In this paper, some of the most relevant patents of the last ten years on compact helical antennas are reviewed. Different technical solutions and their respective advantages and limitations are discussed. Both monofilar and quadrifilar helical antennas are addressed with different radiation characteristics. Some of these techniques can eventually be combined to improve further the axial length reduction. Only cylindrical designs are addressed in this paper, but most of the concepts could easily be applied to other shapes of helical antennas.
Keywords: Helical, helix antennas, monofilar, quadrifilar antennas, normal, axial modes radiation
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