Magnetically tunable millimetre-wave filter with single-crystal barium ferrite

Barium-ferrite (BaFe12O19) single crystals with a high anisotropy field and low millimetre-wave (mm-wave) losses have been grown from high-temperature solutions. The high internal field (17/4¿¿ MA/m) considerably reduces the external magnetic field required for spin resonance at mm-wave frequencies. Due to the progress in single-crystal barium-ferrite technology, it is possible to extend the tuning range of filters up to 90 GHz. A compact tunable filter, similar to y.i.g.-filters, has been built and the first results are reported.