Separate processing of primary and secondary radar data in multi radar tracking

Most radar sensors are equipped with primary and secondary antennas. The primary antenna is used to send intense radar pulses to aircrafts and to receive reflected pulses. The secondary antenna sends trigger pulses to aircraft transponders and receives transponder signals. The radar internal data processing generates target position reports. It uses the time difference between signal send and signal receive and the current azimuth orientation of the antenna. As a separate module radar systems are equipped with a correlation component which combines primary and secondary target position reports to reinforced plots. It is a basic standard radar functionality to combine primary and secondary echoes. Moving this functionality to the radar data processing system seems to be impractical or at least useless. But an operational problem is, that the combining process needs time and causes a delay in the delivery of target reports. In this paper a method is described, how this delay can be avoided and the quality of the air picture generated by the system is even increased. The better quality results from processing both measurements from the primary and the secondary radar antenna instead of combined measurements. The usage of both measurements allows a precise separate alignment of both antennas and increases the available sensor information for tracking. The key to the algorithms for separate radar data processing is centralised multi radar tracking, based upon plot fusion.