Hexagonal Ferrite Isolators

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Abstract
Waveguide bandwidth isolators requiring virtually no externally applied magnetic field have been developed for the millimeter wave frequency range. These ferrimagnetic resonance‐type devices utilize highly anisotropic uniaxial hexagonal ferrites. The specific ferrite compounds used are from the two families BaO·2NiO·ΔAl2O3 · (8‐Δ) Fe2O3 and SrO·δAl2O3· (6‐δ) Fe2O3 denoted Ni2W (ΔAl) and SrM (δAl), respectively. The substitution variables Δ and δ were adjusted to yield different materials whose effective magnetic anisotropy fields were appropriately spaced over the range 16 to 30 kOe. This spacing permitted their use in isolator designs throughout the frequency range 50 to 90 Gc/sec. Five materials from the Ni2W(ΔAl) family were used to cover the frequency range 50 to 60 Gc/sec and 12 materials from the SrM(δAl) family covered the range 60 to 90 Gc/sec. Pertinent electrical properties of these materials are reported as well as techniques essential to their successful application in the isolator structure. Waveguide bandwidth isolators using these materials were developed for the bands 50 to 75 and 60 to 90 Gc/sec.

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