A French Pre-WW II attempt at air-warning radar: Pierre David's “electromagnetic barrier”

Pierre David, a French pioneer of the 1920s in the VHF domain, is best known for his early work on air defense and detection of aircraft. His approach, which he called DEM (electromagnetic detection), was quite similar to the “beating method.” There was experience with this at the same time at the American Naval Research Laboratory (NRL), and this is recognized to have initiated the radar concept in the US. Other developments in Great Britain and more especially in Japan are also discussed. However, David was certainly the person who went the furthest in field applications to develop a French operational system that could meet the pressing threat of German Nazi aviation. The results of the full-scale experiments of his “Electromagnetic Barriers” are described from test reports of the French Air Force, unpublished to this day. A “Compagnie de Guet Electromagnétique” (Electromagnetic Warning Company) was established to build a Chain Home “à la Frangaise” along the German border. The outbreak of the war did not allow its deployment, apart from a limited facility in the Marseille region. However, the principles that David had established to find an efficient solution for a true three-dimensional localization (leading to the “Maille en Z” method) prefigured the modern approach of generalized multi-static sensor systems, which is popularized today under the MIMO (multi-input multi-output) concept.