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In this tutorial article, the resonant radiation properties of electrically small, multiple-arm, folded wire antennas are considered and compared as a function of the antenna's height, the cylindrical diameter occupied, the geometry, and the number of folded arms within the antenna structure. The radiation properties considered include resonant resistance, efficiency, radiation patterns, and the operating bandwidth, which is characterized using the antenna's quality factor (Q). It is shown that electrically small, multiple-arm, folded wire antenna designs offer significant performance improvements relative to simple open-ended wire antennas, in terms of increased resonant resistance, bandwidth, and efficiency. However, when multiple-arm, folded wire antennas of the same height and cylindrical diameter, but having significantly different geometries, are made to be self-resonant at the same frequency, they exhibit similar resonant performance properties. This illustrates that the resonant performance properties of these antennas are primarily established by their height and the physical volume occupied relative to the resonant wavelength. Various design parameters are considered and described for achieving self-resonance and a reasonable impedance match with an electrically small, multiple-arm folded wire antenna. Finally, the performance properties of the multiple-arm folded wire configurations are compared with those of an impedance-matched, non-folded, open-ended wire configuration. It is shown that the multiple-arm folded wire configurations exhibit a lower Q than the impedance-matched, non-folded wire configuration.
Date of Publication: Aug. 2005