An effective design procedure, based on the Elliot’s synthesis method, is proposed to investigate the properties of waveguide slot arrays with multilayer dielectric cover. Then, the features of the designed arrays are analyzed by means of a FEM commercial software, namely Ansys HFSS 13. We show how a proper choice of the dielectric cover configuration allows to increase the array gain and aperture efficiency, while taking advantage of the properties of the radome structure, both in terms of insulation, protection and pressurization of the radiating waveguides. Therefore, a significant outcome of the optimal choice of the multilayer dielectric cover is the reduction of the number of slots with respect to an array radiating into free space with the same gain and efficiency, with a consequent reduction of the production cost.