Correction factor for multiple knife-edge diffraction

The approximation of J. Deygout (1966) recommended the use of a nomograph proposed by G. Millington et al. (1962) to correct the excess of path loss observed when hills having the same individual loss were close to each other. To help realize that the method is not so pessimistic as believed, a simple mathematical expression is given to replace the use of that nomograph. The author shows how the results compare with those obtained by G. Millington and those obtained by C.L. Giovaneli (1984). Extrapolating from those two cases, it is concluded that J. Deygout´s simplified approach, when fully applied, is not pessimistic but rather slightly optimistic. In fact, after hundreds of measurements over obstructed paths in hilly or mountainous terrains with ultra high frequencies, it was found that the mean error between evaluations and measurements is less than 1 dB, with 4-5 dB of standard deviation