MMIC circulators using hexaferrites

Abstract
MMIC circulators operating at K/sub A/-band have been fabricated from single crystal and polycrystalline hexaferrite platelets integrated into glass-microwave integrated circuit wafers. Measurements on circulators utilizing single crystal BaFe/sub 11.1/Sc/sub 0.9/O/sub 19/ showed two-band circulation, below-FMR (at 36 GHz) and above-FMR (at 24 GHz), while those using single crystal BaFe/sub 12/O/sub 19/ showed above-FMR circulation at 32-35 GHz. Self-biased circulators using SrFe/sub 12/O/sub 19/ ceramics showed above-FMR circulation at 32 GHz. All circulators showed reasonable insertion losses and isolation, with the best insertion loss of 1.2 dB at an isolation of 18 dB being found for a BaFe/sub 11.1/Sc/sub 0.9/O/sub 19/ circulator operating below-FMR.

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