Microwave waveguide measurements of negative index media (NIM) are reported. Accurate determination of the frequency variation of the complex scattering parameters yields the refractive index " ' ) ( ~ in n n + = ω for the NIM with ' n varying between -3.9 to -0.3 in the passband region of 9.7-10.5 GHz. The results show that transmission is optimized for 1 ' − ≈ n and small " n . PACS numbers: ...
