Fractal antenna research at University of Birmingham

Abstract

The use of fractal geometry in electromagnetics has been a recent topic of interest. In antenna applications, the Minkowski loop, the Koch curve monopole, the Koch island patch, the Sierpinski carpet and the Sierpinski gasket have been reported. In particular, the fractal Sierpinski gasket monopole antenna which demonstrates a log periodic resonant property. Although the fractal structure from these mathematical functions could provide attractive multiband performance, it has become clear that such geometry requires further modification to enhance their application. However, perturbation effectively varies the structural properties, and hence electrical properties. In this paper, we present two recent developments of these fractal monopole antennas at the University of Birmingham. The first development describes the multiband behaviour of a perturbed fractal Sierpinski gasket and a perturbed Parany monopole antenna. Both antennas have a periodic ratio of 0.75 and 0.775 respectively. The first antenna demonstrates four operating bands while the latter design involves eight bands. Two methods are presented to demonstrate improvements to the inherently poor input impedance match of these antennas with a 50 /spl Omega/ port. These improved feeding methods will allow further flexibility to the application of these multiband antennas. The second development looks into an alternative multi-level structure antenna which may provide bandwidth improvements without sacrificing antenna performance. The design consists of a set of self similar circular rings, as an alternative to the triangular fractal Sierpinski gasket monopole antenna. A comparison of both antennas with scale factor of 0.5 is described.