Far-Field Scattering From an Electrically Small Circular Aperture in a Conducting Screen
Analytical expressions for the electromagnetic scattering in the far-field zone of an electrically small circular aperture in an infinite conducting screen with zero thickness were derived based on a quasi-static model of the aperture. The governing modal distributions of the surface magnetic current density in the aperture are directly related to the radius of the aperture, the angle of incidence and the polarization of the incident plane wave. The problem was formulated using the equivalence principle and the definition of the electric vector potential. The corresponding scattered fields were expressed in terms of surface integrals over the area of the aperture. These integrals were evaluated analytically after introducing the far-field approximation for amplitude and phase terms. The results are valid for any observation point in the lower half plane of the conducting screen. Results based on the obtained analytical expressions are compared and validated against numerical results based on the exact field expressions in the form of surface integrals over the circular aperture. The comparisons illustrate both the validity and accuracy of the analytical field expressions derived.