2. Magnetic materials: what are the requirements for microwave frequencies?

The integration of spinel and garnet ferrites into microwave circuits has led to the development of several signal processing functions. Among these functions, the most important is that performed by circulators, which consists of separating, for example, the transmitted signal from the received signal in a transceiver module (see Box 5 on isolators). These circuits, like isolators and certain phase shifters, exploit the non-reciprocal nature of electromagnetic wave propagation in magnetized ferrites. Non-reciprocity exploits the gyromagnetic behavior of elementary magnetic dipoles and the anisotropy of magnetized ferrites. The creation of frequency-tunable circuits (resonators, filters, couplers, etc.) can also be considered, as the magnetic permeability of the medium, and therefore the conditions for the propagation of radio signals, are modified under the action of a static magnetic...