Multi-frequency linear and circular radio polarization monitoring of jet emission elements in $Fermi$ blazars
Radio emission in blazars -- the aligned subset of Active Galactic Nuclei (AGN) -- is produced by synchrotron electrons moving relativistically in their jet's magnetic field. Under the assumption of some degree of uniformity of the field, the emission can be highly polarized -- linearly and circularly. In the radio regime, the observed variability is in most of the cases attributed to flaring events undergoing opacity evolution, i.e. transitions from optically thick to thin emission (or vice versa). These transistions have a specific signature in the polarization parameter space (angle and magnitude) which can be traced with high cadence polarization monitoring and provide us with a unique probe of the microphysics of the emitting region. Here we present the full Stokes analysis of radio emission from blazars observed in the framework of the F-GAMMA program and discuss the case study of PKS\,1510$-$089 which has shown a prominent polarization event around MJD 55900.