3D Frequency Selective Surfaces

The purpose of this project is to investigate a novel design of three-dimensional frequency selective surface (FSS). FSSs have been the subject of intensive investigation for their widespread applications in communication and radar systems for more than four decades. For practical applications, it is desired to realize a FSS with miniaturized elements and a stable frequency response for different polarizations and incident angles. But these features are difficult to obtain through traditional designs; and a large number of structures and modelling techniques have been proposed. However, most of the research of the FSSs has been in one or two dimensional periodic array of resonant structures. Less attention has been paid to three dimensional FSS. In this thesis, we design and simulate 3D FSSs based on 2D periodic arrays. Firstly, three flat FSSs are designed: the flat cross dipole element FSS, the flat Jerusalem cross FSS and the flat square loop FSS. Then the 2D structures are formed into 3D structures for a fixed unit cell size. The simulations are done using CST Microwave Studio. As a result, compared to the traditional 2D FSSs at the same unit cell size, the resonant frequency of the 3D structures is miniaturized. Therefore the unit cell size of the FSS is sufficiently reduced. Moreover, the frequency responses of the proposed 3D FSSs have achieved excellent stability with respect to TE and TM polarizations and different incident angles. An extension of FSS research is used to design an artificial magnetic conductor (AMC) by applying a ground plane behind the FSS. The FSS is working as a reflective layer to improve the reflectivity of the AMC surface. Such a surface reflects the incident wave in phase rather than out of phase. The reflection phase responses of the 3D AMC surfaces are also presented by applying a ground plane behind the structure.