Conventionally, for the fully polarimetrical calibration of a general non-reciprocal radar system, at least two calibrators such as a dihedral corner reflector plus a sphere are required. A new polarimetric passive radar calibrator for fully polarimetric calibration is proposed in this paper. With the new design, a single calibrator is enough for the same purpose. The electromagnetic scattering characteristic of the new calibrator is calculated by method of moment (MOM), demonstrating that the new calibrator is suitable for fully polarimetric calibration applications.