Magnetically tunable hexaferrite bandpass filter from43GHz to 83.5GHz

In this paper a novel magnetically tunable bandpass filter based on open-ended unilateral finlines is presented. The filter covers a tuning frequency range from 43 GHz to 83.5 GHz with a typical insertion loss between 6.7 dB and 8.5 dB. Hexaferrite resonators are used to obtain high resonant frequencies with comparatively low magnetic field strengths. Although only two resonators are used, an off resonance isolation of about 60 dB is achieved. In the cutoff region of the finlines the filter exhibits an off resonance isolation of more than 80 dB. The use of unilateral finlines as coupling lines simplifies the integration of the filter into a planar transmission line environment what is advantageous for the design of integrated high frequency modules. Further on, a considerably larger operating frequency range is covered, compared to classical rectangular waveguide based concepts.