Multiband Fractal Antenna

Abstract

booming progress of wireless systems and the recent development of a variety of wireless applications have remarkably increased the demand for multiband/wideband antennas. For example, car companies are looking to integrate systems such as AM, FM, GPS, GSM etc and at the same time maintain the good look of the vehicle. Traditionally different antennas were used for different frequency bands, which causes a limited space and place problem. Multiband antennas can be used to overcome this problem. Most of the fractal geometries have self-similarity in their structure and recent research has shown that this self-similarity of fractals can be translated into its electromagnetic behavior. A fractal antenna based on the Sierpinski geometry is designed in this thesis that is capable of operating in multiple bands. The thesis involves design, simulation and fabrication of the Multiband Fractal antenna. The design and simulation of the antenna is carried out using FEM (Finite Element Method) and FITD (Finite Integral Time Domain) based electromagnetic simulators. Two different prototypes have been fabricated and tested. The measured results are compared with the corresponding simulated results, and good agreement is observed between both the results. The input impedance as well as input Return Loss shows a log-periodic behavior with a log-period of 2, the same scale factor that characterizes the Sierpinski Fractal geometry. The radiation patterns at these log-periodic bands also display good similarity. The geometrical scale factor of the Sierpinski fractal is changed and a monopole antenna based on this Perturbed Sierpinski fractal is designed and simulated. Band positions are changed according to the new scale factor but the bands are poorly matched. This poor input matching is improved by utilizing microstrip feed line. This Perturbed Sierpinski fed with microstrip line is fabricated and the measured results indicate that the band positions correspond to the new scale factor as well as the bands are well matched.