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Using multiple antennas in coexisting radio systems can cancel or control the co-channel interference and hence improves the overall spectrum efficiency. However, the hardware complexity and costs limit the usage of multiple-antenna technologies. Antenna selection technology may reduce such costs while partly remaining the advantages of the multiple-antenna technology. In this paper, the authors focus on the downlink of a multiple-input single-output (MISO) cognitive radio (CR) system and apply antenna selection techniques in the transmitter side of the secondary system. Two scenarios have been considered: one is single antenna selection and the other one is multiple antenna selection using linear beamforming. For the first scenario, the authors analyse the performance of minimum interference and maximum data power strategies, and then propose a maximum signal to leak interference power ratio (SLIR) strategy which consider both interference and useful signals; for the second scenario, the authors discuss the optimal, maximum norm, and proposed subset optimal strategy, which has lower computational complexity and less feedback information. Simulations results verified the analysis. It is also shown that the proposed methods achieve a better trade-off and obtain near-optimal performance in terms of SNR.