Abstract: An iterative physical optics(IPO) method combined with multilevel fast multipole algorithm(MLFMA) is used to solve electromagnetic scattering by a three-dimensional complex cavity efficiently and rapidly.The iterative formulations of hybrid algorithm are derived.For slow bending cavities in engineering,a proper subsection structured grouping method is provided to avoid the shelter of facets between two groups.A generalized reciprocity integral(GRI) method is applied to cavities with complex termination.The methods obtain accurate results and improve computing speed.

Key words: iterative physical optics, cavity, multilevel fast multipole algorithm, generalized reciprocity integral