Utilization of entire transmitted bandwidth in continuous transmission FM sonar

Claim 1

A continuous transmission frequency modulated sonar of the type wherein a target range signal is generated in proportion to the difference frequency between a varying transmission frequency that varies linearly during repetitive frequency sweeps and the frequency of a return signal, said sonar comprising: signal generating means for simultaneously generating direct and quadrature signals at said varying transmission frequency, one of said direct and quadrature signals being used to project an insonification signal; complex demodulator means, responsive to said direct and quadrature signals and to said return signal, for providing first and second outputs including first and second sum and first and second difference frequencies, respectively, said difference frequencies being characterized as positive when the target is at such a range that the return signal is received during a predetermined frequency sweep and being characterized as negative when the target is at such a range that the return signal is received during a subsequent sweep; first and second filter means, responsive to said first and second outputs of said demodulator means for rejecting said sum frequencies and passing said first and second difference frequencies; and means, responsive to said first and second difference frequencies, for providing target range signals corresponding only to said first and second difference frequencies characterized as positive, whereby ambiguous target range signals are avoided.