In this contribution, a linear-to-circular polarization transformer based on the employment of electrically small antennas is presented. The proposed setup consists of a circular metallic disk with a sub-wavelength aperture through which two sets of connected circularly polarized electrically small antennas are placed. We assume to use such a structure to close an open-ended linearly polarized circular waveguide in order to change the polarization from linear to circular. The proposed setup works around 1.627 GHz and exhibits 8 MHz of 3-dB axial ratio bandwidth.