A procedure to calculate the in-situ contribution to body scattering caused by conformal cavity-backed apertures

This paper presents a theoretical procedure whereby a conformal aperture´s in-situ contribution to the total radar cross section (RCS) of a body can be efficiently and accurately calculated. The result is equivalent to subtracting the RCS of the body with the aperture shorted from the RCS of the body with the aperture present. In RCS measurements, this technique is commonly referred to coherent fixture subtraction. The approach presented uses the electric current density at the aperture location on the body (computed with the aperture shorted) to derive new excitation and measurement vectors for the fields scattered by the conformal aperture. These surface currents may be obtained from a number of well-validated computer codes, such as JRMBOR CARLOS 3-D or PARAMOM. The electromagnetic characteristics of the cavity-backed aperture are rigorously modelled by an admittance matrix, which is calculated by a finite element method and assumes an infinite planar or singly curved installation environment. Fixture effects, such as surface wave and creeping wave excitation of the aperture, are also accurately accounted for in this procedure.