The invention refers to an add-on device configured to reduce the power level of reflected paths of GNSS signals (612, 613) 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. The GNSS signals are transmitted according to a first polarization, and the add-on device comprises a material (601) configured to be transparent to said first polarization and to reflect GNSS signals polarized according to a second polarization orthogonal to said first polarization.