Effects of adjusting the position of the magnetic layer in magnetic notch filters

We study small thin-layer magnetic notch filters which operate in the 5-40 GHz range. Past theoretical work has concentrated on a structure where the magnetic film was right next to one of the conductive films in a waveguide. Here we present a theoretical model, which investigates the properties of a waveguide with two dielectric films and one magnetic film placed between two outer conductive layers. The results show this more general structure produces a deeper attenuation and a narrower peak compared to the earlier structure. The additional attenuation varies from 0 to 30 dB/cm, depending on the thickness and position of the magnetic film. This article also examines the reflection of the guided waves as they enter the notch filter. The results from an effective medium calculation show that a signal experiences the largest return losses near the ferromagnetic resonance frequency of the magnetic film, with typical losses below -4 dB. The return loss can be reduced significantly if the linewidth in the ferromagnetic film is increased. The effective medium results are compared to an experiment that measured return losses in a microstrip device. The experiment had maximum return losses between -4 and -8 dB.