A classification of system errors in aperture synthesis radiometry applied to Earth obervation is presented. A general procedure to quantify th eimpact of antenna errors on the radiometric accuracy is developed and is then particularized to an L-band Y-shaped interferometer called MIRAS (microwave imaging radiometer by aperture synthesis) currently under study at the European Space Agency. This work analyze in detail the impact of antenna errors on the radiometric accuracy of the instrument. These antenna errors are grouped into amplitude and phase antenna pattern errors, antenna position errors and antenna cros polarization errors. Special attention is paid to antenna coupling effects because of their importance in the selection of a suitable inversion algorithm for large aperture synthesis interferometers: the G-matrix techniques or the Fourier techniques proposed for MIRAS.