Abstract <p>The paper studies the use of multi-frequency signals in underwater acoustic positioning systems with an ultrashort baseline. Reception of a navigation acoustic signal by a circular array with linear dimensions equal to several wavelengths of the signal average frequency is analyzed. A model for measuring the time delays with array elements by determining the full phases at each frequency of a multi-frequency signal is proposed. It is shown that the accuracy of the angular position measurements of a navigating object can be improved.</p>