A time-domain finite-difference approach based on the expression of tile field vectors by the vector potential functions is proposed for the analysis of planar structures. The algorithm is theoretically equivalent to the time-domain integral equations (TDIE) approach but is much faster because the calculation of the vector potentials is carried out by the finite-difference wave equation instead of integration. Still integration can be involved when electrically remote objects are present. Only four tangential to the planar interfaces components of the vector potentials are calculated which makes this algorithm advantegous to the FDTD one in respect with storage requirements.