RIAS

The RIAS (Radar à Impulsion et Antenne Synthétique) was an experimental coherent MIMO (Multiple-Input Multiple-Output) radar operating in the VHF band. Its conceptual design was first described in 1973 by Jacques Dorey of the French research institute ONERA (Office national d’études et de recherches aérospatiales), with practical installation commencing in 1974 at the Centre d’Essais de la Méditerranée on the French island of Levant. The system featured transmitting antennas arranged in a 400-meter diameter circle, with ground plane dipoles on masts spaced approximately 15 meters apart, and receiving antennas distributed in a smaller concentric circle; each transmitting antenna used an individually coded signal. Initial real-time computing power limitations meant that target coordinate calculations took a week in 1975, though these results validated the MIMO radar concept, leading to the development of an operational prototype by ONERA and Thomson-CSF (now Thales), which was installed near Rouen in 1984.

radartutorial.eu: https://www.radartutorial.eu/19.kartei/13.labs/karte015.en.html