The Effects of Mode Filters on the Transmission Characteristics of Circular Electric Waves in a Circular Waveguide

A circular waveguide operated in the TE 0 i or circular electric mode is very attractive for use as a long-distance transmission medium. 1 ' 2 The attenuation coefficient of the TE 0 i mode decreases monotonically with increasing frequency in a given waveguide so that, in theory, one can transmit information through such a system with as low a loss as desired merely by operating at a sufficiently high frequency. In practice, in order for one to take advantage of this low-loss property, the frequency must be so high that the waveguide is operating in the multimode region. This introduces the probability that coupling will occur between the low-loss TE 0 i signal mode and the other propagating modes if there are any deviations from perfect circularity and straightness in the guide. The coupling resulting from a series of imperfections, with the resultant transfer of power back and forth between TE 0 i and other modes, can cause serious degradation of the transmission properties of a long waveguide. These mode conversion and reconversion effects 657