An Experimental Investigation of the Properties of Corrugated Cylindrical Surface Waveguides

The paper describes an experimental study of the properties of externally corrugated cylindrical metal surfaces when used for the support of electromagnetic waves. In particular brass rods of 3/16 in outside diameter and grooved transversely at regular intervals along the length were employed to guide cylindrical surface-waves of the kind familiar in single-wire transmission. Measurements were made at a number of frequencies in the range 2 500¿10 000 Mc/s using a surface-wave resonator. In no case did the depth of corrugation exceed 0.050in. It is shown that a uniformly corrugated cylindrical surface acts as a satisfactory guide for a surface wave if there are at least two corrugations within the guide wavelength. The results of measurements on the surface reactance of corrugated guides are recorded in a number of graphs. An approximate expression for the surface reactance of a corrugated surface is derived in the paper and found to be in reasonable agreement with the experimental results, provided that the slot width is less than the slot depth, and each wavelength includes several corrugations.