Fading patterns and physical mechanisms associated with deep power fading observed on LOS microwave radio links in tropics

The performance of line-of-sight microwave radio links in the tropics is critically dependent on the extreme variability of refraction effects of the intervening medium. The additional stability brought into the nocturnal boundary layer by the frequent occurrence of ground-based inversions coupled with the high humidity content of the tropical atmosphere produce anomalously larger refractivity gradients that persist for hours together and play havoc with the reliability of terrestrial line-of-sight microwave radio links, especially along the coastal paths and those other paths which are intercepted by river valleys. The fading patterns along with the associated physical mechanisms likely to be responsible for the observed nocturnal deep power fading in South-Eastern parts of India have been discussed along with the radio meteorological background of the region. The cumulative distribution statistics of received median signal level and its seasonal variability are presented