In this thesis, the transmission effect of a two-dimensional circular radome with periodic metal gratings is analyzed. We started with the study of gratings consisting of periodic arrays of thin lossy strips surrounded by vacuum. Then we investigated the behavior of such gratings if a dielectric hiyer is inserted between them. Complex line sources are considered to simulate directed beam fields used in practice. The fields on the interior and exterior sides of the radome are represented by modal cylindrical waves. Taking advantage of theoretical considerations recently published, we propose an approximate method and stress the numerical aspect. Data is obtained for the far field solutions and the directivity, and their dependences on different radome parameters. It appecirs that directivity variations with beam orientation are decreased considerably by a proper insertion of the dielectric layer.