Mode S radar
Disclosed is a Mode S radar which specifies an aircraft by transmitting interrogations to an aircraft A equipped with a Mode S transponder, and by then receiving and decoding replies corresponding to these interrogations. In the Mode S radar, detection reports on the aircraft A are generated in a manner that: for a Mode A code necessary for generating detection reports, when identicalness between the Mode A codes obtained in a plurality of scans after the initial acquisition of the aircraft A has been found to exist, the Mode A code thus found identical is adopted without carrying out a Mode A code interrogation (UF=5) thereafter. Accordingly, the Mode S secondary surveillance capable of generating more highly reliable detection reports is achieved.
1. A Mode S radar which specifies an aircraft by transmitting interrogations to a Mode S transponder installed in an aircraft, by receiving replies to the interrogations, and by then decoding the contents of the received replies, the Mode S radar comprising:
acquisition means, which transmits a Mode S only all-call interrogation, and which thereby accomplishes an initial acquisition of an aircraft equipped with a Mode S transponder (a Mode-S-transponder-equipped aircraft);
first obtainment means, which transmits UF=4 interrogations as Mode S selective interrogations to the Mode-S-transponder-equipped aircraft with the initial acquisition having been accomplished by the acquisition means, and which thereby obtains DF=4 replies from the Mode-S-transponder-equipped aircraft;
second obtainment means, which, until an identicalness judgment is issued, transmits UF=5 interrogations as Mode S selective interrogations with each UF=4 interrogation to the Mode-S-transponder-equipped aircraft, and which thereby obtains Mode A codes as DF=5 replies from the Mode-S-transponder-equipped aircraft;
judgment means, which judges whether or not an identicalness exists among predetermined plural Mode A codes obtained by the second obtainment means and issues the identicalness judgment to the second obtainment means; and
generation means, which stores, in a memory, data with identicalness having been judged to exist by the judgment means, and which then generates a report obtained by substituting the Mode A code with identicalness having been judged to exist, as a detection report on the aircraft in each of scans following the obtainment.
2. The Mode S radar according to claim 1 , wherein the existence of identicalness is judged, by the judgment means, between Mode A codes obtained by the second obtainment means in a two successive scans.
3. The Mode S radar according to claim 1 or claim 2 , wherein information on the aircraft is obtained in the first scan after the initial acquisition is accomplished.
4. The Mode S radar according to claim 1 or claim 2 , wherein a first Mode A code among the plural Mode A codes obtained by the second obtainment means for judging whether or not the identicalness exists is any one of a Mode A code obtained in the first scan immediately after a flight status of the aircraft has changed, and a Mode A code obtained in the first scan after the tracking of the aircraft with the replies is lost midway through the tracking.