A negative refractive index metamaterial wave plate for millimetre-wave applications

Abstract

By use of a metamaterial based on the ‘cut wire pair’ geometry, highly birefringent wave plates may be constructed by virtue of the geometry’s ability of having a negative and positive refractive index along its perpendicular axes. Past implementations have been narrow band in nature due to the reliance on producing a resonance to achieve a negative refractive index band and the steep gradient in the phase difference that results. In this paper we attempt to design and manufacture a W-band quarter wave plate embedded in polypropylene that applies the Pancharatnam method to increase the useable bandwidth. Our modelling demonstrates that a broadening of the phase difference’s bandwidth defined as the region 90° ± 2° is possible from 0.6% (101.7 GHz – 102.3 GHz) to 7.8% (86.2 GHz – 93.1 GHz). Our experimental results show some agreement with our modelling but differ at higher frequencies.