A performance analysis in terms of an ultimate's source detection capability for wireless sensor networks configured with antenna arrays is presented in this paper. With recent advancements in microstip antenna technology, it is now feasible to fabricate antenna array confined in close space such that it can be placed on each node of the wireless sensor network. Using the advanced spatio-temporal array processing techniques in conjunction with wireless sensor network, it is shown that the overall's network performance can be significantly enhanced. Specifically, the network performance in terms of the detection capability when two sources are close together is investigated. Under an assumption that most communications within/amongst the networks are in close proximity, the array's near-field assumption is held with the spherical wave propagation. By using the concept of uncertainty sphere in conjunction with the first-order Taylor expansion to approximate one manifold vector in terms of another, an expression for the array detection's lower bound is derived. The theoretical framework is supported by computer simulations to examine the detection capabilities for both node-to-node communications within the network and communications amongst the networks. © 2011 IEEE.