A dielectrically loaded quadrifilar helical antenna, suitable for operation with circularly polarised signals, comprises a solid dielectric core 12 of material with a dielectric constant greater than 5 which has a side surface and two end surfaces and is preferably cylindrical. An antenna element structure 10 provides four pairs 10AA - 10DB of substantially helical conductive paths, where the said paths have different electrical lengths. This structure includes first and second mutually adjacent helical elongate conductive tracks 10CA, 10CB, which may have different average widths and which are separated by an elongate channel or slit 11C which may be formed in a meandering manner. The tracks form an antenna element on the core side surface 12C and the width of the slit 11C is less than half the distance between an antenna element 10CA, 10CB and that of a neighbouring antenna element 10DA, 10DB. Each pair of helical conductive paths may be linked to a feed via linking conductors provided on an end surface 12D of the core 12. The solid dielectric material may be arranged to occupy a major part of the interior volume of the core 12. The antenna may provide a compact arrangement which may operate over a broad bandwidth.
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