The propagation effects of bends in tropospheric ducts

Prediction of electromagnetic propagation in non-uniform tropospheric ducts is possible using numerical grid methods. These methods are not as rapid as semi-empirical techniques used to obtain coverage predictions for a standard atmosphere over large areas. They can be used, however, to obtain parametric dependencies for incorporation into the rapid techniques. The IFDG numerical grid method is used to study the effect of duct bends on the propagation of individual modal contributions. It is shown that the transfer of ducted modal power across the bend is only appreciable for bend angles that do not exceed corresponding "takeoff" angles of lower order modes.