Transformation electromagnetics inspired lens designs and associated metamaterial implementations for highly directive radiation

In this chapter, the transformation electromagnetics (TE) approach for achieving highly directive radiation is introduced and demonstrated by both numerical simulations and experimental results obtained from laboratory prototypes. In addition to conventional approaches for designing directive antennas, the recently developed metamaterial-related techniques, such as the electromagnetic bandgap (EBG) structures, zero-index metamaterials, and transformation optics (TO), are reviewed. In particular, several coordinate transformations which can provide simplified material parameters are proposed, including the conformal mapping, quasi-conformal (QC) mapping, geometry-similar transformation, and the uniaxial media simplification method. All of these techniques are capable of achieving a certain degree of simplification in the transformed material parameters without sacrificing the device performance. The design and demonstration of various beam collimating devices illustrate their unique properties and suitability for different applications such as in compact wireless systems. In all, these TE-enabled lenses with simple material parameters are expected to find widespread applications in the fields of microwave antennas as well as optical nanoantennas.