  We numerically describe the physical mechanism underlying the terahertz
photoconductive antenna (PCA) by the finite-difference time-domain method in
three-dimension. The feature of our approach is that the multi-physical
phenomena happening in the PCA, such as light-matter interaction, photo-excited
carrier dynamics and full-wave propagation of the THz radiation, are considered
and embodied in the simulation. The method has been verified by comparing with
existing commercial softwares. In addition, we use this simulation tool to
characterize the parameter-dependent performance of a PCA,thereby the design of
novel PCA with enhanced optics-to-THz efficiency can be inspired.
