Formulas are given for the direct calculation of the scattering parameters of N cascaded, identical two-ports with the scattering parameters of the single two-port. Transmission lines loaded at regular intervals with a discontinuity, which may be modeled by a discrete component, and transmission lines with periodic steps in characteristic impedance are treated in detail. Simple, real formulas are derived, to calculate location and width of stop-bands as well as the peak-values of the reflection and the transmission coefficients. The characteristic transmission properties of such periodically loaded lines are descriptively presented and a physical interpretation is given.