Abstract-This paper introduces a fast and accurate method to investigate the broadband inductive and resistive behavior of conductors with a non-rectangular cross-section. The presented Iterative Combined Waveguide Modes (ICWM) algorithm leads to an expansion of the longitudinal electric field inside a triangle, using a combination of parallel-plate waveguide modes in three directions, each perpendicular to one of the triangle sides. This expansion is used to calculate the triangle's Dirichlet to Neumann boundary operator. Subsequently, any polygonal conductor can be modeled as a combination of triangles. The method is especially useful to investigate current crowding effects near sharp conductor corners. In a number of numerical examples, the accuracy of the ICWM algorithm is investigated, and the method is applied to some polygonal conductor configurations.Index Terms-Dirichlet to Neumann operator, iterative combined waveguide modes algorithm, triangle, polygonal conductor, skin effect, quasi-TM approximations.