A radio telescope with linearly polarized feeds can be used to determine the angle at which the maximum intensity is measured, from which one can know the orientation of the wave as it propagates through the intervening medium. This is known as polarization.
The polarization will depend on the signal generation mechanism and intervening material, through which the radiation has propagated. By building up a set of Stokes parameters, the parameters needed to fully define the polarization, the characteristics of the source can be inferred. Synchrotron emission is expected to be intrinsically linearly polarized while plasma emission tends to be circularly polarized.