This paper presents an efficient way for overcoming the inaccurate path error encountered in ray tracing for site–specific indoor propagation modeling. The source is modeled using triangular ray tubes each of which consists of three rays which do not lie in the same plane. Each possible source ray inside an arbitrary ray tube is expanded in terms of the three rays defining that ray tube. The variations of the expansion coefficients during the intersections of the ray tubes with dielectric media are derived and used for correcting the paths of the rays toward the receiver. A verification example is presented which proves that the presented method has the ability to be efficiently used in indoor propagation modeling.

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