en 5-Antenna Antenna Research Paper Research Paper The effects of aberration on the Bit-Error-Rate (BER) and reliability of free- space optical (FSO) communication links are investigated. Based on aberrated divergent rectangular partially coherent flat-topped beam formula on the receiver plane and considering the atmosphere losses due to absorption and scattering, numerical values for Power In Bucket (PIB), Signal to Noise Ratio (SNR) and BER are calculated. Using above mentioned values, the effects of source parameters on link reliability is described. The results are illustrated by graphs obtained by calculation and simulation. Aberration,Divergence,Free-Space Optical Communication,FSO,Rectangular Partially Coherent Flat-Topped Beam, 13 19 http://ijeee.iust.ac.ir/browse.php?a_code=A-10-844-1&slc_lang=en&sid=1 B. Ghafary ghafary@iust.ac.ir 180031947532846002283 180031947532846002283 Yes Department of Physics, Iran University of Department of Physics, Iran University of Science and technology , tehran , Iran F.D. Kashani f_dk@iust.ac.ir 180031947532846002284 180031947532846002284 No Department of Physics, Iran University of Department of Physics, Iran University of Science and technology , tehran , Iran E. Kazemian e_kazemian@iust.ac.ir 180031947532846002285 180031947532846002285 No Department of Physics, Iran University of Department of Physics, Iran University of Science and technology , tehran , Iran