In this paper, a finite-element based 3-D FDTD space/time subgridding scheme is presented. A classical Yee scheme is obtained strictly inside domains having different space and time discretizations. Considering one domain, the presence of the other domain is taken into account through an electric-field excitation distributed throughout the mesh interface. The validity of the proposed technique is demonstrated through its application on two test cases: a Hertzian dipole and a mobile-phone antenna. (C) 2002 John Wiley & Sons, Inc.