Browsing by Author "Ajayi, G.O"

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    Evaluation of bistatic intersystem interference due to scattering by hydrometeors on tropical paths
    (International Journal of Satellite Communications, 1999-09) Ajewole, Oludare; Kolawole, L.B; Ajayi, G.O
    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.
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    Theoretical study of the effect of different types of tropical rainfall on microwave and millimeter-wave propagation
    (1999-09) Ajewole, Oludare; Kolawole, L.B; Ajayi, G.O
    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, 50° and 70°, 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 depolarization was also investigated by computing 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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    Open Access
    Theoretical study of the effect of different types of tropical rainfall on microwave and millimeter-wave propagation
    (Radio Science - RADIO SCI. 34., 1999-09) Ajewole, Oludare; Kolawole, L.B; Ajayi, G.O
    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, 50° and 70°, 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 depolarization was also investigated by computing 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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    Open Access
    Variations in raindrop size distribution and specific attenuation due to rain in Nigeria
    (annals of telecommunications - annales des télécommunications, 1996-01) Adimula, I.A; Ajayi, G.O
    Les distributions des tailles des gouttes de pluie ont été mesurées en trois lieux du Nigéria (Calabar, Ile-Ife et Zaria). Les données collectées pendant trois ans ont servi à obtenir des modèles de ces distributions pour divers types de pluie : bruine, averse, pluie étendue, orage. La distribution lognormale constitue un bon ajustement pour tous les types de pluie en des lieux tropicaux, sauf pour la bruine où le modèle exponentiel convient. On discute aussi les conséquences de ces modèles pour des calculs de l’affaiblissement linéique dû aux pluies tropicales. The raindrop size distributions had been measured at three locations in Nigeria - Calabar, Ile-Ife and Zaria. The data collected over a period of three years have been utilized to obtain models of drop size distributions for drizzle, shower, widespread and thunderstorm rain. The lognormal distribution provides a good fit for all the rain types at these tropical locations except drizzle, where the exponential model is adequate. The implications of the models for specific attenuation calculations for tropical rain are discussed. Mots clésPluie-Zone tropicale-Distribution statistique-Goutte eau-Dimension particule-Ajustement-Loi lognormale-Loi exponentielle-Onde radioélectrique-Affaiblissement Key wordsRain-Tropical zone-Statistical distribution-Water drop-Particle size-Fitting-Lognormal distribution-Exponential distribution-Radio wave-Attenuation