A broadband antenna of an antenna system comprises a conductive plate comprising four slots. The slots are arranged in a rotation symmetrical manner in the plate. Each slot extends from a circumference of the plate towards a center of the plate. Each slot has an associated feed point located at its associated slot.The feed points associated with a pair of oppositely arranged slots are arranged to be fed with radio frequency signals, such that that a main radiation propagation direction of the antenna is along the rotational symmetry axis of the plate.The antenna design enables the achievement of flexibility in terms of isolation between the two polarizations. The antenna design may further enable a reduced size and weight. The antenna design also enables an antenna unit and an antenna array.