  We have fabricated a quarter-wave plate from a single layer birefringent
metamaterial. For comparison, an appropriately scaled double layer meanderline
structure was fabricated. At the design frequency of 639 GHz, the metamaterial
structure achieves 99.9% circular polarization while the meanderline achieves
99.6%. The meanderline displays a larger bandwidth of operation, attaining over
99% circular polarization from 615 - 743 GHz, while the metamaterial achieves
99% from 626 - 660 GHz. However, both are broad enough for use with CW sources
making metamaterials a more attractive choice due to the ease of fabrication.
Both samples are free standing with a total thickness of 70um for the
meanderline structure and a mere 20um for the metamaterial highlighting the
large degree of birefringence exhibited with metamaterial structures.
