Sub-Band Modulation in Active Sonar

A method for the simultaneous transmission of multiple sonar signals is described and investigated. The sonar signals are linearly combined as the modulating phase component of a carrier signal, which avoids the transmit energy losses in peak power limited systems caused by a modulating amplitude. These modulating signals are designed to be spectrally separable upon reception, so each sonar signal can be simultaneously processed. Demodulation and echo processing techniques are then presented, and several experiments (both simulated and in-water) were conducted to investigate the detection performance of the modulated signals, as compared to the equivalent unmodulated signals. Results from these experiments indicate that the modulation technique is a viable method of transmitting multiple sonar signals simultaneously, while avoiding amplitude modulation. --Original contains color plates: All DTIC reproductions will be in black and white.