Near-field analysis of frequency selective surfaces and applications in directive antennas

Abstract

A near-field characterisation of two dimensional metallo-dielectric frequency selective surfaces either in a single or double layer configuration is presented in this thesis. Motivated by the current attention of the electromagnetic properties of near-fields, an in-house periodic MoM-based computational tool is developed for the efficient and rigorous estimation of the near-fields in frequency selective surfaces (FSS) illuminated by a plane wave. For this purpose a thorough convergence study related to the calculation of the near fields is initially presented. The near-field estimation allows us to calculate the power stored in an FSS at resonance which, in turn, can be used in the calculation of the loaded quality factor of the FSS. Based on the characterisation of various topologies, new techniques for the analysis of highly-directive and broadband leaky wave antennas are proposed. An initial design based on a perturbed FSS results in a structure with multiband response and near-fields enhanced by more than 70 fold, which can be relevant to sensor applications. Subsequently, the near-field technique is used in combination with reciprocity for the extraction of the radiation patterns in Fabry-Perot cavity antennas formed between a FSS and a metamaterial ground plane. In combination with traditional array theory the complex dispersion characteristics of high-gain sub-wavelength 2-D Fabry-Perot leaky-wave antennas (LWA) consisting of two periodic metallodielectric arrays over a ground plane are extracted. This yields a fast and rigorous tool for the characterisation of this type of antennas. Design guidelines are given throughout to synthesize a highly-directive antenna and a broadband leakywave antenna. This thesis was fully funded by the Joint Research Institute for Integrated Systems in Edinburgh, Scotland.