Meta-materials with wideband negative permittivity and permeability

Recently, electromagnetic materials with negative permittivity and permeability values (sometime called media with negative refraction index) have been given much attention in the literature. Negative values of the material parameters can be achieved in composite media near resonances, which implies very dispersive properties. The material parameters are complex numbers to account for dissipation, and the real parts can be negative only in narrow frequency bands. Here, we show that this limitation can be relaxed in composite materials with active inclusions. It is proven that, using small dipole and loop antennas loaded by certain simple electronic circuits as composite inclusions, the material behaves as an effective medium with real negative parameters in wide frequency bands. Similarly, thin sheets of negative materials can be simulated by strip or patch arrays loaded by active circuits. (C) 2001 John Wiley & Sons, Inc.