Multipath Propagation at 4, 6, and 11 GHz

Although it is a relatively rare phenomenon, multipath propagation constitutes a fundamental limitation to the performance of microwave 321 322 T H E BELL .SYSTEM TECHNICAL JOURNAL, FEBRUARY 1972 radio systems. During a period of multipath propagation, the narrowband output from a single receiving antenna can be reduced to equipment noise levels for seconds at a time. Corrective measures such as frequency diversity or space diversity then must be introduced to provide satisfactory commercial operation. 1 - 3 Propagation data required for economical system design and detailed performance estimates were not available prior to 1966. To fill this need an extensive experimental program was undertaken on a typical radio relay path in Ohio. Previous studies 1,2,4 have reported on the amplitude statistics obtaining during multipath propagation at 4 and 6 GHz, both with and without frequency or space diversity. Data were also obtained for a single frequency in the 11-GHz band. The multipath fading data for this signal have now been analyzed and statistics for the total time faded (P), the number of fades (N), their average duration (t), and the fade duration distribution are presented in Section IV as functions of fade depth. Multipath propagation is by its very nature dependent upon the operating microwave frequency; the variation of the fading characteristics with frequency has been considered by many investigators 5,6 with controversial results.* This is not surprising considering the timevariant, nonstationary behavior of the phenomena.