Conquering extended frequency realms by periodic coaxial structures

In this document we present a method by which we can extend the usable frequency range of a coaxial line into a region where higher order modes would normally propagate. We describe a complete method for designing the periodic ring structure and provide a model which is capable of predicting the dispersion of the (Q)TEM modes propagating in the transmission line. Moreover, all important cut-off frequencies are addressed to enable the engineer to take full control of the branches of higher order modes in the targeted frequency scale. With the help of full-wave simulations we verify our theoretical models and show that a good matching can be achieved when connecting the proposed structure to a conventional transmission line.