Electromagnetic transmission through an annular aperture in an infinite conducting screen

Electromagnetic transmission through an annular aperture in an infinite conducting screen of zero thickness is investigated. The circular aperture is included as a special case. The fields on both sides of the screen are obtained from the free space Green's function by means of the equivalence principle and image theory. An integral equation for the equivalent magnetic current in the aperture is established by enforcing the continuity of the tangential components of both the electric and the magnetic field. This integral equation is solved by the method of moments to obtain the magnetic current, from which other transmission characteristics are obtained.