In this paper, a clustered ad hoc network with virtual antenna array is investigated. Considering the random distribution of the nodes in ad hoc networks, the nodes are modeled as a Poisson point process (PPP). Different from prior analyses, interference in the ad hoc network is taken into account. Outage probability and transmission capacity of a single-hop network are first derived, and the accuracy of the analytical results is verified by simulation results. It is found that the outage probability decays as $\Theta(\lambda_c^{-(2/\alpha)})$, where $\lambda_c$ is the intensity of potential cooperative nodes, and $\alpha$ is the path-loss exponent. That is, the outage probability obeys an inverse-$\mbox{2}/\alpha$ law with the intensity of cooperative nodes $\lambda_c$. Moreover, there exists a unique optimal packet transmission rate to maximize the transmission capacity, and the optimal rate is shown to be within a specific interval that is only related to a path-loss exponent. Finally, the analysis of transmission capacity is extended to a multihop network. The results show that multihop transmission is not beneficial to the transmission capacity, but it does improve the outage performance. The analytical results are meaningful and can provide theoretical guidance on the network design.