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In recent years, the use of directional antennas in wireless networks has been widely studied. Since the medium access control (MAC) protocol of the IEEE 802.11 standard was initially designed for systems with omnidirectional antennas, it cannot perform efficiently when directional antennas are used. In this paper, an efficient two-channel MAC protocol is designed for ad hoc networks that are equipped with directional antennas. The proposed protocol utilizes the large throughput offered by directional antennas using two frequency-division multiplexed channels. The first channel is used for control information, and the second for user-data transmission. The proposed MAC protocol operates in two main modes: the omnidirectional mode, in which one antenna is used for the transmission of usersÂ¿ control frames, and the directional mode, in which antenna arrays are used for the transmission of data frames. The proposed protocol is assessed by means of computer simulations based on randomly generated network topologies reflecting the random movement of nodes in the network. Based on these topologies, performance comparisons with the existing MAC protocols are presented for different system parameters. In all cases, the proposed MAC protocol is shown to offer a significant throughput improvement relative to the existing protocols.