Enhanced measurement of thickness in bulk dielectric materials is disclosed. Microwave radiation is partially reflected at interfaces where the dielectric constant changes (e.g., the back wall of a part). The reflected microwaves are combined with a portion of the outgoing beam at each of at least two separate detectors. A pair of sinusoidal or quasi-sinusoidal waves results. Thickness or depth measurement is enhanced by exploiting the phase and amplitude relationships between multiple sinusoidal or quasi-sinusoidal standing waves at detectors sharing a common microwave source. These relationships are used to determine an unambiguous relationship between the signal and the thickness or depth.