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.
Telescopes for the next generation of CMB (Cosmic Microwave Background) experiments could be based on either
reflective (such as Planck, Clover) or refractive optics (BICEP, LSPE, SPIDER). Both techniques have advantages and
disadvantages. On-axis lens based telescopes can be compact while off-axis reflective configurations can be large. The
RF performances of mirror based telescopes are very well understood, whereas lens based systems have a lower
technology readiness level: specifically, the systematic effects (aberrations such as chromaticity, birefringence, losses,
standing waves and cross-polarisation) that they can introduce need to be accurately quantified at millimetre-wave. This
paper reports on both RF modelling and preliminary experimental studies of a lens coupled to a feed-horn antenna for
which the co- and cross-polarisation beam patterns are characterised.