  Recent theoretical developments for observing the Epoch of Reionization (EOR)
have concentrated on the power spectrum signature of redshifted 21 cm emission.
These studies have demonstrated the great potential of statistical EOR
observations, however, the sensitivity calculations for proposed low frequency
radio arrays have been highly approximate. The formalism developed for
interferometric measurements of the cosmic microwave background can be extended
to three dimensions to naturally incorporate the line-of-sight information
inherent in the EOR signal. In this paper we demonstrate how to accurately
calculate the EOR power spectrum sensitivity of an array, and develop scaling
relationships which can be used to guide the design of EOR observatories. The
implications for antenna distribution, antenna size, and correlator
requirements on the EOR sensitivity are detailed.
