The present invention relates to an antenna comprising a planar dielectric substrate (1) comprising a front (5) and a back dielectric face (6), at least one subantenna means comprising a first (2) and second (3) element for radiating and receiving circular polarized electromagnetic signals, at least one transmission line means (4) for transmitting signals from and to said at least one subantenna means, characterized in that the first (2) and second (3) elements of the subantenna means are slots (2, 3) of a spiral shape and are connected to each other to form a double spiral (9) slot with both spirals (2, 3) having the same sense of rotation, the subantenna means being arranged on the front dielectric face (5) of the substrate and the transmission line (4) means being arranged on the back dielectric faces (6) of the substrate (1). This structure provides a simple configuration which can be produced at low costs and is suitable for the use in a planar array antenna, in particular due to the decoupling of the feed system from the radiating elements.