Introduction
Recent development of the Communication Navigation and Surveillance (CNS) systems tackles challenges emerged with the new requirements for quality of the (Air Traffic Management) ATM of the airspace or specifically the National Airspace System (NAS). The growing number of flights expected in the future as well as new type of users of the airspace like unmanned and autonomous systems (UAS) increases the complexity and diversity of the airspace. Expected higher density of the traffic in the air requires higher performance of the navigation systems. Different type of air vehicles with different level of detectability and various flight dynamics requires new methods to locate them and avoid the collisions. There is an apparent and clear effort nowadays which addresses these challenges-FANS (Future Air Navigation Systems) and Sense and Avoid (SAA) System development.