A NEW SURFACE IMPEDANCE FUNCTION FOR THE APERTURE SURFACE OF A CONDUCTING BODY WITH A DIELECTRIC-FILLED CAVITY

A new surface impedance function (SIF) is presented. This surface impedance function is appropriate for use on the aperture surface of a conducting body with a dielectric-filled cavity. Unlike the usual surface impedance functions that might be used on an aperture, this new SIF takes into account not only the wave transmitted through the aperture but also the wave reflected from the inside of the cavity as well as the shape of the aperture and cavity and the polarization and direction of the incident wave. The new SIF is derived heuristically from the series-reflection solution for a plane wave normally incident upon a infinite flat conducting plate with a flat dielectric coating. The new SIF was developed and used in a combined method of moments (MM) solution for the scattered fields due to an incident plane wave. This combined technique greatly reduces the number of current expansion coefficients to be determined using the method of moments and hence also reduces the number of impedance elements required for calculation in the method of moments. Because of the reduction of the number of current expansion coefficients to be determined, the combined method can be used for objects which are significantly larger than can be accommodated with the method of moments alone. Application of the new SIF in a combined method is illustrated for a two-dimensional object. Both the transverse electric and transverse magnetic cases are considered. Sample results demonstrate the validity and utility of the combined method.