| 摘要 |
The range from which a collision avoidance system at an Own station can receive SSR interrogations and reply messages from Other stations, is extended by utilizing P2 pulses for timing TOA measurement in the event P1-P3 pulse pairs are unavailable from the scanning main beam or its side lobes. The amplitude of the P2 pulses in the SLS radiation pattern being greater than the P1-P3 side lobes of the main beam over an angular sector of about 60 DEG centered on the main beam can insure reception of P2 pulses at much greater ranges than P3 pulses contained in the main beam side lobes can be reliably received. Using P2 timing, interlaced Mode A and Mode C reply messages contained in a main beam burst reply sequence are separated into two "families" of TOAs, the Mode C (altitude) TOAs always being longer than the Mode A TOAs by 13 mu sec. A "true" TOA is obtained by subtracting an appropriate time period from the TOA of each family, from which identity, altitude and range information is readily derived. The system continuously adapts to the best instantaneously available timing pulses, alternating between P3 timing and P2 timing throughout the time it takes for a main beam rotation of the received SSRs, thereby extending the operation area of multiple TOA measurements from multiple SSRs which, in turn, provides added safety and reduced false alarms compared to prior passive collision avoidance systems.
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