Investigations on fractal antennas for WLAN, WIMAX, UWB and mobile applications

Abstract

Wireless communications have been developed widely and rapidly in the modern world especially during the last two decades. The future development of the personal communication devices will aim to provide image, speech and data communications at anytime and anywhere around the world. This indicates that the future communication terminal antennas must meet the requirements of multi-band or wideband to sufficiently cover the possible operating bands. However, the difficulty of antenna design increases when the number of operating frequency bands increases. In addition, for miniaturizing the wireless communication system, the antenna must also be small enough to be placed inside the system. However, in order to transmit and receive more information large bandwidths are required and bandwidth enhancement is currently a popular research area. Typical wireless application use devices which are smaller in size and require the use of small sized antennas with increased bandwidths. In the current research work, Microstrip antennas for UWB applications have been presented. Four fractal antennas are designed and simulated for UWB and mobile applications using CST Microwave Studio V10. These are optimized to improve the performance of each of the antennas by applying suitable performance enhancement techniques. For example a Hexagonal Sierpinski Gasket Antenna is presented with stub and reduced ground which provides an achievable bandwidth of 1.86 GHz and is capable of covering the band for UWB applications. The second design is Pythagorean Fractal Tree Antenna which is fed using CPW feeding technique and is a wideband antenna with a bandwidth of 2.04 GHz with an average return loss of -35dB and an average gain of 4.5dB. The next design presented is Fractal Flower Antenna which is also a CPW fed Antenna which is also a UWB antenna with 4.2 GHz of bandwidth and also a size reduction by an amount of 50% has been achieved with this antenna. In the next design Sierpinski Gasket Bow-Tie Antenna is presented in which the conventional Bow-Tie is combined with Sierpinski which covers GSM, ISM, Bluetooth and mobile applications. In order to validate the results two simulated antenna designs, Pythagorean Fractal Tree antenna and Fractal Flower antenna have been fabricated and tested to validate the results. The simulation and measured results of both the antennas have been compared and studied and they were found in good agreement with each other and hence making them suitable for proposed practical applications.