Size reduction of a folded conical helix antenna

A wire antenna that utilizes spiraling and folding has been reported by Dobbins, and Rogers (see IEEE Trans. Antennas and Propagat., Dec. 2001). We have shown that this antenna, called the folded conical helix antenna (FLEX), performs very well as an electrically small monopole antenna. Using the figure of merit proposed in this work we can quantitatively compare this antenna to other types of electrically small antennas in different size ranges and efficiencies. This highest figure of merit is achieved by the electrically smallest antenna, which has a size of kr=0.1, and it appears to be considerably higher than might be expected. Two different efficiency measurements show reasonably consistent results, and the measured gain bandwidth is consistent with the impedance bandwidth. Therefore, the FLEX antenna should be a practical and broadband compact antenna for the MF, HF, and VHF frequency ranges.