Apparatus for determining a range to one or more targets are provided. In various embodiments, the apparatus comprises a field transceiver module and a computing node in communication with each other. The field transceiver module is configured to generate an electromagnetic probe carrier field; under the control of the computing node, phase-modulate the carrier probe field according to a time-periodic probe modulation waveform having a probe modulation phase that includes a probe modulation frequency and a probe modulation phase offset, thereby generating a modulated probe field; direct the modulated probe field at one or more targets and to receive a modulated reflected probe field from one or more targets; demodulate the modulated reflected probe field and generate a probe signal corresponding to the probe modulation waveform. The computing node is configured to generate a control signal corresponding to the probe modulation waveform; receive the probe signal from the field transceiver module; compute a product of the probe signal and a time periodic reference waveform having a reference phase that includes a reference frequency and a reference phase offset; compute an amplitude or a power of the product; determine one or more reference waveforms corresponding to extrema of the amplitude or the power of the product; and determine the range to the one or more targets based on the extrema of the amplitude or the power of the product.