Adaptive active phased array radars are seen as the vehicle to address the current requirements for true ‘multifunction’ radars systems. Their ability to adapt to the enviournment and schedule their tasks in real time allows them to operate with performance levels well above those that can be achieved from the conventional radars. Their ability to make effective use of all the available RF power and to minimize RF losses also makes them a good candidate for future very long range radars. Radar designers addressed these needs by either designing radars to fulfill a specific role, or by providing user selectable roles within a single radar. This process culminated in the fully adaptive radar, which can automatically react to the operational environment to optimize performance. Conventional radars fall into two categories independent of what functions they perform. The first category has fixed antenna with centralized transmitters which produces patterns by reflector or passive array antennas. The beaming being fixed, scanning can only be achieved by physically moving the antenna. Typically a surveillance radar will produce a fan shaped beam with a fixed elevation illumination profile, the azimuth scanning being achieved by rotating the antenna. A tracking radar will have a pencil beam that is used to track targets by the use of a mechanical tracking mount. Because of the limitations imposed on such radars by their design such radars are "single-function radars".