W-Band Pancharatnam Half Wave Plate Based on Negative Refractive Index   Metamaterials
  Electromagnetic metamaterials, made from arrangements of subwavelength sized structures, can be used to manipulate radiation. Designing metamaterials that have a positive refractive index along one axis and a negative refractive index along the orthogonal axis can result in birefringences, $\Delta n>1$. The effect can be used to create wave plates with subwavelength thicknesses. Previous attempts at making wave plates in this way have resulted in very narrow usable bandwidths. In this paper, we use the Pancharatnam method to increase the usable bandwidth. A combination of Finite Element Method and Transmission Line models were used to optimise the final design. Experimental results are compared to the modelled data. 
Imran Mohamed, Giampaolo Pisano, and Ming Wah Ng
physics.ins-det astro-ph.IM physics.optics