Design and analysis of a class of ultrawideband antennas

Abstract

The wireless spectrum is very crowded due to the exponential increase in the utility and number of wireless devices. This necessitates the exploration of new techniques for sharing the wireless spectrum. The Ultra-WideBand (UWB) technology is evolving as a very efficient solution to address the problem of spectrum scarcity. The unlicensed usage of the frequency band 3.1 GHz to 10.6 GHz is legalized by the Federal Communications Commission for the UWB commercial applications. The antennas used in UWB systems require good return loss and radiation characteristics, to establish stable communication in an environment with very high level of interferences from the licensed users. It is necessary for the UWB antennas to resonate for the entire range of frequencies in the range 3.1 GHz to 10.6 GHz. The printed monopole antennas have a compact size with large resonance bands and hence they are the most preferred structures for UWB antenna design. Antennas developed for narrowband applications are designed for their resonant frequencies but the UWB antennas due to their large bandwidth of operation are designed for their lower band-edge frequencies. The different geometries of printed monopole antennas were analyzed for their return loss performance. The antennas with circular and hexagonal radiator geometries have good return loss characteristics over the entire UWB range of frequencies. However, the antenna with circular radiator has smaller dimension compared to the antenna with hexagonal radiator for the same lower band edge frequency. An Iterated Function (IF) is used to generate a fractal geometry on the printed circular monopole antenna to enhance its return loss characteristics. The printed circular monopole radiator newline