The present invention relates to a circularly polarized directional helical antenna that is capable of being used in RFID devices and more particularly in RFID readers. The antenna is intended to transmit or receive signals in a predetermined frequency band, λ being the wavelength associated with the minimum frequency of the predetermined frequency band. It includes a helicoidal radiating element made of conductive material extending along a longitudinal axis (A) and the axial length (H) of which is less than the wavelength λ, and a cavity made of conductive material having an open end and a closed end and having an axis of symmetry that coincides with the longitudinal axis of the radiating element, at least one lower portion of the radiating element being arranged inside the cavity so that its lower end is in contact with the closed end of the cavity.