The increased flexibility provided by all-digital array architectures allows for the development of improved techniques toward achieving multi-function capability. In an all-digital array, element-level control can be utilized to create a variety of subarray configurations that can be operated independently to form multiple simultaneous transmit and receive (STAR) beams. This thesis describes how STAR can be implemented on an all-digital array by partitioning the array into subarrays, and details various techniques to improve the STAR performance by increasing the isolation between subarrays. A metric to quantify subarray isolation is provided, which incorporates both transmit/receive gain and the leakage power produced by mutual coupling between subarrays. The strategies used to increase subarray isolation leverage knowledge of the scattering parameters of the array, which describe the mutual coupling between subarrays. By formulating the leakage power between subarrays in terms of the scattering parameters of the array, adaptive beamformers can be designed on both transmit and receive to minimize the incident leakage and increase subarray isolation. Digital cancellation of the leakage signals can be used to further increase subarray isolation, with an estimate of the leakage signal provided by the scattering parameters. The proposed techniques for STAR provide insight into the multi-function capability afforded by all-digital arrays, and may become more sophisticated as the use of all-digital arrays becomes ubiquitous.