaAs substrate and, thus, significantly increase the microwave power absorptions at the ferromagnetic resonance (FMR) frequencies. The large tunable range of FMR frequency and the corresponding S21 and S11 parameters measured have verified the simulation results. Simultaneous enhancement of FMR absorption level and widening of absorption bandwidth has been accomplished in a band-stop filter that utilizes a microstrip meander line with four identical step-impedance LPFs, each of 5.70mm long, inserted in a nonuniform bias magnetic field. A tunable FMR absorption frequency range of 5–21GHz, an absorption level of −35.5dB, and a corresponding 3dB absorption bandwidth as large as 1.70GHz, centered at 20.3GHz, have been demonstrated.