Kinematic analysis of a lightweight periodic dielectric structure of pearls for RF coaxial power cables for space applications

The desire to reduce the mass per unit length and to increase phase stability of coaxial radio-frequency (RF) power cables for space application motivates a new design idea, namely to replace solid dielectric with a periodic chain of hollow pearls. The design of the dielectric pearls must allow for bending flexibility of the cable even if they are made from a stiff material such as silicon glass. An important requirement of RF power cables for space applications is their phase stability, which is influenced by the material-dielectric-constant tolerance over a large temperature range as well as by changes in geometry. This paper presents an original closed-form model based on rigid-body motion to predict the kinematic response of dielectric pearls to the bending of the cable. Particularly, the model maps the eccentricity of the inner and outer conductors with respect to each other and the axial strain of the bent cable along its centreline. The model results indicate that mass reductions of the periodic hollow-pearl design over conventional solid PTFE dielectrics are significant.