In this paper, we propose a directional spread-spectrum modulation (DSM) signal transmitted by a switched antenna array for physical layer security communication. The main idea is that the antenna hopping scheme is designed according to a spreading sequence. Fundamental frequency component and all harmonic components generated by antenna hopping are used to form the DSM signal with the characteristic of being directional. This signal is associated with the spreading sequence and the direction of the desired receiver because of DSM signal modulated both in the baseband and the antenna level. In this way, the desired receiver with a single antenna demodulates the receive signal as traditional spread-spectrum signal, whereas eavesdroppers cannot extract any useful information from the receive signal even if eavesdroppers know the spreading sequence of DSM signal. Finally, simulation results show that the proposed signal offers a more secure transmission method for wireless communication compared with the traditional spread-spectrum signal. Copyright © 2012 John Wiley & Sons, Ltd.