Broadband superluminal effects in ENZ active metamaterial

Recently, it has been shown possible to construct an (almost) dispersionless active ENZ metamaterials and transmission lines based on non-Foster elements. These structures are inherently extremely broadband (several octaves) and they may support counter-intuitive superluminal phase and group velocities. However, causality is always preserved due to finite bandwidth of any realistic non-Foster element. Here, the measurements of broadband superluminal phase and group velocity of an active transmission line operating in lower RF regime (10 MHz - 40 MHz) are reported.