An in-depth stability analysis of a typical non-Foster matching network is presented. The investigation is carried out at two levels: considering an ideal implementation of the negative impedance inverter (NIC) and using detailed circuit-level descriptions of all its active and passive components. The ideal NIC model will enable an analytical derivation of the characteristic system and the system poles, which will provide insight into the main instability mechanisms in these configurations. A good qualitative agreement is obtained with the circuit-level analyses, based on pole-zero identification and bifurcation detection methods. The impact of significant parameters, such as the biasing resistors or the value of the reactive component to be negated, is investigated in detail. A circuit-level methodology is proposed to obtain the stability boundaries and margins in an efficient and rigorous manner. For illustration, a non-Foster circuit based on a NIC has been manufactured and measured, obtaining very good agreement with the analysis results.

This work has been funded by the Spanish Government under contract TEC2014-60283-C3-1-R, the European Regional Development Fund (ERDF/FEDER) and the Parliament of Cantabria (12.JP02.64069). The authors would like to thank S. Pana, University of Cantabria, for her assistance with the manufacturing process.