This paper introduces an open access wideband multi-antenna wireless testbed. The testbed is configured as a four transmit antenna by four receive antenna system based on software defined radio techonology. It operates in the 2.4GHz ISM band and supports an RF bandwidth compatible to IEEE 802.11a/g standard. A robotic positioning system has been developed to automatically control the position and orientation of the antenna array, which makes automated testing possible and greatly reduces engineering time. The testbed is configured such that it can be controlled by any computer on the Internet. This makes remote debugging and testing possible. This characteristic of test automation and remote access through Internet was designed into the testbed to make it a valuble resource to the other researchers. A set of software has been developed to support research using the testbed, with the current focus on MIMO channel charaterization and MIMO-OFDM packet communications. A data acquisition system and an offline processing system have been developed for the testbed and have been used for over the air testing to produce results for the ongoing IEEE 802.11n standardization activity.