MTI canceller utilizing fiber optic delay medium and frequency reiteration

摘要

A pulse cancellation system, particularly adapted to moving target indicator (radar) stationary signal cancelling equipment. A cancelling circuit which is basically a signal differencing device compares the signal train within a given scan cycle with that of the previous cycle by delaying the signals of said previous cycle in order to bring them into time coincidence in the canceller circuit. Delay is achieved in a stable electro-optical device by modulating a light source, preferably a laser beam, in accordance with the signal train to be delayed. Signals are passed through a fused silica fiber optic cable, detected at the other end of the cable, remodulated onto a source of a different optical frequency (color) and retransmitted back over the same fiber optic delay means. Several such reiterations can be effected to reduce the amount of delay required in the fiber optic cable. After the last such reiteration the final color transmission is detected and sent to the canceller to be subtracted from signals provided to the canceller directly from the MTI radar receiver output (undelayed).