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In this work, we investigate the impact of the transmit aperture selection technique to alleviate the effect of jamming on a free space optical (FSO) communication system. We consider the FSO system to suffer from a jamming signal and Gaussian noise concurrently. The analysis in this paper is conducted on the assumption that all wireless optical links follow the negative exponential distribution with pointing error. A general <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>N</mi><mo>×</mo><mn>1</mn></mrow></semantics></math></inline-formula> FSO system is studied, which allows the transmitter to select a link with the maximum channel gain to transmit the information. We derive a closed-form expression of the bit error rate (BER) of the considered FSO system in the presence of a jammer. We extract the analytical coding gain and diversity order from the asymptotic behavior of the derived BER. We show that the transmit aperture selection allows the FSO system corrupted by a jammer to attain a diversity order of 0.5 N, equal to that of a multiple-input single-output FSO system, while appreciably reducing the power requirements of (N − 1) transmitters. The theoretical analysis is verified by simulations. We also make a quantitative comparison with repetitive coding (RC) and optical space shift keying (OSSK) and show that the transmit aperture selection has a 3 dB advantage over RC; moreover, for a <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>2</mn><mo>×</mo><mn>1</mn></mrow></semantics></math></inline-formula> system, it provides twice the diversity offered by OSSK. The tenacity of aperture selection is also studied numerically for Gamma-Gamma fading FSO channels.