Abstract : A procedure is described for obtaining the two-way polarimetric properties of a SAR antenna from one-way measurements in a compact antenna test range. The two-way properties are determined by involving reciprocity and computing a polarization distortion matrix (PDM). Next, one-way antenna-only measurements are combined with boresight measurements of the complete system to find an overall PDM. Polarimetric distortions caused by the antenna can be compensated using the inverse of the PDM; however, the Advanced Detection Technology Sensor antenna was found to have adequately low crosspolarization without the need for crosspolarization compensation.