Auto-tune procedure for circulators based on eigenvalue adjustments

The tuning of Microwave Circulators utilizing gyromagnetic materials requires the calibration of the biasing magneto-static field, which is mostly supplied by permanent magnets. The permanent magnets have to be tuned down from saturation to an appropriate magnetization stage by means of specialized magnetizing and tuning equipment. A tuning procedure suited for automated adjustment of the saturation level of permanent magnets is described, based on S-parameter measurements. Eigenvalues of the measured 3×3 S-matrices are used to determine a required setting on a computer controllable magnetizer. This will enable a quick and accurate automated tuning process.