The Influence of Rain on Design of 11-GHz Terrestrial Radio Relay

Terrestrial radio systems employing the 10.7-11.7 GHz common carrier band have been in use for many years. For example, analog TJ and TL radio are used for short-haul applications, and TL has served in cross-band diversity as protection for a 6-GHz system. However, new emphasis is being placed on autonomous 11-GHz systems, wideband digital implementations such as 3-ARDS 1 being attractive in many applications. It is therefore meaningful to re-examine the effects of rain on the propagation of 11-GHz signals; hop-length limitations imposed by rain have impact on the cost of service. Multipath fading, readily accommodated by antennas operated in space diversity, is not discussed. In the interest of designing reliable systems, our prime intent here and in the companion papers of this issue is to determine the limitation on hop lengths imposed by rain attenuation for given fading margin and annual outage time objectives for systems in the United States. 1575 Three major factors are involved in this determination: (i) The 11-GHz attenuation statistics must be properly associated with the rain rate statistics as determined by measurements at a point. There are two reasons for this: (a) It is only by virtue of long-term measurements of point rain rate, from sources such as the National Climatic Center, that a sufficient quantity of data can be obtained to provide reliable temporal statistics for calculation of the path attenuation, (b) It is only from measurements of point rain rates at numerous locations throughout the country, such as those compiled by the National Climatic Center, that the rain environment at arbitrary locations where radio systems may be installed can be suitably determined.