An efficient mode-matching manner involving physical optics approximation is planned for scattering from a large Isosceles Right Triangular Groove (IRTG) in an infinite Perfect Electric Conductor (PEC) plane. By considering two synthetic PEC walls over the groove, the tangential fields inside and outside the groove are expanded as the sums of infinite harmonics modes. These modes are matched over the IRTG and consequently, a system of linear equations is constructed for the expansion coefficients. The examination of the results shows that this method is not appropriate for grooves with a width smaller than the wavelength. Instead, for a large IRTG, it can reduce simulation time considerably and is in good agreement with time-consuming numerical methods such as the Finite Element Method (FEM) and the Method of Moment (MoM). The effects of the angle of incidence and the groove width on the scattering signature are investigated, too.
