Interpolation, extrapolation, and application of the measured equation of invariance to scattering by very large cylinders

Using the conventional method of moment (MoM) calculations, a cylinder of circumferential dimension of 100 wavelengths is considered to be large. Using the measured equation of invariance (MEI) approach, a cylinder of 10000 wavelengths is within the storage capacity and numerical tolerance of a workstation. Although, the MEI has greatly reduced the storage and solution time of the matrix, its overhead to generate the matrix elements is about the same order as that of the MoM. When the target is very large, that overhead can be very time consuming. This paper presents an interpolation and extrapolation technique such that the boundary equations of the MEI for high frequencies may be predicted from those of low frequencies. It is demonstrated that in the optical limit the same set of coefficients may be used for all frequencies, which is consistent with the concept of geometric optics where the same rule is applied to all frequencies