PURPOSE: To realize a high speed and large capacity air-to-surface data linkage function with keeping highly accurate surveillance function by providing the first antenna system having processing function of surveillance data and rotating mechanically at constant speed, and the second antenna system having a mode S response function to individual interrogation and scanning a beam electronically in a horizontal plane.

CONSTITUTION: A mechanically scanning mode S sensor is constituted of a mechanical rotary antenna 1a, a transmitter/receiver 1c, a target detection/ processing part 1e and a surveillance data processing part 1g. The processing part 1g tracks a target in modes A/C and S within a coverage range, and updates and maintains a surveillance data file 1h. An electronically scanning mode S sensor is constituted of an electronic scanning antenna 1b, a transmitter/ receiver 1d, a target detection/processing part 1f and a communication control part 1i. The control part 1i conducts scheduling of a mode S interrogation/ response and beam direction control of the antenna 1b, based upon the content of the file 1h. In this way, with keeping highly accurate surveillance function, a communication function of high speed and large capacity air-to-surface data linkage can be well realized.