An add-on device configured to reduce the power level of reflected paths of GNSS signals reaching a GNSS receiver's antenna, the associated GNSS receiver set, some equipment embedding the add-on device, and the associated method to reduce the power level of reflected GNSS signals are provided. The GNSS signals are transmitted according to a first polarization, and the add-on device comprises a material configured to be transparent to the first polarization and to reflect GNSS signals polarized according to a second polarization orthogonal to the first polarization.