We designed a low-loss double-negative composite metamaterial that operates at the millimeter-wave regime. A negative passband with a peak transmission value of 2.7 dB was obtained experimentally at 100 GHz. We performed transmission-based qualitative effective medium theory analysis numerically and experimentally to prove the double-negative nature of the metamaterial. These results were supported by the standard retrieval analysis method and the study was extended by reporting the fractional bandwidth and loss of the metamaterial as the number of layers in the propagation direction increased. We numerically calculated 2-D field map and experimentally confirmed far-field radiation response of horn antenna and metamaterial lens composite. Finally, we demonstrated that the effective index of the metamaterial was negative by performing far-field angular scanning measurements for a metamaterial prism. We simulated the prism by using the DrudeLorentz model and obtained the scattered field map in two dimensions at millimeter-wavelengths.