This paper reports on an X-band phased-array radar rooftop testbed at Applied Radar, Inc. The testbed was developed to support the integration of Applied Radar's digital receiver/exciter (DREX) hardware and open-systems architecture (OSA) back-end algorithms and real-time processing with a government-furnished active electronically steered array (AESA) antenna developed by Cobham Sensor Systems. We demonstrate the ground-moving-target-indication (GMTI) detection and tracking of vehicles and dismount targets in an open field from the rooftop-mounted antenna array sensor using pulse-Doppler processing. The demonstration system may be scaled up in the future to support air surveillance and include other array antennas and different frequency bands.