EBG substrate synthesis for 2.45 GHz applications using Genetic Programming

In the last decade the study of frequency selective surfaces (FSS), i.e. periodic metal patches printed on a dielectric substrate, has regained interest both in the microwave and millimeter-wave region, with the introduction of electromagnetic band gap (EBG) materials. This entirely new class of structures, encompassing FSS as one of its subclasses (planar EBG), were named in analogy to the bandgaps present in electric crystals and present some very interesting new electromagnetic properties. By choosing the proper geometry of the periodic surface we can shape the electromagnetic behavior of EBGs structures in order to prevent the propagation of electromagnetic waves in a given frequency band. In particular, EBG surfaces can be made to act as artificial magnetic conductors (AMC) ground planes, showing a reflection coefficient with magnitude 1 and phase 0. The ultimate goal is then to design and incorporate such metamaterial-substrates in antenna structures in order to improve antenna performance. Currently there is a growing interest in antennas integrated with an EBG surface for communication system applications, covering the 2.45 GHz and the 5 GHz wireless networking bands. The main drawback of this strategy is the reduced bandwidth of the complete antenna, since the frequency range over which these EBG surfaces behave as an AMC is usually narrowband and fixed by their geometrical configuration. For this reason we focused our research both on the optimization of EBGs and the synthesis of new promising geometries using genetic programming (GP).