Miniature reconfigurable three-dimensional fractal tree antennas

This paper introduces a design methodology for miniature multiband as well as reconfigurable (i.e., tunable) antennas that exploits the self-similar branching structure of three-dimensional (3-D) fractal trees. Several fundamental relationships, useful for design purposes, are established between the geometrical structure of the fractal tree antenna and its corresponding radiation characteristics. In particular, it will be shown that the density and elevation angle of the branches play a key role in the effective design of miniature 3-D fractal tree antennas. Several design examples are considered where fractal trees are used as end-loads in order to miniaturize conventional dipole or monopole antennas. Multiband and reconfigurable versions of these miniature antennas are also proposed, where either reactive LC traps or RF switches are strategically placed throughout the branches and/or along the trunk of the trees. Included among these designs is a miniature reconfigurable dipole antenna that achieves a 57% size reduction for the center frequency of the lowest intended band of operation and has a tunable bandwidth of nearly 70%.