Theses and Dissertations

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Theses and Dissertations (Electrical and Electronics Engineering)

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Browsing Theses and Dissertations by Author "Ajayi, G. O."

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    Development of a Rainfall Attenuation Map for Microwave Terrestrial Application in Nigeria.
    (Obafemi Awolowo University, 1987) Anazodo, Chiedu Charles; Ajayi, G. O.
    The growing need to utilize frequencies above 10GHz for high capacity terrestrial and space radio links due to the congestion at low frequencies has enhanced the necessity to develop a map of attenuation due to rainfall at these frequencies. There is a dearth of instantaneous rainfall data in Nigeria hence the long-term total rainfall data and other meteorological data obtained from some 37 stations in Nigeria have been used to study the attenuation due to rainfall for microwave terrestrial applications in Nigeria. A database has been created for all the data and statistical analysis carried out on them. The Dutton and Dougherty (1974) prediction model used for predicting short integration time rainfall rate from long-term rainfall data for Europe has been modified for use in the Nigerian climatic conditions. Regression techniques have been utilized to obtain a mathematical relationship between the rainfall rate, the average annual rainfall and the number of thunderstorm days for all the available meteorological stations. The computed one-minute integration time rain rate has been used to predict the specific attenuation for some microwave frequencies for each station and the results are presented in form of contour maps. The attenuation map shows that specific attenuation due to rainfall is higher in the southern parts of Nigeria compared with the northern parts. The results obtained in this study will be useful in the design of terrestrial microwave links in Nigeria, especially in the estimation of necessary fade margin to take care of attenuation due to rainfall.
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    Modelling of Raindrop Size Distribution in Nigeria for Microwave and Millimetre Wave Application.
    (Obafemi Awolowo University, 1986) Adimula, Isaac Abiodun; Ajayi, G. O.
    Raindrop size data collected using a distrometer measuring system at three geographical locations in Nigeria namely Calabar, Ile-Ife and Zaria have been analysed for the prediction of rainfall attenuation at centimeter and millimetre wave frequency bands. The modeling of the raindrop size distributions has been carried out using the lognormal and exponential distributions. Models for the three stations as well as a Southern, Northern and a general model for the country have been proposed for the prediction of the effect of tropical rainfall on electromagnetic propagation at microwave and higher frequencies. Rain induced specific attenuation values were computed for a frequency range of 1 to 400GHz using the models obtained for thunderstorm and shower which are very important for communication systems design.