We report on an analysis about the spectral shape of the Saturnian kilometric radiation (SKR) recorded by the RPWS/HFR experiment onboard the Cassini spacecraft. The SKR envelope is found to be very variable in timescales covering a large range, from hours to days. Despite this change, we proceed to a classification of the shape in the frequency range from 3.5 kHz to 1.2 MHz taking into consideration the phenomenology and the state polarization of the radio wave. In the considered SKR bandwidth, we make a distinction between three principal components having different spectral shapes and degrees of total polarization. The well-known SKR component exhibits a degree of circular polarization close to 100% and emits in the frequency range from 80-90 kHz to 800-900 kHz. The two other components become visible in the lower and higher parts of the HFR receiver and show a weak linear polarization less than 10%. The generation of the SKR is linked to particles precipitations in the auroral regions, nevertheless the variability of the spectral shape is still subject of investigation. The present analysis is confronted with the theoretical model of SKR envelope spectrum proposed by Galopeau et al. (1989).