The measurement of cable characteristics at ultra-high frequencies

The paper describes the two main methods of impedance measurement at frequencies above 100 Mc/s which are in general use, and their application to the determination of cable characteristics, with particular attention to the work of the authors. A preliminary account is given of the various conditions in which cables can be measured, and which are applicable to both of the methods described. An outline of the theory of the standing wave method is given, together with a general description of the equipment required. Attention is paid to coned connectors for the attachment of the cable to the measuring line, and the errors liable to be incurred by their use. The theory and equipment for the resonance line method are described, and an account is given of several investigations that have been conducted´ in order to extend its usefulness. These include the measurement of twin cables, the effect on cable attenuation values of reactive discontinuities at the junction of measuring line and cable and at internal supports in the line, the direct determination of the characteristic impedance of measuring lines, and the radiation and reactive effects which occur at their open ends. The application of the resonance line method to the determination of dielectric power factor is discussed, and a method is described which permits greater accuracy than has been obtained up to the present.