The polarimetric multi-frequency radio sources properties

The polarization properties of extragalactic radio sources at frequencies higher than 20GHz are still poorly constrained. However, their characterization would provide invaluable information about the physics of the emission processes and is crucial to estimate their contamination as foregrounds of the polarized Cosmic Microwave Background (CMB) angular power spectrum on scales less than or similar to 30 arcmin. In this contribution, after summarizing the state-of-the-art of polarimetric observations in the millimetric wavelength bands, we present our observations of a complete sample of 53 sources with S(20)GHz > 200 mJy carried out with the Australia Telescope Compact Array (ACTA) between 5.5 and 38 GHz. The analysis clearly shows that polarization properties cannot be simply inferred from total intensity ones, as the spectral behaviors of the two signals are typically different.