Actually , I believe that , while a single sine wave can only locate a delayed signal to within a series of periods , an arbitrarily narrow but nonzero band else it ' s a sine wave can . As you noted the problem here is measuring the delay parameter d for a time delayed signal AfcostftdAwcosftfd . If you plot the phase of the delayed signal w . r . t . the reference as a function of f , you get simply straight line ! slightly complicated due to phase unwrapping problem , wrappedandunwrapped . jpg This line has slope of the parameter d . So a narrow band does allow measuring this . The problem of course is that real life has noise . Detecting this slight slope for every direction quickly means fighting a lot of noise . To mitigate this , the signal is wideband , so you can clearly distinguish the line slope . If this sounds nonintuitive , remember that narrowband signals around frequency f are equivalent to a cosft modulated by a signal of small maximum frequency . So arbitrarily small frequency cosf ' t signals can be carried in there . Now we noted how we could locate cosf ' t up to multiples of it ' s period , T ' 1 f '. By making T ' very large , say 1 second we know our object isn ' t 150 , 000 km away ! , we are done well not in practice because of the aforementioned noise and speed issues , only in principle ! .