By the time he returned to the AMES research center, now in Worth Matravers and renamed the Telecommunications Research Establishment (TRE), major research on the early AI sets had ended in favour of new systems working at microwave frequencies using the recently invented cavity magnetron. Brown had missed most of the development of this system, and he was no longer allowed to fly at high altitudes, so his work on AI ended. He was instead placed in a new group led by John Pringle, a zoologist from Cambridge University, and the two began to study new applications for radar technologies.