Vol. 10(11), pp. 359-363, 16 June, 2015 DOI: 10.5897/IJPS2015.4358 Article Number: A96694253649 ISSN 1992 - 1950 Copyright ©2015 Author(s) retain the copyright of this article http://www.academicjournals.org/IJPS International Journal of Physical Sciences Full Length Research Paper Microwave propagation attenuation due to earth’s atmosphere at very high frequency (VHF) and ultra-high frequency (UHF) bands in Nsukka under a clear –air condition Ernest Benjamin Ikechukwu Ugwu 1,2 *, Maureen Chioma Umeh 1 and Obiageli Josephine Ugonabo 1 1 Department of Physics and Astronomy, University of Nigeria, Nsukka, Enugu State, Nigeria. 2 Natural Science Unit, University of Nigeria, Nsukka, Enugu State, Nigeria. Received 26 April, 2015; Accepted 1June, 2015 The microwave propagation attenuation due to earth’s atmosphere under a clear-air condition for fade depth of 10 dB was investigated using refractivity data calculated from weather vagaries measurement carried out between January and December 2008. The International Telecommunication Union- Radiocommunication Sector (ITU-R) model for multipath fading for small percentage of time with link distance of 100 km was used. The result showed that at this distance, the refractivity gradient has a strong correlation of 0.747 with percentage of time that the fade depth was exceeded. It was also observed that the percentage of time that the fade depth was exceeded increases with frequency until about 1.2GHz when the result becomes unreliable. Key words: Attenuation, fade depth, microwave, multipath fading, refractivity gradient. INTRODUCTION The meteorological effect on microwave signals especially at very high frequency (VHF) and ultra-high frequency (UHF) band is very significant. Several clear- air effects (Oyedum, 2007), such as, sub-refraction, super-refraction, ducting and scattering due to variations in tropospheric condition can seriously enhance or degrade the quality of reception of a microwave communication link (Ayantunji and Okeke, 2011; Falodun and Okeke, 2013). There are several sources of signal attenuations that can affect a microwave signal in the troposphere. These attenuations include beam spreading (defocusing), antenna decoupling, atmospheric gaseous absorption, rain attenuation, tropospheric scattering under a clear-air- condition, and multipath fading among others. Most of these mechanisms can occur by themselves or in combination with each other (ITU-R P.530-8). Multipath fading is the most common type of fading encountered, particularly on line-of-sight (LOS) radio links. It is the principal cause of dispersion, which is particularly troublesome on digital troposcatter and high- bit-rate LOS links. For an explanation of atmospheric *Corresponding author. E-mail: ernestb.ugwu@unn.edu.ng, Tel: +2348066953787. Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License