Polarimetric radars utilize orthogonal electromagnetic polarizations to offer performant target characterizations and classifications. A non-polarimetric, frequency-modulated radar can be extended to a polarimetric system by frequency-dependent, polarization rotating reflect- and transmitarrays which are revealed in this work. The proposed polarizers consist of specially developed compact unit cells optimized for either preserving or rotating an incident linear polarization in closely spaced frequency bands. The development is carried out with the aid of a computational electromagnetic design tool and different models are presented to comprehend the functionality. Various configurations of radars and polarizers as well as the spatial arrangement are addressed. Samples are manufactured and the influence of fabrication tolerances is evaluated by simulations and measurements. An error model and a signal processing chain with calibration methods is discussed and adapted. To practically show the usability in radar applications, a vector network analyzer is used for polarimetric outdoor radar measurements with corner reflector targets that can be classified successfully.