A cosmetic method for ameliorating multipath effects on the ILS localizer

The localizer is that portion of the contemporary instrument landing system which provides lateral guidance to the pilot during his approach to landing. It is especially plagued by the multipath problem because airports encourage the construction of large hangars to allow servicing their aircraft customers. Large hangar and terminal-building walls common at many important airports frequently end up reflecting localizer signals back into the course region. This causes scallops, bends and general beam noise to be produced. The solution presented in this paper is to scatter the signal in a broader region incoherently in order to make the magnitude of the course corruption less at any given point along the approach path. To accomplish the objective, a mathematical model was developed for predicting the effects of irregular surfaces on the effectiveness of multipath to degrade localizer course performance. The next step is a search for some specific type of surface irregularity, a type that could practically be constructed. This paper describes the model, presents the results of the validation work, and reports the best surface for minimizing the deleterious effects of multipath.