Abstract: A frequency-hopping signal design method for directional modulation transmitter is proposed to enhance the wireless communication security of phased array antenna. By quickly switching antenna elements with a varying speed, frequency hopping signal can be produced in undesired directions due to period variation of the phase, while the carrier frequency of a pre-specified direction keeps constant, which makes it hard to eavesdropper to get the confidential symbol. The time-frequency spectrograph in different directions is analyzed and simulated together with the communication performance of BPSK and 2FSK signal. Simulation results show that the proposed method can provide a secure communication signal with low probability of detection.