Mode S system design and architecture

Mode Select (Mode S) is a secondary surveillance radar system that is designed as an evolutionary improvement to the current Air Traffic Control Radar Beacon System (ATCRBS). Mode S provides improved aircraft surveillance through the use of selective interrogation and monopulse processing and provides a ground-air-ground digital data link. The authors provide an overview of the Mode S aircraft surveillance and data link communications characteristics. This includes a description of monopulse azimuth determination, elimination of synchronous garble, time sharing between ATCRBS and Mode S activities, and the monopulse aircraft surveillance characteristics that provide improved ATCRBS performance. The Mode S sensor architecture and design are described, including the techniques used to provide a high level of sensor reliability, error protection, and a fault tolerance capability that supports data link operations. The authors also present an overview of the Mode S data link communications characteristics and a description of the planned data link applications