We present an interference-screen model for the production of the modulation lanes often observed in Jupiter's decametric radiation. As radiation traverses a grid-like screen composed of field-aligned columns of enhanced plasma density downstream from Io, rays scattered on passing through the columns interfere constructively and destructively with those passing relatively unscattered between columns. Due to the geometrical relationship between the radio-emitting flux tube and the interference screen, the resulting rotating lobe pattern received at Earth synthesizes modulation lanes that very closely match those actually observed. ¿ American Geophysical Union 1992