T matrix characterizes the scattering property of a single PEC object and does not depend on the incidence. In this work, we propose a method to derive a reduced-order T matrix for a single 3D PEC object with arbitrary shape. The method is based on the vector addition theorem and the conventional EFIE, MFIE or CFIE methods. Given the T matrix for a PEC object, the scattered fields can be directly calculated from any incidence. For multiple objects, a matrix equation system is built based on the T-matrix and the position of each object. Finally, numerical examples show the accuracy and efficiency for solving the scattering of both spherical and non-spherical arrays. Compared to the moment methods, the computational cost of solving the final matrix equation is reduced by several orders of magnitude.
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