Beam depolarization

Let's say we are observing an extended source with a radio telescope and the resolution of the telescope is poorer than the angular scale over which the source polarization is coherent. Than, within a given resolution element there will be regions with different polarization characteristics. Thus the beam smooths out the polarization of the source and the measured polarization will always be less than the true one or we can say there is a depolarization of the source due to the beam of the telescope. This is beam depolarization.

This effect can not be removed. Only option is to observe with better resolution.