The total radar cross section (RCS) of antennas is the vector sum of structural and antenna mode scattering. These RCS contributions can be described completely by their polarimetric scattering matrices. The paper introduces a new polarimetric network description for three and four port antennas. The total scattering matrix is separated into the individual contributions with a new measurement procedure, based on complex load variations. Two waveguide and two planar antennas are chosen for demonstration and verification. By load variation the antenna mode scattering can be manipulated in phase and amplitude. It can especially be steered to compensate for the structural and aperture contributions. The possibilities for RCS minimization under polarimetric aspects are shown to be limited in bandwidth, polarization and aspect angle.