Radio-frequency Currents in Linear Conductors

Author: Edmund A. Laport

Radio-frequency energy can be guided by the propagation of transverse electromagnetic waves along systems of parallel conductors called "transmission lines." For brevity they are also called "lines" or "feeders." The input energy is stored in the field of the conductors and is propagated along the system at some finite velocity. For conductors in open air, this velocity is 3·10⁸ meters per second. In this discussion it will be understood that the transmission-line phenomena pertain to the quasi-static conditions corresponding to cross-sectional dimensions very small with respect to the wavelength. This means that the time of propagation of the field between conductors is small in relation to a single period. In radio-engineering practice the design of a system is based on the recognition of this condition.