Characteristic Mode Investigation of a Reactively Loaded Electrically Small Dipole Antenna

Reactive loading is commonly applied to monopole and dipole antennas to maintain desirable electrical characteristics as the size of the antenna is reduced. Studies relying on parametric techniques have yielded design guidelines for optimal load placement. The use of characteristic mode theory, however, provides an alternative method to understand the currents on the antenna structure and offers insight for optimal load placement. In this work an electrically small dipole antenna is investigated using characteristic mode theory. Although in the electrically small regime the total antenna current is composed primarily of a single characteristic mode, higher order modes contribute strongly to the change in the dominant mode as the loading magnitude is increased. Understanding the effect of higher order characteristic modes in loaded antenna structures provides insight for load placement strategies.