Stability analysis of active broadband ENZ line

Recently, it has been shown possible to go around basic energy-dispersion constraints that limit the bandwidth of every passive metamaterial and construct a broadband active Epsilon-Near-Zero superluminal transmission line. Published theoretical studies revealed that such a `tank circuit´ formed by negative capacitor and positive distributed capacitor of a host transmission line is stable if the overall capacitance is positive. These studies assumed lossless host transmission line periodically loaded with ideal dispersionless negative capacitors. Here, the stability analysis of realistic superluminal transmission line with negative capacitors with gain/loss is performed in Laplace domain. Obtained results are in a good agreement with those obtained in recent experiments on active transmission line developed at University of Zagreb.