Smith Charts

While working for Bell Telephone Laboratories, Phillip Hagar Smith invented the "Smith Chart". Smith charts allow electrical engineers working with transmission lines to graphically calculate important parameters and unambiguously represent a vast space of transmission lines in a common form.

When AC signals of a high enough frequency pass through a short enough conductor it becomes necessary to account for transmission time effects such as propagation delay and reluctance. Because the impedance on a transmission line consists of a resistive (real) and a reactive (imaginary) component, it is necessary for a smith chart to represent all complex numbers. As seen in the smith chart figure below below, numbers with constant real components are circles while those with constant imaginary components lie on lines curving towards the edge of the circle. Impedances are commonly normalized by dividing them by the characteristic impedance of the transmission line, Z0.