The architecture includes a passive radar using opportunistic transmitters and a plurality of active radars that cooperate in the form of a coalition to assure the surveillance of an area of space. The passive radar and the active radars that form the architecture include means for exchanging information and the passive radar is configured to adopt two alternate operating modes: (i) a “watching” mode in which the passive radar carries out surveillance of the area of space concerned and generates detection information, and (ii) an “on-demand data feed” mode in which the passive radar executes at the request of one or more active radars an object search in a given sector of the area under surveillance or an analysis of certain characteristics of the signal received in a given sector.