In modern military operations the requirements of transmitting large amounts of information have increased substantially during the last decade. This increases the demand for highcapacity radio networks. It is also essential that military decisions be made on recent and correct information, which requires that the delays are known and low. Other requirements are that the performance of the military radio network must be satisfactory in highly mobile scenarios and that the network must be robust against hostile jamming and other interfering sources. We have investigated how the capacity and average delay can be improved in an Ad Hoc network with Spatial reuse Time Division Multiple Access (STDMA) by using antenna arrays. The study is based on different antenna combinations consisting of single isotropic antenna element, beam steering and adaptive beamforming. We have also studied how the number of antenna elements and the terrain affects the performance. The study shows that the capacity is improved dramatically in the examined scenario, with up to 1200%. Also, the average delays are decreased when using antenna arrays instead of single isotropic antenna elements. The study also indicates that the benefit from antenna arrays is higher in a flat than in a rough terrain.