In this thesis, I present the design and evaluation of new techniques for using directional antennas to save energy and to bridge network partitions in a mobile ad hoc network. This thesis advocates close but simple collaboration between the routing layer and the Medium Access Control (MAC) layer and shows through simulations, the effectiveness of this design by modifying the Dynamic Source Routing (DSR) protocol, an on-demand ad hoc network routing protocol based on source routing. First, in order to save energy, Route Requests and data packets are transmitted directionally. Extensive simulations show that without affecting the behavior of the routing protocol noticeably, energy savings of up to 75% is achieved. Second, in order to bridge network partitions, the routing protocol is modified to use the ability of a directional antenna to transmit directionally over longer distance as compared to an omnidirectional antenna, both antennas using the same power. Again, through simulations, the protocol is shown to be able to bridge network partitions. Also, when no partitions are present, the protocol is otherwise equivalent to the version without the partition bridging modifications.