Propagation of the circular H01 low-loss wave mode around bends in tubular metal waveguide

Although there is ample evidence of the suitability of a straight length of hollow metal tube as a waveguide supporting the circular H01-mode for long-distance communication, bends in the guide still present a serious problem. An examination of the conditions required to maintain as nearly as possible the appropriate field distribution at a bend leads to the important conclusion that the wavefront, represented by an equi-phase plane, must remain radial with respect to the centre of curvature. The evidence shows that there are two ways of approaching this requirement: (a) by varying the permittivity of the dielectric medium inside the guide over its cross-section, and (b) by varying the surface reactance of the guide around its circumference. The first of these proposals is simpler in application and more likely to meet the need, if suitable cellular polystyrene or polythene can be obtained for the purpose.