Experimental Investigation of Active Broadband ENZ Transmission Line based on Negative Capacitors

An active dispersionless Epsilon Near Zero (ENZ) transmission line operating in low RF band (1 MHz-50 MHz) is investigated experimentally. The structure comprises air microstrip line periodically loaded with non- Foster negative capacitors based on fast operational amplifiers. Measurements of scattering parameters of active line revealed almost dispersionless relative permittivity smaller than one, within the bandwidth of more than two octaves. Broadband ENZ behavior is accompanied by counterintuitive superluminal phase and group velocities.