Method and apparatus for coherently processing signals from incoherent sources including laser signals

A method of processing signals in a pulsed laser radar system where the transmit pulses are frequency modulated and comprising the steps of:

• generating a sequence of frequency modulated laser pulse signals having an inherent incoherent phase characteristic;
• transmitting said laser pulse signals and receiving return signals of said laser pulse signals, said return signals also having the same incoherent phase characteristic as the transmitted signals;
• mixing a sample of the transmitted laser pulse signals with a signal having a coherent phase characteristic from a relatively frequency stable optical signal reference source and providing a resultant phase signal generated as a result of the step of mixing;
• generating a laser signal having an ideal phase characteristic for the transmitted laser pulse signals;
• comparing the resultant phase signal with the laser signal having the ideal phase characteristic and generating therefrom a phase correction signal;
• processing the return signals utilizing the phase correction signal so as to provide return signals having a substantially coherent phase characteristic.

A system for radiating and receiving return signals of electromagnetic energy, comprising:

• circuitry for generating and transmitting signals of electromagnetic energy having an incoherent phase characteristic,
• a reference signal source of signals of electromagnetic energy having a coherent phase characteristic,
• a signal mixer for heterodyning a sample of the transmitted signal with a signal from said reference signal source, and forming a phase signal therefrom,
• an electromagnetic energy source having a predetermined phase characteristic for the signal being transmitted;
• a signal comparator for comparing the phase signal with the signal having said predetermined phase characteristic and generating a phase correction signal therefrom;
• and,
• a signal processor for processing the return signals utilizing the phase correction signal so as to produce a coherent phase characteristic in the return signals.

A radar system, comprising:

• a transmit signal generator generating a sequence of frequency modulated pulse signals of electromagnetic energy having a random phase characteristic;
• means for transmitting said pulse signals and receiving return signals of the pulse signals transmitted, said return signals also having the same phase characteristic as the transmitted pulse signals;
• a reference signal source generating a relatively frequency stable reference signal;
• a signal mixer for mixing a sample of the transmitted pulse signals with said reference signal and generating a pulse difference signal;
• means for generating a signal having a desired phase characteristic for the transmitted pulse signals;
• means for comparing the phase difference signal with the signal having the desired phase characteristic and generating a phase correction signal;
• a signal processor for processing the return signals with the phase correction signal so as to correct the phase of the return signals so as to have a substantially coherent phase characteristic.