Several approaches to using combined near‐field microwave NDT techniques, utilizing open‐ended rectangular waveguides, and embedded modulated scatterer technique (MST) for the determination of the dielectric properties of a material have been investigated in the past. A technique currently under investigation involves using the ratio of dynamic forward‐ and reverse‐biased reflection coefficients, measured at the aperture of the waveguide. One important aspect of this method is that the ratio of reflection coefficients is not a function of the relative location or polarization of MST probe to the waveguide. Formulation of the ratio of dynamic reflection coefficients is presented, as well as preliminary measurements showing the coherent ratio of reflection coefficients to be relatively constant as a function of location in free‐space. © 2003 American Institute of Physics