The physics of HPM sources

Many countries have for decades conducted research on High Power Microwave (HPM) sources, both for civilian and military purposes. Progress has been made over the years, yet a breakthrough for HPM weaponry is yet to be seen. Still, with an ever increasing dependence on computerized control and wireless communcation systems, the potential gain from applying potent HPMweapons is greater than ever before. There is therefore no observable decline in the research activity in this area. To be able to assess the potential threat from this type of weapons and the current state of related research, we present in this report an introduction to the physical processes utilized in the most common high power microwave sources of today. We also try to point to what we consider, from a military point of view, to be the more promising technologies.