Conception, réalisation, caractérisation et optimisation par les algorithmes génétiques des antennes planaires intelligentes pour les réseaux nomades ou Wi-Fi.

Abstract

This project is the result of a quite simple observation: access to information via the Internet in developing countries and particularly in Cameroon is not affordable for every body and, as such, it remains a very little used means of communication in the general public. Therefore, our purpose is to contemplate solutions aimed at facilitating Internet access at lower costs to a wider public. To meet this requirement, we have chosen the Wi-Fi technology. The Wi-Fi mainly allows for radio links which requires the use of linear polarized radiating elements with very low bandwidth and working within the frequency band allocated to this application. Our contribution to this ambitious project is to design technologically very simple planar antennas which are feasible with affordable and cheaper materials, because the antennas sold on market are too expensive. Despite the advantages of Wi-Fi technology, it has many disadvantages that may reduce the scope of it signal range and thus may cause the degradations of it performances. The main drawback of Wi-Fi networks is their vulnerability to the external environment. To overcome this problem, we have developed a conceptual approach on the study of planar adaptive antennas which offer an effective solution to the interference issue. Adaptive antennas are the so-called smart antennas. They comprise a set of array mounted basic components. Among these basic components, we have mostly been concerned about the microstrip type because of its performance and ease of implementation. The investigation focused on basic components such as the patch, the square ring and the dipole with various topologies. We have developed an approach based essentially on the electromagnetic theory of transmission wave transmission lines. The study included both the electromagnetic simulation, manufacturing and testing developing models that we should implement. We have used other analytical or numerical methods, namely the modal method and the spectral method coupled with the method of moments. The synthesis problem has been addressed in goal to create nulls or shadow zone in the scrambler direction. We have chosen a global optimization stochastic method based on Genetic Algorithms. Three types of synthesis of incomplete and non-periodic array antennas have been discussed in this regard: the synthesis compared to a desired optimal array pattern, synthesis from a template and the signal or direction rejection.