In this paper, radar cross-section (RCS) analysis and antenna simulations based on time-domain calculations are given. A compact, three-dimensional finite-difference time-domain (FDTD) algorithm in cartesian coordinates is built together with time-domain near-to-far field (NTFF) transformation. Both versions, scattered field (FDTD-S) and total field (FDTD-T) are coded which are suitable for RCS calculations and antenna simulations, respectively. For RCS calculations, the object under investigation is located within the FDTD volume, illuminated by a broad band pulsed plane wave and scattered fields are simulated all around the object via FDTD directly in time-domain. Similar simulation Is performed for the antenna analysis and total fields radiated by the antenna under investigation for a pulsed voltage exication are generated. Using NTFF routine, far field responses are obtained for both scattered and total field cases. Frequency-domain scattering and radiation patterns for wide frequency ranges are obtained via off-line discrete Fourier (DFT) analysis.