In this article, we propose a model to obtain negative electrical permittivity in metamaterials using a conductor wire of rectangular cross-sectional geometry. Plasma frequency in the GHz range is determined in terms of the wire geometry. This new composite dielectric, which has the property of negative electrical permittivity below the plasma frequency, opens new possibilities for GHz devices. Finally, we show a unitary metamaterial cell where the refractive index takes negative values over a wide frequency range.