Abstract-The three-dimensional Gaussian beam scattering from the bounded periodic sequence of one-to-one composed isotropic magnetodielectric and bi-isotropic layers are investigated. The beam field is represented by an angular continuous spectrum of plane wave. The problem of the partial plane wave diffraction on the structure is solved using the circuit theory and the transfer matrix methods. It is found that after reflection from the structure, the circular Gaussian beam becomes, in general, an elliptical Gaussian beam, in addition to a displacement of the beam axis from the position predicted by ray optics.