Application of Floquet theory to the large signal stability analysis of microwave amplifiers

Stability has been an issue in the design of microwave amplifier for decades. The case of linear amplifiers was treated first and can be considered completely understood, general techniques having been derived and validated making use of scattering parameters. On the other hand, modern microwave systems call for the exploitation of higher amplifier classes trading efficiency with non-linear device operation. Correspondingly, the circuit operating point becomes Large Signal (LS), and linear stability analysis no longer applies. The simplest case of LS is periodic operation, where stability is assessed exploiting Floquet Theory. From the standpoint of Electronic Design Automation tools, the direct computation of the Floquet exponents is a current research area. We review its implementation within the framework of the Harmonic Balance technique, discussing efficient numerical approaches and their application to amplifier test cases.