In a dielectrically-loaded quadrifilar antenna for operation with circularly polarised signals, four coextensive composite helical elements are plated on the outer surface of a cylindrical dielectric core, each composite element comprising two mutually adjacent conductive tracks defining between them an elongate channel or slit. The track edges bounding each channel are longer than the opposite edges of the respective tracks in that they follow parallel meandered paths, with the result that each channel deviates from a mean helical path and is longer than the corresponding portion of the mean helical path. At a frequency within the operating band of the antenna, the channels have respective electrical lengths equivalent to a half wavelength. The bandwidth of the antenna is greater than the bandwidth of a correspondingly dimensioned antenna having single-track helical elements.