IMPLEMENTATION OF TRANSPARENT SOURCES IN FDTD SIMULATIONS

Sources can be embedded in a finite-difference time-domain (FDTD) grid in any one of several ways. Depending on the particular implementatio n, the embedded source corresponds physically to a hard field source ( applied field), a transparent current source (impressed current), a fi nite-impedance voltage source, or some other physical excitation. Whil e the implementation of any of these sources is a straightforward proc edure in FDTD simulations, ensuring an accurate correspondence between the physical source and its numerical implementation is challenging. In this work, we describe the implementation of a new field source, re ferred to as a transparent field source, that couples the same fields into the FDTD grid as a hard field source. Unlike the hard field sourc e, however, the transparent source does not scatter energy, i.e., the usual FDTD update equation applies to the source node. The implementat ion is described both in terms of a single node and in terms of an arr ay of nodes. The latter is discussed in the context of parallel-plate waveguide excitation.