Circularly polarized compact helical antenna

A circularly polarized directional helical antenna configured to transmit or receive radio-frequency signals in a predetermined frequency band, λ, being the wavelength associated with the minimum frequency of the predetermined frequency band, comprising

• a helicoidal radiating element made of conductive material extending along a longitudinal axis (A),
• a cavity made of conductive material having an open end, a closed end, and having an axis of symmetry that substantially coincides with the longitudinal axis of the radiating element, with at least one lower portion of the radiating element being arranged inside said cavity so that the lower end of the helicoidal radiating element is in contact with the closed end of the cavity,
• wherein the axial length (H) of the radiating element is less than the wavelength A and the open end of the cavity is equipped with a periodic metal structure allowing the height of the cavity to be reduced, the periodic metal structure being in the form of metal wire netting comprising a plurality of square meshes, wherein a length of each mesh is between 0.27λ and 0.3λ;
• and a thickness of the metal wires forming the netting being between 0.003λ and 0.012λ.