Transmission of electromagnetic waves in hollow tubes of metal

Electromagnetic energy may be transmitted through the inside of hollow tubes of metal, provided the frequency is greater than a certain critical value; this value is inversely proportional to the tube radius and to the dielectric coefficient for the tube interior. Calculations and measurements of the more important characteristics of this new kind of transmission system have been made, and the conditions for minimum attenuation obtained Terminal devices for connecting a hollow pipe system to a biconductor system and others, in the form of horns, for directly radiating radio waves, have been developed; these electromagnetic horns may also be fed with ordinary coaxial lines. Certain types of terminals act as sharply resonant hollow tube elements. Several independent communication channels may be established within a single pipe line by utilizing distinct types of waves for each channel in a unique kind of multiplex operation. A section of a hollow tube may be used as a high-pass filter. Although presupposing adequate technique for the generation and utilization of the shortest radio waves, this new system possesses several features, among which are a minimum dielectric loss, substantially perfect shielding, and a simplicity of structure.