Computer generated equivalent circuit models for coaxial-line offset open circuits

Offset open circuits have been investigated at the National Physical Laboratory, NPL (Malvern), as primary impedance standards for calibrating coaxial line measuring instruments such as six-port reflectometers and automatic network analysers. A need has developed for equivalent-circuit models of offset open circuits to assess their physical realisation. The authors have analysed a range of air-dielectric 14 mm, 50 Omega coaxial-line offset open circuits and have produced an equivalent circuit whose elements are frequency independent and which separates the capacitance due to the open circuit from the effects of the length of the line.