Most of studies only consider that wireless sensor networks are equipped with only omni-directional antennas, which can cause high collisions. It is shown that the per node throughput in such networks is decreased with the increased number of nodes. Thus, the transmission with multiple short-range hops is preferred to reduce the interference. However, other studies show that the transmission delay increases with the increased number of hops. In this paper, we consider using directional antennas in wireless sensor networks. We have found that using directional antennas not only can increase the throughput capacity but also can decrease the delay by reducing the number of hops. We also construct a time-division multi-access (TDMA) scheme to achieve this. Compared with omni-directional antennas, directional antennas can reduce the interference and lead to the improvement on the network capacity. Furthermore, directional antennas can extend the transmission range, which leads to fewer hops and the lower multi-hop routing delay.