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Abstract
Multipath fading is one of the most serious events which can interrupt service on microwave communication systems. This is caused by irregularities in the refractive index of the atmosphere which cause the microwave signal to be refracted upwards or downwards such that two or more separate wave components may travel to the receiver over slightly different paths. These components reinforce or cancel each other depending on the phase difference of the independent paths. The irregularities in the refractive index of the atmosphere determine the earth's equivalent radius k. This factor k is thus of critical importance in microwave engineering. However, detailed data on k are not available for India.
An attempt has been made in this paper to present a detailed picture of the factor k, by evaluating its diurnal variations over different regions of India. It has been observed that India can be divided into three distinct zones each with its distinct pattern of k factor variation, namely inland stations in the continent, sea coast stations, and Assam. The paper then discusses the effect of the variations of k on the radio horizon in these three regions.
The investigation has brought out many features in the variation of k factor over India which are useful in planning and optimizing microwave communication engineering in this country. The study also reveals a close correlation between the k factor and the synoptic climate over India.
The paper has, for convenience of publication, been divided into four parts as follows: Part I—Diurnal variation of surface refractivity over India; Part II—Variation of effective Earth's radius factor (k) over India; Part III—Effective Earth's radius factor (k) and the radio horizon in India; and Part IV—The relationship between k and synoptic climate over India.