Partial reduction of the physical optics surface integral to the modified edge representation line integral

In this article, an extended reduction formula is prepared for compensating modified edge representation (MER) imperfectness in the integral reduction, where a part of the surface integration is reduced to the line one while the remaining area is surface‐integrated. To this end, the local errors for the MER integral reduction are defined all over the integration surface. Then the criterion of the MER local errors is proposed in terms of the Fresnel zones as well as the normal vector of the scattering surface. Finally, the surface integration is partitioned into two regions according to this criterion so that the local errors are confined completely in one of them, which is surface‐integrated. The agreement of the field calculated here by the extended treatment of MER and the physical optics is confirmed. The discussion in this paper highlights the effects and the locations of higher‐order terms causing MER integral reduction errors. The study for minimizing the area of the surface integration, which leads us to the future goal of the perfect surface‐to‐line integral reduction, needs the improvement of MER and the analytical identification of the higher‐order terms, which is left for further study.