A linear-to-circular polarization converter, consisting of a suitable arrangement of thin periodic airdielectric slabs, is presented. The uniaxial nature of the periodic structure, highlighted by the field propagation matrix representation, is exploited to perform the required field polarization conversion. The performances of the proposed polarizer are illustrated by analyzing the radiative performance in terms of impedance bandwidth, axial ratio and realized gain of a horn and a wideband planar slot lens antenna.