A method examining an object using millimeter-wave signals includes: (a) providing at least two millimeter-wave signal sources; (b) transmitting at least two millimeter-wave signals having at least two different frequencies from the signal sources illuminate the object; (c) in no particular order: (1) determining whether a return reflected signal is above a threshold level; [a] if yes, processing the return signal to identify object shape; [b] if not, processing another return signal; and (2) determining whether a return intermodulation product or harmonic signal is detected; [a] if yes, processing the return signal to identify object nature; [b] if not, processing another return signal; (d) determining whether checked all return signals; (1) if not, processing another return signal; (2) if yes, proceeding to step (e); (e) determining whether results are satisfactory; (1) if not, changing frequency of at least one of the wave signals; (2) if yes, terminating the method.
