Frequency reconfigurable switchable Koch fractal dipole employing harmonic traps

Embedding fractal technology into an antenna provides desirable reduction of its physical size, as well as increasing its operating bandwidth and directivity. Nevertheless, the embedment of fractals is associated with proportionate increase of undesired harmonic problems associated with higher order modes of the antenna. In this paper, a microwave fractal dipole antenna that has tunable capability of a reconfigurable operation within an observed range of 400 MHz to 3.5 GHz is presented. Harmonic traps in the form of open-circuit linear short stubs are employed to eliminate each undesired harmonic of higher order mode. In addition, a small size linear tapered balun is employed at the antenna feed to improve the impedance patch. This technique is suitable for developing reconfigurable antenna with harmonic suppression or for single band antennas. The antenna prototype can be tuned from 691 MHz, 725 MHz, 743 MHz, 865 MHz, to 3010 MHz at a time. At the same time the antenna can suppress undesired harmful harmonic frequencies present from 1.8 GHz to 3.5 GHz within the observed range. Simulation and measurement results obtained are in good agreement, which have confirmed the design concept.