Is the 3D-wire medium isotropic?

The metamaterial concept is today of great relevance in applied electromagnetics. It potentially allows synthesizing new structures where the propagation of electromagnetic waves is fully controlled. That includes the dispersion characteristic of the medium and the polarization eigenstates. In this paper, we are interested in modeling uniquely the interaction of electromagnetic waves with the array of metallic wires. The objective is to discuss whether a metamaterial based on the 3D-wire medium geometry discussed before is indeed isotropic or not, and in this way assess the validity of the standard plasma model (D.R. Smith, et al., Phys. Rev. Letts. vol. 84, p. 4184, 2000). In fact, it was recently proved that the standard plasma model is insufficient to describe the electrodynamics medium (in which the wires are all oriented in the same direction), since strong spatial dispersion emerges at very long wavelengths. The importance of this effect in a structure with increased symmetry is also discussed.