Passive and active nano cylinders for enhanced and directive radiation and scattering phenomena

In this chapter our main objective is to review our previous and current research efforts in this promising area of directive NP -based NAs. Focus will be placed on both symmetric and asymmetric two-dimensional (2D) and three-dimensional (3D) passive and active (with constant gain model) cylindrical NPs with appropriate layer designs, perforations or eccentricities. We will illustrate how perforations essentially only enhance the near-field radiation properties, while asymmetries introduced through the layer eccentricities also enhance the far-field radiation behaviors. We will also describe how symmetric multilayered cylindrical NPs with tailored scattering coefficients lead to super-directive and needle -like radiation patterns in forward as well as backward directions. Our results will be illustrated by various near-and far-field distribution results obtained either analytically and/or numerically with full-wave commercial packages. The canonical problem solutions prove not only to be essential reference results to build intuition and knowledge, but also to guide and verify more complex numerical simulations.