SMALL APERTURE MODELING FOR EMI APPLICATIONS USING THE FINITE-DIFFERENCE TIME-DOMAIN TECHNIQUE

A method for modeling small aperture scattering in the Finite-Difference Time-Domain (FDTD) method is described and evaluated. The method replaces a small aperture in a perfectly conducting screen with pairs of oppositely directed electric and magnetic dipoles on either side of the short-circuited screen. Equations are derived which determine the electric and magnetic currents induced by arbitrary fields within the FDTD computational domain. These currents are induced by the short-circuit fields at the aperture. To determine the short-circuit fields it is necessary to subtract out the fields of the electric and magnetic dipoles. An analytical solution for dipole radiation is used to determine the dipole fields, and it is shown that the FDTD dipole fields deviate from the continuum dipole fields at distances close to the dipole. The method is evaluated for an isolated circular aperture and the results are compared with other methods. An analysis of the various errors inherent in the method is given. The analytical solution to the FDTD equations is used to determine the extent of discretization error inherent in FDTD. It is shown that a very accurate solution for the power transmitted through small circular aperture can be obtained using the proposed method.