Transformation optics collimating lenses for multi-beam antenna applications

Transformation optics (TO) is a flexible design process for electromagnetic and optical devices with a wide range of applications including cloaking, waveguides, and antenna enhancement. Many TO designs for antennas have been proposed, such as invisibility-cloaking radomes and collimating lenses; however, these designs all require inhomogeneous and anisotropic material parameters with extreme values that do not promote a practical implementation. Thus, the choice of transformation is a critical part of the TO design process and determines whether the device can ultimately be fabricated. In this paper, we review two transformation designs with simple material parameters for the conversion of radiation from an embedded isotropic source into multiple highly-directive radiating beams.