A novel time domain integral equation based algorithm is proposed for analyzing EMC/EMI problems where the problem geometry is modeled by three dimensional arbitrarily shaped perfect electrically conducting surfaces and wires. For example, the proposed algorithm enables the analysis of radiation from modules on motherboards, cables, and shielding structures with and without apertures. The algorithm is constructed by augmenting a classical marching-on-in-time (MOT) scheme with the plane wave time domain (PWTD) algorithm. The PWTD algorithm enables the fast evaluation of transient fields by decomposing them into transient plane waves. The computational complexity of the resulting PWTD-MOT algorithm scales as O(N/sub T/N/sub S//sup 1.5/log/sup 2/N/sub S/) as opposed to O(N/sub T/N/sub S//sup 2/) for a classical MOT algorithm, where N/sub T/ and N/sub S/ are the number of temporal and spatial basis functions discretizing the current density on the geometry.