Improving the frequency characteristics of the electronically steerable passive array radiator antenna

Electronically steerable passive array radiator (ESPAR) antennas have been shown to be a significant adjunct to wireless ad-hoc networks. One of their limitations however is their restricted bandwidth of operation due chiefly to the fact that the port impedance of the antenna changes in accordance with the configuration of the reactances employed to load the parasitic elements. We propose a technique to optimise the loading patterns used by adding an extra degree of freedom in the form of variable impedance at the central antenna element and thereby providing the ability to perform dynamic matching of the port impedance. This improves the frequency characteristics of the ESPAR antenna so that it may be used in different types of communication systems as a result of having wider bandwidth performance while retaining good beamforming characteristics.