Non-Foster element and dispersion engineering approaches to bandwidth enhancements in active metamaterial-inspired structures

Because many metamaterial structures rely on resonances to achieve their interesting properties, they tend to exhibit narrow bandwidths. This is particularly true for resonant scattering and radiating structures, which are themselves intrinsically lossy and dispersive. Recent applications of non-Foster elements to overcome impedance and directivity bandwidth restrictions imposed by fundamental physics limits associated with passive elements will be described. The relationships between this active element approach at lower frequencies and gain material approaches at high frequencies for optical metamaterial structures will be reviewed. It will be demonstrated how the passive-gain-based multiple resonance line dispersion engineering approach and the non-Foster element techniques are interrelated.