Lower Modes of a Concentric Line Having a Helical Inner Conductor

The natural, undamped modes of propagation in a concentric line having a circular outer conductor and a tape‐helix inner conductor are investigated. The investigation is primarily concerned with a study of the propagation characteristics of the modes and, by making suitable approximations, closed expressions for the propagation factors of a few of the lower modes are obtained. Numerical results are then presented for a system having typical geometrical parameters, and generalizations of a qualitative nature are indicated. In the course of the work, the natural‐mode field expressions are derived.