Otimização de estruturas DGS e PBG em antenas de microfita retangular usando algoritmo genético

Abstract

Microstrip antennas have attracted the attention of researchers worldwide because of their interesting features for various applications. However, disadvantages such as low gain, narrow bandwidth and low radiation efficiency can limit its use in a given system. Besides, this type of antenna can excite higher order modes in addition to the fundamental. This feature is particularly important for systems with multiple operating frequencies, in other cases, it is necessary to use filters to eliminate the unwanted modes. Alternatively, arrangement of defects can be added to the antenna‟s ground plane or substrate to achieve the same aim, such structures are called Defected Ground Structure (DGS) and Photonic Band Gap (PBG), respectively. However, the development of really efficient projects involving these types of structures presents great dependence on the correct specification of the physical parameters of the used arrangement. In this context, aiming at eliminating and/or attenuating higher order modes, without significantly affecting the performance of the antenna to the fundamental mode, the present work studied the application of a Genetic Algorithm (GA) in the development of new models of DGS and PBG structures. The proposed models consist of circular holes, filled with air, in the hexagonal and rectangular patterns, for the periodic configuration, and with micro structured pattern, for the quasi periodic configuration. The proposed AG was responsible for specifying the following parameters of the analysed arrangements: diameters of the holes, distance among them and the location of the arrangement along the length of the antenna. All the analysed antennas were constructed manually, by using a milling machine and/or corrosion by iron perchloride. Based on the simulated and measured results, was verified that the proposed GA was able to optimize the studied structures in order to preserve the fundamental mode, while the higher ones were eliminated and/or considerably attenuated. It was verified that for the same type of arrangement, the antennas with DGS presented better performance in relation to those with PBG, considering the reflection coefficient of the fundamental mode. In addition, the optimized structures did not cause significant changes in the total gain value or in the shape of the radiation pattern and, in the case of the DGS, exhibited important characteristics for miniaturization of the antennas. The obtained results are particularly important, assuming that the optimized structures can be used to eliminate unwanted modes in applications with passive or active microstrip antennas, which also operates as resonators.