Coordinate Transformation Based Electromagnetic Design and Applications.

Abstract

The main objective of this thesis is to take one step forward to practical and realisable devices for antenna and microwave engineering, using the technique of discrete coordinate transformation (DCT), which is a practical implementation of the coordinate transformation method. During this thesis, the DCT technique was demonstrated and analysed from the theory, and was proved to provide an all-dielectric approach to design devices under certain conditions. Two schemes were proposed on how to use this technique in a practical design. The first one is to transform an existing device into a flattened profile, meanwhile maintaining its electromagnetic performance. As examples, a flat reflector and a flat lens were created from a parabolic reflector and a convex lens, respectively. The second scheme is to project the propagating paths of an electromagnetic wave, and then generate a distorted space according to the paths by engineering the electromagnetic properties of the media. In this scheme, two examples of application were presented: an undetectable antenna composed of a carpet cloak and a conducting cavity, and a broadband device which can extraordinarily enhance the transmission through a sub-wavelength aperture. Numerical simulations based on the Finite-Difference Time-Domain (FDTD) method were implemented to verify all the designs. Several specific configurations were employed in the modelling in order to simulate the DCT based devices more efficiently and precisely. Performance of these devices was validated and analysed, and the advantages and disadvantages of this technique were investigated. Realisation and fabrication methods i were also studied, and a prototype was designed, fabricated and measured. At the end, as an extension, a multiple discrete coordinate transformation method was proposed and presented. This multiple transformation was proved to effectively relax the limitation of the one-step transformation, and was used to design an all-dielectric thin absorber from a conventional pyramidal one for demonstration.