OWN TRANSMISSION CANCELLATION FOR CONTINUOUS FREQUENCY MODULATION SONARS

A PROBLEM IS RECOGNIZED IN THE PROPOSED USE OF CONTINUOUS TRANSMISSION FM ACTIVE SONAR IN THE INTERFERENCE FROM THE TRANSMITTED SIGNAL MAY EXCEED THE RECEIVED ECHO LEVEL BY AS MUCH AS 190 DB. THE USE OF A CIRCUIT IMMEDIATELY FOLLOWING EACH RECEIVING HYDROPHONE IS PROPOSED TO EASE THE PROBLEM BY CANCELLING OR OTHERWISE REDUCING THE SIGNAL DUE TO THE TRANSMISSION. IT IS RECOGNIZED THAT THE INTERFERING SIGNAL WILL CONTAIN SOME RANDOMNESS DUE TO THE MOTION OF SHIP AND ARRAY THROUGH THE WATER, AND THIS RANDOMNESS WILL LIMIT THE EFFECTIVENESS OF THE CIRCUIT. A MODEL STUDY IS PROPOSED TO PREDICT THE DEGREE OF RANDOMNESS, AND HENCE THE LOWER FLOOR OF THE CANCELLATION CIRCUIT WHICH MAY BE ACHIEVED. A GENERIC CIRCUIT IS DERIVED WHICH SATISFIES THE NEED TO ADAPTIVELY FILTER OUT THE OWN TRANSMISSION INTERFERENCE. THIS CIRCUIT WILL BE FINALIZED AND BREADBOARD, AND THE PERFORMANCE OF THE BREADBOARD MEASURED FOR COMPLIANCE WITH THE DESIGN GOALS. A REPORT WILL BE ISSUED DOCUMENTING THE RESULTS OF THE ACOUSTIC STUDY, THE CIRCUIT DESIGN, THE CIRCUIT PERFORMANCE, AND, MOST IMPORTANT, A VALUE FOR TRANSMISSION SUPPRESSION WHICH CAN BE EXPECTED IN A REAL SONAR SITUATION.