10. Early Warning Against Stealth Aircraft, Missiles and Unmanned Aerial Vehicles

Since the 2nd World War and during the Cold War, the air defense radar has proven to be the main surveillance sensor, where each radar would cover a radius of more than 200 nautical miles. Apart from the electronic warfare, more recently the emergence of stealth or low observable technology, the evolution of ballistic and cruise missiles, as well as the democratization of UAVs (Unmanned Air Vehicles) or drones, have contested the capabilities of the typical surveillance radar. All these targets are difficult to detect, because they exhibit low RCS (Radar Cross Section), potentially flying at the upper or lower limits of the radar coverage or outside the expected velocity range (being either too slow, e.g. some UAVs, or too fast, like ballistic missiles). This chapter begins with the estimation of the RCS of various potential targets, as a function of the radar frequency band. In this way, the expected detection range against a set of targets can be calculated, for any given radar. Secondly, different radar types are taken into consideration, such as low frequency band radars or passive/multistatic radars, examining the respective advantages and disadvantages. Finally, some issues are discussed concerning the “kill chain” against difficult-to-detect targets, in an effort to defend efficiently the air space.