Polarization observations with the SMA are currently carried out using quarter-wave plates that convert each linear feed of each receiver to a switchable circular feed. To obtain all four stokes parameters, each antenna is switched between polarizations in a coordinated sequence to sample quickly all four combinations of circular polarizations on each baseline. Plates are available with central frequencies near 230/690, 342 and 240/400 GHz.
Ram Rao, Ya-Wen Tang
Dan Marrone. Meredith Hughes, Josep Miguel Girart