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William J. Hartman

Abstract: Historically, multipath problems have been handled on an ad hoc basis requiring liberal portions of hindsight, engineering ingenuity and serendipity. However, as is often the case, once the underlying principles are identified, theoretical developments advanced rapidly. Implementation of the techniques suggested by the theory has proceeded more slowly. Thus, many theoretical results remain unverified or only partially substantiated by experiment. In this handbook, we have collected theories and techniques which have one or more of the following qualities: It has been in frequent use by engineers; it has been shown to be accurate; it can be applied to a wide variety of problems; it offers an easily obtainable upper or lower bound. Most of the problems arising because of multipath cannot be solved or described precisely, but instead involve assumptions or approximations, the effects of which cannot be quantified. The responsibility for the decision on which approximation or assumption to use for a particular problem is with the reader. Since the handbook is directed toward air traffic control (ATC) frequencies, most of the material presented is oriented toward frequencies above VHF, and toward line-of-sight paths. Two special sections, one on Omega and one on Loran are included. No information on HF propagation or ionospheric scatter is included. Finally, selection of the material in this handbook has been heavily influenced by the systems presently used by the FAA.

Keywords: multipath; diversity; OMEGA; path loss; air traffic control frequencies; Doppler; radar refractivity; scintillation; LORAN

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