Superluminal propagation in metamaterials: Anomalous dispersion versus non-Foster approach

A classical superluminal propagation in systems with anomalous dispersion is compared with recently introduced superluminal propagation in non-Foster active epsilon-near-zero (or mu-near-zero) metamaterials. It is shown that the underlying physics of non-Foster superluminal propagation is fundamentally different from physics of anomalous dispersion. The non-Foster-based simultaneous superluminal phase and group velocities are extremely broadband (achieved relative bandwidths vary from 1:20 (more than four octaves) to 1:400 (more than seven octaves)). Foreseen applications are in transformation electromagnetic devices and squint-free leaky wave antennas.