In this thesis, the transmission effect of a grid structure is analyzed. The grid structure is intended to model the metallic support elements of a radome. The total field for the real and complex position line sources surrounded by the grating structure is obtained in both TM and 7'E polarizations in the far-field region. The grid is considered to be a cylindrical array of perfectly conducting cylinders parallel to the z-axis. The radius of each cylinder is small as compared to the wavelength and the length of the cylinders is infinite. We started with the study of a single perfectly conducting cylinder illuminated by a line source and obtained the formula for the electric and magnetic fields in the far-field region. Then, we calculated far-zone total field for a set of cylinders which form the surface of the radome as a cylindrical periodic grating. The equation for the total electric field in the far-field region is found by using superposition and applying the boundary conditions at the conducting cylinders to find scattering coefficients. Complex line sources are considered to simulate directed beam fields used in practice. The power pattern and directivity are computed for different parameters of the grating and cylinders. A set of figures is presented to show the relationships between the power pattern, directivity and different parameters of the structure.