  Metamaterials are artificially made sub-wavelength structures arranged in
periodic arrays. They can be designed to interact with electromagnetic
radiation in many different and interesting ways such as allowing radiation to
experience a negative refractive index (NRI). We have used this technique to
design and build a quasi-optical Half Wave Plate (HWP) that exhibits a large
birefringence by virtue of having a positive refractive index in one axis and a
NRI in the other. Previous implementations of such NRI-HWP have been narrow
band ($\sim$1-3%) due to the inherent reliance on needing a resonance to create
the NRI region. We manufacture a W-band prototype of a novel HWP that uses the
Pancharatnam method to extend the bandwidth (up to more than twice) of a usual
NRI-HWP. Our simulated and experimentally obtained results despite their
differences show that a broadening of a flat region of the phase difference is
possible even with the initially steep gradient for a single plate.
