The Nature of and System Inferences of Delay Distortion Due to Mode Conversion in Multimode Transmission Systems

This paper gives some quantitative estimates of the delay distortion due to mode conversion to be expected in multimode transmission lines such as the millimeter-wave circular electric waveguides. In principle, the results apply to any multimode system, including optical guidedwave systems; in the latter case, however, it is likely that the magnitude of delay distortion will be too small to be a limitation in practice. In millimeter waveguide systems, delay distortion effects can be important. A very simple analytical approach is used, based on modes coupled through power-transfer coefficients. This permits a direct translation of the spatial distribution of mode conversion into the effect on the output waveform without recourse to the frequency domain as an intermediate step. The case treated herein is mode conversion that is an independent random function of distance, but the physical reasoning employed can be used to indicate the changes which alterations in the conversion distribution would cause. A perturbation method is employed, and limits are found for the distance for which this perturbation calculation is valid. In a companion paper Dale T. Young1 has shown how the powertransfer coefficients of the coupled-mode equations used herein are related to the more familiar coefficients between the amplitudes of coupled modes; this makes more quantitative the relation between the present work and the work of H. E. Rowe and W. D. Warters.2 In another companion paper, L. H. Enloe3 presents a precise technique for