Radiation Resistance of Concentric Conductor Transmission Lines

An expression for the radiation resistance of a cylinder is derived, following the "tangential field" or "induced electromotive force" method as adapted by Pistolkors. The result is used to determine the radiation resistance of a segment of a concentric cylinder transmission line, as used in ultra-high-frequency oscillator circuits. A comparision is made with the more conventional parallel wire line segment. Numerical computations are made for the case of a line one-half wavelength long, with a radius (for the concentric line) and a spacing (for the open line) of one-twentieth of a wavelength. These are believed to be the largest dimensions to be encountered in practice. The resistances are, respectively, 0.086 ohm and 3.02 ohms, showing the concentric line to be definitely superior as far as radiation losses are concerned.