1210 THE BELL SYSTEM TECHNICAL JOURXAL, NOVEMBER 1954 



The general outlook, based on 'present knowledge, is that a waveguide sys- 

 tem micjht transmit hasehand widths as large as 100 to 500 mc using a rugged 

 modulation method such as PCM. Some form of regeneration is likely to be 

 required at each of the repeaters, which may be spaced on the order of 25 

 miles. A total rf bandwidth of about 40,000 mc may be available in a single 

 guide. 



Table of Contents 



Introduction 1210 



( )idinary Versus Circular Electric Waves 1211 



Theoretical Characteristics of the Circular-Electric Wave 1213 



Some Results of Transmission Experiments 1219 



Mode Conversion and Reconversion as a Signal-Loss Effect 1229 



Mode Conversion and Reconversion as an Interference Effect 1230 



Analysis for Continuous Mode Conversion 1239 



Direct Evaluation of Mode Conversion Magnitudes 1243 



The Bend Problem 1247 



Improved Forms of Circular Electric Waveguide 1250 



Surface Roughness 1252 



Circular Electric Wave and Millimeter Wave Techniques 1253 



Modulation Methods 1256 



Conclusion 1259 



Appendix — Theoretical Analysis for Continuous Mode Conversion 1261 



INTRODUCTION 



The circular electric wave in round metallic tubing possesses a prop- 

 erty so unique that some early research workers doubted the reality of 

 the wave. This unique property is an attenuation coefficient which, in a 

 given pipe, decreases without limit as the frequency of operation is in- 

 creased. In parallel wire, coaxial, or ordinary waveguide lines the "skin 

 effect" at the surface of the conductor causes the loss to increase as the 

 frequency increases indefinitely, so the predicted circular-electric-wave 

 loss characteristic aroused considerable interest as soon as it was dis- 

 covered by S. A. Schelkunoff and G. C. Southworth in the early 1930's. 

 Since that time considerable work has been done at Holmdel to explore 

 the reaUty of the circular electric wave and to evaluate its usefulness to 

 the Bell Sj^stem. It is the purpose of this paper to report on the status 

 of this work and to give a description of some of the basic characteristics 

 of circular electric wave propagation. 



The Bell System is interested in knowing whether waveguide can be 

 used as a long distance communication medium in the manner in which 

 coaxial cable or the radio relay system is now employed. Our interest in 

 long distance waveguides is due in part to the fact that radio-wave 

 propagation through the atmosphere becomes progressively more se- 

 verely' handicapped by rain, water vapor and oxygen absorptions at 



