We report on a double negative metamaterial operating at 0.5 THz. The structure is based on a stack of several metallic arrays patterned with subwavelength apertures. Following the characterisation via TeraHertz Time Domain Spectroscopy, (THz-TDS), dispersion parameters are retrieved using a Fresnel inversion technique. A left handed-band is evidenced around 0.48 THz corresponding to a -3dB level of transmission. This high value is explained by impedance matching condition, as a consequence of the holes shape optimization. The left-handed propagation is explained by means of a lumped element circuit, used to model multi-mode propagation. Finally, we give some simulation results of the negative refraction trough a prism-like structure while the experimental verification is under progress. This work paves new ways in the domains of beam conforming and far field imaging at submillimeter and far infrared wavelengths.