The losses of microwave ferrites at communication frequencies

Abstract

Microwave ferrites have been used for many years in non-reciprocal devices such as circulators and isolators. These are widely used in base stations to protect the high power amplifiers from mismatch and subsequent damage. At the current time the international standard for the measurement of ferrite losses is the measurement of linewidth at 9.4 GHz at GyroMagnetic Resonance (GMR). Unfortunately most ferrite devices are used at much lower frequencies, especially 1.8 GHz, and there is significant uncertainty in how the losses vary as a function of frequency. Also most ferrite devices are never operated at GMR as this is the point of maximum magnetic loss. Therefore a measurement system has been developed to characterise both real and imaginary parts of the tensor permeability matrix. This can be done for ferrite materials at communication frequencies, such as those used in a typical circulator, and at varying bias levels. Results are presented for a range of commercial materials.