Evaluation of bistatic transmission loss cumulative distribution is very useful in assessing the effect of interference due to hydrometeor scatter between the communication links operating at the same frequency. Out of the many factors that could be responsible for the intersystem interference between the microwave communication systems, this paper presents the result of computation of intersystem interference resulting from the hydrometeor scatter on tropical paths. Interference is computed in terms of the cumulative distribution of transmission loss. The effect of varying common volume formed by the intersection of the antenna beams on the transmission loss is investigated. Results show that at frequencies higher than 10 GHz, for antenna separation longer than 100 km, common volume will be in the ice region, leading to a higher interference level at the interfered terminal. Also, results obtained show that because total path attenuation at 30 GHz is lower than at 20 GHz (this is due to the decrease in water vapour attenuation in the 22·2–30 GHz window), transmission loss tends to be higher at 20 GHz than at 30 GHz. In addition, increasing the antenna gain of the interfering station will result in the increasing interference level at the interfered station. Evaluation of the effective transmission loss shows that this parameter gives a better assessment of interference on the tropical propagation paths noted for high‐intensity convective precipitation. In this case, the effective transmission loss has been evaluated in terms of the joint occurrence of additional rain attenuation on the wanted path, and the cumulative distribution of transmission loss on the intersecting paths. Copyright © 1999 John Wiley & Sons, Ltd.

Abstract. In this paper, the effects of tropical rainfall on the propagation of microwave and millimeter-wave signals on terrestrial paths have been investigated. Quantitative evaluation of spheroidal raindrop scattering parameters such as the scattering amplitude functions, total and scattering cross sections, and so on, were carried out for linear polarization (horizontal and vertical), using the least squares fitting method over the frequency range 1-100 GHz. Incident radio signals are assumed plane and arrive normally on the raindrop axis. For the purpose of application to slant paths, two other incident angles, 500 and 700 , were considered. The computed forward scattering amplitude functions were employed to compute the complex effective propagation constant of the radio signals in four tropical rainfall types: drizzle, widespread, shower, and thunderstorm. The corresponding specific attenuation and specific phase shift were computed. Specific attenuation and phase shift due to the rain types for circularly polarized radio signals were also derived. The parameters of the power law relationship between attenuation, phase shift, and rain rate were computed for each rain type and compared with existing temperate and tropical models. The problem of rain-induced alepolarization was also investigated by COlnputing the cross polarization discrimination for the four rainfall types over the frequency range 1-50 GHz, which is of immediate importance to system designers.

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The effects of the variation in canting angle of falling raindrops and the distribution of raindrop sizes in different types of rain on cross-polarization discrimination (XPD) on line-ofsight propagation paths in a tropical location in the frequency range 1-50 GHz are investigated. The dropsize distribution (DSD) model of [1] has been used. Although, some previous studies of XPD assumed equi-orientation of the raindrops along the propagation paths, the present study employs the more realistic distribution of canting angles along the path. The results obtained show that the XPD improves by about 4-7 dB over those based on the equi-orientation model. It is also shown that for the same copolar fade and for frequencies greater than about 10 GHz, the variation of the XPD with copolar attenuation (CPA) is relatively insensitive to the assumed DSD in rain and that the deterioration in signal quality or outage will be influenced more by the signal attenuation rather than by the cross-polarization interference.