A mode-matching approach to determine the shielding properties of a doubly periodic array of rectangular apertures in a thick conducting screen

The application of the mode-matching technique to determine the shielding properties of a thick doubly periodic conducting screen of rectangular apertures is presented. Floquet waves are used to represent the reflected and transmitted fields, while waveguide modes are used to determine the fields within the screen. Expressions for all fields are formed using Hertzian potentials. After enforcing boundary conditions and forming a system of linear equations, the mode coefficients are determined using standard techniques. Numerical results show the effect of increasing thickness and incidence angle variation on transmitted power. It is shown that by selectively choosing the number of waveguide modes, meaningful results for transmission can be obtained for screens whose thickness is several times the size of the apertures. The results also demonstrate the relationship between this approach and application of the waveguide below cutoff principle. It is also noted that at higher frequencies, higher order Floquet modes will propagate and contribute to the transmitted power.