This paper attempts to apply the principle of radar polarimetry to wideband synthetic aperture FM-CW radar and presents a basic polarimetric detection result of a linear target in a laboratory measurement. Although the principle of radar polarimetry has well been established for the completely polarized wave and for the monostatic case, it still needs to be extended to wideband radar system. The FM-CW radar utilizes a wideband signal and the resultant beat signal whose frequency is proportional to range is different from the scattered wave in pulse radar. This paper points out that the Fourier transformed complex beat spectrum obtained by an synthetic aperture FM-CW radar acts like an element of the scattering matrix which plays the most important role in polarimetric imaging. The fact was verified by a polarimetric detection in a laboratory, demonstrating the validity of FM-CW radar polarimetry and indicating an establishment of a full polarimetric and synthetic aperture radar system. >