AbstractFuture versions of data relay satellite systems are currently being planned by NASA. Being given consideration for implementation are on‐board digital beam‐forming techniques which will allow multiple users to simultaneously access a single S‐band phased array antenna system. To investigate the potential performance of such a system, a laboratory simulator has been developed at NASA's Lewis Research Center. This paper describes the system simulator, and in particular, the requirements, design and performance of a key subsystem, the phased array antenna simulator, which provides realistic inputs to the digital processor including multiple signals, noise and non‐linearities.