Attenuation of the Fundamental Dipolar Mode of the Shielded Ring Line

The theoretical attenuation of the shielded ring line operating in the fundamental dipolar hybrid mode is discussed and this guiding structure is shown to be low-loss when the distance between the rings and the shield is large. Measurements on a line consisting of equally spaced rings held by a teflon pipe and surrounded by a 10 cm diameter metallic pipe agree with theory. The shielded ring line can be a low-loss guide, but the attenuation value (12 dB/km for a copper structure) is somewhat higher than that of the open ring line (less than 5 dB/km).